Talk to me about induction upgrades...
Discussion
I know I can buy something from ACT that will work, but before I spend a pile of money, I'd like to understand how it all works and what I'm getting... I'm an engineer after all. 
The flexible tubing is certainly not going to help and will be replaced as soon as possible (ie when the AFM has gone).
The air filter is in a half-reasonable place. It must be in a reasonably high pressure zone, so I'll leave this alone. (If I could stop it scooping up all the grot on IOW roads, then it would be perfect )
I understand that the primary gains from trumpet upgrades come from length and taper. The fancy bits are just that - they do little in comparison. Is this a correct assumption?
Can trumpets simply be considered as an extension of the inlet manifold runner? The idea therefore being to make it as long as required for your requirement. If this is the case, then why have them in the 1st place? Simply for reasons of space and getting a decent plenum volume?
Can I have right angle trumpets and a double-sided plenum with 2 (or more!) throttle bodies (assuming there's space) so that I have something a bit like a Cerbera intake arrangement, just without the individual throttle bodies?
Looking at the standard plenum on a Griff 500, I thought it was, in a word, nasty. It's too short (in height) for the current stacks and is very much on the small side for volume. The throttle body is quite small too. (although choking this down always was a way of increasing torque) I also dislike the two square section bits from the TB - this is surely going to cause turbulance in the wrong place. Am I about right?
Assume there are no ECU limitations, that we're not going to use individual throttle bodies for now, that there's enough space to fit it in, the cam is reasonably wild but not excessivly so and the exhaust is sufficiently upgrades (the ACT performance system with cats)
Any suggestions/comments/ideas? (or offers of FE modelling time? ) 
The flexible tubing is certainly not going to help and will be replaced as soon as possible (ie when the AFM has gone).
The air filter is in a half-reasonable place. It must be in a reasonably high pressure zone, so I'll leave this alone. (If I could stop it scooping up all the grot on IOW roads, then it would be perfect
) I understand that the primary gains from trumpet upgrades come from length and taper. The fancy bits are just that - they do little in comparison. Is this a correct assumption?
Can trumpets simply be considered as an extension of the inlet manifold runner? The idea therefore being to make it as long as required for your requirement. If this is the case, then why have them in the 1st place? Simply for reasons of space and getting a decent plenum volume?
Can I have right angle trumpets and a double-sided plenum with 2 (or more!) throttle bodies (assuming there's space) so that I have something a bit like a Cerbera intake arrangement, just without the individual throttle bodies?
Looking at the standard plenum on a Griff 500, I thought it was, in a word, nasty. It's too short (in height) for the current stacks and is very much on the small side for volume. The throttle body is quite small too. (although choking this down always was a way of increasing torque) I also dislike the two square section bits from the TB - this is surely going to cause turbulance in the wrong place. Am I about right?
Assume there are no ECU limitations, that we're not going to use individual throttle bodies for now, that there's enough space to fit it in, the cam is reasonably wild but not excessivly so and the exhaust is sufficiently upgrades (the ACT performance system with cats)
Any suggestions/comments/ideas? (or offers of FE modelling time?
) Hmm delicate one this one as many people have different views!! my view is trumpets are critical for the radius and taper, the length not so critical, you cannot have a butterfly that is too big imho, the gas speed is contolled by the trumpets and the port size not butterfly, individual runners have no restriction and make more power and torque than a plenum and these have no restriction other than the bore of the throttle bodies which are the same as the trumpets in a plenum, for me a plenum makes less power at low rpm because of the crap that the cylinders throw back out on the overlap period of the cam, dont be fooled by a plenum being too close too the trumpets, this actully helps, even when i run down draught throttle bodies i put a solid plate around an inch form the trumpet, it helps with power, to be honest i am not a scientist and cant explain why but i reckon it is because the air is coming from the side and is accelarating around the trumpet and into the inlet!! hope all this makes sense as the beers were out several hours ago!!
As an aside to this Rob .. I'm trying to organise getting some trumpets manufactured for me .. when I've got a spec I'm happy with would you like to try them on your engine dyno and compare to what else is available on the market? I'd like to get a set of 8 trumpets made for under 100 pounds a set but it hinges on whether the person I've contacted can get the correct grade of material that will withstand petrol/oil for years and years.
I'm intrigued to know why it is so good to have a plate above the trumpets, any theory why it works?
