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Discussion Starter #1
I heard that on a cast manifold the turbo will spool faster than on a tubular.. is that true.?
Has any one done any testing to see if this is actually true..?
Im thinking of going with the cast just b/c of this rumor that I heard, I want to spool the fastest that I can. So I want to make sure this is true.
 
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Discussion Starter #3
I heard the same thing, but haven't seen anyone able to prove it. It makes sense to me because the manifold will have more pressure because the air has a smaller area to fill up. In my head I make the comparison to a larger exhaust housing on the turbo. THe larger the AR the more lag, but larger top end you will have. Can anyone shed some light on the subject. I also heard that under hood temperatures are drastically lower, but again a rumor.
 
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Discussion Starter #4 (Edited)
I have no problem believing the cast manifold would give you slightly better spool up than the tubular manifolds out there. More volume requires more exhaust energy from higher rpm to increase the pressure in the turbine to spin the turbo. I'd have to say it's give and take though, what you'd gain on the bottom end is probably lost in top end power, at high boost once you have a lot of exhaust energy, I'm sure the cast manifold is a bit of a restriction. At what point is it too much a restriction?

I did a lot of searching to see what people's experience is with this, and I saw only one somewhat definitive post regarding this:
IME, the cast manifold spools 200-300RPM better than the header.

With the same turbo.

Andi

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Andi B.
'98 Quicksilver Supra Turbo, Sold
'04 Millennium Yellow Z06
Boostaholic.com
OneLapSupra.com
That was posted in this thread

IME = in my experience, meaning I believe Andi has tried this, as he was having problems with different manifolds. Hopefully he'll jump in here.

FWIW, relating experience to other turbo vehicles - Turbobuicks have several options of header to go with. For the longest time people would go with Hooker headers, which had a design with a lot more volume, which to the eye, looked like it would flow a lot better. Their stock manifolds are decent, tubular design, but are prone to cracking. It was quickly learned that the Hooker headers were a far inferior design, and introduced a TON of lag. Now, they might have performed better at a higher boost level, or with a more modified car, but for 95% of the cars out there using those headers, they just did NOT work.

If a shop had the psychotic willingness to test all of the combinations out there, I'm betting you'd find out that using the SP budget or cast setup would work well up to 400-500rwhp, then started to become a restriction to top end hp, at which point you'd benefit going to a tubular design (HKS/BL/SP/Greddy/RPS).
 

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My understanding was that properly designed tubular should be able to spool as well as a cast shorty manifold. Keep in mind that our motor is creating exhaust gas to spin the turbo way before it actually is at a point where it "spools" up. It's not like the motor isn't already pushing exhaust gas out before you gun it. This isn't like having too big piping on the intercooler side where you suddenly have to fill air into the intake piping/ic. I'm may be bastardizing what I've read before on this but I do know that i've seen no SOLID proof that the tubular is laggier enough to even notice.
 
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Discussion Starter #6
I hear ya Silvino - it would probably take a pretty detailed dyno run, or high resolution datalog to see the difference.

Seat of the pants difference? Doubtful, but if you have a sensitive backside ;)
 
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Discussion Starter #7
Im suprise none of the shops have done a test by just swaping manifolds to see if there is any diff. up to the 500rwhp. which by the way is what Im aim at tops...
 
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Discussion Starter #8
Well the cast manifold locates the turbo different than the rest of the kits out there, so the downpipes wouldn't be interchangeable. It would also require a different wastegate setup....so basically it'd require a complete turbo kit removal & reinstallation - but you could do it using the same turbo obviously.
 
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