Shunting.

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DaveG

Original Poster:

111 posts

256 months

Sunday 26th July 2015
quotequote all
Shunting. (The insoluble!)
I thought I would share my experiences-observations.
I have a 1995 Griffith 500 bought in the UK in 2002 and shipped out to Oz. During 2002 and 2009 the car ran beautifully, good power and was taken to the track regularly. Having got my license suspended in 09, I decided to pull the engine and replace the cam (38k miles). (Also purchased MS2Extra for later fitting). Cam was local and nothing wild, heads were reconditioned, big ends, rings, performance clutch, trigger wheel, WBO sensor fitted and the Pre-Cats removed, everything else standard.
In 2010 after my rebuild there were signs of shunting/hesitation. I tried all the usual tweaks for a std engine including variable fuel regulator, but could not resolve. Having purchased the Megasquirt (fuelling & ignition- now 3.2.5) I thought I would install this and tune out the problem.
Continuous tuning 2010-2015 and I still have the problem. This is how I define my shunting – light or easing throttle between 1200-2100rpm causing a light snatching in the transmission. If not corrected by dipping clutch or more throttle, becomes shunt proper (kangaroo).
Only evidence in the log is 50-100rpm superimposed on revs. (TPS, and other datalogs – nothing.). Here is my list of extensive tuning tests (4yrs) attempting to cure:
Non-Mechanical tests:-
- Untold logging runs varying every combination of tune maps (VE, AFR, Spark) plus/minus 3/4 points
- Multiple Req.Fuel ratios settings (14-17)
- Speed Density (variable MAP/TPS) based tuning for 3yrs
- AlphaN / TPS tuning based for 1yr (current)
- Simultaneous/alternating fuelling
- Idle PID, CL PID, no PID
- Ignition events (12 – 32)
- Loads of MSQ and logs available

Mechanical tests:-
- Timing 9 - BTDC, 28 – 3000rpm
- CAM (Dur 283, overlap 60, phase 112)
- Plenum spacer (3mm), no spacer
- New stepper
- With and without stepper
- Base idle adjustment (0 – 6 turns)
- Injectors, change from std to 4 pintle (19lb)
- New fuel regulator
- Flared carbon trumpets
- New coil packs(2)
- No detectable air leaks, servo, PBR, dip stick, breathers, etc (except inlet manifold)
- Oil catcher added
- HT Cables /boots interchanged (spare sets)
- Plugs – BP7ECS / BP6ES

All of these and combinations thereof have not resolved. Suggestions from Phil and Shaun have been incorporated at various stages all to no avail!!

As a final test, I have now removed Megasquirt and re-installed dizzy/14CUX, rechecked the setup (ignition, MAF, TPS, base idle, etc). The car fires up beautifully and runs well, BUT still shunts !!

I have concluded that it is not a ‘soft’ issue, but mechanical. The slight easing of the throttle presumably causes a small increase in vacuum which starts the shunt. It is that balance point when holding the throttle in any gear between 1200 – 2000rpm. (especially 3rd and 4th) These tests appear to point to:-
- CAM
- Induction / manifold changes?
- Exhaust back pressure (no pre-cats)
- ?????

I will be in UK (Aug/Sept) and have an opportunity to buy parts (i.e. cam, etc), but really at a loss for a solution.
- Experts advise that it will not be the CAM.
- Induction manifold/plenum/butterfly,etc has not changed (manifold gasket leak?)
- Put cone baffles in the exhaust?
- Desperate !

Anyhow I thought I would share my experiences and my disappointment that she does not run as sweet as when I bought her!! (I have learnt a lot and it has kept me occupied for 4 years.) I have not really looked at Roverguage, but as an aside, would be interested to hear if it could be used to create an exact copy of the 14CUX maps for MS (i.e. spark, AFR) and let it create the VE?
Feel free to add your pennies worth!!
(I have probably not included all the tests I have done, - just off the top of the head.)


Edited by DaveG on Sunday 26th July 14:12


Edited by DaveG on Sunday 26th July 14:17

ChimpOnGas

9,637 posts

178 months

Sunday 26th July 2015
quotequote all
It looks like you've really covered all bases to me but have you tried running the car without the spark plug extenders?

