got-a-ls1

iTrader: (12)

Have a kit coming from josh at kytp and im going to be putting it on a 5.3 liter i picked up for 400 bucks until i build my ls1(spun rod). So at this point im trying to figure out if the ls6 heads would be worth it on the 5.3. I believe they will lower the compression to around 9.0 correct? heads are unmilled. Already have pac 1518's installed so atleast i wouldnt have to swap them lol..

So basically are the ported heads really worth more power with FI and will the 9.0 compression make the engine feel doggy without boost while making it a little safer. Also will be running a ls6 cam and intake. Goals are 600 rwhp and living for a couple years.

shanemilleresp

i believe the 5.3 heads are 58cc and the ls6 62cc, but since the heads are aluminum... id get them milled and a valve job...unless they're brand new.
personally id just do a gasket match and valve job on the 5.3 heads, then they'll flow about the same and still keep some compression, if you dont know how to port just go to youtube and search they have a few good how to vids there for about 150 bucks in tools you could do it yourself.

headed-ws6

iTrader: (34)

Sell ls6 heads and:

Option 1: Get some 241's heads these will yield a 9.1:1 compression and will not be to sluggish out of boost.

Option 2: Get some 317's heads these will give you a 8.5:1 compression, some say a car like that feels sluggish out of boost but, flow as good as a stock 243 just have a bigger cc.

I would for sure put ls9 head gaskets and a dual valve spring on and of the heads.


The 5.3's are not as good as any ls1 head better yet a 243 or 317. The 5.3 has a smaller intake valve i think a 1.89 compared to the other's 2.00 Valve.

My opinion is to get a set of 317's and mill them form 72cc to 67cc so you yield a 9.1:1 compression.

got-a-ls1

iTrader: (12)

5.3 heads actually flow almost identical to 241/853 heads even with the smaller valve. Surprising i know... i didnt think they would be close. I have a pair of 853's from my stock motor. Thats not an issue.

The reason i was thinking of keeping the ls6 is one it will lower compression slightly over the 5.3 heads but not as much as 241/853 plus being cnc ported should yield more power everywhere at lower boost. Just trying to find out from people who have tried this combo before and if it was worth it.

shanemilleresp

If your not too worried about the comp lowering go ahead and use the ls6's you'll prob be able to squeeze a couple pounds more of boost just might not spool as quick you could just mill the ls6's then you'd have the comp and the flow

Fbodyjunkie06

iTrader: (10)

Use your LS6 heads. Period.

Drewhelm

iTrader: (7)

+1 - use the Ls6 heads...

rod442

agreed, use the ls6 heads. and you probably wont notice it being doggy out of boost....

you have an automatic, which will keep things spooled up anytime you want. Just 2 foot the gas and brakes a little if you need some boost built up.

postal14

iTrader: (8)

Couple of points:

Turbo motors build HP because the intakes are pressurized, not because they have high static compression ratios. An 8 to 1 5.3L at 23psi will make 2 to 2.5 times the hp of a 12 to 1 NA 5.3L. You will make more HP running a lower comp ration and more boost especially on crappy gas, and you will actually be less likely to hurt the motor. Now there is a trend to run more compression than what was considered "the norm" for a forced induction motor. There has also been a trend to just run more compression period. Hell we have factory pick ups and SUV's at or over 10 to 1. As I type this it makes me think that the high compression era of the 60's is actually being exceeded by the factories today. This would only apply to " an average car", the big factory race motor compressions of the 60's will likely never be eclipsed. Anyway advances in fueling, ignition control, combustion chamber designs blah blah blah is whats allowing the car manufacturers and hot rodders to run these higher compressions on this lower octane fuel. So the real question comes down to wether you want to use this technology to run a higher compression ratio on your turbo motor, OR if you want to use it to run more boost? I have been messing with turbo cars for about 18 years and helping people set them up. Any cam guy will tell you its better to err a little on the small side for a street motor than to go to big, and any real turbo guy will tell you its better to err a little on the low side for compression on a street motor than to go to high.... Now this is a guess but i imagine that the majority of turbo charged drag cars out there are in the 8.5 to 9.5 to 1 comp ratio range. At 9 to 1 you are in the middle of the "race" engine compression ratio range. If you are under the impression that 9 to 1 compression may be to low for a turbocharged street motor.......

