3.91 or 4.10? Help Me Decide

[67Satty]

I'll be ordering up a center section in the next month or so for my '67 Satellite Street/Strip car. The particulars of the motor are in my signature. The trans has a 9.5" Dynamic Street/Strip converter. I'll run 9X28 slicks at the strip. I'll be driving it to the strip, maybe 50 miles away. Other than that, I'll take it to cruise nights. I'm not worried about RPMs on the highway, more worried about best ET at the strip. It will be raced on both 1/8 mile and 1/4 mile. :HappyNewYear:

 

[696pack]

You need to check one of the one quarter mile calculaters. To be as accurate as possible with the calculater you will need to know you h.p. rear end ratio, launch and rpms at shifts. You can use the same info sans the rear end ratio to compare the two different ratios you are considering.

You need to determine where your cam peaks, where you want to shift and at what RPM you are going to launch at. With slicks (screwed to the wheels) for max 1/4 mile you will probably need to launch around 6,000 if the track has good traction.

With my Hemi car It bothers me to launch at 6,000 rpms as it is terribly hard on the whole car, engine, trans, drive line, and body. My Hemi has the original engine. It being 1 of 11 built I can't bring myself to do it. I don't want to invest another $20,000. in a second engine just to race it so I think I am going sell it and just race the 6 pack car in a F.A.S.T. type class where I am forced to run factory type tires and it will be much easier on the car due to the launch tecnique.

 

[Commando V8]

There is'nt a big differnce in 3.91's to 4.10's on the street, maybe a hundred RPM's or so @ 60 mph. But in the 1/4 mile, you don't want to be taching out on the the top end, slowing your mph. I went with 4.10's in my street car with no regrets. Depends on your RPM range. Good luck and happy racing!

 

[69 Runner]

Unless you burn it all up in your converter you'll want the 4.10's for the quarter....especially with a 28" tall tire. I can tell you a 440+6 really WANTS (and runs best with) a 4.10, even with something short like a G70-15 tire.

 

[Rob R]

There's a 1/10 of a sec differance in ET between 3.91 and 4.10 if that's any help.

 

[RacerAL]

I've experimented with a few different gear raito's..everything from 3.91 to 4.30 in my car over the last year..and the et gains or loss is minimal from 3.91 to 4.10..at least for my car...the real question is how many rpm are you willing/wanting to turn..not only through the traps but your shift points as well..Will your combo spin at 6500 rpm's.. live and make power.?the intake you have listed is good for 6500,as well as the cam you have listed(actually alittle more).If you think it will stand that much rpm,and your soley looking for et gains..go with the 4.10's...IMO...all of my experience is with a 30x9 tire..my car is spinning about 6200 or so w/ the 4.10's..i'll be going to 4.30come spring..should get me an extra 300-500 rpm..which is real close to my 6600 i'am hoping to get...hope this helps............AL

 

[383man]

I run 4.30's in my 63 street car. I use 29 x 11.5 Hoosier QTP tires and I drive it everywhere including to the track. I tach about 3200 at 60 mph and it dont bother me at all as I did it all the time in the 70's. There wont be much difference between the 3.91 and 4.10's. If cruising rpm bother's you go with the 3.91's but if you want the best 60 ft go with the 4.10's.

Hey Al our cars are alot alike as I run a 906 headed .030 over 440 (446) with the MP .557 cam. I use the Holley Street Dominator intake with an 850 DP and my best et is 11.52 @ 116.84 so far. And my 63 weighs just over 3700 lb's with me in the car. Ron

 

[RacerAL]

yea Ron,our cars combo's are pretty close..what rpm are you turning through the traps..and what rpm are you shifting at?...if you don't mind sharing....love your car!!!!!...........AL

 

[four40cuda]

4.10 will be fine..I have 4.10 in my cuda with a 28 inch tire turns 3600 rpm at 70mph

 

[383man]

yea Ron on cars combo's are pretty close..what rpm are you turning through the traps..and what rpm are you shifting at?...if you don't mind sharing....love your car!!!!!...........AL

Al I am shifting about 6200 and trapping about 6300. It seems to like that best. I really like your car also and would love to see some bigger pics of it. And thanks for the kind words. Ron

 

[ykf7b0]

You want the 4.10 gear because that will work better with 9.5 converter. If you had stated that you were running a 10 converter I would suggest the 3.91. Having said this, the optimum 1/8 mile gear would be the 4.57 but the 4.10 will be great in the 1/4 mile. Either way the 3.91 will be a minor step backwards especially with the 9.5 converter. I've learned this through my experiences and I think it will apply to you as well.