exhaust manifolds question

[Adriano]

The more you increase the boost the higher the reversion, as the exhaust manifold pressure increases.

[WidebodyWoody]

EPIC FAIL!!!


Hey isn't that Rodger Cordia's "Special" Manifold rofl

[docile]

how does high boost cause reversion? I thought boost reduced reversion

Only in an optimised system can you keep EBP = IMP, but usually EBP > IMP.

Having the Wastegate (boost control) on the exhaust side exacerbates this pressure difference.

[TomVR4]

yeah i understand, but a supercharger would decrease reversion wouldn't it?

[redzone]

It is a quite well known fact that having the shortest runners possible is more important then equal length.

from my personal experience, and obviously that of the 80's F1 teams, thats a well known old wives tale

Lol, have you actually seen an old F1 Turbo Engine dyno plot ? It only starts to make some reasonable numbers at 7000rpm so of course its going to run a set of inertia tuned length exhaust manifold to help reduce lag (by increasing VE) and reversion due to the high-boost levels plus using inconel 625 helps offset the heat lost through the use of longer runners also, but I assume you knew that ?

ok, so would you consider 1.25" ID 400mm runners too long for a street 8v starion engine with a GT2871R? what is your definition of too long?

and what do you think of the american scene's usage of rear mounted turbo's on US domestic V8's?

[panda]

Many moons ago, like in the mid 90's, I crewed for an off-road race team that had long equal length exhaust runners to the turbo. Nearly every event the exhaust cracked somewhere from differing expansion rates in the runners. :( :(

[docile]

Redzone, there is a noticeable reduction in Turbine speed every doubling of exhaust manifold runner length. Things only become blurred more so because turbine efficiency is ~ 70% and therefore effect of runner length isn't as dramatic as it should be.

One thing that is constant is that stainless steel has a much lower thermal conductivity then mild steel and inconel 625 is even lower than 304.

I also wouldn't recommend 1.25" runners for a 38mm exhaust port, I know that volume decreases and velocity increases but you are dealing with intake air flow volume x 4.x trying to flow through a runner that is smaller in diameter than the intake port choke. Sure it'll work but you'll see a definite gain by going back to the normal 1.5" ID.

[redzone]

the manifold in question was HPC coated inside and out, and was the one i built for this car:



i suppose we've proved that HPC coatings work pretty well then?

1.25" ID was chosen as it was a close match for the exhaust ports at the head face.


also this one:



had a 1.5" ID manifold, not HPC coated, of slightly shorter length. power drops off because it was using a stock starion cam.

[sigmaproject]

I think this guy tried to replicate a stock manifold for a 4g54.

Failed miserably

[MR Bender]

any idea on how much that coating costs??
the manifold is done just need to coat it now!

[redzone]

HPC inside and out will probably cost you about $300 or less i'd say

[docile]

HPC coatings don't work as well as true ss304 or Inconel 625. You don't have to beleive me, call HPC up yourself and ask them. Even they are humble enough to state the real facts for you.

I'm not sure what cylinder head you've been using (maybe the 4G62) but the exhaust ports on a 4G63 sohc are 35mm in diameter so stepping down to 31mm id is significiant.

Sure it'll work, just like log manifolds still work and make power.

I'm not here for a pissing contest btw, just stating the real facts and trying to help others who do have the opportunity to design and build their manifolds, to think about what they use and how they design it more in line with decades of theory and data as its not such a "magic science" anymore.

:beer

[redzone]

i'm not really up for a pissing contest either, i'm the first to admit i dont know everything. but i have a habit of doing things people say wont work, and getting amazing results.

and i mean the way i've designed manifolds previously has obviously worked pretty damn well, what you're saying though (about shorter being more important than tuned length) is at odds with almost every bit of practical experience i've had with manifolds, and seeing how 6boost for example makes his, and knowing people that have used his manifolds and gotten quicker spool and more top end.

also my brother's ST185 GT-4 i built a 1.25" ID tuned length manifold for, after pulling a shorter length chinese stainless 1.5" ID one off that had a nasty angle into the collector, we gained about 200rpm earlier spool and about 500 rpm of useable rev range up in the top end with EVERYTHING else being the same.


have you tried any cars back to back with different types of manifolds on them? any pics aswell? would be good to see. and what is your definition of too long a manifold runner on a 2.0 4 cyl?

[docile]

I agree collector angle is paramount along with exhaust manifold (i.e length) volume according to whatever maximises cylinder head + cam timing and Turbine effeciency the most. I know a longer manifold can make more top end (in a non-optimal setup) but there is still a basic trade off in spool if you build two almost indentical manifolds, just of different lengths. The difference is on average 500rpm depending on which material you use.

You can't really think of it as optimal lengths, more as volume. There is a trade off and for each setup its different. For an oem setup where your only increasing power output by 25-50% a shorter manifold is usually fine but when you start increasing power by 150+% then you really need to make a few manifolds before you find the best compromise.