ryanleiker

iTrader: (2)

I built my dual exhaust this last weekend and went to drive the car. Before this I just had a downpipe exiting out under the car.
The car is dramatically quieter now but at a WOT it bogs down and the A/F ratio shoots to 10:1.
I'm only running about 3-4psi right now and am wondering if there's too much backpressure or maybe my tune is just wrong or if I need more boost to even it out.
My tune came from my friend's engine and has worked flawlessly before the exhaust, but he was also running 15psi with a drastically more efficient turbo, so maybe my engine is just expecting more cfm when I floor it.

I'm also now having a warm idle issue, which I think is more due to the warmer air outside and just needs some tune adjustment.

Thoughts?

Johnv

Get a custom tune to suit your car, using someone elses tune on a boosted car is just asking for trouble, no two setups are identical so neither will the tune required be.

Ratical

iTrader: (82)

What kind of exhaust? What size pipes, what brand and style mufflers, do they exit out the back or just dump under the car further back?

Cold the computer is in open loop and runs off the set parameters, warm the car goes into closed loop and runs off the sensor. Also in the cold weather the air is denser so at least with a carbed application you need to fatten the carb up. In warm weather you need to lean it out. I would think that might play a factor too even with fuel injection especially if the tune was already on the fat side of the range. Sounds to me like your tune is out of the o2 sensors range to adjust it now.

Just my thoughts. I am no fuel injection specialist. That **** is like voodoo to an old dog like me.

Agent_Orange_Shuvel

iTrader: (8)

Did you log the event? if so post the log.

Like Ratical asked you should let us know what type of muffler you are running.

When I ran my full exhaust system with Spintech mufflers vs open downpipe there were very minimal changes necessary in the tune. But I'm running dual 3" and Spintech's have great flow ratings.

Ratical, If I remember correctly he is running a stock pcm with HP tuners and has it setup for open loop speed density.

Ratical

iTrader: (82)

Thanks Agent.

I noticed the build thread link and read abut the build. Looks like 3.5" split a dual 2.5" exiting the factory location. The pipes seem large enough, so I don't think that is the issue. I do not see the muffler type in there though. Maybe if you are using a chambered or turbo style mufflers I could see some back pressure issues, but any straight through type muffler should easily flow enough.

I also read about the rich tune issues and MAP issues. (Good catch BTW on the MAP not reading Agent) It looks like the car was running rich before and you mentioned when you got it to switch to closed loop with HP tuners it cleaned up some which sounds like the sensors read the condition and tried to correct it. The thing about sensors is they only have a narrow effective range to adjust from your base tune settings. IMHO, get the base tune closer and I think it will clear up. A copy of the log would be very helpful so someone that has more experience with HP Tuners might see something stand out.

Cool build BTW.

ryanleiker

iTrader: (2)

Well, his was a 5.7, and mine's a 6.0, but I'm using his camshaft and his injectors, so it actually was working great before the duals, when I was running straight out of my downpipe, but I still think you're right.

ryanleiker

iTrader: (2)

The exhaust is a universal dual 2.5" GM kit from Summit with Turbo mufflers, which I'm betting my main problem is these mufflers. The system exits out over the axles behind the rear tires.

ryanleiker

iTrader: (2)

I'll try to get a log up in the next few days. The mufflers are Turbo mufflers from the universal GM dual 2.5 kit from Summit.

http://www.summitracing.com/parts/sum-680101

Agent_Orange_Shuvel

iTrader: (8)

You're absolutely right and with the stock PCM it goes back into open loop at wide open so the base tune has to be spot on.

I bet you are right, those mufflers look pretty restrictive on the cutaway shot of them.

Johnv

Also twin 2 1/2 " don't flow as much as a single 3 1/2", you should be looking at twin 3" exhaust.

Ratical

iTrader: (82)

Turbo mufflers are the worst flowing of the 3 types of performance style mufflers out there. I used to have a chart with all the flow numbers of the different brand and styles of aftermarket mufflers. Turbo, chambered and straight through in that order from worst to best, size being equal of course. Even if you get the tune spot on I will almost guarantee those mufflers will cost you power once you turn up the boost. As far as the tune running rich I think it was already rich and the back pressure just put it over the edge of its effective range. Just like an NA carbed car needing you up the jet sizes when you uncork the exhaust at the track, adding back pressure usually requires less fuel.

Fix the mufflers, then fix the tune and crank it up!

stevieturbo

Unless you welded the exhausts shut, there isnt a chance in hell the exhaust is the cause of the problems, even more so at 3-4psi boost.


If you're running a tune for a completely different engine, no wonder it isnt running correctly.

ryanleiker

iTrader: (2)

I'm still going to play with the tune a little, but I took it out today and hammered on it and it didn't choke itself rich once. So that's odd. But at 3-4psi, it's certainly slower than an open downpipe.
Almost time to turn up the boost.

Question: anyone tried Jones Exhaust MAXflow mufflers? I may end up trying them out soon.

alowerlevel

iTrader: (1)

I have one on my car but its not turbo'd (yet). Looks & sounds like a Magnaflow for less than 1/2 the price

oscs

iTrader: (19)

2.5" exhaust pipe has no place on a turbo LS motor unless its the cross over. You should expect nothing more than sub-par performance from your car until that is fixed.