Tube sizing of manifolds

To get back in discussion regarding piping size of manifold:

Some interesting articles from US-tuners (who formally thought “bigger is always better”) – some guys in this forum still believe this as well…
First, Perrin:
His manifold, really a long one (problem is the engine – available space) “…This header uses 1.5" (OD!!!) primary tubing that is expanded at the flange to fit the Subaru exhaust port size. This size of tubing is perfectly designed for cars up to 400WHP. You can see from our dyno graphs that even on cars with well over 400 wheel horsepower there is a significant gain in HP and TQ across the entire RPM band over a stock header. For those looking to go way beyond 500 wheel horsepower, check out our Big Tube Equal Length Header”
We speak about a four cylinder with 4x 38mm ID (~34mm ID), which is sufficient for 400WHP (not engine HP!)
Now they introduced a new header with bigger tubing, have a look here:

http://blog.perrinperformance.com/bigtube-equal-length-header/

Excerpt: …As expected a bit of low end/off boost power lost, but some HP gain at higher HP levels. 10HP with no additional boost or tuning is pretty good and for sure those who are planning on buying a header and running close to 500WHP, should for sure consider this header over our regular one. What we didnt show is that at 20psi there is almost no HP gains or at least something I felt ok with publishing.
What is the downside of this new Bigger Header? For sure the thing not seen on the dyno is the off boost power change. This is something that is noticeable on the street, and almost completely masked by the dyno. Its hard to put a figure on how much less torquey this feels, but its noticeable for sure. If you look at this as nothing more than an RPM when the turbo reaches full boost, you will see there is no change there.
Unfortunately I do not know the new diameter, but the result is clear! Bigger is not always better. Please have a look to the graph as well!
Manifold is absolutely the same like the thinner one – only difference is diameter.

Second manifold supplier: full-race, one of the most experienced manifold builder is USA.
http://www.full-race.com/store/turbo-manifolds/
They recommend 36,6mm ID for 4-cylinder cars with up to 800whp – the big runner manifolds with 40mm ID are recommended for drag race and >>2bar of boost. Remember – for a 4 cylinder!
Tests show a gain of about 300rpm better spool between 36,6mm and 40mm…

I hope that most people now realize that the Tigart manifold is more than sufficient for almost all applications of Fiat Coupe at additional sufficient response. If someone wants to build a drag race car with >>800HP – please do with 38mm ID or even more…

Juergen

Juergen,

First off no one is saying that bigger is always better, only that the diameter of the tubing should compliment the head, if it does that and the engine is free to breath then there is nothing else that can be done.

Don't think I'm talking about fast street cars either, because if you tune an engine where you find you even NEED a tubular manifold, you are in fact building a race engine that will be used on the street, thats the big difference.

The best exhaust for any engine is no exhaust at all (obviously excluding a short megaphone or similar) this is because the pressure in the cylinder at blow down needs to see the largest pressure diferential possible out of the exhaust port to make good VE and lessen the pumping loss the piston needs to do to push the remainder out. Obviously we need to silence the engines noise and we have a turbo to drive so it's necasery.

It's all about the efficiancy of the engine, not how quickly you can move hot gases along the pipework to "Spool" the turbo up. The turbo has it's own method of doing this in-built into the housing, necking down the manifold right after the exhaust port can't do any good for the most important part of the system (the engine) afterall it's crankshaft connected to the wheels, not the turboshaft.

If you read the subaru page again you will notice this sentance.. Other notables is this car has the stock TGV housings installed and working, stock heads and cams

Typicaly I would suggest that the fact the larger OD primary made more power but lost some 'off boost' torque is down to the standard head and cams not being suitable for the bigger tube, it's all application dependant, is it not ????

I'm not sure it's worth replying Richard, I've been through this with Juergen and he isn't for swaying.

You are right though, the runner sizing is determined by the port dimensions which in turn are determined by the valve size.

The companies mentioned are selling manifolds to people who bolt them onto pretty much standard cars, a bolt on bit of bling. These manifolds are not an optimised performance part. Perrin shows how much credability can be taken from his writings when he says "10 hp with no additional boost or TUNING"

Like I've said before, there's no reason to increase / adjust the pressure / velocity in the exhaust manifold runner after it has left the cylinder head port which someone should of taken great care to dimension correctly, if you do you are ruining their good work. This presumes that the port exit needs adjusted, some heads don't and then the correct sized runner will need swaged out to fit the port or the port will need welded up and reworked.

