What gear to run in my 9"
 

I was thinking of changing my rear gears. I mainly drive it in the city with some hwy but not a lot. What rear gears would you all run if you had this set up in a 61 Impala (4000 lbs)........



ENGINE
-383 stroker 442hp/470ft lbs of torque )
-Chevy 350 bored 30 over and stroked to 383ci
-Scat crank 3.75 Stroke Cast 9000 series
-Scat 5.7 forged I beam rods with 7/16 arp cap screws
-Forged Flat top Probe Sportsman Race Series Pistons
-Comp Cams Roller Cam Duration-Intake 230deg Exhaust 236deg @ .050 / Lift Int .510 Exh .520 and 110 lobe separation
-Air Flow Research 195cc Heads 74cc chambers
-9.7:1 compression
-Headman Block Hugger Headers
-Holley Fuel Pump
-Speed Demon 750cfm Carb Vac secondaries
-Polished Air gap Intake
-Edelbrock aluminium water pump
-MSD Plug Wires
-All Bolts Are ARP
-Mini Starter
-Edelbrock double roller timing set
-Comp cams roller lifters
-Crane cams roller rockers
-Full Mandrel bent Flowmaster American Thunder exhaust With 50 series deltaflow mufflers


CHASSIS
-700r4 tranny
-3170 rpm Edge Racing 9" converter
-B+M super cooler tranny cooler
-9 inch ford rear end
-Auburn Pro series limited slip
-Air lift easy street air ride kit
-4 wheel disc brakes
-18x7 in front and 20x8.5 rear Intro Twisted Vista Wheels
-Boxed trailing arms in rear by spirit engineering

And the dyno specs....

Intake center line 105 1/2
jets 76 front 85 rear
vac sec spring short yellow
timing 35 deg
RPM----HP---TQ---A/F--Vol Eff%

3900 - 328 - 442 - 13.3 - 97
4000 - 340 - 447 - 14.0 - 97
4100 - 356 - 456 - 14.2 - 97.3
4200 - 370 - 462 - 14.0 - 97.5
4300 - 381 - 465 - 13.9 - 97.5
4400 - 390 - 465 - 13.9 - 97.4
4500 - 397 - 463 - 13.8 - 97.4
4600 - 404 - 461 - 13.7 - 97.2
4700 - 410 - 458 - 13.8 - 97.1
4800 - 416 - 465 - 13.8 - 96.9
4900 - 422 - 452 - 13.8 - 96.7
5000 - 427 - 448 - 13.8 - 96.3
5100 - 430 - 443 - 13.8 - 95.8
5200 - 433 - 437 - 13.9 - 95.2
5300 - 435 - 431 - 13.9 - 94.9
5400 - 436 - 424 - 13.8 - 94.6
5500 - 437 - 418 - 13.9 - 94.3
5600 - 439 - 411 - 14.0 - 94.0
5700 - 440 - 406 - 13.9 - 93.5
5800 - 442 - 400 - 13.9 - 92.8
5900 - 442 - 393 - 14.0 - 92.1
6000 - 440 - 385 - 14.0 - 91.5

you neglected to include tire specs and that makes it impossible to determine the effective gear ratio based on tire diameter.

I have a similar engine / trans / car weight -- I'm running a 3:70 Ford 9" and love the combo.

The "ultra deep" low gears of the 700r4 get the torque feeling going immediately - but the overdrive allows a nice cruise rpm at 2200ish. I'm running
25.6" diameter rears.

Note I mistyped the gear ratio as 3:73 and meant 3:70

I still think you're running LEAN btw... Typical best torque numbers are going to made at WOT with a number somewhere in the mid 12's on the A/F. Even in a modern EFI motor the WOT numbers are going to be far fatter than what your dyno run is showing.

I was at the dyno all day yesterday with a EFI 598 ci whipple supercharged motor - and when the A/F got anywhere near 14's the run got aborted. Now, we'll all argue about the fact that this is a supercharged motor and they like "fat", but my point is that 14's on a performance motor at WOT is quite possibly close to hurting something.

Thanks greg the car is going on a chassis dyno in the spring when I get the motor back togeather and re tuned in the car so I will adjust then.

My bad they are a 27" tall tire. I for some reason am not getting the email notifications for the forum so I missed your reply.

Stick with what Greg said for best all around performance. If you want better city "Red Light to Red Light" driving, you could go with a 3.89. Have fun with it!

Well I already have the 3.89's in there now and definitely do not want to go to a taller gear so maybe I will just stick it out with the 3.89's.........

Greg,

I had togo see my engine guy due to some other issues I have right now with my heads being porous and asked him why my #'s are lean. he said with the brake specific numbers and the fact that it was dynoed at WOT with open headers out of the car that it will be running richer in the car. He also said just by looking at the chambers on my heads that I should be real close if not a bit rich..........Just a fyi for his reasoning. I still plan to chassis dyno it to dial it in, IN the car.

Kevin