Shunting Solved
Discussion
Odd thing I noticed messing around with fuel maps, on the a non catalyst fuel map the RPM holds up as you slow down, slightly disconcerting, but on the catalyst map its perfect, and Ive not seen any fault codes generated. To start with the simple things, try unplugging the ECU for a moment to clear down any fault conditions and You could try changing the tune resistor to 400 ohms (non catalyst) just to see the effect, but not on a permanent basis. I can email you Lucas manual for the 14CUX if you drop me a line.
There is quantities about the shunting issue if you search both this and the Griff forum. There was a brilliant one called Kangarooing Griff a couple of years back that was about 10 pages long. The issue is very specific, it occurrs at about 1700 rpm in the higher gears, and really snatches the drive train. The 4.5 are know to be worse. but does not occur so badly with the non cat map and shorter duration cams. Happy searching
There is quantities about the shunting issue if you search both this and the Griff forum. There was a brilliant one called Kangarooing Griff a couple of years back that was about 10 pages long. The issue is very specific, it occurrs at about 1700 rpm in the higher gears, and really snatches the drive train. The 4.5 are know to be worse. but does not occur so badly with the non cat map and shorter duration cams. Happy searching
Just a word off caution on the non cat map, its likely to be the unmodified fuel map used in the Range Rover, which can run lean under higher RPM, and has not been modified by TVR in any way. So just use it as a test to see if the low speed running improves and nothing more. The CO trim on the side of the AFM also comes into play to set the low speed (up to 2500 rpm approx)so if it has been altered at some point the car can run rich or lean at idle, but its fairly obvious as the engine either bogs down as it overfuels, idles really roughly if its too lean. You can set it up with a DC voltage measurement on the AFM connectors, or just do it by ear. On my car turning the screw anti clockwise makes it leaner, so you wind it back until the idle becomes rough, and then back again until it becomes smooth.
Setting up the DC voltages on the AFM.
Applicable to NON catalyst cars only. Using a voltmeter between red and black wire and blue and red wire check the voltage with the ignition on, but the engine not running. The recessed Hex head screw allows you to set the carbon monoxide base line with these voltages. NOTE these are base settings ONLY. Turn the adjustment screw clockwise to richen the mixture, and anticlockwise to lean the mixture. The screw has multiple turns, that will go from 0 volts to over 3.5 volts.
This AFM has 4 connections:
Red/black. Ground
Blue/Green Air flow signal- should be .2-.7 volts (no air flow). Tick over on the 3.9 is about 1.7 volts
Brown Orange +12v
Blue/red CO trim value. This is factory set 1.8 volts for catalyst engines, although I believe this setting is ignored with Lambda correction. Non cat cars are in the range of 1-1.5 volts, although accurate setting will require the use if an exhaust gas analyzer.
Setting up the DC voltages on the AFM.
Applicable to NON catalyst cars only. Using a voltmeter between red and black wire and blue and red wire check the voltage with the ignition on, but the engine not running. The recessed Hex head screw allows you to set the carbon monoxide base line with these voltages. NOTE these are base settings ONLY. Turn the adjustment screw clockwise to richen the mixture, and anticlockwise to lean the mixture. The screw has multiple turns, that will go from 0 volts to over 3.5 volts.
This AFM has 4 connections:
Red/black. Ground
Blue/Green Air flow signal- should be .2-.7 volts (no air flow). Tick over on the 3.9 is about 1.7 volts
Brown Orange +12v
Blue/red CO trim value. This is factory set 1.8 volts for catalyst engines, although I believe this setting is ignored with Lambda correction. Non cat cars are in the range of 1-1.5 volts, although accurate setting will require the use if an exhaust gas analyzer.
Blitz,
How do I tell if I have the cat or non-cat ECU map ? I thought all Chimaeras had Cats, unless they had been removed post-production ?
Mine is a 1997 and has all Cats still installed.
Have fiddled a bit with the AFM and voltage measurements before; was speaking with MA at the time. Got the voltage measurements from AFM and throttle pot and got them to MA but he never responded, too busy I guess. Some of them seemed out of range but I didn't know what that indicated. Adjusting the screw on the AFM appears to make no difference and I understood that it was disconnected. Similarly, the throttle pot is not slotted like the early cars so could not be adjusted. I slotted it and had a play around to see if it was the ECU not recognising that the throttle was opened was the problem but seemed to make no difference.