Actually I was wrong when I said there's no reason to ADJUST pressure/velocity in the runner, I can think of one good reason but it doesn't involve increasing.

I expected your answers...
Sorry, but please Please reconsider your answer…
You stated "...The companies mentioned are selling manifolds to people who bolt them onto pretty much standard cars, a bolt on bit of bling."
We talk about 800WHP!!!
If this is your standard engine tuner, then I want to see your car, if it has been finished (it's still soon, very soon).
All you can argue is to reduce your engine to VE, only…
VE is not all (it is very very important, without question), but there is for example also a thermal efficiency and other aspects you have to consider.
First of them is the gas velocity – if it is too low, you don’t get enough mixing. Thus for example smaller valves are better in low revs, because the gas velocity is higher…
Fiat never would have built two different 20V heads for same engine – but they saw an advantage to build a head with smaller valves for the smaller 2l engines to have enough torque in low revs.
Only the bigger 2,4l engine got a head with bigger valves – the bigger lift compensated the weakness in lower revs…
The bigger 2,4l head definitely has a better VE – why not use for the 2l 20V turbo?! They had this bigger head, why not use?!
I know the answer. My friend and ex-formula1 tuner Hartmut Lohman (a fan of the 20V turbo engine) bought a 20VT engine years ago directly from Italy from Fiat plant – it was one of the last complete engines directly from Fiat plant and it had been on a test stand – therefore this engine was very very cheap.
He took this engine and built it directly into his daily business Fiat Coupe (he has 3 Coupe). Suddenly he recognized that the engine was bad in low revs, but very very strong in higher revs – definitely more power than before.
He decided to dismantle this engine and found … the big 2,4l head… at this moment (years ago – I think it was early in 2000) we did not know, where this head had come from.…
Hartmut thought that this was a test head especially made from Fiat for tests – later on abolished, because of too low torque in low revs…
Now we know that this head was from Stilo / Kappa.
Note: Do you know, that the former Kappa 2,4l heads have much bigger ports than the newer Stilo 2,4l heads?! – YES – there they reduced the ports as well!
Smaller VE – Fiat must be crackbrained in your eyes!
Next example: Take a cam with more hub, VE definitely will get better – you will get the same problem like with bigger valves… too small velocity, too small mixture.
VE, VE, VE… bigger is not always better.
And now to one of the most important things of a turbo engine – the turbo itself, which lives from velocity and temperature! This is the part, which affects the VE significantly.
It has to be secured, that the turbo will respond to a small amount of exhaust in lower revs -> you will need small tubing of the manifold to keep the velocity high.
In higher revs you will need big tubing to get enough exhaust through complete exhaust system to avoid backpressure.
But you won’t get both!
Therefore – if you want to have a high power engine without consideration of response in low revs, then please build your manifold with stove pipes…
You will get an engine with lot of fun above 5000rpm…

Thermal efficiancy of what ?

Obviously we all realize putting the turbo 5 miles away from the engine as in 'the rear of the car' will loose some efficiancy through heat loss, but do you really think a slightly larger OD manifold runner that fits the port will loose so much heat the turbo will never ever spin up ??? I don't think so somehow.




The turbo doesn't need any extra help from increased heat or velocity, (which incidently I think you confuse with flow) All turbos will spool from exhaust gases, the turbo's speed is regulated, we dont want it to go any faster only to hold its shaft speed that produces the requierd boost level. In fact half the energy goes out the wastegate anyway, not much point speeding hot gas out of a wastegate pipe is there ?



Fit a smaller turbo then ! You are obviously another one who is hell bent on "lag" and spool up. Again what are we disscussing ? 1> road cars with race engines or 2> Race engines in race cars ?

Juergen, What do you mean when you say 'hub'? Do you mean 'lift' (upwards movement)?


I don't think it's a good idea to compare what comes out of a factory and built within strict constraints (meet emission laws and most of all cost etc) with something which is specially built with neither of these in mind.

80% of road cars won't see over 4000rpm in their lives...

