Tom I don't think there's any allowance for tire growth , anytime I check mine the calc comes out tighter than I see on datalogger. Dubuick How much gear do you have in the car? It may want more . Like Tom suggested, My 69 ran 9.80's at 132 Best 60ft was a 1.29. You may drop et with no mph change by changing gears , Your finish line rpm probably won't change that much either as the converter will become more efficient. Dave
Dave is right. The data logger in my old race car told me the same thing. Convertor slip will change when you change gearing. When my my car was running mid to high 9s, I tried 4.56, 4.30, and 4.11 gears. The finish line rpms did not change as much as the calculators predicted. Although the exact numbers are fading in my memory, I believe the 4.11s gave me about 11% slip, the 4.30s gave about 9%, and the 4.56s gave me about 8% slip. All of this with the same motor and Coan convertor (4600 stall, around 6500 through the traps). As far as tire growth, I also believe that the formulas don't account for it. A call to your tire manufacturer may help here. Until you really get up there aound 130 mph or more, I doubt if tire growth accounts for much. I would also expect that 32" and 33" tires will grow more than a 28" or 29" would. As mentioned in an earlier post, the new radial slicks do not really grow at all.
I was in line to get a Coan 9" but after a few weeks of waiting the stator they wanted to use for my application they didn't have and Craig was honest to say he could not built it. From that alone I WILL buy my next one from him for true honesty. So I was talked about PTC in Alabama (performance torque converters) I was running a TCI 8" and I had over 18% slippage with best of 1.43 60 footer and 132 mph. I tried PTC 9" and we got down to 1.37 60 ftr and 2.5 mph in the 1/8 and 3 mph in the 1/4 with about 3-400 rpms down. But still have a 10.2% slippage, a best of 9.80's at 136 mph Now I have another custom made PTC 9.5" an half inch bigger and hopefully get the slippage down another 5%. I should crap my pants with these one if it leaves like we think it should. So far I have had good luck with PTC but will see next time out. I guess one day I could try a Coan to really compare. I might just borrows MIke Nussells and see what it likes!!!:laugh: ps: I'm the converter trying fool I can change them in my sleep, at the track, on the trailer, anywhere, just make them better and faster and I'll try it.
I run 4:11 gears and a with a tire that is 29.3" tall 92"cir trap rpm is at 6900 and with a 30" tall 94 cir it was 6750 .The thing is that ati told me that the convertor i have is not to be used with a trans brake and that a 9" would slow the car down. and i have read on here many time that lots of buick guys are running 9" convertors so that is what made me want to shop around . Hopefully it works out .I have wanted to try a gear change but I was thinking to with 3.73 I thought I go with 4:30 or4:56 the trap rpm would be over 7000 even change in tire height made a diffenrtance 150 rpm that is also what is making think the 8" I have is just wrong for my set up.The convertor worked great when the car weight 3700lbs and only ran 10.80's @ 121 ou:
The New Converter seem to work out great so far only ran 1/8 mile but right of the trailer 1.36' 6.31 107mph and it was 80 degrees + sicky the air was 2700 feet with the front tires 4' in air :kodak: got a little scary got to put limiters in the front end try to keep it down. The last run on the 8" was a 6.35 at 105mph and the air was better and the tracck was much better so can't wait till the 21st there a buick shoot out at New England dragway anyone from here going?
ill be at new england hopefully with the new car, I am still looking for a decent short block to throw my heads and intake on until finishline wraps up my motor. Dubuick whats your current engine combo. Thanks Herb
The Converter is great right were it needs to be 1.36 60' 132mph at 6600rpm and ran 10.003 in the heat so soon will have a 9 sec slip....thanks for the info..:TU:
have you figure out the total slippage percentage? I was at 10.5 and have the new one in but haven't made it to the track yet. Hopefully it will be around 5-6%. That should help me even more and another 1 to 2 mph. You are where I was just at. I could off tasted that 9 second pass and the new tight 9 inch got me there to a best of 9.85 at 135 mph at 6700 rpm. Looking forward to 137-138 mph with this new 9.5 inch converter they say about the same stall of 4700 rpm and we'll see what she does. I'm waiting on new front springs, the old one had no stored energy and car just could come out worth a ****. With the trans brake at every different rpm the best was 141 then with out no changes only leaving on the foot brake and the car carries the front tires pass the 60ft mark with a 136 60fter. So I have a bunch to improve with suspension then I can start bringing the 2 step up and up to give it a good kick in the ass and make my slug jump out. We have messed with rear and front shock adjustment and not much changes, no doubt we are in for a shock with new springs. I'll keep you posted.
