1.69 low gear

[afuelcoupe]

well that now makes sence to me........I should have asked about your combo before I assumed anything....... I agree that the change to 4.71 would be a good move with the 1.69 low...... its not much help on the starting line but you should net a sizable gain with the shorter 1-2 split allowing a longer run at first gear as well as caring a higher level of enertia into the shift much less RPM drop at the shift keeping the rpm up where the engine is happy....

[JrFuel Hayden]

OK Bill, I've been running a 1.68 [ light carrier] 1'st gear for about 6 years. We changed from 1.76 because we could hit the slicks a little too hard sometimes, so 1.68 helped off the line, helped with tire shake, and the motor would climb quicker after the shift because the drop between 1.68 and 1:1 is closer. Our 60' improved too.
So here are some RacePak numbers;
 Hemi,1.68/ 4.56, ET 7.21, shift 9317, converter flash [ after shift] 7960 rpm , 185.4 mph, @ 9214 rpm , 31x12x15
 Hemi 1.68/ 4.71, ET 7.22, shift 9444, flash 8462 [ looser converter] , 184.2 @ 9500, 31x12x15
 Hemi 1.68/4.56, ET 7.07, shift 9130, flash 8037, 189.4 @ 9400, 33x12x15 tire
 RR SBC 1.68/ 4.88, ET 6.99, shift 9660, flash 8700, 188 @ 9921, 31x12x15
 RR SBC 1.76/ 4.71, ET 7.06, shift 9879, flash 8108, 188.5 @ 9700, 31x12x15
 The converters are flashing at different RPM's because of different 7" converters, but keep in mind more HP = higher flash points.
 Hemi makes 870 HP, RR SBC makes 850 HP, but 100 lbs lighter than Hemi

1.76 x 4.56 = 802 start-line ratio
1.68 x 4.56 = 7.66
1.68 x 4.71 = 7.91
1.68 x 4.88 = 8.20
1.80 x 4.56 = 8.20, but less 1/4 rpm, and more likely to spin tires at hit.

I hope this info helps !
Jon Hansen

[masracingtd1167]

Jon That's exactly the kind of imformation I was looking for ! I am really not sure where my motor falls of because I have never dynoed it . My heads are old Comp eliminator 18 degree heads Done by Jimmy Bell and they flow very well 391 cfm at 850 lift so I think this thing wants more rpm . Thank you so much for the info ! Bill 

[JrFuel Hayden]

Bill, WOW 391 cfm, that's more than my RR iron SBC heads flow, 357 cfm, so yes I think your motor wants more RPM. We run 9500-10,000 rpm. The more the heads flow the better it runs at higher RPM. In some cases the more they flow, you need more RPM so you can get the air speed you want for more HP. Parks A/ND 14° Chevy heads flowed over 440 cfm, so they needed a converter that flashes at 9200 rpm, and launch no lower than 9000. With their 5.37 rear gear the finish line rpm is around 10,500 . And they own the A/ND record at 6.76, but they need the high rpm to get enough air speed with their monster heads.
Your .850 lift is close to what we run .937" and again we run a lot of 7.0's, 189 mph with my 4.88, and 31x12x15 GY .
I assume you have good valve train parts for higher rpm. One tip we learned is for years we used Ti valves with a SS tips, but our team and other teams learned that when we started running 10,000 rpm, the tips broke off at the retainer grove, so we all run solid Ti valves with lash caps, no more problems.
Ask your cam guy what rpm range you should be running at, no sense over rev it beyond it's power band.
Have Fun !

Jon Hansen, Hayden Wheels

[wideopen231]

Jon and Bill, 

  Since you both run SBC hitting 10k are.I have a question have either of you ever ran the lash cap /lock piece.I think you both will know what I am talking about they are made so lash cap is made as part of the locks. Not to jsck thread but since Jon had mentioned valvetrain and I have these sitting here,thinking woule eliminate kicking lash caps off or breaking them,for what ever reason crap happens.