I knew you'd be waiting for an answer from me, it seems I get under your skin, simply because I offer a different opinion to what you are used to hearing. We can't all be the same and I realise I'm different to most in what I try hard to get you to see. I don't want to get involved with you in this repetitive issue, as I said already we've been through this in enough detail before now (I don't want to broadcast all my thoughts/opinion). I would only urge you to research gas velocity in exhaust ports (and the targets that top flight head porters look to achieve in their work, you'll find them to be of very high velocity and effort is spent on reducing them on the small ports our engines have, no massive American V8 ports or even too big Honda/Mitsubishi ports for us to worry about and we have to be careful not to choke the port) and of considerable mass involved. This large mass is constantly being displaced by repeated exhaust cycles and the mass is what you should be looking at before you stake so much importance on just velocity. I can (already have in the past) show you turbo systems that have crazy long manifold lengths which if what you say is true would hardly ever spool the huge turbines they use, I think if you look back through out previous discussions that this just isn't the case. Do you not agree that the HUGE turbo rear mount system on that truck hauls ass?

Most importantly is the need to look at the whole engine package, ALL of it. An opinion of a particular part can be clouded by there being an inferior part elsewhere that is influencing the so called incorrect part. Bolting a manifold that uses bigger runners than you recommend onto an otherwise standard engine does not make it wrong. I see the smaller runners as a bandaid to the imbalanced package rather than being the best way.

Let us not fight, let us both try and research each others opinion with an open mind then we can further advance in our interests.

OMG Martin, a sensible post, well done you

By the way Juergen, the "soon, very soon" relates to the 20vt I bought a few years ago that was a non runner and needed a new engine, in that regard the soon has been and gone. Look through my early posts. I should edit it out eh!

Hi Juergen, 1NRO

Can I ask, is there any issues with the length of the manifold regarding exhaust pulsing to the turbo?

On the one hand I'm thinking short is best, but then I'm thinking well would that give the turbo a hard time with such aggressive pulsing in which case a manifold a little longer would be better. I can understand that having the manifold to long would not help, but then when you look at an old F1 design, the manifold are long. I can see that the rev range is completely different between them but at what point does this allow manifold length to become a secondary factor.

Juergen, my engine is supposed to be an all out race unit for the track, so any ideas from anywhere are appreciated and duly considered, many thanks in advance.

Roger.......
131 turbo project Toad

Not necessarily the case Roger and whilst it might have been the dogs' in it's day, it's what, 20yrs? Out of date now. Google images: 'Honda F1 turbo manifold'

What you will find is that there is more than one way to kill a cat....

The requirements of a V6 exhaust manifold are quite different from and I4 or I5 manifold.

Try Googling 'BMW F1 turbo manifold' or 'Hart F1 turbo manifold' or look for V8 turbo engine manifolds for Le Mans or Indy cars from manufacturers such as Alfa, Ferrari, Porsche, Mercedes and Cosworth

Roger,

You'll have to PM or email me on Osbornenk@aol.com for my opinion, I'm done with this thread.

Nik

Unfortunately there are different opinions regarding length of manifolds…
There are two opinions:
1. long manifold to get better torque in low revs because of oscillating gas within this longer tube.
2. the short tube for higher power output. I am a fan of short up to medium length – shorter means hotter gas with more kinetic energy. But on the other hand you need a certain length to avoid interaction between single cylinders…
It is not as simple as it seems…
Best in my eyes is very very short in combination with dual scroll – then you use the kinetic energy of every singe pulse (stroke) without getting problems with interaction between the cylinders. But to do this you will need a 4-cylinder or 6cylinder … and no 5cylinder :-(
If you ask INRO , he will tell you another story :-)

My opinoins on twin scroll are

A: suits cast iron stubby manifold runners for packaging reasons in OE form.
B: Sometimes used on a normal tubular manifold and small displacement engine, (yes 2.0l) fitted with a massively oversized turbo, to gain some kind of lower boost threshold back.

Other than those two situations I dont really see the benifit.

I have a different opinion, Mitsi Evos' being the common OE twin scroll could easily have their TS manifolds replaced with a common collector, there is no packing advantage, just look at the earlier evo models pre TS scroll with a generic log cast manifold. There are other advantages IMHO

Also on the oversized turbo's and TS (well strictly speaking divided manifolds as most aren't TS) it's a far broader topic than boost threshold - though this is a benefit, think about the exhaust gas pressure to intake manifold pressure relationship, cam overlap, interference etc. Keeping those runners seperate has a lot of advantages and little physics down side, the downside being cost/complexity/packaging

I suppose it like a Snicker or a Marathon bar, just because its new doesn't make it better. A Zakspeed Capri is still quick however you look at it.

Roger

P.M. in process

I seem to remember marathon was much better, lots more nuts.

We must both be a pair of old farts I'm thinking.

Wet farts perhaps ??

Did you ever start your inlet manifold project Roger ?

