Shunting Solved
Discussion
roysum said:
Looks like this thread came to a sudden halt a month ago, probably with some input from TVRPower. So generically what should I do with my 400 trumpets.....
leave em alone
carbon flared (ACT)
45mm and match/blend the intake manifold (if so what lenght/s)
Should I fit an insulating plate (probably don't need a spacer on a 400)
I have been advised that a 71mm/72mm throttle would achieve no real gains on the 400
thoughts welcome ........ta
Now I may be corrected if I am wrong, but I have been led to believe that 45mm is too large for the 400 unless you had some really high rev limit, BV heads etc - gas speed will drop etc... So I would have thought that the 45mm option is probably not the one to go for if you don't already have substantial modifications (including upgraded trumpets)...leave em alone
carbon flared (ACT)
45mm and match/blend the intake manifold (if so what lenght/s)
Should I fit an insulating plate (probably don't need a spacer on a 400)
I have been advised that a 71mm/72mm throttle would achieve no real gains on the 400
thoughts welcome ........ta
Dom
Golflion said:
Chimpaholic said:
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.
Lord B
Please let me know how you get on.
Dropping the trumpet base off at SC Power to shorten trumpets and fit bell mouths in the next week or so.
Will let you know how i get on
Golflion said:
Chimpaholic said:
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.
If you want any fitting advise just shout.
I wouldn't mind betting you will love the results.
Best regards, Dave.
Cheers Dave will probably need to get in touch when it comes to the trumpet setting.
Lord B
Please let me know how you get on.
Dave its been a while but i have eventually bought the gasket and spacer!
Will let you know how i get on
Dave
Thinking of using Tim's at ACT Carbon fibre trumpets instead of using the existing ones,as Tim has a good package with the smooth bore induction and trumpets package.
Do you have any views on this bearing in mind i have the same 4.0L HC engine as you and Lord Grover??
Quick reply would be much appreciated from yourself or Lord Grover
Chimpaholic said:
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.
If you want any fitting advise just shout.
I wouldn't mind betting you will love the results.
Best regards, Dave.
Cheers Dave will probably need to get in touch when it comes to the trumpet setting.
Lord B
Please let me know how you get on.
Dave its been a while but i have eventually bought the gasket and spacer!
Will let you know how i get on
Dave
Thinking of using Tim's at ACT Carbon fibre trumpets instead of using the existing ones,as Tim has a good package with the smooth bore induction and trumpets package.
Do you have any views on this bearing in mind i have the same 4.0L HC engine as you and Lord Grover??
Quick reply would be much appreciated from yourself or Lord Grover
Edited by Golflion on Wednesday 30th June 21:40
Early this year I had the dreaded shunting problem, all of a sudden it just happened. I was driving back from London pull in to get some petrol all was fine started the car up and in first it just sputtered then went like normal. It was due for a 12k service so I let my man know what was happening his response was ‘could be the plugs’, all the leads and lead holders were changed, plugs, oil, etc… and poof the shunting was gone.
Until Monday. Its back. Now with out taking it back for another service is there anything simple and cheap (I know it a tvr) that I can start with. I’ve read thru the above posts but don’t really know where to start. It’s a 500 by the way.
Until Monday. Its back. Now with out taking it back for another service is there anything simple and cheap (I know it a tvr) that I can start with. I’ve read thru the above posts but don’t really know where to start. It’s a 500 by the way.
If the shunting appears suddenly, is likely the ECU is trying to compensate for something that has go out of tolerance. First place to look is at the plug colours and see if they are sooted up (chronic overfueling). If they are black then first point of failure is likely to be AFM or a misfire (HT or leads etc).
Ozmira said:
BliarOut said:
Crap tank of fuel?
it was bp fuel and I've filled up since Monday may have to start with the ecu but again don't know what to look for. It's a start though. For instance, something like the coolant temperature sensor that the ECU reads to alter mixture on cold start.
You may have one of a number of faults or a few of them so I also would start by looking at the plug colours just as blitzracing is telling you.
The plug colour can tell a thousand stories.
Then, if you can, get it checked with an ECU fault code reader, it can save hours of guess work.
I wouldn't eliminate something simple like a partially blocked fuel filter or an HT lead that's breaking down.
