[BruceWilkie]

Originally Posted by slowbird

Fyi a good exhaust should show very little change in et/mph on or off. I ran 9.0@147 with and with exhaust.

Did you test collector lengths when you had the exhaust disconnected to verify you couldnt do better with open exhaust? Did you need any jet changes?

When you add exhaust pipes to collectors you effectively make them longer...

Some lengths tune better than others(see pipemax for best and worst ranges) surprisingly some lengths can be much longer than one would think. Also collectors do not add peak power! They help torque below the power peak.(if length and volume are reasonably close to whats needed)

(pipemax usually gives odd diameters so go up to nearest common size and adjust length to match volume you would get at the suggested pipemax diameter/length.)

Pre pipemax it was charts and graphs from articles to get your system in range... It's quite surprising to run pipemax and see the comparison to the graphs.

My own testing with collector length... the burnt paint method seems to work when collector is a few inches too long but if starting out just a little short you can get mislead thinking its ok when its not and I'm not certain why.
I had good results with the old charts/graphs. (Pre-pipemax and pre internet. Started messin with this stuff about 40 yrs ago and last played with it on a chassis dyno in 2001 )

[johnta1]

Have you ever tried painting the collector again after you cut it?
Then paint it again after cutting it again?
(then repeat?)

[slowbird]

Originally Posted by BruceWilkie

Did you test collector lengths when you had the exhaust disconnected to verify you couldnt do better with open exhaust? Did you need any jet changes?

When you add exhaust pipes to collectors you effectively make them longer...

Some lengths tune better than others(see pipemax for best and worst ranges) surprisingly some lengths can be much longer than one would think. Also collectors do not add peak power! They help torque below the power peak.(if length and volume are reasonably close to whats needed)

(pipemax usually gives odd diameters so go up to nearest common size and adjust length to match volume you would get at the suggested pipemax diameter/length.)

Pre pipemax it was charts and graphs from articles to get your system in range... It's quite surprising to run pipemax and see the comparison to the graphs.

My own testing with collector length... the burnt paint method seems to work when collector is a few inches too long but if starting out just a little short you can get mislead thinking its ok when its not and I'm not certain why.
I had good results with the old charts/graphs. (Pre-pipemax and pre internet. Started messin with this stuff about 40 yrs ago and last played with it on a chassis dyno in 2001 )

I've done the testing. The paint method is crap imo.

[Tiger Paw]

I've done a lot of exhaust testing because it was cheap and real easy on my car. Haven't done any X pipe. Typically the results in any direction that I went were fairly small. So when you're trying to decipher if a change helps/ hurts it's best to have a weather station or some means of know if the change or lack of change is due to conditions or your tuning. A lot of performance improvement will be small, the ability to recognize it tough sometimes. And treat that weather station like your first born. Transport in foam.

[ta man]

Had to go back and check my timeslips..picked up .8 to 1mph in the same weather in the 1/8th by dropping my 2.5 inch tailpipes off my 3 inch x pipe system..car runs 7.2's at almost 98 mph..I'm sure a full 2.5 inch system would choke it down even more..

[Slick Poncho]

Ran Friday night, only change was back to my Mickey et SS tires. Pretty much the same times as my slicks the week before. Saturday morning I added 18" lengths of 3" pipe to the headers, car ran 11.80@113. Backed it up with a 2nd run of 11.78@11, the two fastest passes the car has ever made. And this was back on the slicks, track prep was getting iffy late Friday so I put them back on and left them on for the day.