Looking to build a twin 76mm turbo 5.3 for drag purposes only. Do you think i could get away with using the 317 heads since it drops my compression to 8.5 - 1 I've seen people avoid them due to the very weak bottom and Power . I've done some searching and I can't find a lot of people who are specifically using their cars for drag racing I posted the same question in the drag racing area and no one seems to really know or respond yet.

Don't get me wrong I understand that 317 heads aren't necessarily the best choice but they seem to be pretty readily available for about $250 and I'm looking for something that has a little bit better of a flow rate and larger valves. Port and polishing the 862 that I have would seem kind of dumb and a waste of money. Any other suggestions would be highly welcome I'm kind of stumped and I don't want to spend $1,000 for one head from trick flow

 

Unless you have a dished piston it wont drop your compression that low. I used a set on a dished piston 5.3 motor with ls9 HG's and it net me 8.6:1 or so. Ran great, even with the $100 LS9 cam everyone says is horrible. It did drive like a mini van out of boost. At the track I was never out of boost. It made plenty of boost on the brake and ran low 9's for a full year, then dipped into the 8s before I broke it. Was a gen3 engine with weak rods. I believe the autozone timing chain is what did me in, but Ill never know. The lack of low RPM power is what kept it alive IMO.

 

Right now youre my idol, my goal is 5sec et in 1/8th. Im also running dished on a 3rd gen. What was your peak psi and ring gap? Im planning on .025

 

What about a dished 5.3/CNC ported 317 combo with a T56, 3.73 gears and a T7875?
Still think it would be enough of a pig to warrant 4.8 flat top pistons or 243 heads?
I've got all the above and am really torn about it since the car sees only street time and very rarely ever sees a track.

 

On E85 I gap the tops at .022 and bottoms around .024. No reason to go with more IMO. Ran 26bs on the 1.10 t4 S475 but it needed more turbo. The cheaper 1.32 t6 is the way to go.

I wouldnt run the compression that low with a manual. U really need a converter and trans brake to help build boost when u dont make much power NA

 

S475 is a bad little beast. Im starting cheap and going with CXracing 76mms with 88lbs injectors on E85. But have no idea what ARs to run on turbos

 

How much power u want?

CX 76s arent a great choice IMO. The turbine wheels are too small compared to the comp wheel. They will be lazy. Look at the 72/68 rev 9 turbos. Or the gt3582s for really quick spool depending on the power u want. Both are cheap.

 

Thats why im here, to learn. Im looking to build an engine i can grow into. Ultimate goal is est 900-1000 hp in 3400lb car doing mid 5 in 1/8th

 

That won't happen on a gen3 but the 72/68's could do it and should spool up quicker than the 76/65's you were looking at.

2 of these would be nice and give you room to grow on once you pop the gen3 engine.

http://www.ebay.com/itm/Rev9-TX-72-6...RVtqBn&vxp=mtr

 

Im not too concerned about spool time since it's a dedicated dragger.

 

Right, but it will need to make boost on the brake and it will have an easier time of it with better matched turbos. 76/65's are just crap by design.

 

Touche'. Well how about this, forget brands, what are the proper numbers and AR. To look for. I know we are starting to go off topic but it all applies. Im new to boosted ls engines.

 

Have to be a little more specific on the question. The proper numbers will vary depending on what you want out of the engine. You can't expect a "stock" gen3 low compression 5.3 with cheap china turbos to make 1000hp. If thats really the goal, save up for a gen4 5.3 at minimum... really should be looking at an aftermarket rotating assy with those goals. You can comfortably make 600-700hp with the gen3 depending on the vehicle weight and tuneup.

Ideally you want the exhaust wheel and compressor wheel similar in size. With twins on a 5.3 at mild RPM... .68 housings will provide better response and is about as small as your gonna get in cheap china T4 turbos with exhaust wheels large enough for a an LS.