I found deleting them combined with a set of the excellent MSD Super Conductor leads and 8 NGK BPR6EIX made a massive difference on my car.

The other thing that really improved the way the car drove around the 1200 - 1800rpm mark was removing the cats, I can't say for sure they were blocked but mine were clearly a big restriction as the car was transformed with them removed.

I remain massively impressed with the MSD Super Conductor leads, switching out the dreadful Magnecors for the MSDs could be felt immediately, the extenders are another clear point of ignition failure too so my advise is get shot of them and use proper heat socks instead.

Here's what I've done to ensure the leads don't get heat damaged by the hot exhaust maifolds.

http://www.pistonheads.com/Gassing/topic.asp?h=0&a...



swisstoni

16,850 posts

278 months

Sunday 26th July 2015
quotequote all
First, a declaration; I barely know a spanner from a hammer.

The cam seems to have been ruled out by 'experts' without further investigation. With so many other things already checked out, I wouldn't be so sure about that.

andy43

9,548 posts

253 months

Sunday 26th July 2015
quotequote all
swisstoni said:
First, a declaration; I barely know a spanner from a hammer.

The cam seems to have been ruled out by 'experts' without further investigation. With so many other things already checked out, I wouldn't be so sure about that.
I concur. The spanner's always the tool nearest to hand when a hammer is needed, in my considerable technical experience (not much) smile

I kind of agree regarding cam - was ok before, then problems started? If it's lairy-er (even standard but not worn out) compared to old cam, then maybe it is the cause? And throttle pot - an amateur guess - was the same part used with the other ecu system?
There was a shunting thread on here somewhere started by blitzracing - looks like OP has tried a completely different ecu system anyway, but theory was that you can remap the 14CUX to dump more fuel in just within the narrow shunting rev range - may be worth asking him if you could try it with rovergauge. Please note I know nothing!

Sardonicus

18,928 posts

220 months

Sunday 26th July 2015
quotequote all
I would never have removed the MS confused when it was clearly not the problem frown and this combo may not work for every set up but I have to run in the high 12 AFR's inc my target AFR values to eliminate shunting my engine config is also more severe than what you currently have i.e bigger cam with narrow LSA no trumpets etc, even pre rebuild my almost stock 4.0 at to run low 13's to stop the dreaded lurch but I have found I have found 1500 - 1900 the real bd area anything over 2 k and the motor is cloud9 but this time where as before retarding the ign timing in this area improved things I have added adv and improved things further with the new build scratchchin I cant complain really because my cam is quite radical and was never going to improve the cross contamination in the plenum situation severe cam timing and the RV8 plenum dont bode well redface however its strange that no matter what the RV8 capacity or tune cam specs etc the lurch area is always consistent in this RPM area. Just added to say your 14-17 AFR's will never work at those RPM's by diff would try removing itself from my chassis at these I cant even get a nice idle at those, I also run speed density (for the road it has benefits) even though my vacuum signal is now piss poor 60 KPA due to said mechanical/solid cam there are many in the states running successfully with bigger cams and worse vac signals but I do run with an inline filter and a weber fuel jet in the vac line to smooth the vacuum signal to the MS its always worked great for me and gives a steady consistent operation.








Edited by Sardonicus on Sunday 26th July 15:03

ChimpOnGas

9,637 posts

178 months

Sunday 26th July 2015
quotequote all
Sardonicus said:
I do run with an inline filter and a weber fuel jet in the vac line to smooth the vacuum signal to the MS its always worked great for me and gives a steady consistent operation.
Hi Simon, can you educate me further on this please teacher

Sounds interesting scratchchin

And to the OP, you should definitely put the MS back on as Simon says yes

In fact listen carefully to everything Simon (Sardonicus) is telling you, he speaketh the truth.

I'm on the Canems system and she's smooth as a baby's bum, but I've still seen further improvements recently from the excellent MSD Super Conductor leads cool

I once thought to get these cars super smooth at the difficult 1200 - 1800rpm area would take a dual plane inlet manifold, but with a mappable engine management system and good ignition components and I've found my Chimaera can be made to drive like a complete pussy cat.

