Blue88Coupe

iTrader: (1)

Hey all, I'm a LS newb coming from SBF. I've got a stock bottom end 5.3 and I was wondering in a boosted application if the 317 heads or the 862 heads would be best? I have both an they're off the motor so It makes no difference which ones I run.
Thanks

3pedals

iTrader: (3)

My opinion is to run the 317's.
It will take less boost to make the same hp with a better flowing head(317's are a much better head). This is beneficial because the less boost yiu run, the less the compressor heats the intake air. This will make the engine less detonation sensitive at the same power level.
I personally would flat mill the 317's to try keep as close to stock 9.5:1 compresssion as possible

Twin turbo c5

If I had to pick . It would be the 317's for me.

RedRocketZ28

iTrader: (19)

If you are going to run the heads as is, then run the 862's. 317's on a 5.3 will make it a dog out of boost.

71 chevy

iTrader: (18)

862s

ive run 862 vs 799 no difference in power. one flows more and one has more compression. in this case i believe the 862 will be better overall

novaflash2002

iTrader: (51)

862's. unless you have a 5.3 with flat top pistons...

Forcefed86

iTrader: (4)

Man I hate this statement. It's total BS. Your talking about 4% loss in power. Thats like 13 flywheel HP on a 5.3. Missing 13hp sure doesnt make an engine "a dog out of boost". I'd bet you couldn't even feel a difference. And for the small hit you take NA you'll be able to run much more boost.

IMO if your on a pump gas setup 317's are the way to go. My 8.6:1 (317's with dished pistons) 5.3 made boost too quickly to be streetable. My current 10:1 5.3 doesn't feel noticeably different out of boost.

RedRocketZ28

iTrader: (19)

Thanks for your opinion. I shared mine as well. I would never put 317's on a 5.3, but that's just me.

Forcefed86

iTrader: (4)

Nothing against U personally. I just hear that quote a lot. Coming from someone that has actually had both, I don’t agree with it. I believe its something people pick up and regurgitate with no personal experience on the matter.

If you've had personal experience with both, I don’t know how you could feel that statement is true. A point of compression is not a game changer power wise on any engine IMO.

NicD

iTrader: (7)

Yup. If it's a pump gas setup that is surely to be octane limited the answer is easy. If it's on race gas/E85 then it really doesn't matter what head/compression ratio you choose.

71 chevy

iTrader: (18)

with all due respect, youre also regurgitating the 4% hp loss. the difference in IMEP is more than the difference that simple thermal efficiency gains would suggest

vht

I would like to hear from others that have run both. I talked to a guy that switched from 317's and went to 862's and said it ran better. He also said it was a dog with the 317's on low end. Myself, I have no experience, so I can't say either way. Some say to put 2 in valves in the 862's and clean the ports and valve pockets up and they work great on boost. Anyone out there with dyno results from both?

Forcefed86

iTrader: (4)

Yes, but I am regurgitating it from a book written on the subject with data to back it up. As well as direct personal experience. This is not the same as mimicking what you read on a forum where anyone can throw out these so-called "facts" with no personal experience or knowledge on the subject. Yes depending on the cam and initial compression and many other things results will vary. I did say "about 4%" and that is a very commonly accepted "rule of thumb" for 1 pt of compression. Especially when dealing with OE engines with typical compression ratios, small cams, reasonable RPM etc...

71 chevy

iTrader: (18)

in your personal experience did you cam both engines differently to take advantage of the increased compression?

Chicago TDP

iTrader: (3)

I guess my personal experience might hold up here if you want to hear it and believe it:

4.8L with 317 heads = dog on the street
4.8L with 862 heads = snappier response and better spooling

This was with THE SAME TUNE, only adjustment was to the VE table to smooth it out.
T56 trans, PTE7675 turbo.

317 heads will make the motor a pooch, hands down.
I have done it and regret doing it.
All it did for me was waste time, head gaskets, money and a few months of trying to get the car to be more responsive
At the time, I wanted that "low compression high boost" set-up that "all the cool guys had"

Well, 9-9.5:1 compression + boost is awesome!
If the is right and you keep your timing within reason, no need to have an 8:1 motor or anything less then 9:1 for that matter.

3pedals

iTrader: (3)

Mill the 317's and run em with 9 to 9.5:1

snapc3

I agree. I have a 5.3 with 317s, s475 with the big 1.32 hotside. I personally don't have experience with the same setup with more compression, but to say it is a "dog" out of boost is silly. Automatic btw.

Saying that, I wouldn't hesitate to run one with stock 862's if I didn't already have the 317's ready to go.

KCS

iTrader: (20)

Consider this: 13hp at an RPM low enough to be out of boost is 30-40ft-lbs of torque. I bet you'd feel that.

Forcefed86

iTrader: (4)

Your arguing over semantics... How much gain is to be had by doing what you say? Like I said it's a general rule. We aren't talking about an "optimized" race motor here. We are talking about a JY 5.3. Compare each stock for stock with nothing else but a 317 head swap. A 317 head swap is not going to result in enough power difference to consider it "a dog" compared to the 862 head.

A 317 head flows more than an 862, period. 1pt (or less if it's a flat top 5.3) of compression is not enough to tip the scales in the 862's favor.

First off I’d like to say I made a typo… I did not mean a 4% loss in HP. The “rule of thumb” indicated 4-5% in power (aka torque) Not HP.

No way there is 40ftlb difference in two 5.3’s stock for stock with a 317 head swap alone. Also most aren't pulling tree stumps with their turbo LS setups and could care less about the power curve under their stall RPM. As far as an "RPM low enough to be out of boost". What auto setup has any kind of RPM band out of boost at WOT over the stall speed? Are we talking about a 200-500rpm window? Is that window what makes the engine a "dog"? I'd see positive pressure WOT as soon as the converter "flashed".

Blackpanther99

iTrader: (8)

Good info on here. Id just run the 317s to be honest.