He is running a 3" exhaust and an external wastegate with separate exhaust

...seems you are in exactly the same position as me Rob.

Ignore the turbo, my engine spec is virtually identical, except for manifold.

Chatted to Barbz today about a lot of tweaks for my coop to come, suffice to say, the manifold can wait, although as the years roll, my engine needs a few tweaks to the CR & timing of the cams & a few other bits.

As I found out ages ago, the manifold is crucial, when I changed from a 0.64 turbine to a 0.86 housing, i gained almost 100hp, HOWEVER, even so, the engine is still struggling to breathe, so much so, I don't have a high rev limit ( for now ).

Fair play to the manifold supplier, however unless you start moving the turbo about, the larger use of primaries will be a monster for space...

Keep going, but to be honest a 2.0l will attain 500hp more easily than the 2.4 - 2.5 simply because of the extra volume being shifted.

Once the manifold is sorted, then you may attain JohnS figures.

good luck But don't expect overnight miracles, these aren't Jap engines

Sorry, but you are talking out of your bottom.

500 bhp will produce the same mass of exhaust, whether it is coming from a 2 litre engine or a 2.5 litre engine.

If you know different, please explain here....

ok, I guess I am

ever heard of compressible flow theory...

a 2.4 engine has a bigger volume ( positive displacement ), thus it shifts more gas, simple.

hence why a bigger engine can move a bigger turbo. Or am i missing something.

rated horsepower can be down to tons of variables... RPM, fuel, gearing, and of course cc.

A 2.0l will make the power easier as the stock manifold is better matched for the 2.0l block, whereas it's not for the 2.4l ( simply put, the flow is getting choked before even getting to the turbine ).

Or did you misunderstand my post ?

cheers

No, I understood your post. You seem not to have a grasp of the basics though.

500 bhp will produce about 50 lbs per minute of exhaust gas. A 2 litre engine will have to spin faster to produce 500 bhp than a 2.5 litre due to the fact it will make less torque, all other factors being equal, but the same mass of exhaust (and volume, if temperatures are the similar which they will be) will be produced for the same horsepower.

Think about it - if a turbo is rated at 500 bhp, will it make more power on a 2.5 litre than a 2 liter engine? No - because it is still only capable of flowing the same mass of air......

So, at 500 bhp, a manifold will be flowing the same amount of exhaust, whether fitted to a 2 litre or 2.5 litre engine.

And I would be pleased to be enlightened as to how gearing affects BHP - so please tell me.

I can assure you my grasp is good

So, each cylinder on my coop is say 20% bigger, compresses MORE air per stroke, burns MORE fuel per cycle, YET it goes down the same sized exhaust manifold ?

You will get higher gas velocity, but eventually it WILL choke, I've already found that out by changing turbine housings... ( wheel size the same ).

Don't confuse POWER with Torque, they are very different. My 2.4 makes less torque than the 2.0 on some others, as the head valve sizes are large, thus my gas velocites are different.

you also mix up the application of a turbo ( a centrifugal pump ) to an engine, a positive displacment.

The engine WILL choke if the outlet pipe is the same size & the cc has been increased.

Proof of the pudding anyway is that virtually most of the 2.4s don't make mega high figures, whereas the smaller cc 2.0 will make 500hp ( higher revs, higher boost ).

As I said, it's the manifold

A manifold has it's runner diameter decided by the valve size, nothing to do with the engine capacity. Whether the valve size suits the capacity is another matter again. A runner diameter wouldn't vary with target power changes but feasibly the length can be tailored to suit a power target.

If back pressure is a problem it's manifold or turbo (though the exhaust port can be left lacking too as target increases but I'll presume it's doing ok?) to blame but that's not to say a bigger exhaust wouldn't crutch the problem.

Yes. Because the 2.5 litre engine will be revving slower to make the same power as the 2.0 litre - funnily enough 20% lower rpm.....

Do you know what causes flow to choke in an exhaust manifold? 36mm id primaries will not choke the flow on a five cylinder, 2.5 litre engine producing 600 bhp.

