This shunting thing!
Discussion
Had I been in charge of selecting the term, I would have described it more as 'surging', rather than 'shunting'.
Would that term match what yours is doing?
I would suppose for most people, it's experienced as a surge followed by a slight hesitation, then repeat until you reach the required rpm for your car to start running smoothly.
Alternatively, keep the throttle in the original position, and it can carry on for a while.
In my case it's at low rpm, light throttle.
TBH I'd never come across the term until I joined PH. After quite a few years driving high lift, long overlap camshaft big block chevy's, it's what I expected of a 'high performance' engine, and have always avoided it by driving 'appropriately', (i.e. loud pedal mashed into the carpet
).
Would that term match what yours is doing?
I would suppose for most people, it's experienced as a surge followed by a slight hesitation, then repeat until you reach the required rpm for your car to start running smoothly.
Alternatively, keep the throttle in the original position, and it can carry on for a while.
In my case it's at low rpm, light throttle.
TBH I'd never come across the term until I joined PH. After quite a few years driving high lift, long overlap camshaft big block chevy's, it's what I expected of a 'high performance' engine, and have always avoided it by driving 'appropriately', (i.e. loud pedal mashed into the carpet
).
Goaty Bill said:
Had I been in charge of selecting the term, I would have described it more as 'surging', rather than 'shunting'.
Would that term match what yours is doing?
I would suppose for most people, it's experienced as a surge followed by a slight hesitation, then repeat until you reach the required rpm for your car to start running smoothly.
Alternatively, keep the throttle in the original position, and it can carry on for a while.
In my case it's at low rpm, light throttle.
TBH I'd never come across the term until I joined PH. After quite a few years driving high lift, long overlap camshaft big block chevy's, it's what I expected of a 'high performance' engine, and have always avoided it by driving 'appropriately', (i.e. loud pedal mashed into the carpet ).
Thats exactly it, its surging! Thank you Would that term match what yours is doing?
I would suppose for most people, it's experienced as a surge followed by a slight hesitation, then repeat until you reach the required rpm for your car to start running smoothly.
Alternatively, keep the throttle in the original position, and it can carry on for a while.
In my case it's at low rpm, light throttle.
TBH I'd never come across the term until I joined PH. After quite a few years driving high lift, long overlap camshaft big block chevy's, it's what I expected of a 'high performance' engine, and have always avoided it by driving 'appropriately', (i.e. loud pedal mashed into the carpet
).
Simon says said:
The real cause is intake related , but not made any better by the lean AF ratio in that light throttle part of the map and slow switching lambda probes trim.
Yes, I should have qualified that, especially as even the 5L doesn't have an especially high lift or long duration camshaft.I have heard that it's not that common or drastic in 4.0L/4.5L cars? Though I only test drove a couple of cars of those engine sizes and it was long time ago.
So as I see it my options are:
A plenum spacer plate.
Torquev8's stuff 72mm AFM, 72mm Smooth flow pipe, 72mm Plenum,
ecu chip.
A Weber 4 barrel downdraught carburettor (my sort of technology)
A megasquirt system or similar. ( I would have no idea what to do with any of that, so its going to be too expensive for me)
Something blitzracing mentioned years ago about resistors and other electrickery?
A plenum spacer plate.
Torquev8's stuff 72mm AFM, 72mm Smooth flow pipe, 72mm Plenum,
ecu chip.
A Weber 4 barrel downdraught carburettor (my sort of technology)
A megasquirt system or similar. ( I would have no idea what to do with any of that, so its going to be too expensive for me)
Something blitzracing mentioned years ago about resistors and other electrickery?
EGB said:
Driving technique make it tolerable. In traffic at 2k rpm use throttle on, coast, throttle on, coast etc etc. Works for me.
Agreed absolutely.It just isn't an issue for me, I almost never get it, because I don't do the things that cause it.
Have to say though, unless I miss my guess, you won't do it any harm by adding the plenum spacer, or smooth flow intake.
It might or might not cure it. Probably make it a little easier to avoid, and won't cost a lot to find out.
Major Fallout said:
So as I see it my options are:
A plenum spacer plate.
Torquev8's stuff 72mm AFM, 72mm Smooth flow pipe, 72mm Plenum,
ecu chip.
A Weber 4 barrel downdraught carburettor (my sort of technology)
A megasquirt system or similar. ( I would have no idea what to do with any of that, so its going to be too expensive for me)
Something blitzracing mentioned years ago about resistors and other electrickery?
we went with the Weber, was a huuuuge improvementA plenum spacer plate.
Torquev8's stuff 72mm AFM, 72mm Smooth flow pipe, 72mm Plenum,
ecu chip.
