Finally got out to the track today for some test and tune and had a chance to test my exhaust system both capped and uncapped -- thought I would post the results.

Exhaust system is as follows:
Hedman 1-3/4" long tube headers with 3" collector.
3" Pypes x-change X-pipe, 3" in, 3" out.
3" dumps after the X pipe.
Flowmaster 3" to 2.5" megaphone style reducers just prior to the mufflers
2.5" Dynomax Ultraflow mufflers
2.5" Flowmaster tail pipes, exit in the stock location.

The track was a little slick today so my 60' times (and ETs) were a little off but my MPH was dead-nuts on each and every run so the MPH was a good comparison on power capped vs. uncapped.

With the exhaust uncapped:

best ET was 11.28 @ 119.6 with a 1.61 sixty foot. I made 5 runs with a 119.6x trap speed, 1 run with a 120.0 trap speed.

With the exhaust capped:

Best ET was 11.44 @ 118.74 MPH with a 1.69 sixty foot. While the ET was .16 off from my best, I spun out of the hole which IMO makes the ET not comparable to the uncapped runs. I think the key was that MPH was only .9 MPH slower so my conclusion is that the exhaust system flows pretty good without uncapping it.

I jetted the engine a little on the fat side prior to racing and left it there throughout the day so the engine wouldn't be lean with the engine uncapped.

PS. I also got some really cool in car video -- if anyone knows how to host a video on the web shoot me an email . . . I have 30 MB of free space I can use to host if I can figure how.

That's great feedback. Looking forward to the video. How was the fuel pressure after all the work you did?

Fuel pressure was rock solid 7 psi at idle between 6 and 7 at WOT. Did not test f/p at the track though -- just on country roads . . .

No breaking up at all, the engine rev'd clean and felt pretty crisp.

Interesting results.

My thinking is that you turned the tire on the 1.61 60ft as well, correct?

Sounds good Eric,
although I thnk if you had 3" mufflers and tail pipes it would run the same capped & uncapped.

Brian, yeah it turned the tires all day to varying degrees each pass. When I figure how to post my video you can feel it in the first 60'. Not sure why it turned the tires so easily . . . maybe there isn't enough rubber / VHT down being opening day. Although I never seem to 60' or ET as well at US131 Dragway as I do at MidMichigan Motorplex where I usually race. The car has gone 1.54 in the first 60 and is pretty consistent in the 1.5's at the other track on race days.

Rafel, you really think it would run the same MPH with 3" all the way back? I always thought if it was within one MPH capped vs. uncapped the system was pretty good. The MPH was closer than I expected . . . I figured it would probably be loosing more power than it did . . .

are the tires new for this season?

No, they have about 75% left on them . . . bought them in the middle of last season. Maybe I should rotate them -- they haven't been off the car all winter (the car was on blocks)

75% based on? The wear indicator or the typical amount of passes before the sidewalls are dead and the car doesnt hook? Based on your car of course.
80-90 passes seems like stretching the limits of the life of a tire in my opinion for a moderately heavy, 3 speed car.

I used to rotate mine everytime i went last season since i swapped them at the track. This season i'll rotate mine every 15 passes.

75% left based on tread depth . . . since I don't have a new tire to compare to I suppose it could be as little as 50% left.

I agree on number of passes -- I usually go right about that, maybe 100 tops. That is typically right about one season.

I need to get the car hooking hard and I need to find that extra 1-2 MPH of trap speed. The trap speed might be a matter of jetting a little leaner, the new fuel system provides much better pressure than the old . . . I was jetting rich last year to compensate so maybe . . .

If I rotate tires and race at the other track and still have traction problems I will probably get a new set of tires and maybe some Caltracs. Need to get teh bugs worked out prior to the start of the real racing . . .

Caltracs work pretty good, my friend Adam's B/SA car uses their setup, and his car breaks the 60ft beams with the back tires on a 9" wide slick.

http://www.iwantthatmusclecar.com/images/69bscamaro.jpg

Caltracs arent the only reason the car leaves like that though.

that's good.

mine picked up .4 in ET and 4 MPH taking off my 2.5" dual ex with dynomax hemi super turbo's this last sunday. But i like it quiet on the street.

Here's that link . . . it's kind of a fun little video I think. Its cut down to 3.3 MB so be ready to watch the hour glass if you don't have high speed.

You can kind of "feel" the tires turn a couple times right out of the hole. Other than that its a decent run

http://www.turbo-jet.com/eric68.html

Thanks a lot to WildBillyT for hosting it for me. One day I'll figure out how to do that myself

Brian, what kind of ET's is your friend running? That's a sweet looking 69 and a killer launch.


PS. I STARTED A NEW THREAD FOR THE SUSPENSION DISCUSSION

cool i'll join in that.

He's running .90 under or more on a good day. Cars almost done being painted for this season.

So the ET's are 10.50's