more flow = lag?

[Wayne Barbaza]

ok.  so I've read that with more exhaust flow (eg. 3" instead of 2.5" downpipe), you run into lag issues.   Can anyone please explain why?  I always thought more flow = less lag no matter what....but I guess its to a certain extent?

thanks
wayne

[Chris Andrews]

ok.  so I've read that with more exhaust flow (eg. 3" instead of 2.5" downpipe), you run into lag issues.   Can anyone please explain why?  I always thought more flow = less lag no matter what....but I guess its to a certain extent?

thanks
wayne

Can you tell us where you read that? Or post the link?

[Wade Carlson]

i don't think thast true
i got a full 3" turbo back exhaust done up and i get full boost out of my 14b at like 2200-2300rpm
i can'tr exactly remember ow it was before but i think its even faster now

[John Hartman]

ok, no, you won't get more lag with better exaust flow, it will help.

You might be thinking about intercooler pipes and huge intercoolers.  With too much volume to fill in this area, a small turbo might take a little longer to build up pressure.

3" systems can contribute to boost creep for sure,as the exhuast system outflows the capacity of the wastegate, but not lag.

[Mike Schmid]

Yeah, John's right.  If you increase yor exhaust flow (ie 3" turboback) you will increase the pressure differential across the turbine wheel which will make the turbo spool quicker, and less lag.

Now better flow on the compressor side means larger piping, IC, etc, which means more volume between the compressor wheel and the pistons.  So it takes longer to fill that volume, increasing lag.

[Kevin Standeven]

so anyone care to explain why people buy 3" UICP then? better top-end once she's spooled up?

[JamieSibley]

people run 3" uic pipes because after the air inside a pipe or tube reaches a certain velocity it become turbulant and causes huge resistance to the flow of air.

bigger pipe = more area = less velocity for the same cfm = less turbulance = more flow = more go

[Wayne Barbaza]

hmm...sorry guys, I may have worded my question wrong.  If you read through the link below, several guys mention that there's a loss in 'low end torque' when using 3" rather than 2.5" dp.  For some reason I assumed 'loss in low end torque' was the same as lag....but in any case, I'm still wondering why there's a loss when going with a bigger dp...

http://forums.evolutionm.net/showthread/t-24145.html

[Mike Schmid]

A loss of low end torque is due to the flow being optimized for the higher end.  So you get a bit of a loss on the low end... As with most things in life, compromise is the name of the game.

[Kevin Standeven]

aha, merci jamie...makes sense

[John Hartman]

and while that holds true for most cars, ours really are not effected by it too much, espeically with the stock O2 sensor housing