Could it be that the abrupt turn acts as a sort of 'one way valve' reflecting negative pulses but not positive ones? Because suction is non-directional, you would get different resistance characteristics sucking than blowing.
Another potential theory is that the effective length of the primary reflection could depend on how abruptly the cross section changes at the top of the trumpet. I think I'm right in saying that if you put a plate over the top and turn the air flow into an annular jet, you get a much sharper change in cross section area. This might mean you get a cleaner reflection so a stronger pulse around resonance. Maybe.
Open question, why do *you* think it works?
Could it be that the abrupt turn acts as a sort of 'one way valve' reflecting negative pulses but not positive ones? Because suction is non-directional, you would get different resistance characteristics sucking than blowing.
Another potential theory is that the effective length of the primary reflection could depend on how abruptly the cross section changes at the top of the trumpet. I think I'm right in saying that if you put a plate over the top and turn the air flow into an annular jet, you get a much sharper change in cross section area. This might mean you get a cleaner reflection so a stronger pulse around resonance. Maybe.
Open question, why do *you* think it works?
I think it's cos when you get a change in area as you say you get a wave reflection, but in the case of going from narrow bore to open air (in effect, as the wave travels back up the trumpet from the valve) yuo get a negative wave reflected back down the inlet, this sucks mixture back out of the combustion chamber at the resonant frequencies the waveform interrupts with.
What you want is to take advantge of the momentum ramming effect of a correctly sized inlet runner, and have a positive waveform reflected back from the end of the trumpet to aid trapping of the mixture particularly at low air speeds where momentum ramming is least and mixture reversal in the inlet runner is most likely. The trumpet only reflects negative waves back down so you need to introduce something to make a positive waveform reflection.
You can only get a positive waveform reflection off a hard surface, so the flat plate gives this .. they call them pulse plates and they're widely used. it's one reason that open sidedraught carbs work best with a filter .. it's not the filter per se that helps, but the pulse plate effect of the filter casing ...
I've got a stepped plate inside my plenum so effectively the plenum roof is equidistant from all the trumpet ends .. I'll say it here publicly so if "an induction specialist" steals and markets it before me you all know where it came from
What you want is to take advantge of the momentum ramming effect of a correctly sized inlet runner, and have a positive waveform reflected back from the end of the trumpet to aid trapping of the mixture particularly at low air speeds where momentum ramming is least and mixture reversal in the inlet runner is most likely. The trumpet only reflects negative waves back down so you need to introduce something to make a positive waveform reflection.
You can only get a positive waveform reflection off a hard surface, so the flat plate gives this .. they call them pulse plates and they're widely used. it's one reason that open sidedraught carbs work best with a filter .. it's not the filter per se that helps, but the pulse plate effect of the filter casing ...
I've got a stepped plate inside my plenum so effectively the plenum roof is equidistant from all the trumpet ends .. I'll say it here publicly so if "an induction specialist" steals and markets it before me you all know where it came from
dnb said:I've often wondered about this.Does the smooth bore silicone pipe really work?The original flexi pipe is definately large enough diameter wise,and i dont understand why the 'smooth bore' of the silicone pipe helps?I know the silicone that its made of is a good insulator(though black has to be the worst choice of colour),but this would only be benificial when stationary surely?Therefore i could understand why the smoothbore pipe in silicone would improve rolling road figures,but not when actually driving the car out on the road.Anyone care to explain please?
The flexible tubing is certainly not going to help and will be replaced as soon as possible (ie when the AFM has gone).
>> Edited by mongoose on Thursday 19th January 08:49
yes the smooth bore pipe does work, mainly the flow inside the corigated pipe is very disturbed and tumbles which slows the air speed down espeicialy around the bends, tests we have done on the dyno just by swaping the 90 deg bend o the plenum and putting a straight pipe on there increases bhp by 6 bhp!! i guess the smooth bore pipe is like looking at a flowing stream! the edge of te stream that is all rough you can see the water swirling and bouncing off the banks!!
greenv8s said:
Open question, why do *you* think it works?
Another couple of ideas.
