Thread: 454 build - what intake and cam ?

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Many thanks for that very informative response techinspector1 ! your input is very much appreciated and is very important !

I am an automotive engineer so I know better than to guess at any of this and end up with money spent and something undrivable.
That is why I am taking the time to measure and calculate everything and get your expert advice before spending money.

I want to build this engine right.

All measurements were taken using the correct instruments.

Cylinder volume was obtained by measuring the bore with a bore micrometer and the stroke with a depth gauge.

Chamber volume was measured with a medical syringe.

Gasket volume same as above

Piston dome was measure by inserting the piston exactly 1" down the bore, sealing the crown to the cylinder and then measuring with the syringe and then calculating.

ring land volume was calculated from measurements.

These are the figures

Cylinder 958cc (109.38x102mm)
Chamber 115cc
Dome 41.6cc
Gasket 13cc
Ring land 1.1cc

If I take off 20cc worth of dome, I get 9.9:1 compression which is acceptable for 91 octane ?
I can use a thicker head gasket when I assemble so that will help.

I can start off by cutting the piston 90 degrees to center-line but I would be cutting from the sharp edge of the dome, thus removing very little material per depth of cut.
I would need to cut parallel to the flat angled surfaces to take off 20cc worth of material.

What do you say techinspector1 ? should I mill them first 90 degrees as far as possible and then along the angled plane to arrive at the required dome volume ?

Originally Posted by ceejay

If I take off 20cc worth of dome, I get 9.9:1 compression which is acceptable for 91 octane ?

If I were building it, I would shoot for 9.5:1. That will work best with the cam recommended, to make the best cylinder pressure and avoid detonation with iron heads.

Originally Posted by ceejay

I can use a thicker head gasket when I assemble so that will help.

BBZZZZZZT That's the sound of the wrong answer buzzer. It is not the function of the head gasket to set the static compression ratio. That's done with piston crown volume and combustion chamber volume. Block deck height and gasket thickness are used to set the squish/quench, possibly the most important aspect of building a pump gas motor. It's the distance from the flat crown of the piston to the underside of the cylinder head with the head gasket in place. Again, if this were my motor, I'd be shooting for a squish/quench of 0.040" (0.1016 mm) by first choosing the head gasket I wanted to use, then cutting the block decks to give me the squish/quench I wanted. I might even go a little tighter if the pistons were cast or cast hypereutectic, but with forged pistons, you have to run a little more piston to wall clearance, so the piston rocks a little more in the bore and it's possible, with part of a pop-up left on the crown, that it could rock enough to make contact with the head. A little kiss at max revs wouldn't necessarily be a really bad thing, but you wouldn't want a "thud". I have seen motors using flat-top pistons that left the imprint of the piston part number on the underside of the head. Now, that's gettin' 'er down pretty close.....

As a matter of interest, it has been found that a motor that has used a thicker head gasket to lower static compression ratio will be more detonation-prone than a motor with a thinner head gasket and slightly higher static compression ratio, due to the wider squish/quench measurement with the thicker gasket.

Originally Posted by ceejay

I can start off by cutting the piston 90 degrees to center-line but I would be cutting from the sharp edge of the dome, thus removing very little material per depth of cut.

Personally, I would want to get the dome height out of the way first, to help with propogation of the flame front across the chamber. Having to navigate around that tall dome isn't the best way to light the fire completely across the chamber in my opinion. Once you've done all you can with height, twist the piston around and begin cutting on other angles, all the while keeping the 7.64 mm minimum thickness in mind. Cut and measure, cut and measure. You'll likely end up at around 21-22 cc's for the pop-up, to achieve 9.5:1. Don't forget that the motor will have to be rebalanced for the lighter pistons.

Originally Posted by ceejay

What do you say techinspector1 ? should I mill them first 90 degrees as far as possible and then along the angled plane to arrive at the required dome volume ?

That would be my plan if I were doing it for you, paying attention to the minimum 7.64 mm crown thickness.

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Originally Posted by DennyW

((I am an automotive engineer so I know better than to guess at any of this and end up with money spent and something undrivable.
That is why I am taking the time to measure and calculate everything and get your expert advice before spending money.))

I hope you are also figuring in the spark plugs you plan to run also. It's those little things that will bite you.

You are correct Denny, that's why I gave him a pretty good lesson on plugs in post #15.

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