Don't worry, you can put the 1.74 or even 1.81 valves in there and they'll be fine.
Big Block Cylinder Heads "915 vs 906"
- Thread starter 69 Cuda 440
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Don't worry, you can put the 1.74 or even 1.81 valves in there and they'll be fine.
txstang84
Well-Known Member
But didn't you say those heads suck--worse than 906s??
nitrojunkee
Well-Known Member
So that's what, 1.54hp/ci? Out of a low deck 451" 9.7:1 compression? I'd love to see what the duration is on that camshaft for one. It's not a secret that you can crutch cylinder head with a ton of camshaft. I'd also love to see that actual dyno sheet.
Crutch? That's hilarious. How do you break down dyno numbers to tell what's crutchin what? You should do stand up comedy.
nitrojunkee
Well-Known Member
Duration, and lots of it. Builders having been using that trick for years to "crutch" a cylinder head that doesn't flow all that great. You should read up on it. Asking for the actual dyno sheet had nothing to do with me asking about the camshaft.
It's funny to me how you always have to get nasty, with your replies. I don't think you know as much as you think you do. I certainly wouldn't listen to much of what you have to say. Is that funny enough for you? ;)
"915" Cylinder Heads on a 383
The 1968 and 1969 '383' had Flat Top Pistons with 10.0-1 Compression
with the top of the piston set 'above deck' @ .021".
And a 'factory' 'Shim-Type Head Gasket {.020"}
Despite that, it didn't stop many guys from attempting to pop on the
#915 Closed Chamber Cylinder Heads {swapping off the #906 Open-Chamber Heads}.
Sometimes it worked, and sometimes it didn't. It all depended on how the 383
Block {Piston Height} left the factory.
On a 'stock' swap out, if it worked, you gained about 1.1 in Compression.
If it didn't, the Piston had a 'party' with the Cylinder Head, and you usually
smashed the Top Land of the Piston, and ruined the Top Ring and smashed the ring-land slot.
The 1968 and 1969 '383' had Flat Top Pistons with 10.0-1 Compression
with the top of the piston set 'above deck' @ .021".
And a 'factory' 'Shim-Type Head Gasket {.020"}
Despite that, it didn't stop many guys from attempting to pop on the
#915 Closed Chamber Cylinder Heads {swapping off the #906 Open-Chamber Heads}.
Sometimes it worked, and sometimes it didn't. It all depended on how the 383
Block {Piston Height} left the factory.
On a 'stock' swap out, if it worked, you gained about 1.1 in Compression.
If it didn't, the Piston had a 'party' with the Cylinder Head, and you usually
smashed the Top Land of the Piston, and ruined the Top Ring and smashed the ring-land slot.
If you met RustyRob you'd love him even in grouch mode, I do. The man is one in a million. He fits his spot in this universe perfectly. Just as you and I do.
As to the cylinder head, the poor thing won't flow much beyond 340 cfm. The exhaust is the bad part on those heads, as we refer to those 906s as the 'boat anchors'. They were working better but we tried to fix 'em some more better, oops, we lost flow.
I truly wish I'd had a smaller cam and the time to test it, but it was just a test run to see what we might expect with the same cam and heads on a 500 ci engine with more compression. To bad Comp Cams blew the 500 up on the dyno by not turning the water on to it.
Now, please, tell me you want to see the actual dyno sheet because you don't believe the 9.7:1/451 could actually do what I claim it did. I mean, it's okay to want to see the sheet for some other reason, but I want it to be you don't believe! I'm used to it.
txstang84
Well-Known Member
I still have yet to find a replacement piston for such an application. Even the speed pro forged flat tops that many people use are mathemitcally 0.012" in the hole, and that's assuming the decks are machined to blueprint specs (which I'm told is less than rarely the case)...so unless I knock 0.030" off the block, it'll still be in the hole. Now, that being said, if I had pistons proud of the deck, using 906s would be preferable to me if I were going for stock heads...it would certainly open up a few more options.
In any case, I did a little number crunching regarding a flat topped 383 with open chambered heads...assuming true zero, true flat topped piston, and an 88cc chamber with an .030"x4.35" gasket, I got 9.3:1 CR. Not bad at all; certainly able to run a decently sized cam despite a 383s short stroke. But, cam timing events would be of utmost importance since no valve reliefs.
Sorry...got a little carried away with desktop engine building...
Tx,
The only 'Back-in-the-Day' 383 Pistons that had a true positive deck height without
decking the block, were offered by 'Forged-True'.
They offered a 'special' 383 Flat-Top Piston, with an extended compression height
for the 1968 and 1969 '383'.
The only 'Back-in-the-Day' 383 Pistons that had a true positive deck height without
decking the block, were offered by 'Forged-True'.
They offered a 'special' 383 Flat-Top Piston, with an extended compression height
for the 1968 and 1969 '383'.
