Log Type headers on a BBC

[calereeves]

I'm sorry for this not being a buick question, but this is the only turbo site I could find where there were fellow domestic muscle owners instead of ricers!!

Anyway, I'm going to be building a 468 to go in my 78 Trans Am. I was wanting to go either twin turbo, big single, or supercharged. If I go super, it will be a centrifugal, just from a hood clearance standpoint.

My question is this:

If I built my own "log-type" headers that fit within the space confines of the 2nd gen T/A, would they provide sufficient exhaust pressure to spin up a set of turbos? The engine will have plenty of headwork on aftermarket heads, a hydraulic roller valvetrain, forged internals, and about a 9.5 or 10:1 CR.

For the log types, I was planning on 2" "primaries" running into a 3 or 4" collector, then bolting a turbo right onto the end of the collector.

Would these work, or would I have to spend an exorbitant(sp?) amount having headers fabricated? I found a site that shows how to make a nice set of headers, but that is too much time and effort for me.

Thanks,
Cale Reeves

 

[Black Box]

I am no thermodynamics engineer, but I think the closer to the exhaust ports the turbo is, the more efficiently it will work. Standard "full length" BBC headers probably wouldn't work well. As for the primary size....don't know too much about that. Most BBC headers for performance apps seem to run around 2" to 2 1/8", don't know if that's too big to kill the spool up of the turbo. Small pipe diameters maintain the exhaust gas velocity (to a certain point).

Try asking Jack Cotton www.cottonsperformance.com
or the guys at PTE www.precisionte.com

They could give much more accurate advice than I could.

Steve

 

[KendallF]

Someone will likely bump this post over to the lounge shortly...this is Buick tech only. I'll still give you my opinion, though.

I think the log intake will work fine, especially if you're doing a single. The stock GN headers are essentially a shorty header on the driver's side, and a log on the passenger side with the crossover from the driver's side feeding in the rear of it and the turbo at the front. I think you might consider a log diameter slightly bigger than 2"...think collector size here but err on the small size. Maybe 2.5"?

I have a friend who does import turbo conversions and he has done many very effective simple log-style manifolds using Schedule 10 (I think?) elbows and Ts. Durable and cheap. He's converted at least one of those to a nice equal length header and picked up boost response and HP, but they still work.

 

[REDS HOT AIR]

i would think it would work just fine

if going twins you may want to stay with a 2 1/2 to 2 3/4 log and weld the primaries into the log in the direction the exaust will flow.

if going single turbo then id say stick with then sizes and y the two together at the turbo flange.

as far as primaries you cant go smaller than your port but dont go any bigger than nesasary

 

[calereeves]

sorry about posting it here, I wasn't sure where to put it since it wasn't a Buick tech question, but I wasn't sure where to go...sorry.

Thats what I figured, about the header definitely giving better boost and hp, but the log would be so much simpler to fabricate myself and much cheaper. I think I'll try and get it running with the log types, then start making my normal headers and once they are made swap them in and do dome dyno testing to see what kind of gains there are and write up an article about it.

Thanks Guys!!
-Cale