Think about this before you look for HP

[LS1GN]

I was so excited about building a motor for power in my GN clone that I devoted all my energy to the engine and didn't spend a lot of time thinking about the rest of the car.

In the two years since it has been on the street (and strip) I have gone through 3 rear ends, and 4 transmissions. This car makes a real-world 480 foot lbs of torque and has a propensity for shredding the drivetrain.

I currently have an 8.5 10 bolt with a girdle and 30 spline axles and am praying it will hold up.

I paid a lot of money for a "race" 4L60 which quickly went south. After two or three trips for warranty repairs the trans shop said my engine power output wasn't designed for my choice of trans.

So I saved and got a Turbo 400, indestructible, right? Now it is slipping in 3rd gear.

 

[Chris Van]

You'll be fine with the 8.5 rear end. Providing it's set up right.
Same goes for the 400 trans. Did you have it built or just find a used one and put it in? A built 400 trans will stand pretty much what any mild street/strip car will throw at it.
My 8.5 rear took many years of transbrake launches. But it went from breaking a gear every couple years to breaking one every couple of months so I went with a 9 inch.

 

[chevy2480]

Cant speak for the TH400 because I am running a TH350 with a transbrake have launched at 3800 off the brake still going strong 2yrs later. Now I can speak for the 8.5 rear. My 8.5 has moser axle,spool,cclip elims and a girdle has over 200 passes on this setup and probably another 400 on the stock posi and axles that where in it. Only reason i removed the stock stuff was posi was toast. Car currently is running 11.18-11.23 on this rear never misses a beat. With the stock setup it went 11 .52-11.68. I think from my experience it will be fine.

 

[JBreu]

I think you'll be fine with the 8.5, I've seen really built cars with that 8.5 and they have never haad an issue with them. The 12 bolt rear is also a pretty much bullet proof rear end and I have one and don't think I'll ever hurt it. I believe that your TH-400 or even the O/D transmission you have, so long as built right will handle what you have. You never said where you got your transmission. You oughta check out CKPerformance.Com , they build excennt stuff. Btw, what numbers on the Dyno does your car have?

 

[pontiacgp]

before you change the transmission make sure the hose going to the modular isn't collapsing and cause problems with shifting. The original line was made of hard line so it would not be affected by heat and collapase

 

[clean8485]

I have a friend who owns a 1987 Monte SS. She was seriously bitten by the drag race bug. She started out with the stock powertrain, then went through a couple of built up small blocks. She modified the 200R4 and stock 7.5 axle, but started breaking the rear control arms. Long story short, she decided to go big block, and installed one of the GM 502/502 crate engines. When she had the engine installed, she went for a Dana 60 rear axle, with 4.10 gears and a complete ladder bar rear suspension. That part of the car has held up well, with no problems. She was still trying to use a very well built up 200R4, but breakage became an issue, so she went with a built up 4L80E, with a full manual valve body. She does drive the car on the street (not much), but she has to do all of the shifting both up and down manually. She hasn't had any driveline breakage issues since the 4L80E was installed. I know its a bit overkill for most people, but it worked well for her.

 

[LS1GN]

before you change the transmission make sure the hose going to the modular isn't collapsing and cause problems with shifting. The original line was made of hard line so it would not be affected by heat and collapase

Thanks for the help, the vacuum line is mostly steel with rubber hose on the ends.

I got the turbo 400 through Summit. It looked "brand new" to me even though GM hasn't made one in a decade or two.

 

[LS1GN]

I think the 3rd gear clutches cant take the revs - it shifts at 6500

 

[lilbowtie]

There is something wrong in the trans and its not the RPM's. Had one behind my 350 for 5 years racing w/no problems and know
people tossing a lot more that that at them.

 

[thrasher]

Yea a correctly built 400 should easily take that power.
You might want to take a peek over at http://www.chevelles.com/forums/
A lot of guys making that power and a whole lot more over there as it's a BB dominated forum