Sarg

iTrader: (6)

Just curious if anyone has tried this combination or knows of any issues it might cause. I am planning to build and boost a 5.3 liter and thought the 317 heads should drop the compression a bit (8.6?) for 20ish lbs of boost, 25 on race gas. Would these be ok on the stock 5.3 bore or would it be better to bore out the 5.3 to a 5.7 for these heads?

My thought is this:
-Lower compression for pump gas.
-Larger intake valve already so no need to fit the 5.3 heads with new valves
-Larger chamber and better flow
-can always go to flat top pistons if I want to bump compression later

I searched around and found this quesion a few times, but no real cons or experiences other than people saying compression would be too low (turbo WRX is actually lower at 8.2 from the factory!).

72montecarlo

Well figure this much down low with tht 1 point of compression loss it'll be about 10 percent maybe more power loss naturally aspirated I believe so if u can do tht go for it

LA WOOSH WOOSH

They should work im running stock 317s with my 6.0 and runs good

NightmareTA

iTrader: (20)

This combo has been around forever. I'm sure if you do a search you'll find 100 people using 317's on a 5.3, including myself. It'll bring compression to right around 8.5:1 so you can safely run some pretty high boost on pump gas. I'm going to run around 15-16 PSI on my T76 on pumpgas on my combo. I would use 317's over the stock 5.3 heads anyday.

I also doubt you'll have many driveability issues on 8.5:1. Almost every 70's gen 1 small block chevy ever made ussually came with that compression and there were no issues with them. Plus I have a stick in mine which will only help it.

Sarg

iTrader: (6)

Yup, I did a search but not a ton of discussion on the idea. Like I said, the main response was compression will be too low. I really didn't see too much on any of the other talking points. For me, the larger valves are an attractive feature as are the larger chambers. Larger valves means I don't have to buy more valves and have the heads cut for them.

Supposedly, from what I have read the heads in stock trim flow better than the 61cc 5.3 heads as well. My guess is the majority of that is the difference in valves more than the difference in the size of the chambers.

pwrtrip75

iTrader: (8)

I ran one like this for 3 years. Built it back before I had any experience with it. If you have a stock 5.3L there is no reason to do it, because it wont hold enough power to constitute the lower compression. It also makes it a real dog off boost and spool slower. Manual trans is worse, at least with a auto you can have some stall speed to make up for it for drivability.
If you can only get 87 octane gas then it would be ok. You can max the reliable HP out on these stock engines with 93 octane.

You cant really compare an LS engine to a subaru engine.

Not sure what exactly your HP goal is and if yours is stock or rebuilt?? But my opinion....I wouldnt worry about the flow numbers between stock heads...sure the 317s flow better... but not enough to better yourself over the loss of that much compression. (my opinion).

Ive built 2 5.3s like this... one for my Nova and one for a friends BMW. Now I wish I had left the 5.3 heads on.... would have been wy faster. The BMW is a 70mm w/ a T56 and we had to swap the smaller .68 exhaust housing on it so it didnt spool so slow.

NightmareTA

iTrader: (20)

I've heard from a bunch of people that the driveability really isn't bad at all. Obviously if your comparing it to an all motor larger cube V8 then no, it won't be close. But compared to say, my 1990 honda civic daily driver....I'm sure My TA will drive like a dream. It's all just opinion. Personally, I like knowing my 5.3 is set up for low compression and that I can run whatever I need to on my motor safely. Theres a guy on the forums with a turbo van making around 700 AWHP on a bone stock 5.3 with 317's and meth. I think he's around 18 PSI, and it's been going strong for a while now. These engines will take abuse, and most of the ones lasting under big power numbers have the 317 heads. A freinds 2JZ supra motor is only 8.5:1 comp on a 3.0 inline 6 and he has absolutely no complaint about driveability even with his slow spooling 67mm turbo on it. Like I said, all preference.

pwrtrip75

iTrader: (8)

It will drive fine... My nova was as fast as a stock civic off boost... just sucked ***...lol.
Im just saying you dont really need 8.5:1 compression to run 15-20lbs of boost.

Sarg

iTrader: (6)

It's an automatic car that should have a 4000-4500 rpm converter

73 nova guy

iTrader: (8)

im running a 5.3 with a 317 head with a mpt70 in a nova also and i do find it is a dog out of boost. i run 8 pounds of boost on the street with 93 octane i would say is way safe. i kinda would like to have some work done to a set of 5.3 heads and stick them on more for street driving..

my thought is if your going all out drag car go with the 5.3/317 and turn the boost to the moon. if your running an all around street car stick with the stock heads

NightmareTA

iTrader: (20)

8 lbs of boost would be perfectly ok on the stock 5.3 heads. I plan on running 15 psi off the bat on a 76mm turbo and possibly going to around 18 or so on meth which is why I planned on using 317's from the start. Really comes down to what your end goal is on the setup. Under 10 lbs, stick to stock heads. If you want a high boost setup, 317's are highly recommended for longetivity.

Uranium238

Deleted

forcd ind

iTrader: (7)

I built a 5.3 with some stock flat top pistons, was going with 317 heads, but chose 241's as kind of an in between-I wanted the pep out of boost, but prob wont be able to run a lot of boost now with the comp. In hindsight the 317's were prob the way to go, but more so because of the pistons, lol.
You could always cut a slice off the 317's, make a compromise.

mightyquickz28

iTrader: (8)

I had a Vigilante 4200 stall converter behind by turbo 5.3 but at the track, it just blew thru the converter. RPM's would only drop about 200 rpm on the shifts. I talked to a few converter pros and they said that stall was out of the efficiency range of my turbo'd engine. After checking with several knowledgeable people, they steered me to a custom PTC. With that lone change, my 96 Z28, in full street trim and drag radials on both passes took me from 11.5's to a 10.6.

My mentioning of this is so that you'll rethink the converter aspect, or at least, check with some specialists about a better choice for your converter needs.

Best of luck to you on your build!

nakedpants

Thanks for the advise guys.

I plan on using ARP head and main studs.

What head gasket can you recommend for a boosted 5.3?

I read that the one from the LS9 works well although its bore openings are slightly too large?

Or are there better options?

I assume the eagle cranks are from China? What other manufacturers produce their cranks in China?

What about Scat and K1?

Do you think stroking the engine to 363ci makes sense or should I leave the stroke as is?

What is the highest compression ratio I could run which would still be safe for around 15psi?

Pro Stock John

iTrader: (34)

I suggest buying the rotating assembly and all the small parts you need all from Summit Racing, I have all the parts sourced from Summit for my all-forged LC9 build.