85Iroc

iTrader: (12)

I have a 2008 G8 GT. It already has a cam and headers. I have a set of 229cc CNCd 243s and a fast 90/90 that I was going to put on my Camaro but I’m thinking of putting them on the G8. How would that compare to just having my LS3 heads ported?

brandon6.0

iTrader: (32)

Ls3 will flow more. Its really up to u. The 243s with the fast will put it easily over 450rwhp

Guys making around 500rwhp with the ls3s stock

85Iroc

iTrader: (12)

What about the 243s vs the stock LS3?

G Atsma

Yes. A cam will do it. Stock LS3 heads can support 600HP.

Darth_V8r

iTrader: (4)

That's an interesting combo. What camshaft are you running in your LS3? Your compression ratio with that arrangement will be 11.5, assuming a 0.048" head gasket. So if you still have the factory cam, you might find detonation to be an issue. if you are running an aftermarket cam and your IVC is around 46 degrees, you would find that this arrangement works pretty well.

Overall, Youd likely get better midrange results but drop off sooner at high RPM. The LS3 heads seem to shine at higher RPM with stock displacement

85Iroc

iTrader: (12)

I didn’t realize the stock heads would support that much. It has 224/228 cam on 111 lsa. Not sure what the ivc is.

sounds like I should just get a valve job and cleanup on my heads, mill them .025, get a bigger cam and raise the shift points. Save the 243s for another project.

85Iroc

iTrader: (12)

I haven’t had my car dynoed but it doesn’t feel like it’s making as much power as it should in the upper RPMs. I don’t know if I did something wrong on the rebuild. Its rattling a little bit in higher RPMs, which would explain the loss of power I guess. I didn’t mic and shim the Valvesprings. Also just put in 7.4 pushrods and didn’t check. Maybe they’re too short without the heads being milled.

You guys think those those things would make it feel like it’s down about 50hp?

Patron

Yep if you think somethings wrong ...... fix it 1st Then decide. Add up the cost of new heads,intake etc for the Ls3. Just do the right thing then decide you may like the way it runs if it's right with what you Already have. You can alway do another top end.

Darth_V8r

iTrader: (4)

The guys getting 500 hp are getting it in the 6500-6800 rpm range. So if your valvetrain is holding you back from revving, yes it'll feel down on power. Rattling can be lots of things. Spark knock, loose rocker, etc.

Without knowing more details, it's hard to diagnose but if I had to guess I'd say you're dealing with valve float. But there are so many variables. Like what cam you're running

85Iroc

iTrader: (12)

224/228, .6xx lift, 111 lsa with .660 lift btr springs.

A.R. Shale Targa

iTrader: (2)

That cam is so close to a single pattern with only having 4 more on the exhaust side, and with the narrow lobe separation, it's less than ideal for factory LS3 heads. It'll peak early and not carry long after peak.
A very popular one is that 229/244 that quite a few people are making near the 500 rwhp with....you wont be able to mill the heads much if at all.
Make damn certain the spring kit is installed at the correct height....sometimes -.050" locks will help achieve the proper seat/nose numbers
Texas Speed has complete combos to get you there

Darth_V8r

iTrader: (4)

If PatG tuned it he would have likely noticed valve float. Personally, I think that cam is a bit small and might actually be a better match for the 243 heads vs the 823. But that's for my tastes and goals. Typically LS3 heads like more split like 224/238.

85Iroc

iTrader: (12)

I would be happy to change cams. I didn’t even check the Valvespring installed height. Could that cause valve float? Could they be that far off?

So if I don’t need to mill the heads do I likely need 7.425 pushrods?

85Iroc

iTrader: (12)

Also I didn’t notice the valve float til after a few hundred miles

brandon6.0

iTrader: (32)

rattling is most likely spark knock. bad gas or something.

U said he mail order tuned it? not in person? this could be the issue. Makes a big diff with someone sitting in it and tuning it. Not all cars are the same!

If It was mine I would sell the cam u have or save it for the 243s. Actually not a bad cam for them. Get PatG to spec u another cam with a wider split. I would want something in the 6800-7k rpm range. Should really wake it up with the higher shift points.

Mill your heads to achieve a lil more compression if u can. Check PTV first! Doint a decent valve job wouldn't hurt. Sell the fast u already have for a ls3 102mm.

Done! if that don't get u 500rwhp I don't know what to tell ya. Make sure u have some good flowing exhaust.

Darth_V8r

iTrader: (4)

That makes sense. I think I'm getting my thoughts crossed, because I saw people saying 500 HP, and you're not going to get there with that cam regardless of heads. Again, you should have pretty strong midrange (2000-4000 rpm) torque though. I still think that cam is a better match for the 243's than the 823, but PatG knows more than I do, so take that comment with a grain of salt.

Your current combo, you're probably in the 400-420 neighborhood

Valve float was a guess on my part. Typically, you'll see it on the dyno. I'd talk to PatG about it and see if he thinks it is possibly an issue.


Good call on spark knock. OP, if it sounds like you're shaking a spray paint can, that's spark knock. With a PatG tune, I assumed that would not be the case.

Jenson

iTrader: (32)

I bolted an LS3 with PRC 2.5 243 heads together for a buddy with a 235/243 cam, did 506rwhp M6 with a fast 90/90. Not hard to do. One thing though, did you swap the G8? If not thats an L76 and not an LS3. And for reference the stock LS3 intake runner cc is about 258 IIRC and probably flow better than the 243's you have depending on who ported them.

85Iroc

iTrader: (12)

I think it is spark knock. It's a 93 octane tune. It rattles consistently, so not just one bad batch of gas. I guess all of the 93 octane around here could be questionable. I was thinking of running some race gas and see if it still rattles.

He remote tuned it so it isn't a canned "mail order" tune. I logged files and sent them back to him and he sent me new tunes. Still probably not as good as in person.

I've decided to stick with the factory heads and get a valve job and have the bowls blended. Get a new cam and probably have it tuned locally, just because I think it's easier/better to tune that way. And have the shift points raised.

It feels strong in low and midrange, but having a 9.5" 3400 stall helps that.

I'm gonna use the 243s and fast90 on my son's s10.

How much better are the LS3 fast 102s than the stock intake?

85Iroc

iTrader: (12)

That is exactly what it sounds like. If I remember correctly, I didn't start hearing the spark knock until after a few hundred miles, so it was after I had exchanged log files with PatG, so he wouldn't have seen it.

I had problems when I first put it back together because of a bad cam sprocket, of all things. Would barely start and had cam position sensor code. I'm wondering if that may have affected it or damaged something?

85Iroc

iTrader: (12)

No, it's still the L76. Only difference is the 6.0 vs 6.2 right? I mean I know the DOD stuff and cam was different, but the heads and intake are the same aren't they?

I'm definitely keeping the square port heads.

And I don't expect big rwhp numbers through this 6l80. In fact I don't care about dyno numbers at all.

I want the combination that will make it through the 1/8th mile the fastest. No 1/4 mile tracks close.