question about BB heads

[Nacho-RT74]

I know open champers heads best choose are 452s mainly beause the hardened valve seat stuff, but whats the best choose on CLOSED chamber heads ? I can't remember right now

[firefighter3931]

The big valve 915's....1967 440 hp heads with the 1.74 exhaust valve. 


Ron

[mopar400]

I have a set of 915 heads about to go on my -73 400 engine, I heard that there are both closed chamber and open chamber 915s
i sure hope I,ve got the closed ones   so Is there a way of telling by looking at the casting nr ? or do u have to messure?
//Linus

[68chargerboy]

hey nack i have a set of the 67 915's if you are interested in trades or anything.  they are closed chamber i know for sure.  shoot me a pm if you are intrested

[Challenger340]

I have a set of 915 heads about to go on my -73 400 engine, I heard that there are both closed chamber and open chamber 915s
i sure hope I,ve got the closed ones  so Is there a way of telling by looking at the casting nr ? or do u have to messure?
//Linus

There is only 1 version of the venerable "915" Head.
The full Casting Number is 2780915 and they are ALL Closed Chamber design, with the Chamber only about 2/3 of the Cylinder diameter.

The "906" Head, full Casting Number is 2843906, is an Open Chamber Head, with the Chamber a "full circle", fairly equal in Diameter to the full Cylinder Diameter.

The "915" and "906" Intake Ports are Identical, "Huber Hump" High Floor/Short turn Ports with 2.08" Valves, this may be where the confusion exists in being 2 versions.

Basically, the "915" is the "Closed Chamber" version, of the later "906" Head,
albeit,
most 915's had only a 1.60" Exhaust Valve, save for the "HP" installed Heads which were fitted to the 1.74" Exhaust Valves.

Hope this clears up any confusion.

Bob out

[Nacho-RT74]

hey nack i have a set of the 67 915's if you are interested in trades or anything.  they are closed chamber i know for sure.  shoot me a pm if you are intrested

I'm outside USA

I have 3 pairs of 452 availabe, one pair not in hands, but at a dealer, NOS. Nobody will buy those

[mopar400]

I have a set of 915 heads about to go on my -73 400 engine, I heard that there are both closed chamber and open chamber 915s
i sure hope I,ve got the closed ones   so Is there a way of telling by looking at the casting nr ? or do u have to messure?
//Linus

There is only 1 version of the venerable "915" Head.
The full Casting Number is 2780915 and they are ALL Closed Chamber design, with the Chamber only about 2/3 of the Cylinder diameter.

The "906" Head, full Casting Number is 2843906, is an Open Chamber Head, with the Chamber a "full circle", fairly equal in Diameter to the full Cylinder Diameter.

The "915" and "906" Intake Ports are Identical, "Huber Hump" High Floor/Short turn Ports with 2.08" Valves, this may be where the confusion exists in being 2 versions.

Basically, the "915" is the "Closed Chamber" version, of the later "906" Head,
albeit,
most 915's had only a 1.60" Exhaust Valve, save for the "HP" installed Heads which were fitted to the 1.74" Exhaust Valves.

Hope this clears up any confusion.

Bob out

Thank You Bob, very good answer there!
Then I´ll just have to put them on, cant wait to see what they will do to my low comp -74 engine!!
As for the valves, I´ve put the 2,14 int and 1,81 exh stainless on them and they´ve been ported!
just gotto find me the right camshaft, I got the "musclecar cam" recomended by Hughes engine, what do you think?


//Linus

[b5blue]

The 452's are a good head why are you wanting closed chamber? I had highly reworked closed chamber heads on my car when I got it and I'm glad there gone it was a pain in butt running a daily driver with that high of compression! 915's are going to need seats for unleaded gas also. I say if you can get the brand new 452's for a good price get them and port them out. Do you have 346's now? Do you know 346's out flow 906 on the exhaust side? 

[375instroke]

You can run more compression with closed chamber heads if there is .040" piston to head clearance, AKA quench.

[b5blue]

Right, but he's just doing heads, not putting new pistons in the block....I think. 

[Challenger340]

A "low-compression" '74 engine, will respond far better to the compression increase gained by the 915 heads, than bolting on a set of 452's.
He'll also gain some quench effect.

As for the Valve Seats, Heres a secret
"just add a coupla hundred Ml of top end Oil(2 stroke Oil) to a tank of gas, and it'll protect the seats just fine."
After about 10,000 miles, they'll harden up just fine on their own and you can quit.

NO, it won't blow blue !

I don't know the specs of the Muscle Car Cam from hughes, but it'll probably be great. They use good stuff.(Engle ? )

Bob out.

[b5blue]

Hey Bob now I get it...I was thinking 74 are dished=no quench, and that it was Nacho's motor 

[375instroke]

My '69 440 doesn't ping, and isn't it 10.5:1 with open chambers (no quench) or so?  Wouldn't a '74 400 be around 8:1.  It could use a point of compression increase.

[firefighter3931]

My '69 440 doesn't ping, and isn't it 10.5:1 with open chambers (no quench) or so?  Wouldn't a '74 400 be around 8:1.  It could use a point of compression increase.

The factory compression ratio ratings were allways generous...most HP engines were closer to 9.5:1 even though they were advertised as 10:1 static. Tolerances were all over the map...to achieve a true 10.5:1 with a 90cc chamber you would need a positive deck flattop piston or something with a dome. I've yet to see any stock 440 that came with a piston above the deck surface....most were at least .020 below, at least.


The closed chamber will help a low compression build....no doubt about it. 



Ron

[mopar_nut_440_6]

As for the Valve Seats, Heres a secret
"just add a coupla hundred Ml of top end Oil(2 stroke Oil) to a tank of gas, and it'll protect the seats just fine."
After about 10,000 miles, they'll harden up just fine on their own and you can quit.

Bob out.

Great Information, thank you!

[mopar400]

Right, but he's just doing heads, not putting new pistons in the block....I think. 

Thats right! only heads for now!
and I´ve also heard about, and tried, the 2stroke oil in the tank method!
I also used to put some led additive in the tank due to the unledded fuel,
got it from the local gas station

/Linus

[Nacho-RT74]

wow, never thought on this thread getting that long, specially being an old one...

The used 452 heads ( not the one at my car ) are in very good conditions, no need for the NOS now, unless machine shop, tell me something. heads are on hot tank right now. I don't have 346. Dunno why when got my car found it had 452s and not 346. Dunno why, dunno the past on the engine. The fact is did it have ebough play on valve guides, enough to need oversized steem. Ended fit 015 valve steems.

Yes I'm replacing pistons, KB240s. I'm expecting to get 9.2 to 9.5 CR with heads milling job. Not proceding with that yet, because I have to be sure about deck height. My block was sleeved so deck was cut to make the plain

just wanted to know which ones were the best closed chamber heads, because quite often get confused with those numbers. If I find ( don't think will be a chance ), won't need to change anything of the geometry ( rod lenghts or anything).