So, I want a Chinese typhoon spooli Boi on my 3.9 v6 powered rx8.
I want to build a log manifold because space is tight beside the engine and I can fit a log manifold on each side pointing forward.
My thought was to use 1.5" I.D tubing to merge into a 2" tube that then feeds the turbski.
Is that too small for 400 hp?
The stock exhaust is smaller than that at its smallest ID. The headers I built for NA are 1.625" and they seem sufficient.
It will have a 2.5" open exhaust out the back of the car post turbo.
Whatchyall think?
You'll probably want a bigger exhaust/downpipe for that power level. I'd want at least 3".
Can't comment on the manifold tubing size, but sometimes the correct answer is "what fits" :) The cross section of your turbine inlet may be smaller than a 2.0" pipe. I'm pretty sure our manifolds are smaller than that and they'll support that power level.
Keith Tanner said:
You'll probably want a bigger exhaust/downpipe for that power level. I'd want at least 3".
Can't comment on the manifold tubing size, but sometimes the correct answer is "what fits" :) The cross section of your turbine inlet may be smaller than a 2.0" pipe. I'm pretty sure our manifolds are smaller than that and they'll support that power level.
So, are you saying that the pipe / tubing size to the turbo is less important than post turbski?
I can do 3" post turbo. That's the easy part. I just can't fit much more than 1.5" log to the turbo.
So, let me ask another question.... what happens when your pre turbo manifold is too small of diameter? Poor spooling? Lower hp? What?
Thank you for your responses!
like dis. The two elbows back to back will be cut and welded together and attach to the turbski.
You want as little restriction as possible post-turbo. It's all about the pressure differential.
I think you'll be okay with that size, especially if it's what fits :) Each of those manifolds is only feeding half of the turbo. Too small would get you lots of backpressure, which would start giving you trouble with detonation. I don't actually know what it would do for spool, I'm a bit weak on that.
Adding comment so I can follow along.
Nothing to add, unfortunately...
Post turbo you want as little restriction as possible.
Pre turbo, you've got a big restriction which is the turbo itself. Any major restrictions pre-turbo are limiting the energy that the turbo can use, so if you really choke it down, you're going to hurt your spool and your overall efficiency. That said, I'm not sure what kind of numbers are considered acceptable, and I know if you go too big, that hurts too. My limited experience building inappropriately turbocharged cars and eventually upgrading the manifold suggests that performance is still in the right ballpark with a non-optimal manifold, but fuel economy can really take a hit.
On my turbo M42 E30 specifically which was about a 230 hp 1.8 liter, I used a log manifold and switched to an equal length tubular manifold. I gained about 3 mpg on the highway which shocked me. I didn't have enough data to compare on-track economy. Boost threshold was a few hundred rpm better, but spool rate was similar enough that my butt couldn't tell a difference. I'm in the process of rebuilding that car, and since the tubular manifold eventually cracked, it's going to be replaced - with a log manifold, but with small runners to a big log rather than having the runners and log all the same size. The tubular manifold was not worth the effort, at least for that one case with that particular engine and turbo combination. Getting rid of an oversized intercooler and optimizing charge pipe routing for less volume made more difference to spool than the manifold did.
The tubular manifold did sound much nicer than the log manifold.
The above photo of the weld el's is fine. Post turbo stuff should never be less than 3"
Lots of backpressure leads to the cylinders not emptying all the way, which limits power and hurts spool. You can also get valve float on the exhaust valves.
I agree the weld-els should be fine, though.
First benefit of log is thick-ass tubing, so as to not be a fool and try to hold up a turbo with thin header tubing that will immediately break. Second benefit of log is simplicity. Turbos make headers generally pointless. Your small tubing size will be great. One of the greatest sins of turbo kit making is using too big a tubing diameter pre-turbo. You need smaller tubing to spool that thing with a vortex screaming "squeeze me out of here . . ."
Ugh, that was so Hawk Tuah. Sorry.
