BB cylinder head question

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31pickemup

31pickemup

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I have a 67 Formula S fastback 383 auto. I'm pulling the motor out to freshin things up and check out what needs replaced. The motor was rebuilt in 98 and is supposed to have around 5000 on the rebuild. The car definitely needs a transmission rebuild and the stall is utterly shot. Im pretty sure they didnt use the correct 10:1 pistons but I won't know that til I do a compression test. My question is what is the difference in the big block heads of 68 and 69 compared to 67. I know the 67 heads are a non quench type. Would it be benifical to replace the 67 head with a later 906 head?
 
You mean going from a open to a closed chamber swap. The cc amount should be known between the heads along with the gasket to be used so you can calculte the new ratio. You'll have to weigh it out if pump gas is still doable.
Otherwise, as far as head flow goes, theres really not alot to hoot about.
 
Whenever the question of what BB heads are what, I always post this link and just because it's a 67 or 68 engine you can't be sure what heads you've got (and there are differences) until you check the casting numbers. The biggest performance enhancer is if you've got the 915 or 516 closed chambered heads and still have the smaller exhaust valve they will benefit with the larger valve.

http://www.moparmusclemagazine.com/techarticles/5115_cylinder_heads/index.html
 
31pickemup said:
My question is what is the difference in the big block heads of 68 and 69 compared to 67. I know the 67 heads are a non quench type. Would it be beneficial to replace the 67 head with a later 906 head?
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Incorrect , the 67 heads are closed chamber , making it a quench type , but your piston is probably too low in the hole to benefit from it unless you got lucky and someone was smart enough to use the TRW forged replacement and a steel shim gasket , then you got quench baby.

Beneficial to switch to a 906 which is an open chamber head and LOWER your already lowish compression ratio, NO not really.
 
Well whoever rebuilt this motor used KB pistons back in 98 on the rebuild. Im hoping they put the right ones in it. If they didnt they will be coming out. I wanted to stay with the 915's to gain the bigger valve benefit and still keep the compression the same instead of going worse with the 906 head. I know the 517 heads are the closed chamber as well so thats the only direction I can go at the moment. I ending up finding a set of 915 magnum cylinder heads.
 
The '67 915 castings are really the only true performance heads ever made for the big block engines, with the exception of some of the Max wedge stuff, like the 518s. All the others including the 906s everyone cherrishes were used on every thing under the sun from 440 Road Runners to 440 taxi cabs to 2 barrel 383s in grandmaw's station wagon. The 516s can be made to flow very similar numbers though if you use the larger exhaust valve. Those '67 castings were the only year Mopar installed the big valves in the 915s, and not all 915s that year had the big valves. Just the HIPO stuff. The 67 915 big valve castings outflow ALL other stock castings ever made by mopar with the exception of some of the Max Wedge stuff. That includes the 906s and all their derrivitives. the 346, and the 452. All three of those castiungs flow the same.....in fact, the 452s outflow the 906s......although by such a narrow margin, you'd never know it except on a flow bench or a dyno. Mopar Muscle magazine has a real nice article on the big block heads and highlights all these points in depth. They are indeed a quench head, as JohnRR pointed out. the flat area opposite the spark plug is where the squishin takes place. This is why they are such good heads.
 
The Mopar Muscle article Demon Seed posted shows the 915 does not flow any more than any other head. I believe if you read the article, you will see they state it uses the same port design as the 906. The ONLY benefit to the 915's is the closed chamber, which can be of a great benefit depending on your application. At least based on the samples used on their flow bench, saying they outflow all other heads is incorrect. Airflow is basically within a few Cfm's of most of the other castings.
 
BBBCUDA said:
The Mopar Muscle article Demon Seed posted shows the 915 does not flow any more than any other head. I believe if you read the article, you will see they state it uses the same port design as the 906. The ONLY benefit to the 915's is the closed chamber, which can be of a great benefit depending on your application. At least based on the samples used on their flow bench, saying they outflow all other heads is incorrect. Airflow is basically within a few Cfm's of most of the other castings.
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Okay.....maybe outflow was the wrong word. Out perform. Is that better? Because of their quench design, they are better than all the rest....except the max wedge stuff. Fair enough?
 
If you choose to use the 516 casting heads, just know that the exhaust valve is only 1.80". An upgrade to the 1.96" exhaust valve is a must with these heads for any kind of performance. Geof
 
cosgig said:
If you choose to use the 516 casting heads, just know that the exhaust valve is only 1.60". An upgrade to the 1.74" exhaust valve is a must with these heads for any kind of performance. Geof
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Fixed it .
 
StrokerScamp said:
Okay.....maybe outflow was the wrong word. Out perform. Is that better? Because of their quench design, they are better than all the rest....except the max wedge stuff. Fair enough?
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Thats probably a fair statement. I can envision a few circumstances where the open chamber would be of benefit, such as lowering the compression to a more pump gas friendly area. I wonder too about valve shrouding in a certain area of lift, as it appeared the 915 trailed the others until a higher valve lift, and then it jumped ahead, maybe the valve finally made it far enough out of the chamber to change the flow characteristics?

FWIW, I have a set of the 516's that many despise, with the 1.74" exhaust added, and a mild bowl port with a 3 angle valve job. They flow in the 240 cfm range at around .500" lift, 28" of water. Thats a fair increase over any of the stock heads flow #'s. The fellow who ported these did tell me they take a good bit more work than the newer port designs, but if you really want the closed chamber....
 
BBBCUDA said:
Thats probably a fair statement. I can envision a few circumstances where the open chamber would be of benefit, such as lowering the compression to a more pump gas friendly area. I wonder too about valve shrouding in a certain area of lift, as it appeared the 915 trailed the others until a higher valve lift, and then it jumped ahead, maybe the valve finally made it far enough out of the chamber to change the flow characteristics?

FWIW, I have a set of the 516's that many despise, with the 1.74" exhaust added, and a mild bowl port with a 3 angle valve job. They flow in the 240 cfm range at around .500" lift, 28" of water. Thats a fair increase over any of the stock heads flow #'s. The fellow who ported these did tell me they take a good bit more work than the newer port designs, but if you really want the closed chamber....
Click to expand...

There are better ways to lower compression , removing the benefit of quench , if you have it , is not the way to do it , a piston change wit ha D shaped dish or switching to a closed chamber alum. head would be a better choice.

I just had a set of F casting 906's done , one flows about 237 at .450 and the other 231ish, nothing fancy other than a 3 angle valve job and back cut the valves ... NHRA stock legal minus the acid porting ... I have to use them for the build I'm doing. It will be either 10.2 or 10.8 for compression, I haven't decided yet , I'm leaning toward 10.2ish so I don't have to buy a 55gal drum of race fuel and store it in my garage .
 
I am running the 452 's with K/B pistons it works well, here's some pic's.
 

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66 Dartman said:
I am running the 452 's with K/B pistons it works well, here's some pic's.
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That's a good piston choice for the 452's , unfortunately KB does not make that style piston for a 383 which is what is being talked about here .
 
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