Longlife Exh Quote

[Jay]

@Andy

I'm glad your 'friend' and your own engineering back ground are proving the point, and thank you for taking the time to research your advice I used to teach engineering but dont profess to know all!

With regard primary tubes I agree in principle just not to sure how the restiction of the turbo has on the pull of the pulses in the primarys, exhaust port, combustion chamber or does the turbo when spinning aid this function??

I'm going for a PeterG manifold (sames as Zlobo) for the above reason!!

As said before don't believe all you read on the net etc, but there are people on here with the background and proven knowlledge to rely on their experience and advice! nice one Andy-Casey lets see what else you come up with

Re Longlife, theres a brance by Bristol, I think Ians the manager hes a Audi fan and has done these S2 systems before with no bulls**t!! quoted me £600 2 years ago and wanted the car for 6 hours to make sure it didnt touch.

Finally having seen them in the flesh I would say the 034 product from Corey is far better quailty/design with fewer welds, better bends and 'V' band joints... just my 2p worth

Jay

[Keeper of The Kitten]

The thing to remember is, when people refer to wanting "backpressure" they actually want scavenging - and that's a vacuum pulse in the exhaust that coincides with the opening of one cylinder's exhaust valves, to draw the gases out more effectively and with some overlap, to aid the intake of new air/fuel mixture.

This can only be tuned to occur during part of the rev range using pipe lengths, diameters, and to a certain degree by introducing restrictions to the exhaust flow - and really is applicable only in non-boosted situations - ie N/A engines or turbo motors that are off-boost.

Given that the vacuum will struggle to pass the exhaust turbine when off-boost, and given that when the engine is on-boost, the EM will be constantly pressurised (or at least, almost constantly pressurised), I doubt there is any advantage in restricting the exhaust system of a turbo car. The entire point is to get the engine working in the rev range where it is on-boost as much as possible.

I've spoken to the former F1 engine builder here at work, and he says pretty much the same thing - turbo motors need to get rid of the gases as quickly as possible, to speed up spool-time (though that is only a small gain) and to aid in generating boost more efficiently (that's a bigger gain). Also, you don't want to back-up extra heat in the exhaust system beyond what is sufficient to make the turbo work. Any restriction after the exhaust turbine is also going to create a corresponding restriction to the boost potential on the intake side.

__MDC__

[Rusty]

@Andy

I'm glad your 'friend' and your own engineering back ground are proving the point, and thank you for taking the time to research your advice I used to teach engineering but dont profess to know all!

No worries, he is actually a friend and not me! I do mechanical design for micro-electronic devices but love dabling in tuning theory as it directly affects my choices when spending my cash. Spending wisely can become a bit of a hobby when on a budget and trying to restore the car too. He's used contacts in the company he works for to answer my arguements and address the content of this thread and I am happy to post my findings.

Cheers K-o-t-K too, I did think about scavenging effects off boost but decided that they were negligable. I think we're in agreement there.

Initial thoughts into the exhaust diameter (over and above a Reynolds Number arguement) centre around the belief that the momentum of the exiting gas would create a suction effect in the exhaust between pulses and therefore help to effectively 'drag' the next exhaust pulse through the system. If the pipe is too large then this effect can be lost due to slow exhaust gas speed and subsequent pressure equalisation with atmosphere.

More thought to be done on this to understand Marco's numbers of 65mm (2.5"/2.75") for the K24 and up to 3.5" for 500+bhp.

T2Andy, hope you don't mind us slightly hijacking your thread here! It is on-topic afterall and hopefully has given you the answer and supporting arguement to your original question! Basically, the less restriction the better, 2.75"/65mm on a K24, 3" for RS2 / GT3071 etc. Bigger if you're chasing Doug / MarkH etc!

[Markarina]

Their have been a number of comments about using back pressure to create a vacuum at the exhaust port at the time when the exhaust valve opens, unfortunately this is only of benefit if the length of pipe from each exhaust port to the end of the exhaust is very near identical.