Cheers,Matt
How do I tell if I have the cat or non-cat ECU map ? I thought all Chimaeras had Cats, unless they had been removed post-production ?
Mine is a 1997 and has all Cats still installed.
Have fiddled a bit with the AFM and voltage measurements before; was speaking with MA at the time. Got the voltage measurements from AFM and throttle pot and got them to MA but he never responded, too busy I guess. Some of them seemed out of range but I didn't know what that indicated. Adjusting the screw on the AFM appears to make no difference and I understood that it was disconnected. Similarly, the throttle pot is not slotted like the early cars so could not be adjusted. I slotted it and had a play around to see if it was the ECU not recognising that the throttle was opened was the problem but seemed to make no difference.
Cheers,Matt
Edited by taylormj4 on Thursday 12th November 13:21
Just come back to this after my post at the beginning which now seems a bit abrupt and dismissive. Anyhow having had a good read it all sounds very interesting.
I had fairly bad low speed shunting (I am talking about in traffic) and a slight hesitancy at mid throttle until I did a full decat, removing the precats and fitting "Clive's Y Piece". This did totally eradicate all shunting and the car has been much more responsive throughout the rev range. And loud!
I have just put the main cat back on after five months shunt free driving to get the car through the MOT and guess what... slight hesitancy at mid throttle is back, however at low speed the car is still fine.
So in my case it would appear that low speed shunting is caused by the restrictive nature of the precats and the hesitancy at higher speed is cause by the main cat.
I am now wondering how the car would drive with all the cats removed and the induction sorted.
I had fairly bad low speed shunting (I am talking about in traffic) and a slight hesitancy at mid throttle until I did a full decat, removing the precats and fitting "Clive's Y Piece". This did totally eradicate all shunting and the car has been much more responsive throughout the rev range. And loud!
I have just put the main cat back on after five months shunt free driving to get the car through the MOT and guess what... slight hesitancy at mid throttle is back, however at low speed the car is still fine.
So in my case it would appear that low speed shunting is caused by the restrictive nature of the precats and the hesitancy at higher speed is cause by the main cat.
I am now wondering how the car would drive with all the cats removed and the induction sorted.
Edited by STEV8E on Friday 13th November 18:34
taylormj4 said:
Blitz,
How do I tell if I have the cat or non-cat ECU map ? I thought all Chimaeras had Cats, unless they had been removed post-production ?
Mine is a 1997 and has all Cats still installed.
Have fiddled a bit with the AFM and voltage measurements before; was speaking with MA at the time. Got the voltage measurements from AFM and throttle pot and got them to MA but he never responded, too busy I guess. Some of them seemed out of range but I didn't know what that indicated. Adjusting the screw on the AFM appears to make no difference and I understood that it was disconnected. Similarly, the throttle pot is not slotted like the early cars so could not be adjusted. I slotted it and had a play around to see if it was the ECU not recognising that the throttle was opened was the problem but seemed to make no difference.
Cheers,Matt
I have done a lot of measurements and I dont personnaly believe the CO trim pot does anything on the catalyst fuel map. The prove was to disable the lambda feedback and then alter the value of the trim pot. If it did have an effect, then the ECU could not correct the mixture, so the exhaust mixture would change, which it did not. I also rapidly altered the trim pot with lambda feedback, and it should have been possible to see the lambda cycling rate and values change as the ECU compensated, but again I saw no change. MA does say in one of his posts it skews the mapping process if it out to start with, but I cant access the values of fuel trim the ECU is adding as I cant get the required hardware / software to read the ECU's serial port output. As for the fuel map, the ECU will run either cat or non cat, depending on the trim resistor value fitted to the wiring loom. No car fitted with catalysts (All chim's ) should run the non cat map other than testing or to locate fueling faults. As for the TPS, The original 14cux manuals are not that critical on setting its base setting up, the voltage swing between max and min is what counts, and Im told the ECU can work the rest out itself. Its possible however that if TVR could not get the mapping as needed that the TPS position could be more critical.How do I tell if I have the cat or non-cat ECU map ? I thought all Chimaeras had Cats, unless they had been removed post-production ?
Mine is a 1997 and has all Cats still installed.
