[ctsb]

So the long and the short of it is, I now have a TH400 trans which also required a custom length/built driveshaft to link up to my stock auto rear diff.

Id like to swap to the M6 rear diff for the 373 gears for my build, but I just want to make sure the diff's are the same size/specs, or will i need to get another drive shaft made?

Im sure this may have been talked about already but i could not find the exact answer in the search bar.

Thanks in advance.

 

[MrSurly]

Same.
The stock driveshaft part number is the same for all GEN2 Vs in all three body styles and both transmissions. Aftermarket shafts for use with OE trans and diffs are all the same, no matter how you mix and match trans selections.
Your custom shaft will should fit the 3.23 and the 3.73 the same.

 

[MrSurly]

I'm curious the path that led you to the TH400(?)

 

[ctsb]

I'm curious the path that led you to the TH400(?)

Thanks for the info, very much appreciated.

What lead me to the 400 was over 1000 to the wheels on blower only and about 1400 on nitrous. I know people claim the 6l90 can handle that but for me, it did not. Then i had one built and ran into a bunch of trouble codes with the TCM and it just became a nightmare trying to chase it down. I did not really want to go to the 400 but it was what I knew could handle what Id be throwing at it and what would have the longest life.

 

[MrSurly]

Well a well-built 400 is a beast, you shouldn't be breaking it anytime soon. Have you considered swapping planetaries to drop low gear from 2.48 down to 2.75?
Although it doesn't matter, as NONE of us is sweating MPG, especially we of the 427 guild... but I just couldn't help thinking that if there were a 'worst MPG' prize, man, between building a fire-breather 427, losing TWO overdrive gear ratios, losing the lock-up converter AND looking at a 3.73 gear... you have really stepped up your game!

 

[Rubber Duck]

I'm curious the path that led you to the TH400(?)

Good Choice in my opinion: If built correctly, you won't break one, with the typical HP / Torque these engine platforms make.

Well a well-built 400 is a beast, you shouldn't be breaking it anytime soon. Have you considered swapping planetaries to drop low gear from 2.48 down to 2.75?
Although it doesn't matter, as NONE of us is sweating MPG, especially we of the 427 guild... but I just couldn't help thinking that if there were a 'worst MPG' prize, man, between building a fire-breather 427, losing TWO overdrive gear ratios, losing the lock-up converter AND looking at a 3.73 gear... you have really stepped up your game!

Just for discussion purposes:
These engines are typically InFlow restricted.

Increasing the numerical value of a gear, such as trans or rear gear, serves to multiply torque.

-regarding street driven cars-
These cars cannot be fitted with a sufficient tire size for drag racing, especially with the modified high-power engines some build.

Because these engines are InFlow restricted, and they use a DD / PD Blower, they make huge low engine rpm torque numbers. However; the fwHP (Peak HP Engine RPM), will be limited because of the restricted InFlow; <=TB & Small Blower. We see this happen in two stages: 1) VE% turns over just past peak torque rpm number. 2) Induction system gives up once cylinder fill reaches ~100% to ~120%. This is given as %VE.

--------------------------------------------------------

With the above in mind:
Should we actually be considering using a Numerically Higher Gear Ratio?

Would this not increase torque at lower engine rpms; <=Spin Tires Easier!
Would this not serve to decrease the Peak MPH Capability of these cars.

Simply food for thought..

Cheers

 

[ctsb]

I’m not sure what the gears are inside the trans. I got the transmission from Mikes in southern cal and just told him what the car had and what we would be doing. He took it from there. As far as the rear, the tuner said 373 would be better than the 323’s not to mention the stock rear I had has been through some stress. So just decided to go and get a new one from gm

 

[MrSurly]

I’m not sure what the gears are inside the trans. I got the transmission from Mikes in southern cal and just told him what the car had and what we would be doing. He took it from there. As far as the rear, the tuner said 373 would be better than the 323’s not to mention the stock rear I had has been through some stress. So just decided to go and get a new one from gm

Good plan!

