big block head questions

[midnightrider1818]

ok guys. I have a question on heads for big blocks. I am building a 383. casting number is 2468130-1. The heads that I have on the engine now are 516 heads. casting number 2406516-10. I understand from research that the 516 heads and the 67 only 915 heads are the only closed chamber heads that were produced. the head that suceeded the 915 was the 906 and all the heads there after were open chamber heads. I understand the closed chamber heads give you more compression while the open chamber heads have a better burn effect. Can someone here fill me in on the pros and cons of open chamber heads vs closed and maybe some pics to show it. Im not 100 percent sure even how you tell the difference between open and closed. Also which heads should i go with. I want to keep the motor more unless stock. I will probably throw a little bigger cam in but want to keep the cast heads and so forth. I read that the 915 heads are the best but only if you get the ones that came on the magnums which had the bigger exhaust valve. all the other 915s still had the small exhaust valve. I also read the 915 intake and exhaust ports flow better. Also i was wondering which heads were the ones designed for unleaded fuel. Come on all you head gurus out there. :hello2: give us info on heads. are 516 heads good or junk.

 

[Seax440Dodge]

516's? Eh, I'd much, much rather have a set of 915's or 906's or 452's

 

[HT413]

The difference is mostly in the combustion chamber. Here's a pic of the open chamber 906's vs the closed chamber 915's. These are just pix I grabbed from the internet and you'll notice the 906's (2nd pic) have been worked on.

'Open chamber' means the chamber extends above the whole bore (or about the while bore). Closed means it only extends to where the valves are, 'closed' for the rest of the bore.

If you decide to go with the 915's, I have a nice set of the big exhaust valve heads assembled available.

 

[midnightrider1818]

so if i take this right. if i use 915s you can still mosty run a flat top piston and keep compression up higher. if you go with a open you almost need to run a dome top to get compression up. yet the 906 and 915 do flow about the same

 

[Garys1969RR]

I have a 451 with 14cc dome Ross pistons in it, and had 906 heads on it with mild porting, stock ex manifolds, Holley Street Dominator intake, and 509 cam. It ran a best ET in the 1/4 mile of around 13.60@100 MPH with the mufflers unhooked. I ported a set of 915s, using 2.14 intakes and 1.81 ex valves. Installed these and Patriot headers at the same time, with no other changes. Now it runs consistent 12.40s @ 110 MPH. Best of 12.33. Thats an improvement of almost 1.3 seconds. So how much increase in power was due to the higher C/R ? Or the headers? Or the ported heads with larger valves? Don,t know but it all helps.

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My C/R went from 12.5 to 13.3 to 1

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I also was able to get a nice tight .037" squish with the closed chamber 915s.

 

[IQ52]

I just wish this cylinder head stuff was as simple as we all would like it to be, but it's not. The more I learn about them the more I realize how stupid I am......hence the IQ52 moniker. Here on post #65 are the results we found when we switched from stock 906 heads to ported 516s.

http://www.forbbodiesonly.com/moparforum/showthread.php?58687-Iron-head-test-starting-on-78-440/page4&highlight=dyno+testing+stock+440

Just the cyliner head swap resulted in a peak horsepower change from 387 HP to 449 HP. That is a 62 horsepower increase.

 

[383man]

I have a 451 with 14cc dome Ross pistons in it, and had 906 heads on it with mild porting, stock ex manifolds, Holley Street Dominator intake, and 509 cam. It ran a best ET in the 1/4 mile of around 13.60@100 MPH with the mufflers unhooked. I ported a set of 915s, using 2.14 intakes and 1.81 ex valves. Installed these and Patriot headers at the same time, with no other changes. Now it runs consistent 12.40s @ 110 MPH. Best of 12.33. Thats an improvement of almost 1.3 seconds. So how much increase in power was due to the higher C/R ? Or the headers? Or the ported heads with larger valves? Don,t know but it all helps.

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My C/R went from 12.5 to 13.3 to 1

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I also was able to get a nice tight .037" squish with the closed chamber 915s.

I would think going to headers really had alot of the hp pickup change on this. Thats 10 mph pickup as I cant see 1 point in comp and some porting on the 915's doing that much but I have seen headers pick up alot when going on a car. Did the original 906's have the stock size valves or did they have 2.14 & 1.81's like you did on the 915's ? Ron

 

[Garys1969RR]

The 906 heads had stock size valves. I also had a 440 with flat top pistons and similarly ported 915s on it. TM 7 intake. It ran 14s at below 100 MPH. Put the exact same top end on a 413 with 14cc dome pistons in it and that motor pushed the 65 Belvedere to 12.80@108 MPH. Only change was C/R from 10.5 to 1 in the 440, to 13 to 1 in the 413. Ran a Isky .510 lift solid cam. 292 duration, about like the 509 hyd cam. The throttle response with the dome pistons and tight quench is really amazing !

