how much power can L98 heads support on a 350 smallblock running 9:1 compression?

I'm looking at a hydraulic roller cam w/ .520 intake valve lift and .540 exhuast w/288 degrees intake and 294 exhaust duration on a 110 degree cam center with the intake center at 106 degrees

any thoughts?

thanks-

Eric

 

Plan on replacing the valve springs at a minimum (springs and retainers recommended).

You'll most likely need to cut the top of the valve guides to get .540" lift. Positive type valve stem seals would be a good upgrade and would provide the clearance when the guides are cut for them.

Basic port clean-up will help support a healthy cam.

Why only 9.0:1 CR?

400 GFWHP isn't unreasonable.

 

the shortblock I have has dished pistons an the l98s would pust me at just about 9:1 I would go higher if I could find a set of heads with smaller chambers, (I can get a set of l98s locally for 75 dollars) I'm also eyeing a set of alluminum 'vette heads with 58 (9.5:1 roughly) cc chamber, it just depends on cost.

Thanks!

 

For effective compression, 58cc aluminum heads = 64cc iron heads.

Find a set of LB9 heads. Same port sizes, 1.94" intake valves can be installed by a shop while you're doing the other things. Or, replace the pistons with flat tops.

 

why is that?

 

Aluminum transfers heat more readily out of the combustion chamber than cast iron. Heat = energy = power. To make up for the lost heat/energy/power, you need to raise compression. Losing heat also means detonation won't be a problem at higher CR.

So, 58cc Al = 64cc cast iron on a 350, all else being equal.

 

I was confused because I thought you were refering to the actual compression ratio when you were refering to detonation resitance.

the lb9 heads are you saying that they are the same as he l98s except for smaller chambers? also are those swirlports?

 

Only the TBI got swirlport heads.

 

LB9 heads are cast iron, 58cc chambers, 1.84" intake and 1.50" exhaust ports, intake port volume is about 160cc.

L98 f-body heads are cast iron, 64cc chambers, 1.94" intake and 1.50" exhaust ports, intake port volume is about 160cc.

L98 '86-1/2 & up Vette heads are aluminum, 58cc chambers, 1.94" intake and 1.50" exhaust ports, intake port volume is about 160cc.

None of them are swirlport. They are pretty much the same in all other respects.

Static CR and detonation are only linked when everything else remains the same, including head material. Dynamic CR adds cam events to the mix, but the head material still needs to be the same for apples-to-apples comparison. When you go from cast iron to aluminum heads, if the rest remains the same (including port shape), you need to add about half a point of static CR to get the same power out of an everything-else-the-same engine.