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View Full Version : Gearing for my 'Dere


BelvedereII
09-25-2012, 10:26 AM
I've been racing at an 1/8th mile track, car is pretty much right where I want it as in Sportsman class (NHRA ET racing) you cannot dial quicker than 7.50 . Bad air gets the car into 7.8's, it's run a couple 7.5's in the spring and last year at the finals in Brainerd it ran a 7.49 as part of one of its quarter mile passes. In the 1/4 you cannot dial under 12.00, and the car has run high 11.90's with a best of 11.86 in a time trial. This year when we hit the 1/4 mile I dialed back the distributor a few degrees and the car ran 12.02/12.04, right where it belongs.

With the "official" racing over, I decided to see what a gear change would do and swapped out the 4.30s for a 3.55 set. Much better for driving down the highway to the local track, and I figured the car would get right around 8.0s. A friend with a lot of experience racing Mopars guessed maybe 7.85's. Wouldn't you know, first run was a 7.504. When the day was done, and the headwinds died down, it ran a 7.48 best. Obviously we had good weather last weekend for this kind of performance (MPH was in the ballpark at 90 and change) and one other potential variable is that I did not check the timing after dialing it back to where I have it marked on the block and distributor housing. Could be a degree or two additional in it, it's marked for 34 total.

Details are, the car weighed 3540lbs on Topeka's scale, has S/S springs, and the motor's a typical build as in Chuck Senatore's Big Block Mopar book. 440 .030" over, Holley Street Dominator intake, Demon 750, ported iron 906s, 10.25:1 pistons at .005" down, Racer Brown SSH-44. Shifts at 5400 rpm according to the chip in the shift light. Manual valve body 727, 9.5" Dynamic converter.

I called Dynamic to tell this tale, and the estimation is that the 440 is getting into a somewhat better launch RPM as the converter sees a different loading from the gear ratio change. Could be what kept the 60' time in line with the times from the steeper gears. I'm just glad to have the lower highway RPMs and no change to the overall performance.

http://lh4.ggpht.com/-y0-kijFM2Dg/UDKRKgATnmI/AAAAAAAAY8E/WYJ46RQPMjY/s800/DSC_1670.jpg
http://lh6.ggpht.com/-2bga0uUbrTc/UCnOdWUjELI/AAAAAAAAX_g/c05SRr0yM-4/s800/DSC_0894.jpg

BELVEDERE2
09-27-2012, 07:08 PM
Sounds good. Hoping to do the same thing to mine; go from 4.10s back to my 3.55s when I swap out my 340 for a 380. I was planning to take it to the track with the 4.10s just never have. Put alot of miles on the street though. Always was enjoyable with the 3.55s. Not so much with the 4.10s.
What's the stall on that Dynamic? Mine's 3k felt "different" when I had taller gears. Just wondering if that's normal for the gear change.

BelvedereII
09-27-2012, 11:53 PM
I haven't checked the stall of the convertor yet, it's run to over 3500rpm sitting in the driveway to check when it would overtake the tires in first, but the correct way apparently is to put the car in 3rd and whap the throttle to see where the RPMs climb and stay as the car accelerates. I haven't done that yet and in fact don't currently have a tach on the thing. Just a shift light with the 5400rpm pill. I should be getting a tach this week though.

GARYS69RR
10-06-2012, 05:46 PM
Those are some pretty fast 1/4 mile times, Belvedere II. This is Gary from Golden. How much faster do you think my 69RR with a 451 would go with headers? Currently have 12.5 to 1 C/R, 906 heads mild porting, Holley Street Dominator Intake, 700 dbl pump, 509 cam, 11" converter, 3.91 gears.stock ex manifolds. Fastest 1/4 mile has been 13.76@103. Thats at 5400 feet MSL, street tires, and mufflers un hooked.

BelvedereII
10-06-2012, 07:06 PM
That's a tough call, Gary, as I haven't done such an A to B comparison as that. Closest was a 318 Challenger with an automatic and factory single exhaust. It ran a 17.77 at under 80mph, and when I sold it to a friend who put duals on the factory iron manifolds he gained nearly a second in that same quarter mile. Headers in place of existing duals would have to be noticeable on your car with all of its mods though. Would likely sound better, too!

My exhaust is made up of TTI 1 7/8" headers and a set of Classic Chambered 3" Cobrapacks, dumping right in front of the rear axle. When I had the glasspacks installed and pulled out of the shop I couldn't believe the noise--resonates off the ground and throughout the interior. Figured the cops would pull me over first chance, but the guys at the muffler shop loved it. It's also not so bad outside of the car. I haven't done anything stupid on the street and the cops leave me alone, probably because I'm old compared to the high schoolers they seem to sit around waiting for. Harleys are louder than my car, anyhow.

Kirk

GARYS69RR
10-06-2012, 09:51 PM
Cool, now do you run thru your ex system when racing? Or pull the glass packs off? And it looked like the left front wheel was almost off the ground when you left the starting line. But there is a red box in the way. Couldn't tell, but sure looked like the tires are gettin off the ground! Must be those ported 906 heads and the 9" torque converter.

BelvedereII
10-06-2012, 11:58 PM
I'd like to run with the exhaust off once, but figure it'll only gain from the weight loss. I'd want some extensions in place at least, don't really care for straight open header sound in the other cars. I wound up with this current setup just so I could hear my own car at the track over the other racer's exhaust!

I've only seen air under the tire once, and that was a photo at the racing in Brainerd last year--most of the others look close, but no cigar. I think the tire's only in the air a millisecond and most photographers aren't that quick! ;)

cudabob496
10-07-2012, 04:30 AM
http://wallaceracing.com/calcrgr.php