The T3 sized inlet on the turbo will be having to flow the gasses from all five cylinders, and if it was circular it would only be 55.6mm ID, so the gas speed there is 209% of the gas speed in the manifold runners. If there was any choking going on, that is where it would be happening.

my engine will never get close to 600hp ( in fact the only one was JohnS ) with lots of extras...

partly due to the turbo needing to be a damn sight bigger & the manifold isn't up to it.

RE : my previous post on gearing, that is aimed at rated hp on a rr ( my fault ), however... the rest stands

If you know what chokes the flow ( other than the most obvious part, being the turbine wheel ), you'd make Barbz a happy man.

Anyway, you fail to recognize a 2.0 / 2.4 will all be revved to the same limits ( circa 7-7.5k ), hence the 2.4 literally chokes itself at the top end.

doubt it's the exhaust downstream, but more the critical part between the cyl head / turbo.

cheers.

I haven't seen any dyno figures of a 2.4/2.5 revving to 7.5K. If they do/can then at the same boost I would expect them to make 20% more BHP than a 2.0 litre. I don't know that the inlet and exhaust valves are up to flowing enough at those engine speeds though.

My take on things is,
2.0 flows x amount of gases,
then a 2.5 flows X amount of gasses times by 1.20 per bang.
therefore a turbo on a 2.0 might flow well up to 7k but on a 2.5 it will flow well only till 7k times by 0.8. Hence the bigger turbo is needed for 2.5. To match up well,
more volume or displacement ,

Therefore turbo on the 2.5 must flow x1.2 more than the 2.o turbo
And same goes for pipes,

Because we are talking about displacement here,


No point to prove here , just adding some input

Very good post - this is absolutley right!
It also is right, that the diameter of one exhaust tube depends on the valve size. Diameter should be at least as big as the effective valve size of both exhaust valves. To be smaller means a better torque in lower revs, but minor top end. To be bigger means lower torque in lower revs, but more top end.
Ciao
Juergen

Come on Barbz, settle this and explain...

I agree about the sizing of the primaries. However, once again if the exhaust valves and manifold on the 2 litre engine will flow XXX BHP then the same size valves and exhaust will flow the same amount of exhaust gas, and therefore the same BHP, on a 2.4 or 2.5 litre engine. The same amount of exhaust per second to be flowed will be at lower RPM on the larger engines than on the 2 litre engine.

IF it is intended that the larger capacity engines will produce maximum power at the same engine speed as the 2 litre engine, then in that case larger exhaust valves - and manifold primaries to match - will be required.

I am sure I mentioned my cyl head also has bigger inlet / exhaust valves ( I assume you knew that too ), thus the above is valid.

Not too sure what Stichl was agreeing to

That was my point. In fact it makes more power per rpm point ( up to a point as it still has the standard manifold, even though it has had the collector ported & the gaskets matched ). Not sure why you talked about 20% less rpm, I don't drive about at 20% less RPM

Full circle discussion ? Think so.

i can't argue technicalaties as i don't have the knowledge..all i know is put a 2871r on a 2l and you have full boost around 4k and it will rev out fine..put it on a 2.4 and full boost is 2800 rpm and it wont rev past 5500rpm as it chokes.thats fact..
another fact is we have tested and eliminated everything ..it is the manifold thats choking at just over 400bhp again thats a fact now..
whether its due to pulses,id or collector or amount of gasses it matters not it doesn't work so i have to find a solution
the 2.l has i think 28mm valves mine has 32.5 or 33.5 (will ask barbz as i cant remember) but with the seats done etc they will be a little better flowing anyway

the solution is what matters to me and though finding out why would help with that its likely to be more trial and error now i have more information..this is all helpfull whether it pins down the issue or not so please carry on with any suggestions you think may help with how to build the next one...as i mentioned i have an idea to try but if it does not work i will have tig art build to my spec so all help to this end is gratefully received

You previously posted: Proof of the pudding anyway is that virtually most of the 2.4s don't make mega high figures, whereas the smaller cc 2.0 will make 500hp ( higher revs, higher boost ).

If the larger capacity engines were able to flow 20% more air at the same RPM, then they would produce 20% more power. IF they did, they would need larger diameter exhaust manifolds. But you have said they don't, which is fair enough, but that also means you have to agree they don't need larger manifolds! What I am saying is that to produce the SAME power, the larger engines only have to flow the SAME amount of air - both on the inlet and exhaust sides. What I am further saying is, that because of the larger displacement, a 2.5 litre engine will flow the same volume of air as a 2 litre engine at 80% or the RPM. So we can agree on that too.

