Heads from 5.7L on 5.3L?

[JDFester]

I have found multiple posts where people have put heads for a 5.3L engine on a 5.7, but I was wondering if the reverse would also work. I have a friend who has a brand new set of 5.7L heads he can give me for free if they will work. I have a cracked head and therefore must replace, and was wondering if they will work properly, or have a different compression ratio, or any other issues I am not considering. Does anyone have any thoughts on this?

Thanks!

[silicon212]

If it's a Gen-III (LSx) 5.7, I don't see why it wouldn't work, although the combustion chamber might be a little larger leading to a lower compression ratio.

If that 5.7 is a Gen I or Gen II, forget it.

[bobo383]

Originally Posted by silicon212

If it's a Gen-III (LSx) 5.7, I don't see why it wouldn't work, although the combustion chamber might be a little larger leading to a lower compression ratio.

If that 5.7 is a Gen I or Gen II, forget it.

What he said. Compression would be lower but you'd never be able to tell it in an otherwise stock motor. Look to see if the 5.7 heads have very tall, very skinny, evenly spaced intake ports (like a 5.3). If so they'll probably work. Older intakes and heads had siamesed rectangular-shaped ports (not eveny spaced, the ports were paired up), like my 64 Impala's 283. These would physically bolt onto your block but would not bolt up to the intake or exhaust manifolds.

[BlenderWizard]

Originally Posted by bobo383

What he said. Compression would be lower but you'd never be able to tell it in an otherwise stock motor. Look to see if the 5.7 heads have very tall, very skinny, evenly spaced intake ports (like a 5.3). If so they'll probably work. Older intakes and heads had siamesed rectangular-shaped ports (not eveny spaced, the ports were paired up), like my 64 Impala's 283. These would physically bolt onto your block but would not bolt up to the intake or exhaust manifolds.

I'm not sure a Gen I or Gen II head would even go as far as bolting onto a Gen III block.

I think you'd have a better chance of getting a Ford head to work.

[silicon212]

Originally Posted by BlenderWizard

I'm not sure a Gen I or Gen II head would even go as far as bolting onto a Gen III block.

I think you'd have a better chance of getting a Ford head to work.

Not even close (to the first statement). You're probably right about the chances with the Ford head - both the Gen III and the Ford use 10 bolts for head mounting, providing 4 bolts per cylinder for sealing. Gen I (1955-2003 standard small block) and Gen II (1992-1997 L99/LT1/LT4) require 17 head bolts, providing 5 bolts per cylinder for sealing.

[jveik]

yeah if by a 5.3 you mean an old school 327 and by a 5.7 you mean an old school 350, then it would work, but if you mean the 5.7 old school 350 and the newer 5.3 whatever cubic inches it is, then theres no way in hell. maybe you have the 5.3 confused with a 5.0 old school 305?

i doubt that putting 305 heads on a 350 would really make any difference. In fact i bet it would hurt your performance since i bet the valve sizes are smaller for the 305 heads or something, i have always heard that the stock 305 heads were worthless

[silicon212]

Originally Posted by jveik

yeah if by a 5.3 you mean an old school 327 and by a 5.7 you mean an old school 350, then it would work, but if you mean the 5.7 old school 350 and the newer 5.3 whatever cubic inches it is, then theres no way in hell. maybe you have the 5.3 confused with a 5.0 old school 305?

i doubt that putting 305 heads on a 350 would really make any difference. In fact i bet it would hurt your performance since i bet the valve sizes are smaller for the 305 heads or something, i have always heard that the stock 305 heads were worthless

305 heads on a 350 (Gen I) will give more compression, and better torque on the low-mid range due to the smaller valves, but will cough and weeze past 5000 RPM on a 350. Intake runners are also less than optimal, in most cases. There are exceptions - some 305 heads can be made to accept 1.94/1.5 valves which are good on a 350.

Gen I/II 5.7 liter = 350 cid
Gen III 5.7 liters = 346 cid
327 - gen I motor - 5.4 liters
Gen III/LS 5.3 liter = 325 cid
Gen I 305 = 5.0 liters

[wannablast]

With the center cyls on the 5.7 having siamesed exhaust valves and the 5.3 not, then the cam shaft lobes would not jive with what the valves should be doing if you changed to the 5.7 heads. It isn't going to make it displace any more cubic inches so what would be the motivation for the swap anyway?