To me getting the car driving nicely in the low RPM window has been the best improvement I've made to the car, I can now concentrate on enjoying the drive not driving in an unnatural way to compensate for a nasty trait.
  • Ditch the cats
  • Fit decent extended electrode spark plugs
  • Ditch the plug extenders
  • Fit decent HT leads
  • Put the MegaSquirt back on
  • Follow Simon's mapping tips
Do that lot and it'll drive like a dream thumbup


ch427

8,858 posts

232 months

Sunday 26th July 2015
quotequote all
The thread about changing the fuel maps is a very good read, most of the programming goes over my head but my hat goes out the guys who have worked very hard on this.
Im sure one of them will be along soon to advise further but it may be worth enquiring about trying one of their modified chips/maps.

DaveG

Original Poster:

111 posts

256 months

Monday 27th July 2015
quotequote all
Thanks for responses and suggestions. I have taken onboard the comments with the following reservations:
Leads & shrouds:
I have different leads used for 14CUX and MS (Both could be faulty?). The shroud's are original, used when it was good and when shunting.(Possible culprit? Maybe one, but not all eight)
CAM.
One expert who specialises in RV8 race engines indicates that you can probably be up to 2 deg out and still not show those distinct problems. Also said the pre-loads could be up to 80 thou and still work ok. My first instinct was to change the CAM again, but 400Pds and a lot of work for possibly no result?
14CUX vs MS
I only reverted back to prove a point. You would imagine that after 4 yrs of mapping that I would have had more success - hence the mechanical focus.
AFR's
I have set the map down in the 12's and varied the spark +-3/4 degrees. Also in the 15's. ??
Vacuum/MAP
My vac is 51-53Kpa at idle (875rpm, can drop it to 49-50 at 900-1000rpm) It has been consistent with this CAM.
My MAP noise is pretty good. (Lag Filter=40) I tried an inline fuel filter - no change. I now have inline restrictor, probably similar to your Weber jet.

Exhaust back pressure?
No comments here. It will not be easy putting baffles back into the exhaust manifold and may also be a no result effort.

MS
I can easily re-install MS. I could go to MS3, but if I cannot fix with MS2?? If it is 'mechanical' then I should be able to fix with 14CUX?

Keep the comment coming guys.
Thanks
D.


Edited by DaveG on Monday 27th July 07:37


Edited by DaveG on Monday 27th July 07:38

spitfire4v8

3,990 posts

180 months

Monday 27th July 2015
quotequote all
I have two conflicting experiences with lucas v aftermarket.

On the lucas I've always found better low speed manners with slightly retarded timing , this may be because with the lucas and cats you're clamped to a lambda=1 mixture and it benefits the low speed running to retard things slightly and pick up air speed in the ports.
Indeed, one of the key benefits with going to a larger AFM on the lucas is that you can pick up power from the large bore AFM and have the luxury of then retarding the timing .. you still make a good HP gain from the AFM but can often tidy the lower speed running up on the slightly less advance you're then running. Not ideal still but better than before in all respects.

However on aftermarket where you can run whatever mix you want I've always found better results running slightly richer and very advanced .. not a few degrees .. I mean you might have 10deg adv at idle but the first load row up from there you might be running 30-50 degrees advance.
It really is a case of trial and error but I would agree with getting the MS back on there in open loop , going throttle angle v revs for your map, and run lots of advance on light cruise and see what happens.

Sardonicus

18,928 posts

220 months

Monday 27th July 2015
quotequote all
spitfire4v8 said:
I have two conflicting experiences with lucas v aftermarket.

On the lucas I've always found better low speed manners with slightly retarded timing , this may be because with the lucas and cats you're clamped to a lambda=1 mixture and it benefits the low speed running to retard things slightly and pick up air speed in the ports.
Indeed, one of the key benefits with going to a larger AFM on the lucas is that you can pick up power from the large bore AFM and have the luxury of then retarding the timing .. you still make a good HP gain from the AFM but can often tidy the lower speed running up on the slightly less advance you're then running. Not ideal still but better than before in all respects.