This is hard to explain.... when an engine gets more air in a cylinder it can then burn a larger amount of fuel in the cylinders. This larger amount of air and fuel make more torque, which makes more HP. Now turbochargers put more air into a engine, but they dont make the engine "Breath" better, they compress the air and put more air molecules in the same space (this is called a density ratio). The main approach on a turbo motor is to make more power by increasing the density ratio, so better more efficient, turbos and intercoolers and of course more boost. Basically you try to do an even better job of putting more air into the same space. Now with a naturally aspirated engine the main method of increasing its power out put is to get it to breath better or basically get it to pump more air thru it. Heads, cams, intakes, exhaust are the biggies for the NA crowd. Guess what the really fast trubo guys do.... they address both making the motor breath better and putting more air in the same space issues. Now here is an argument....

Guy A has a 400 hp NA motor, and he puts $1500 into a set of heads to pick up 60 hp. So he spends about $25 per hp to get 60 more. Peeps on the net and his buddies will tell him that was a great idea and as soon as they get $1500 they are going to run out and do the same because that extra 60 hp was well worth it.

Guy B has the same motor and it will make 400 hp na just like Guy A's motor. Except Guy B is running a turbo and at 15 pounds of boost his 400 hp motor is making right at 800 hp (basically his turbo is putting 2hp worth of air in 1hp worth of space). Now if Guy B asks "should I put better heads on my motor" he will get some arguments about how he doesnt need them you are just forcing the air into the motor anyway blah blah blah. Well guess what those heads that make the motor breath 60 hp more worth of air will add 120hp to Guy B's motor! That turbo set up was putting 2 hp worth of air into 1 hp worth of space. So Guy B gets twice the gain from heads as Guy A did for the same $1500. So the guy who is going to pick up 60 gets told hell yeah go for it! and the guy who is going to pick up 120 hp gets told "Dont waste your money!" That one always kills me! Anyway turbo motors always get more "bang for the buck" out of "breath better" mods than the na guys.
Just be carefull not to go to over the top on something. Think of a turbo as a magnifier, the gain from going to a better head and or cam will be magnified. If you go to over the top with some hogged out head and or cam that soft on the bottom buts pulls hard on the top scenerio
will also be magnified.

You mentioned if you dont run enough compression youre afraid the car may be to sluggish off of boost.. I have ZERO experience with turbos and manual transmissions. This post is getting to damn long but if some one asks I may post some info / input on that. You may be suprised about the stuff that goes into that and there is a HELL of alot more involved than compression ratio.

HTH Jason
btw this is too long to proof read so i probably have tons of grammar errors in it and I doubt I could find half of them anyway

Fbodyjunkie06

iTrader: (10)

^Lots of good info there.

Long story short, the LS6 heads will breathe better, and the CR difference will be negligible because you will be in boost faster than you think. Anyone that talks about lag this lag that turbo's lag blah blah blah, has never actually owned a turbo car. Maybe a manual, but with my auto, I never have to worry about lag.

got-a-ls1

iTrader: (12)

thanks for replies guys. I know the ls6's will ultimately make more power and flow more air, thats why i bought em haha. When i said worth more power i was talking $$$ wise as i was planning on selling them so i have to talk myself into keeping them lol... i know the 5.3's can still make power with boooost... and I realize the 5.3 heads dont flow as much air which will result in higher boost pressure but its not like it would be pushing the pt76 out of its efficiency range at 600 rwhp.

Regardless i decided im just gonna run em, i want the compression a little lower and the extra flow will be good for all around power everywhere, in boost and out.

