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Basic turbo manifold design question

546 Views 18 Replies 7 Participants Last post by  Judas
Just a short question about turbo manifolds, im considering turboing my AW11 and noticed most but not all turbo manifolds are very short and all the runners(if thats the proper term) merge as quickly as possible into the turbo. Im used to N/A exhaust headers and I know they are tuned to lengths with longer runners so that each time a pistons exhaust valves open they merge with another pulse from the other cyclinders to get a smooth flow.

Does this not apply to turbos since the gasses are spooling the turbo, thats what im getting out of it but dont know im just trying to confirm.
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Also Im trying to modify a manifold(possibly from a 1.8t VW/Audi) to work and to my understanding the turbo flange must face downwards, possibly sideways to fit withou hitting the firewall/engine lid, correct?
the idea is to keep the heat in the exhaust gasses which does effect power.
But... saying that... on a street car putting the turbo in say, the trunk, and just using a stock manifold, and running the intake piping from there (aluminum pipe would allow you to not have to use an intercooler if the boost is not too high) you will get the same power. But with slight increase in lag. But lag is relative. Once you get driving the car you will not even notice it. Plus while keeping the turbo in the back the turbo itself will stay cooler thus not really needing a intercooler. Plus oil last longer, seals last longer, the engine lasts longer.
Plus while keeping the turbo in the back the turbo itself will stay cooler thus not really needing a intercooler. Plus oil last longer, seals last longer, the engine lasts longer.
Does turbine temperature really affect the heat to the compressor side that much? Shouldn't the watercooled intermediate section largely prevent this?
Ha thanks bills, I just say your 20 valve turbo manifold on ebay, looks awsome! Im goign to consider making my own custom set up.

Ok, so im new to this but... if... if.. [yes, one of you is going to shoot me down on this one saying its impossible or ineffeicent] the 4 runners go to a flange to a turbo... could I use a commonly available turbo manifold, that doesnt work due to the turbo not having enough room, and connect one larger pipe in which all 4 runners led into from the flange to a new location (above transaxle/lower/ or wherever) then on to a new flange to a turbo in a location that it would fit.... could that work?? It would make things alot easier for the tight AW11 bay. Ive never seen it so im doubting that it would work. It seems rather silly, almost like putting a turbo after the downpipe.
Okay... this is where the MK1 guys are really good at thinking outside the Import Box.
You can do anything you want. You may not get maximum horsepower, or the killer dyno sheet. But pretty much anything will work. some longer than others.
What is cool about hot rodding is that there are a gazillion ways to do things, not all work, not all work great but they work, and not all get bazzoka dynos. But everything has been tried.
Indycars mount the turbo over the trans. though they have a loose pipe joints to allow flexing and expansions.
Manufactures build the manifolds like they do to last 500,000 miles and to fit a certain chassis, and to keep things cheap. If Toyota truely designed their manifold for performance then the car would have been 10x what they charged for it :)

Play with your ideas. many will poo-poo... but you will learn a ton in trying.
Yes i think wierd and thanks for your words of motivation, but do you personally Mr strong, think that merging the exhaust into a pipe then going to a flange and turbo would work decently or as you elegantly put it "poo-poo"?
Look at this...
Turbo mounted in the back of a Camaro, engine in the front
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I'll be doing this soon to my 1998 BMW 318ti 1.9litre N/A.
All I want is 200hp. That should be plenty fine for a car that weighs in at 2200 pounds
I have never seen something like that. Interesting.
Then I take it that it can work. Interesting... To the junkyard!

But dont camaros have plenty of room under the hood for a turbo that size, and that would be nasty lag with such a long intake system. I would think *shrug*.
That is very interesting.
Concept here... use stock 4age heades and weld a flange at the end before the downpie for turbo... simple. The turbo would get decent cooling that way too :p.

The stock headers could take it i presume. And I wouldnt have tow orry about fitment obviously. I think there is enough room down there for a small k04/k03 turbo.
there's also a kit for chevy silverados, the turbo mounts up in the rear almost where the stock location is. they say its to "keep the engine bay looking stock"
There was a thread about these turbo kits on here a few years ago, and again last year I think. Maybe I keep bringing it up :)
Read the testimonials. They say it is no different than any other turbo when it comes to lag. But then remember that you are keeping the compression high, so the compression helps to spool the turbo faster.
We will find out. I'll probably put my old gen 1 CT26 under the rear of the BMW where the big muffler sits.I have a 5 psi wastegate. that should be plenty.
Interesting I read their site and they use stock headers etc etc. They even keep the cat in front of the turbo (seems dumb to me) I think ill consider trunk mounting the turbo.
The remote-turbo concept is viable, but not what you want if you're going for peak performance. Especially if you're driving a camaro or truck with the turbo back by the muffler, the exhaust gas heat will be waaay down and the density will be pretty much uniform...where turbine wheels like the pressure spikes that they get from being very close to exhaust valves, as far as spool time goes. Plus using all that piping will cause a pressure drop, how much exactly you can't really guess at.

[/poo poo]

Using a nice ball-bearing turbo can help alleviate the problem, and low turbo temp[s would make it easy on the bearings. Like Bill said. underhood temps go down, intercooling may not be needed, stock headers can be used. Since response is obviously not the goal of this setup, a lot more corners can be cut.

And it still surprises me how you see so many people unwilling to consider setups like this because they're not maximum-performance, when the setups they are using aren't even max-performance setups anyways.
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Hmm, what about using an NA header and putting a turbo flange on that? I know its a good idea to have it as close as possible, but can you use the tuned part of a header to help something? Maybe less power overall, but more flat curve? A car has 420hp, but at 5600rpm and the max between 2000-3000 is like 210hp thats weak, Id much rather prefer 300 over the whole spectrum.
FyreDaug that is what I suggested on post #13.

Im gunna have to go look under the car, I really dont think the pressure drop or responese would be any where near as bad when putting the turbo feet back into the trunk vs how many feet back into the trunk of a camaro.
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