Plenum vs. Throttle bodies
Discussion
I'm planning on converting my Pinto powered Tiger to fuel injection this winter and am trying to decide between the two options. I'll be using Megasquirt to control the injectors.
Which setup is best for drivability? I use the car mainly on the road with the odd trackday here and there. Also, some fuel economy will be welcomed at the twin 45 Webers I'm currently using aren't exactly fuel efficient :D
If I go plenum, I will have to either make a custom one up or modify a Sierra one, as space is tight under the bonnet.
Bike throttle bodies have the problem of mating them to the engine either via a DCOE manifold or the Sierra injection one (advantage there is I can use the existing injector locations).
Any thoughts folks? :)
Which setup is best for drivability? I use the car mainly on the road with the odd trackday here and there. Also, some fuel economy will be welcomed at the twin 45 Webers I'm currently using aren't exactly fuel efficient :D
If I go plenum, I will have to either make a custom one up or modify a Sierra one, as space is tight under the bonnet.
Bike throttle bodies have the problem of mating them to the engine either via a DCOE manifold or the Sierra injection one (advantage there is I can use the existing injector locations).
Any thoughts folks? :)
The plenums are great for mid range power which is why so many manufacturers use them in road cars. The throttle bodies should release quite a bit of top end power but possibly at the expense of low end grunt.
I have a friend who runs a company called Balance Motorsport. He has been experimenting with bike throttle bodies so maybe call him 0845 226 3717.
I have a friend who runs a company called Balance Motorsport. He has been experimenting with bike throttle bodies so maybe call him 0845 226 3717.
Plenums are cheaper and easier because you only have one throttle etc, and as a manufacturer you would want to use a MAF based load sensor which suits a single air intake.
Multiple throttles are more complicated/expensive, need more work to set them up and balance them, imply a TPS based load sensor which makes the tune more vulnerable to variations in the engine characteristics. Two big advantages of multiple throttles: they tame a wild cam to give a vastly improved idle, and they enable you to have a bigger intake area so less pressure drop on the way in. (If you put a collector upstream of the throttles then you lose this second benefit.)
Multiple throttles are more complicated/expensive, need more work to set them up and balance them, imply a TPS based load sensor which makes the tune more vulnerable to variations in the engine characteristics. Two big advantages of multiple throttles: they tame a wild cam to give a vastly improved idle, and they enable you to have a bigger intake area so less pressure drop on the way in. (If you put a collector upstream of the throttles then you lose this second benefit.)
GreenV8S said:
Why the mid-range loss? Would it be possible to put a plenum-like top over the intakes (i.e. just a box open to the filter, no throttle etc) while keeping the throttle bodies downstream, and get the best of both worlds?
That's just an air filter/box.
Do this, make it work and you could be a very rich man
Plenums are known for their torque and secondary thingymebobbeeepers charachteristaticas
That's why most manufacturers use them. Boosted.
At the moment I'm running twin Weber 45s, which I guess are very similar to throttle bodies. I've not noticed any lack of torque I must say. In fact the rolling road result shows I have more torque than bhp, although I have since changed the camshaft.
The only reason I'm considering a plenum is because I'm thinking of fitting a supercharger. I believe this can't be done with throttle bodies as the throttle butterfly should be before the supercharger, not after it?
The only reason I'm considering a plenum is because I'm thinking of fitting a supercharger. I believe this can't be done with throttle bodies as the throttle butterfly should be before the supercharger, not after it?
boosted ls1 said:
Plenums are known for their torque and secondary thingymebobbeeepers charachteristaticas
Is it possible that cause and effect are the other way round? If you want to use a really lairy cam in a highly tuned motor you would probably need throttle bodies to get it to idle properly, and be more willing to pay the extra expense of TBs. So plenum works fine for a budget stump puller, TBs called for if you have a screamer.
Plenum volumes are carefully calculated and their use isn't just about cost. I'd need to look at my books to get some more info but they impressed me so for all sorts of reasons I won't go near tb's. My understanding is that plenums give you bags of mid range torque whilst maybe loosing a bit of upper end bhp. So, for road cars plenums are really cool things and plenty of high performance road cars still use them. For high rpm cars t/b's are better but they would be expected to lose low down torque. Their gains will be at the upper end of the rev scale.