The thing is its almost impossible to correctly diagnose a fault like this on a forum.
If you are not confident with engine fault diagnostics you really need the services of a good mechanic with diagnostic equipment and ideally knowledge of the TVR/Range Rover fuel system.
A bad mechanic will just replace components until he stumbles on a fault, a good mechanic will diagnose the faulty component and get you sorted much quicker a for less money.
I really hope you find the fault mate, like I say its almost certainly something simple.
Chimpaholic said:
Ozmira said:
BliarOut said:
Crap tank of fuel?
it was bp fuel and I've filled up since Monday may have to start with the ecu but again don't know what to look for. It's a start though. For instance, something like the coolant temperature sensor that the ECU reads to alter mixture on cold start.
You may have one of a number of faults or a few of them so I also would start by looking at the plug colours just as blitzracing is telling you.
The plug colour can tell a thousand stories.
Then, if you can, get it checked with an ECU fault code reader, it can save hours of guess work.
I wouldn't eliminate something simple like a partially blocked fuel filter or an HT lead that's breaking down.
The thing is its almost impossible to correctly diagnose a fault like this on a forum.
If you are not confident with engine fault diagnostics you really need the services of a good mechanic with diagnostic equipment and ideally knowledge of the TVR/Range Rover fuel system.
A bad mechanic will just replace components until he stumbles on a fault, a good mechanic will diagnose the faulty component and get you sorted much quicker a for less money.
I really hope you find the fault mate, like I say its almost certainly something simple.
Regarding trumpet lengths and plenum spacers-
What’s the best move to reduce shunting on a stealth cammed 4.0 Rv8?
“When you look at the Inlet tract, it is clear that the tract lengths are all different lengths and shapes. Although the center ones have longer trumpets (cylinders 3,4,5,6), the tract lengths are shorter than the end ones (cylinder 1,2,7,8). This is because the runners on the end cylinders cross over to feed the opposite bank, whereas the center ones feed the adjacent cylinders.
Additionally the first two runners (cylinders 1,2) run alongside the coolant exit from the head and the back of the thermostat housing. This means that the air entering these two cylinders is heated more than the others, so they actually run very slightly richer than the others due to the less-dense charge. Overall, the different tract lengths tend to spread out the torque curve whilst slightly reducing the peak value.
The options for changing inlet tract length are really rather limited, and there are other factors that dictate the trumpet length that is best used in the circumstances. Adding a spacer between the manifold and the trumpet base will obviously increase tract length (apart from any heat transmission benefits), and slightly increase plenum volume.
The shape of the top of the trumpet is important, and all the information on this topic contained in Mr Vizard's "How to Modify Your Mini" is still absolutely relevant.
However the most critical thing you can control within the plenum is the distance between the end of the trumpet and the underside of the plenum. It is highly beneficial (as a rule of thumb) to have approximately the same distance between the end of the trumpet and the underside of the plenum, as the diameter of the trumpet. This will take advantage of shock-ramming the inlet at particular engine speeds. Obviously the addition of a spacer between the trumpet base and the plenum will change this relationship.
On a dyno test we did at V8D some years ago, the peak torque of a 5.2 Litre motor could be varied by up to 40 lb/ft by this technique. We pulled the plenum of this motor whilst it was at full blast, to check the effect of the AFM and throttle restriction. The motor immediately lost 40 lb/ft. However by placing a flat plate over the top of the trumpets and adjusting the distance, this could be restored and optimised.
This is one major area where removing the trumpets and blending the base will loose out. Although the peak power can go up by 3-4 BHP, a massive chunk of mid-range torque is lost.
However there is another issue here too. Before the engine comes on cam (even with a standard camshaft), there is a large reverse flow of exhaust gas up the inlet tract during the camshaft overlap period (when the inlet and exhaust valves are open at the same time). When the inlet tract is very short, this reverse flow of gas can reach the top of the trumpet and even spill over into the plenum. Once it is in the plenum, it will contaminate the charge drawn by adjacent trumpets.
Since fuel is generaly injected into the inlet port before the inlet valve opens, any fuel will be caught in the backflow up the inlet too. Therefore adjacent cylinders can be contaminated with both fuel and spent exhaust gasses, in uncontrolled quantities.