Following calculation:
36mm ID will give 1017mm^2 of area.
Your 28mm valves of your stilo head will give 923,6282402 [mm²] at 10,5 lift, with regard to your valve rod it will be ~800mm^2, only...
The 36mm ID are more than sufficient...
If you are going to install a bigger manifold than 36ID you will loose tons of torque, only...
Juergen

ok it has 28mm valves one side and 33.5 on the other

i only mentioned the 2871r above as an example of how differently the 2 engines act on the same turbo/manifold..all the calculations in the world can't alter the fact it doesn't work with the engine and turbo set up ..whether it should work or not doesn't really matter

also the engine revs happily to 7500 and on barbz the power is still climbing

does anyone have any suggestions as to what they think would be a good design?

any ideas on why it might not be working ?

Now you have confused me, because above you said "and it wont rev past 5500rpm as it chokes"

i think you may have misunderstood the post if you read it again you will see i said ..when you put a 2871r on a 2.4 that happens and it was not mine or barbz it was robs that ran a 2871 every time he changed his turbo to a bigger one he was able to rev it further untill now he has a 3076 .86 and can finally red line..

A pair of 28 mm dia exhaust valves does not warrant a runner with a 36 mm id, thats an area of 1018 mm2 which is not enough. It NEEDS to be 1 3/4" tube, NOT 1 1/2".

OK - so what size primaries does Rob have?

Also, what RPM is the "red line"?

Have you got any pictures of the manifold in question ? some of the inside of the collector and one of the whole outside would be helpfull in trying to diagnose the issue.

well it looks like i have jumped the gun a bit as have just had barbz on the phone wondering what i am up to and telling me not to worry i don't need to do this as he has already bought the bits and got a solution..apparently its not primary id or any of the things so far discussed though it is a manifold issue to do with collector and back pressure..he has explained whats happening in a way i understood but wouldn't care to try and repeat as i am likely to not do him justice..so it goes back to barbz monday..
on buying the manifold we knew there were 2.0l cars well over 500 with them and were assured they would be good for 600 though they did say they had not had them on a 2.5 so it was a bit of trial and error..
since the last dyno i have been speaking with the manifold makers who offered to make me one to any spec i want (and i return this one) hence me asking for ideas but barbz had, it transpires, been sorting it out anyway ..
knowing he had other work on for a few days i thought i would try and sort it out seems i don't need to
well thanks for the suggestions i would like to have seen where it got us but i will leave it to him as he wants to finnish it himself understandably, i don't suppose he needs my help

1nro i am interested to know what you think the id should be by your calculation

I' talked to Hartmut Lohman... (he was one of the engine builder of F1, when the cars had >1200HP turbo engines). It does not make ANY sense, to build manifolds with an area of much more than the "effective area" of the valves...
You will loose the velocity of your exhaust fumes, only which will result in a worse respone of the turbo because of lost kinitic energy.
Maximum acceptably is the area of the port at the end of the cylinder head, that’s about 10mm^2 of the Fiat Coupe...
Therefore 36mm ID is ok.
Juergen

A runner made from 1 3/4" tube will have an I/D of about 41 mm, this suits the dimensions of a correctly ported head (one with 28 mm dia exhaust valves) much better than 36 mm. It's not my calculation, it's common sense and a rule of thumb used the world over.

40mm ID are enough for 700HP cars with four cylinder...
I do not know your source, but it seems to be a good one :-)
Try it - you will see, what response you will gain...
Meanwhile almost all car producer tend to use the kinetic energy of
exhaust fumes by using extemely short tubes and divided / twin scroll technology.
This is most effective technology to get the energy of every single stroke of the engine...
But if you like to use the old technology of big / long tubes... it's your decision.
Juergen

Not sure why you'd call it old theory, if anything it's only in recent years that people have started using long runners. It's not a big pipe size, it's the right size. The dimensions of the port tell you to use this size, anything smaller is a restriction after the head and that's wrong. Pressure differential is what moves gases, to provide a runner that increases the pressure after the head is wrong, all day long :-)