I'd still use a plenum on a hugely expensive stump puller if it's a road car.
Boosted.
I'd still use a plenum on a hugely expensive stump puller if it's a road car
. Boosted.
IMHO Both are as good as each other, it depends on what is underneath them!! if you have a normal compression, low duration cam then you will not see anyincrease in any rpm range, generaly if you are fitting TB's you already have high compression long duration cams etc ant the TB's will win hands down throughout the rev range, BUT ONLY if you use the right size and run with a filter that uses a solid plate about an inch away from the bell mouths, on a 300 ftib engine the plate can be worth up to 15ftib!!
v8 racing said:
IMHO Both are as good as each other, it depends on what is underneath them!! if you have a normal compression, low duration cam then you will not see anyincrease in any rpm range, generaly if you are fitting TB's you already have high compression long duration cams etc ant the TB's will win hands down throughout the rev range, BUT ONLY if you use the right size and run with a filter that uses a solid plate about an inch away from the bell mouths, on a 300 ftib engine the plate can be worth up to 15ftib!!
That's interesting because on my home made plenums I look for a 1" gap from inlet to the lid. Doesn't this effectively double the inlet tract length which increases torque.
Boosted.
boosted ls1 said:
IMHO Both are as good as each other, it depends on what is underneath them!! if you have a normal compression, low duration cam then you will not see anyincrease in any rpm range, generaly if you are fitting TB's you already have high compression long duration cams etc ant the TB's will win hands down throughout the rev range, BUT ONLY if you use the right size and run with a filter that uses a solid plate about an inch away from the bell mouths, on a 300 ftib engine the plate can be worth up to 15ftib!!
That's interesting because on my home made plenums I look for a 1" gap from inlet to the lid. Doesn't this effectively double the inlet tract length which increases torque.
Boosted.
Waiting for the reponse to this with interest
. Is the ideal height of the plenum ceiling away from the top of the trumpets a function of the diameter of them as opposed to 1"
, refelective pluse tuning or somesuch. I put an insulated 25mm spacer between my plenum and base and it killed the power and torque by at least 20 across the board, never did find out if it was the increase in 'roof' above the trumpets or the side inlet blowing across the trumpets tops
. Which leads me onto a related query....I currently have short 45mm trumpets fitted which are further away from the top of the standard RV8 plenum roof, what differencee is there between say them and the longer 38mm ones then
, you must have seen hundereds of these on V8D bench dyno Rob . Harry
I dont know the real answer to this in technical terms, i guess you need some very very expensive kit to find out exactly what is happening inside a plenum to get the true facts? This is just my opinion though, i think that by running a plate approx an inch from the trumpet tops restricts the air from being pulled straight down and instead a certain amount has to be pulled from the side of the trumpets, as the air does this it has to accelerate around the curve of the trumpet hence a faster pulse of air going into the head? in all the testing i have done on throttle bodies on the dyno this method has never increased max bhp but always increases max torque, by using the same engine and same plenum top, on the dyno using different companies trumpet bases there was a difference of 25ftib from the best to worst i am not going to say who's was what though!! but the peak hp was all the same!!
boosted ls1 said:
Plenum volumes are carefully calculated and their use isn't just about cost. I'd need to look at my books to get some more info but they impressed me so for all sorts of reasons I won't go near tb's. My understanding is that plenums give you bags of mid range torque whilst maybe loosing a bit of upper end bhp. So, for road cars plenums are really cool things and plenty of high performance road cars still use them. For high rpm cars t/b's are better but they would be expected to lose low down torque. Their gains will be at the upper end of the rev scale.
I'd still use a plenum on a hugely expensive stump puller if it's a road car
Boosted.
Listen to Peter he knows what he's talking about.
Individual throttle bodies alone don't give top end performance, they CAN give top end performance if you combine them with wild cams. The allow the use of wild cams without compromising idle quality and without allowing too much exhaust gas residual into the cylinder to the point where it deteriorates combustion.