Obviously this problem becomes worse with wilder camshafts, due to the increased overlap creating increased backflow up the inlet. Clearly the bigger the engine, the greater the volume of spent gas that will be pushed back up the inlet. If the inlet tract is big enough to contain this reverse flow, then the unwelcome symptoms are heavily reduced.
Due to the layout of the trumpets in the plenum, all cylinders will receive different amounts of contamination in this particular area of operation (i.e. before the engine comes on cam). Exhaust gas in the inlet charge tends to slow the flame front, so more ignition advance is required to ensure the most complete burn. The peak burn temperature is also reduced, and this reduces the undesirable production of oxides of Nitrogen (NOx) which is implicated in Acid Rain formation (see http://en.wikipedia.org/wiki/Acid_rain)
Note that this reverse flow characteristic is used by many engine manufacturers to reduce NOx production without the use of specific Exhaust Gas Recirculation (EGR) equipment. NOx reduction is the whole point of EGR, although EGR also has the welcome side effect of making a petrol engine more economical during cruising.
Hence a really short inlet containing little volume, especially on a large motor, will make the cross-contamination problem worse just before the engine comes on cam. This is one of the reasons in general why throttle bodies can help tame wild camshafts when the inlet tract is long enough, because any contamination does not cross to adjacent cylinders.
In summary this is the reason why (regardless of the engine management system in use) on a plenum-equipped engine (i.e. single throttle upstream of the plenum) where the inlet tracts are not long enough to contain the reverse flow, you will get uneven combustion. Usually this shows up to the driver as "shunting".
Back in the days of carburetors, this reverse flow would appear as "stand-off" above the mouths of the carburetors just before the engine came on cam. This is an interesting one to see on the dyno, and it appears as a dome-shaped cone of fuel above the carburetor mouth (usually a trumpet) an is sometimes over 30cm tall.
This process is how carburetors set fire to foam air filters. First they soak them with fuel during stand-off, and it only takes one cough up the inlet to ignite it. Almost all the V8s I have seen equipped with downdraught carburettors and foam air filters over the trumpets catch fire from time to time. It's no problem if you know how to deal with it - full throttle if possible and keep a fire extinguisher in the car”
What’s the best move to reduce shunting on a stealth cammed 4.0 Rv8?
“When you look at the Inlet tract, it is clear that the tract lengths are all different lengths and shapes. Although the center ones have longer trumpets (cylinders 3,4,5,6), the tract lengths are shorter than the end ones (cylinder 1,2,7,8). This is because the runners on the end cylinders cross over to feed the opposite bank, whereas the center ones feed the adjacent cylinders.
Additionally the first two runners (cylinders 1,2) run alongside the coolant exit from the head and the back of the thermostat housing. This means that the air entering these two cylinders is heated more than the others, so they actually run very slightly richer than the others due to the less-dense charge. Overall, the different tract lengths tend to spread out the torque curve whilst slightly reducing the peak value.
The options for changing inlet tract length are really rather limited, and there are other factors that dictate the trumpet length that is best used in the circumstances. Adding a spacer between the manifold and the trumpet base will obviously increase tract length (apart from any heat transmission benefits), and slightly increase plenum volume.
The shape of the top of the trumpet is important, and all the information on this topic contained in Mr Vizard's "How to Modify Your Mini" is still absolutely relevant.
However the most critical thing you can control within the plenum is the distance between the end of the trumpet and the underside of the plenum. It is highly beneficial (as a rule of thumb) to have approximately the same distance between the end of the trumpet and the underside of the plenum, as the diameter of the trumpet. This will take advantage of shock-ramming the inlet at particular engine speeds. Obviously the addition of a spacer between the trumpet base and the plenum will change this relationship.
On a dyno test we did at V8D some years ago, the peak torque of a 5.2 Litre motor could be varied by up to 40 lb/ft by this technique. We pulled the plenum of this motor whilst it was at full blast, to check the effect of the AFM and throttle restriction. The motor immediately lost 40 lb/ft. However by placing a flat plate over the top of the trumpets and adjusting the distance, this could be restored and optimised.
This is one major area where removing the trumpets and blending the base will loose out. Although the peak power can go up by 3-4 BHP, a massive chunk of mid-range torque is lost.
