Exhaust question

[funkbuster]

Hello everyone. I have a quick question about my exhaust. I have a Megan Racing 3" dp and 3" Test pipe. Then I had the exhuast shop run back 2.5" exhuast back to the axle, where it is the stock pipe back to my stock muffler, the only one I had. I didnt have money at the time for another muffler. I was wondering how much could this be hurting my performance? On another note, I was looking over my engine this morning and noticed a place for a hose on the intake manifold, it didnt have a hose on it. I hooked up my aftermarket boost guage to it, so now it works, and it fixed my idles surge. I am going to try puting my MBC on later and see if that was my problem with it not controlling boost.

 

[Gregory]

with the exhaust, you generally want to go from smaller to bigger piping.. you have your set-up completally backwards with a 3" to 2.5" to stock muffler... work from the back up... get a better flowing muffler, and i'd recommend changing you dp and test to 2.5 or changing the rest to 3... keep in mind what you're going to do when buying the muffler so you know what size induct you want. you're performance i dought is much better than stock if at all because the freer flowing exhaust early on doesn't matter with the stock muffler restricting it. i would almost think it's hurting your performance over the stock exhaust because it might mess with the pulsing of the exhaust and probably flows terrible.

 

[DSMunknown]

I was wondering how much could this be hurting my performance?

In terms of airflow, it's a significant restriction. Get it fixed ASAP. You'll be happy you did.

 

[Dorifto]

Run a simple test to see what performance you're missing by running like that.

First, take a quick run or two up your street. Come back, and unbolt the exhaust after the test pipe. Make another quick run or two. $20 says your car will boost earlier in the rev range, will pull harder, possibly even run higher boost.

While it's great for a sleeper, downsizing exhaust components like that really hurts performance.

If it were me, I'd get an electric cutout after the test pipe, so when you desired balls-out performance, you could just crack that bad-boy open and have a free-flowing exhaust, but still be quiet and low-key when it's closed.

 

[Gregory]

the electric cuttouts are sweet, but are out of a lot of our price ranges...

 

[funkbuster]

my brother has a fart can he said I could use. I might go have the exhaust shop put it on for me, see if that helps. If seems like it is having to push hard to get past 4500rpms. Before I got the DP I had stock exhuast with a side pipe and no muffler, and it ran to 6500 with no problem.

 

[Gregory]

Well, you are going to have pull problems as long as you have your exhaust set up like that. Exhaust pulses (although slightly less in turbo cars, it still does) and each pulse, more or less, drafts behind the one in front of it and is pulled by the negative air behind the pulse before (you've seen NASCAR, right?). When you make the exhaust flow from larger to smaller, you are destroying this flow. The biggest thing for you right now is opening up the muffler, but I would look into getting everything up to 3" since your down pipe is. Think of your current exhaust setup as a funnel: it's dumping in at the top, but getting all backed up at the bottom. Hope this helps.

 

[Echo5Zulu]

the electric cuttouts are sweet, but are out of a lot of our price ranges...

Both JCWhitney and Summit sell mechanical cutouts that werent too pricey. If you want to go that route the mechanical would probably be more reliable.

 

[funkbuster]

I would love to do an electric or cable cutout, my only problem is that when I was running open downpipe and then open testpipe for a few weeks, my boost creeps really badly. Anyone have a link to a good electric or cable cutout on the cheap?
Thanks
CHase

 

[tqmx1]

The biggest thing for you right now is opening up the muffler, but I would look into getting everything up to 3" since your down pipe is. Think of your current exhaust setup as a funnel: it's dumping in at the top, but getting all backed up at the bottom. Hope this helps.

The differance between the funnel and a exhaust is the heat, The farther back the exhaust flows the cooler it becomes. From the exhaust port to the turbo through the turbo to the down pipe through the cat and back the charge is cooling(and taking up less space). By the time the exhaust gets back to the muffler it is dam near cool from what left the port so a smaller muffler can be used. In years long past I was running Pontiac 455s through 2 2.5" mufflers after the cans we ran 2.5" pipes and then for fun and games we bent up a set of 2.25" pipes there was no differance on performance.

As for NASCAR they are tuning for all out performance the only time they tune for anything different is when the run at sears or the glenn then comes the mid range tuning. So comparing them to what we are doing is comparing apples to oranges.

Not thying to step on any toes.
Kim

 

[DSMunknown]

The differance between the funnel and a exhaust is the heat, The farther back the exhaust flows the cooler it becomes. From the exhaust port to the turbo through the turbo to the down pipe through the cat and back the charge is cooling(and taking up less space). By the time the exhaust gets back to the muffler it is dam near cool from what left the port so a smaller muffler can be used. In years long past I was running Pontiac 455s through 2 2.5" mufflers after the cans we ran 2.5" pipes and then for fun and games we bent up a set of 2.25" pipes there was no differance on performance.

As for NASCAR they are tuning for all out performance the only time they tune for anything different is when the run at sears or the glenn then comes the mid range tuning. So comparing them to what we are doing is comparing apples to oranges.

Not thying to step on any toes.
Kim

Be careful what you say, Kim. You may have not "noticed" or "felt" a difference in performance, but you still would be restricting the airflow of the exiting exhaust gases in your example, which ultimately would lead to a loss of performance.

 

[funkbuster]

Ok. I went to the exhaust shop today, had them cut all the back stuff off and ran a 2.5" side exit without a muffler. Helped alot, car goes to redline now without any hesitation, throttle response improved a little now too, not to mention how great it sounds, straight race. Should be ready for the track now.