It works on LS6 but not SBC, Why???

Say you want to make a pre 92 small block chevy motor that pulls real good on the low end and a killer top end.
Why do the big port volume LS6 heads work ok on a daily driver, but when You try to go big port with SBC heads every one says it will be a bad daily driver.
The Big port (230cc+) SBC heads have big 2.05 or 2.08 valves most of the time, are the big valves bad?
Why are small ports so good for SBC?
Then why are the biggest Vol. stock heads with same old stock 1.94/1.50 small valves (170cc vortecs) make power like no stock head before, with killer low end torque and strong top end?
Why are Smaller valves (about 2.00'') good for LS1's?
On big cc SBC heads small valves look like a great way to make power like GM Fast burns(2.00'' valve and 200cc ports).
Or is it the cam, long duration Hyd flat tap vs. the short duration Realy high lift of the rollers?
How many Stock SBC heads have over 200cc ports? (as far as I ever herd, none)
When I say SBC I'm mean non LT and LS heads in this post.
Any one know a lot about this?

Originally posted by oil pan 4
Say you want to make a pre 92 small block chevy motor that pulls real good on the low end and a killer top end.
Why do the big port volume LS6 heads work ok on a daily driver, but when You try to go big port with SBC heads every one says it will be a bad daily driver.
The Big port (230cc+) SBC heads have big 2.05 or 2.08 valves most of the time, are the big valves bad?

Nope but a SBC has a bore size of 4.030, while a LS1 is 3.900 so the max valve size that fits in the bore is much less.


Originally posted by oil pan 4
Why are small ports so good for SBC?
Then why are the biggest Vol. stock heads with same old stock 1.94/1.50 small valves (170cc vortecs) make power like no stock head before, with killer low end torque and strong top end?

Mostly because the RPM range of the motor is not concentrated in the higher end of the scale, small ports like small RPM/

The Vortec heads are just a better design vs a old camel hump head. They flow better and have a better chamber, basically they are more modern design.

Originally posted by oil pan 4
Why are Smaller valves (about 2.00'') good for LS1's?
On big cc SBC heads small valves look like a great way to make power like GM Fast burns(2.00'' valve and 200cc ports).

Bore size is the main reason. A larger valve gives the air a larger window to look at and usually allows more air thru the port.


Originally posted by oil pan 4
Or is it the cam, long duration Hyd flat tap vs. the short duration Realy high lift of the rollers?
How many Stock SBC heads have over 200cc ports? (as far as I ever herd, none)
When I say SBC I'm mean non LT and LS heads in this post.
Any one know a lot about this?

A roller will give you more lift and more lobe area so you can run less duration to achive the same area.

I've never heard of a stock GM head on a production SBC be over 200cc.

Bret

So if you sleved a LS1 block with 4'' bores would bigger 2.05'' or 2.08'' valves be the greatest thing ever?
Just say they would fit, I don't realy know if they would or not.

The biggest difference is the valve angle on the LSX heads, leading to a much more efficient runner/valve/chamber combination. Think of the old 23 deg heads (or even 18 or 14 degree heads) compared to the SB2 stuff now being used...

Originally posted by oil pan 4
So if you sleved a LS1 block with 4'' bores would bigger 2.05'' or 2.08'' valves be the greatest thing ever?
Just say they would fit, I don't realy know if they would or not.

Nah, maybe something like a 4.125" bore like a 388 LS1 would be a much better setup. That works out to be around 6.3-4L which is what the new high HP vette motor is expected to be.

Bret

The reason big port volume works on LS engines and not on standard SBCs is the shape of the port. The LS engines have very tall, narrow ports which facilitate higher air velocity even at low rpms. That's how they get away with the bigger ports.