gnx7

iTrader: (28)

I purchased an '06 GTO LS2 shortblock and installed new rings and some rod bolts as #7 was at 165psi vs. 180 in all the other holes and had some oil consumption shown on the plug.

I'm torn between doing LS3 heads or some ported 5.3 heads I have already. My buddy will sell me a set of ported LS3's for a good deal which is enticing.

I've read about the valve shrouding issues running the LS3 heads on the LS2 bore. Wondering if I should just stick with the 5.3's I have....

I have an LS6 intake with ported TB already and 42lb injectors; however the LS3 intake complete can be bought for $300 easily.

So what will make more power? I'm building this to go road racing.

Thanks!

1nasty86

iTrader: (63)

MY vote gets prc 2.5 5.3's

Samer

Go for the ported LS3 heads and never look back

Just check with your buddy if they are milled or not and what's the combustion chamber size.

LS2 guys are making 450 - 470 rwhp with STOCK LS3/L92 heads and a mild cam

oakley6575

iTrader: (3)

Seems like people are making great power with LS3 heads and a small cam.

1nasty86

iTrader: (63)

the ls3 heads really hurt you on not letting you run a bigger camshaft unless you flycut. Agreed ls3 heads would seem to make more hp but he already has a ls6 intake and injectors etc. and cathedral port heads can make awesome power too. I myself made 463 with a set of 317's on a ls2 with a 230/238 camshaft

Fbodyjunkie06

iTrader: (10)

Plain and simple the 5.3 heads will make superior low end and midrange where as the LS3 heads will really start to shine above 5200rpm and when you get into .400, .500, and .600" in valve lift. The big intake port is really lazy down low and it might be even more pronounced with the 6 c.i. loss you have over a LS3 block. It all depends on if you want to have great airflow for potential deep breathing up top, or do you want it to scream up to 6200-6400 and have a great torquey car that will kill 4 cyl. and turbo porches off the line and out of the corner.

Choice is yours my friend

COPO9560

First question is who did the porting on both sets of heads and what condition are the springs in. The ported LS3 heads will flow more and have a higher peak hp potential - not sure what you need for road racing.

The LS3 assembled intakes for $300 usually don't come with a TB - don't forget to add this into the price.

briancb1

For LS3 heads, Most people can't run a proper cam because of PVT issues. If u were able to cut valve notches in the pistons and run a decent sized cam it would make 450ish torque and almost 500 to the wheels. Look at the the camaro5 forum, it's been done a 100 times. Problem with LS2 guys is that we all mill the heads to much and get cams that are too small, then the cathedral LS2 guys will chime in and say how much better they are doing.

In conclusion do it right flycut the pistons for the LS3 heads, get a good LS3 cam with low 230's intake and low 240's exhaust (MTI and vengeance have ideal LS3 cams this size) and make some awesome power.

litle88

iTrader: (20)

Ls3 and be done with it.

You don't need alot of lift on Ls3 heads, from my research all you need is more exhaust duration to complement how well the intake flows. Remember its not lift you have to worry about for PTV Issues, it's the LSA and duration. I'd also swap the stock exhaust valves for some inconel valves. But that's just my .02

Samer

Yes, LS3 heads will have PTV issues if you are going for a big cam but in fact, you don't need a big cam to make power with LS3 heads !!
Patrick G have mentioned this fact in several threads.

People are making very high dyno numbers (460+ rwhp) with samll cams and STOCK L92/LS3 heads.

Have a look on this thread to know what I mean.

https://ls1tech.com/forums/generatio...s-learned.html

gnx7

iTrader: (28)

The heads are hand ported 5.3's milled 30 over, 59cc chambers, with 2.02/1.57 ferrea 6000 valves, and patriot extreme gold springs rated @660 lift. I dont have the flow chart anymore but flowed right at 310cfm. 2K miles on the new springs.

I have an LS6 intake and just bought a complete LS3 intake off of eBay. I'm not worried about the extra cost of the 90/92mm TB in the grand scheme of this build. Losing a little mid range power is ok... just not a ton.

The LS3 heads have a few thousand miles on them are SDPC ported heads with upgraded valves/springs I got from a local buddy who stepped up to some MAST LS3 heads.

I don't want to run a huge cam. I need good mid range power that will carry all the way to 6500rpm Only when a little extra power is needed will I shift above 6500rpm to pass someone etc.

In reality the engine will rarely see below 3000rpm during track duty and spend most of its life in the 3K-6500rpm range. Car will be about 2800lbs wet with fuel including driver maybe less. Mazda FD RX-7 is the chassis. Running a Dailey billet dry sump system to ensure proper oil supply from a Pontiac GTP car.

litle88

iTrader: (20)

You'll also be at 11.89 on the compression side if you use the 5.3 heads using stock GM MLS gaskets.

Just another angle for you to think about too.

gnx7

iTrader: (28)

This engine is going in a race car so it'll either be run on e85 or a mix of 100 octane and 91.

I'm leaning towards the LS3 setup as the heads flow from SDPC about 350cfm on the intake and the 90mm TB will flow more as well than the ported stocker. I just picked up a C6 K&N cold air intake setup with filter to go with the combo.

Do you guys think I can make 500rwhp with the ported SDPC LS3 heads, Patrick G 226/234 114LSA cam, home ported LS3 intake, 90mm TB, the C6 K&N cold air, 1 7/8" headers, dual 3" into a single 3.5" exhaust thru a T56 with Cobra IRS 8.8" diff running 3.73 gears?

67RSCamaroVette

iTrader: (63)

I would say that it depends on the compression ratio...

Gregory

iTrader: (4)

-- No --

WKMCD

iTrader: (2)

I really can't believe people are still repeating 3-4 year old BS about L92/LS3 heads having no bottom end power.

Run the LS3 heads with a smallish cam every time.

Just my $.02

Samer

YES, you will be very close to 500rwhp with good tuning

gnx7

iTrader: (28)

I'll be dry sump and have a lightweight clutch/flywheel combo so that may eeek the combo closer to 500rwhp.

LS3 top end here we come.

oakley6575

iTrader: (3)

Only people without LS3/L92 heads say bottom end power is sluggish. I've never talked to anyone with LS3 heads say they were disappointed with there low end performance.

I think with a good port on the heads and manifold, you might see your 500rwhp goal. Good luck in your build

Fbodyjunkie06

iTrader: (10)

Well obviously with 450+ rwtq your not going to complain, but how hard does that tq. curve come on and how much more violent is that midrange to redline not just 5500+ where it is screaming. I understand this concept perfectly, I don't experience any tq. in my car until 4000 rpm. Once it's there though I do not complain about it at all because I can usually 9/10 run right around the guy, but for road racing on a tight twisty course unless your at Talladega or Daytona your not going to need 500 rwhp at 7200 rpm. This is just my .02 as the guy asked us for it.

Either way your combo is going in a 2800-3000lb car so that extra 30-40ft-lbs. 1000rpm earlier will likely never be felt or lost. Sounds like it's going to be a freaking awesome slot car of a combo. Have fun giving it to the vette and porsche guys