3" Downpipe has arrived - warning Shiny!!
- Thread starter GPF
- Start date
ORIGINAL: Diver944
Are you sure that blue tape on the turbo is heat resistant enough []
[
][][]Apparently the blue tape will be fine as long as I don't start the engine.....
The turbo and crossover are actually back on now following a few more tweaks. Hopefully everything else will go back on easier than those did!!
TTM
Well-known member
Oh yes I know that all too well. My wallet does too.
Yes, sadly the cross pipe is double-skinned. When the inner skin collapses it will have shape a bit like an "8" - Now that I think about it I should have dropped some object in it to see how far it went to make sure it hadn't collapsed.
When it's collapsed the loss of power is very significant and if your engine was working fine before then your cross pipe should be fine, but maybe you should still try this test for the sake of it.
Missed that.
Personally, I can't really see it - but then I'm no expert!
I know Lindsey Racing, and probably others, will sell you up to a full 5" exhaust and claim it's better but I would prefer to believe specialists like Hayward & Scott who seem to provide a well made, well thought out design rather than say bigger is always better - but then I suppose you always like to think that you bought the right thing....[8|]
I know there is a school of thought that says the turbo itself produces all the back pressure an engine needs and that the best exhaust after the turbo would be no exhaust at all. I presume this is where the simplistic "progressively bigger to minimise (additional) back pressure" concept comes from - but I wonder if that is just a low tech alternative to designing the exhaust to flow properly in the first place?
I do know that getting the 3" H&S exhaust in and up to the 3" downpipe is tight enough! [
]Maybe there is a certain tunability to turbo exhaust pipes as with N/A rather than just bigger is better. Essentially the best exhaust would be a straight dump to vacuum.We dont have a vacuum we have an atmospheric dump. So it depends wether an appropriately sized and shaped exhaust system can create better conditions at the turbine outlet than just dumping to atmosphere which is essentially what masssive exhaust would achieve.
But maybe you can design an exhaust which at peak engine power output creates some dynamic effects which give better conditions at the turbine outlet at that mass flow rate than would be achieved by dumping straight to atmosphere. Maybe this is why H&S recommend a 3" front and 2.5" rear at <400hp. Although I suspect shape has as much to do with it as size. I would like to see a nice tapered down pipe from the size of the turbine outlet to full 3". This should help stop turbulence at the turbine outlet and help clear the gasses away.
But maybe you can design an exhaust which at peak engine power output creates some dynamic effects which give better conditions at the turbine outlet at that mass flow rate than would be achieved by dumping straight to atmosphere. Maybe this is why H&S recommend a 3" front and 2.5" rear at <400hp. Although I suspect shape has as much to do with it as size. I would like to see a nice tapered down pipe from the size of the turbine outlet to full 3". This should help stop turbulence at the turbine outlet and help clear the gasses away.
TTM
Well-known member
...not to mention the amount of ground clearance lost with the installation of a bigger exhaust [8|]
I also think that most of the backpressure is created by the turbine and that installing a bigger exhaust might not help much if any when using a "small" turbine. Did you take your car out since the turbo & exhaust swap? How does it spool?
Do you mind me asking the diameter of the turbine outlet? Would like to put it in perspective with mine.
Over the last months I have been pondering about the need to install a larger exhaust as the turbo performs really well in any condition (spool, mid and uprange) and the turbine is rather smaller than big - I might see a little gain with a bigger exhaust but I just might, and I'm not sure it would help reduce backpressure to a significant margin.
Edited : just read your post in the other thread, thanks for the update.
Hi Thom,
By "turbine outlet" do you mean the diameter of the hole in the outlet flange? If so, I believe it is the same as on a standard #8 hotside - about 2.25"?
Spool up is as good as the previous SFR turbo, but with stronger top end - although I've not really had much chance to play with it yet as I want to make sure the EBC and the fueling are under control first.
I know what you are getting at here - I thought the same at first but I've changed my mind having listened to Ian at H&S.
Going from 2.25" to 3" instantly won't produce turbulence in itself (bit like the no exhaust scenario) and the exhaust velocity is so high that the flow through the short length of the downpipe will will be fine. The critical bit is that the DP is the full 3", as is the joint where it meets the main exhaust. I think if you start out with 2.25" it wont's hurt it - I just don't think it's necessary.
Also, what if you change turbo later to something with a different outlet? I know, you'd change the DP to match but.....
I just mean you could remove the exhaust leaving the downpipe attached and see how it behaves. It would give you an indication of how much additional pressure the rear section of the exhaust is creating at the turbine outlet.
When you say back pressure do you mean at the engine? If so then no it probably won't reduce back pressure but *might* increase the differential pressure across the turbo meaning a better torque curve as the turbine could produce more power at any given back pressure.
When you say back pressure do you mean at the engine? If so then no it probably won't reduce back pressure but *might* increase the differential pressure across the turbo meaning a better torque curve as the turbine could produce more power at any given back pressure.
sawood12
New member
The exhaust post turbo is all about extraction of the exhaust gases. And as always there is an optimal size for any given application so it is not a case of bigger is always better. If the exhaust is too large you will get turbulence and stagnation of the exhaust gases which will increase back pressure (having a detrimental effect on the turbine performance) and reduce the extraction effect. Sharp bends and changes in diameter should also be avoided. Bigger is never better - there is always an optimal design solution.
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