Forum for competition engine enthusiasts. RIP Guy Croft 09/11/2020 - This forum will continue both as a source of information and as a memorial to Guy.
Have a few questions, I'm designing an inlet manifold for the 16v Peugeot XU9J4 engine and need a few things cleared up.
First, the inlet ports are 40mm wide. I'll go for 220mm long runners, now what's the best/max inclanation angle?
And second, which throttle control is best? Butterflies or slide throttles? And how much do butterflies disturb flow if they are positioned right at the inlet port (direct to head)?
Is it better to position them further up the runner and benefit from blades cutting fuel drops (if running 8 injector setup, or having injectors further up) and also butterfly and spindle not to disturb air path at narrowset part of the runner?
Well like I said, I'm in a proccess of designing it, so no real life pics yet, only computer models, but I hope I'll have CNC machined flange on my desk by the end of next week.
I have asked those questions in order to continue with modeling.
So far I have modeled head flange
Runners, velocity stacks and plenum will be made out of carbon fibre
and a semi finished individual throttles right at port inlet
Now spindle and butterflies surely restrict flow if they are positioned next to port inlet?
What about the inclination angle of runners? firstly I designed them to gradually increase ID from 40mm to 45mm at the end of the runner, but is it better to design them with inclination angle in mind? like 7‚° angle from 40mm inlet over 220mm runner?
And what about slide throttles? Worth fitting them? What about flow control at part throttle?
firstly one of the pictures of the manifold says 'designed by CF'. With respect (it may be your firm) who is that? I assume that these pictures are of your property? One must beware of infringing copyright as you know.
I think you're include angle of 14 deg (taper) is fine. That said if the 40mm pipe flows enough you may not need any taper at all. The radiused enttry looks good. I'd just come straight out horizontal from the port. That is more-or-less my experience of the S16 head (similar to yours I understand from your pm), the manifold in the picture worked well. Don't forget that a turbocharged head is a lot more forgiving of changes of angle and section than a normally aspirated one.
Regarding throttles - as opposed to throttle bodies) I have had some interesting conversations lately with Phil Lanes who owns GG Motorsport, about the effectiveness of individual throttle plates or slides when turbocharging. The questions arose when he came to GCRE to chat about an Integrale I'm doing. He was not in favour of split throttles on turbo units.
Of course when the engine is normally aspirated one can see readily that split intakes separate pipes from head to air filter) are going to give superior pressure-wave cylinder filling, but how necessary or effective that is on a turbocharged unit where there has to be a common plenum we're not entirely sure.
Might be better (and is certainly simpler) just to have one large throttle on the plenum entry, after all, what are you going to gain by having four of them? Nothing, Phil suggested to me. Just more to go wrong and more potential for air leaks. Interesting point and I must confess I had never given it much thought. Not that I get much time to think these days.
If anyone including of course Mandic has another view let's hear it.
Guy Croft wrote:
firstly one of the pictures of the manifold says 'designed by CF'. With respect (it may be your firm) who is that? I assume that these pictures are of your property? One must beware of infringing copyright as you know.
Well on all foreign forums I use my surname as nickname, but on domestic forums I use nick CitroenFreak, I'm amazed by Citroen's engeneering and clever and inovative solutions. Therefore CF stands for CitroenFreak.
Thanks for reply GC,
The thing is I'm putting turbo on my engine and by doing so I get lots of unpleasent things with conversion such as turbo lag, turbo gap and so on, and I'm doing everything to minimize those effects.
And since individual throttle bodies are well known for superior throttle response on naturtally aspirated engines I'm wondering how and in which way they contribute, if at all, in forced induction world.
Then again, there is a question of ratio between effectivness and costs, but like with all things, getting them 95% done is pretty easy, but to get 100% out of them is a hard and costy way. But since I don't do things by halves, I'm willing to extract those 5% out of my engine and my pocket as well :)
Let's be clear - that in this case, the position and type of the throttle itself -by which I mean the air metering device - not the cylindrical body - be it butterfly/slide or whatever, has nothing to do with the throttle response.
The only gain for you, I think with 'throttle bodies' (as most people understand them) is that they likely flow more air than a basic factory system. In your case, you are going to have the high flow runners but you can remove the air metering device (throttle) to the plenum entry for no loss and have the best of both worlds without the complexity of 4 unnecessary throttles.
Isnt throttle response affected by throttle position? ie. the distance from valve? as lets say, when engine is under vacuum condition (shut throttle) and when applying the throttle air wave has to move and this takes time.
So throttle response should vary between throttle positioned 50mm from the runner entery and 500mm away from it? Or is this effect so rapid that it's negligible (considering speed of sound and runner length I would say it is)?