However there is another issue here too. Before the engine comes on cam (even with a standard camshaft), there is a large reverse flow of exhaust gas up the inlet tract during the camshaft overlap period (when the inlet and exhaust valves are open at the same time). When the inlet tract is very short, this reverse flow of gas can reach the top of the trumpet and even spill over into the plenum. Once it is in the plenum, it will contaminate the charge drawn by adjacent trumpets.
Since fuel is generaly injected into the inlet port before the inlet valve opens, any fuel will be caught in the backflow up the inlet too. Therefore adjacent cylinders can be contaminated with both fuel and spent exhaust gasses, in uncontrolled quantities.
Obviously this problem becomes worse with wilder camshafts, due to the increased overlap creating increased backflow up the inlet. Clearly the bigger the engine, the greater the volume of spent gas that will be pushed back up the inlet. If the inlet tract is big enough to contain this reverse flow, then the unwelcome symptoms are heavily reduced.
Due to the layout of the trumpets in the plenum, all cylinders will receive different amounts of contamination in this particular area of operation (i.e. before the engine comes on cam). Exhaust gas in the inlet charge tends to slow the flame front, so more ignition advance is required to ensure the most complete burn. The peak burn temperature is also reduced, and this reduces the undesirable production of oxides of Nitrogen (NOx) which is implicated in Acid Rain formation (see http://en.wikipedia.org/wiki/Acid_rain)
Note that this reverse flow characteristic is used by many engine manufacturers to reduce NOx production without the use of specific Exhaust Gas Recirculation (EGR) equipment. NOx reduction is the whole point of EGR, although EGR also has the welcome side effect of making a petrol engine more economical during cruising.
Hence a really short inlet containing little volume, especially on a large motor, will make the cross-contamination problem worse just before the engine comes on cam. This is one of the reasons in general why throttle bodies can help tame wild camshafts when the inlet tract is long enough, because any contamination does not cross to adjacent cylinders.
In summary this is the reason why (regardless of the engine management system in use) on a plenum-equipped engine (i.e. single throttle upstream of the plenum) where the inlet tracts are not long enough to contain the reverse flow, you will get uneven combustion. Usually this shows up to the driver as "shunting".
Back in the days of carburetors, this reverse flow would appear as "stand-off" above the mouths of the carburetors just before the engine came on cam. This is an interesting one to see on the dyno, and it appears as a dome-shaped cone of fuel above the carburetor mouth (usually a trumpet) an is sometimes over 30cm tall.
This process is how carburetors set fire to foam air filters. First they soak them with fuel during stand-off, and it only takes one cough up the inlet to ignite it. Almost all the V8s I have seen equipped with downdraught carburettors and foam air filters over the trumpets catch fire from time to time. It's no problem if you know how to deal with it - full throttle if possible and keep a fire extinguisher in the car”
Golflion said:
Golflion said:
Chimpaholic said:
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.
If you want any fitting advise just shout.
I wouldn't mind betting you will love the results.
Best regards, Dave.
Cheers Dave will probably need to get in touch when it comes to the trumpet setting.
Lord B
Please let me know how you get on.
Dave its been a while but i have eventually bought the gasket and spacer!
Will let you know how i get on
Dave
Thinking of using Tim's at ACT Carbon fibre trumpets instead of using the existing ones,as Tim has a good package with the smooth bore induction and trumpets package.
Do you have any views on this bearing in mind i have the same 4.0L HC engine as you and Lord Grover??
Quick reply would be much appreciated from yourself or Lord Grover
how did you get on?Chimpaholic said:
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.
If you want any fitting advise just shout.
I wouldn't mind betting you will love the results.
Best regards, Dave.
Cheers Dave will probably need to get in touch when it comes to the trumpet setting.
Lord B
Please let me know how you get on.
Dave its been a while but i have eventually bought the gasket and spacer!
Will let you know how i get on
Dave
Thinking of using Tim's at ACT Carbon fibre trumpets instead of using the existing ones,as Tim has a good package with the smooth bore induction and trumpets package.
Do you have any views on this bearing in mind i have the same 4.0L HC engine as you and Lord Grover??
Quick reply would be much appreciated from yourself or Lord Grover
Edited by Golflion on Wednesday 30th June 21:40
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