Which gears!?????

ridelikehell · #1 (**permalink**) 09-20-2003, 07:53 AM

I've just purchased a kit up here in Canada and I am at the point where I need to make some final desicions so I can have everything ready when the kit is delivered. I've decided to go with a carbed 302, with a new cam, and edelbrock intake and carb...with that in mind, and considering the car weighs 2200 pounds, I can't decide which gears to use in the rear...I'm leaning towards 3.55's or 3.73's...I'm not going to be racing the car, but it will be driven on a semi-daily bases and to cruise nights... I want it to "get up and go" when I pound it, but I don't want to turn the car sideways whenever i lay on the gas....any suggestions would be great!

--Dave.

Bob In Ct · #2 (**permalink**) 09-20-2003, 09:35 AM

What are your transmissions ratios?

I've got a Tremec 5 speed with a 0.68 OD. I have it in front of a 3.73. If I had it to do again I would go with a milder rearend. In first gear it's too low with the Tremec. At 60 I turn about 1850-1900 RPM on 275-60-15 BFGs.

Bob

ridelikehell · #3 (**permalink**) 09-20-2003, 09:55 AM

Bob, I don't know for sure about the tranny ratios yet, its off to the rebuilder next week...I figure I'll just stick with the stock gearing...(It's a T5)...I'm hoping to get around 300 hp out of the motor so I thought that since I'm not pushing HUGE power that'd I'd be better with a 3.73???

Thanks for the input so far

--Dave.

Jack21 · #4 (**permalink**) 09-20-2003, 11:04 AM

For a 302, I would tend to lean toward the 3.73's for torque on demand.

That being said, go back to your trans rebuilder an ask him to install the T5Z, close ratio (2.95 first) gearset along with the other Z options such as steel throughout bearing retainer. Retain, however, the .62 (or .68) fifth gear. This will give you good cruising with the 3.73's in back.

Stock T5 gearing is based on the stock gears in a stock Mustang, 2.74.

If you decide to go with 3.55's in back, use tha smaller OD fifth in the trans (.80) or your RPM's will drop too much when cruising.

For comparison, I'm running a 351W so the engine has more torque. Rear gears are 3.55. Trans is T5Z with .80 fifth. My highway RPM is 2300 - 2500. Even with the close ratio 2.95 first, I tend to short shift it to second for normal driving.

Excaliber · #5 (**permalink**) 09-20-2003, 11:36 AM

302 EFI, basically stock motor here. 3.55 gears, 5 speed with .8 OD. Don't know what my first gear ratio is but 25-30 mph and it's time to shift.

Worried about not being able to "bring the rear end around" on demand from the throttle? I have NO problem doing that, in fact I STILL have to drive the car "heads up". If I punch it in a corner or grab second gear to hard it WILL break the rear loose and put the car sideways.

I believe the .8 over drive IS the "tall gear" ratio, by the way. I wish I had the .6 ratio which is a little "lower" allowing more RPM at cruising speed. .8 is common, .6 you have to specify!

3.73 with MY LOW first gear ratio would be WAY to low!

Ernie

Cal Metal · #6 (**permalink**) 09-20-2003, 05:22 PM

Dave:

A 2.95 is still a very low gear. A true close ratio would be in the 2.20 to 2.40 range. A WIDE ratio Toploader uses a 2.78 first gear.

As Jack21 pointed out, stay with the .80 OD. The .68 is useless with a 302. You don't have enough low to mid range torque to make it manageable when cruising at 70 mph. You will be downshifting to make it up every small grade.

Excaliber · #7 (**permalink**) 09-20-2003, 06:50 PM

,,,,boy am I confused over the .6 vs .8 over drive gear ratio now!!!!

I gotta get my calculator out or something.

.8 over drive make the engine turn lower rpm at 60 mph, ie a "taller" final gear ratio?

.6 is "shorter", the engine turns a higher rpm at 60 mph?

Less downshifting on "hills" with a .6, more downshifting on hills with a .8 ?

......man I thought I had a handle on this, now I'm not sure!

Ernie

EDIT: Got it! .68 is higher mph gear than .80, heres the link.

http://www.prestage.com/Car+Math/Gea...H/default.aspx

6650 rpm with a 30" inch tire and a top loader (1 to 1) with a 3.0 rear ratio = 198 mph

An interesting number, if you know what I mean!

Dwight · #8 (**permalink**) 09-20-2003, 07:13 PM

I HAVE A 5.0 EFI + - 370 HP. I HAVE A TKO WITH 3:55 REAR END. AT 70MPH I'M TURNING ABOUT 2000 RPM. I HAVE TO DRIVE AROUND TOWN IN 4TH GEAR. I HAVE ALL THE POWER I NEED FOR HILLS. FOURTH OR 5TH GEAR NO PROBLEM. MY BUDDY MIKE HAS ABOUT THE SAME ENGINE IN HIS FFR, BUT HAS 3:73 GEARS. I THINK HE DOES A LOT BETTER AROUND TOWN. NEXT TIME I'LL GO 3:73.

SPRING FLING FOUR, I CAN WAIT!!