I've always been guided by my mentor that less than 6 degrees (12 inc.) is ideal in order to maintain laminar flow.
The R32 Nissan Skylines have six 45mm individual throttles right up against cylinder head, if that's anything to guide by. Although the point of leakage is a good one!.
and the reason I'm asking around for different oppinions is just that, one gets loads of info on internet from more or less reliable sources and they vary a lot.
Some say this, some say that, some even back it up with theoretical background and all sounds fine and logical, then some say throw that out of window...
I'm really curious what's the thing behind direct to head throttles, do they restrict flow, if so by how much. If they were so bad or wouldn't give increase Nissan wouldn't have bothered fitting them to GTR and GTi-R as stock in the first place.
And why are slide throttles inferior according to jenvey, here. Surely This is way better than if there were spindel and butterfly in the middle.
But then again, what happes when You have pressurised induction and when having a gap on the left side of the throttle, does This represent a restriction.
Has anybody access to some direct to head TB so can make flow test?
But then again, with turbo engine I think this restriction is less than in NA engine as You can run more (very slightly) boost to overcome this effect but still retain superb throttle resopnse. But as GC wrote, maybe it doesnt contribute to throttle response at all.
Well without some proper research and data we will never know, will we? We can talk and talk but as always each of us will have different oppinion.
The aerodynamic rule of thumb is 15 deg included, but less is better, air doesn't generally 'like' any change of section. That said we all know it's usually inherent in the design.
Throttle response: Mandic - you raised a fair question.
When we refer to 'throttle response' it's the ‹Å“transient¢ž¢ response of the engine to the throttle being opened that we're referring to, not the behaviour of the throttle (butterfly or slide/roller) itself.
Ignoring variables like engine speed, it's essentially the rate of flow past the throttle plate that controls how much air is available to fill the cylinder.
On a normally aspirated engine the mass flow across the throttle plate for given angle, is dependent on the cylinder depression relative to atmosphere ¢‚¬Å“ atmosphere being somewhere at the downstream end of the throttle plate, eg: rampipe or filter box. On a turbocharged engine we substitute boost pressure for atmospheric and the filling - volumetric efficiency point of view - is even better.
One cylinder volume, in practical terms, is large compared to its associated port and intake runner volume and thus at part throttle the region inboard of the throttle plate is at low - cylinder pressure ¢‚¬Å“ more or less irrespective of where the throttle is placed.
We can¢ž¢t make the intake volume huge because we need good velocity to achieve high mass flow (it being a function of air density, port cross-sectional area and air velocity), and anyway why should we? We don¢ž¢t want a lot of air going into the cylinder when the throttle is closed.
Opening the throttle allows high-pressure air to flow in, and we can¢ž¢t consider the port region inboard of the throttle plate/device as a separate chamber to that on the other side (leading to atmospheric or turbocharging pressure), because that inboard volume needs constant replenishment.
So what gives good ‹Å“throttle response¢ž¢ if it¢ž¢s not the position itself of the device? Let¢ž¢s assume the throttle is ‹Å“snapped open¢ž¢, because that¢ž¢s where it¢ž¢s called for. You have to look at the same factors that make for good volumetric efficiency. Good response means getting the air into the cylinder quickly when the throttle condition changes and on all engines we want a good valve and seat combination, with minimum losses, the same is true of the port/intake.
On normally aspirated units we especially want good cylinder purging (from camshaft overlap or cross-scavenge) so that the incoming charge is not diluted by exhaust residuals.
On turbocharged engines scavenging is not such a critical issue as the intake air (on boost) is higher than the exhaust gas pressure anyway, but we have to be aware of the risk of cylinder contamination due to high turbine back-pressure - good matching of turbine to engine is imperative.
We can depend on a degree of ‹Å“momentum¢ž¢ in the inlet tract ¢‚¬Å“ air moving in and trying to fill the cylinder, but on normally aspirated engines, that alone is too slow moving to develop high power. So, since the cylinder is below atmospheric on the intake stroke, we can make up tuned lengths of intake runner to match engine speed and characteristics and thus utilise negative waves that emanates from the intake valves to ‹Å“¢ž¢ram charge¢ž¢ the cylinder. Those negative waves, when meeting a change in volume - or a higher-pressure condition such as at the open end of a rampipe are reflected as positive and ‹Å“rams¢ž¢ air into the cylinders. With linked intake runners, joined in common plenum the effects are less effective and far less easy to determine and I don¢ž¢t want to go into detail with n/a units.
Does the same pressure wave effect apply to a turbo unit? Well, it depends.
