Just wondering how much do your cars pick up or drop off with full exhaust. I have never run mine with exhaust until yesterday and it slowed up bad. I only have 2.5" exhaust and I know that hurts it some but I didn't expect it to lose .4 in the quarter. What are some of your experences?

thats about what mine was...

My last car ran 9.90 through a 3.5" X-pipe with 3.5" Magnaflows and turnouts. Very quiet and ran 9.90 the same day with open headers.

The 69 Dart Has about 18" of 3.5" pipe, then 3.5" PYPES Race Pro mufflers, and soon to have turnouts.
I thought it would slow the car down without a crossover pipe but in the 1/8 mile it only slowed a hundredth or less.

Here's a vid with the Race Pro mufflers and bad traction.

http://www.youtube.com/watch?v=bcKV5j1pG-0

a good exhaust might even pick it up a bit..

1969 Dart 440,727 12.23 at 109.6 with a set of 2.5 turbo mufflers feeding directly out of a set of Hooker A body (2 inch x 3.5 collectors) fenderwell headers with a short side pipe coming out in front of the rear tires. I removed the exhaust from the headers back and the car ran 11:39 ET at 117.75 MPH on the next run in a 1/4 mile My Duster had the same headers with a three inch pipes feeding to a set of Magnaflow 3.0x14 long oval muffs mounted at the rear bumper and the car only pick up .04 ET and about a 1/4 MPH increase in the 1/8 mile, probally due to the weight removal I haven't tried removing the exhaust at a 1/4 mie track yet on the Duster

Now you really got me wanting to uncap my 63. Ron

Last saturday picked up almost two tenths.
10.32-34 to 10.14. Also picked up 1.75 mph.

on my gtx 493 rb 2in headers into 3 in ex with flowmasters.12.00 full ex.i have side extentions so i can uncap the headers without removing the ex.11.70 un capped.

My 340 Dart had TTIs, 2.5" exhaust with Flowmaster 40s turned down at the rear axle went from 7.45 (1/8) with to 7.25 without the exhaust. This was on back to back runs maybe 15 minutes apart.

After running open exhaust and tuning the carb for it for many years, I installed a 3" TTI X-pipe with Dynomax Ultra Flo mufflers terminating at the rear end housing. After removing 60 lbs from elsewhere in the car that the extra exhaust system weighed and tuned on the carb a bit more - going leaner actually, the car picked up at least several hundredths! (Not same day back-to-back, but using detailed record keeping.) So, despite the inconvenience when having to swap transmissions or center sections, the system has remained on the car.

Just like swapping intake manifolds, cams, headers, etc., it depends on the overall package and carb tune-up. A single different part can alter jetting requirements, so only re-tuning & testing to know the best tune-up for each will provide the best comparison between the part changes.

A 2.5" exhaust system would tend to be a choke-point. Going to open headers or a larger exhaust system will likely change the optimum jet sizes as well as squirters. Just different mufflers can have a similar affect because of backpressure changes. (i.e.: A current set-up is a little on the rich side, so it's not "optimized" or as fast as it could be. A change is made that would require a richer tune-up, but it's already richer than the previous set-up needed. So the results appear better than the should be.-----If the previous set-up was too lean and a change was made that needs richer jetting, then the results of the change would be worse than they should be.)

Carb tuning for each change is not easy and is time consuming. But each combo, as well as tune-up, is different and that explains the wide variety of ET changes when adding, changing or removing an exhaust system - as well as other parts.

When I had 2.5 Dynomax at 12.00 would be 11.70 open so your right there.
Now My 3" dynomax welded with X pipe on my old 542 .10 and they weigh 55 pounds so .045 and real quiet.

Thanks for all the info. I guess with what im reading is my car is about average for exhaust vs no exhaust. Plus a real slippery track. No more exhaust for me at the track

My Scamp with a 360,slowed down almost two tenths without the muffs. I installed extensions, but I didn't jet up the carb.

How much more jet do you need with open exhaust?

Dennis Jokela