Shunting Solved
Discussion
I have been suffering with a shunting problem on my Cimaera 4.0HC, I hope this will help others with a similar problem?.
When I bought the car in the spring it had suffered from very little use and shunted quite badly until the engine spun over 2200rpm.
After about a 1000 miles of Shell Optimax/VPower fuel it started to get progressively better but at 3000 miles it had stopped improving and the shunting, although reduced, was still a pain.
Three weeks ago I replaced the leads, plugs and extenders, it got a bit better.
Number 8 lead shroud was badly burnt though, it was arcing on the exhaust manifold, so to be honest I had hoped for more of an improvement.
Last weekend I added the ACT smooth bore elbow & a K&N air filter, it got a lot better, actually it surprised me how much these relatively simple changes made to the throttle response.
Then yesterday I really went for it and fitted a SC-Power plenum spacer, heat insulating plenum base gasket, trumpet bell mouths and cut the trumpets themselves down just a little bit (8mm).
I wanted to start with a small reduction in trumpet length first so I could experiment in small stages.
The spacer already had the effect of moving the trumpets away from the plenum roof by 20mm so in total they are now 28mm further away from the roof and live in a plenum that has had its volume increased by half a litre.
The car is now a totally different animal, it runs sooo smoooooth and gear changes are much cleaner.
I cant comment on any power increases I may have added but I can defiantly say its a much easier and more enjoyable car to drive.
The engine fuels & breaths fantastically well all the way from idle to the very upper limits.
Because I can now grab the gears faster, get on the power earlier it feels faster and easier to drive faster.
Early tests seem to indicate its using less fuel too.
Perhaps a bit of a cheque-book cure to the problem but hope my ramblings help others with the same issues get their cars running better?
Regards, Dave.
When I bought the car in the spring it had suffered from very little use and shunted quite badly until the engine spun over 2200rpm.
After about a 1000 miles of Shell Optimax/VPower fuel it started to get progressively better but at 3000 miles it had stopped improving and the shunting, although reduced, was still a pain.
Three weeks ago I replaced the leads, plugs and extenders, it got a bit better.
Number 8 lead shroud was badly burnt though, it was arcing on the exhaust manifold, so to be honest I had hoped for more of an improvement.
Last weekend I added the ACT smooth bore elbow & a K&N air filter, it got a lot better, actually it surprised me how much these relatively simple changes made to the throttle response.
Then yesterday I really went for it and fitted a SC-Power plenum spacer, heat insulating plenum base gasket, trumpet bell mouths and cut the trumpets themselves down just a little bit (8mm).
I wanted to start with a small reduction in trumpet length first so I could experiment in small stages.
The spacer already had the effect of moving the trumpets away from the plenum roof by 20mm so in total they are now 28mm further away from the roof and live in a plenum that has had its volume increased by half a litre.
The car is now a totally different animal, it runs sooo smoooooth and gear changes are much cleaner.
I cant comment on any power increases I may have added but I can defiantly say its a much easier and more enjoyable car to drive.
The engine fuels & breaths fantastically well all the way from idle to the very upper limits.
Because I can now grab the gears faster, get on the power earlier it feels faster and easier to drive faster.
Early tests seem to indicate its using less fuel too.
Perhaps a bit of a cheque-book cure to the problem but hope my ramblings help others with the same issues get their cars running better?
Regards, Dave.
Chimpaholic said:
I have been suffering with a shunting problem on my Cimaera 4.0HC, I hope this will help others with a similar problem?.
When I bought the car in the spring it had suffered from very little use and shunted quite badly until the engine spun over 2200rpm.
After about a 1000 miles of Shell Optimax/VPower fuel it started to get progressively better but at 3000 miles it had stopped improving and the shunting, although reduced, was still a pain.
Three weeks ago I replaced the leads, plugs and extenders, it got a bit better.
Number 8 lead shroud was badly burnt though, it was arcing on the exhaust manifold, so to be honest I had hoped for more of an improvement.
Last weekend I added the ACT smooth bore elbow & a K&N air filter, it got a lot better, actually it surprised me how much these relatively simple changes made to the throttle response.
