In planning out my turbo kit, I had planned from the get go to custom fabricate a set of one off stainless power logs. But I've been looking more into headers, how they help with power by scavenging, etc. Now I'm thinking about custom making some headers which would both point toward the flexplate side of the engine, with v-bands on the end of the collectors. So that I can do basically a secondary collector/crossover if you will, which would have the turbo flange on it, above the trans bellhousing. What do you guys think about this?

 

The first issue is that scavenging tends not to be particularly effective on this engine due to the oddball firing order and typical cam profile / overlap characteristics. IMO that is one of the big reasons headers in general dont make the same big power gains that they do on other platforms. So I certainly wouldn't expect some kind of massive gain with it. There was one RWD Australian car that built headers for actual scavenging gains on the 3800, but it was a real mess of pipes connecting primaries from opposite banks.

The second issue is that you'll have a hard time getting any concrete info on actual gains / what design works best / etc on max effort turbo setups as virtually no one does it. Most seem to get up to 600 ish whp on plogs and end up demodding for the typical 3800 / trans / FWD issues.

No doubt there is some power gain to be had by going with equal length longer runners, the hard part will be the packaging.

Not exactly what you're looking for, but similar for ideas off a record setting car that was proven to work well


The other thing to keep in mind is that while this will increase power if done right, it also hurts drivability. If you look at the trend with modern engine design to drastically reduce lag - primaries are short to nonexistant (sometimes ti the point of being cast right into the head they're so short), tube volume is kept way on the small side, and the turbo is mounted very close to the head. This sacrifices some peak hp, but keeps exhaust gas very very fast for quick spool.

On a drag car like the above, spool time doesnt really matter. Its going to leave off a loose converter and likely with a bit of spray to get it going. But driving around on the street is a different story (not that the car above would hook on street tires anyways).


IMO, rather than bog the build down with extra time and cost, I'd just slap some used PLOGs on there and get it up and running first. Itll still make more than enough power for you just starting off, and it's easy enough to swap out down the road if you want to keep tinkering later.

 

I don't really know if I want to go the used or even new plog route. Yes it would cut cost and time out of the overall build, but ontop of custom fabing the manifold/headers, as well as a fender exit, I planned on cerakoting the exhaust, to keep underhood temps down. So I'd rather fab the exhaust, and cerakote it all at once, and be done with it.

Like with the log manifold, I had header ideas floating around in my head. So I went and 3d modeled a set. They aren't exactly equal length, but like you said, scanvenging isn't all that effective on this engine, so whatever. But packaging is another thing you mentioned. This setup would theoretically be as far away from the heads as stock manifolds would. So radiator clearance should be fine. Thats one thing I've had an issue with in my cars. The shorter dog bones in my daily, and trans swap in the junker put the manifolds pretty close to the radiator fan shroud. I'm highly considering replacing the stock fans with aftermarket ones that attatch to the radiator, and are slimmer.

 

Are you going to be able to change plugs on that front head without pulling the exhaust?

Given how hardcore of a build you're shooting for, I'd try to make easy plug access a #1 priority as you'll be pulling them often, especially as you dial it in.

 

I did take that into consideration when designing these. I couldn't find a 3D model of a 3800 V6 head, so I substituted it with an LS3 head. It should be easy to access the plugs with a ratchet. I can also use a universal joint to make it easier. There is approximately 1.6 inches from the tip of the left spark plug to the middle exhaust primary.