Performance upgrade

medpilot6915

New Member
Jan 12, 2013
7
Jacksonville, FL
Own a 74 numbers matching Type LT with automatic transmission. Has approximately 39k miles. Would like to have engine rebuilt and increase the horsepower to 300-350. What is the best route with this engine to accomplish that? Also the TURBO 400 turns a lot of RPM on the highway. So has anyone tried an overdrive on this transmission or is it better to replace with an aftermarket upgrade.
 

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Bobs RPO Z/28

New Member
Mar 10, 2021
12
Illinois
Re: 300-350 hp. Guess it depends if you want old school or new school. I had the exact car as yours back in the early 1990's but in white. I went old school solid cam (I like the clatter), LT1 intake and Holley plus thin steel GM head gaskets and carefully decked the block leaving the numbers intact and a light pass on the heads. Lost track of the car in Illinois 1998. Yes the problem with these is they spin pretty high RPM's on the road. Not sure which new(er) GM automatic would be a good switch as far as fit and if it might need electronic controls.
 

ULTM8Z

Veteran Member
May 19, 2000
10,498
Los Angeles
Overdrive swaps are one of the easiest upgrades (have been for decades).

For most cars a well built 700R4 or it's electronically controlled sister the 4L60E. Plus you get the benefit of the much steeper first gear for better acceleration off the line.

If you get into really high horsepower like 500 or more, probably want to look at a 4L80E. A little better gear spread than the 700/4L60, but bigger and heavier and not as good an overdrive gear.

But any of those should fit in place or the TH400 with just a cross member relocation and shortening of the driveshaft.
 

Lowend

Administrator. .a car, a man, a maraca.
Staff member
Lifetime Gold Member
Mar 25, 1999
16,759
San Jose, CA, USA
There are A LOT of options here. Although with an earlier car, with this few miles, I'd be at least somewhat committed to preservation.

Let's talk about the most important part of any automotive project:
What's the budget?"
 

medpilot6915

New Member
Jan 12, 2013
7
Jacksonville, FL
There are A LOT of options here. Although with an earlier car, with this few miles, I'd be at least somewhat committed to preservation.

Let's talk about the most important part of any automotive project:
What's the budget?"
Hopefully around 10k. The only thing the car does have headers ( looks like a cheaper set on when I bought it). I may change from number match is transmission they just turn too many RPM on highway ( preserve
the 400) Was kinda of wondering what can be done as for cam / lifters with the stock heads and carb. Also maybe raise compression. Still has smog pump. How good are the heads. I see the 74 has the .202 heads but not the double hump ones. A good driver with a little better performance.
 

Lowend

Administrator. .a car, a man, a maraca.
Staff member
Lifetime Gold Member
Mar 25, 1999
16,759
San Jose, CA, USA
OK - now we're cooking. We've got $10K to make this '74 a better driver, without cutting the car up too much.

An overdrive transmission is definitely the key to this, The TH700R4 is probably the best one from a cost and availability standpoint.
We live in a glorious time when the entire 'kit' can be had in a single part number

This is a good solid street build that will live fine behind an original-ish motor for ~$3500. You could go with a 4L80E instead, but frankly, it's a lot more expensive and it has strength you don't need. Someone will probably bring up the 200R4 - good luck actually finding one.

Figure with incidentals (and if you are paying someone to do the work) we've burned up about half your budget there.

---
For the engine itself - Heads/Cam/Intake manifold are the key here. The factory heads of that era are... junk with 76cc combustion chambers.

We are once again in a glorious time when single-part numbers can work wonders. Take all of your factory top end stuff and throw it in a storage container somewhere
And order this
Good aluminum heads with 64cc chambers that will bring the compression from 8.5 to ~9.6 -1
Matching intake manifold
and a good Hyd Roller Cam with 234/238 @050 with a 112 Lobe Separation which will have some chunk at idle, but isn't crazy.

Combine with with a Holley 80508s carb - and you've got a damned nice street motor
 

ULTM8Z

Veteran Member
May 19, 2000
10,498
Los Angeles
Could potentially save some money on the engine if all we're looking for is ~300-350 hp.

Vortec heads ~$1100


Vortec intake $300


Flat tappet cam in the range of [email protected] on the intake $150


Probably all told, get away for <$2k?
 




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