Archer Fabrications
10+ Year Contributor
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- May 9, 2011
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Scottsdale,
Arizona
You've built such a manifold for a HX35 user? If so, what RPM were they seeing 30psi?
The reason people choose a 2G head vs. a 1G head is for the improvement in velocity. Up to a certain point the ports in a 1G head are unnecessarily large for the power level the user is looking to make...and an exhaust manifold is no different. You don't need primaries that large on a 54mm turbo being fed by a T3 flange with an ID of roughly 2.35" x 1.85".
I've seen it happen first-hand with the FP Race manifold...folks forget that "race" exists in the title for a reason, it's not for a 14B/16G car. A friend bolted one on his 16G-powered 1G in place of a ported 2G manifold and the car suddenly no longer got on the converter at the line, lost almost a whole second on the ET and was 3mph slower at the end of a pass as a result. Went back to the ported 2G manifold and it was a 12.4x @ 112mph car again.
Small turbos don't need big manifolds- it hurts more than it helps. Now if you were trying to do the opposite with a big T3 turbo like a Super 99, I could definitely see where the smaller runners could pose a problem due to the sheer volume of the exhaust energy...no denying that. In this case, the OP specifically noted he wanted a quick-spooling setup and I posted the HY35 on a cast manifold which is proven. Anything else adds a degree of uncertainty depending on how the manifold is built and what turbine a/r will be used.
My response was not specifically aimed at stock flange turbos or necessairly at the op. or any specific power level for that matter, Just a response to the general statement you made that large runner manifolds “murder spool” sure they may not have as much a benefit for a small turbo, and with a small turbo they are low rpm efficiency and Low flowing) but a runner size smaller then the head port is going to be a restriction period. maybe you dont see the effects of that restriction until you have a turbo worthy of out flowing it, but as a rule of thumb less back pressure = better response and power gains. What bastard is saying about large long runners basically killing exhaust pulse due to the larger volume? maybe in a super extreme senario like runners the length of a car, but not when we are talking about primaries less then a foot long. And even less then 1/4” of interior volume difference between the two. There is a point to which going to the extreme side of the data spectrum are invalidating to the argument.
Also, Thin wall runners radiate heat into the engine bay which is lost heat energy that could be otherwise transferred to the turbine. Thicker wall, similar to a cast manifold. Keep the exhaust gases hotter inside the runner, with less of that heat energy lost through radiation. This theory has been proven by speed factory and their world record hondas where they gained 500rpm Spool going from an .065 wall tube manifold to a sch40 pipe manifold of similar design, runner length and primary Diamiter.
And even if the runners are longer, the exhaust never goes cold. But again, if we move to extremes. An exhaust may get cold and loose pulse velocity after say 10 feet? But we arent talking about 10ft long manifold runners. That is just my 2 cents.
Justin, I understand what you are getting at though about small turbos. But when trying to max out ANY turbo, I’d think the less restriction the better the flow. And for the record, I’m not suggesting by any means that everyone with a 16g needs an upgraded manifold at all, but the theme seems to be above 500whp you could get more out of your setup with a larger runner, @bastarddsm good luck with your goal of 8’s, I’m looking forward to it, but how much easier would you get there with less back pressure are you logging backpressure?
Anyway I’m done my rant OP, hope you get the turbo you are looking for that beat suits your intended use of the car.
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