Have fiddled a bit with the AFM and voltage measurements before; was speaking with MA at the time. Got the voltage measurements from AFM and throttle pot and got them to MA but he never responded, too busy I guess. Some of them seemed out of range but I didn't know what that indicated. Adjusting the screw on the AFM appears to make no difference and I understood that it was disconnected. Similarly, the throttle pot is not slotted like the early cars so could not be adjusted. I slotted it and had a play around to see if it was the ECU not recognising that the throttle was opened was the problem but seemed to make no difference.
Cheers,Matt
Edited by taylormj4 on Thursday 12th November 13:21
As for exhaust effecting the shunting, mine disappeared completely when I fitted some extra decibel tubes, but my exhaust is somewhat different to the TVR however with no cat's and straight through side pipes. I assumed the fraction extra back pressure was causing less unburnt mixture to go down the pipes at overlap but may be complete rubbish???
t up the inlet 
STEV8E said:
So in my case it would appear that low speed shunting is caused by the restrictive nature of the precats and the hesitancy at higher speed is cause by the main cat.
blitzracing said:
As for exhaust effecting the shunting, mine disappeared completely when I fitted some extra decibel tubes, but my exhaust is somewhat different to the TVR however with no cat's and straight through side pipes. I assumed the fraction extra back pressure was causing less unburnt mixture to go down the pipes at overlap but may be complete rubbish???
Just to add my 5p and buck the trend - mine has TVR 885 cam with stainless steel manifolds & Y-piece (precats removed and hi-flow 100-cell cat) and straight-through exhaust with no silencers - and it shunts like a b*tch...Dom
Edited by domV8 on Friday 13th November 22:31
what works on one car is no guarantee to work on another 
not telling no one to suck eggs mind 
STEV8E said:
Just come back to this after my post at the beginning which now seems a bit abrupt and dismissive. Anyhow having had a good read it all sounds very interesting.
I had fairly bad low speed shunting (I am talking about in traffic) and a slight hesitancy at mid throttle until I did a full decat, removing the precats and fitting "Clive's Y Piece". This did totally eradicate all shunting and the car has been much more responsive throughout the rev range. And loud!
I have just put the main cat back on after five months shunt free driving to get the car through the MOT and guess what... slight hesitancy at mid throttle is back, however at low speed the car is still fine.
So in my case it would appear that low speed shunting is caused by the restrictive nature of the precats and the hesitancy at higher speed is cause by the main cat.
I am now wondering how the car would drive with all the cats removed and the induction sorted.
Well my pre-cats are coming out soon, I have a slight blow on warm up from the O/S manifold to Y piece join.I had fairly bad low speed shunting (I am talking about in traffic) and a slight hesitancy at mid throttle until I did a full decat, removing the precats and fitting "Clive's Y Piece". This did totally eradicate all shunting and the car has been much more responsive throughout the rev range. And loud!
I have just put the main cat back on after five months shunt free driving to get the car through the MOT and guess what... slight hesitancy at mid throttle is back, however at low speed the car is still fine.
So in my case it would appear that low speed shunting is caused by the restrictive nature of the precats and the hesitancy at higher speed is cause by the main cat.
I am now wondering how the car would drive with all the cats removed and the induction sorted.
Edited by STEV8E on Friday 13th November 18:34
So I figure if I need to do some work in that area anyway I may as well remove the pre-cats while I'm at it.
I know I'm a sucker for punishment, who need skin on their knuckles anyway?
So looking at this from the other way I will be able to report on any additional improvements to my very successful induction mods by freeing up the exhaust side too.
The main cat stays in for now as I expect a bit a back pressure will help with cylinder scavenging, plus I don't need the potential MOT hassles in Feb 2010.
I have to say I am very happy with the way things are going so far, from what I have heard, with the pre-cats removed I should enjoy even better throttle response.
I will report on my findings as soon the job is complete.
Dave.
Hi Guy’s.. Sorry to come in late on this one.. but maybe you could offer me some advice here… I’ve spent a fortune and my car is not behaving like it was….
I apportion no blame here (except myself) and I’m not criticising any parts used (already been flamed on that one!).. but what I’ve ended up with is not what I set out to do… and I’m a lot poorer to boot!!
It all started a couple of months ago.. I had my 500 Griff (cat) at V8D for the White metal shells doing… Whilst in there I asked them to look at the cam and they said it was starting to show signs of tip’s going… so I thought I may as well have it done..
Before, my car was standard, with the exception of pre-cat’s out and the silencer opened up a bit and showed 280 BHP at the Growl.. a nice healthy engine…
Shunting was not a problem although at times I could feel a bit when in 3rd gear crawling in traffic.
