just wanted to get some input on a question i have, will dropping my exhaust lower my ET? my motors a 30 over 454, mild cam, ported heads, weiand 180 2p manifold, holley 770 street avebger, 2200 stall ( stalls lower.. like 18-1900) 373's posi. any input welcome, i know opening the headers slowed my 69 elk down by almost a 10th but it was a stock small block graemlins/sad.gif . thanks

Jay

I picked up about a half mph going to open headers with collector extensions. Without the extensions, I saw no change. You may need to re-jet. This is with a SB shifting at 7000 rpm.

On my combo its worth 2.5 tenths, but my primaries are too small for it. I have a 406 winging to 7500rpm. I have 1 5/8x 2 1/2 supercomps. Really needs atleast 1 3/4

I think it has a lot to do with the primary header tubing size. I've done numerous tests on my car with:

- just open headers
- headers and merge collectors (no mufflers)
- headers with merge collectors and straight pipe
- headers, merge collectors, straight pipe and dynomax bullet mufflers w/turn downs
- and lastly running with headers, merge collectors, Straightline Performance large case race mufflers and tail pipes

During each of the above mentioned tests I tried different jetting/squiters/timing to optimize each configuration. My car has better 60' times and ET with full exhaust (including tail pipes). I was able to get it to run nearly the same with the dynomax bullet muffler configuration by jetting up 4 sizes. I think what this tells my is that my primary header tube size is too big. The car seems to run better with the added back pressure that the full exhaust provides. In fact just this week I put my entire old exhaust system back on. My exhaust systems is as follows:

Hooker Super Comp headers with 2" primary and 3.5" collector
FlowMaster Scavenger merge collectors
Straightline Performance 3" in/out large case race mufflers
Torque Tech 3" tail pipes

I'm actually glad that my car runs best with a full exhaust system as I prefer to have a quiet race car. It surprizes a lot of people when you can click off 10 second passes in a relatively quiet car with full exhaust. The times in my signature were running through full exhaust.

My best was with open headers and slicks-11.78
3" exhaust,ultraflos,w/dumps and drag radials-11.85 and I too like racing with the exhaust on much better. If no problems arise I'll have some results from a th400 swap back to a th350 with the current ATI 10" converter in the next couple weeks,weather permitting.

my primarys are 1 7/8", sounds like ill have to do some testing, but it also sounds like i wont lose anything opening them unless its a bit in the 60', with my primary size though i bet ill be alright. what i wanted to do was weld in a couple of those exhaust cut outs, ive heard that they will leave a little back pressure as not 100% of the exhaust flows through them since it still hase 2 paths it could take. i don tliek the electric ones, ive seen a few cars they the seal gets bad on and they leak all the time.

My setup in sig has 1 5/8" primary shorty headers. I've got an electric cutout behind my Y section.... Opening that at the track got me from 13.6 to 13.3 and a mph or two.