[10secbird]

This was my first trip to the race track in a very long time. The last time it made a track pass was in 1987 with slicks and open exhaust

This time I ran in street trim ...mufflers and street tires. (3.5 exhaust with Flowmaster 40 series dumping at the rear axle, tires are 275 60 15 MT ET Street Radials)

I only got 2 runs as I arrived later than I wanted to..... drove it in off the street on a 100 degree day, passed tech inspection, changed spark plugs and made first pass at close to 9pm. On the first run it hooked and then broke loose about 20 feet out spinning through the top of first gear and into second gear causing the car to pitch towards the guard rail forcing me to let off of the throttle. The next pass the hook was solid enough to lift the front tire off the ground about 6" carried for about 1 foot (more wheelie than it used to get with the wrinkle-wall slicks)

After a lot of fooling around with the MT ET Street Radials on the street testing how well they hook, I was disappointed in them, but at the track after the wet burnout I did a small test dry hop before pulling up to the line and I finally felt these tires hook and giving me that feeling like the slicks used to.

11.27 @ 120.09 ..... 60ft time was 1.639 leaving on foot brake with a 3000 stall 11" converter ...gearing is 4:10 rear and Th400


Last time it raced was in 1987 and ran with 11.5x29.5 Firestone Wrinkle-walls and open exhaust......usually ran 11.00s to 10.87 @ 122 to 124.89 mph

Changes to the engine from the way it was in 1987 are as follows...slightly bigger Camshaft, some exhaust port work on the 48 heads, differnt headers with bigger primaries and collectors (maddog 1,7/8 x 3.5), and different 2x4 manifold (old one was a DougNash 2x4, but now running a ported wenzler1 2x4 with the same 660s I ran before

In this configuration (street trim) it is faster than it ever was due to the big 3.5 exhaust and the specialty street tires. My old exhaust system was 1 7/8 pipe and killed nearly one full second off my ET. (from a 11.86 with the mufflers on to the next pass being a 11.09 after pulling off the exhaust with no other changes.)

What I have noticed from watching the old video of my car running 10.9 on slicks with no mufflers is the car seemed to go through the gears a little quicker (spending less time in first and second with not much audible difference in rpm drop at gear change. The video of the run Saturday night sounds like the car is winding slower through the gears even though the gear ratio should be around the same as when I ran 4.56 with the 29.5 tall slicks to now with 4.10s and the 275 60 15s which measure right at 28" tall. I am getting just over 3000 stall out of the converter .. I cant flash it from a lower RPM because it produces a carb induced hesitation unless the RPM is at least 3000

I need a apples to apples comparison but I know I cant get exact due to engine changes .... but next time out I want to pull the exhaust off and see if the mph will come back up to the 124-125mph it ran back in 1987 with open exhaust ....and hopefully a little more.

If after pulling off the exhaust and the mph doesnt come up to what it had before (124.89) I need to figure out why. The way the car sounds as though it is winding slower through the gears makes me think maybe the Wenzler1 may be making the engine a bit lazy and maybe now a real race converter (10 or 9" with 4000 stall)could be utilized. Unfortunately I did not note my RPM accross the finish line even though I intended to......Im just wondering if after the launch the RPM that the engine is brought down to at the beginning of first gear is now below where the power band starts and thus causing the slower climb through the gears. I feel the bigger headers, exhaust port work and bigger camshaft are all mods that should move the power band up a bit and perhaps a converter will make it spend more time in the powerband

Sorry for the long post ...wanted to give as much info as needed to get some input from you guys

How much is typically lost form a good exhaust system with 3.5 inch pipe and performance mufflers like 40 series Flowmasters ... I have many people telling me I wont gain anything by puling the exhaust ...

[Mikes455Wagon]

Flowmasters historically cost some power. I am running a 3.5" x pipe and pypes mufflers (for now) and actually picked up slightly (.5 mph) at the 1/8th. If you have a good exhaust system, the loses are minimal. I matched the x pipe diameter to the size of the header collector based on other's experiences and reduced to 3" after the X. My performance didn't seem to suffer any and the car is much more pleasant to race.

[meanone]

I ran a full 3" exhaust that had 3.5" head pipes back to the crossover with MagnaFlow mufflers. One day at the track I put the caps back on and made two passes through the exhaust. My car slowed almost 2 tenths and 2 mph in the quarter.

[455firebird1969]

Two tenths is what I saw between full exhaust or open headers. I'd guess half of that comes from the weight difference. A 3" system with two mufflers and and over the rear tailpipes is not light.

It sounds like you need more converter too.

[beemergary]

MT told me not to do a dry hop after burn out with same tires.

[Tim Corcoran]

put the old cam back in and old headers back on with a Victor and an 850 Holley