Rear end gears

[JP MEIER]

I have 302 bored 40 over with f 303 cam edelbrock intake and carb a t-5 tranny with a centerforce dual friction clutch spinning 215 gears with 2955015 tires.
The problem I have is shifting(4800rpms):
1st- 0-55
2nd- 55-70
3rd- 70-100
4th- 100-125
5th- Never needed to go there
I am thinking there needs to be more shifting, so I will have less stall or drag when transfering from one gear to the next? What would be a alternative gear. I love the quick get up but not the momentary drag I am experincing after shifting. I would also like to be able to lay a little rubber as required by fellow on lookers.

Please don't tell me to get a larger motor!
Thanks in advance for your input!

[CobraEd]

Never heard of 215 gears. Strongly suspect that you have that wrong. 215 gears are what they would use at the Bonneville Salt Flats :-) Double check the ratio by marking the tires and driveshaft . Then spin the tires one complete rotation and see how many times the driveshaft spins. For example, for one tire rotation, if the driveshaft spins just a little over three rotations, then you have 3.08 gears. If it spins two and three quarter times, you have a 2.73 ratio. etc etc.

Anyway. put in 3.73 gears and you will love the car. perfect ratio for a strong 302!! Don't forget the nylon gear in the transmission where the speedo cable goes in for the proper speedometer readings.

You will need to determine if you have a 9" rear or an 8.8" rear in order to order the proper gear sets. Everything I stated above applies regardless of which rear you have.

(PS. Get some good aftermarket aluminum heads and you will pick up a good 60-70 hp just with that alone. If you have stock heads with that manifold and cam, your heads are a big bottleneck).

Ed

[Excaliber]

The 1st gear ratio in a typical 5 speed is fairly low. The fact that you can run to 55 mph at only 4800 rpm does indicate you have a really HIGH rear gear. In my opinion WAY to high. I would think you could not even run 5th gear without lugging the engine rpm to low (unless your doing 100 mph ).

3.73 would give you a top speed of around 100 mph in 4th and overall with your 5 speed I think is a bit on the low side. Certainly would give you some tire spinning power all right! I'd go with a 3.5, which is more suited for the over drive trans (in my opinion), and still let you fry the tires.

The lower rear gear is a whole new ball game, a good ball game, but will come with problems. Like axle hop, loss of traction, much easier to "spin out" due to the tires wanting to break loose under power in a corner. After you change rear gears be careful driving until you get a feel for the new setup.

Concerning shift point. Yes the 302 with the cam you have starts to loose horse power after 4800 rpm or so. This is a great "torque" cam, not good for high rpm. I would recommend a shift point at 5000 or a little more because when you shift the rpm tends to drop to low for the next gear. My rule of thumb is: A couple of hundred rpm ABOVE max horse power rpm of your motor output. Granted MOST people tend to shift well beyond the point where their motor is still making good power.

[Ron61]

Both statements above are good. But if you change the rear end make sure you look at your axels and get the correct spline count.
I am running 3:27s in my car and love them, but I have quite a bit more power and torque than you do. Only problem I have is I picked the wrong transmission split for 5th gear. I went with the .6 and should have gotten the .8 as all my 5th is good for is crusing down the freeway. I can't break through that wall of air in 5th to even get close to my power band with my split, as it effectively brings my gear ratio to 2:10s, which as stated above are Bonneville type high speed gears. I tach 1900 RPM at 70 in 5th. Crap, if I could get to my power band in 5th I would be over 200 MPH and that wall of air would blow every huose within 50 feet of the road over.
But I also have no problem burning both tires in any gear except 5th. I don't do much of that though and then mostly by accident.

Ron

[Excaliber]

Out of curiosity sometime back I looked into what it would take to find one of those lower 5th gear OD trans.

Turns out there pretty scarce, most all of them run the .6 over drive. I was not able to find a single source for the .8

OR vice versa, I get it mixed up which number is the lower gear overdrive! But you get my point I think.