 

In reality i dont expect 1000 hp out of a gen 3 5.3. I predict 700, with forged bottom. Eventually i will "grow" into a 6.0L but i dont want to change the turbo sizes every time i add a new thing to engine. If that makes sence. The reason for OP is to see if it has worked effectively on a stock dished bottom end with gap rings, even though 8.6:1 is almost too of a low compression, yet have larger valves amd better cfm due to size of the 317. But since its a non competition dragger i assumed spool wasnt my enemy. My idea would be to run a turbo(s) capable of 1k+ hp but only run it at a reasonable tune/hp then replace dish pistons with true flat tops bringing my cr back up to 9.1:1 and h beam rods. The increase in cr will yield a 5% hp gain without changing turbo duty psi. If you like, i wrote another post in drag racing tech named new member, same questions

 

Easy to help with a budget and reasonable HP goal listed. Lower compression has the ability to produce more power at like effective compression ratios since boost is more efficient at making power than compression. The catch with low compression stuff is lazy response, poor emissions, and you have to run higher boost levels…meaning bigger more capable turbos. The 72/68’s I linked should be more than capable on a mild 6.0 or a 5.3 around 1000hp.

8.6:1 VS 9.1:1 Won’t give you 5% increase in NA power. 1 full point usually gives closer to 4%. .5 bump is like 2% and not worth farting with IMO.

With a like rotating assy, a 6.0 is actually weaker than a 5.3. The meat between the cylinders isn’t as thick and tends to eventually split at big power levels. Especially if the 6.0 block is bored/stroked.

You really don’t need a forged bottom for 700hp. Pick up a 2005+ 5.3, gap the rings and add tons of boost. The 317 head is fine, but also not necessary for 700ish hp. You can easily meet that goal and more with the small valve castings. You can also look for gen4 rods/pistons (ebay, ls1tech classifieds, etc) and drop them in the engine you have now.

I ran a bone stock 2006 4.8 with a small 212/212 @112 .56x lift cam. Small valve heads, untouched. And went 9.01 @ 151 on 19lbs of boost. (s476 t4). Depending on your chassis weight, gearing, and tune up… I’m pretty confident I could make a gen3 low compression SBE 5.3 last at 700hp for a long time if that’s your goal. Going by weight and trap I was over 700hp all season. Lower to mid 800 range when I turned it up and went 8’s. That’s with a pretty light 2800lb car. (+200lb driver).

If you build the turbo kit correctly with small 2” piping, correct torque converter good flowing IC core, decent intake manifold (stock truck is great), and proper cam…. 8.6:1 is not “too low” in my experience. Should be able to light it off easy and you’ll have a ton of extra cushion in the tune. Great for a first time turbo build.

 

All the research im doing it telling me that the hp goals are within reach. It will be a little harder to get my 98-01 Fbody down to 2800. Especially since im 250lb. I believe my current weight is 3700, that includes me and full stock car. Much wrenching and chopping will happen soon

Youve been a great help man

 

I wanted a spare engine for my 6.0 incase I damaged it, and didn't want to be down for a while, so I picked up a 5.3-it was pretty icky, so I figured I would freshen it up.
I scored a set of gen 4 rods and flat top 5.3's off here, so I figured with 317 heads the comp. wouldn't be to far off, and I would have a little more power our of boost. So far I haven't needed it, lol. But the flat tops gave me the option of the 317 heads, but I understand the boost can make it up if needed, lol.

 

Judging by your statement you actually never installed the 317 heads on the 5.3? What kind of number is were you producing on the 5.3 without them?
If I remember correctly when adding those flat top pistons it brings your compression up to about 10.1:1. I'm not too worried about the compression as much as I'm wanting to have better flowing heads and bigger valves without spending thousands of dollars trying to port and polish the casting 862 that come with mine

 

I ran a gen 3 5.3 with cnc 317's (8.5cr) for a very short while and it was a lil doggy out of boost but with any throttle it was hard to keep the tires from spinning. At the track I was never out of boost and it ran great for what it was. I was able to run 18 degrees of timing with 18psi with 91 octane as well

 

Was it a short while because you kept spinning? Would you recommend i pick up a pair?