Anyway.. I had a Stealth cam fitted and some induction mod’s… 72mm Plenum, Trumpet base. smooth bore 90* and ported manifold…45mm I think
When I got it back, the shunting was more pronounced so I took it back.. they tested her out and said it was running very lean and I’d have to get it on the rollers….
So enter Mark Adams… Great guy and very knowledgeable… He suggested I fit red top’s, Bosch MAF.. move the vac pipe forward a bit (so 2K when it comes in),,, Improve the induction pipe.. fit a K and N etc… We also replaced the plugs, coil and HT leads, Pot… and set it all up… end result is… it still shunts….
Although in other areas it’s much better now (fueling)… my power has moved up the RPM band so not as aggressive off the mark… but goes for ever on the top end… Problem is… driving in town is a sod….
I have a 10mm spacer fitted also but was thinking of trumpet length or may be even the manifold as it appears they close it down at the heads over the standard one to get faster flow… maybe it’s worth opening this up again?.. Mark did say he thinks a lot of the issue is due to my heads having big ports?? It did appear to get a bit worst when I fitted the spacer for some reason?
So all in I’m about £3.5K out of pocket and have a car I’m not keen on driving now (Wish I could go back) and a BHP of 294 and a slight drop in the torque.. …
Not sure what the cam will do over standard but the V8D guy’s say it should be fine.. so suggest it’s on the induction side…
Any thoughts would be appreciated… Cheers…
I apportion no blame here (except myself) and I’m not criticising any parts used (already been flamed on that one!).. but what I’ve ended up with is not what I set out to do… and I’m a lot poorer to boot!!
It all started a couple of months ago.. I had my 500 Griff (cat) at V8D for the White metal shells doing… Whilst in there I asked them to look at the cam and they said it was starting to show signs of tip’s going… so I thought I may as well have it done..
Before, my car was standard, with the exception of pre-cat’s out and the silencer opened up a bit and showed 280 BHP at the Growl.. a nice healthy engine…
Shunting was not a problem although at times I could feel a bit when in 3rd gear crawling in traffic.
Anyway.. I had a Stealth cam fitted and some induction mod’s… 72mm Plenum, Trumpet base. smooth bore 90* and ported manifold…45mm I think
When I got it back, the shunting was more pronounced so I took it back.. they tested her out and said it was running very lean and I’d have to get it on the rollers….
So enter Mark Adams… Great guy and very knowledgeable… He suggested I fit red top’s, Bosch MAF.. move the vac pipe forward a bit (so 2K when it comes in),,, Improve the induction pipe.. fit a K and N etc… We also replaced the plugs, coil and HT leads, Pot… and set it all up… end result is… it still shunts….
Although in other areas it’s much better now (fueling)… my power has moved up the RPM band so not as aggressive off the mark… but goes for ever on the top end… Problem is… driving in town is a sod….
I have a 10mm spacer fitted also but was thinking of trumpet length or may be even the manifold as it appears they close it down at the heads over the standard one to get faster flow… maybe it’s worth opening this up again?.. Mark did say he thinks a lot of the issue is due to my heads having big ports?? It did appear to get a bit worst when I fitted the spacer for some reason?
So all in I’m about £3.5K out of pocket and have a car I’m not keen on driving now (Wish I could go back) and a BHP of 294 and a slight drop in the torque.. …
Not sure what the cam will do over standard but the V8D guy’s say it should be fine.. so suggest it’s on the induction side…
Any thoughts would be appreciated… Cheers…
TVR Beaver said:
Hi Guy’s.. Sorry to come in late on this one.. but maybe you could offer me some advice here… I’ve spent a fortune and my car is not behaving like it was….
I apportion no blame here (except myself) and I’m not criticising any parts used (already been flamed on that one!).. but what I’ve ended up with is not what I set out to do… and I’m a lot poorer to boot!!
It all started a couple of months ago.. I had my 500 Griff (cat) at V8D for the White metal shells doing… Whilst in there I asked them to look at the cam and they said it was starting to show signs of tip’s going… so I thought I may as well have it done..
Before, my car was standard, with the exception of pre-cat’s out and the silencer opened up a bit and showed 280 BHP at the Growl.. a nice healthy engine…
Shunting was not a problem although at times I could feel a bit when in 3rd gear crawling in traffic.
