Performance upgrade

G72Zed

Veteran Member
Sep 8, 2015
3,822
Canada
If the engine is all original, it most likely has the 76cc chambers, combined with the GM steel shim HG, original deck and the 4 valve relief dished pistons, add these cc's up and you are at 95cc @ TDC, and that's 8.5:1 CR, just what GM claimed I think.

So, staying with the stock bottom end and head gasket style, but with 64cc chambers like mentioned in post #6 & 8, you will be at 9.6:1 CR with those heads.

To me, Lowend and ULTM8Z make the 2 best options, if you want to stay hyd FT, I like the GM #24502476 that comes in the 350 crates, 435/460 lift, 212/222 @ .050 on a 112.5 LSA, so does not tax the springs and easy on the valve train, and great vacuum for power brakes with good cranking psi.

I like the GM alum high rise vortec intake # 12366573 as well.

It may come down to price and availability....but with those options, 300-350hp is easy-peasy.
 

zfool

Veteran Member
May 19, 2014
702
Rochester, MN
I’m surprised it has a th-400. I had a couple 74 LT’s with 350 4bbl and both were th-350’s. With that low of mileage I’d leave it alone or swap out the mtr trans and driveshaft, if I wanted to get more perf. Does it have a limited slip? These cars are getting more popular. And all original will get you the best return on your investment so having an unmolested power train with an oddball (very cool) # matching th-400 will be a premium on resale.
 

mallard

Veteran Member
Oct 3, 2013
1,804
SK, Canada
I’m surprised it has a th-400. I had a couple 74 LT’s with 350 4bbl and both were th-350’s. With that low of mileage I’d leave it alone or swap out the mtr trans and driveshaft, if I wanted to get more perf. Does it have a limited slip? These cars are getting more popular. And all original will get you the best return on your investment so having an unmolested power train with an oddball (very cool) # matching th-400 will be a premium on resale.
The pics in his OP show the "z28" stripes, so I'm presuming it's a T Code Type LT which would explain the Turbo 400.
 

rchydzik

Veteran Member
Lifetime Gold Member
Nov 13, 1999
919
Colbert, WA USA
74 Z28 is the L82 350. Forged bottom end, true flattops, four bolt main, relatively large factory cam. Probably has pushrod guideplates as well. You may get close to 300 hp with tuning if you already have headers. I wouldn’t modify the original drivetrain, that is the entire value of the car. If you do make changes, I would store the original engine and transmission so it can be put back if you ever want to sell.
 

Z28PILOT

Veteran Member
Lifetime Gold Member
Oct 8, 2009
2,310
Emerald Isle , NC
if Your automatic Z28 car has no factory AC , the turbo 400 could be ordered with a 3:73 axle ratio . I have seen a couple factory like that , and it will suck the gas down like crazy . You might find a 3:42 gear set to give you some relief from the RPM’s . The car was tuned , carb and trannie Shift point all from the factory set up to work together and delayed shift at high rpm s to get the max performance stock . If you put in the 3:42 gear set , I would have a professional retune the engine , dizzy, carb , after I put on a less restrictive exhaust pipes and use dual mufflers . A set of 1969 corvette 350-350hp heads or similar with higher compression will help things too. That’s too nice or car to mess it up .
 
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