Fbodyjunkie06

iTrader: (10)

Your gonna need a cage too. I wouldn't even mess with a 5pt or 6pt. roll bar like mine. Go ahead and put a 8 or 10 pt. in there and get it good to 8.50's. Trust me you will want to go faster eventually and judging by your NA times you should have the experience behind the wheel to run faster than what a roll bar will get you too.

got-a-ls1

iTrader: (12)

well funny thing about that is im just building this car now to have fun daily driving as im switching to t56. Dont want to deal with door bars on a car i drive daily and only go to the track occasionally which is why i kept getting "talked to" at the track about bars lol... now when i go to the track the challenge is to see how high i can mph without going over 7.35 haha Ran a couple 7.37's @ 99 on street tires with the 100 shot. that was a close one hehe

kmracer

iTrader: (1)

uhhh... how about we ask. street or track, and how much of either? and you're switching to a manual? rear gear? A/R of the turbo?

you do realize 1350 hp has been made with 317's with just a valve job. cyl head flow has little to do with over all power at 600whp.

camaro383

iTrader: (13)

This is interesting, im putting together a 5.3 right now with my pt88 truck manifold kit since my forged 370 is down right now, u think it would be wiser to leave the stock 5.3 heads and adding valvesprings than to put my ported 317's on.. Btw im running a th400 and 3.73's, but i already purchased the 3.08 gears i am planning on swapping in

got-a-ls1

iTrader: (12)

street 99% of the time, track will be for fun only...

currently 3.23 gears. gonna try them out and see how i like them with the 6 speed. Probably not going higher then 3.42.

a/r is a .81. The heads i was talking about are 862 heads, dont the 317's flow like a 243? thanks for reply

kmracer

iTrader: (1)

exactly. its not worth the spool time you're gonna lose IMO. the fact that you have an M6 is already strike one, and a quick spooling setup will be more fun on the street.

and no, you're not going to gain 120hp from a head swap, thats ridiculous.

postal14

iTrader: (8)

It has everything to do with it. Its why the LS motors make so much power. All LS heads flow real nice compared to old SBC heads, and any of them can hit 600hp with a turbo easy. The question is how much boost and what rpm you will need to run to hit the 600 hp. The better the head the less boost you will need to run to hit that 600hp.

The 120hp is from a scenario to explain a principle. If you are only aiming for 600hp with a turbo your not going to find a head that bumps you from 480 to 600, your set up is just going to be to mild. However if you take a 2000hp turbocharged LSX motor with high end heads and swap them out for stockers then that motor will loose ALOT more than 120hp.

The best way to sum up the principal is that turbos are multipliers. Because of this the gains from making the motor breath better are actually larger than on NA motors. There is a false concept that "You're forcing the air into the motor so it doesnt matter as much". This is wrong and the fact that the turbo acts like a multiplier makes addressing these issues even more worth while. BUT if you are limiting yourself to 600hp there isnt much of anything I would worry about spending money on, but you have a better set of heads just sitting there already.

I am new to LS stuff and I have been researching up like crazy. In my online researching I cam across an article a couple years old. I think it was a hot rod article. In this article they had some nasty twin turbo LS build. This was NOT that newer 4.8 @ 1200hp article. I cant remember all the details but it was some twin turbo LS they had on a dyno and they where at 1200 hp or so. They felt like something was holding them back and they wound up unhooking the dyno exhaust. The motor immediately jumped to 1500hp!! That was a 300hp gain from changing the exhaust. They even stated that they where surprised because the dyno had a freakin 5" exhaust system on it, and they thought it was more than enough. If you are wondering HTH a motor can gain 300hp from an exhaust mod then read up in my original post about making the motor breath better and turbos multiplying the gains from these types of mods.

HTH

Fbodyjunkie06

iTrader: (10)

In the new GMHTP magazine they address this exact same issue when they swapped heads and a cam into their project GN. They had to go to a bigger turbo to support the added flow from the heads that the motor gained because the powerband was peaking way earlier than it did with the stock heads and cam.

kmracer

iTrader: (1)

the same principles apply above. backpressure was obviously a massive issue on that engine. TURBOS DO NOT MULTIPLY THINGS. i have no idea where you're getting this information, but you're wrong. there is no x4, x2, +6, -2, /5 with selecting turbocharged engine components.