EL5DEMON340
Well-Known Member
My 68 383 is at zero on one side and -.004 to .014 from front to back on the other side, sloppy machining by Ma but it could be worse most guys I have talked to have said there's were more like -.020 down. 9.2cr with the 906 and 10.3 with the 915.
txstang84
Well-Known Member
Exactly what I was driving at-thanks for the "heads up"...pun intended. I know I can purchase a custom piston that would clear up all the issues with being below deck (or have the decks equalized) or even use a domed piston (which for some reason, I'm not a terribly big fan of--no real idea why), but I've been conditioned to believe one of the best friends of a well built engine is close quench, and doing that with open chamber heads is a bit tricky compared to running a zero deck flat top, with a closed chamber type head.
I dunno--numbers look a little peaky ;)
Here's what I know. What the dyno says is what the dyno says. Whether you think something is a crutch or not doesn't change that one bit.
'1970' 383/335 HP
The 1970 383 came thru with 9.5-1 Compression Flat-Top Pistons, and
the deck height was below the deck {-.004}, per factory minimum specifications.
These 383 Engines never had a problem when swapping on a set of #915 {Closed Chamber} Cylinder Heads.
Since the Piston {when it left the Factory} was down in the hole about {-.030"}
The 1970 383 came thru with 9.5-1 Compression Flat-Top Pistons, and
the deck height was below the deck {-.004}, per factory minimum specifications.
These 383 Engines never had a problem when swapping on a set of #915 {Closed Chamber} Cylinder Heads.
Since the Piston {when it left the Factory} was down in the hole about {-.030"}
roccodart440
Well-Known Member
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Ever drive something that has a relatively low compression and massive duration anda huge carb under 3000 rpm around town? Dyno results and tuning are just that and are 2nd to chassis dynos and are 3rd to strip tuning and all fall under real world driving use.
My father and I just built a new engine for his truck. mid 400 cubes, 439 duration @.050, 10.7:1. 513hp@5500 and 547ft/lbs@3900. how?, great heads and runs on 91 octane crap gas.
moper
Well-Known Member
I always liked the 915s. I could get an easy 270 from them with 2.14/1.81 and they always made great power. But - my first choice is 346s. They had what I feel are a better exhaust port with the "identical" intake port to the 915/906 and the same work and parts would get 280+. I'm guessing the chamber shrouding would explain the difference but because I test as a final step for validation - I never experimented with that. The 906F would be a 2rd behind the 915s.
'915' vs. '906' vs. '346'
For 'Street Performance,
Despite the confusion and mythology,
Pretty much 'equal' across the board on 'flow' characteristics.
The #3462346 {1971 and 1972} Cylinder Heads have a slightly better
Intake Port configuration.
And the '346' Exhaust Port had a 'miniscule' greater CFM Flow-Rate.
A good argument back then was, regarding the 1968 thru 1971 '440' Engines,
Stock Flat-Top Cast-Pistons with '915' Closed Chamber Cylinder Heads.
or
TRW {11.0-1} Forged-Pistons with the {'906' or '346'} Open-Chamber Cylinder Heads.
For 'Street Performance,
Despite the confusion and mythology,
Pretty much 'equal' across the board on 'flow' characteristics.
The #3462346 {1971 and 1972} Cylinder Heads have a slightly better
Intake Port configuration.
And the '346' Exhaust Port had a 'miniscule' greater CFM Flow-Rate.
A good argument back then was, regarding the 1968 thru 1971 '440' Engines,
Stock Flat-Top Cast-Pistons with '915' Closed Chamber Cylinder Heads.
or
TRW {11.0-1} Forged-Pistons with the {'906' or '346'} Open-Chamber Cylinder Heads.
80fbody
Well-Known Member
Moper: Got any closeup pics of a home ported 346? I've got a pair on the shelf that were worked on probably 30 years ago but never run. Wondering if there is any more I should do to them. I would love to get them into 275-280 range for my 451 build.
A crying shame,
That Mopar never offered up another version of the 440 {1967}
with Max-Wedge Heads, or 'special' Big Valve #906 Heads {1968 thru 1970}
on factory produced cars.
That Mopar never offered up another version of the 440 {1967}
with Max-Wedge Heads, or 'special' Big Valve #906 Heads {1968 thru 1970}
on factory produced cars.
txstang84
Well-Known Member
Amen to that
moper
Well-Known Member
I think I may have one downstairs I think. I went through one of them and I think that's the one down there. Might be rusty at this point but let me see what I can find.
1962 and early-1963 {Casting #2402286}
1962 = Plymouth 'Super Stock 413' / Dodge 'Ramcharger 413'
1963 = Plymouth 'Super Stock 426' / Dodge 'Ramcharger 426'
Intake........ 2.08"
Exhaust...... 1.88"
At one time {early days} thought to be the 'Cats Meow'.
Monster Size Exhaust Valves and Exhaust Ports.
1962 = Plymouth 'Super Stock 413' / Dodge 'Ramcharger 413'
1963 = Plymouth 'Super Stock 426' / Dodge 'Ramcharger 426'
Intake........ 2.08"
Exhaust...... 1.88"
At one time {early days} thought to be the 'Cats Meow'.
Monster Size Exhaust Valves and Exhaust Ports.
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