Hot Rods big block chevy head swap

Good morning, can I use 3931063 oval port heads on my 1970 LS6 454+0.30/450 (TRW 2349) using rectangle 291 heads (closed chamber) now. The cam is a L88 540/560 solid lifter. Any help will be very much appreciated. Thanks.

 

Yes you can but why do you want to change them

Pat

 

should work. You really want 188 or 990 heads though

 

Hello Pat, Thanks for your reply. It seems to be the better choice for street use. I never had any problem with the 291s in the very early 70s, just thought the 063s may work better at low end now and the 063 s have more work in them. Thanks again for the help. Charlie.

 

I'd change the cam long before changing the heads....that cam is way too long duration for what you're trying to do with it. The rect port heads are fine on a street car. Although compression ratio may be an issue, depending what fuel you want to use.

I had a 454 with 291 heads, it worked well, although the car needed more gear than I had in it at the time.

 

Thanks for the reply, I agree but I have had these since the 70s and never used them after the head work. Thanks.

 

This is my last time around still love the solid lifters. Everything is much better than over 50 years ago for me and its only for local drives. Thanks again.

 

Let us know how the head swap works out

 

When I ran this motor over 50 years ago I ran it with 5.13s. Thanks

 

Will do.

 

heh...I had 2.75 in mine!

 

My question would be which intake are you using? If it's not designed for oval port heads then the mismatch of intake ports might not work as well as an intake specifically designed for oval port heads.

 

I have a Weiand Stealth (8019) oval port with a AED 850. I have seen guys do the mismatch and it seems deliberately. Maybe they know something I don't know, I wouldn't try/do it. Thanks.

 

from guys who've done it, it doesn't seem to be a problem.

 

I don't know, it just may help to atomize the fuel or have a savaging effect. It was done on exhaust headers in a similar way a few years back although I don't see it anymore. Thanks.

 

Mercury marine ran mismatched heads and intakes
on there 454 boats for years with no problem I believe..

 

You might be kicking yourself in the ass for swapping the head's instead of the cam.

 

I recall reading about oval v rectangular.
As I recall it’s okay to use oval intake on rectangular port heads, but not vice-versa

 

That makes more sense

 

Hello, if you're talking about the duration of the cam, not so good for the street. If it's the solid lifters I'm a fan. My intentions are use it as a street car. In its day (1970) the car ran 11,60s 123 +/- M.PH through a M21 if the car runs high 11s I'm happy. Thanks for your input.

 

My “knowledge “ came from the late 70’s. I had no idea if my LS5 had rectangular ports or oval.
When we had real speed shops and I wanted a high rise intake, I was asked what I had. Like a deer in headlight “I dunno”

Fella at the counter told me let’s go with oval ports to be safe.
Then sometime later I most likely read it in an HRM.

 

L88 cam is too much for oval ports. As already mentioned, change the cam. If you use oval port heads use a good oval port intake.

Absolutely not. Ideally the intake would be port matched to the heads.

 

I ran a L88 cam in my 1966 SS 396 chevelle 350 hp back in 1971 4 spd 4:10 gears oval heads and intake.

 

There's nothing wrong with solid lifter's, personally, I prefer them, and use them in every engine I build, be it flat tappet or roller. The problem is the cam, it was designed for 12:1 compression and a free breathing intake and head's, with ton's of top end power. Oval port's were designed for bottom end and mid-range. To use the 063 head's with the L-88 cam would be like neutering your dog... It want's to but it can't. The stock LS-6 cam with the 291 head's you already are using, would be much more streetable, and still run mid to low 12's with a 4 series gear, instead of a 5 series gear, and running mid 11's. If you still want to use the 063 head's, the LS-6 cam would still be the better choice, IMO. Less is more when it come's to streetability. If gas was still 30 cent's a gallon, It wouldn't matter, you could run the high RPM that the L-88 cam need's to make it work. But why waste all that money on gas when you can use a more street friendly combination to get close to or the same result's? JMHO

 

^^^Bingo!

 

Hello, the stock LS6 came with 3955143 .500/.500 which was in the stock 454/450 motor and also 396/375 motor with 11 to 1 compression, closed chambered motors. The 2nd.design L88 cam was an (427 L88 over the counter) up grade for the LS-6 with 11to1 compression at .540/.560 closed chamber motor (the one I am running) The ZL-1 cam .560/.600 was used with the open chamber LS-7 at 12 to 1 compression. It was an over the counter motor/ parts only based on the "512" engine block platform. I up graded the cam to the 2nd. design L-88 cam. When I bought the LS-6 the short block was $800.00 The valve train and 291 heads, cam, lifters, valves and triple valve springs were additional. At that time the LS-7 short block and alum. heads was too pricy for me. Thanks to all for the input. Really appreciated.

 

If you have the car geared to work with the cam, then it should work Ok with the oval port heads, you just won't make as much power, especially up top. But if you're doing this swap to make it so you don't need to run steep gears, you're changing the wrong thing.

 

This cam was for the 11-0 comp. closed chambered motors not the open chamber 12.0 motor L-88 and is very street friendly. I always held them at 64/5 thou. R.P.M which is why I feel the oval ports will work well. These are stump pulling motors. I was really hoping to find someone who runs this combo. but am thankful for all the reply's.

 

The LS5 had oval port heads and hydraulic cam. 390 H.P.

 

You then have to wonder why Mercury marine would deliberately do it.