Rear Gear Recommendation For Viper T56

[AU Doc]

I've got a Viper T56 that I'm planning to put in my 69 Camaro. I'm getting close to deciding what I'm going to do for a rear and I need to pick a gear. Ultimately the car will have an LS swap, but it's currently got a plain old SBC.

I believe the Viper T56 has the 0.5 6th gear, so I'm leaning towards a 4:10 rear gear. I think that'll put me at about 1800 rpm at roughly 70 mph in 6th.

Does that seem reasonable? Should I consider less gear?

[silo84]

I have an GTO 6 speed (t56) in my 94 blazer with a ls1 and 4.10 8.8 in the rear I can start out in 3rd and still get out of the way of traffic, so I definitely wouldn't go any lower than a 4.10.

Maybe a 3.73, that would put you at 1700 RPM with a 26" tall tire

what year viper t56? so I can find the 1-5th gear ratio and compare to GTO t56 and make a better recommendation from my experience

[AU Doc]

I'm not sure what year. It's a Borg Warner unit, so pre 1999 (I think that's right). The trans tag is missing as well.

[TomsResto]

Just had a similar question/thread over on the automatic transmission side ... https://www.pro-touring.com/threads/...gears-in-700R4

Some good links to couple online calculators where you can throw tire height, final gear ratio, etc. against various rear end gears and get your rpm/speed, etc. that should help address your question.

[AU Doc]

Thanks! I've toying around with some of the online calculators as well. I suppose the question I'm trying to answer is what rpm is idea for cruising at highway speeds? Approximately 70 mph in 6th gear.

I think for my case, that will pretty well set the rear gear.

[TomsResto]

Thanks! I've toying around with some of the online calculators as well. I suppose the question I'm trying to answer is what rpm is idea for cruising at highway speeds? Approximately 70 mph in 6th gear.

I think for my case, that will pretty well set the rear gear.

Lot of factors there... exhaust note, tire pattern acoustics rolling on various types of asphalt vs concrete pavements, whether interior is dynomated, etc.

Since this isn't my daily driver I tolerate quite a bit of what others would call "noise"/drone by daily driver standards ... but at the same time, if I was regularly driving an hour+ at 70mph I personally wouldn't want things much over 2,000rpm because by the time I have the windows down, the headers/free flow exhaust breathing 2,000 revolutions a minute and two 10" subs in the trunk pushing some rolling stones through the rear seat my ears would be ringing like I just left a rock concert if the exhaust note was louder and the stereo had to go up even louder :D

[TomsResto]

Lot of factors there... exhaust note, tire pattern acoustics rolling on various types of asphalt vs concrete pavements, whether interior is dynomated, etc.

Since this isn't my daily driver I tolerate quite a bit of what others would call "noise"/drone by daily driver standards ... but at the same time, if I was regularly driving an hour+ at 70mph I personally wouldn't want things much over 2,000rpm because by the time I have the windows down, the headers/free flow exhaust breathing 2,000 revolutions a minute and two 10" subs in the trunk pushing some rolling stones through the rear seat my ears would be ringing like I just left a rock concert if the exhaust note was louder and the stereo had to go up even louder :D

Guess to add on to my last point you have to decide what you want to hear in what order of priority ... do you want to "hear" your car/exhaust making it's own music for you, and everything else is secondary. Or do you want to ensure you can hear your music at highway speed without having to have stereo volume up to what would be an uncomfortable level at idle. Do you want to enable a general conversation about nothing important about whoever is in the passenger seat without them raising their voice to talk to you while at 70mph (i.e. do you want to hear everything the wife has to say when you are in your car, or make her think about what topics are worth raising her voice to convey while in the car... maybe sharing that story about that annoying co-worker can wait for some other time when you aren't in your happy place driving your favorite ride)

[AU Doc]

I'm to the point where I don't have to hear the exhaust nearly as much as I used to. After having a 94 cobra with exhaust dumped under the car as a daily driver for years, I'm ok with quiet on the interstate.

However, with a 0.5 overdrive, it looks like I'd still be rolling along at 1800 rpm at 70 mph. I'd like to go with a numerically lower gear just to get my driveshaft speed down, but I don't want to end up lugging the motor at highway speeds. So how low (rpm) can I go before I have to start worrying about stressing the motor?

BTW, here's a cool calculator that has several different transmissions with gear ratios already built it.

Edit: If I go with a 3.91, that'd put me at about 1700 rpm at 70 mph. Not sure if that's too low or not.

[rchaskin]

I have a gen1 small block (425hp) with a LT1 style T56.
2.66, 1.78, 1.30, 1.00, 0.74, 0.50 Ratios with a 3.73 rear and 255/40/18 Tires.
I dont think they could be any better.
1st gear will kill the tires, and 6th will run 75 at just under 1900.

[AU Doc]

That's a good point. 75 mph is a more realistic cruising speed around here (more like 95 in Atlanta ).

[Craig@Bowler]

One other factor to consider in your final drive RPM is what your cam will allow for. Most mild and stock cams can handle cruising along at low RPMs 1500-1800 range, but I've seen some engines that aren't happy under 2600(extreme other end). So be sure to factor that in as well just so you don't end up with any unpleasant surprises. But otherwise I think you're on the right track as far as gear ratio selection.

[Z06vet]

The GTO 6 speed has steeper ratios than the viper (if its the .50 OD gearset in the viper). I'd go 3.90 or 4.10 without question. I run the Fbody T56 with 4.10s and 335/35/18 rear tires. 2100rpm @ 80mph. 22-23 mpg with a head/cam LS3. I've run 3.73 in my car & driven several others with that setup, and for me personally its not enough gear. The car is so much more responsive, and keeps it in the meet of the powerband in every gear. I say this thinking of your future plans of an LSx swap. My old C5 Z06 with the M12 6 speed (like the GTO) with steeper ratios, 3.73 was perfect.

[AU Doc]

Thanks for the info!!!

Any issues with driveshaft speed/vibrations?

[AU Doc]

One other factor to consider in your final drive RPM is what your cam will allow for. Most mild and stock cams can handle cruising along at low RPMs 1500-1800 range, but I've seen some engines that aren't happy under 2600(extreme other end). So be sure to factor that in as well just so you don't end up with any unpleasant surprises. But otherwise I think you're on the right track as far as gear ratio selection.

I missed this reply. This is what I'm looking for. I suppose I can shoot for 1800 rpm at 70, and should be pretty safe. I'm planning for a well mannered street car, so radical cams are out of the picture.

Thanks!