LA360 compression

[Matt1968]

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.

 

[70bigblockdodge]

I'm not a small block guy, but a 360 has a longer stroke than a 383/400 which makes a nice street engine. The cam you have listed is not a barn burner so it is a little more tolerable to the lower compression. Could he give you any numbers for how far down in the hole the pistons are? Do you have the part number for the KB pistons? You could get the compression height and plug all that into a compression calculator.

 

[PurpleBeeper]

1. Calculate your static compression ratio....be sure, don't guess
2. IF it is 8:1, you have 3 options.
a. run it at 8:1
b. change heads
c. change pistons
3. If the engine isn't balanced (or maybe even if it is) and the short block is fresh, then domed pistons seem like the cheapest option....don't even need to re-hone I would guess.

 

[71Beeper]

I second the motion to get the block zero decked. You can also have the heads shaved to bring the chamber cc's down.
Hopefully your KB pistons are the KB107's.
I agree, the cam is a little tame - go for the ol school .509 purple shaft.

My .030 over 360 has the KB107's.
My block is zero decked.
My 'J' heads are shaved to give a 60 cc chamber.
I'm at 10.9:1 and that's with the thicker head gasket.

 

[Matt1968]

I second the motion to get the block zero decked. You can also have the heads shaved to bring the chamber cc's down.
Hopefully your KB pistons are the KB107's.
I agree, the cam is a little tame - go for the ol school .509 purple shaft.

My .030 over 360 has the KB107's.
My block is zero decked.
My 'J' heads are shaved to give a 60 cc chamber.
I'm at 10.9:1 and that's with the thicker head gasket.

@71Beeper Its been decided that these are not the 107's like the seller told me. They appear to be stock replacements, possibly KB's but not 107's.

 

[Matt1968]

Here's a pic of the pistons in the block

 

[71Beeper]

Matt, you would be correct - those are not 107's.
If cylinder #1 in the photo is at top dead center, then you definitely have alot of deck height that can be removed.

Here's what the KB107's look like.

 

[beanhead]

The question is what do YOU want out of the engine/car?

Are you wanting ground pounder/street race power, or just a nice fun classic that can roast the tires and pin you to the seat when you want it to?

No offense but your builder sounds like he doesn't really want the job if he can't sell you all the go-fast stuff and build the type of engine HE wants to build (he is in business to make money after all).
If a racer is what you're after, cool....but that mill will not be a "dog" in a fun cruiser. It goes without saying but match the entire combo properly.
If street-race power and getting it on with the late model stuff is what you're after, then he's right in saying it needs a total re-do.
Again, it's all about what you want and if you guys aren't on the same page, find someone else.

 

[dvw]

It certainly will make more power at zero deck. I'm assuming .030" over. At Zero deck it'll be arond 10.8, -100" in the hole 8.7, -.150" in the hole about 8.0. Right now it'll run on 87 octane. I built a similar Magnum motor at 8.0-1. Hyd roller, Eddy head, RPM intake, 650 Eddy carb, headers. 3.23 with a low gear set 904. It ran very nice for a street motor in a 68 Satellite convertible. By the seat of the pants very low 14 or high 13 second car. The 360 in my Challenger is 9.0-1, ported factory heads, .220 hyd roller, LD340, 650 holley, headers it's been 12.70's w/3.55. With full exhaust and air cleaner in place. At most the difference between 8.0-1 and 11.0-1 is roughly 10% or less. At max 40hp. At 9.5-1 5% or 20hp. But with the small cam you are using the difference will be even less. So if you want to run premium fuel? The easiest thing right now would be to swap pistons. Reuse the rings. It's already honed fresh. You could mill and deck. But then everything has to come apert. Intake will need to be cut. Pushrods will need to be custom length.
Doug

 

[yella71]

So buy a set of pistons.