LA360 compression

[Matt13]

ok engine builders. Here is my dilemma. I bought a Mabbco rebuilt 360 short block from a member. Some upgraded stuff like KB high compression flat top pistons, moly rings, 272 muscle cam (272/272 duration 454-454 lift) Cloyes HD timing chain and sprokets. .30 over bore. Got a nice brand new set of Speedmaster aluminum heads with 68cc combustion chambers.
  Here's the problem; my engine is at a builders for finishing. Went by there yesterday and he said this engine will be an absolute dog as it sits now. He doubts it will make 8:1 compression. Yes, the pistons are below deck a little, but he says I am losing a lot of quench with them. He suggests new pistons, rods, roller cam and new crank. That's an expensive prospect, considering what I already have in the motor. Also, this guy is a very well known builder with a great reputation and is well known in the racing circuit. His shop is incredible and he rebuilds engines for a living, and has many many great reviews. He does not even want to assemble the rest because he says he knows I will be disappointed.
  What to do? Will this motor be a dog like he says? I don't know that I have the scratch to have him tear down this motor and upgrade it to a stroker.
  TIA.

[Mr Cuda]

How far below deck are the pistons?
Math will give you compression ratio
Factory 8.0-8.2 would be down around .100"
  -.010 with normal. 030" gasket and no piston dome is approx 9.8

[Cudajason]

Is the builder a Mopar guy?

[Matt13]

Is the builder a Mopar guy?

@Cudajason Yes. He's the only guy running Mopars at the Prostock level. Alan Prusiensky.

[Matt13]

How far below deck are the pistons?
Math will give you compression ratio
Factory 8.0-8.2 would be down around .100"
  -.010 with normal. 030" gasket and no piston dome is approx 9.8

@MrCuda Yes, they are down at least .100". Flat top pistons. Engine is .30 over. He did the measuring/calculations before I got there. He basically said in a heavy Ebody this motor will be a real dog. He wants to up the compression to get more torque and hp. Right now, he says the compression will be too low for any performance. And its not like he's hurting for business. He had at least 4 engines ahead of mine and about 5 finished. Gorgeous work.

[Mr Cuda]

 I made that mistake once.
It's not that ebodies are heavy,  it's just that 8.2 is too low to have a real cam.
You are stuck.  New pistons.
Or put a 4" crank in it, not that I would.

One more question,  the  opening statement said kb high compression pistons???

[70 Challenger Lover]

I just went through this drill with my 318. Pistons were down in the bore .120 and the head gasket I removed compressed to .044 with 70 cc chamber heads. The math on my set up put compression at 7.4 to 1. Abysmal.

The cam that the previous owner put in was a couple steps bigger than a stock 318 cam. Normally that cam would do well with 8:1 but at 7.4:1, it had zero power compared to another stock 318 car I have that's never been rebuilt.

I agree that the selected cam cannot perform with the low compression you have.

I wanted to use closed chamber heads with 56 cc chambers along with thinner .027 head gaskets. Those two things alone would have got me to 8.7:1 but you need more than that for your set up. In the end, I switched motors and now I'm going with a hotter 340.

I think you can go that route with small chamber heads and thinner gaskets but you'll probably still need to go down a step or two on the cam.

[Mr Cuda]

 I have an '83 D350 and when i cleaned the motor up, I decked the block .100" and shaved the heads .020, and the iron tq intake still fit. It runs well, but is still coming out for a 440.
Cam charts should be shown with a required  compression ratio,  instead of a rpm range.  Everyone overestimates what rpm they will run at.

[Matt13]

I made that mistake once.
It's not that ebodies are heavy,  it's just that 8.2 is too low to have a real cam.
You are stuck.  New pistons.
Or put a 4" crank in it, not that I would.

One more question,  the  opening statement said kb high compression pistons???

@Mr Cuda , yes, they were advertised as "high compression" pistons by the guy I bought the engine from.

[Mr Cuda]

 Wasn't that engine for sale here?

[Matt13]

Wasn't that engine for sale here?

@Mr Cuda Yes

[Matt13]

Here's a pic of the pistons in the block.

[Chryco Psycho]

I agree , it will be disappointing at best , wrong cam for sure , I never use Hyper pistons , only forged , might as well throw in a crank & stroke it to 408 CI & use a far better cam .
You could resell this engine & pick up a 360 block for $100 & build the short block with that .

[Matt13]

@Chryco Psycho , the big issue is that a shop has had my car for three weeks now, just taking up space and they want to get moving on this. The engine builder is at his own shop. I really don't have the time or finances to get another block and have all the work done. It's pretty much work with this 360. I just wish the builder was open to doing small things that wouldn't require a full tear down, like changing the heads, using a thinner gasket, perhaps decking the block. He said that at the very least, I need to change the pistons, at which point it would just make sense to change the cam and crank because were already there. I just don't have the $$$ for a new crank, roller cam, lifters, rods, pistons....it all adds up. I don't think this is a bad build as it sits, we just need to bump up the compression but he really feels we should stroke it. I'm really out of options....

[RUNCHARGER]

Mill the heads and intake as much as you can and still be able to seal up the intake. Phone Hughes and stick in whatever camshaft they recommend. Other than that start from scratch. You won't be able to run 9's with it but it can be made to feel okay.