SBF Gear Recommendation Please

[FireSale]

I'm going to scrap the 3.89 gears and Detroit Locker in my 3355 lb Mustang and am looking at a spool and gear combo for a Strange Pro Iron 9 inch carrier. 28 spline street gears will probably do it strength wise but I could afford the 35 spline Pro Gears that would require a different pinion support. More $$.

Does a "built for SS/MA 302" that pushed a street legal car to a best ET of 12.65 and a top speed of 116 mph need all that beef in Pro Gears?

Axles are 31 spline alloy Strange street. Tires are 26X10 MT at the present time. 28s for the next set now that I know they will fit.

I'm thinking 4.29 or 4.56 as a gear ratio.

Thanks in advance.

Dale

[Sean Marconette]

Dale,

The issue I ran into with street gears in my 8.8 stick stocker was stress fractures of the pinion teeth. Your engine will make quite a bit more power and not be as violent as a stick car, I would run a Pro gear if available.

Sean

[pmrphil]

With an automatic car that runs 12's (or even 11's) a pro gear seems unnecessary. Don't forget that the pro gear will wear much quicker than a standard gear, and while we're at it, needing a pro gear when using only 31 spline axles is kinda overkill as I see it.

[FireSale]

Thanks for the info. Forgot to mention that the trans is a C4. Current converter stall is 3500 (I drive it to the track). That will be replaced with 4500 or above as part of the differential upgrade.

Index for GT/MA is 11.75. Looking for 11 flat or better to be competitive around here.

Dale

[Lou Jeffery]

Standard gears will be more than sufficient. I ran a 8 inch rear axle in my Maverick going 11.30s, only upgraded to a 8.8 for more ratio options.

[HR9121]

I would also think the standard gears would be fine also and I would think you would need the 4.56 to get you up in rpm power range also.
I ran a 302 in a fox body bracket car, it was only 2950# but ran a 30" radial like stockers run and ran a 4.88. It ran 10.50-10.60 and would trap at 6900-7200. With those little motors rpm's are your friend.

[Chris1529]

what kind of RPM do think its going to run? I'd look at a 4.86 at least.
probably lean toward 5.14

[FireSale]

Originally Posted by Chris1529

what kind of RPM do think its going to run? I'd look at a 4.86 at least.
probably lean toward 5.14

The Comp Cam that is giving me the mid 12's at 105 ish is a solid roller with a 3000-65000 power band. It's on the way out for another solid roller that will give me at least 7000 in the traps. I'm currently maxing out at 5500 when I hit the lights so I'm not using the power I have on tap. According to AFR the AFR 1399 heads I have will take up to a .600 lift cam. Looking at Crowers that are rated at 4000-8000 and 3000-7000 and Lunatis rated at 4400-7500 and 4400-7200. The Dynamic Compression Ratio from the Crower cams would be 8.9 and 9:1 respectively and the Lunati cams clock with a DCR of 8.6:1.

My block is the Ford Racing M-6010 BOSS302 4 bolt main rig. My machinist went nuts over it. Rods are forged Crower Sportsman from the Accepted Products list and the crank is a forged Eagle. I pulled the heads recently after a season of driving to the track and bracket racing and everything looks brand new.

The bottom end is underused.

I used gear calculators based on 7000rpm and 28 inch tires to determine speeds for gearing. I know it doesn't factor weight and HP, but it was all I could find to mess with. 4.56 gave me 128 and 4.29 gave 136. 136? OOPs too fast, scratch that. 4.86 yields 120 and 5.14 is good for 113.

Dale

[Chris1529]

To run 11.00 or better in your car, its going to need to run about 119 MPH.
I think you will find that the motor will want to run at least 7500 RPM and that is taking it easy on it.
Even switching tires with differences in roll out will make a big difference in how the car performs or doesn't perform.

[stang321]

I run an aluminum head 302 with 4.30 gear shift at 6500 traps at 6600 its runs 12.30s with a 26 inch tire I would go with 4.88 or 5.14 if you change to 28s