I have a crate GM LS2 I have had ratted back for the last couple of years waiting for the right GTO to come along. I dropped a GM ASA cam and matching valve springs into it and buttoned it back up soon as I bought it.

Is there much more power to be had by swapping out the 243 heads to a set of late model rectangle port heads and intake on it. I'm looking and waiting for the perfect dark blue 6 speed car to show up and get deal done and put this motor into it.

 

I personally wouldn't do the swap.... The rectangular port heads will only outshine the 243 heads after 4000 rpm. If I was in your shows I would consider having the 243 heads ported or go to a serious cathedral head such as MMS heads if not them go with tfs...

 

I would use a set of 821 ls3 heads on the ls2 block it will turn circles around the 243 casting.

 

Boy oh boy the same saying always comes up: The TFS or the AFR heads make more TQ and add to more MONEY go price a pair of either. Man I'm so tired of the same saying cause FAST intakes and Cathedral do make some serious TQ. It is the guy who can Cam the heads correctly. With that being said all you cathedral port guy's go look @ the most basic Cathedral VS Rectangular .....1 was in Hot Rod with a 408 and the other was in GM High Tech Performance Mast Cathedrals heads VS there Rectangular Ports ....Nothing special there. Or how about WKDM with LS3 heads.......Most people just see bad TQ numbers but DO NOT want the real reason why they didn't make TQ.
Camming is the real issue. Tell all your friends so this LIE can DIE.

 

IMO if youre 4 inch bore or bigger the best bang for the buck is the LS3 heads. To get the same flow you'll spend double on aftermarket heads.

 

However flow is not the end all when it comes to power. On a 4" bore I'd rather take a small runner (205-215) 310cfm head with strong midrange rather than one with huge 260cc runners that *flows* 320-330.

As far as the OP, it's all in really what you want for the car and how you drive it. Do you want a topend monster with big stall and/or gears then you can't beat the power capabilities of good flowing big runner/valve heads like the LS3 rectangular heads. If you want an overall good performer with plenty of punch down low also then look into a ported version of your 243s.

 

Tamu.... is your car a 6 speed or auto?

 

Heres a post for all the lost souls. Do you Cathedral head lovers want more post as YOU KNOW I got IT.

https://ls1tech.com/forums/dynamomet...226-234-a.html

Cam choice!!!!! I won't say what I really want to say about this. As it would start A LOT of $H!+

My question is what do you do once you want to go bigger....Oh go buy some new heads...LS3 go from stock to supporting over 800hp and *1 cheap with 1 overall theme I can use the same head for *2 stock engine setup to a *3 all out ls drag engine. Seen both. You can't get all three with a cathedral port.

 

You know, not everyone drives at WOT 100% of the time. So unless this is a dedicated drag or road racer then just purely looking at dyno numbers and completely ignoring all other driving aspects is silly. Also, a cam can only do so much...it's not going to change the physical aspects of the heads themselves.

Why can't a fully ported 243 match the power capabilities of a stock LS3? And once you get into modding the LS3s to go with *3 over there you are far from "cheap" and at that point you can find used big runner aftermarket cathedrals to make all the power you want.

My point is, there's a pro/con for both types of heads and OP really needs to tell us more how he drives and uses the car to say which one might work better for him. Until then, you're just swinging off the nuts of LS3 heads and just spewing whatever you think is good regardless of what goals the OP has and whether or not the LS3s will even fit those.

 

No...No ..No . I own ls3 heads. So let get this straight that cam choice was nice for a ls3 6.0 build not a WOT race engine. And it made TQ BTW. I don't just ride ls3 heads as I'm getting better heads this MOURNING. All I'm saying is **** a pair of cathedral style heads. * And the horse they rode in on* If you want me to be point blank. YOU CAN NOT GET ALL THREE THINGS LISTED above:
1)CHEAP
2)Works well as a stock basic head
3)Can Flow like a ***** for dirt cheap and still support a all out 450 ci + engine with solid roller and high compression.

Now tell me, you can get all 3 with a Cathedral style head.
Run tell that to ANYBODY.

 

Have you ever stopped for a second and thought to yourself that maybe, just maybe, that guy doesn't give a rat's behind about getting all those 3 things? If he flat out came in here and said "guys, I want a cheap head that works well on my stock crate LS2 but will also support a 450 cube high compression monster" then I would agree with your statement.

