All this talk about rect vs ovals has my head spinning!

The general Concensus is that the Ovals are a better street/strip head.

I have a neighbor that wants my Ls-6 (crate motor) heads, and hes willing to trade me a set of ovals for em.

The Ovals are 702's, the Rects are stock ls6 style heads.

Would I see a gain in performance with the ovals?
And more importantly, can I even bolt these one with my pistons? (SRP 10.25:1)

Oh, and combo is

496
10.5:1 compression
Ls6 heads milled .020
Lunati Solid Roller 292* 300*, 260* 268* @.050 .685 lift
Victor Jr Single plane (i still have the ls6 intake)
Holley 950hp
2" hooker super comps

What's your current performance?

i would sell the rect heads and use the money from it to buy ovals.... that is if you want ovals...

With those cubes and cam, keep the rectangle ports.

Originally posted by Rmchevelle:
What's your current performance? Current performance is....
Unknown. The track in my neck of the woods is pretty far, and I havent had a chance to take her up there yet.

Itll smoke the tires from a 30mph though,as long as you want, with 275/60r15 Bfgs

My first 2 gears are pretty useless, even with the drag radials. :D tongue.gif

2-3 tenths.

GM iron oval ports worked by the right hands are good up to 700hp and 7000rpms! Which means they're perfect for a street/strip application

Is the 702 a closed or Open chamber?

the 702 is a early 396/427 head with about a 96cc chamber. they would give to about another point of compression.

There closed chamber.
Nearest I can figure, they'll give me about 11.3-.5 compression. Im fine with running better gas, but I want to make sure these heads will really give me better performance...
Are all ovals really equal?
What are Ed's ovals? Ive heard you can hit water jackets really easy with these heads..

If you don't race at the track and can't hook up now why bother?

Originally posted by Doug F.:
If you don't race at the track and can't hook up now why bother? I normally run at the 1/8th mile thats about 45 min from here, but I havent gotten her down there with the new motor. With the ls6 crate in bone stock form, I ran a 7.9. Unfortunatley, the track only has Reaction time and et on there slips

I also have some 28x12.5 et streets on the way,
and some new suspension pieces (qa1 adjustable shocks, dick miller rear suspension pieces)

On a 496 cube motro cammed up that size I think the rectangulars are a better head...

I'm an oval fan, and even used them for my 505 motor but with a mellower camshaft and slightly less compression.

I doubt you will gain anything with the ovals in this case. If you had fewer cubes, or lesser cam maybe.

I also doubt you would lose much using a ported oval with the same size valves too... Jut not worth the trouble or expense of the swap with your combo.

i would probably use the rectangle heads also for that motor but oval are good too. there are peanut ports to stay away from but most of the other oval ports are about the same size. try www.mortec.com (http://www.mortec.com) for head specs.

Hm.. thanks for the replies guys..
Got some decision making to do. tongue.gif

Which LS-6 head? 291s or 880s. The crate motors came with either. I have gone really fast with a mildly ported set of 291s (faster than a set of alum raised ex port heads)

Its a later set of heads, the block is stamped 7.4L,
and the heads have Hi-Perf cast on em,
Ill get the casting #'s when I get home.
I think it was the predecessor to the modern 454 HO crate motor...
10:1 compression and solid lifter cam, GM dual plane, etc.
Im pretty sure there 880's

This will be an unpopular response, but I would be inclined to change the GM rec Ports for aftermarket raised exhaust runner rec ports. Otherwise, work on your suspension to actually make the car quicker.

one thing i see that nobody touched yet, the crate 454 rec ports are open chambered, and the oval ports in question are closed chambered, if you have open chambered design pistons the oval ports won't work, at least not without cutting on the pistons.

6272990
Heres the casting number.... stamped "hi-perf"

Why would you take heads off and change if you haven't run the car with the current heads?

If it were me, I'd run the car as is and see how it does and if your satisfied with how it performs. If you wanna go faster at that point, then maybe look into a different set of heads.

If yours are currently open chamber and you need/want to keep the compression the same, then search out a set of 049 or 781 heads large oval heads.

BTW, the 990 head is a popular performance head. I would NOT trade them even up for the oval ports your neighbor/friend offered. You can easily sell your heads for more than his are worth.

EDIT: Sorry, didn't see his heads were ported. I assumed they were stock castings in need of reworking. Either way, run the car and get a baseling of it's current performance, then make your decision about a possible head swap.

If you can wait until tomorrow night I will be able to tell how a pair of 702's perform on a 461 (I'm headed to the track).... They've got the big valves and have been mildly worked. The guy that did the head work didn't act like he was worried about hitting the water jacket, but he said he thought that a pair of open chambered heads (like yours or 781's, 049's, etc...) were more efficient....

if you got 990 casting heads, then the 702`s won`t work. like stated by another member, open chamber pistons won`t work with closed chamber heads. you can run closed chamber pistons with open chamber heads. i would stay with the 990`s. my buddy had them on his low 11`s 9 to 1 454 and then low 10`s when he bumped the compression to 12.5 to 1. just do a little bowl work and maybe a gasket match on the intake and you should have a pretty good running motor.

Thanks for the replies guys,

10secbeu- I will get a baseline first, I just get impatient sometimes tongue.gif

sschevellefan- That was one of my big q's, thanks.

Purs- let us know how she runs!

I think im going to stick with my 990's for now, and maybe save for a set of AFR's down the road. graemlins/thumbsup.gif

Why not have the 990's reworked with epoxy to make an oval port, perferably done by someone whose got alot of experience in doing such work.

Motor Martyr :confused:
never heard of such a thing graemlins/clonk.gif

:D send me an email i'll refer you to someone who can do the work.

Motor Martyr.. youve got mail!

I have seen intake runners reshaped like that, but I was unaware that they did heads that way. I would assume what they do is raise the floor and fill in the corners to get an oval shape.

Id never heard of it before, but im quite interested

Definately keep the 990's for that combo.

Oh gads.
Keep the 990's. Maybe have them pocket ported by someone who knows what they are doing.
Sure oval port heads can work real well, but only when ported by the right person. There is more to it than slapping in the bigger valves.
If you really want to make more power.....do some research and buy something from the aftermarket.
Ron