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The_Judge · 10-09-2006, 12:24 PM

Help me.

I have an engine 428 and I it am constructing and not that compression ratio to handle.

It is advisable a compression Ratio from 12.7 to 2235 meters to level of the sea and for that.?

Ron H · 10-09-2006, 12:38 PM

Holy cr&p, did you read what you wrote after you typed it?
12.7 with aluminum or steel heads is race gas territory.
11 to 1 with aluminum at high altitude is close on 91.
10 to 1 max steel heads. 9.5 to 1 preferred for street engines.

Jack Ferris · 10-09-2006, 12:42 PM

Im still having trouble understanding the grammar portion of the post.

The_Judge · 10-09-2006, 03:49 PM

Quote:

Originally Posted by Jack Ferris

Im still having trouble understanding the grammar portion of the post.

You forgive for the grammar, I am of Argentine And my Englishman is not good.

The question is.

It is advisable, To have a compression Ratio from 12.7 to 2235 meters to level of the sea and for that, With Fuel of 92 octanes?.

Ron H · 10-09-2006, 04:10 PM

Is it advised to have a 12.7 to 1 CR for 2235m or 7333' with 92 octane fuel?No
11 to 1 for aluminum and 10 to 1 for steel heads. You may get away with a bit more. 11.5, 10.5.
It is important to consider the camshaft being used as the dynamic CR can be higher or lower than static.

harry k · 10-09-2006, 04:11 PM

what is " It is advisable, To have a compression Ratio from 12.7 to 2235 meters to level of the sea and for that" means ?

do you mean that your in high altitude /elevation?

tc · 10-09-2006, 08:37 PM

For 12.7 compression ratio on your 428 you will have only 75 cc's in your heads,gasket,valve reliefs in the pistons. Is this your amount of cc's when you add up these items?

Are the heads aluminum or cast iron?

What is your goal for this engine. Race only with race gas, street with pump gas? Some of both?

The_Judge · 10-10-2006, 09:47 AM

[QUOTE=tc]For 12.7 compression ratio on your 428 you will have only 75 cc's in your heads,gasket,valve reliefs in the pistons. Is this your amount of cc's when you add up these items?

Yes 75cc´s

Are the heads aluminum or cast iron?

Of aluminium with combustion chambers of 72 cc

What is your goal for this engine. Race only with race gas, street with pump gas? Some of both? Both

Ron H · 10-10-2006, 09:51 AM

Quote:

Originally Posted by Ron H

Is it advised to have a 12.7 to 1 CR for 2235m or 7333' with 92 octane fuel?No
11 to 1 for aluminum and 10 to 1 for steel heads. You may get away with a bit more. 11.5, 10.5.
It is important to consider the camshaft being used as the dynamic CR can be higher or lower than static.

This is your answer if running 92 octane

The_Judge · 10-10-2006, 10:06 AM

Quote:

Originally Posted by Ron H

This is your answer if running 92 octane

Thank you Ron H

I believe best is 11.5 CR with heads aluminum.

you that think ?.

Ron H · 10-10-2006, 10:14 AM

Yes I think that for your altitude you could get away with 11.5 to 1 with aluminum heads depending on the camshaft you are running. Do you have the specs for it?

The_Judge · 10-10-2006, 10:38 AM

Quote:

Originally Posted by Ron H

Yes I think that for your altitude you could get away with 11.5 to 1 with aluminum heads depending on the camshaft you are running. Do you have the specs for it?

Yes

Cam Style: Mechanical
Basic Operating RPM Range: 3,500-6,500 RPM
Lobe Separation (degrees): 108
Advertised Intake Duration: 17 degrees dtc and 49 degrees abc
Advertised Exhaust Duration: 53 degrees pbc and 13 degrees apc
Advertised Duration: 246 degrees

Half-Inch Stud · 10-10-2006, 11:00 AM

what kind of car do you have?

The_Judge · 10-10-2006, 12:53 PM

Quote:

Originally Posted by Half-Inch Stud

what kind of car do you have?

Firebird Formula 1973 with an engine 428, with Crankshafts of 455 and Bore Size of 4.151in. To obtain 468 Cubic inches.

Half-Inch Stud · 10-10-2006, 10:05 PM

Now we're getting somewhere. Very clear to me that you need to run the Ram III STYLE Head (48, 12, 16, 13, and many other 2-digit numbers cast on the center exhausts such as 64, 5C) to get the 10:1 or 9.5:1 with a dished piston.

Heads to avoid: pressed-in studs or small-valve-heads that you can pass a match between the valveheads)

Then you will only have minor ping with 93 Octane.

Mo · 10-10-2006, 10:40 PM

Quote:

Originally Posted by Half-Inch Stud

Now we're getting somewhere. Very clear to me that you need to run the Ram III STYLE Head (48, 12, 16, 13, and many other 2-digit numbers cast on the center exhausts such as 64, 5C) to get the 10:1 or 9.5:1 with a dished piston.

Heads to avoid: pressed-in studs or small-valve-heads that you can pass a match between the valveheads)

Then you will only have minor ping with 93 Octane.

Alloy aluminum head 72cc has he. Think I he does,well. or

Mark, he has 72cc aluminum heads. Well, I think he does. lol.

Half-Inch Stud · 10-11-2006, 11:57 AM

I see has he amodified boxite heads. They he gonna need the same type stuff for pistons. with a slight dish to keepa the ping down.

Tim Corcoran · 10-11-2006, 02:45 PM

You need to lower your compression to 10:1 or lower for 91 octane. Easiest way is to change cylinder heads.

Tim C

Ron H · 10-11-2006, 04:48 PM

He is at 7333' above Sea Level.

The_Judge · 10-11-2006, 05:51 PM

Quote:

Originally Posted by Tim Corcoran

You need to lower your compression to 10:1 or lower for 91 octane. Easiest way is to change cylinder heads.

Tim C

Hi Tim Corcoran

I committed the mistake of buying cilinder head with combustion chambers of 72 cc, the correct thing would have to be of 82 cc.

I buy custom pistons Forged Type top dish with compression ratio of 11:1 with Gasket thickness of 45mm.

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