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This is going to be my setup:
'74 convertible
LS3 480HP
T56 Magnum SST kit. I haven't decided on close or wide ratios yet.
Std 3.55 or 3.73 differential. I haven't decided. It's currently being rebuilt so I can choose whatever I want.
295/50R15 tires on Ridetech offset trailing arms. (I think they should fit)
My concerns are that this is a convertible and I don't want it to sound like a diesel at highway speeds. I care more about the 0-80 range than high speed racing. It'll probably have a decent muffler on it as I removed the sidepipes due to excessive noise for a cruiser. I enjoy brisk acceleration more than top speed but I'm worried about getting too low a ratio if I can't use it due to being traction limited.
I'm leaning towards the close ratio T56 with 3.55 rear-end. However, it runs about 500 RPM more at highway speeds than a base C6.
3.73
dont want to lug it hard, not good for it. I have 4.11s and sometimes wish I had even more gear.
I'm assuming that a stock manual C6 with 3.42 rear end, the same LS3 I am using and an overall taller ratio than a 2.66 T56 + 3.55 isn't lugging at 70MPH on the highway? Or maybe it is? I have an A6 C6 so I never pay attention to what gear I am in on the highway.
I'm assuming that a stock manual C6 with 3.42 rear end, the same LS3 I am using and an overall taller ratio than a 2.66 T56 + 3.55 isn't lugging at 70MPH on the highway? Or maybe it is? I have an A6 C6 so I never pay attention to what gear I am in on the highway.
Multiply the rear ratio by the 1st gear ratio.
10.0 or close to it is the commonly preferred total.
Look also at your power range of your cam and make sure the 5th and 6th gear do not drop out of that range when comparing engine rpm and highway speed.
Me personally, I have 2 T56 from LT-1 Camaros 93-97 converting over to LS1 versions and will be coupled to 4.11 rears.
Based on my personal experience with my 505 NET HP 427 SBC LS7, these motors like to and can rev extremely low with zero issues...that is how they can have tremendous power AND great fuel economy. I can rev my C6Z06 to 7,000 RPM and cruise all day at 1,700 RPM at 80 MPH AND get 28 MPG doing it. Any speed less than 65-70 MPH, I use 5th gear and 6th for anything over 70 MPH. BTW-The Z06 pulls fairly well in 6th gear at 1,700-1,800 MPH on the highway..most of the time I don't even have to downshift for a moderate pass on a car....5/6th gears are for cruising, nothing more on the street. 1-4 are for acceleration, not the OD's. There always seem to be much confusion over OD's on the forum for the street. Road racing is different.
My LS7 has a .50 OD 6 speed with 3.42 gears. You certainly do not need 4.11's or even 3.73's with that motor and power. I can spin the tires in my Z06 with traction off , MOVING, in 1, 2 or 3rd gear. Why would you want a gear numerically higher than 3.55 with that type of power?
You mention 480 HP? Is that Gross or Net like the factory rating?
My recommendation would be go 3.55 gears, no higher, and you can chose between wide or close ratio T56's from there. With 480 HP and a 3.55 gear, you are looking at acceleration like my 10 C6Z06 in a C3 body.....good luck with that on the street....Personally, if you are not racing, go wide ratio. Ditto, no 3.73/4.11 unless you are racing which you said clearly you are not, just cruising with occasional acceleration blasts.....My 2 cents of practical experience with what you are asking...
You mention 480 HP? Is that Gross or Net like the factory rating?
Since it's a crate engine I would imagine it's gross HP.
Originally Posted by jb78L-82
My recommendation would be go 3.55 gears, no higher, and you can chose between wide or close ratio T56's from there. With 480 HP and a 3.55 gear, you are looking at acceleration like my 10 C6Z06 in a C3 body.....good luck with that on the street....Personally, if you are not racing, go wide ratio. Ditto, no 3.73/4.11 unless you are racing which you said clearly you are not, just cruising with occasional acceleration blasts.....My 2 cents of practical experience with what you are asking...
This is kind of my reasoning. I'm assuming the Z06 went with the base ratios and not the Z51 ratios because it was already traction limited on tires that were 1.5 inches wider than the Z51. I won't have the rubber that a Z06 has, nor the traction control so unnecessarily shorter gears will end up being wasted. However, what do I know, as all my Vettes have been auto up to this point so I have no experience with it.
Multiply the rear ratio by the 1st gear ratio.
10.0 or close to it is the commonly preferred total.
Look also at your power range of your cam and make sure the 5th and 6th gear do not drop out of that range when comparing engine rpm and highway speed.
Me personally, I have 2 T56 from LT-1 Camaros 93-97 converting over to LS1 versions and will be coupled to 4.11 rears.
I've never heard of that rule of thumb. A 3.55 with narrow T56 is 9.5, with a wide it's 10.5. Thanks for the info.
I've never heard of that rule of thumb. A 3.55 with narrow T56 is 9.5, with a wide it's 10.5. Thanks for the info.
For whatever it is worth, those formulas in my opinion are a very broad guideline since a big V8 (I mean any SBC BTW is a BIG V8) does not need hugh torque multiplication to get a car going like a weak 4 cylinder etc. My L-82 close ratio Super T-10 with a 3.70 rear has a first gear total ratio of 8.99 which is essentially useless ...Can't imagine a10+ total ratio for the street.....
