Downpipe Length
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Downpipe Length I may soon become involved in a LSx based ProStreet project that would involve mounting a pair of GT3582R turbos low in the rocker panel area. It would be using Ford style 5 bolt T3 turbine housings. The discharge pipes off each turbine wheel would immediately be expanded to 3" diameter, but would only be about 1 foot long. Being "unmuffled" is not an issue...the turbines will keep it quiet enough. The car will be required to be streetable enough to complete street cruises that may involve city/highway driving for up to 1 hour, so a closed loop engine management system will be used, requiring O2 sensors to be placed in these very short turbine discharge pipes. The wastegates would be plumbed into 1 3/4" piping through 44mm external gates. Due to this layout, the total length of the wastegate piping would actually be longer than the main turbine discharge pipes. Is the short length of these downpipes going to cause any issues? How far from the turbines should the O2 sensors be placed? How much pipe is needed after the O2 sensors? Any feedback would be greatly appreciated.
you should put the o2 sensors right after the colletors of the exhaust, preturbo, put the wideband sensor after teh turbo about 6" downstream of the turbo, then id run atleast another 6" of pipe after that.
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Originally Posted by smokinHawk
you should put the o2 sensors right after the colletors of the exhaust, preturbo, put the wideband sensor after teh turbo about 6" downstream of the turbo, then id run atleast another 6" of pipe after that.
He's got cast manifolds that will fit perfectly, but they do not have O2 bungs, and I'd rather not hack 'em up if I don't have to. I have an extra PLX wideband controller. I was thinking about putting a standard narrowband O2 at the midpoint of one of the downpipes, and running the PLX "double duty" (wide and narrow) on the other side. Do you think that might be okay?
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Originally Posted by cablebandit
i drive mine daily and its OLSD...just wondered why you NEEDed o2s
I was running my daily driver C5 'Vette open loop speed density last winter. The tune-up was dead on until the weather heated up as summer rolled around. Wouldn't be such a big issue for me, but not the combination I'd want to hand over to someone who is just a "casual car guy". The purpose of this build is to provide him with a turnkey ProStreet vehicle that is both show and go, and won't require anything more than a few oil changes and maybe one plug change every year.
Last edited by RAACCR; Jun 8, 2007 at 09:23 AM.
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Originally Posted by smokinHawk
you dont have any pipe from the cast manafolds to the turbo do you? if you dont then youll just have to run it after the turbo, about 6" from the turbo like the WB.
Turbos bolt directly to the cast manifolds. We've sourced a set that will work perfectly, but their placement limits our exhaust options to very short downpipes (unless we really compromise ground clearance...and this car is going to be in the weeds, so that's a big concern). I don't want to attempt installing bungs into these manifolds becasue they're very expensive and difficult to find, so I'd rather not risk screwing them up.
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WB's preturbo can be subjected to excessivly high temps and pressures. Hi temps will kill them, and hi psi will skew the accuracy.
Mounting them in a 1' pipe will likely expose them to outside air, and skew the accuracy. [Most significantly at lower engine speeds.]
Mounting them in a 1' pipe will likely expose them to outside air, and skew the accuracy. [Most significantly at lower engine speeds.]
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Originally Posted by Old Geezer
WB's preturbo can be subjected to excessivly high temps and pressures. Hi temps will kill them, and hi psi will skew the accuracy.
Mounting them in a 1' pipe will likely expose them to outside air, and skew the accuracy. [Most significantly at lower engine speeds.]
Mounting them in a 1' pipe will likely expose them to outside air, and skew the accuracy. [Most significantly at lower engine speeds.]
Yup...I remember that from my old turbo 6 days (Buicks, TTAs & SyTys). The narrow bands can hold up okay pre turbo, but the widebands must go in the downpipe. Unfortunately, due to packaging constraints, all O2s will need to go in the downpipes in this case. You've exactly stated my concern that the short length may cause some issues with the O2 signals. If its just a low speed problem, I can safely tune around it. I often find that aggressive timing and a slightly rich a/f seems to tame alot of low speed driveability issues in these types of applications anyway. As long as I'm able to get decent readings at higher rpm and under boost, it won't be a problem. The reason for wanting to close loop the system in the first place is to make sure it safely corrects for different conditions under higher loads.
Last edited by RAACCR; Jun 9, 2007 at 01:27 PM.