Hi Martin,

It may be old but if you can give me 1100 bhp from what I believe is a 1500cc engine, well then I'll concede the point. Personally I would be more than happy with a twenty year old F1 Honda turbo, old tech or not, and that is my point, old or not if it works use it.

Roger......

Hi Tricky,

Its all research so far, like my question above about the exhaust manifold lengths, Big Toad is still having work done on the sump, I've had to get my Thema on the road for work, and then back onto Little Toad which also needs an inlet made, its all fun around here you know. So any engine does and don'ts are most welcome

Roger.....

Bye, Bye, Martin Crabtree.

Hi Stichl,

But short to middle, Ok I understand that, but can it be to short i.e doing damage to the turbine ?

Roger.......

I did my Masters by Research on this subject. "Investigation of pulse tuning the exhaust manifold on a turbocharged engine and its effects on engine output." There are very interesting results into pulse tuning with regards to pipe length and diameter including the effects from camshaft timing and how EGT effect the speed of pressure waves. I had pressure sensors in the exhaust system measuring primary pulse waves and how they reflect/refract and attenuate as the engine is running. I measured in cylinder pressures and have many results. I would be happy to show all my research paper once submitted in November.

Fantastic - and very generous of you. I look forward to November!

Here is a two page extract/sample from my 87page write up

In order to achieve maximum cylinder efficiency it is essential that the primary wave (PW) is controlled, this is often referred to as pulse tuning. The PW can be of negative pressure or positive pressure. The PW can be reflected, refracted and attenuated depending on its surroundings. After the combustion process the exhaust gasses are released into the exhaust stream via the exhaust valve. These exhaust gas particles travel at a local gas speed whereas the PW travels at the speed of sound, which is governed by the exhaust gas temperature. The PW travels down its cylinder’s primary until it reaches the effective end of its pipe, the collector. At this point any or all of three instances can occur.

“
1. The positive component is refracted up the adjacent primary pipes.
2. Part of it continues onwards and is lost to attenuation.
3. A negative component is reflected straight back up the pipe to where it came from.
”

(CROFT, Guy, 2010, p.231)

These three instances apply to naturally aspirated (NA) engines and turbocharged (TC) engines however on a TC engine the turbocharger is placed at the end of the collector effectively closing the pipe. In general terms it could be crudely suggested that an NA engine’s exhaust system is an open pipe system and a TC engine is a closed pipe system. This crude statement means that when instance (3) occurs; on an NA engine a portion the PW is reflected as a negative pressure wave (NPW) back up its own primary due to a change in volume whereas on an TC engine there is no negative element to reflect as there is no change in volume therefore the majority of PW wave is reflected as a same sign wave, a positive pressure wave (PPW). With a TC system it is less likely for the PPW to exchange its energy to drive the turbine blade and attenuate down the rest of the exhaust system but more likely to refract its positive element up adjacent primaries and/or reflect as a PPW back up its own primary. The latter is the most likely event to occur therefore it is essential to try and dampen down the magnitude of the PW. The reason for damping is the sheer fact that a reflected PW is still a PPW and provides no benefit to a TC engine whereas an NA engine relies on this PW to become reflected as a NPW due to the change in exhaust volume at the collector as this offers two benefits......................

Outlined Test Sequence:
1. Install engine into dyno cell and setup race ECU with data logging and exhaust monitoring instrumentation.
2. Map the stock engine/manifold/turbo to maximum power output with stock mechanical timing values.
3. Record all data logged information/exhaust monitoring instrumentation.
4. Leave inlet timing fixed and adjust exhaust cam timing ±2° and remap again back to step 2.
5. Once tested all different mechanical exhaust cam timing variations move onto next step.
6. Install tubular exhaust manifold and re-test from step 2.
7. Install tubular exhaust manifold with primaries 50% longer in length and re-test from step 2.
8. Install tubular exhaust manifold with primaries 50% shorter in length and re-test from step 2.
9. Make an exhaust manifold with primaries 50% larger in diameter and re test from step 2
10. Analyse all the data achieved and decide on what length/diameter to make and test next.

I Have some quick images:

sign me up for that please

I too would love to read more about your study, please copy me in on that.

Thanks, Richard

So would I, can I please be added to the list for circulation when the time comes, very interesting stuff

thanks

Wow this sounds really really good! Please keep us updated!
Thanks
Juergen

Now that would be interesting info indeed. Sadly november is still a long long time if you have to wait .

Regards,

Remco