John To Answer your question I have had 4 different brands of 9 inches in my car for some reason I seem to be able to drive through them. Three of those were not mine so I could not have them worked on. They might have been able to get them right. The converter that is mine he worked on three different times to the conclusion that with the weight to power he was over his head and could do nothing more with it. Mind you it still works but it slips about 11% so the car is off a little with it in and revs a bit higher. PTC is who is doing the converters for me now, they build converters for Bob Curren and Tony Bishoff both are top extreme street guys in the NSCA. Their cars run 190 + mph at 3000 pounds so I figured this guy knows his stuff. We tried 9-inch converters and they were pretty harsh in the transition. Locked up hard and early. He looked at time slips and the combo after some deliberation He felt that the 10inch (its actually 9.5 on the box I looked today) would transition better on the short side of the track for better short times. He said he could get the smaller converter to work for me but thought It would still not be as good as the 9.5 I have now. I guess he was right I'm very happy with how it was working at Cecil Like I posted earlier it was up a full MPH and the rpms were down 300 to 350 over the others. I've read and been told the efficiency of the smaller converter on the top end is a big issue. I know some of these really fast guys in the nsca are running pretty large converters to get them to work right the weight is a big factor I think. I don't want you to think I know anything about converters I don't. I just work with the converter guys and let them tell me what I need so far I'm happy with everyone I've worked with even my old guy new he was past were he could help me and told me to try someone else and see if they could get me were I needed to be. I don't know if I answered your question John with all this but I hope so.o No:
Hey Bobb, The weight you guys are trying to push has to put quite a load on those torque converters. A few years back I talked with Carl Rossler (automatic trans top sportsman racer and trans builder) about the converter in my 464 powered Skylark. He said that my little 464 was making the TQ of a 540 Chevy but wasn't producing enough HP to pull it through the top end and therefore I would probably never be happy with any converter I put in the car. So I can imagine you guys having converter issues with the heavy cars. Another thing that could cause excessive converter slip is (rear gear/tire dia.) choice. Having a tire that is to tall with a rear gear that is to low will cause the converter to work to hard and therefore it will slip too much. Just for giggles I through together some numbers. Let me know if any of these are close for your car. Combo #1 29" Tire @ 136 MPH 4.10 gear = 6450 driveshaft RPM + 7% converter slip = 6901 engine RPM 4.33 gear = 6800 driveshaft RPM + 7% converter slip = 7276 engine RPM 4.56 gear = 7200 driveshaft RPM + 7% converter slip = 7704 engine RPM Combo #2 30" Tire @ 136 MPH 4.10 gear = 6250 Driveshaft RPM + 7% Converter slip = 6687 engine RPM. 4.33 gear = 6600 Driveshaft RPM + 7% converter slip = 7062 engine RPM 4.56 gear = 6950 Driveshaft RPM + 7% converter slip = 7436 engine RPM Combo #3 31" Tire @ 136 MPH 4.10 gear = 6050 driveshaft RPM + 7% converter slip = 6473 engine RPM 4.33 gear = 6400 driveshaft RPM + 7% converter slip = 6848 engine RPM 4.56 gear = 6700 driveshaft RPM + 7% converter slip = 7169 engine RPM Which of these combos is close to your combo? If any? I am sure you have been through this but I am a bit bored and need something to think about. :grin: Later
John Do it again with a 4.22 gear and 6% and you will be there with a 30 in tire 92.5 circ. Man I have run more numbers than you can imagine.
Hey Bobb, Here are the figures.... Starting with a tire circumference of 92.5. 92.5 divided by Pi (3.142) =29.44 diameter tire So..... Combo #4 29.5" Tire @ 136 MPH 4.22 gear = 6525 driveshaft RPM + 6% converter slip = 6916 engine RPM 4.22 gear = 6525 driveshaft RPM + 7% converter slip = 6981 engine RPM 4.22 gear = 6525 driveshaft RPM + 8% converter slip = 7047 engine RPM 9% converter slip = 7112 engine RPM 10% converter slip = 7177 engine RPM 11% converter slip = 7242 engine RPM OK... thats it... I have been on vacation for a few days and I find myself sitting here crunching numbers.... I have to get out in the garage today or I am gonna go crazy :laugh: Take Care
Jerry what do you mean? and where were you at the B.O.P. this year we came all the way down there to race with you and you were a no show. p p
Bobb, Great... now we have the combo kind of nailed down. Soooo... lets throw out a few more ideas!!!!! Just for giggles. Combo #4 with the 4.22 gear with a 29.5 tire @ 136 MPH we know has as converter efficiency of 6%. Lets change the rear gear to a 4.33. I say this because I am sure your engine will make some additional power up to 7200 rpms. Sooo.... 7200 minus 6% converter slip (with the higher gear the converter may even become more efficient... maybe 5% slip??) = 6768 drive shaft speed. With a drive shaft speed of 6758 and a 4.33 gear with a 29.5 tire should = 137 to 137.5 mph. At 137 mph you should ET in the mid to low 9.70s. :3gears: That pig would be flyin!!!!! Thanks for playin along! Later
John To be honest what I've looked at is going to a 4.33 with a true 30 inch tire(94") and try to spin it to 7200. If I was going to go a direction that might be the way I would go. But unless you have forgaoten my car has to go to the body shop for awhile if that was going to happen. LOL
Convertor Slip Good thread guys. On my BBB tube chassis GN, if I changed rear gears only, the convertor slip was a good bit different. I would calculate how much rpm change should take place (with the same convertor slip), but it never actually happened that way. My convertor slip would vary from about 12% w/ a 4.10, 10% w/ a 4.30, and about 8% w/ a 4.56 gear. These numbers are rough ones from my ever worsening memory. I was on my 5th convertor before I got into the 7% range (this is a car that only weighed 2400 lbs). This convertor was an 8.5" built by a Super Gas racer named Greg Slack, and was about $1100! It stalled at 5500 w/ my Stage 2 482", and locked up great at 7000rpm in the traps. Interestingly, when I think back on the 5 convertors I went through, the price seemed to track the quality and performace pretty close. It seems that every couple of years, convertor technology really improves. I would suggest that just about anyone out there with a really old convertor needs to look into a new one (and save up some serious $$$). Jeff Peoples
