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newbie with new engine in my 81



I'm getting a new engine put in my 1981 vette. It's a 383 with 550hp. I'll be getting it tommorow (saturday) and I was wanting to know what I can do with it. The rear end was rebuilt about four years ago (I was 13 at the time, and didn't know anything about cars), and now my dad doesn't remember exactly what was done to it. He thinks they put just normal (stock) parts replacing the old stuff (maybe half-shafts, u-joints and that stuff? It cost us $1000, so they must have done something to it). It also has the stock transmission in it (I believe it's a th-350).

Well, with this new engine, I was wanting to take it to the drag strip every once in a while. I got to talking to the guy who is putting in the engine today, and he said that I should never drag race it because of the back end. He said I would throw it out really easily! I was really excited about this new engine......until I heard this. I mean, why have 550hp if you can't even use it?

Well, what I really want to know is how far can I push it without worrying about breaking anything? If I were to take it to the drag strip, how should I launch it? A brake stand, and if so, at what rpm? I'm really just worried about blowing out the back end, mostly because I have no money left to pay for it if I were to do any damage....but I also want to have a bit of fun with it. It's also a daily driver, and the only way I can get around. The guy said if I were to drag race it, give the new engine atleast 1,000 easy miles before I race to make it last longer. What do you guys reccomend I do? Could I atleast smoke the tires sometimes without worrying about it? And just how far can I push it?

If I do need a new back end, how much will it cost me for it to be able to take all this hp? Well thanks for the help! Anything you have to say will help me, anything at all.


Well-known member
Jul 3, 2001
Auburndale, Florida
1969 Killer Shark
Welcome to CAC.

We must think alike. I am shooting for 550 out of my big block project.

For once in a great while drag strip use, I don't think you have any problems at all. Remember, serious (like on television) drag racers rebuild the entire drive train inbetween rounds. Then again, they may push up to 3,000 hsp and they are running drag slicks.

Your best bet is to let your tires take the abuse. The problem with the rear suspension is that if you ever get a solid bite of traction with that kind of hsp, you might break something. However, that is the fun in this sport after all..........isn't it? That is taking chances and hanging it all our on the hairy edge of destruction?

There is little you could do different to the actual rear diff to make it any stronger for drag racing it.

I hope you are putting a higher stall torque converter in there while you are at it. I don't know of any small block that can make that kind of hsp at the lower RPM range. Meaning, if you want that car to run as fast as it should, you need to spin it up on the launch, let the tires smoke a little, and ease into traction as you launch around 3,500 RPM.

You are going to have a blast. Welcome to the family here, and please keep us posted on your adventures.


Welcome Lance007

Just a comment on the $1000 rear end work...
...you commented that you felt something must have been done for that amount of money. I personally feel that only what was neccessary was done, with nothing more spectacular added. Our rear diff change, with stock replacements, ran $1400 about 7-8 years ago.
Silver aka:Heidi

ps, have fun with your ride! ;)


Hi Lanceh007. I have a TH350 aswell. I have 3.55 gears in the back end. My vette mechanic told me that this setup should be able to handle up to 450-500 hsp. BUT no more. I will break things if I push it past that. That is just my $.02.

Scott :w


Well, the engine runs great. It barely fit under the hood! They put a Holley Street Avenger carb on the new engine, and when they went to put the old air cleaner on it, it wouldn't fit due to the big bolts on both sides of the carb, so they got some tiny little airfilter and just stuck that on there. I think the old style with the forced air induction thing is better, and I know that the new one won't do very good, but the hood is too low to get anything else under there. What would you guys reccomend?
I was thinking about getting one of those hoods with the big air scoops in it, and has a bit more rise, but how much would it cost to get one of those, and then get it painted? And where can I find one?
I was also wondering if anyone knows what the stock gear ratio is on my '81? Another thing is that we told them to put on a new Torque Converter on it when they installed the new engine...but somehow forgot!? Well, we're taking it back in the shop monday and getting them to put one on...but I was wondering, is the torque converter the same thing as the stall converter? They asked me what stall speed I wanted, so what would you guys reccomend? thanks!


Hello Lance. Good to see more power onboard. I think that stall speed concerning torque convertors is one of the most misunderstood performance upgrades. Things like vehicle weight, rear end ratio and the car's overall combination must be taken into account for the proper application. The listed advertised stall speed should just be used as a general guideline, so you should contact the manufacturer for the best advice. One torque convertor can create different stall speeds in a high or low horsepower car. Comp Cams has taken the initative to work with TCI (I believe) to recommend the right convertor with specific camshafts. There are a lot of tech lines out there, so use them to your advantage.

I think Heidi's advice holds the most truth. Never overestimate the work that was done, if you're not sure. Taking that into account, I would recommend that you not get so hung up on aggressive launching. This would prevent the fasest way to grenading that rear end. Since it's your daily driver and you have budget concerns, wait till you're ready to make the commitment. If nothing else, try finding a donor car with a numerically higher differential ratio, on the cheap. If you blow that up, maybe you won't feel so bad and will still have the original to fall back on. Of course, that's just my opinion.


Black Thunder

Well-known member
Oct 14, 2001
Port St Lucie,FL
1968 Black Custom Vert 454 BB
The 81 comes with 2.87 std & 3.07 optional. Either one should require less torque converter, stall speed than a car equipped with a more aggressive rear end.
Bullitts advice of contacting an application specialist at one of the major brands is wise. Also you must be ready to accept the slushy feeling of your A/T after one is installed. Some can't live with this, but its doing its job to keep the power only being absorbed when you nail it.
Your shifts will not be crisp anymore but your A/T will last longer. Get an aftermarket trans cooler as it will help & they are readily avaliable at Summit, Jegs, ect.
If you have any weak parts other than the rebuilt rear end you will soon know. Good luck & keep a fund going for tires :)

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