Dieselwelder67

Quick question guys, Igot a 5.3 and under further investigation it turns out I have the castech 706 heads. I have a set of 317 heads but since I'm not planning on boost will it run alright? Should I just keep the 706 heads on?

ls1charged

iTrader: (8)

317's will kill your compression and it will run like crap if your staying NA

Aaron at SDPC

If the heads aren't giving you any issues I would continue to run them. Like mentioned above the 317s are going to hurt compression a lot.

Mercier

iTrader: (15)

Are you having any problems currently? AFAIK, Castech heads were the heads more likely to have cracking issues *IF* they cracked, but not all Castech heads were problematic.

Early 5.3s have dished pistons and need that small combustion chamber of the 706/862 heads to get to 9.5:1 SCR. I don't think you can mill a 317 down enough(safely and still have the intake fit) to get it to the chamber size of the 706/862. And if you put the 317s on stock, it would likely run like a 70's 305(badly).

A.R. Shale Targa

iTrader: (2)

OUCH
never ever wanna be compared to one of those
Or worse yet, the 3.50" bore by 3.48" stroke 267 cid

Dieselwelder67

Awesome guys I really appreciate it, the motor looks good no water in oil, I was getting ready to put it into a 1940 chevy coupe and as I was checking the valve train I saw that dreaded battery symbol! From the stamp on the block it looks to be an 02, idk if that makes any difference on the year?

Mercier

iTrader: (15)

That's the LM7. True workhorse. It should have dished pistons so you need to keep your combustion chamber size low to keep compression in a usable range.

I'd have those heads milled .015 or so to get your compression up near 10:1. They can check for cracks at the same time. I don't know what your other goals are so take this with a grain of salt--you can take a 2" LS1/LS2-sized intake valve and have the existing 706/862 seat cut out to fit the 2" valve without installing a new seat. May not benefit your particular build but that is a budget-friendly option.

Mercier

iTrader: (15)

Please stop before I start having that "rebuilding a Quadrajet in the dark in the rain in December" nightmare again.

Dieselwelder67

Thanks Mercier, my goals is just to get this thing running good and dependable bit maybe tuned for a little more power. I'm actually trying to get this going asap so I really won't have no time to take off these heads to do any work on them. Since I have a lq4 short block on the side, will the stock cam benefit this motor?

Mercier

iTrader: (15)

What year is the LQ4? I think some of the older LQ4s had a similar cam to the LM7. Some may have had something more like the LQ9 cam.

Here is some good reading on factory cam swaps in the LM7. Stock LS1 cam is actually a nice waker-upper for the 5.3. you can usually find them cheap, too, and they drop right in. I have a couple I paid $50/ea. for sitting around. They aren't hurting my feelings sitting here but if it would help you out, let me know.

http://www.hotrod.com/articles/ls-cam-test-comparison/

Dieselwelder67

Hey thanks for the article Mercier, I really appreciate it! If I do end up needing a cam I'll hit you up for sure!

gagliano7

Not all 706 heads are bad. I had 706 heads on my 5.3 with a 100000 miles with no problems. I then bought texas speed 5.3 heads ported and they used 706 heads and i have no problems.

MuhThugga