[Ron61]

Ernie,

The .8 is the lower overdrive as it is closer to 1:1 than the .6 is. Where my .6 changes my ratio to 2:10s I think the .8 would just change it to around 2:50s. I just got them backwards when I ordered the transmissioon way back then.

Ron

[The Dreamer]

Guys, he has a Venom, so he is using a BMW diff. I suspect that is where a 2.15 rear comes from.

JP,

I'm not familiar with what rear end gears BMW has available, but there are many gearing calculators out there that will allow you to play with the calculations. Here is a decent one:

Gearing Calculator.

I would look at how I drive and where are good places to require and shift play with to calculator to see what gear gets you close to what you want.

[relaxinrob]

The highest I would run is 3.27 and the lowest for the street would be a 4.11......IMO

[EarlsflyinCobra]

I did the turn test and my wheel turned twice to the drive shafts connections 2 3/4.....does this mean I have a 2.75?????????? Is that good or bad????????

[Excaliber]

Yeah, about that, you would be in the ball park doing that way. And 2.75 is pretty darn high!!! Anything in the "two's" is what you find in a typical automatic trans application. Anything in the 3's you could associate with a standard transmission. Anything in the 4's would typically be a drag racing application, limited top speed but quick acceleration!

With a BMW rear gear it must be hard to find a ring and pinion with the right ratio?

Run the Gear Calculator, use a 1 to 1 ratio for your final drive in the trans. That would approximate 4th gear. Assume a 25" tall tire. I haven't run the specs but I bet 4800 rpm, 25" tire, 1 to 1 trans ratio and 3.5 rear gear (all fairly standard numbers) would put you around 105 mph top speed. A nice over all ratio for street and SCCA "cone racing". 5th would work OK for the long straight away on a road course (assuming your engine has enough power to pull the gear).

Lets say your modest engine does not have "that much" power. So 105 mph in 4th and then you shift to 5th. The rpm drops a bunch but the speed may stay about the same! Not enough power to increase top speed with the "drag" of the over drive gear. I would not count on 5th for any other than a "cruise" rpm gear on the highway, which is worthless with your current rear gear!

[CobraEd]

a 26" tire is closer to the norm. 5th gear should be for cruising only. I - 4 for drag racing.

3.50 - 3.73 rear end would be great

[RallySnake]

JP,

I just rebuilt my Jag rear end. I pulled out the worn and noisy 3.31 gears and put new Dana 3.73s in. The 3.31 is a great cruising gear and gives great gas mileage. My 356 ci engine like to rev and the new lower rear gears gets me to 100 in 9 seconds, it's great!

But the primary reason for my choice is creeping up the 405 freeway in rush hour. I can idle in first gear at 5 mph, perfect! I use the .68 fifth gear a LOT more now, even cruising at 60. It should turn 3,000 rpm at 100 mph with 26.9 inch 275/60/15 Toyo tires. But, I haven't had a chance to try this yet. The acceleration is stronger and the gas mileage is a bit worse.

I am looking forward to my next high speed cruise (100+) when I find out what that's like. I have a feeling I should have gone for the 3.54 gears for that. Otherwise, the 3.73 is a great gear with the Tremec 3550 and an engine that likes 7,000 rpm.

Paul

[DC COBRA]

If he has the BMW rear end which I think the Venom has, unless it was ordered with posi-option I believe turning the tires one round and counting driveshaft rpm's will not work on open diffs. Most the BMW drivelines came with 3.15 gears pretty high geared my opinion. Mine had similar numbers as JP's when mine was geared with the 3.23 posi optioned gears upon delivery, darn thing would run 100mph in second at 7000 rpm. I have put 3.73 in a while back, completely different animal. Never have hit rev-limiter in fifth gear yet, pretty scary, but fourth gear at rev-limiter (7500) she does 135 mph, still pulling hard when she touches limiter quite exhilerating.

DON

[Excaliber]

Well, the numbers just don't add up for a FORD T5.
But they DO add up for a GM Borg Warner T5.

Assuming 26" tall tires and 2:20 rear gear and 4800 rpm = 55 mph in 1st gear.

