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Old 10-07-17, 09:20PM   #16
Gach
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Originally Posted by Mr.Pontiac View Post
Just asking ok, i am just asking, best way to up compression mill heads??? Gach, don,t get involed but if it was you???
Yes I would mil the heads.
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Old 10-07-17, 09:37PM   #17
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My notes suggest you lose about 1cc of volume for every .005-inch of material removed, this on a 72cc head. Your also going to affect the amount of airflow slightly.


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Old 10-07-17, 09:51PM   #18
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040 over 400 cid zero decked .039 felpro gasket 72 cc heads. I'm not going to do the math but it not 9.5 or 8.5. Back in the day that was 10.50 -10.75.
I canít remember what the standard bore size is on a 400, or I would. You have to allow for valve relief think thatís something like 6 cc, but anyway I did it a long time ago and came up with 9.50.

Little education Thomas... letís say for argument sake, we came up with 10.50 as his compression, with a iron head that would be fine. With aluminum head NO! BECAUSE! It dissipate the heat more or doseínt build the heat like a iron head. so affectively itís actually only 9.50 get it. Ask just about any Engine builder and heíll tell you that.

Steve agreed SD going to give a safe compression ratio, not knowing who heís dealing with or person experience on Tuning. Yes on a 462 with a 2.100 storke 10.50 would be safe. For a Idiot

Stroke greatly affects compression ratio of 400 with a 3.75 stroke Will tolerate more compression, Iíve built quite a few.

Also Thomas although he hasnít made it clear Iím guessing that he doesnít have any cylinders low on compression.
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Old 10-07-17, 10:05PM   #19
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On my previous motor, I ran 10.75, on the most recent motor I ran 12.1 no issues what so ever on 93 octane gas. Thatís with a 4.250 stroke.

I never ran a 400 with aluminum head, but with iron head was 10.75 on the money, if I was to build a 400 with aluminum heads it would be at 11.75.you can run as much as 2 points more compression with aluminum head. I proved that to myself.

Hereís the thing, thatís important when you call the cam company make damn sure you say itís a pump gas motor. Cams are completely different. Thatís a whole Nother subject on why. That gets into dramatic compression static compression.

Rich you will have to definitely changes those Valve springs, their not going to hang with more cam. Like gtofreak says a minimum of 130 seat.
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Old 10-07-17, 10:16PM   #20
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"letís say for argument sake, we came up with 10.50 as his compression, with a iron head that would be fine."

Serious .... 10.5 compression with iron heads ? This with race gas ?

Agree on the shorter stroke in conjunction with the compression. I spaced that.

Standard 400 bore 4.120

Simple calculator here in restore section:

http://www.classicalpontiac.com/

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Old 10-07-17, 10:25PM   #21
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In the words of the Butlers last week, 110 pounds is good, falls to 95 id be worried. 1.795 installed height. everything looks good so far. Oh yes Gach, i am very well aware with new cam new valve springs are in order. i understand that. we are just having a chat here, i am learning alot, Thanks again fellas
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Old 10-07-17, 10:29PM   #22
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AGAIN, what spring at that 1.795" ?

Call Kerry at Crower / 619-690-7805

Tell him you have 110 lbs with that 60243 cam, see what HE says !
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Old 10-07-17, 10:38PM   #23
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.050 255 intake 263 exhaust .020 288 intake 296 exhaust . lob lift .3600 intake .3706 . lobe sep 110 . gross lift .540 .556 . intake timing 39btdc 69 abdc exhaust timing 83 bbdc 33 atdc ..
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Old 10-07-17, 11:04PM   #24
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I'd be real curious how far he is away from coil bind with his net valve lift. Especially with weak valve springs in use !

"Running a valve spring in a condition where it has excessive clearance between the spring coils at maximum valve lift can also contribute to surprisingly destructive forces being generated within the valve train, especially in the valve spring itself."


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Old 10-07-17, 11:17PM   #25
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Steve are you kidding, weak i called Butler there fine. Sorry, one thing i cannot tell you is what name bran springs are on the heads. I don,t have that info. sorry.
Its really simple just bring up Crower web site it says same thing, 110 to 115 pounds
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Old 10-07-17, 11:29PM   #26
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Lou I don't really understand you. Ok if in 1969 a new 400 had a compression ratio of 10.75 with the same 4 valve relief pistons an 72 cc #62 heads ( running just fine with the gas back then) is the same 10.75 as with 72cc alum e head. That's all I'm saying now because a alum head has better cooling letting you run on today's piss gas. With alum heads you can run 1 full point over a cast head But again still 10.75 with both 72 cc heads
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Old 10-07-17, 11:49PM   #27
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Sorry, I agree with Paul Carter on the springs.

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Old 10-08-17, 12:02AM   #28
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"Its really simple just bring up Crower web site it says same thing, 110 to 115 pounds"

Ask yourself, is the Crower information based on a 'stock' pontiac valvetrain mass and the factory installed height ? Uh ?


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Old 10-08-17, 01:04AM   #29
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Quote:
Originally Posted by Mr.Pontiac View Post
Steve are you kidding, weak i called Butler there fine. Sorry, one thing i cannot tell you is what name bran springs are on the heads. I don,t have that info. sorry.
Its really simple just bring up Crower web site it says same thing, 110 to 115 pounds
I agree with Paul too. Itís called bounce were the lifter is actually bouncing off the cam, not necessarily having Valve float. If only street use not much of a concern, maybe what Butler was thinking, itís really a street cam, more of a Ram 4 design
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Old 10-08-17, 01:25AM   #30
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Lou...With alum heads you can run 1 full point over a cast head But again still 10.75 with both 72 cc heads
Your catching on, so 11.75 with aluminum head would be equal to 10.75 with a iron head.

So if he’s running 10.75 with aluminum head it’s equal to 9.75 with Iron head. So affectively he’s only running 9.75.

If Cam overlap calls for say 10.75, he’s a point short in compression, there’s a reason the Ram 4 has 10.75 compression. At that level every point in compression is worth 20 hp which is equal to a tenth.

My last motor had 12.1 compression, absolutely no issues with 93 octane.
15 dyno pulls to boot. There’s a reason why they say run 1-2 more point compression with aluminum heads. If I went by your thoughts and only ran
10.75, I’d be down 40 hp.

A pump gas cam is designed by dramatic compression and overlop. Completely different animal. Were as a cam design for race fuel has more overlop and dose’nt care what the dramatic compression is.
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