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Flow and performance of Log Style Manifold
#1

I did some searching and couldn't find anything. Does anyone have any data/experience on the performance and flow of a log style manifold versus ported E6/Gnari versus tubular, etc.? I will be swapping over to a stage 3 head with Bo 2.1 cam in the spring and I'm thinking of changing my current manifold and turbo setup; currently running a ported gnari manifold with a BB GT35 turbo.
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#2

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The E6 & Gnari cast manifolds essentially ARE log manifolds, 88TB.  Tubular (long-tube) headers probably flow a little better and might offer slightly more performance ~ BUT.....they're arguably more prone to cracking (especially in DD street use). Bob Myers has gone 9.62 with his stick-shifted Capri, using a center-mount Bob's log (NLA, but virtually the same as Chip's log that's currently available). OTOH, Marty Buth (who holds a few NHRA Stock-Class records) has tried several different tubular headers and likes the old (NLA) ATR version best. Soooo.......YMMV! <shrug>
Placerville, California
(former)  '78 2.3T Courier w/blow-thru Autolite 2bbl carb ~ (current)  '87 2.3T Ranger w/PiMP’d EFI
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#3

How much power are you looking to put down or aiming towards.
88XR4TI:T67/T4 Turbo,85lb inj,PIMPV1.3,LS2-Coils,255LPH,3" exh, Stg4 Head, BoPort Header, Bob's Inline, Cus.body kit, 16" Rims, Supra 3.73 LSD, Rasp.PI3 dash
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#4

I feel there is a point the log header starts to hurt performance, but it’s also likely out there further than what the cam you mentioned would support.

As Ray mentioned, I’ve been 9.62@140 mph on an old Bob center Mount log header (I’ve been using it since 2010). Car weighed 2805 on calibrated racetrack scales.

I will say, I keep feeling the log is a bit of restriction, but from fall to winter only swapped turbine on my turbo and picked up an effective 2 mph so what do I know. What I know for sure is I shift a lot lower RPM than a lot of guys do (6600 rpm) so something bottlenecks my deal.

Unless you somehow end up flowing a lot more than I think that cam can support, you aren’t going to see much with a different header… at least not enough to justify the added complexity.
84 Capri RS Turbo
1/8th 6.29@110, 1/4 - 9.87@137
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#5

Thank you for the replies everyone; this is great information. 325 to 350 at the tire is the goal. The final configuration would be the stage 3 head, 2.1 cam, gutted/ported upper (currently on car), and ported lower (currently on car). I have the ported gnari and GT35 turbo as mentioned but I'm playing around with different ideas. I do want to eventually road race the car. (Already have a ton of suspension and brake work done).

I think I will probably keep the gnari manifold and go with a slightly smaller T3/T4 turbo. The GT35 is great; I just would prefer something that spools quicker.
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#6

Across all applications the performance of tubular manifolds verses a decent log style are fairly well documented and similar.

If you hold boost constant, there is typically a 5-10% benefit to a proper tubular manifold.    If your actual goal is something like " I want optimum power at a given boost level" or "I want the most pump gas power I can make,"  then a tubular manifold "may" be worth the expense and packaging to you.   

If your goals are more related to how fast you can go on a track with a good fuel and a given turbo, then it will not matter measurably on the type of combo you are buidling.
86 Mazda RX7, 2.3 swap, t5, MS3 sequential, BW EFR 6758
"If you can't dazzle them with knowledge, baffle them with bull sh*t"
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