You have not once actually asked what the OP wants, just started spewing "**** cathedrals they are crap". To me, that doesn't sound helpful but just pushing your agenda...which is quite well known around these parts.

 

What would anyone in there right mind want. Do you like having 1 option or three, simple as that. He asked what heads would someone recommend, and I gave him the most straight line answer. Stop living in 2002.....when cathedral heads were the ______.

 

Me personally? I would want a set of heads that EXCELLED at 1 thing rather than be just AVERAGE at 3 (with that thing being the type of power I use and what I would want out of a driving experience).

A head swap is simple, especially if someone goes from a stock cubed LS2 to a 450 cube LSX. If he at a later time goes to a huge build, he's gonna have to pull the heads off anyway at which point he can upgrade accordingly. No sense in compromising now just for the sake of future compatibility...which may never ever happen.

 

You don't think he would or could be happy with a set of stock LS3 heads VS Porting a set of 243's. And when you say accordingly you mean spending $3000+ when a good set of ls3 just need a good CnC program $990 to $1200. BTW... I'm just messing with you RED.
My WHOLE thing is LS3 don't make TQ which is TOTALLY WRONG......

CAM Choice!!!!!!!!!!!! With that being said we are back to the point of 1 option VS 3 options.

Someone may remember this line from Seinfeld: Jerry insists that his new girlfriend has implants. But she keeps insisting that they're "real and spectacular"
Same goes for ls3 heads it's a "Baller on a budget type of head.

 

I never said he wouldn't be happy, but I have no way of knowing that without more information from him. I do think that both of these heads have their weak and strong points and that neither are a "one fits all" type thing.

Which is why I go back to my point of getting all the facts from him on how he wants the car to peform before suggesting something.

 

It will be a 4:10 geared 6 speed and 99% of time on the street. I'm not looking to spend big bucks on aftermarket parts. My goal is a set of production GM rectangle port heads or GMPP CNC ported heads with my GM ASA cam as the cam. Big dyno numbers are cool but that's not my goal. If it's a real worthwhile gain and *** dyno noticeable then I'm game. It will have kooks headers and ORY and probably borla catback FWIW if it helps lay out my plans. I want a great stone reliable driver. That can lay it down here and there.

If it's really worth doing then I'll hunt a set down. If it's not really worth doing for X amount of horsepower gained then I wont mess with it and I'll leave 243s on it and call it a day.

This engine was originally slated for my TA which has been in paint jail the last 1.5 years I'm about to pull the plug on that project sell off all my Fbody parts and slide right into a GTO. I'm looking for the right car right color right price and well cared for so I don't have to rebuild the whole damm car.

 

Geez I say no aftermarket parts mega buck build and everyone loose interest.

 

The one and only flaw I see with qouting the Hot Rod 408 article is the fact that engines are just air pumps. These cathedral VS rectangle poo flinging argumants come up when folks want to put them on a 4" bore LS/LQ style engine where the 408 has 5.5 more cubic inches per cylinder tugging (NA) on the larger volume runner so of coarse it's going to make great streetable torque since at the very least it also has the 4" arm swinging down below. You are right that plenty combos tend to improperly cam their rectangle headed 6 liters because everyone always wants thump; then wonders why there's no jump.
The other dilemma being faced is the compression ratio of a 6.0 is hard to get or gain as the giant intake valve quickly begins to marginalize piston to valve clearance and then if someone wacks the 68cc chamber down and runs a thin gasket, well then a 222 sized intake lobe is all that will fit and then again there just is NO LUMP......
I'm old enough to not really give a crap what it sounds like cuz to me it's all about the butt cheek dyno.
GM clearly did their homework on the LS3 stuff and your "baller on a budget" statement is true...especially considering what the factory LS3 intake can be had for when the FAST cathedral stuff is near a grand or so.
Flow per volume is a real thing though and while the stock LS3 head easily eclipses the 300 cfm mark, it does so with a 260cc runner using a 2.165" intake valve. IMO most but not all street cars will fair better with a 300cfm runner in the 225cc range and doing so with a 2" or 2.05" valve.
I would have loved to see how Dr. Whigam's 240cc MAST rectangles would have done on his 346 vette but unfortunately we'll not get that test result now........
For my own generality sake, anything stock stroke, whether 4" or 4.065" bore, when running the LS3 head, consider camming conservatively with a 10-14 degree exhaust split and unless the rest of the combo (gears,converter, etc.) is wrong, it will perform great in most all driving situations.