For a street motor, I think there is enough tq to pull the wide ratios for the first 4 gears.
Since i would like to do a half mile or full mile event.
I would want 5th-6th to be close ratio to get some top end.
I actually have...worthless for a STREET car, in my opinion....
my 2.87 X 4.11 first gear was so easy to drive. Look at how many mph that you can do in first gear. I learned how to make it through an intersection stop light drag racing even with my 427 motown and street tires. Oh I have a light flywheel. You hardly slip the clutch
with OD trannies. You just have to worry about top gear rpm and speed first gear just falls where it falls
On my BMW E36 LS/T56 magnum swap I ran 3.91 gears and first gear was mostly worthless. Almost all the time I started out in second.
Was that a 2.97 first gear or a 2.66 in the T56 Magnum?
If 2.97 then the ratio was 11.61 which is pretty high....more like a truck that needed the torque to get moving. Much like my father's old 72 C10.
If 2.66 then the ratio was. 10.40....big difference.
Since it's a crate engine I would imagine it's gross HP.
This is kind of my reasoning. I'm assuming the Z06 went with the base ratios and not the Z51 ratios because it was already traction limited on tires that were 1.5 inches wider than the Z51. I won't have the rubber that a Z06 has, nor the traction control so unnecessarily shorter gears will end up being wasted. However, what do I know, as all my Vettes have been auto up to this point so I have no experience with it.
Ok I'll give this one more try since you seem to be on the right track with your thinking.
Above ^ is the 78 owner's manual and the gear ratios used on the L48/82. For my L-82 with Stock 220 Net HP/260 TQ @ 3,600 (earlier L-82 were TQ at 4,000 RPM which is what I produced on the Dyno, not at 3,600) with my 4 speed close ratio Super T-10 1st gear is 2.43 X 3.70 Rear gears=8.99 total ratio, which is barely useful, even with the L-82 that does not have good bottom end torque. I have always tried to get out of first as soon as possible since it is barely useful on the street, this outcome with the stock low TQ L-82. I cannot imagine the L-82 with the wide ratio 4 speed 2.64 first X 3.70=9.8 total ratio, since it is probably worthless BUT GM made VERY few L-82's with this combo. BTW-With the stock L-82 motor/4 speed combo, I never had an issue starting from a standstill with either no throttle or very little to get the car moving .....another words the 8.99 TQ multiplier with this V8 (TQ again) was still over geared. The rebuilt/upgraded L-82 355 has MUCH more power/TQ and I rarely have to use any gas from 600/700 RPM from a stop with the clutch with this gear box/rear but get out of first quickly....I could easily start with 2nd gear with the current combo with this engine...no problem, which is NOT what you want.
Even more bizarre is the L-48 which not only has more TQ 280 BUT at a much lower RPM@2,400. The L-48 has good bottom end (but dies at mid RPM) and GM coupled the L-48 wide ratio 4 speed with this motor with 2.85 1st gear X 3.36 rear gears=9.6, again way too high for typical street driving and this motor that had great TQ at a low RPM, even with these relatively V8's, especially the L-82, with poor bottom end TQ.
I have had so many conversations with 4 speed C3 owners over the years that just use their C3's as hobby cars and often complain about the useless 1st gear ratio, like I have been trying to explain FOR THE STREET, not racing. We all wonder why GM made first gear so short...even with V8's. Heck it was not a 4 cylinder Monza with a standard transmission like my brother had in high school with zero TQ..that car needed these ratios.
Granted almost 475 TQ @ a fairly high 5,000 RPM BUT this motor probs has BIG TQ at a very low RPM since the peak is 473 TQ @ 5,000 RPM. My 10 LS7 has 470 TQ @ 4,800 RPM. YOU WILL HAVE NO ISSUES WITH A LOWER TOTAL RATIO FIRST GEAR. NONE! The Z06 gearing is not only great on the street but well suited to racing, as one would suspect since the C6Z06 is a track car for the street.
Based on my personal experience with my 505 NET HP 427 SBC LS7,
My LS7 has a .50 OD 6 speed with 3.42 gears. You certainly do not need 4.11's or even 3.73's with that motor and power. I can spin the tires in my Z06 with traction off , MOVING, in 1, 2 or 3rd gear. Why would you want a gear numerically higher than 3.55 with that type of power?
If you haven't tried something, you really can't comment on it. It's like saying I own a hopped Volkswagen beetle. It is the only car you'll ever need! Why would anybody ever want a water cooled big V-8!
I also have driven and raced Your LS7 and your posters LS3. No you don't have anything in the way of power compared to the now 625, 650, and above supercharged Vettes. I've worked on my friends 67/LS3 480hp TKO 600 .64 OD 4.11 I don't consider it a power house. I got on it once and the motor went dead. rev limiter shut off the motor for like 2 seconds. I have a sequential rev limiter so I can hear it. Then even 4.11 equipped doesn't have the jam that lots of guys 383 stroker motors have. I'm not sure what you resistance is to progress? Also if you have traction problems in 2 and 3rd gear? You just don't have enough tire under it. I have NO problem driving my buddies I think 2007 ZR1with the traction control off, but he uses very sticky tires.
12-06-2018, 10:41 PM
Opinions on which T56 ratio and rear-end ratio?
Why would anybody ever want a water cooled big V-8! 