Jack21 · #9 (**permalink**) 09-20-2003, 07:48 PM

Cal, given the two gearsets available for the T5, the 2.95 first is the close ratio set. And is only available as an aftermarket retrofit gearset, or a complete new transmission, the T5Z. And even the T5Z is available with both wide ratio (3.37 first), and close ratio (2.95 first).

Close ratio T5's were not installed in any production cars, so forget about picking one up in a wrecking yard.

Keep in mind that the factory Stangs had 2.74 rear gearing which explains the wide ratio first in the trans.

Agreed, true close ratios in the 4 speeds of yore had 2.20 first gears, and were coupled to 4.11 rear gears. Don't think the cars could go much over 90 MPH top end, and were totally impractical on the street, but thats what guys were buying in '57 - '63.

Ernie. Now for the fifth or overdrive gear. Stock, over-the-counter fifth gear is a .62 in the stock T5's, and T5Z's. Optional gearsets that can be retrofitted is the .80. (And there may be others like a .75)

Keep in mind that for mostly stock Stang use, given the tall rear gearing, very mild cam, and EFI; 70 MPH cruise at 1600 - 1800 RPM in fifth is fine. Not so with a Cobra (or modified Stang either). Modified Cobra engines like to be kept over 2000 RPM when cruising. (My 351W pulls like a diesel from 1100 RPM up, but is happier as revs get near 3000 RPM. Can go into fifth as low as 40 MPH, and not have to downshift for passing unless I'm in a hurry.)

Fortunately, T5's enable you to dial all this in. (Tremec's, unfortunately, do not.)

There are a lot of guys out there running Tremecs for their alleged strength over the T5Z's who are not overly happy with the gear ratios available. For over 400 cubic inch applications the Tremec may be a good compromise (provided you've looked at the Richmond 5 speed also). For 302, and 351 motors, including strokers, I think the T5Z (with the gearset you want) is a better way to go.

Discussed this at length (T5Z vs Tremec for the street) with Liberty Racing Transmissions who I bought the blueprinted, .80 fifth trans from. Joe Liberty has been doing this for 30 years so he ought to know. The T5Z he blueprinted for me shifts like a Honda. It's phenominal!

The way I drive, the trans will likely last 100,000 miles before rebuild time. If I go the 393 stroker route, or break it horsing around, I'll be talking to G-Force about a gearset and bearing upgrade good to 600 HP for the T5Z.

Junket · #10 (**permalink**) 09-20-2003, 07:48 PM

I think you got it Ernie the higher # U go on the rear end 3.55 3.73 4.10 the faster the engine goes and the closer you get to 1.00 on the trans. 1.80 1.68 the faster the engine goes.

Ken

squeeeg · #11 (**permalink**) 09-21-2003, 01:37 AM

FIrst of all I would go with more then a stock t5 trans. They aren't built for that much power. A stock 5.0(225hp) will kill a t5 in just over 100k miles. I would recomend upgrading to a t5z(93 cobra) or a tremec transmission for the added reliability.

I would def go with 3.73 gears they really give all the power you want still keeping the driveablity

347 · #12 (**permalink**) 09-21-2003, 03:03 AM

I am running a tremec 3550 with 4.1 rear end
1st is short,its over in a heartbeat,second is over in 2 heart beats
at 66mph in 5th 2500rpm with 26inch wheels

I am running a 347 with a 248@.050 cam power range around 3000plus

I would say go for the 4.1's,they will give awsome acceloration,its very very cheap power
but maybe you dont need to keep your engine rev's up!

Bob In Ct · #13 (**permalink**) 09-21-2003, 06:14 AM

Hey Excaliber:
I think you have it backward, 0.6 is a taller gear than is 0.8. Both are taller than 1:1. 0.6 will result in fewer RPM than will 0.8.

Bob

Excaliber · #14 (**permalink**) 09-21-2003, 09:57 AM

Bob, your right! I DID have it backward! .68 IS taller.

I originally was using this formula:
mph = (rpm x tire diameter) / (gear ratio x 336)

For "gear ratio" I used 1.68 and 1.80, which WILL result in misleading numbers! I THINK you should use the "rear end ratio" for "gear ratio". But that doesn't seem to work either!

See the "link" in my EDIT section for a great calculator!

Ernie

DonC · #15 (**permalink**) 09-21-2003, 10:24 AM

For theoretical gear/rear end/speed results I've found the following calculator to be a lot of help. Remember, these are theoretical values, your results may vary, but it's a handy starting point for comparisons.
www.torinocobra.com/gearratio.xls.
It has macros in it so you'll have to enable them if you've got them turned off or set to warn if they're present but it's a clean program.
DonC

djseed · #16 (**permalink**) 09-21-2003, 10:39 AM

I have a 501 in the SPF and .68 overdrive in the T5. For me, any gear numerically lower than 3.73 would make it terrible on the highway. If you build a radical engine (high lift mechanical cam, high compression and single plane manifold) you will not be able to use 5th gear unless you are doing 80 or 90 mph. You can always scream around in 4th but that seems like mechanical cruelty. In town you can pick your poison - 2nd to 4th. My engine thumps along at 1500 to 2000 on the highway. I have a mild hydraulic roller cam, 9.9 to 1 compression and a dual plane manifold.