A positive pressure wave in the inlet runner reflects back up when the valve closes, the postitive pressure is expelled into the bell mouth local area and a negative pressure wave reflects back towards the valve. This then reflects off the valve back upto the bell mouth. The wave recovers a positive pressure and then reflects back in time for when the valve opens. If the pressure around the bell mouth area is higher because it has impacted on the plate and collected around the local mouth area, then the positive pressure absolute value will be higher. (Conversely if there was no plate then the first positive pressure wave would expel unimpeded and desperse more readily) First rule of fluids high pressure always flows to low pressure.
The other more unlikely scenario is that there are 2 waves, one from the valve to bellmouth (the primary ) and another from the valve to plate (the secondary). These two waves will have slightly different frequencys but if timed just right may superimpose their amplitudes at the valve when the valve opens.
Where's Marquis Rex when you need him!
Cheers
Phil
dnb said:
I understand that the primary gains from trumpet upgrades come from length and taper. The fancy bits are just that - they do little in comparison. Is this a correct assumption?
Can trumpets simply be considered as an extension of the inlet manifold runner? The idea therefore being to make it as long as required for your requirement. If this is the case, then why have them in the 1st place? Simply for reasons of space and getting a decent plenum volume?
Hi Dave
Yep, the trumpets are an extension of the inlet manifold runner, I'm guessing they had them because so they could easily change the length of trumpets in development to match the different applications of the engine. I think the plenum volume seems about right for a 5.0 litre (6-8 litres plenum volume?) but with lots of dead volume around the base of the trumpets. At work we have a design guide for throttled volume of maximum 1.5 times capacity, otherwise the fill time of the plenum (and hence throttle response) gets too long.
dnb said:
Can I have right angle trumpets and a double-sided plenum with 2 (or more!) throttle bodies (assuming there's space) so that I have something a bit like a Cerbera intake arrangement, just without the individual throttle bodies?
I too have had thoughts on what to do with the induction side of things, probably the best thing to do is ditch the manifold entirely as the intake runners in the manifold-base are so tortuous and unequal. But if you want to keep the manifold base then the old efi manifold has an interesting design feature in that the front and rear inlet runners cross banks. That may allow you to make the best out of the existing EFi manifold-base with something (funnily enough with two plenums fed with two throttles on a new trumpet base) roughly like this:
I've always been unimpressed by the old standard EFI manifold and it seems Land Rover were too as they went to the "Thor" manifold. I don't like all the 'trumpets' being grouped very closely together and because a V8 has a firing event every 90 degs cylinders 1&2, 3&4, 3&6, 5&6 and 5&7 are all next to each other with overlapping inlet valve events, 'robbing' each others air/charge. This has got to be terrible for cylinder-cylinder variation and generally for torque. The runners crossing banks on the front and rear allows you to split the two sides into two plenums (one plenum with cyls 1,4,6,7 and the other 2,3,5,8) and because of the firing order of 1,8,4,3,6,5,7,2 means that each plenum sees a firing at every 180 degrees and much reduced charge-robbing (more like a 4 cylinder) A side effect of this is the possibility of resonance boosting each plenum from Helmholtz Resonance (spring-mass system). Porsche on the late 928 used resonance tuning and had a valve between the 2 plenums which opened at selected revs creating a single plenum and changing the Helmholtz frequency. When these resonances happen could be roughly predicted but are probably best determined empirically by changing the volumes.
It's all very interesting (perhaps?) but it's probably less work to ditch the lot and make a new manifold and put individual 40mm throttle bodies on them.
dnb said:
Looking at the standard plenum on a Griff 500, I thought it was, in a word, nasty. It's too short (in height) for the current stacks and is very much on the small side for volume. The throttle body is quite small too. (although choking this down always was a way of increasing torque) I also dislike the two square section bits from the TB - this is surely going to cause turbulence in the wrong place. Am I about right?
A throttle has to be sized just right because if you go too large then the bigger the flow change for a given throttle plate angle (called tip-in) but a sparky like you could do a electronic throttle!
Great pics and stuff - exactly what I was hoping for, and exactly the sort of idea I was looking at. Nice to know it's fairly straight forward to have 2 plenums with 180 degrees between firings.
The plenum size might be about right, but as you say, there's a lot of "dead" space in it. Looking at pictures of the rangerover engine, it seems the TVR stacks are longer, thus making more dead area than otherwise necessary. I've always felt (since getting the STi RA) that the initial throttle response on the Griff could be a bit better than it is.