Then yesterday I really went for it and fitted a SC-Power plenum spacer, heat insulating plenum base gasket, trumpet bell mouths and cut the trumpets themselves down just a little bit (8mm).
I wanted to start with a small reduction in trumpet length first so I could experiment in small stages.
The spacer already had the effect of moving the trumpets away from the plenum roof by 20mm so in total they are now 28mm further away from the roof and live in a plenum that has had its volume increased by half a litre.
The car is now a totally different animal, it runs sooo smoooooth and gear changes are much cleaner.
I cant comment on any power increases I may have added but I can defiantly say its a much easier and more enjoyable car to drive.
The engine fuels & breaths fantastically well all the way from idle to the very upper limits.
Because I can now grab the gears faster, get on the power earlier it feels faster and easier to drive faster.
Early tests seem to indicate its using less fuel too.
Perhaps a bit of a cheque-book cure to the problem but hope my ramblings help others with the same issues get their cars running better?
Regards, Dave.
You have probibly hit the nail on the head, as I think shunting caused by a series of things that boils down to a lean mixture and poor burn, and possibly poor cylinder filling on the longer duration cams at lower RPM, so as you have found improvements in any of these areas helps. Odd thing though my engine did it slightly on the catalysts map after porting the engine and fitting a 270' cam, but after fitting some decibel tubes to reduce the noise from my side pipes, the shunting dissapeared completely, so a bit more exhaust back pressure helped. Maybe less mixture was lost down the pipes at overlap with a bit more back pressure ???When I bought the car in the spring it had suffered from very little use and shunted quite badly until the engine spun over 2200rpm.
After about a 1000 miles of Shell Optimax/VPower fuel it started to get progressively better but at 3000 miles it had stopped improving and the shunting, although reduced, was still a pain.
Three weeks ago I replaced the leads, plugs and extenders, it got a bit better.
Number 8 lead shroud was badly burnt though, it was arcing on the exhaust manifold, so to be honest I had hoped for more of an improvement.
Last weekend I added the ACT smooth bore elbow & a K&N air filter, it got a lot better, actually it surprised me how much these relatively simple changes made to the throttle response.
Then yesterday I really went for it and fitted a SC-Power plenum spacer, heat insulating plenum base gasket, trumpet bell mouths and cut the trumpets themselves down just a little bit (8mm).
I wanted to start with a small reduction in trumpet length first so I could experiment in small stages.
The spacer already had the effect of moving the trumpets away from the plenum roof by 20mm so in total they are now 28mm further away from the roof and live in a plenum that has had its volume increased by half a litre.
The car is now a totally different animal, it runs sooo smoooooth and gear changes are much cleaner.
I cant comment on any power increases I may have added but I can defiantly say its a much easier and more enjoyable car to drive.
The engine fuels & breaths fantastically well all the way from idle to the very upper limits.
Because I can now grab the gears faster, get on the power earlier it feels faster and easier to drive faster.
Early tests seem to indicate its using less fuel too.
Perhaps a bit of a cheque-book cure to the problem but hope my ramblings help others with the same issues get their cars running better?
Regards, Dave.
blitzracing said:
Chimpaholic said:
I have been suffering with a shunting problem on my Cimaera 4.0HC, I hope this will help others with a similar problem?.
When I bought the car in the spring it had suffered from very little use and shunted quite badly until the engine spun over 2200rpm.
After about a 1000 miles of Shell Optimax/VPower fuel it started to get progressively better but at 3000 miles it had stopped improving and the shunting, although reduced, was still a pain.
Three weeks ago I replaced the leads, plugs and extenders, it got a bit better.
Number 8 lead shroud was badly burnt though, it was arcing on the exhaust manifold, so to be honest I had hoped for more of an improvement.
Last weekend I added the ACT smooth bore elbow & a K&N air filter, it got a lot better, actually it surprised me how much these relatively simple changes made to the throttle response.
Then yesterday I really went for it and fitted a SC-Power plenum spacer, heat insulating plenum base gasket, trumpet bell mouths and cut the trumpets themselves down just a little bit (8mm).
I wanted to start with a small reduction in trumpet length first so I could experiment in small stages.