However on aftermarket where you can run whatever mix you want I've always found better results running slightly richer and very advanced .. not a few degrees .. I mean you might have 10deg adv at idle but the first load row up from there you might be running 30-50 degrees advance.
It really is a case of trial and error but I would agree with getting the MS back on there in open loop , going throttle angle v revs for your map, and run lots of advance on light cruise and see what happens.
That all makes sense, I also found less advance with the Lucas paid off this was back in the day when I was playing with Blitz-Racings/Mark's AFM interface and 02 gizmo that allowed me to alter the fuel trimming thus knocking out the O2 sensors feedback (locked out) many moons ago snatching could be virtually eliminated and this was on a 4.0HC scratchchin since the more radical new build I have found that advance also pays off where as before things got worse its a real minefield ill grant you frown

steve-V8s

2,899 posts

247 months

Monday 27th July 2015
quotequote all
In my experience the only real solution is to throw away the plenum and fit individual throttle bodies. You can then run a fairly aggressive cam have really nice driveability and a much improved throttle response.

carsy

3,018 posts

164 months

Monday 27th July 2015
quotequote all
Everything Sardonicus and ChimponGas say. If you still cant dial it out with the MS2 i would be looking at the cam; its the only thing you have changed. I know you say its not a huge cam but it maybe bigger than you think. Do you know exactly what it is. Go for an known quantity that is known not to shunt such as Powers 885 or similar. Or as above some nice throttle bodies.

Nice engine bay BTW.

dnb

3,330 posts

241 months

Monday 27th July 2015
quotequote all
With plenty of work you can get a 5 litre with H404 cam to not shunt and to run smoothly. Nothing much is impossible really if you solve the real problems and understand what you're trying to do.

Sardonicus said:
Lots of good advice and ...but I do run with an inline filter and a weber fuel jet in the vac line to smooth the vacuum signal to the MS its always worked great for me and gives a steady consistent operation.
I too use a restrictor in the vacuum line. It acts to stabilise the pressure signal and smooth out transients. It's a bit of a balance here between lag and stability, but it's not all that critical - remember that the throttle position sensor is there to add (or subtract) fuel for transient operation. It's well worth trying this if your MAP signal is noisy from having a lumpy cam.

In my limited experience, shunting seems to be caused by bad positive feedback loops from some weakness in either the engine control or actuation. E.G. Closed loop fuelling getting confused by reading misfires as lean and increasing fuelling until a misfire is really serious.

Best of luck with it all.

DaveG

Original Poster:

111 posts

256 months

Tuesday 28th July 2015
quotequote all
Thanks again for the additional suggestions, thoughts.
My thinking at present has 4 possible options all of which would revert back to MS2 for the extra control:

1. Look at installing some cone baffles to compensate for removed pre-cats.
2. Book a comprehensive Dyno session and get a good spark map to suit the engine (always a bit of an unknown) and good AFR's.
3. Change the induction side characteristics with these:-

4. Swap the CAM again for say a 885. (Could be just repeating my past tuning experience?)

Those are probably in preferred order, but would need to find good Dyno tuner to work with MS (Has anybody used dyno-tuning for the spark map across the range?)
The twin throttle kit is from a Triumph/Rover specialist here in Oz and I like the idea of some 'mechanical' change?
On the controller side, I too have felt that there is some positive feedback getting introduced (I can see this 50-100rpm cycle superimposed on the 'steady state' revs log.) However similar must be happening with 14CUX, I just have no way of seeing it?

I am going to be in the UK/Europe for 6 wks so have some time to ponder/review.
Thanks, more comments and experiences please.
D.

Edited by DaveG on Tuesday 28th July 01:40


Edited by DaveG on Tuesday 28th July 08:20

dnb

3,330 posts

241 months

Tuesday 28th July 2015
quotequote all
Taking your points in order:

No idea if baffles instead of cats will help. My suspicion is they won't make much difference.