 

[Rubber Duck]

I’m not sure what the gears are inside the trans. I got the transmission from Mikes in southern cal and just told him what the car had and what we would be doing. He took it from there. As far as the rear, the tuner said 373 would be better than the 323’s not to mention the stock rear I had has been through some stress. So just decided to go and get a new one from gm

Just another viewpoint to consider. . .

I don't know who Mike is, but he stated:
"As far as the rear, the tuner said 373 would be better than the 323’s"

If a car is properly geared (rear gear) with, let's say 500 rwHP,
and you add, even another 50rwHP, the car's rear gear will most likely have to be changed.

If your car has 500rwHP, and your friends car only has 450rwHP,
the two cars will require a different rear gear (and most likely a different tire) at the track.

How does one actually know which gear is correct for one's car?
Go to the track and find out..

Finally; these cars make 'Extreme' torque once modified.
Fully modified, these cars can exceed 800 ft Lbs of Torque.

To put a perspective on this; an NHRA 500 CID NA Engine, makes around 865 ft Lbs of Torque.
But it makes, right about 1500 fwHP, while these engines will struggle to make +900 fwHP.

The equation for calculating rear axle torque is:
((Engine Torque * Trans Gear * Rear Gear) / Tire Radius)

And we find that the NHRA 500" Engine, producing maybe only 65 ft Lbs more engine torque, uses a tire that is substantially taller, and about 44% wider. The taller tire helps to kill the torque (via the formula given above) while the wider tire helps to plant more rubber to the track.

Also, for the record:
Horsepower is simply Engine Torque, multiplied by Engine RPM.

-regarding street driven cars-
Since it is difficult to put a tire on these cars, that can handle even 750 ft Lbs of torque, why would one consider increasing rear axle torque, by multiplying the engine torque more?

Possibly it relates to the car's engine torque not being sufficient?

 

[ctsb]

Just another viewpoint to consider. . .

I don't know who Mike is, but he stated:
"As far as the rear, the tuner said 373 would be better than the 323’s"

If a car is properly geared (rear gear) with, let's say 500 rwHP,
and you add, even another 50rwHP, the car's rear gear will most likely have to be changed.

If your car has 500rwHP, and your friends car only has 450rwHP,
the two cars will require a different rear gear (and most likely a different tire) at the track.

How does one actually know which gear is correct for one's car?
Go to the track and find out..

Finally; these cars make 'Extreme' torque once modified.
Fully modified, these cars can exceed 800 ft Lbs of Torque.

To put a perspective on this; an NHRA 500 CID NA Engine, makes around 865 ft Lbs of Torque.
But it makes, right about 1500 fwHP, while these engines will struggle to make +900 fwHP.

The equation for calculating rear axle torque is:
((Engine Torque * Trans Gear * Rear Gear) / Tire Radius)

And we find that the NHRA 500" Engine, producing maybe only maybe 65 ft Lbs more engine torque, uses a tire that is substantially taller, and about 44% wider. The taller tire helps to kill the torque (via the formula given above) while the wider tire helps to plant more rubber to the track.

Also, for the record:
Horsepower is simply Engine Torque, multiplied by Engine RPM.

-regarding street driven cars-
Since it is difficult to put a tire on these cars, that can handle even 750 ft Lbs of torque, why would one consider increasing rear axle torque, by multiplying the engine torque more?

Possibly it relates to the car's engine torque not being sufficient?

I have a 15 conversion on the rear with a full slick, have not tested it yet but at this point the car is a full race car. The rear will also be replaced when I get some more money for a built rear. A friend works at the dealer and was able to get me the new 373 rear end for a price and since my rear has seen better days, it made sense to get the 373 rear for now. At least in my eyes. Also, it should be noted the car has the full holley dominator system with traction control and all the features that come with the holley system. so hooking may not be as hard as it seems.. only time will tell..

 

[Rubber Duck]

Thanks for the additional info…😊
As you say, we will see…

More food for thought. . .
Let’s say the tire is going to stick hard now.

If one is making X amount of horsepower, at X Engine RPM,
to use a higher numerical rear gear, one must increase engine rpm.

If one shifts at the same engine rpm, but makes more horsepower, then one must decrease rear gear numerically.

Agree?. .