You'll need a set of intake rockers, and of course valves. The rest of it works fine. I'm a fan of the square port heads, a lot of guys don't care for them, but I've seen super nice results from them. Be careful with the cam selection--I'd get someone who knows their business to help you select one.

 

Intake

 

^I don't know how I left that out! Lol!

 

Need ls3 rocker stands too

 

All said above....but were your 317's milled ?
Depending on cam and/or milling, you may need to fly~cut the pistons due to the valve size.

I ordered everything from SDPC. (heads complete and springs upgraded for my cam)
I was looking for used heads, but by the time I added springs, and shop time for rebuilding, it was way higher than new.

LOOK AROUND.

 

for velocity on a 6.0 you are better with a proper ported cathedral. The big ports on the ls3 loose velocity with the smaller bore and the valves on the ls3 heads get shrouded on the 4.0 bore.

I have been through this recently. Seeing How I ended up stroking to 408 .030 bore it helps unshroud the valve for flow and I then am running the ls3's with a proper cam for it.
You will have slightly better throttle response with the smaller ports and HP In the usable range rather than toward the to with those large ports.

but I think in the end you start to split hairs it comes down to where you want your power to be vs a dyno peak number


That's just my .02 anyway

 

What are you going to be doing with them?

 

They are bad heads. I have no cathedral numbers to compareto, but my car does ok I guess. times in sig.

 

2 questions, why change the valves, and does anyone have a dyno sheet from a 6.0 with ls3 heads on it?

 

LS3 heads stock for stock are better than 317s. No question. For N/A they will outshine a set of 317s, 243s, etc.

H/C LS3s can make 500rwhp, stick, Dynojet, not going to see a 317 or 243 headed engine routinely make those kinds of numbers.

 

Proof of times from the 2 On a 6.0? Track times not Max dyno HP. Id be willing to send stock 799s to compare.

 

The square port is a whole different animal than the cathedrals. Right down to how the engine behaves and drives its totally different and imo they are more prone to detonation too. I do prefer the behavior of the square ports after trying both on the same car. They are tricky to cam properly and there is a LOT of testimony out there about less than stellar performance on the 4" bore with shrouding complaints which I cannot speak to as im on a 4.065" bore.

I still think properly cam'd Id build a 4" bore with the square over most of the cathedrals out there. It takes quite a decently ported/prepped cathedral head to out run a stock square port

 

Ive used both heads. The square ports are lazy down low under 3k. The 317's were way more responsive and more fun on the street. With the square ports, all power came in later as the 317's had more velocity.

 

That has NOT been my experience with square port heads. I've not tried a big whopper cam in one, and I think a lot of people over cam them.

 

for anything under 400ci N/A i'd stick with a nice ported cathedral head. once you get over 400ci you can utilize the big 260cc runner the LS3 head has to offer. until than you lose the velocity that a well ported cathedral will give you. just my .02

 

I can believe that, especially if the cam was optimized for the 317s . I don't think the LS3s want nearly as much intake duration as the cathedrals, but I'm just going off of what I've put hands on. Do you know the specs on the cam? I text messaged my friend with one of the cars I was speaking of earlier. He's supposed to text me a dyno graph when he gets a chance.

 

Edit: I need to read better lol! The cam in his car was substantially smaller and made very respectable power. It never ran hard on the track because it was an M6 GTO, and well, yeah. We duplicated the setup on another car with a 6L80 and it ran very well for such a minimal setup.

 

Not many people put in the effort to get a stick car to work properly. It way more difficult than an auto.
I love the square port heads

 

Agreed. This car was his daily at the time so slipper clutches and proper suspension for drag racing weren't going to happen. The car was just as comfy going 180 MPH as it was putting around town, and it got 26 mpg when I drove it home from Valdosta a few years ago.

 

Don't get me wrong, the square ports would blow the tires off at 50mph. It's just that they didn't make great power until 3k and up. I felt the square ports made more peak hp but the 317's made more average hp and the torque came on substantially sooner. This was 9.4:1 compression 6.0.