Off boost at low engine speed - when the cylinder pressure is low - the intake system is going to behave like a normally aspirated engine and the intake reflected wave is going to propagate from the first region of large volume it sees. That will tend to be where the runner meets the plenum. Designing the runners means getting them right for the cams and the rest of the engine (considering it as a n/a unit). The exhaust header has an important influence too, and, again, can be considered to act as a n/a one would in that condition.
As the throttle is opened and the boost comes on, that region could be in the inlet tract itself (perhaps downstream of the throttle plate if that¢ž¢s where it is) or where the runner meets the plenum ¢‚¬Å“ but whether it reflects beneficially depends on the size of the inlet tract and the rate at which high-pressure air arrives from the compressor.
At full throttle (ie: full boost) the negative wave is going to tend to be of smaller magnitude because, compared with a n/a unit, at any given point in the intake stroke the cylinder pressure is going to be higher. The incoming air is going to be moving so fast that any reflected wave (that exists at all) will tend to have no effect, and it doesn¢ž¢t matter because the compressor boost pressure has given us all the massflow we need anyway.
All in all, the entire turbo pressure wave manifold response is fearsomely complex to compute and few firms have the software to do it. Most ignore it. And, it might be said that the end result is still going to be a compromise.
Remember that when the throttle is closed, there isn¢ž¢t going to be any manifold boost. The boost comes only when the throttle is opened (depending on the turbine response) and the large mass flow has to get to the cylinder at the right time.
So the instant the throttle is opened do we get high mass flow right to the cylinder? Does the throttle position have a bearing on that response? I don't think so, excepting maybe the case where an anti-lag system is feeding pressure to the manifold outboard of the throttle under all conditions. The most critical consideration by far is the distance from the compressor to the cylinder, and what the losses are on the way (eg: intercooler) because the response of the air in the system is ‹Å“elastic¢ž¢ to say the least...
Insofar as injection is concerned I'm of the view that it wants to go direct to the back of the valves. Yes, people put it in other positions, but I think 'in the cylinder' is where we want it, not floating around in the airstream or the inlet tract.
Are slides or rollers better than butterflies? Sure, but really only at full throttle. At part throttle I would not care to be too categoric because I've never modelled or tested them.
OK, its fair to say throttle position and its role has been examined,
And I also agree that turbo-valve position if far more imporant than playing with throttle position, so better focus on sloving that matter.
But what about injection, You said having them "direct to the back of the valves" is where we want them. Yes it is true that batched system will cool inlets down to some degree and that at low speeds we want them as close a possible due to low air mass speed, but what happens when we speed the air mass up?
Do we gain anything if we position injectors (second set) further up the runner? I think yes, as firstly fuel atomisation will be better, and it's much easier to controll 2 sets of small injectors than 1 set of big ones. as high output injectors are not so controlable at lower duty cycles.
You never said what you were going to use the car for? This would be a major influence in determining the use of seperate TBs V one large throttle plate, It would also help with the decision on inlet tract length.
I am in the 'same boat' as yourself and have made a decision based on a lot of thought and investigation, here is a link to an earlier post made by me and where my thoughts were at back then, also some good advice by others:
Evodelta wrote:
You never said what you were going to use the car for? This would be a major influence in determining the use of seperate TBs V one large throttle plate, It would also help with the decision on inlet tract length.
Well I'm just making a car which will suit me and extracting the best out of it => making the torque curve as flat as possible when it comes on boost. And since I'm using "only" GT25R turbo this will happen very early in the rev range, hence the short runners, to flatten torque close to rev limit.
If everything goes as planned TQ should look like this:
So almost flat torque of 300Nm from 3000RPM all the way to fuel cut at 7200 RPM. Combined with short ratio 6 speed box it should be fun enough :)
Regarding its usage; well it will be driven on road as well on the track. And more and more I think about it, it will probably be driven more on track than on the road.
Evodelta wrote:
Have you given much thought to your plenum and equal sharing of air to each cylinder?
Actually too much and am also using FlowWorks, it's a sub program which works with conjunction with SolidWorks and can determine flow through objects. So I'll know exactly how much flow each cylinder will recieve, at least in theory.
Good points about Throttle response, I'd just like to throw a few thoughts into the pot when working with fuel injection.
Throttle response is as much about all the transient calibrations within the ECU calibration.
It is absolutely important that the compensation tables for transient conditions are calibrated correctly, after all - if there is too much or too little fuel when the throttle is moved rapidly then response has gone!
Also on F/I the main calibration will have to be based on either airflow or MAP. This makes it even more important to spend time setting up the transient conditions with a throttle possition sensor.
What sort of ECU are you intending using for this project? I notice that 8 injectors have been mentioned.