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Both motors were used in the same car.

 

[Cranky]

None of the 516, 915 or 906 heads were produced for use with unleaded fuel but that doesn't mean you can't run them on unleaded but some have had problems with seats being sunk. Imo, pros with closed chamber heads usually means higher compression ratio and generally a better quench/squish dimension. If you have a 0 deck piston and closed chambered heads and use a composition head gasket, you will have right around .038" quench depending on how much the gasket compresses. I shoot for tighter quench and have gone as tight as .019 however, that's really not recommended. With the open chamber head, you may want to use a reverse dome piston to have a good quench dimension.

 

[Meep-Meep]

For a mild street build it's going to boil down to economics. The 915's and 906's have the best intake port shape but I wouldn't put my self out too far to get that feature. It has been proven over and over again that a well prepped set of "flat floor" heads can get the job done. And by flat floor I'm referring to the 516, 346, 452 and the old Direct Connection Stage IV iron heads. The cam selection will be the most important decision and will make or break the build.

 

[Garys1969RR]

so if i take this right. if i use 915s you can still mosty run a flat top piston and keep compression up higher. if you go with a open you almost need to run a dome top to get compression up. yet the 906 and 915 do flow about the same

Flat tops with a 915 head will work well. Thats what the 67 440 came with from the factory. An Edelbrock alum closed chamber head should work even better due to improved air flow. Since I leave at a higher elevation in Colo, I like to run alot of C/R. That has always worked well for me. Keep in mind that at C/R above 10 to 1, and below 2500 feet elevation, you will need to boost your octane somehow. I am using a mix of 3 gallons of 91 octane premium, 2 gal of E 85, and 3 gal of 100 octane Sunoco race fuel. Gets it to around 98 octane. The more E 85 you use, the larger the jets need to be.

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And I have my Holley 850 double pumper at 86 main jets all around. (Stock is 80). The plug color is just right.

 

[383man]

so if i take this right. if i use 915s you can still mosty run a flat top piston and keep compression up higher. if you go with a open you almost need to run a dome top to get compression up. yet the 906 and 915 do flow about the same

You can run the KB quench pad piston as thats the ones I ran on my old 440 with 906's. It has a small quench pad that sticks up into the chamber so you can get quench if you work the heads and the math just right. The piston almost looks like a pop up piston but it just has a small flat quench pad on the part to go up in the head chamber. I think I still have a pic of some in a block when I was mocking them up. Ron

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Here is a pic of the quench pad piston. I ended up with 10.0 comp using these with 906 heads. I got about .046 quench with them and the 440 ran fine on 92 pump with these pistons and 906 heads at 38 total timing. These are not in right as I was just mocking these up at that time. Ron

 

[Garys1969RR]

so if i take this right. if i use 915s you can still mosty run a flat top piston and keep compression up higher. if you go with a open you almost need to run a dome top to get compression up. yet the 906 and 915 do flow about the same

You can get C/R up to around 10 to 1 or a little higher with open chamber heads, and quench dome pistons. The same with flat top pistons and closed chamber heads. 906 and 915 heads have the same port design/shape. Go to the KB piston website and you can pull up the C/R calculator. Just input all your head cc specs, gasket thickness etc. Then hit calculate and it will tell you your exact C/R.

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For examploe, I put into the calculator these specs: Head cc of 75, o on piston head volume (flat top piston) .017" below deck, .020 gasket thickness, stroke of 3.75" gasket bore of 4.4 inches. The calculator said I would have a C/R of 9.070 to 1.

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OOPS! I had the put wrong bore size in there. With a bore of 4.375" (451 engine), it comes to 11.97 to 1. With an 80 cc head, you would get 11.36 to 1. 80 cc is about the volume that a 915 head actually measures

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Change the piston to a 14cc dome, and you come up with 13.29 to 1. That is what I run in my drag race car, and it really flys!

 

[zyzzyx]

For a street engine I like the 452's because they already have the hardened seats, and I would run a flat-top-piston as Mopar Engines manual suggests.

They say :"typically, an engine with 11.0:1 compression ratio will make more power with a flat piston than it will with a domed piston."

 

[Bruce]

If you want to stay with the stock steel heads use a set of 452 heads they flow the best of the big block heads except for the max wedge heads. They also have hardened exhaust seats. Ported they flow around 280 CFM or better. I have done hundreds of them over the years.

 

[Cranky]

In stock form, all of the open chamber heads flow pretty close to each other but all of them have terrible valve pockets or bowls. Just doing a bowl job improves them a bunch....and btw, this thread is a year and half old....

 

[Mike67]

Loved the discussion/info...but I got a little lesson the other day, and not that it's relevant but I'm starting to check the date of the last post to the thread ....just sayin....