LA360 compression

[Xcudame]

Heminut gave you the best advice. The place you're at now whats to build you a 500 horse power 408 stroker flame thrower. You need to find a machine shop that will swap the pistons to something with more compression (KB107). That, with the .454 lift cam and speedmaster heads should put you in the 340 - 360 horse power easy and I think that's what you want. It will be very streetable and a pleasure to drive. You'll have a lot more torque and horsepower than the 318 and you'll love it!

 

[Matt68]

Were I a reputable machinist-engine-builder with a positive reputation, I might cringe given an assignment (by a client) to complete an engine rebuild in a way that could make me look bad.

If this one says he will only do certain work, and not simply a piston change, respect him, his shop, and his request. Go elsewhere. It's not a big deal.

@pschlosser , and I do respect that its his shop; his rules. But in the interim, I've lost three weeks of my car just sitting at a shop with no progress. There have been many suggestions as far as ways to raise the compression, but the only one this builder wants to do is stroke it. All other suggestions were shot down. I am thinking of just getting some new heads with 63cc or less combustion chambers and a thin gasket and be done with it. I can always sell the brand new Speedmasters.

 

[pschlosser]

@pschlosser , and I do respect that its his shop; his rules. But in the interim, I've lost three weeks of my car just sitting at a shop with no progress. There have been many suggestions as far as ways to raise the compression, but the only one this builder wants to do is stroke it. All other suggestions were shot down. I am thinking of just getting some new heads with 63cc or less combustion chambers and a thin gasket and be done with it. I can always sell the brand new Speedmasters.

IMO, your three week loss is on you, not the shop owner. Just go elsewhere. It's not a big deal. A shop owner should be allowed to decide what he does and doesn't do for a client. Sorry.

 

[Matt68]

IMO, your three week loss is on you, not the shop owner. Just go elsewhere. It's not a big deal. A shop owner should be allowed to decide what he does and doesn't do for a client. Sorry.

@pschlosser The loss really isn’t on me. I didn’t choose this guy; the shop taking out my 318 and installing the 360 sent it to this builder with the task of finishing it. I’m not asking him to do anything illegal or dangerous by trying to bump up compression without spending $6,000 doing it. He should have just come out from the beginning saying he wants $6,000 to stroke it. If he was upfront and would have said that three weeks ago, my short block would be back at the original shop by now.

 

[Matt68]

Well, I've returned the Speedmasters with those big 68cc chambers. Going with a rebuild of the late 80's swirl port 714's that are on my 318. Anyone know the chamber size of those? I've read 65cc, also saw 63cc.

 

[heminut]

Well, I've returned the Speedmasters with those big 68cc chambers. Going with a rebuild of the late 80's swirl port 714's that are on my 318. Anyone know the chamber size of those? I've read 65cc, also saw 63cc.

3 to 5 cc drop won't significantly change your compression ratio.

 

[Matt68]

3 to 5 cc drop won't significantly change your compression ratio.

@heminut Well, the builder won't do the piston change and I'm running out of time. The original shop wants to get moving on this, so I'm just going to work with what I have and save for later. I've now read that the 714's have 62cc combustion chambers, so that with the slightly better cam, roller rockers, dual plane intake and headers and hopefully I can live with it until I can build better. Mabbco is saying that the engine build I have should get 9:1 compression (they built it), and that's with stock heads, intake etc. Already hemorrhaging money on all this work. I just don't have the $6,000 to stroke it.

 

[Steve340]

A 5 cc smaller combustion chamber will raise the compression around 0.5 of a point.
8.5 would go to around 9:1
If you can get the engine up to around 9:1 I think it will probably go OK.