The spacer already had the effect of moving the trumpets away from the plenum roof by 20mm so in total they are now 28mm further away from the roof and live in a plenum that has had its volume increased by half a litre.
The car is now a totally different animal, it runs sooo smoooooth and gear changes are much cleaner.
I cant comment on any power increases I may have added but I can defiantly say its a much easier and more enjoyable car to drive.
The engine fuels & breaths fantastically well all the way from idle to the very upper limits.
Because I can now grab the gears faster, get on the power earlier it feels faster and easier to drive faster.
Early tests seem to indicate its using less fuel too.
Perhaps a bit of a cheque-book cure to the problem but hope my ramblings help others with the same issues get their cars running better?
Regards, Dave.
You have probibly hit the nail on the head, as I think shunting caused by a series of things that boils down to a lean mixture and poor burn, and possibly poor cylinder filling on the longer duration cams at lower RPM, so as you have found improvements in any of these areas helps. Odd thing though my engine did it slightly on the catalysts map after porting the engine and fitting a 270' cam, but after fitting some decibel tubes to reduce the noise from my side pipes, the shunting dissapeared completely, so a bit more exhaust back pressure helped. Maybe less mixture was lost down the pipes at overlap with a bit more back pressure ???When I bought the car in the spring it had suffered from very little use and shunted quite badly until the engine spun over 2200rpm.
After about a 1000 miles of Shell Optimax/VPower fuel it started to get progressively better but at 3000 miles it had stopped improving and the shunting, although reduced, was still a pain.
Three weeks ago I replaced the leads, plugs and extenders, it got a bit better.
Number 8 lead shroud was badly burnt though, it was arcing on the exhaust manifold, so to be honest I had hoped for more of an improvement.
Last weekend I added the ACT smooth bore elbow & a K&N air filter, it got a lot better, actually it surprised me how much these relatively simple changes made to the throttle response.
Then yesterday I really went for it and fitted a SC-Power plenum spacer, heat insulating plenum base gasket, trumpet bell mouths and cut the trumpets themselves down just a little bit (8mm).
I wanted to start with a small reduction in trumpet length first so I could experiment in small stages.
The spacer already had the effect of moving the trumpets away from the plenum roof by 20mm so in total they are now 28mm further away from the roof and live in a plenum that has had its volume increased by half a litre.
The car is now a totally different animal, it runs sooo smoooooth and gear changes are much cleaner.
I cant comment on any power increases I may have added but I can defiantly say its a much easier and more enjoyable car to drive.
The engine fuels & breaths fantastically well all the way from idle to the very upper limits.
Because I can now grab the gears faster, get on the power earlier it feels faster and easier to drive faster.
Early tests seem to indicate its using less fuel too.
Perhaps a bit of a cheque-book cure to the problem but hope my ramblings help others with the same issues get their cars running better?
Regards, Dave.
Hi blitzracing,
Thanks for your comments, my methods were a bit hit and mis but fundamentally based on some old school theory.
At first I had looked at the Mark Adams chip but before spending the cash on fuelling I went back to basics.
I came to the conclusion the shunting was something to do with volumetric efficiency at low rpm, the Lucas fuel system seems to be pretty good at compensating for most conditions so I focused on the induction side.
It struck me that the induction side is more suited to Range Rover tasks, as I am not planning on driving the Chimaera up a muddy mountain I reasoned there could be some benefit in moving the peak torque further up the rev range.
I figured this would better suit a car weighing just over 1000kg thats fitted with a moderately aggressive cam profile.
Honestly the results are very pronounced, today I happily drove through central London on my way back home to Watford, something I would definitely avoid before my mods.
The car is so much more pleasurable to drive now, it just feels right, where before it made me feel tense driving at low rmp.
So next comes the pre-cat removal, the main cat stays retain sufficient back pressure.
Any tips on removing the pre-cats?
Nice website by the way.
dogbucket said:
So was that the SC Power complete kit @ £195?
Their photos seem a little confusing as to what you get in regards of the bell mouths, did it include the new pipes of various lengths to fit into the base plus the trumpet tops?
