.040 over in 318

[hwy2]

I am losing 2 cc in I am losing 2 cc in the combustion chamber in my new heads. My motor is 40 over. Will that pretty much equal out or will I still be losing compression because of the 2 cc loss?

 

[AJ/FormS]

If I understand you correctly , then yes.
A loss of 2cc in the head will equal a gain of 2cc on the bore.
But
an overbore is a GAIN of cc in Swept volume, making it a Net gain to the Compression Ratio.

Here's what I mean;
at 3.91 bore, the swept is 652.26 cc. and for an 8/1 engine, the TOTAL chamber volume would need to be 93.18cc or less.
If you bore that engine out to 3.95, that makes a swept of 665.68cc, which is an increase of 13.42cc; yeah I did the math three times.
If you then subtract 2cc from the total chamber, making it 91.18, then the compression ratio will climb from 8/1 to 8.3/1

Way more important than this modest increase in compression, would be a Quench reduction to, in the window of .030>.040. Good luck with that.
--------------------------------------------------------
Can it be done; Sure. but it would be cheaper to start with a 360.
First; for a 318; yur gonna need custom pistons for open chamber heads, or different custom-design pistons for closed-chamber heads.
Secondly, for a modest street cam, you'd need to modify the pistons to get the Dynamic Compression ratio into a zone that will not detonate on pump gas, or
Third; install water injection to prevent that same detonation.
Whereas;
in a 360LA with KB107s, the pistons will drop in around .012 below deck. Install closed chamber heads with an 028 gasket and the Scr will climb to around 10.7 Install a cam with a typical late closing intake, and the pressure will come in close to 175/180. With alloy heads that will run all day/everyday, on 87E10. Pump it up a lil, to 185/190psi and you got a torque-monster.
Total cost is ;
>with the 318; custom pistons/ custom fitted, closed chamber iron heads to keep the cost down, needs best pump gas or may need water injection. Before long, you'll be wishing you had just dropped in a 360.
>with the 360; off the shelf pistons, alloy heads, runs on skunk-pee, and on the street, you'll never need a bigger engine.
I mean, that's the gist of it.

But I'll tell ya, if I had to stay with a 318, not because of budget restraints, dang rights I'd pump it up! and, I'd run water injection too.


Edited cuz I screwed up the first time.

 

[hwy2]

If I understand you correctly , then yes.
A loss of 2cc in the head will equal a gain of 2cc on the bore.
But
an overbore is a GAIN of cc in Swept volume, making it a Net gain to the Compression Ratio.

Here's what I mean;
at 3.91 bore, the swept is 652.26 cc. and for an 8/1 engine, the TOTAL chamber volume would need to be 93.18cc or less.
If you bore that engine out to 3.95, that makes a swept of 665.68cc, which is an increase of 13.42cc; yeah I did the math three times.
If you then subtract 2cc from the total chamber, making it 91.18, then the compression ratio will climb from 8/1 to 8.3/1

Way more important than this modest increase in compression, would be a Quench reduction to, in the window of .030>.040. Good luck with that.
--------------------------------------------------------
Can it be done; Sure. but it would be cheaper to start with a 360.
First; for a 318; yur gonna need custom pistons for open chamber heads, or different custom-design pistons for closed-chamber heads.
Secondly, for a modest street cam, you'd need to modify the pistons to get the Dynamic Compression ratio into a zone that will not detonate on pump gas, or
Third; install water injection to prevent that same detonation.
Whereas;
in a 360LA with KB107s, the pistons will drop in around .012 below deck. Install closed chamber heads with an 028 gasket and the Scr will climb to around 10.7 Install a cam with a typical late closing intake, and the pressure will come in close to 175/180. With alloy heads that will run all day/everyday, on 87E10. Pump it up a lil, to 185/190psi and you got a torque-monster.
Total cost is ;
>with the 318; custom pistons/ custom fitted, closed chamber iron heads to keep the cost down, needs best pump gas or may need water injection. Before long, you'll be wishing you had just dropped in a 360.
>with the 360; off the shelf pistons, alloy heads, runs on skunk-pee, and on the street, you'll never need a bigger engine.
I mean, that's the gist of it.

But I'll tell ya, if I had to stay with a 318, not because of budget restraints, dang rights I'd pump it up! and, I'd run water injection too.


Edited cuz I screwed up the first time.

I was kind of thinking that the 40 overboard and larger CC heads would equal out. If I find a cheap 360 block in Craig somewhere I will probably use it but for now I’ve got a bunch of parts 318 can be switched over to 360 as long as my roller lifters link set up will fit in the block, I would just need another torque converter

 

[AJ/FormS]

I would just need another torque converter

Actually you could theoretically use the same TC, just with a weighted flex-plate or weight welded on to the 318 one, in the correct place and amount.
As to the retro-fit roller lifters, if they dropped into a 318LA, they should drop into a 360LA just as well. but not onto the flat-tappet cam, obviously.

As to the tight quench;
This lets you run about a half a point more Compression without detonation, . More with alloy heads.
But what it really does is help emissions, increase fuel-economy, make throttle response snappy, and it makes a lil more power by decreasing the amount of fuel going out in the exhaust, unburned.
And because, getting a tight-Q almost always means to bring the pistons up to the deck, or a bit higher, that situation helps the headers work better during the overlap cycle, by keeping the path smoother and the negative pressure signal consistent as it travels across the piston and up into the plenum. Of course, with log exhaust manifolds, this counts for nothing.
A long time ago, I was running a Zero deck 360 , closed chamber heads, and .028 gaskets for a really nice tight-Q.
But the thin gaskets couldn't take 11.3Scr.
So I took the engine apart and had it decked again, this time to put the pistons up above the decks at ~.007. Then I installed .039 FelPros, leaving the Q sitting at .032. and I never lost another gasket. But, you know I lost a hint of cylinder-pressure, with the loss of 8/10ths of a cc, lol..