The biggest benefit with ITBs is throttle response because the throttles are much closer to the engine intake valves and any change demanded by the driver is "seen" by the engine alot sooner than a single throttle set up.
Individual throttle bodies are also often associated with high power applications compared to a single thorttle body with a ducted plenum because there is a lower intake loss- and usually no 'bottle neck' associated with a MAF.
For high performance TOP END you want as big a plenum as possible and there's NO REASON why this can't be combined with ITBs. The BMW M3 has a 14 litre plenum!
I can't see a reason why ITBs would have less low speed torque. ITBs straight to atmosphere versus ITBs into a plenum- the existence of the plenum may strengthen the reflection pulse (probably 2nd or 3rd wave) during ram induction tuning- this might stregthen mid range torque a bit-some Nms perhaps depending on engine capacity. Could be noticeable on some configurations.
Plenum size is critical on engines that use 'resonace tuning' in the intake system. (This is NOT the same as variable intake runner length). This is when the natural frequency of the plenum(s) are tuned to match a particular running condition of the engine (running condition (= engine speed, cam timing) so that resonance tuning will occur. This work very well on V6s (such as the Jaguar S type) but in the case of resonace tuned plenum/intakes you could have gotten more top end by going for a bigger plenum.
Few other engines use resonance charge tuning on the intake, V8s have tried, such as the Porsche 928 S4- but it doesn't work as well on V8s and the only 4 cyl I know of really is a BMW DISA engine and the original toyota MR2.
>> Edited by Marquis_Rex on Saturday 8th October 01:52
boosted ls1 said:
IMHO Both are as good as each other, it depends on what is underneath them!! if you have a normal compression, low duration cam then you will not see anyincrease in any rpm range, generaly if you are fitting TB's you already have high compression long duration cams etc ant the TB's will win hands down throughout the rev range, BUT ONLY if you use the right size and run with a filter that uses a solid plate about an inch away from the bell mouths, on a 300 ftib engine the plate can be worth up to 15ftib!!
That's interesting because on my home made plenums I look for a 1" gap from inlet to the lid. Doesn't this effectively double the inlet tract length which increases torque.
Boosted.
I ran a V6 engine on a dyno once, fully instrumented up with kistler dynamic pressure tappings and some Druck static ones throughout the intake geometry.
On the one bank of the V6- the "wall" of the plenum was very close to the inlet bell mouths (about 1/4 D-where "D" is the diameter of one of the intake runners), the other side had alot more space between the wall and the bell mouths. There was no air flow difference bank to bank, so basically both banks breathed as well as one another. They tuned identically too. In this case the plenum wasn't very "active" and it wasn't designed for resonace charge tuning.....
HarryW said:
Waiting for the reponse to this with interest
Is the ideal height of the plenum ceiling away from the top of the trumpets a function of the diameter of them as opposed to 1"
Harry
The rule of thumb Ive heard is 1.5 x the diameter of the trumpet. I shortenen the trumpets on a westfield style rover v8 plenum (the one that is rotated 90') because the trumpets just looked too close to the roof to flow any air. We only cut 40mm of them though, as any more just looked too short.
Marquis_Rex said:
v8 racing said:
IMHO Both are as good as each other, it depends on what is underneath them!! if you have a normal compression, low duration cam then you will not see anyincrease in any rpm range, generaly if you are fitting TB's you already have high compression long duration cams etc ant the TB's will win hands down throughout the rev range, BUT ONLY if you use the right size and run with a filter that uses a solid plate about an inch away from the bell mouths, on a 300 ftib engine the plate can be worth up to 15ftib!!
That's interesting because on my home made plenums I look for a 1" gap from inlet to the lid. Doesn't this effectively double the inlet tract length which increases torque.
Boosted.
I ran a V6 engine on a dyno once, fully instrumented up with kistler dynamic pressure tappings and some Druck static ones throughout the intake geometry.