Their photos seem a little confusing as to what you get in regards of the bell mouths, did it include the new pipes of various lengths to fit into the base plus the trumpet tops?
Yep thats the kit, its the option four (last one in the list) titled "Plenum Spacer, Insulating gasket, extended bolts and Bell Mouth Trumpets".
It looks a bit confusing in the photo because the bell mouths are sat inside the insulating gasket.
I can not recommend this kit highly enough, it (along with the ACT elbow) transformed the way my Chimaera drives.
Ask away if you need any further advice. Dave.
thanks, so did you have to bake the base in the oven to get the old pipes out? So the new pipes are ready cut to length like the photo above the kit, then you lobbed another 8mm off first?
My only other thought is how they compare to the carbon superflare trumpets which cost twice as much but claim better gains, although I guess knowbody has done back to back testing.
My only other thought is how they compare to the carbon superflare trumpets which cost twice as much but claim better gains, although I guess knowbody has done back to back testing.
dogbucket said:
thanks, so did you have to bake the base in the oven to get the old pipes out? So the new pipes are ready cut to length like the photo above the kit, then you lobbed another 8mm off first?
My only other thought is how they compare to the carbon superflare trumpets which cost twice as much but claim better gains, although I guess knowbody has done back to back testing.
My only other thought is how they compare to the carbon superflare trumpets which cost twice as much but claim better gains, although I guess knowbody has done back to back testing.
Your old pipes are retained, what you get are the bell mouths, which is why its cheaper than the ACT carbon trumpets.
The bell mouths are effectively rings with rolled edges that fit in top of your existing pipes.
You could argue that the ACT carbon trumpets are a more complete design as the SC-Power bell mouths are a mixture of your existing parts and some improved mouths.
You choose how much you want to shorten your existing pipes and then fit the bell mouths to the end of them.
When you look at your standard pipes you will see they actually already have the bell mouth shape, this is why they are known a trumpets.
But the standard trumpet mouths are not as close together or as big as when the SC-Power bell mouths are fitted.
Fitting the bell mouths and the shortening of trumpets can be done by Colin at SC-Power for £50 if you want to take some of the hassle out of the job.
I reasoned that the big advantage of the SC-Power kit over fitting the ACT trumpets is that you can reduce the pipe length in stages.
The ACT trumpets make a big jump in the length, I have no doubt this has been well tested but it is fixed.
The point is the shorter the trumpets are the further you move peak torque up the rev range.
I was looking to create a smooth linear power delivery right from idle so I have ended up with trumpets that are somewhere between the ACT trumpets and the standard ones.
Also for the same money as the ACT trumpets the SC-Power kit gives you the very useful plenum spacer and the heat insulating gasket.
I believe the plenum spacer played a big part in improving my throttle response, it not only increases the plenum volume but has the effect of bringing the trumpet mouths 20mm further away from the plenum roof.
Its a bit like shortening the standard trumpets by another 20mmm, but better, as you expand the plenum volume by 0.5 ltres at the same time.
The fitting of the SC-Power kit is very simple, Colin will send you some longer plenum bolts in the kit and I can talk you through the job if you need help.
I have had dealings with ACT and Tim is fantastically helpful and his parts are very well proven too.
So which ever way you choose to go I am sure you will see improvements, however I can only comment on the path I took and the result achieved on my particular car.
And believe me, the results were worth every penny.
Dave.
Chimpaholic said:
I have been suffering with a shunting problem on my Cimaera 4.0HC, I hope this will help others with a similar problem?...........
Hi Dave, At the risk of asking a stupid question. When you say shunting, do you mean the feeling that the car wants to keep moving forward while not pressing on the accelerator? Similar to incorrect timing?
This sounds awfully similar to my Chim, but mine is a non HC engine? at least i think it is!!!! Could the standard 400 engine have the same issue?
Chimpaholic said:
Last weekend I added the ACT smooth bore elbow & a K&N air filter, it got a lot better, actually it surprised me how much these relatively simple changes made to the throttle response.
Regards, Dave.
Secondly, sounds good about the smooth bore elbow, do you know why that elbow is more efficient than the standard item? Is it just the fact that the airflow is smoother along the silicone tube?Regards, Dave.
