Hi John, I am definitely interested as to how to make the engine quieter without restricting flow too much. Thanks!

I'm not sure how much interest there is, but if it's any help, I could post up some more info, carrying on from where I left off, detailing stepped primaries (I think merge collectors speak for themselves most likely) - and about the only other thing that might be of interest - since most racers now have to fit under a certain noise level, what can be done to drop the noise down, without affecting the exhaust scavenging (in short, generally any time you add mufflers, you add back pressure and as soon as that is present most of the power increase from exhaust scavenging go down the drain, there are ways to 'trick' the exhaust into behaving like it's an open pipe not too far past the collector, but it actually has mufflers further down and so the noise can be dropped under the required level. I didn't 'invent' any of this obviously, it's been worked out by people a hell of a lot smarter than me, but I do have some info I could share if anyone wants?

Heres a good link to have a browse at, it mentions peak velocity like jmac was talking about in an earlier post

4-2-1 header tech

Cheers, not sure how a setup like this would compare to a 4 into 1 with the same length primaries etc, I guess there would be less resistance to flow due to less bends, although would there be turbulence at the collecter and I am also guessing that if there was a scavenging effect in a 4 > 1 system then the effect would be weaker as it would draw on all pipes at once in comparison to only one at a time for a 4 > 2 > 1 ??

also another thing to think about is the initial angle of the exhaust coming out of the exhaust manifold. I have notice in both of the extractors that I have for A series, the inner 2 exh. pipes turn sharply straight at the manifold.

qik1000, if you do decide to get them custom made, see how much clearance you have to play with (also check if you plan on changing carbs, manifolds etc later on, check those clearances too) and steer towards making them as straight as possible when they come out of the head, or atleast a smoother bend then the headers I have seen so far...

Hope the ideas help mate.

Spend the time/money and make or buy a decent merge collector, those formed collectors are disgusting, they make a decent difference to power right across the rev range. Also with a merge collector you can run a smaller collector diameter with a megaphone and reversion cone. This has the upside of increasing velocity (venturi effect) which has a good effect on mid range torque with out losing topend. Really it comes down to how much time and money you want to spend. But even just having a decent merge collector will make a decent difference

There was an example (i think it was edlebrock) where the only thing they changed was the collector on a set of headers to a merged collector from a formed collector, no other changes to the header in terms of diameter or length (i can't remember exactly what it was some big yank v8 with about 530whp) and the thing picked up about 20-30 whp, a substantial amount anyway. So that would probably equate to about 3-5whp on an A12 I guess for not a lot more money.

u r more or less correct there, what u are talking about is also known as scavenging. Your design would work well as the firing order is 1342, so with your design the pulse from 1 draws the pulse from 3 in the first Y then the pulse from 4 will draw the pulse from 2 in the 2nd Y, the pulse from 1&3 then draws the pulse from 4&2 into the main pipe,
this is why V6 or V8 with a T intersection can run smooth without increased backpressure in one bank of cyls,
hope that makes sense.

Hi fellas, I am about to build a set of extractors for my rig as the old ones are really rusty and a new set of painted steel ones from the exhaust shop here cost $330!
I want to build these ones out of stainless. no more rust!

I was planning on building an equal length 4 > 2 > 1 as I am of the impression that they utilise the effect of the negative/low pressure created after each exhaust pulse passing through the pipes?

For those that arent familiar with this concept I drew a basic diagram of how I understand this effect to work, but If I am wrong then please correct me:




Red path is positive exhaust pressure pulse travelling down pipe.

Blue path is negative (or low) pressure created from the passing of the high pressure exhaust pulse.

Using this design the negative/low pressure pulse "pulls" the next pipe's positive pulse through the first Y collecter.

Then each pair of Y's collects again and the effect is repeated through the 3rd Y, thus 'pulling' through each of the first Y's.

Is this correct?
I was of the impression that this makes the Tri Y design more effecient.

maybe you can shed some light Jmac?

Not a fan of cobys at all. Atleast the ones for a series. Always fouled the idler arm, and never seemed to line up with anything.
Might be different now but I really don't want to have to deal witht them again, weather they're the D1 or D2 style ones.

Really good information here, keep it going.

That book is a great read, I have a copy myself aswell. Its covers most things on car preparation for street and track. I have read it and re-read it many times.

It has a whole chapter covering exhaust systems.

Quote:


Thats a killer book, Full of relitivly easy to absorbe information!?