Anyway.. I had a Stealth cam fitted and some induction mod’s… 72mm Plenum, Trumpet base. smooth bore 90* and ported manifold…45mm I think
When I got it back, the shunting was more pronounced so I took it back.. they tested her out and said it was running very lean and I’d have to get it on the rollers….
So enter Mark Adams… Great guy and very knowledgeable… He suggested I fit red top’s, Bosch MAF.. move the vac pipe forward a bit (so 2K when it comes in),,, Improve the induction pipe.. fit a K and N etc… We also replaced the plugs, coil and HT leads, Pot… and set it all up… end result is… it still shunts….
Although in other areas it’s much better now (fueling)… my power has moved up the RPM band so not as aggressive off the mark… but goes for ever on the top end… Problem is… driving in town is a sod….
I have a 10mm spacer fitted also but was thinking of trumpet length or may be even the manifold as it appears they close it down at the heads over the standard one to get faster flow… maybe it’s worth opening this up again?.. Mark did say he thinks a lot of the issue is due to my heads having big ports?? It did appear to get a bit worst when I fitted the spacer for some reason?
So all in I’m about £3.5K out of pocket and have a car I’m not keen on driving now (Wish I could go back) and a BHP of 294 and a slight drop in the torque.. …
Not sure what the cam will do over standard but the V8D guy’s say it should be fine.. so suggest it’s on the induction side…
Any thoughts would be appreciated… Cheers…
I apportion no blame here (except myself) and I’m not criticising any parts used (already been flamed on that one!).. but what I’ve ended up with is not what I set out to do… and I’m a lot poorer to boot!!
It all started a couple of months ago.. I had my 500 Griff (cat) at V8D for the White metal shells doing… Whilst in there I asked them to look at the cam and they said it was starting to show signs of tip’s going… so I thought I may as well have it done..
Before, my car was standard, with the exception of pre-cat’s out and the silencer opened up a bit and showed 280 BHP at the Growl.. a nice healthy engine…
Shunting was not a problem although at times I could feel a bit when in 3rd gear crawling in traffic.
Anyway.. I had a Stealth cam fitted and some induction mod’s… 72mm Plenum, Trumpet base. smooth bore 90* and ported manifold…45mm I think
When I got it back, the shunting was more pronounced so I took it back.. they tested her out and said it was running very lean and I’d have to get it on the rollers….
So enter Mark Adams… Great guy and very knowledgeable… He suggested I fit red top’s, Bosch MAF.. move the vac pipe forward a bit (so 2K when it comes in),,, Improve the induction pipe.. fit a K and N etc… We also replaced the plugs, coil and HT leads, Pot… and set it all up… end result is… it still shunts….
Although in other areas it’s much better now (fueling)… my power has moved up the RPM band so not as aggressive off the mark… but goes for ever on the top end… Problem is… driving in town is a sod….
I have a 10mm spacer fitted also but was thinking of trumpet length or may be even the manifold as it appears they close it down at the heads over the standard one to get faster flow… maybe it’s worth opening this up again?.. Mark did say he thinks a lot of the issue is due to my heads having big ports?? It did appear to get a bit worst when I fitted the spacer for some reason?
So all in I’m about £3.5K out of pocket and have a car I’m not keen on driving now (Wish I could go back) and a BHP of 294 and a slight drop in the torque.. …
Not sure what the cam will do over standard but the V8D guy’s say it should be fine.. so suggest it’s on the induction side…
Any thoughts would be appreciated… Cheers…
Hi TVR Beaver sorry to hear about your plight, sounds like you have had some good brains on the problem already.
I would say it must have something to do with how the air is passing down the inlet tracts, it may be pulsing or moving too slowly in the lower RPM bracket.
When tuning for power most people focus solely on the more air more fuel approach.
Its as important, if not more important, to understand how the air is flowing at different RPMs and how this also effects fuel atomization and cylinder filling.
Five years ago I had the pleasure of seeing some software simulating all this at the former BAR HQ in Brackley.
I may also be able to put you in touch with a couple of ex-Lotus development engineers that have just completed some similar modeling on a 1933 Talbot 75 special a friend is building.
They have used their software (In-part) to help extract 173 HP from a naturally aspirated pre-war 2.5 litre straight six and it fuels perfectly from 800rpm to over 5000rpm.
Short of reversing your mods one option that I wouldn't mind betting would solve your problem is forced induction.
The problem is you will probably need to throw a minimum of £4k at it to get a decent supercharger installation.
