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Early SBC heads

plym49.2

plym49.2

Sasquatch49.2
Joined
May 20, 2020
Member Number
550
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405
I've got a '68 307 SBC motor. It's a 283 block with a 327 crank.

My understanding is that the stock heads provide something like a 76cc combustion chamber, with a CR of around 8:1.

Head casting is #3911032. Block casting is #3914636.

I can score any of these junkyard heads:

#3884520 60-67 283-327
#3795896 62-67 283-327
#462624 71-85 350-400
#3731539 1957 283 4bc-FI

I am told that some or all of these would be a 61cc chamber with 9:1 CR. I plan to keep the bottom end stock (pistons and all)(there is not even a ridge).

Questions:

Is this information correct?
This will be a motor for my YJ. I want to run it on regular (87 octane) gas. Is 9:1 too much?
Should I just keep the stock heads? (I hear they don't flow too well.)
What cam should I be looking for? Thinking RV or whatever.

This will be a budget motor build.

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Redtruggy said:
If you are talking rv cam, there is absolutely no reason to worry about what the heads flow.
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Good point. But I am not really sure what kind of cam I should use. Motor will run a stock SBC cast iron manifold - I have both 2 bbl and 4 bbl flavors. 2 bbl would be a 2GC and 4 barrel would be a 4GC. Looking for more power than the stock 4.2 6 in the Jeep, which runs out of breath by 2500 rpm, and decent highway cruise mpg. Tranny will be the AX-15 or an SM420.
 
With that small of an engine even a normal RV cam like a erson tq10 will be pretty solid. I'd do 305 vortec heads, they're 64cc and flow well. You'll have to modify the center bolt holes on the intake slightly but it'll be a good combo in that rig.


The ax15 will be fine as long as you don't get happy and power shift it.
 
DWT said:
With that small of an engine even a normal RV cam like a erson tq10 will be pretty solid. I'd do 305 vortec heads, they're 64cc and flow well. You'll have to modify the center bolt holes on the intake slightly but it'll be a good combo in that rig.


The ax15 will be fine as long as you don't get happy and power shift it.
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I have a vortec head to carburetor intake taking up space in my garage if you decide to go this route.
 
Same answer you got on the HAMB, try to find an uncracked set of 305 HO 416 heads, cam of around 205 degrees @.050 lift...
 
I think most 305 heads are 58cc, 9:1 in fine on cheap gas. Shoot for 214 duration and .450 ish lift cam. Unless you deck the block and or use thin head gaskets you can knock. 1/2 point compression off most estimates.

Watch the vortec’s for cracks. My second choice would be 882’s, I just tossed a good set because new heads are cheap when compared to rebuilding. I’d look for some used good aluminum heads on ebay rather than spend money on rebuilding cast heads.

That ax15 will hate you :)
 
Vortec heads are your best bang for the buck.

The heads you listed, I don't think any of those have hardened seats. Meaning non lead fuel will eat them up.
But it has been years since I dealt with that stuff.
 
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DWT said:
With that small of an engine even a normal RV cam like a erson tq10 will be pretty solid. I'd do 305 vortec heads, they're 64cc and flow well. You'll have to modify the center bolt holes on the intake slightly but it'll be a good combo in that rig.


The ax15 will be fine as long as you don't get happy and power shift it.
Click to expand...

M92PV4U said:
I have a vortec head to carburetor intake taking up space in my garage if you decide to go this route.
Click to expand...

Good advice and appreciate the offer. Not sure if I am ready to bite the Vortec bullet.
 
Tiha said:
Vortec heads are your best bang for the buck.

The heads you listed, I don't think any of those have hardened seats. Meaning non lead fuel will eat them up.
But it has been years since I dealt with that stuff.
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Yep, that is a concern and potential additional cost. When did all SBCs get heads with hardened seats?
 
plym49.2 said:
When did all SBCs get heads with hardened seats?
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Depending on model 72-74, so most of the early performance heads need seats and valves. If you can find vortecs it's ~$500 to rebuild them at a shop. You can buy ready to go US made aluminum heads for $1100 new, but then you need pushrods and rockers.

76cc 882's are cheap smog era heads that decent and cheapish. The older shit will cost you more than it's worth and the flow is not very good by todays standard. Find a good used set of used 882's and put new seals in them is probably the cheapest route.
 
Norm said:
Depending on model 72-74, so most of the early performance heads need seats and valves. If you can find vortecs it's ~$500 to rebuild them at a shop. You can buy ready to go US made aluminum heads for $1100 new, but then you need pushrods and rockers.

76cc 882's are cheap smog era heads that decent and cheapish. The older shit will cost you more than it's worth and the flow is not very good by todays standard. Find a good used set of used 882's and put new seals in them is probably the cheapest route.
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882 heads at 76cc are bigger than what I have now (70cc). I don't want the CR to go down.

It is looking like the 305 416 heads might be a good alternative as they have hardened seats, accessory holes, and are 58cc so compression should be up a point - hopefully, still within the realm of regular gas. I am not sure if 416 305 heads are the thin castings.

I have to weigh cost/benefit. I can keep the heads I have, but would likely need hardened seats. That would be an expense, unless I just threw it back together as-is.

It's looking like none of the heads listed in post #1 are the right choice for me.
 
plym49.2 said:
882 heads at 76cc are bigger than what I have now (70cc). I don't want the CR to go down.

It is looking like the 305 416 heads might be a good alternative as they have hardened seats, accessory holes, and are 58cc so compression should be up a point - hopefully, still within the realm of regular gas. I am not sure if 416 305 heads are the thin castings.

I have to weigh cost/benefit. I can keep the heads I have, but would likely need hardened seats. That would be an expense, unless I just threw it back together as-is.

It's looking like none of the heads listed in post #1 are the right choice for me.
Click to expand...
I just mentioned 882 because they are cheap and have decent flow. That would put you compression around 8-8.5. Stick with a RV cam and they will be ok. I ran the old baja beast - 204 duraton .414 lift on a low compression truck motor with 882's plus headers and it worked pretty well. Stock cam was about 194 duration and .400 lift .

The 58cc 305 416 heads will help with compression, but it will be harder to find a good set cheap. I think the 416's were a 5.0 HO option.
 
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