 

The owner of this LS3 got a peak of 476 hp during the same dyno session at vengance, this was with a little timing backed out for pump gas safety.

The Corvette we put the identical cam in ran 11.20s with no other mods except some OBX headers and bi-mode exhaust. Still on the stock converter. I'm pretty confident it could have run 10's with a converter and some tire under it.

 

Ive run many engines in the same car. Last two back to back were a 346 LS1 with stg2 ported cathedrals, 224/224/112, LS6 intake did 380ish whp ran 12.1@112 and was a SWEET street car as it almost never blew the tires off.

Next engine box stock L92 longblock with a 222/230/114 cam, LS3 intake and otherwise identical parts/gears etc. Same exh and other components as LS1 set up. Ran 11.8 @120 blowing the tires off 1&2. Lots more in it.

On the street? The square port heads make so much more snap that its almost impossible to just roll out smooth WITHOUT blowing the tires off. The increase in torque below 4000 RPM is so noticeable it feels like a completely different car. Up top? Damn thing WAILS too, pulls to 7200 with that little cam.

Square port > cath port? Gets my vote. Easy vote too.


Over camming the square ports is a big risk and easily done imo. Worth noting I also retained the VVT and run a phase that rolls retard in around 4500 and maxes out at 5500. I start with +4 in the cam grind and roll it up to -4 with the phaser.

 

Make sure I read that correct, 5.7 compared to a 6.2? 315hp stock vs 405hp stock? I'm confused

 

Similar combos in terms of target goals. Only difference being 9% more cubes with the 378 vs the 346, heads, intake manifold. Thats it. The entire rest of the drivetrain and combo is identical and after 3+ years of running around both combos in the same car I really prefer the LS3/L92 head over the cathedrals behavior. Theres more range up top, and more torque down low. Lots more than 10%

 

The LS2 we pulled out of the GTO was in that very same boat. It made less peak power and WAY less under the curve. It also had quite a bit different strategy on the camshaft. About .050 more lift and 15+ degrees more duration on both sides IIRC. He remarked many times about how much more fun the car was with the LS3 in it.

 

have no low end problem here. Basically the same combo prostockjohn quoted. I should be in the 9.8-9.9 range this year.

 

LQ4/LS3 combo, heads shaved, 10.5:1 comp, pistons notched, 23x/24x cam on a 110LSA, +.600 lift.
4500 stall (was, now a 5000) so no worries about low end TQ

11.3's with issues and base tune in a 3300ish pound car.

 

I have no doubt you can make more peak HP for less money with LS3s especially with the price of GMPP CNCed heads but I've never seen a good apples to apples comparison, IE same size/compression ratio with optimal cam for both combinations.

It seems like a lot of guys are looking for high MPH or peak dyno #s rather than a combination for wining rounds.

Can any of you guys that have tried both say if either has a consistency advantage for bracket racing?

This kind of reminds me of the BBC square port oval port argument. There was a time I'd rarely see oval ports on a race car then people started porting them & a few guys I knew found the were nearly as fast as square ports on their cars & were more consistent and won a lot more with them.

 

I've got L92 heads on my GTO, BTR cam 22X/23X 114 LSA. Putt putts around town just fine at 1k rpms in 6th gear. Heads are stock, I purposely didn't shave them because I wanted the compression drop 10.9:1 -> 10.4:1 because I'm going to turbocharge my car. I don't feel like I gave up any throttle response or low end compared to when I had my 243s, but I also was running the stock cam with my 243s.

As mentioned by others, I think people over cam the L92/LS3 heads and then are disappointed with the results. Don't need as radical of a cam as the cathedral heads.

Honestly, with as much luck as people have turbocharging the 5.3L's, my rect. port heads are pretty much the only thing keeping me from selling my LS2 and dropping in a Gen IV 5.3L. I don't want to give up my L92's.