The Lotus guys are available but certainly not cheap, you may find yourself spending as much as a blower installation, let me know if you need and introduction.
Dave.
Thanks Dave's,,, for the offer and info... Spending more on the car is not an option if I'm to retain all my bodily bits so the wife tell's me... and I did want to keep it kind of standard (what happened to that!!).
One thing that was of interest on the rollers was a loaded run as if your going up a slight hill and then stop.. it showed the cylinders to be fueling differantly at the 1800 RPM point, so I'm sure your right on the air flow / air waves / movement in the plenum etc... but trying to think which part has caused it... Creating a bigger gap over the trumpets with the spacer appeared to make it shunt more so I will try with that removed... but if I get into re-sizing the trumpets on length I need to understand a bit more about how they function...
My car does run a bit cold also so I need to try it with a new stat to ensure I hold 80 deg or so..
Just a tad annoying going from a £200 bearing replacement to a £3.5K upgrade and ending up with 10 BHP and a shunter....
It was more apperant after the V8D work so if it's not the cam (and people say it won't be?)... It can only be the Trumpets or the manifould?... but which one... and what to do first??.. The joy's..
One thing that was of interest on the rollers was a loaded run as if your going up a slight hill and then stop.. it showed the cylinders to be fueling differantly at the 1800 RPM point, so I'm sure your right on the air flow / air waves / movement in the plenum etc... but trying to think which part has caused it... Creating a bigger gap over the trumpets with the spacer appeared to make it shunt more so I will try with that removed... but if I get into re-sizing the trumpets on length I need to understand a bit more about how they function...
My car does run a bit cold also so I need to try it with a new stat to ensure I hold 80 deg or so..
Just a tad annoying going from a £200 bearing replacement to a £3.5K upgrade and ending up with 10 BHP and a shunter....
It was more apperant after the V8D work so if it's not the cam (and people say it won't be?)... It can only be the Trumpets or the manifould?... but which one... and what to do first??.. The joy's..
TVR Beaver said:
Thanks Dave's,,, for the offer and info... Spending more on the car is not an option if I'm to retain all my bodily bits so the wife tell's me... and I did want to keep it kind of standard (what happened to that!!).
One thing that was of interest on the rollers was a loaded run as if your going up a slight hill and then stop.. it showed the cylinders to be fueling differantly at the 1800 RPM point, so I'm sure your right on the air flow / air waves / movement in the plenum etc... but trying to think which part has caused it... Creating a bigger gap over the trumpets with the spacer appeared to make it shunt more so I will try with that removed... but if I get into re-sizing the trumpets on length I need to understand a bit more about how they function...
My car does run a bit cold also so I need to try it with a new stat to ensure I hold 80 deg or so..
Just a tad annoying going from a £200 bearing replacement to a £3.5K upgrade and ending up with 10 BHP and a shunter....
It was more apperant after the V8D work so if it's not the cam (and people say it won't be?)... It can only be the Trumpets or the manifould?... but which one... and what to do first??.. The joy's..
Indeed our women folk can be the biggest barrier to performance improvements, I have the same issues this end.One thing that was of interest on the rollers was a loaded run as if your going up a slight hill and then stop.. it showed the cylinders to be fueling differantly at the 1800 RPM point, so I'm sure your right on the air flow / air waves / movement in the plenum etc... but trying to think which part has caused it... Creating a bigger gap over the trumpets with the spacer appeared to make it shunt more so I will try with that removed... but if I get into re-sizing the trumpets on length I need to understand a bit more about how they function...
My car does run a bit cold also so I need to try it with a new stat to ensure I hold 80 deg or so..
Just a tad annoying going from a £200 bearing replacement to a £3.5K upgrade and ending up with 10 BHP and a shunter....
It was more apperant after the V8D work so if it's not the cam (and people say it won't be?)... It can only be the Trumpets or the manifould?... but which one... and what to do first??.. The joy's..
I've built many engines from mild to wild, mostly pre-war stuff, no RV8's although the fundamental principles of any four-stroke are always the same.
In my experience its never as simple as finding which part is giving you a certain characteristic.
Its all about the relationship between a number of components, finding the right combination is the difficult part.
With a common engine like the RV8 you will be sure to find that others have done this hard work already, its essentially a recipe.
That's why its always much easier to build an engine from the crank up with a clear brief right from the start, you just follow a known recipe to get a known result.
