how much HP can a 78 handle?????
Thread Starter
Burning Brakes
Joined: Jan 2006
Posts: 957
Likes: 6
From: Burlington wisconsin
how much HP can a 78 handle?????
I'm now looking at a Blueprint Engines brand crate motor, but how much horsepower can a "78" vette w/a stock TH350 with a Transgo shift kit, 3:55 gears & torque converter handle? I'm hoping at least 400 HP / 440 ft. lbs torqe, as thier 383 comes with. Am I going to break things? Comments welcome...
Instructor
Joined: Aug 2005
Posts: 218
Likes: 6
From: SF North Bay California
Depends on the condition of the rest of the driveline. If I was putting in a crate engine with 400+ hp I'd pull the rear-end and give it a serious once over. Make sure everything is in really good condition back there and if in doubt, swap it out.
Remember these years came with very low hp engines, so the driveline probably hasn't been stressed like an older vette would be...but its best to check everything to prevent future problems.
Remember these years came with very low hp engines, so the driveline probably hasn't been stressed like an older vette would be...but its best to check everything to prevent future problems.
Intermediate
Joined: Feb 2006
Posts: 37
Likes: 0
I put a 417ci SBC in my 78 also and at the time it still had the THM350 w/ a shift kit, ran just fine, but I didn't abuse it. But before I installed the 417 I had rebuilt literally everything on the driveline and suspension, and I mean everything. Since then I've pulled the THM350 and installed a Munice 4-speed. This thing is a blast to drive, especially with the t-tops removed. Have fun!!!!!!!!!
Drifting
Joined: Mar 2005
Posts: 1,806
Likes: 3
From: Burlington WI
Cool !!!
Originally Posted by cherrybombc3
I'm now looking at a Blueprint Engines brand crate motor, but how much horsepower can a "78" vette w/a stock TH350 with a Transgo shift kit, 3:55 gears & torque converter handle? I'm hoping at least 400 HP / 440 ft. lbs torqe, as thier 383 comes with. Am I going to break things? Comments welcome...
The TH350 will be ok for a while, depending on how much you "PLAY".
Chris B
Thread Starter
Burning Brakes
Joined: Jan 2006
Posts: 957
Likes: 6
From: Burlington wisconsin
Hey Chris,
as you can see I think I have my crate motor decision pretty much made ??? I just don't want to open a can of worms & find out I need thousands more in other parts, because of too much power. (Is there such a thing?) The rear end is being re-done @ Corvette Perfection in Beloit w/ 3:55's & Kevlar clutch discs. The trans I've had apart, she is a tight unit w/ a transgo shift kit. I plan on replacing the 1/2 shafts in the rear and all should be good. Well for a couple weeks
as you can see I think I have my crate motor decision pretty much made ??? I just don't want to open a can of worms & find out I need thousands more in other parts, because of too much power. (Is there such a thing?) The rear end is being re-done @ Corvette Perfection in Beloit w/ 3:55's & Kevlar clutch discs. The trans I've had apart, she is a tight unit w/ a transgo shift kit. I plan on replacing the 1/2 shafts in the rear and all should be good. Well for a couple weeks
Burning Brakes
Joined: May 2004
Posts: 1,201
Likes: 2
From: Frederick Md
Originally Posted by 74vettecvt
If I break something I "have to" buy one better than what broke.
It saves a lot of arguments with my wife....
It saves a lot of arguments with my wife....
I may be wrong...as I have only run each of my Corvettes a few times at the track...My 68 SS 396 Chevelle was my track car until I sold it last year to someone with more money then brains...
Anyhow... I always considered the Half Shafts as the weak point with Corvettes and the amount of Horsepower
one can put down...
Bob G.
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Michael S. Palmer
Race Director
Joined: May 2005
Posts: 10,674
Likes: 122
From: Millington Illinois
St. Jude Donor '08-'09
435 HP was available stock in 68, 69. The 1978 Differential has a larger pinion shaft and bearing, and larger 3" Half shafts than the older rear ends. This is the weak point on these cars and GM beefed them up in these areas even when the horsepower was declining in the later C3's The 78 differential is strong but needs heavier posi springs, a heavy duty posi clutch pack and a bigger cap with bigger bolts on the left side holding the pumpkin in. Should handle to 500 HP with street tires and can be built to handle more but it gets expensive.
Pro
Joined: Jun 2004
Posts: 700
Likes: 0
From: Lantana TX
Originally Posted by cherrybombc3
I'm now looking at a Blueprint Engines brand crate motor, but how much horsepower can a "78" vette w/a stock TH350 with a Transgo shift kit, 3:55 gears & torque converter handle? I'm hoping at least 400 HP / 440 ft. lbs torqe, as thier 383 comes with. Am I going to break things? Comments welcome...
Just my 2 cents... just installed a Year one motor 430 hp and 430 lbs of tq. The engines do not make much off the line until 3300 RMS so I would not be too worried about off the line rear end damage. I also have 3.55 gears and a 11" tci stall and it still is not great off the line. I am now swapping the 11" tci for a 10" puting me around 3000-3200 stall, which will hopefully wake it up finally.
BTW go to Year one and buy their 350 engine. I paid $2995 for what I received...look at my sig below.
Le Mans Master
Joined: Apr 2005
Posts: 6,360
Likes: 429
From: Seattle Area WA
Years ago I ran a 383 with Nitrous in my '78 with an Art Carr converter and B&M transpack in the TH350. I autocrossed it on weekends and drag raced it at the old Orange County International Raceway.
Basically I drove the snot out of it for 50K miles and never had a problem and it would run 12's all day in street trim.
Basically I drove the snot out of it for 50K miles and never had a problem and it would run 12's all day in street trim.
Tech Contributor
Joined: Aug 1999
Posts: 15,187
Likes: 4,008
From: Connecticut, USA
Those fiber clutches are junk. Use solid steels, no springs - tuned and polished carrier. The left steel brg cap is good but not needed with 400 hp, replace the stock brg hex heads with socket caps. You have to tap the LH brg holes perpendicular and 1/2-13 thread if you go with the steel cap and fit it to .001 rock. Solid sleeve is good, Heat treated 10-17's are better then stock but at 400- 500hp they should be ok. If you're getting a stock type rebuild you won't get any of these custom pieces, it will also cost you a lot more. Look up my post it will have a lot of pictures on all this stuff.
Gary
Gary
Racer
Joined: Dec 2005
Posts: 399
Likes: 0
From: Kearns UT
I've got the zz502/502 in my 78, they claim it has 502HP and I am having some issues now. My 4 speed Borg Warner is slowly dying, mostly my fault for driving it like I stole it. I'm even running 295-65-15 street slicks and the only rear end problem I've had so far has been a few half shaft bolts came loose and the french lock came off. I ordered new ones and put loctite on them and haven't had any issues yet.
If you are considering a new transmission I would recommend http://www.classicchevy5speed.com
You can also get all kinds of parts to beef up the rearend at http://www.tomsdifferentials.com. He's kind of rude and cocky, but he knows his stuff better than anyone else.
Hope this helps.
If you are considering a new transmission I would recommend http://www.classicchevy5speed.com
You can also get all kinds of parts to beef up the rearend at http://www.tomsdifferentials.com. He's kind of rude and cocky, but he knows his stuff better than anyone else.
Hope this helps.