If you look at an F1 engine the complicated twisting exhaust shape is partly to fit in the space available but also to ensure that the pipes are the same length. In the past I have written input manifold control software that adjusted the length of the input manifold (trumpets) according to RPM and throttle position in order to produce the necessary standing waves.

[Rusty]

Their have been a number of comments about using back pressure to create a vacuum at the exhaust port at the time when the exhaust valve opens, unfortunately this is only of benefit if the length of pipe from each exhaust port to the end of the exhaust is very near identical.

I also have it on good authourity that, in order to achieve the best exhaust reinforcement waves in a road car <6k rpm, the exhaust manifold would need to have primary pipes in the region of 1m long! As this is not possible, manufacturers group the ports together to try and use the gas exiting the exhaust from one cylinder to 'drag' the gas from the other down the exhaust, hence a 4-2-1 manifold on 4 cylinder cars, I am sure that this also causes reinforcement waves but for 2 cylinders, not 1.

How does the inlet / TBs change length? Are there multiple routes as with modern cars using a flap or is it nice and technical?

[Keeper of The Kitten]

If you look at an F1 engine the complicated twisting exhaust shape is partly to fit in the space available but also to ensure that the pipes are the same length.

I'd say it has everything to do with getting the same length primary pipes into the available space, and nowt whatsoever to do with the packaging in itself! Some sacrifice would be made for packaging reasons because it is sometimes more important to keep everything hugged close to the rest of the engine for aero reasons (keeping the bodywork as small as possible).

Interesting to read about your variable inlet algorithms, I got involved with F3 shortly after variable inlets and exhausts were banned (sadly) ...but I think they were more likely to be mechanically or pneumatically actuated as the ECU software was a little less sophisticated at the time. I think the MuGen engines were running variable length inlets at least, and possibly Speiss Opel too.

__MDC__

[Keeper of The Kitten]

@ Andy - you can have a telescopic section on the trumpets, that was the method for F3 AFAIK - as long as the whole intake (from the airbox to the cylinder head flange) fitted within a box 0.5m x 0.5m x 1.0m the scrutineers would be happy.

In the static condition it would have the runners at their greatest length (shortening for higher revs) so the unit would be at it's largest possible size when the scrutineers measured it.

__MDC__

[Jay]

I think the new R1 and R6 have varible length trumpets done by hindging the tops to the trumpets and is ecu controlled, but these have just 2 lengths.

Lots of road cars from Pugs to BM's have varible length inlet manfolds, just of 2 lengths agian normally done with vacuum valves opening little valves and redirecting the air flow.

This again has more use on NA cars.

Jay

[Rusty]

I think the new R1 and R6 have varible length trumpets done by hindging the tops to the trumpets and is ecu controlled, but these have just 2 lengths.

Lots of road cars from Pugs to BM's have varible length inlet manfolds, just of 2 lengths agian normally done with vacuum valves opening little valves and redirecting the air flow.

This again has more use on NA cars.

Jay

The S2 has just one length inlet... phooking long as you like!

[Jay]

Not on mine:mischeif:

Jay

[Al Wyn]

Beans and spill them Jay (if its not a secret :mischeif: )

[Corey]

It is

[Al Wyn]

I will find out using my secret contact

[Desmonds Dad]

why not ask Mr Milltek for some advice?

[Markarina]

Interesting to read about your variable inlet algorithms, I got involved with F3 shortly after variable inlets and exhausts were banned (sadly) ...but I think they were more likely to be mechanically or pneumatically actuated as the ECU software was a little less sophisticated at the time. I think the MuGen engines were running variable length inlets at least, and possibly Speiss Opel too.

__MDC__

It was back around 1998 when I did the trumpet software, it was for TWR Arrows F1, I still miss the buzz from writing software one week and it racing the next week, or the extreme case of making a change and less than 24 hours later the software being raced with no formal testing !!!