My early findings lead me to think the RV8 responds well to changes in the length of the inlet tracts.
Without the induction/exhaust modeling software and accesses to a rolling road its a case of experimenting with different lengths of velocity stacks (sorry that's trumpets in the RV8 world).
I just guessed with my mods which is appalling practice, but I did get lucky.
A great option would be to source a spare plenum base and some tubing so you can alter the trumpet lengths until you find a nice match with you cam profile.
In simple terms shortening the trumpets should push the peak torque further up the rev range, but adding in other variables its really more complicated than that.
Ideally what you want and need to see could only be shown on a 3D graph.
For example an F1 engine will have variable inlet and exhaust tracts that shorten or lengthen by following a map after the processing of sensor data by an ECU.
In practice on the simple old RV8 you need to find the best relationship between inlet tract length and your cam, exhaust side, ect, ect.
I bet someone here has the same cam as you and a similar setup, try creating a post to see if anyone has found a good combination.
Sorry I cant be of more help.
Kind regards and good luck. Dave.
All sounds brilliant... but the EFi manifold does not have anything like equal inlet tracts so its pretty much a load of rubbish.
Long trumpets (ie extended port volume) may just keep cross contamination on overlap to a minimum. Are you sure it isn't pathetic throttle response due the increased plenum volume that you are experiencing?
You could ask Rob if it is worth advancing your cam? I'd try it if it was my problem and nothing else worked.
Long trumpets (ie extended port volume) may just keep cross contamination on overlap to a minimum. Are you sure it isn't pathetic throttle response due the increased plenum volume that you are experiencing?
You could ask Rob if it is worth advancing your cam? I'd try it if it was my problem and nothing else worked.
spend said:
All sounds brilliant... but the EFi manifold does not have anything like equal inlet tracts so its pretty much a load of rubbish.
Long trumpets (ie extended port volume) may just keep cross contamination on overlap to a minimum. Are you sure it isn't pathetic throttle response due the increased plenum volume that you are experiencing?
You could ask Rob if it is worth advancing your cam? I'd try it if it was my problem and nothing else worked.
Long trumpets (ie extended port volume) may just keep cross contamination on overlap to a minimum. Are you sure it isn't pathetic throttle response due the increased plenum volume that you are experiencing?
You could ask Rob if it is worth advancing your cam? I'd try it if it was my problem and nothing else worked.
Cant remember saying anything abut the inlet tracts being equal?
I am more basic principles than rubbish.
Lets all get on here shall we.
I had a couple of ideas, but not tried them out. Firstly nice and simple was to reconnect the preheat on the plenum chamber to improve the fuel vaporisation, and also to reduce the air density. One owner said the car was much worse in the cold and damp weather and it struck me if it was running lean on cold dense air and the ECU was mis interpreting the amount of fuel needed due to the type of pulsed airflow over the hot wire at low RPM, then putting in less dence air to burn might be enough to make it run a tad richer. The airflow meter should compensate for air temperature changes, but if you have already hit the correction limit of the ECU, this may be enough to bring it back in line. The second more radical was to put in one of those horrible electric "superchargers" you see on ebay (fart in a thunderstorm), but only have it running or piped in at low RPM. You dont want it in the main airflow,(far too restrictive) but off the in a side pipe to suppliment the natural draw of the engine. Just a thought......
Thanks Guy’s… from the post’s above I’m sort of thinking what my way forward is here.. It’s always good to hear others experiences with these things and try pick out the relevant bit’s for your problem…
With regards to building to a pre-determined recipe.. that’s what I thought I was doing… I thought getting all the induction mod’s from V8D would be a sure match for the car / cam etc… and may be they are but just don’t go with my heads?... Rob did offer to put it all back to standard (except the cam).so it’s an option if all else fails but probably won’t go there as the plus side of the work could outweigh the negatives. I did mail them the other day on this but no reply….
Stack length is something that interests me though… Before, I had bit’s of tube in the base but now I have bigger diameter and I think longer Trumpet ended stacks… So increasing the diameter here will slow the speed of air entering the manifold… the increased bore in the manifold will receive this okay and it will then speed up as it goes to the other end where the manifold is closed down on what I had before… If I have big ports in the heads does it then go pear shaped?? I’m thinking opening them out again to match the heads?
