Hazmatt81

Can somebody help me I have been all over the forum and internet trying to find the answer to my agony.
I have my Sonoma torn down and I want to get my GM MLS headgaskets (12498544) and ARP studs in. My problem is is that I am torn on what to do about the heads. I have the 862's that I was running while this truck was NA with the Z06 cam and it ran really well 313hp and 320tq on the rollers.
Now that I want to go forced induction with the MPT70 I cant make up my mind if I wanna do the 317 and shave about .015 off the bottoms (maybe get the compression up to 8.8, or put my 862s back and run less boost, on or spend more cash and put some 243's on.
I figured that if i put the 317s on it would be safer to run boost, and then if I needed i could turn it up if I wanted to. Where as the 862 i probably couldn't.

As you can tell I am new at FI but I am willing to listen. And before someone says that I didn't need head studs, I did it because this is a 2000 5.3 and it had graphite head gaskets on it so while I tore it down I put the added security in place as I went.

Any help would be appreciated. Thanks in advance.

71 chevy

iTrader: (18)

what fuel?

lsxtreme17268

iTrader: (2)

I'm sure others will chime in . Im doing a similar build and sticking with the 862s. I've read where people have switched them out for lower compression and the motors are a dog out of boost

Hazmatt81

91 octane is all I can get around here 93 used to be plentiful but not anymore.
e85 is an option if I can figure out how GM used that think in the tank to sense what fuel was in.

Black98s10

Like lsxextreme said, you don't want the compression too low. You can run a little higher seeing that E85 is an option, water/meth works miracles too. How much boost you going for?

LS1NOVA

iTrader: (12)

I'd go higher compression, it will be more enjoyable to drive and still make good power.

Hazmatt81

Ok great info. I think what I'm really leaning toward now is the 243 heads since the 862's are 9.5:1 and the 317's are like 8.6:1 I would be lead to believe that the 243/799's with their 65 cc chambers would yield me right about 9:1 or so (correct me if im off) but with the better flow of the 243's and a smidge lower compression ratio I couldn't really go wrong.
I'm looking to run about 11-12 psi. And would like to stay away from meth because of space and since it's bad for your skin and teeth.

Wicked69

Run the E85 and the heads that are on it. I ran mine with no issues and the stock heads make it so it runs pretty decent out of boost. I was running 20lbs of boost with no issues at 118mph in the 1/8th with twin 62's. Now I have twin 70's. Now once I ran 23lbs of boost I had issues. You can run 10.1 compression with E85 so I wouldn't sweat it.

Next year I plan to try running the 4.8 flat top pistons in my 5.3 with E85 and that would put the compression near 11.1. E85 and meth injection keep it all cool. I don't even run an intercooler. I wouldn't waste any money on anything but the stock heads.

Hazmatt81

I like how radical you've gone and appreciate your opinion.

But I cant always guarantee there is going to be e85 everywhere i go. This is just gonna be my driver with some track use. basically building it to whoop my friends supercharged mustang. hahaha and go on power tour with him.

So that being said ill probably run 91 octane most of the time. does this change your opinion any.

NightmareTA

iTrader: (20)

From someone that has a 5.3/317 combo, it is not a dog out of boost. Granted I have a T56 and 3.55 gears which help. In an auto, IDK how it'd feel. I went with the 317's because they outflow the stockers by a bit and it's safe assurance on pump gas. You'll make good power with any of the 3, but personally if I were you, the optimal setup would be the 243's for me. Good luck.

T76s10

iTrader: (6)

best of both worlds i have a set of ported 799's ill sell you for $150 shipped. that way they will flow better than the stock heads and still keep that compression above 9:1. on only 10-11lbs i wouldnt even worry about too much compression.

T76s10

iTrader: (6)

plus since their ported you will make the same power your stock heads will make with less boost.

Hazmatt81

Thanks for everybody's contributions. I'll be running my 862 heads and putting enough psi to the cylinders to eat any mustang in this area

Cronic_Moronic

Have ou thought of picking up a set of 241s? they would lower your compression but not as much as the 317s.

pwrtrip75

iTrader: (8)

Compared to what? Ive built two of these combos with 5.3/317 heads.... Out of boost my stock 96 tahoe would whoop its ***.

BOBS99SS

iTrader: (2)

Ya dont need boost to eat mustangs,really all ya need is a quarter tank of gas in any ls based car lol,good luck on the build

Old Geezer

iTrader: (3)

"And would like to stay away from meth because of space and since it's bad for your skin and teeth."

Only if you smoke it, or brush your teeth w/ it, or take a bath in it...

As far as getting in a wad over the 1/2 point compression between the 862 and 243 choice, I'd not spend the $$, but instead tune to what you have.
LOTS of turbo Buicks around on pump gas, alky, and boost at double what you are looking to run. BTDT.