I have done a bit of mapping of ignition on the dyno. It was mostly getting the top end right on my old engine, but we did work on drivability for a while and got some interesting results - it was much harder to make shunting occur because of the way the dyno was set up to apply a constant load - but well worth getting data from this sort of experiment if the hourly rate isn't too high. (I am looking at doing this again for my new engine)

My opinion is that while there may be a power benefit from the twin throttles on a single plenum, it won't help with the shunting because it isn't fixing the "charge robbing" problem - there are still 8 cylinders breathing through one plenum.

DaveG

Original Poster:

111 posts

256 months

Wednesday 29th July 2015
quotequote all
Thanks DNB. Points noted. I am hoping a "steady state" dyno can be used to give me a good cross range result. I must say the std dizzy gives a pretty good result. I'm surprised nobody has mapped the std dizzy - KPa vs RPM for MS. I guess it means plotting with weights only and adding a 'band' of advance for the vacuum? (I might see what dizzy reconditioners do and what they can plot?)
The back pressure is an interesting one and I personally think it could be a contributing factor - just don't fancy pulling the exhaust manifolds again now they are nicely sealed!

blitzracing

6,387 posts

219 months

Wednesday 29th July 2015
quotequote all
Id suspect the new cam is causing more exhaust gas to contaminate the inlet charge during valve overlap as it mixes with the low volume of fresh air in the plenum at low throttle openings. All the frigging about with mixture / plugs / leads / timing is simply a way of trying to get the contaminated inlet charge to burn properly. What I dont understand is its cyclic nature- Ive yet to find a sensor input that the ECU uses that reflects the same cycle period. Id expect the AFM output to show if the engines breathing changing as the car shunts, but I don't recollect seeing this. It would be interesting to have a logged output of a MAP sensor on the plenum during shunting to see if there is something tangible there.

andy43

9,548 posts

253 months

Wednesday 29th July 2015
quotequote all
If the old cam was worn circular the increase in valve lift would make sense.
And trumpets - on twin carbs I seem to remember the inlet tract for power is stumpy and short, for torque it's longer, admittedly that's for one choke per cylinder - but have much longer trumpets (which would reduce mixing of individual cylinders?) and a huge inch high plenum spacer ever been tried?
My standard 4.0 HC will pull lovely from 30 in 5th when it's reached temp. When warming up it's nowhere near as settled though.

blitzracing

6,387 posts

219 months

Thursday 30th July 2015
quotequote all
andy43 said:
If the old cam was worn circular the increase in valve lift would make sense.
And trumpets - on twin carbs I seem to remember the inlet tract for power is stumpy and short, for torque it's longer, admittedly that's for one choke per cylinder - but have much longer trumpets (which would reduce mixing of individual cylinders?) and a huge inch high plenum spacer ever been tried?
My standard 4.0 HC will pull lovely from 30 in 5th when it's reached temp. When warming up it's nowhere near as settled though.
I have my doubts about the plenum spacer bit- the thinking that a spacer gives more fresh air volume is fundamentally flawed as the plenum chamber is on the vacuum side of the throttle plate, so increasing its size simply means you have a larger chamber to fill as you open the throttle, so I dont see the advantage.

domV8

1,375 posts

180 months

Friday 31st July 2015
quotequote all
carsy said:
...I know you say its not a huge cam but it maybe bigger than you think. Do you know exactly what it is. Go for an known quantity that is known not to shunt such as Powers 885 or similar.
TVR885 cam is not "shunt-proof". Mine shunted like a pig after my rebuild, even on Emerald, until I managed to get it mapped out after many on-road mapping sessions. Doesn't shunt at all now, but I didn't do the mapping so I cant tell you the secret frown


blitzracing said:
I have my doubts about the plenum spacer bit- the thinking that a spacer gives more fresh air volume is fundamentally flawed as the plenum chamber is on the vacuum side of the throttle plate, so increasing its size simply means you have a larger chamber to fill as you open the throttle, so I dont see the advantage.
Surely the larger plenum volume means the contaminant going back into the plenum is a smaller percentage of the entire volume = marginally less contaminated charge than a non-spacer plenum volume?

I would have thought anything that reduces the contaminant "ratio" has to be a positive step for those suffering the effects of shunting...

Dom