Differences in 906 heads....

[mopar_chuck]

At 0.062", my guess that the deck has been cut, probably 0.020" or so.. The piston probably has a 1.991" CH.

I get 9.7:1

9.7 would be ideal in our case but that just seems really high when the pistons are literally 1/16” down in the bore. This is the on line calculator I use....
http://www.csgnetwork.com/compcalc.html

 

[mopar_chuck]

FYI, un-milled 906 heads are about 88 CC. If the block has been milled straight, get the correct piston for the CR you want. As Gary said 2.067 gets you in the ballpark with about .010 down in the hole. That's where I ran most of my 440's. The 915 head gets you about .75 + CR increase. Both 906 & 915 really like pocket porting. The area under the valve seat is very poor in stock shape. The new valve job machine equipment can correct for this. A little work with the grinder makes big power improvements. I have done several dozen sets of 906 & 915 heads, not so much variability in them. I grind out the differences in the ports. Mill the deck to your specs. If you measure everything, you know what you got. Later head castings have bigger CC chambers.

I can definitely confirm that you are correct about the factory combustion chamber cc. Having.025” shaved off got us down to 84cc but we have already established this. Also agree to the pocket/bowl porting. My father has done several sets of 906 heads with great success. We are hoping to get an honest 400 hp out of this build. The rest of the combination is .484 solid cam, 1 3/4” headers, holly street dominator intake, and 750 carb.

 

[66Satellite47]

More cam would greatly improve power. If the heads are pocket ported they will like .550 or more lift & 250+ @.050. Just say'n.

 

[mopar_chuck]

That sounds like a really big cam for a 383 street engine..... max power is not the goal. We want as much as possible but must be street friendly. Also it has 3.54 gears.

One thing I have read on here by a lot of guys is it’s important not to over cam a 383

 

[PRHeads]

When that motor was redone originally there may have been some other “replacement” piston choices available than there are now.
Sealed Power and Silvolite now both have a cast piston with a C/H of 1.848, which would put it down the hole .084 on an uncut block.
So, either your block has been decked, or there was another stock type piston option when that motor was done.

I’d confirm the block deck height before I ordered something new.

Using my “on desk” calculator(as opposed to on line), I get 8.6:1 out of what you have there.

If you change to a more modern piston(like a KB), they will likely be enough lighter than what you have now that you should rebalance the crank.

 

[mopar_chuck]

Yes we were actually looking at KB pistons last night and are not really that much money. But you are right about measuring the deck height. Dad is bringing home the 6-12" mic kit from his workplace so we can do this. I believe the pistons that we currently have are TRW, not 100% sure though.

 

[BSB67]

9.7 would be ideal in our case but that just seems really high when the pistons are literally 1/16” down in the bore. This is the on line calculator I use....
http://www.csgnetwork.com/compcalc.html

I missed or forgot that this is a 383. That makes everything I said in my last post meaningless, which some might say is usually the case anyways .

 

[mopar_chuck]

I missed or forgot that this is a 383. That makes everything I said in my last post meaningless, which some might say is usually the case anyways .

Hahaha, no not at all. I have learned from everyone that has replied to this thread and appreciate the feedback. I kind of figured that your stroke length was off to get 9.7:1

 

[PRHeads]

TRW’s usually have the part number stamped into the top.

The only TRW forged piston for 383’s that’s been available for several years is the L2315F, which would be down the hole roughly .012 on an uncut block....... so we know it’s not those in your motor.

 

[Garys1969RR]

I can definitely confirm that you are correct about the factory combustion chamber cc. Having.025” shaved off got us down to 84cc but we have already established this. Also agree to the pocket/bowl porting. My father has done several sets of 906 heads with great success. We are hoping to get an honest 400 hp out of this build. The rest of the combination is .484 solid cam, 1 3/4” headers, holly street dominator intake, and 750 carb.

Sounds like a good combo. Bear in mind that the more you shave the intake face, the end rails on the Block will not match the intake face properly. Some guys shave the block down, but then that block will only fit that head

 

[Garys1969RR]

Sorry, I also was thinking about a 440. So the recommended 2.067 C Height is for a 440.

 

[mopar_chuck]

I wish it was a 440.... the car was originally a 383 and my dad found a date code correct block shortly after he got the car. However, as luck would have it, that block was ruined by the machine shop by decking too much off of it. By this point, he already had the rotating assembly balanced and machine work done on the block. So the shop found a 1968 replacement and “redid” everything on that one. Looking back on it, should have told them to find a 440 as a replacement to help make up for their mistake.

 

[66Satellite47]

The 383 is still a worthwhile motor. It doesn't have the toque of a 440, but as a street build will do very well. Pocket ported 906 heads can make pretty good power with the right cam. Hope your CR comes near 9.5 with today's 92 gas & iron heads. Aluminum heads would like 10.5 or a little more. A 383 won't generally outrun a 440 but will stay pretty close. Good luck.