360 smog heads or J heads??

[swing69]

I've got a 78 360 complete, with smog heads. Assuming a bottom end that is fully rebuilt with ~ 9:1 pistons, what are my head options for a 90% street car. I'm going to put in a summit cam kit (nothing radical), performer intake, spitfire headers. 904 trans, 3.23 or 3.55 rear, 2500 stall converter in a 904 autotrans. (early A car and a 727 trans is alittle tight)
Rebuild the smog heads? or should I find older "J" heads, how do they compare with the smog ones? Aftermarket are out of the question $$ wise. Any real advantage in going to the 2.02 in the J's?
what's the market rate for a "rebuilt" set of Js? core Js? thanks

 

[rumblefish360]

J head cores can run about $100 - $150 while rebuilt J heads can run around $500. Used J heads complete ready to run and reasonably clean can fetch about 200 - 300.
Ethier had will be fine for street useage. Alot of this choice IMO depends on cam shaft selection. Also, intended useage of the car. Considering the basic idea you gave, I'd run preped smog heads, port them if need be. Stay with the smaller 1.88 valve, just back cut it.

The smog heads seem to fall in around/between 180 - 190 cfm intake flow while a 2.02 J head can flow around 200. This is within a margin and placed in the middle of possible flow rates since theres alot of factors that can change this. Core shift, prior rebuilds, valve sinking into there seats, actual valve brand used.

If your cam is mild, The smog heads with the 1.88 valve back cut and bowl ported will be more than enuff for a good street car. These smog era heads can be made to flow 230/240 cfm without getting crazy on the port job, work involved and final price. Though porting a iron head is "WORK!", just ask anybody that has ported a set of iron or does it for a living.
Expect mad amounts of torque with a good valve job and bowl porting.

The J heads would be better suited to a more radical cam shaft and really blossum when fully ported. Even more so with the 2.02's in them. In stock for or with the above similar work, you can expect anywhere between another 10 - 20 cfm as a posssibiliy.

The bigger valve size plays a roll in the upper RPM range where it really begins to shine. A fully ported J head is a great head for a full assult engine. If you have to stick to a factory iron head.

 

[lead69]

I would stick to the smog heads,they flow almost identical in stock form and can be ported to the same level as a j head.I actually like the smog head exhaust short turn better for porting.

 

[SRT_DSTRHOLC]

and the smog heads I believe have hardened seats right?

 

[stevedemon340]

They all flow about the same. 8)

 

[needsaresto]

They all flow about the same. 8)

Yes in the end the smog head can flow with a J. I' have an article here somewhere. I think it was mopar muscle tthat did a set of smog heads and they performed very well.