blackeg

how much difference would there be in my tune (afr...) if i dyno tune my car with a 3" open dp that ends under the drivers seat if and then add a full 3" exhaust with a straight through 3" muffler?

i dont think im gonna get my exhaust in time for my dyno appt this weekend.

fjt

Going Open downpipe will make the car leaner compared to Full exhaust.. it will also push some PSI more...

When i tuned my car at 18PSI we took the exhaust off for the final 2 runs just to see the difference and the car went from 18PSI to 22PSI and we didnt touch anything..That will oviously affect your AFR making it run leaner... So if you tune with Open DP and then put the exaust back it should be the opposite..The car will run richer

HiProfile

I made a thread asking for open DP/full exhausts on the same setups w/adjusted tunes, and people were making +20-50whp on even mild setups. If you're at 12:1 AFR's and make 15% more power, that means you need around 15% more gas. 'Missing' 15% of the gas raises that 12:1 to 14:1. Thats very unsafe, even with a very conservative ignition tune.

As for making more psi - thats if you have bad leakage around your WG valvestem and aren't using an electronic controller. Less pressure in the exhaust means less leaking into the WG, meaning the valve opens a bit less.

JDogg

it dosnt change much.. the last car i tuned with the cutout right after the oil pan didnt really need anything different with it open or closed, it just made 30 more hp/30more tq

blackeg

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JDogg &raquo;</TD></TR><TR><TD CLASS="quote">it dosnt change much.. the last car i tuned with the cutout right after the oil pan didnt really need anything different with it open or closed, it just made 30 more hp/30more tq</TD></TR></TABLE>

ok, this is close to what i thought i might hear. ive run a 3" cutout for over a year now but that was with a stock catback. this new setup is a 3" dp and will be 3" kteller and a 3" magnaflow straigth through..


is it the length of piping that would create more "resistance to flow" or is it the muffler itself?

95accordh22a

it wouldnt lean it out if you got the car tuned with an open dp and then put on the exhaust right? that would be the better option no?

JDogg

i tuned the car with the cut out closed, then ran it with it open, there was not enough difference to require any additional tuning.

this was 3inch dp with 3 inch cutout and a 3inch thermal exhaust, around 450ish hp with the cutout closed, 480ish with it open.

mike93eh2

i had mine tuned with full 3" with no cat and a 3" amgnaflow and then added a cutout after the oil pan and it didnt raise my boost or screw with my afr's..

blackeg

ok cool, thats the exhaust i have in the mail, 3" no cat no resonator and 3" magnaflow straight through.

i just finished up my downpipe tonight, its a 3" w/flex that has a turndown at the end. it stops right under my shifter

mike93eh2

but all setups and climates are different. youre going to lose some power though.

Tippyman

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by blackeg &raquo;</TD></TR><TR><TD CLASS="quote">

i just finished up my downpipe tonight, its a 3" w/flex that has a turndown at the end. it stops right under my shifter</TD></TR></TABLE>

That's what I plan on doing.