Transmission Ratios, standard issue Ford T5:
1st gear is 3.97
1st: "3.97" 2nd: 2.34 3rd: 1.46 4th: 1 5th: 0.8
RPM\MPH 1st 2nd 3rd 4th 5th 6th
1000 9 15 24 35 44 0
1500 13 23 36 53 66 0
2000 18 30 48 70 88 0
2500 22 38 60 88 110 0
3000 27 45 72 105 132 0
3500 31 53 84 123 154 0
4000 35 60 96 141 176 0
4500 40 68 108 158 198 0 (this aint near 55 mph in 1st)
5000 44 75 120 176 220 0
5500 49 83 132 193 242 0
6000 53 90 144 211 264 0

BUTT, if it's a BORG WARNER T5 GM trans!
1st gear is 2.95

Borg Warner T5 with "2.95" 1st gear ratio (2.20 rear gear).
RPM/MPH 1st 2nd 3rd 4th 5th 6th
1000 12 18 26 35 48 0
1500 18 27 39 53 71 0
2000 24 36 52 70 95 0
2500 30 45 66 88 119 0
3000 36 54 79 105 143 0
3500 42 63 92 123 166 0
4000 48 72 105 141 190 0
4500 54 82 118 158 214 0 (Thats close to 55 mph in 1st).
5000 60 91 131 176 238 0
5500 66 100 144 193 261 0
6000 72 109 157 211 285 0

With BMW running gear that trans has GOT to be a Borg Warner. If it's a FORD T5 the rear gear would have to be like 2.00 for 4800 rpm to equal 55 mph.

This is the best calculator I've found BUT, you have to "register" to use the site. No cost, no personal info, but kind of a hassle. Turn off "Pop Up's" or it won't work.

http://www.smokemup.com/auto_math/mph_range.php

[JP MEIER]

Thanks for the input, I've been at work!
I do have a Venom with a BMW rear end.
I checked her out and she has one tire rotation to approx. 3/4 shaft roatation? I have plenty of get up 0-60 in less than 4 sec. However she stalls around 120 mph. and she bucks in traffic. I have to ride the clutch to go less than 10 mph or I start bronc riding a little em bare ass ing. So gentelmen whats the solution?

Side bar!!!!!!!!!!!!!!!!!

[EarlsflyinCobra]

Not trying to hijack the thread, just trying to get the same question answered;

I did the turn test and my wheel turned twice to the drive shafts connections 2 3/4.....does this mean I have a 2.75?????????? Is that good or bad????????

I am running a 302 and a T5 tranny...any help appreciated, Please.


And again, I am not trying to hijack the thread!!!!!!!!!!!!!!

[JP MEIER]

Side bar continued!!!!!!!!!!!

Venom Owners!!!!!!!!!!!!

While checking the rotation I noticed difflection on the tranny mount bracket. Upon further investigation the 1/8" steel (less than the thickness of a bed frame) was not only bent but tearing at the frame. I pulled it out and fabricated some 1/4" u channel for it, that ought to do it the clanging underneath I thought was wheel hop or something was the dang drive shaft thumping the frame when I added just a little torque. Ed was right! I checked and tightened up and inspected everything under her!

[CobraEd]

Yes, 2-3/4 turn is a 2.73 rear. Not too good at all (Sorry)

For those of you with a non-posi rear, you must mark and turn BOTH rear wheels one complete rotation and then count the rotations on the driveshaft.

Ed

[Ron61]

Earl,

Do you have an open or posi rear end. Cars rear end I mean.

You should just have to turn the wheel one turn and count the drive line turns. CobraEd is correct as two turns would equate to about 1.9 drive shaft revolutions per wheel turn. So you must have the higher gears. In 1964 Ford used mainly 3:00 - 350 gears in the Galaxies, so you can see that yours are somewhat high. The lighter car helps though.

Ron

[EarlsflyinCobra]

OOOOOOOOOOOPPPPPPPPPPPSSSSSSSSSSS, I meat to say the wheel turned once to the drive shaft couplers 2 3/4 turns.