On the one bank of the V6- the "wall" of the plenum was very close to the inlet bell mouths (about 1/4 D-where "D" is the diameter of one of the intake runners), the other side had alot more space between the wall and the bell mouths. There was no air flow difference bank to bank, so basically both banks breathed as well as one another. They tuned identically too. In this case the plenum wasn't very "active" and it wasn't designed for resonace charge tuning.....
MR, This is the sort of stuff I read about, where plenums can average things out across the board and make more overall torque but perhaps not as much peak torque. I believe the same applies for exhaust headers. Tuned length headers raise peak power but something of unequal length cobbled up at home may give a broader spread of power.
I made a plenum for a v6 and noticed little change with or without trumpets. What did change was the 'coming on cam' sensation at 4k. That dissapeared completely and the car pulled stronger everywhere in the rev range (according to the driver). The plenum smoothed out the peakiness and gave a broader power delivery. It was a Cosworth 24v by the way. What do you think?
Boosted.
boosted ls1 said:
boosted ls1 said:
v8 racing said:
IMHO Both are as good as each other, it depends on what is underneath them!! if you have a normal compression, low duration cam then you will not see anyincrease in any rpm range, generaly if you are fitting TB's you already have high compression long duration cams etc ant the TB's will win hands down throughout the rev range, BUT ONLY if you use the right size and run with a filter that uses a solid plate about an inch away from the bell mouths, on a 300 ftib engine the plate can be worth up to 15ftib!!
That's interesting because on my home made plenums I look for a 1" gap from inlet to the lid. Doesn't this effectively double the inlet tract length which increases torque.
Boosted.
I ran a V6 engine on a dyno once, fully instrumented up with kistler dynamic pressure tappings and some Druck static ones throughout the intake geometry.
On the one bank of the V6- the "wall" of the plenum was very close to the inlet bell mouths (about 1/4 D-where "D" is the diameter of one of the intake runners), the other side had alot more space between the wall and the bell mouths. There was no air flow difference bank to bank, so basically both banks breathed as well as one another. They tuned identically too. In this case the plenum wasn't very "active" and it wasn't designed for resonace charge tuning.....
MR, This is the sort of stuff I read about, where plenums can average things out across the board and make more overall torque but perhaps not as much peak torque. I believe the same applies for exhaust headers. Tuned length headers raise peak power but something of unequal length cobbled up at home may give a broader spread of power.
I made a plenum for a v6 and noticed little change with or without trumpets. What did change was the 'coming on cam' sensation at 4k. That dissapeared completely and the car pulled stronger everywhere in the rev range (according to the driver). The plenum smoothed out the peakiness and gave a broader power delivery. It was a Cosworth 24v by the way. What do you think?
Boosted.
The "evening out" sounds about right.
I ran the forth coming Aston V8 engine on the bed with the inlet plenum off- so it was simply 8 trumpets to atmosphere ( I no longer had a MAF sensor but that's another story)- the Volumetric Efficiency curve became REALLY spikey - with peaks and troughs in the mid range. I summised that perhaps the plenum in this case was acting as a damping volume.
On older fixed cam timing engines I know of alot of folk that use the exhaust tuning for TOP END- some of my ex-Lotus colleagues, however on engines with Variable Cam phasing- there is usually so much overlap at low speed (rememeber the inlet cam is very advanced) that THIS is where most of the benefit to the torque curve comes in these cases. The overlap facilitates "scavenging". Only problem with lots of overlap is that you'll also get a region of "anti tuning" where the exhaust tuning works AGAINST you and there's usually a huge dip in the VE/torque curve here. It doesn't usually matter to me at work, as most of the engines I play with have Variable cam phasing of some sort so at that "anti tuning region" I usually simply minimise the overlap to minimise the dip!
As for uneven lengths on the exhaust, yes it makes sense that they would broaden your torque curve because each cylinder is tuning differently now. You're alot luckier than I, in that you CAN do this, I CAN NOT, because I would be left with air flow imbalance- and therefore AFR imbalance- such that it would be very difficult to meet emissions. You perhaps don't have to contend with this.
Again your Cossie V6 experience makes sense- it's dampening out the "peaky/troughy" pulsations.
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