A Weber 4 barrel downdraught carburettor (my sort of technology)
A megasquirt system or similar. ( I would have no idea what to do with any of that, so its going to be too expensive for me)
Something blitzracing mentioned years ago about resistors and other electrickery?
Major Fallout said:
So as I see it my options are:
A plenum spacer plate.
Torquev8's stuff 72mm AFM, 72mm Smooth flow pipe, 72mm Plenum,
ecu chip.
A Weber 4 barrel downdraught carburettor (my sort of technology)
A megasquirt system or similar. ( I would have no idea what to do with any of that, so its going to be too expensive for me)
Something blitzracing mentioned years ago about resistors and other electrickery?
For some reason some cars seem worse than others. As has been said it is mainly down to a lean mixture in the affected rpm and the use of a decent cam with the plenum setup.A plenum spacer plate.
Torquev8's stuff 72mm AFM, 72mm Smooth flow pipe, 72mm Plenum,
ecu chip.
A Weber 4 barrel downdraught carburettor (my sort of technology)
A megasquirt system or similar. ( I would have no idea what to do with any of that, so its going to be too expensive for me)
Something blitzracing mentioned years ago about resistors and other electrickery?
Many have reported the plenum spacer helps things. This is probably the quickest and cheapest mod to try first.
Failing that a new ecu will sort things and keep the car looking original. But not cheap. If you are not bothered about staying original a Webber carb should sort it as has been stated above. Certainly less to go wrong and if set up right will give a nice ride.
A cam change for something like an MC1 will likely get rid of it. Not an expensive option if you can do it yourself. If your cam is worn this will not help matters either.
Decisions decisions.
carsy said:
Major Fallout said:
So as I see it my options are:
A plenum spacer plate.
Torquev8's stuff 72mm AFM, 72mm Smooth flow pipe, 72mm Plenum,
ecu chip.
A Weber 4 barrel downdraught carburettor (my sort of technology)
A megasquirt system or similar. ( I would have no idea what to do with any of that, so its going to be too expensive for me)
Something blitzracing mentioned years ago about resistors and other electrickery?
For some reason some cars seem worse than others. As has been said it is mainly down to a lean mixture in the affected rpm and the use of a decent cam with the plenum setup.A plenum spacer plate.
Torquev8's stuff 72mm AFM, 72mm Smooth flow pipe, 72mm Plenum,
ecu chip.
A Weber 4 barrel downdraught carburettor (my sort of technology)
A megasquirt system or similar. ( I would have no idea what to do with any of that, so its going to be too expensive for me)
Something blitzracing mentioned years ago about resistors and other electrickery?
Many have reported the plenum spacer helps things. This is probably the quickest and cheapest mod to try first.
Failing that a new ecu will sort things and keep the car looking original. But not cheap. If you are not bothered about staying original a Webber carb should sort it as has been stated above. Certainly less to go wrong and if set up right will give a nice ride.
A cam change for something like an MC1 will likely get rid of it. Not an expensive option if you can do it yourself. If your cam is worn this will not help matters either.
Decisions decisions.
Shunting is not really a misfire as I understand it it's a low speed fuelling issue, and any shunting that I had was solved by a new 885 cam. My car also has the larger plenum (no spacer) and intake setup along with a Mark Adams chip.
My car will now happily burble along at 30mph at 1500 rpm in fifth.
My car will now happily burble along at 30mph at 1500 rpm in fifth.
The general consensus is its poor mixture burn at low gas flows- Some of this can be due to due to the longer cam duration on the TVR cam- this allows more burnt mixture back up into the plenum back up the inlet port as the valves are held open for longer, and this exhaust gas then mixes with the slowly moving clean inlet charge, (thats why the plenum chamber is soot black inside!) which then does not burn well. The moment you open the throttle a bit the increased gas velocity of the inlet charge helps prevent the exhaust gas getting into the plenum, so the burn is then OK. Its not quite that clear cut however, as there are multiple things that can make the burn better or worse- such as the mixture at that point, or the condition of the spark and its timing. The mixture should be clamped at lambda 1 by the ECU, but it has problems accurately measuring the somewhat "lumpy" airflow when when exhaust reversion is taking place, so it may not set the initial mixture correctly in the first place, then when the lambda probes pick up the mixture is wrong, the ECU then starts making corrections after the burn has taken place, and this can lead to some fairly wide swings in mixture as the ECU battles to keep control that adds to the shunting.