Re the throttle body - I thought several small TBs might give a more linear flow variation than one large one, but the difference from the maths isn't worth talking about, so maybe if it's a problem at low openings (it's not a problem at meaningful opening angles) I could tweak the airflow using something like a large idle controller (a kind of hybrid fly-by-wire scheme).
I like the idea of being able to switch between twin plenums and single plenum. There's even an aux output on the ECU I could use for that too.
I can see some experiments happening soon
The plenum size might be about right, but as you say, there's a lot of "dead" space in it. Looking at pictures of the rangerover engine, it seems the TVR stacks are longer, thus making more dead area than otherwise necessary. I've always felt (since getting the STi RA) that the initial throttle response on the Griff could be a bit better than it is.
Re the throttle body - I thought several small TBs might give a more linear flow variation than one large one, but the difference from the maths isn't worth talking about, so maybe if it's a problem at low openings (it's not a problem at meaningful opening angles) I could tweak the airflow using something like a large idle controller (a kind of hybrid fly-by-wire scheme).
I like the idea of being able to switch between twin plenums and single plenum. There's even an aux output on the ECU I could use for that too.
I can see some experiments happening soon
great stuff 
Interesting that engine dyno experience (rob V8racing) likes big throtle plates ,wereas the theory seems to be too big can be bad, affecting throttle response. Question for the 4ltr RV8 is there any benefit to the 71mm throttle plate as opposed to the standard which I think is 65mm
. Re reflected pluse tuning effect felt by putting a plate over the top of the trumpets, is there an ideal standoff height for this
, is it expressed in terms of the intake overall length or is it a function of the diameter of the trumpet. If so what is it? I seem to recall reading once that a plate placed at 1 - 1.5 times the dia of the trumpet can have this affect. Another grey cell memory was that a plate underneath the the lip of the trumnpets stopped air being pulled up and over the lip which disturbs the air flow being pulled directly down through it. That works for trumpets on the same level, but I assume this would have to be stepped also, alla joolz plenum roof. Enjoying this so much I might hang on to the RV8 to play with more
.Nice one Dave, keep updating us!
Sorry should have said 'tip-in' is only a problem for initial throttle opening at light pedal application. A trick that car companies also used (before the advent of electronic throttle) was a variable radius throttle linkage, where for initial pedal movement there is larger throttle plate opening at the start and progressively less the further pedal goes down. Great for a 'sporty' feel and perceived throttle response, just bad for control/drivability.
A change from 65mm to 71mm doesn't sound too bad (only a 20% increase in area), if a LS7 uses 90mm for 507bhp then (equivalent for area) 71mm equates to 315bhp. Assumes the vette is right of course!
Sorry should have said 'tip-in' is only a problem for initial throttle opening at light pedal application. A trick that car companies also used (before the advent of electronic throttle) was a variable radius throttle linkage, where for initial pedal movement there is larger throttle plate opening at the start and progressively less the further pedal goes down. Great for a 'sporty' feel and perceived throttle response, just bad for control/drivability.
A change from 65mm to 71mm doesn't sound too bad (only a 20% increase in area), if a LS7 uses 90mm for 507bhp then (equivalent for area) 71mm equates to 315bhp. Assumes the vette is right of course!
IMHO you just cannot have a throttle that is too big on a plenum, if you are losing power by fitting a larger plenum i think your trumpets and inletmanifold is too big? on the dyno i have ran 4ltrs upto 5.5 ltr rover engines and taken the plenum completely off so you are just running with the trumpet base no throttle control at all and they always make more power!!
v8 racing said:
on the dyno i have ran 4ltrs upto 5.5 ltr rover engines and taken the plenum completely off so you are just running with the trumpet base no throttle control at all and they always make more power!!
That's very interesting. Didn't Mark Adams report that he had tried this and found a substantial drop in torque?
I seem to remember that trumpets work best when they are proud of the backplate, i.e. raising the trumpet base up to the lip of the trumpet would reduce the flow capability slightly. The goal is to increase the flow cross section area and hence drop the local air speed as quickly and as far as possible, to minimise the coupling between the primary and secondary intake. (Once you get away from the primary runners and their resonance effects it is better to have a short fat column of air being accelerated by a small amount than to have a tall thin column accelerated by a larger amount.)
