kellyr073

Going to start rebuilding my 350/270HP original motor from my 71.

Obviously want more HP and torque, but want to keep the stock heads block, and intake. The quadrajets gotta be repalced with a Holley or the like, and I'll go with the MSD tach drive and 6AL box set-up I currently have.

I will definately have the block bored since it has 100k miles on it. Want to go with forged pistons since I may want to add NO2 for the fun of it.

What would you recommend to accomplish more base HP and Torque? How much could I expect? Should I do something to the heads as well? Don't want to deck the block and heads and lose the serial #'s though.

7T1vette

The one component that you should want to keep is the Q-Jet. The heads are weak, the cam is too mild, the block is OK as-is. If you want more power, change the cam, heads and exhaust manifolds/pipes. The Q-Jet is a 750 cfm, flow regulated, economical 'wonder' compared to most Holley's. Just rebuild it. Oh, you would benefit from a better intake manifold, too. [P.S. I have the same engine.]

markids77

Think LT-1. 350/365. Think about doing that with a replacement setup if your block and heads are OE and numbers match. NOS is HARD on parts and original engines are irreplaceable. Replacement stuff is plentiful and cheap! Have some fun and keep perhaps 25 percent of the car's value intact by not lunching your original mill. A 50HP cheater plate on 360HP equals lots of tire smoke and broken parts. Be sure you upgrade the trans, u-joints , cooling system and posi as well!

billla

All of these discussions need to start with your budget

There are a lot of mixed messages here - you want to spray NOS and use forged pistons, but keep the stock heads and intake (?) Bottom line is that your goals and your constraints don't match. If you're keeping the stock heads, no NOS and limited to around 300 HP (flywheel) max.

A performance overhaul of a 350 will deliver:

Around 1 HP/CID for about $3500
Around 1.2 HP/CID for about $5500
Around 1.4 HP/CID for about $8500

These are real general numbers to point out some options and start the discussion.

FWIW, there are no serial numbers to loose on the heads, and a competent machine shop can cut the block and keep the pad...but get it in writing with a penalty clause.

Budman68

Buying forged pistons for a stock bottom end and heads is kind of a waste. With nitrous, there are a ton of other issues that come into play also. Running lean and burning a valve, throwing a rod in a stock bottom end, and the dreaded nitrous pop. If your going to run nitrous, build a nitrous motor.

If you just going to spray a 100 shot then just save your money on the forged pistons and buy nice heads.

jackson

Are we to understand your 71 has a NOM 383, 4 spd & 3.36 gear?

But you are asking about rebuilding another separate motor for same 71? ... and that motor is the original numbers-match 350/270 (L48) that came in your 71?

If so, rebuild it w/ small-dome pistons like Sealed Power H618CP (5.7" rod hyper) or H101CP (6" rod hyper) or LW2304F (5.7" lite forged) or LW2626F (6" lite forged). With thin felpro 1094 head gaskets & your OE 76cc heads, any of those pistons (+2.4cc to +3.5cc) will yield about 9 1/2:1 scr ... with an eye to the future, perhaps 9.5 is a fair limit for iron head carb motor. Better get good bolts or studs if you shoot those 2 bolt mains. Keep your OE intake & freshened QJet. L48 needs compression & cam; its heads, intake & QJ will support a good bit. There'll be plenty cam suggestions from others.

kellyr073

[QUOTE=jackson;1570940950]Are we to understand your 71 has a NOM 383, 4 spd & 3.36 gear?

But you are asking about rebuilding another separate motor for same 71? ... and that motor is the original numbers-match 350/270 (L48) that came in your 71?


Yes to both Jackson.

And good suggestion from all. I am little surprised that the L48 can't be toughened up with existing heads. I think I'll go with Jacksons suggestions and forget the NOS. Just thought that would be a little fun kick in the butt once in a while.

I thought the 71 L48 is a 4-bolt main though. Someone said 2-Bolt.

TimAT

Why not pull your original engine, pickle it, wrap it up and stick it in the corner. Build a killer 383 or something with some real kick. If that one gets lunched it's no big deal. Build another one. And you always have your matching engine setting there resting for later. And $ wise, it's not a lot more cash than rebuilding the stock engine.

billla

Do a search here; the head flow it lousy, and the D-shaped smog chambers take 20HP out before we even get started.

Again, if you're planning on keeping the stock intake, there's no reason to build to power levels > 300 HP as the intake simply won't support it.