Cheers
Allan
The ones I have come across are all very simular. It occurs at around 1700 RPM in the higher gears under light throttle openings, and starts as a slight hesitation but rapidly becomes snatching or shunting that can really hammer the drive train if its left to continue. It will dissapear the moment you give the car more throttle, or dip the clutch.
allanb said:
Chimpaholic said:
I have been suffering with a shunting problem on my Cimaera 4.0HC, I hope this will help others with a similar problem?...........
Hi Dave, At the risk of asking a stupid question. When you say shunting, do you mean the feeling that the car wants to keep moving forward while not pressing on the accelerator? Similar to incorrect timing?
This sounds awfully similar to my Chim, but mine is a non HC engine? at least i think it is!!!! Could the standard 400 engine have the same issue?
Chimpaholic said:
Last weekend I added the ACT smooth bore elbow & a K&N air filter, it got a lot better, actually it surprised me how much these relatively simple changes made to the throttle response.
Regards, Dave.
Secondly, sounds good about the smooth bore elbow, do you know why that elbow is more efficient than the standard item? Is it just the fact that the airflow is smoother along the silicone tube?Regards, Dave.
Cheers
Allan
As an ex-mechanic with a many years in the classic and vintage restoration world I would prefer to call it "hesitance".
Its more of a sensation, a feeling that would normally have me searching for an induction leak or a fuelling fault on the older stuff I am more familiar with.
Its doesn't exactly make the car un-drivable and you can get used to it, I just knew that with all that torque and a 4.0 litre V8 in such a light car things should be feeling much smoother.
The thing we need to understand is what TVR Power did to the the Range Rover engine, but more importantly what they didn't do.
The Range Rover setup is perfect for pulling a horse box or driving up a vertical slope at 4mph.
You need low down power to perform these tasks, so the induction side was carefully set up (by people who know what they are doing) accordingly.
A set of long induction tracts is what you need in the pony club world.
Then the well meaning guys at TVR Power got hold of the Range Rover lump and with a limited budget made some changes that better suit a sports car application.
I believe the problem is they only did half the job.
With a steeper cam profile and a different fuelling map they got some nice power improvements, but at the expense of drive-ability.
I bet they knew they could have done a better job too, but there is always a budget to work to in any business.
In fact from what I have seen TVR Power did do a crude job of cutting the trumpets down on the 5.0 litre cars to try and help.
I bet if you tried to run a 5.0 litre car on the standard Range Rover trumpets that you get in the 4.0 litre cars it would shunt like a b
h.I take no credit for the improvements I have made.
I just listened to all the advise & used my experience to filter out the bull.
All the trade guys I spoke to that seemed to be talking sense were saying the same thing "look at the induction side".
I figured the ones that know had spent many ours and lots of money getting to the answers, so I just followed the good advise of the true experts.
The results are unquestionably a monumental success.
If your RV8 TVR is hesitant at light to part throttle openings, if it makes you feel tense driving it below 2000/2300 rpm then just fit the parts I have added and you wont be diapointed.
Today I did some rolling acceleration tests to see what it could do:
4th Gear at 30mph which is roughly just 1200rpm and the car runs along without a single hicup.
Push on the throttle peddle and the car just accelerates from 30mph all the way until you feel 5th is needed.
If I had tried this before the mods, well lets just say it would have been a nasty experience.
garfys v8s said:
Mr Plow said:
I have the same issue with my 450 and was planning the same approach, winter projects I think though 
Hi Liam how are you ? i am picking up my new 500 tomorrow.
You've got a PM.
Didn't want to highjack the thread.
Looks like I have a bigger shopping list from the above. Great write up.
Thanks Chimpaholic
Edited by Mr Plow on Tuesday 27th October 18:27
Golflion said:
Fantastic,thought about this before but never got round to asking the question if it improves shunting in any way.
November is going to be a busy month,off road any way...
Hi Mark, I see you run a 4.0HC like me, let me know how you get on.November is going to be a busy month,off road any way...
If you want any fitting advise just shout.
I wouldn't mind betting you will love the results.
Best regards, Dave.
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