The stacks are different lengths in an attempt to make the induction side all the same length from plenum to port… so you could in theory shorten or lengthen them all by the same amount… I’m not sure what the height of the tubes were in the standard unit as I never measured them?… Worth a try messing all the same and thanks for the offer Dave on the bases.. will give you a call if needed.. always nice to swap things out and see what happens.. at least that way you can potentially identify the offending item… but the last post also may have a point… My car as I said before can run a bit cold this time of year especially… When Mark set it up it was on the rollers and must have been about 85-90 deg as the fans kept coming in… I’ve noticed now that the ECU is running rich when it’s at say 75 as it don’t go to tickover right away… something that it does do at 80… so I need the temp up a bit… Will fit an 82 stat this week and see what it does… But another point here is warming up the air a tad.. When I fit the spacer to the Plenum I used a thermal insulating material to machine it from… end result is the top run’s slap cold. Now you’d think this would improve things, but may be not… so another argument for trying it without it fitted and seeing what it does.
Poor throttle response… definitely not… If anything its too sensitive now and I have to take care on bumpy roads in the wet.. It’s off like a rocket when you floor it…. I know I’m moaning about the shunting here… but the advantages are also very good… Throttle response is the best I’ve ever felt from the few 450 / 500’s I’ve driven.…
The cam is dialed in at 110 deg by Rob and he said this would be fine… don’t really want to mess with this as I’m into unknown territory here on the RV8…
Okay plenty to go at on the top end first… I don’t want to un-do much of Marks work as for one, it was expensive and two, did show other benefits… but it’s all about how the car feels to me rather than max BHP on the rollers..so can justify doing a bit of messing just to see..… I think I’ll remove the spacer and see what that does… then may be think about the stacks etc… thanks muchley for all your comments (and sorry to hijack the post a bit with my issues)… will report back when I get chance to play… cheers….
With regards to building to a pre-determined recipe.. that’s what I thought I was doing… I thought getting all the induction mod’s from V8D would be a sure match for the car / cam etc… and may be they are but just don’t go with my heads?... Rob did offer to put it all back to standard (except the cam).so it’s an option if all else fails but probably won’t go there as the plus side of the work could outweigh the negatives. I did mail them the other day on this but no reply….
Stack length is something that interests me though… Before, I had bit’s of tube in the base but now I have bigger diameter and I think longer Trumpet ended stacks… So increasing the diameter here will slow the speed of air entering the manifold… the increased bore in the manifold will receive this okay and it will then speed up as it goes to the other end where the manifold is closed down on what I had before… If I have big ports in the heads does it then go pear shaped?? I’m thinking opening them out again to match the heads?
The stacks are different lengths in an attempt to make the induction side all the same length from plenum to port… so you could in theory shorten or lengthen them all by the same amount… I’m not sure what the height of the tubes were in the standard unit as I never measured them?… Worth a try messing all the same and thanks for the offer Dave on the bases.. will give you a call if needed.. always nice to swap things out and see what happens.. at least that way you can potentially identify the offending item… but the last post also may have a point… My car as I said before can run a bit cold this time of year especially… When Mark set it up it was on the rollers and must have been about 85-90 deg as the fans kept coming in… I’ve noticed now that the ECU is running rich when it’s at say 75 as it don’t go to tickover right away… something that it does do at 80… so I need the temp up a bit… Will fit an 82 stat this week and see what it does… But another point here is warming up the air a tad.. When I fit the spacer to the Plenum I used a thermal insulating material to machine it from… end result is the top run’s slap cold. Now you’d think this would improve things, but may be not… so another argument for trying it without it fitted and seeing what it does.
Poor throttle response… definitely not… If anything its too sensitive now and I have to take care on bumpy roads in the wet.. It’s off like a rocket when you floor it…. I know I’m moaning about the shunting here… but the advantages are also very good… Throttle response is the best I’ve ever felt from the few 450 / 500’s I’ve driven.…
The cam is dialed in at 110 deg by Rob and he said this would be fine… don’t really want to mess with this as I’m into unknown territory here on the RV8…
Okay plenty to go at on the top end first… I don’t want to un-do much of Marks work as for one, it was expensive and two, did show other benefits… but it’s all about how the car feels to me rather than max BHP on the rollers..so can justify doing a bit of messing just to see..… I think I’ll remove the spacer and see what that does… then may be think about the stacks etc… thanks muchley for all your comments (and sorry to hijack the post a bit with my issues)… will report back when I get chance to play… cheers….
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