I've been readin a book called Maximum Boost by Corky Bell and I am on the exhaust systems chapter. This is what it says about choosing the size of your exhaust.
BASIC TUBE SIZE. It is easy to get overeager on fitting large-diameter pipes into an exhaust system. "The larger the better" is not the case. As indicated in Chapter 5, there is an exhaust velocity that ought not be exceeded. I am going to suggest that for exhaust calculations, this velocity is apporiximately 250 ft/sec. The considerable expansion of exhaust gas due to the temperature increase also requires a significant increase in the desired volume of the tailpipe. The tubes for the hot gas on the exhaust side should therefore be larger than the tubes for the cooleer intake side. Base the calculation on the same conditions as for intake tubes, but use a maximum velocity of 250 ft/sec rather than 450 ft/sec. To size a tailpipe, you can adhere to this exhaust velocity or to the simple guidline of selecting a tube diameter approximately 10% larger than the turbine outlet diameter. Figure 11-4, exhaust tube size versus bhp, offers a good guide to choosing an adequate tailpipe size.
Figure 11-4.
According to this we should only have stock size exhaust. What's the stock size anyways? 2.25? That's right about what this graph suggests for our bhp. Going by this graph, my 3" exhaust is not reccommended unless pushing 750 bhp!
98 Metro Hatch Daily Driver :)
91 SS EJ20G Engine/Tranny/Diff Swap Build Thread Here
"Your testes are close to your bottom but you still play with them all the time." Jeremy Clarkson
Not that I don't wholeheartedly agree, but does he mention whether that relationship is empirical or derived? I would guess it's calculated because systematic experimental/control groups would be impossible to attain across such a hp spectrum, which implies that these are under ideal conditions (i.e., non-turbulent flow once exhaust gas has passed through the compressor). Does he mention how the introduction of turbulence effects exhaust exit velocity?
I'm not surprised at all that it's non-linear, but it's actually a bit unexpectedly close to linear. I would be very interested in how that relationship looks compared to torque... Does he discuss that at all?
Cheers,
morgan
1992 Legacy BF
1946 Ford 1.5 Ton Truck (The Beast): http://community.webshots.com/user/fishbone79
I have not read anything about that yet but I just started reading the exhaust systems chapter today and only got a couple pages into it.
98 Metro Hatch Daily Driver :)
91 SS EJ20G Engine/Tranny/Diff Swap Build Thread Here
"Your testes are close to your bottom but you still play with them all the time." Jeremy Clarkson
I've said this before but I didn't notice a huge difference when I "upgraded" to my CES 3" TB systems, other than boost creep of course
I think the fact that its "louder" it has an effect on our "butt" dyno or in this case our "ear" dyno to tell us "wow it sounds louder so I'm making a ton more power!!!"
My .02
-Mike
2011 Infiniti G37x Sedan - Current
2007 Ducati 800ss - Current
1994 Subaru Legacy Sport Wagon (White)
1994 Subaru Legacy Sport Wagon (Silver)
2003 Infiniri G35
1998 Infiniti I30t
1995 Honda Civic DX
1987 Subaru GL Wagon
1987 Subaru Loyale
I'd love to make 35 lbs of boost! Where do I sign up?
I was under the false impression that 3" exhaust was necessary for the turbo to spool quickly and easily. So I now have a full 3" exhaust waiting to be put together by the exhaust shop.
Do you think that extra 3/4" makes a big negative difference?
98 Metro Hatch Daily Driver :)
91 SS EJ20G Engine/Tranny/Diff Swap Build Thread Here
"Your testes are close to your bottom but you still play with them all the time." Jeremy Clarkson
And as far as JDM goes...I've got quite a bit. Entire engine, tranny and rear diff.
How much JDM does a guy have to have to build 35lbs of boost these days? Shit I swear the honda guys just get the JDM air freshener and JDM bumper city light and a couple stickers and they're building all kinds of JDM boost!
98 Metro Hatch Daily Driver :)
91 SS EJ20G Engine/Tranny/Diff Swap Build Thread Here
"Your testes are close to your bottom but you still play with them all the time." Jeremy Clarkson
I seem to remember lots of substantiated dyno tests, on numerous different, cars that say a nice downpipe and exhaust make documented improvements. Magazines from the late 80s to current all have back to back dyno tests that show these improvements.
On a turbo car, I'm 100% sure that you will see improvements from a proper exhaust.
Is 3" overkill? Possibly. Does it help? Yes.
'93 Winestone SS Auto, '91 Pearl White SS.
'93 Pure White SS EJ20G slanty intercooled, SIDESWIPED! In stasis.
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How much JDM does a guy have to have to build 35lbs of boost these days? Shit I swear the honda guys just get the JDM air freshener and JDM bumper city light and a couple stickers and they're building all kinds of JDM boost!
Not sure exactly how much,but a nice car length vinyl dragon with some japanese writing on the side of your car will get you pretty close.Maybe one of those e-bay steering wheels that looks like a throwing star?
94SS.Wiseco forged pistons,TD04,TMIC,WALBRO 225,440's,3" all the way,revtronix stage 2,enough other crap to fill the internet.
THE TRIBUTE BUILD>>>LINKY LINK>>> http://bbs.legacycentral.org/viewtopic.php?p=295455#295455
How much JDM does a guy have to have to build 35lbs of boost these days? Shit I swear the honda guys just get the JDM air freshener and JDM bumper city light and a couple stickers and they're building all kinds of JDM boost!
Not sure exactly how much,but a nice car length vinyl dragon with some japanese writing on the side of your car will get you pretty close.Maybe one of those e-bay steering wheels that looks like a throwing star?
How could I forget! I'm on it.
98 Metro Hatch Daily Driver :)
91 SS EJ20G Engine/Tranny/Diff Swap Build Thread Here
"Your testes are close to your bottom but you still play with them all the time." Jeremy Clarkson