I cant say what marks findings were i am just basing my findings on hours on the dyno doing various things, maybe when mark did this it had a very mild cam, and posibly only standard heads which didnt need anymore airflow than the standard plenum could flow, basically what i did was run downdraught throttle bodies instead of a plenum!
wheeljack888 said:
The other more unlikely scenario is that there are 2 waves, one from the valve to bellmouth (the primary ) and another from the valve to plate (the secondary). These two waves will have slightly different frequencys but if timed just right may superimpose their amplitudes at the valve when the valve opens.
Where's Marquis Rex when you need him!
Cheers
Phil
I seldom come to the TVR forums. Shame, because at least the TVR guys talk technical and don't seem to mind getting their hands dirty.
The Porsche lot seem more concerned with the latest release from Stuttgart,spending henious amounts of money at some German tuner or they're after market tuners themselves trying to convince everyone on the board how they have achieved more power than anyone at Weissach as proven on their very own dyno
Enough bitching!
I think WHeeljacks this assesment sounds right.
On a dyno I saw very little effect of having the plenum wall very close to one bank of cylinders- while the other cylinders were less impeded.
If the positive pressure wave hits the open end of the bell mouth unimpeded- it will change sign. If there is an obstruction nearby - the amplitude will be effected of the 'changed sign' returning wave, and another wave will superimpose.
My bigger worry would be the restriction caused by having a plate or plenum wall close to the runner/trumpet- although you can get alarmingly close with minimal effect. Rememember there are 3 dimentional effects to think about (where the air is being fed from if inside a plenum etc etc), not just the the periphery circumferal area around the gap between the hypothetical plate and the runner bell mouth.
>> Edited by Marquis_Rex on Thursday 19th January 20:36
GreenV8S said:
That's very interesting. Didn't Mark Adams report that he had tried this and found a substantial drop in torque?
I remember that one too.But then again he also said its better to keep the airflow meter for torque,yet several tuners i had talked to advised me to bin it for maximum bhp-I'm glad i binned mine now With no disrespect to Mark intended,he has a vested interest in keeping your car using the Lucas ecu,and praising the merits of the airflow meter is only to be expected i guess,as if you keep the afm,youll probably be keeping the Lucas ecu.When i posted a reply to his comment about the loosing the afm will cost you torque,i asked if loosing it would help make bhp-he never replied
mongoose said:
That's very interesting. Didn't Mark Adams report that he had tried this and found a substantial drop in torque?
With no disrespect to Mark intended,he has a vested interest in keeping your car using the Lucas ecu,and praising the merits of the airflow meter is only to be expected i guess,as if you keep the afm,youll probably be keeping the Lucas ecu.When i posted a reply to his comment about the loosing the afm will cost you torque,i asked if loosing it would help make bhp-he never replied
Why should having an Air flow meter gain torque?
Explain to me please
Cheers Rup, thought you might be interested.
As far as taking the plenum off and getting more power, yep sounds right if the primary lengths are right. The air has no extra bends to take, no other pipes to travel through, etc. Also if the ports are sized just right for port velocity vs flow restriction, maximising air-momentum (ram-effect) and correct IVC to trap. But what effects would it have had on other points of rev-range? Does a plenum act as a damper reducing torque spikes but maybe slightly increasing volumetric efficiency at other points, I've heard it could.
To be fair to Mark Adams an AFM is the most accurate way of measuring the amount of air you've got (speed density is only as good as the VE figures put in the map) and allows a more accurate derivation for how much fuel you need, thus maximising the torque. However an airflow meter is a restriction in itself and also it must be plumbed in, reducing overall airflow.
>> Edited by wheeljack888 on Thursday 19th January 22:00
As far as taking the plenum off and getting more power, yep sounds right if the primary lengths are right. The air has no extra bends to take, no other pipes to travel through, etc. Also if the ports are sized just right for port velocity vs flow restriction, maximising air-momentum (ram-effect) and correct IVC to trap. But what effects would it have had on other points of rev-range? Does a plenum act as a damper reducing torque spikes but maybe slightly increasing volumetric efficiency at other points, I've heard it could.
To be fair to Mark Adams an AFM is the most accurate way of measuring the amount of air you've got (speed density is only as good as the VE figures put in the map) and allows a more accurate derivation for how much fuel you need, thus maximising the torque. However an airflow meter is a restriction in itself and also it must be plumbed in, reducing overall airflow.
>> Edited by wheeljack888 on Thursday 19th January 22:00
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