[1965gp]

Is there a difference in the 350 HO 48 casting heads vs the 400 48 casting head? I have the opportunity to buy a 69 350 HO but was curious if I could use those heads on a 400 or 455?

[Dragncar]

The 350 HO 48s can have heads with ccs down in the 65.5 range.
400 heads and a few more ccs.

[1965gp]

Thank you- apparently it was a strong running motor but the owner wanted to swap to an LS. Would be a nice back up motor.

[steve25]

It would be nice to pick it up and keep it all intact.
The less then 70 CC chamber volume means in the least E85 or cutting race fuel with pump fuel for a 400 cid motor and with the 11.5 comp you wound have with a 455 it’s straight up race fuel.

[Kenth]

This issue has been discussed over and over again, still
NO-ONE has ever shown proof of two different size chambers #48 heads from factory.

#12 heads are the eqivalent RAIII and M/T heads for 1970 and there is only one size from factory on those too.

I have owned several pairs of each and have not once noticed different sized chambers.
#48 and #12 are the same 66 cc heads.

Use them on any size engine with proper piston tops, dished on larger than 400.

[RAIIIJudge]

1965gp, I hope you don't mind if I jump in with a tangential Q re 48s as coincidentally, as I type, my browser is stuffed w/ past threads on 48s and D ports in general.

My 69' has it's original WS 400 + it's 48s in it .. if I wanted to stick w/ the 041 thats currently installed and for convenience stay w/ D ports but set up a pair that's flowing around 290cfm .. is it foolish to have the work done to the original 48s or should I just grab pair from KRE, Butler etc?

Mike
Ma

[steve25]

The very first and most important question I need to ask to give a good answer to the above are these two.

1) how much hp are you looking to make?

2) why do you need 290 intake cfm, as this would indicate that indeed you have a certain level of hp in mind, or maybe you are just following along with what everyone else think they need when they go for a aftermarket heads to bolt on.

[RAIIIJudge]

I'd like to stick w/ the stock raIII exh manifolds, poncho intake and Q jet
it's my understanding that heads that flow better than 290cfm are wasted w/ raIII manifold .. this is where I came up w/ the 290 number.

[b-man]

A 290 cfm D-port will be difficult to achieve, paper thin port walls when you’re getting close to that number.

Settle for 260 and do it with non-original to your car heads.

Grinding on the original heads trying to achieve huge numbers shouldn’t even be a consideration. Getting 290 from a set of aftermarket aluminum heads that pretty much start out at 260 is a walk in the park, iron D-ports hitting 290 is for race-only situations and it’s risky to do so.

[Jay S]

With the right pistons you can use 48s on any Pontiac and get the compression to what ever you want.

If your a flat top only piston person the compression is too high on anything bigger than a 400 on pump gas.

You won’t find much difference between any of the 48 heads.

[steve25]

Although a iron D port head can be ported to 290 intake cfm@28” it’s very hard to find a head that has no core shift which is what’s required to do that, and with no one Now CNC porting iron hand porting to get those big flow numbers is 60 hours of hard hand labor time to do it right since the exh ports will need to be highly reworked also.

Let’s say your heads are like that and you where running everything else needed to really make use of that 290 cfm ( as in headers and no exhaust manifolds ) then the motor would have a Power potential of 75 hp per cylinder.
Cam’ed right to make that level of power the lift would need to be at or above .600”and plus the motor would need to be spun to 7000.

Now let’s say you back down some and have your heads reworked to flow 265 cfm at a far more sane .580” lift .
Assuming your running everything else needed to make full use of that 265 intake cfm you can make 560 Hp .
Even in this form, no less the above, with only 400 cid it will not be a fun street motor with they way it will need to be Cam’ed.

Once you get a true street motor set up to make full use of even 260 cfm at let’s say ..500” lift you are really going to want at least 428 cid pumping away under the heads.

It is such a waste of money and Erik’s me to no end when a guy slaps on a set of aftermarket heads that flow 300 to 325 cfm @.650” and then only run a cam of .525 “ lift.

Due to the port volume that goes a long with that 300 cfm your leaving a whole bunch of torque on the table below 4000 rpm when you do that, but I guess you have paid for the bragging rights of having 300+ cfm heads under the hood!

[1965gp]

This is all helpful. If I bought it as a complete engine it would just be a spare in case something happens to one of my motors. Probably worth it in the long run.

[nytrainer]

Where are you located? I would be Interested in the 350 HO complete and have 455 and 400 short blocks I could sell/trade with you.