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Engine Specific Info and Questions => IDI Engine => Topic started by: carrizog60 on February 28, 2007, 12:29:31 pm
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hello
i have one question that i would like to be answered by using some technical info,not just a "because i think"...
in a turbocharged engine what is the best option for maximum HP?regard that no noise or legal issues are in the line,just max hp in sight
-no exhaust at all?(i see dragster use that)
-exhaust with the same diameter of the turbo manifold?
-exhaust with smaller diameter than turbo manifold?(to create some back pressure)
and what about not just max HP but also low and midrange power?
any differences?
please give me your thoughts and i would appreciate that it was complemented with some technical backup 8)
thank you 8)
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Alex, "What is a 6" pipe through the hood?"
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I properly fitted downpipe with a transition right off the turbine with the small end being the same size as the turbine outlet, than transitioning 1" or more from that diameter. :twisted:
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so on turbos the bigger the better?
doesent any backpressure is needed?
and why is that?
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you don't want back pressure on a turbo charged car because for one it is completely unecessary because you want backpressure at the manifold, at the head and the actual motor, have a turbo blocking up the ehxaust supplies more than enough back pressure. so the bigger the exhaust the faster the spool the faster you get moving. the other thing is also that diesel cam shafts have no over lap, so even on na diesels the bigger the better.
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Alex, "What is a 6" pipe through the hood? :D I can't put a big enough smiley face. That is just mint! LMAO
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didnt understand that 6" post...
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Other than the obvious overtones, I'm assuming he meant a short upturned exhaust straight up through the hood like some people do. Zero backpressure post-turbo, short run of large diameter pipe.
I've got a shot of a Mk4 Jetta drag car with the exhaust pointing right up by the windshield... Pretty wild. I doubt you'd want to run that on the street, but I believe there are a few people that are running "straight pipes" under the car without mufflers or resonators.
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but dont we need some king of backpressure for the best results?
and what is the size of stock 1.6 td exhaust?
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Just as Trev0bor said...
"you don't want back pressure on a turbo charged car because for one it is completely unecessary because you want backpressure at the manifold, at the head and the actual motor, have a turbo blocking up the ehxaust supplies more than enough back pressure"
So...in effect, the turbo supplies the backpressure needed to prevent reversion, etc. After the turbo, the exhaust can be as free as possible.
what is the size of stock 1.6 td exhaust?
On my mk1 TD, the exhaust was probably 1.75" or so at the downpipe. Probably some metric size. Now I've got a 2.5" downpipe and exhaust from the turbo back. Fits fine and isn't loud. I'm running a Giles pump and 20 psi and I can tell you that the thing runs great.
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but dont we need some king of backpressure for the best results?
yes. backpressure is provided by the turbo.
and what is the size of stock 1.6 td exhaust?
IIRC its around 1.5" but not exactly 1.5" as i think it was spec'd in metric.
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This is what a 6" pipe through the hood is.
(http://webpages.charter.net/sidneyt/Pictures/WildExhaust.JPG)
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that is a very inspiring image!!! lmao!
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LOL :lol:
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:lol:
new giles monster pump? :lol:
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Nope, just PhotoShop. Sorry there is no "complemented with some technical backup" with that picture that carrizog60 wanted. I just took an exhaust off of a Pro-Stock Tractor at a NTPA Tractor Pull and pasted it on my hood.
I do have what I have been told is real technical data though. I have heard that with diesel pickup trucks, i.e. Chevy Duramax Diesel, Dodge Cummins Diesel, and Ford PowerStroke Diesel, that when you straight pipe these trucks, you gain about 25 hp. This is gained, as others have said here in this post, by allowing the turbo to spin more freely which in turn pumps more air in the engine for more power. So, I would imagine that straight piping a VW TD that you would gain some horsepower. Stock, these trucks run about 250 hp, 25 hp to that would adding about 1/10th more hp to it. So, adding 1/10th to a VW TD would be about 7 hp. This is a rough estimation tough, but still some technical data and there are many other variables that could make this estimation total inacturate when trying to compare it to a VW TD.
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I would say you could easily gain ponies just from dumpin the factory exhaust and runnin some larger pipe. I personaly think the turbo is more than enough of a silencer so straight pipe here i come.
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You can easily gain 10 whp and 20ft lbs of torque with a vw diesel engine from upgrading the downpipe, the power figures however dirrectly relate to your current state of tune (read: fuel).
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I read this thread with interest as I am trying to decide what size exhaust to run on my turbobus conversion. I was more or less down to 2.25" or 2.5". I went to a roundy-round shop today and they had a good selection of 2.25" mandrel bent pipe so I went with that. My gut feeling is that 2.25" is plenty for a 1.6TD, especially since the exit from the turbo is barely over 2" diameter, and the 2.25" is going to be much easier to fit than the 2.5". If I am wrong, well... I suppose I may lose a couple of hp but I think I can live with it.
Now I have to pick a muffler - straight pipe is not an option for me, I need it Q U I E T but I think I can still get plenty of flow with a low-restriction, big bore muffler. Is there any difference in mufflers for gas vs. diesel applications?
-Dave
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The turbine outlet size has NOTHING to do with pipe sizing for a turbo diesel engine, mass flow does and remember that the exhaust gas is still EXPANDING after the turbine housing.
As for mufflers get a muffler you can see straight through, kind of like a glasspack.
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Dave,
Now come on, the turbine outlet size has *something* to do with pipe sizing. :) I broke out the vernier caliper and the turbine outlet size on the KKK K24 turbo is exactly 2.0" in diameter. Not to mention that some of that diameter is displaced by the turbine itself so it is effectively less.
Yes I know that the exhaust gas is still expanding and that I *might* lose a couple of peak hp by using the smaller pipe but like I said, I'm okay with that. I do not have a lot of space behind (well, in front in my application) of the turbine outlet which also factored into my decision.
When I think about the factory pipe which is what, 1-7/8" and crimped like mad at the turbine outlet for firewall clearance, going to 2-1/4" with mandrel bends ought to get me the vast majority of gains that are possible from a larger exhaust, wouldn't you agree?
-Dave
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No actually the turbine outlet really doesn't have anything to do with the pipe sizing, if that was true the stock 1.9tdi should have a 1.5" downpipe... 2.25" mandrel bent will be fine for most applications still, you'll be fine.