I have a 1967 396 Bored 30 over, Its a mildily built motor with a XE 274 Cam, Double roller chain, Speed Demon 750 carb,and MSD ignition. Now I have the stock heads that came on the 325hp motors, I believe they were 2.06 intake and 1.72 exhaust? Not sure, They are Oval port closed chambered heads. I just recently purchased a pair of rebuilt #353049 heads, The valves have been enlarged to 2.25 intake and 1.88 exhaust, New Valves and springs, They are 119cc open chambered heads. What can I expect? I know I lose a little compression going from a closed chambered to an opened chambered head. Will I gain horse power or lose any? Let me know what you guys think.
Thanks

I have that same cam, mines solid.It makes huge torque those heads should work well.You should see about 70hp.

I may be interested in your 67 heads if you're looking to sell 'em.

So you think I can expect a 70hp gain? Don't you lose a little compression going from a Closed chambered head to an open chambered head?

I bet it runs better with the stock heads. You will loose more than a little compression. Your 67 came with as good a set of oval heads as there is.

I see we opened a little debate, Anyone else? Now I'm really interested if I should make the swap over or not :confused:

My guess is the over 1 point compression loss will not be offset by the larger valves gain equalling a horsepower loss.

Need more input guys, Help me out :(

I run a 67 closed chambered head on my 496. I think your going to lose a lot of compression depending on what it is now, I believe it will go to low. What you could do is sell the 049's and have your stock heads worked with bigger valves(2.19/1.88), bowl grind, and have the valves unshroued by the chamber. I believe that will help you out the most and be able to keep a reasonable amount of compression. What casting number of head is on your car right now?

Matt

NOt sure of the casting number, I'll have to look into that. I got a great deal on these 049 Heads too :(

396's have a hard time building static compression with it's small bore. It takes a pretty good come size to give any compression, especially if using an open chambered head.

The 049 head is an excellent piece although it can only really be used on 396/402's with larger dome pistons to keep the compression ratio up. This fact is why you see closed chambered heads on most all 396/402's.

What about some rectangular 840 heads? They are closed chambered and 107 cc I believe, Would these create more power for me?

The casting numbers on the other heads I'm think are 3919840, What about these?

This could be debated all day, but if you stick with doing work to your closed chambered oval ports you won't have to wind the crud out of the motor to hit it's power band, like(correct me if I'm wrong somebody) you will with the rectangular ports. It depends as to what your looking for as far as low end torque is concerned.

Matt

Originally posted by 70ss496:
This could be debated all day, but if you stick with doing work to your closed chambered oval ports you won't have to wind the crud out of the motor to hit it's power band, like(correct me if I'm wrong somebody) you will with the rectangular ports. It depends as to what your looking for as far as low end torque is concerned.

Matt Agreed. I would rework your current closed chambered oval port heads. This will give you the results you are looking for. All you need is 2.19/1.88 valves, 3 angle valve job, bowl blend, short turn radius smoothed and possibly match the intake runners to your manifold. Other than that simply have the heads rebuilt with new guides if needed, and have the springs set up properly to match your cams requirements.

This could be debated all day, but if you stick with doing work to your closed chambered oval ports you won't have
to wind the crud out of the motor to hit it's power band, like(correct me if I'm wrong somebody) you will with the
rectangular ports. It depends as to what your looking for as far as low end torque is concerned.While theoretically true, its not as drastic as you might think... I used to have my 396 running stock closed chamber Rectangular Port heads (1966 #858s). With the TRW pistons I had, it was around 9.0-9.5:1 CR (low enough that I could run 87 octane all day long). The motor did scream well past 6500 RPM, but I never had any big loss in low end torque. I was running 3.42 gears and an M20, and it pulled pretty well all the way through the gears. I never directly compared it with other heads, but other similar setups I have run (with closed chamber oval heads) didn't seem to have a significant increase in low end torque...

But, I wouldn't expect to gain any power either from just switching the heads...


I think going with the 049 open chamber ovals will actually drop some power. The larger valves and chamber might support some more power, but the drop in CR will most likely negate any potential improvements... Plus, the improvements you will see will be upper end in the RPM range, and not so much down lower for a street driven car ("mildly built engine")... Naturally the 049s have better potential, but the combo needs to be optimized for those heads (new pistons!)...

Unless there is an actual problem with your heads, I think its not worth the switch. Maybe just hang on to them until you are ready for a rebuild and go from there...

I think it has all been said.... unles new pistons, the loss of CR will be the most notable thing here.

I did the same thing as you - got a great deal on a set of 781s, only to find out later they were larger chamber than what I had. I hope that 063s will set me right. Good luck.

SSpete67, As with any head change be sure to notch the block where the valves are the nearest so they don't hit the block which they will do on a small bore (anything under 4.5").Especially bad on a 396-402. Also check vale to piston clearance using Reher-Morrison method as it takes into account depth and radial issues and can be read about on their website i think.

Thanks Guys, I think I just may stick with the heads I have and get some work done to them. I have to see if I can get out of these 049's Bought them for $400 rebuilt with new 2.25 intake and 1.88 exhaust, New valves and springs

Bought a 396 awhile back with #781 open chamber heads on it. The pistons had a huge dome, bigger than the 375HP's, probably 12to1 with closed chamber but the guy said it ran all day long with 92 octane gas with the #781's.

Originally posted by SSpete67:
Thanks Guys, I think I just may stick with the heads I have and get some work done to them. I have to see if I can get out of these 049's Bought them for $400 rebuilt with new 2.25 intake and 1.88 exhaust, New valves and springs