You can improve the burn by adding more fuel, which is the fix if you say run a carb', but is almost impossible when the ECU is trying to keep the mixture at lambda 1- no amount of trickery with the AFM will alter the basic mixture setting, unless you drive the AFM output so high the ECU looses control completely and can no longer pull the mixture back to where it should be- this is what was happening on the Torqueflow system as its low speed air measurement is very poor, so you may have less shunting, but you may also find the car grinding to a halt with black plugs as its over fueled. I would like to add- before the Torque flow supporters club jump on my head- this is from my findings from the modified Lucas 5AM systems- Ive not looked at any the current products, but if you retain the 14CUX in catalyst mode, you simply cant richen the mixture without serious bodging.
You can run the 14CUX on the non catalyst fuel map- and then manually set the mixture with the control on the side of the AFM, but you need to have a specific non catalyst fuel map for the TVR- its likely to be a Range Rover fuel map if you simply change the tune resistor. Also if the catalysts are fitted, the wider range of fuel air ratios now allowed can cook the catalysts, so its dangerous. The ECU will run well with no catalysts at all, plus say a Mark Adams non catalyst fuel map- but MOT's then become a problem without catalyst.
You can run aftermarket ECU's for a price, and then try and richen the mixture at the shunting point, and still have enough control to let the catalysts work in the rest of the RPM range- but its a serious investment that may not fix the issue.
The jury is out on the plenum spacer- its possible that a slightly larger plenum volume may reduce the effect of any exhaust contamination, plus it opens up more space between the top of the trumpets and the top of the plenum, which is generally accepted as a good thing- not a huge investment if it does not work.
The first thing to do is make sure everything you have is spot on service wise- Chimpaholic (I think anyway) was praising iridium plugs for an improved burn that may be worth a go. As you may have gathered, many have tried and failed to cure shunting, as there are so many variables.
You can improve the burn by adding more fuel, which is the fix if you say run a carb', but is almost impossible when the ECU is trying to keep the mixture at lambda 1- no amount of trickery with the AFM will alter the basic mixture setting, unless you drive the AFM output so high the ECU looses control completely and can no longer pull the mixture back to where it should be- this is what was happening on the Torqueflow system as its low speed air measurement is very poor, so you may have less shunting, but you may also find the car grinding to a halt with black plugs as its over fueled. I would like to add- before the Torque flow supporters club jump on my head- this is from my findings from the modified Lucas 5AM systems- Ive not looked at any the current products, but if you retain the 14CUX in catalyst mode, you simply cant richen the mixture without serious bodging.
You can run the 14CUX on the non catalyst fuel map- and then manually set the mixture with the control on the side of the AFM, but you need to have a specific non catalyst fuel map for the TVR- its likely to be a Range Rover fuel map if you simply change the tune resistor. Also if the catalysts are fitted, the wider range of fuel air ratios now allowed can cook the catalysts, so its dangerous. The ECU will run well with no catalysts at all, plus say a Mark Adams non catalyst fuel map- but MOT's then become a problem without catalyst.
You can run aftermarket ECU's for a price, and then try and richen the mixture at the shunting point, and still have enough control to let the catalysts work in the rest of the RPM range- but its a serious investment that may not fix the issue.
The jury is out on the plenum spacer- its possible that a slightly larger plenum volume may reduce the effect of any exhaust contamination, plus it opens up more space between the top of the trumpets and the top of the plenum, which is generally accepted as a good thing- not a huge investment if it does not work.
The first thing to do is make sure everything you have is spot on service wise- Chimpaholic (I think anyway) was praising iridium plugs for an improved burn that may be worth a go. As you may have gathered, many have tried and failed to cure shunting, as there are so many variables.
So the plenum is designed for standard engines ,it works fine on Range Rovers and my old 4l MGRV8(working 14cux) was very smooth .Maybe TVR should of designed a different plenum to suit high lift cams ..
Could you imagine buying a 27k Chimaera and then you start kangarooing down the road,i bet there were plenty of cars returned !
Could you imagine buying a 27k Chimaera and then you start kangarooing down the road,i bet there were plenty of cars returned !
Edited by SILICONEKID340HP on Sunday 14th October 19:23
SILICONEKID340HP said:
So the plenum is designed for standard engines ,it works fine on Range Rovers and my old 4l MGRV8(working 14cux) was very smooth .Maybe TVR should of designed a different plenum to suit high lift cams ..
It's not the lift but the duration. Cams with lots of overlap don't work nicely at low rpm with single plenum intakes; end of story. You might mask it a bit with rich mixtures and by backing off the ign advance to force wider throttle openings (and therefore more air) but that's all you're doing. Either drive 'round it or fit throttle bodies (and even then odd things can happen)Gassing Station | Chimaera | Top of Page | What's New | My Stuff