LA360 compression

[Mr Cuda]

 If I  recall,  this is a later thin wall block  of no intrinsic value.
Disassemble the motor and have the block decked as much as you can.  I believe you have newer aluminum heads so you won't want to ruin them for future use.
I do all my engine assembly,  so easy for me to say but this should be a quick pop apart and re assembly for the machine shop.
You may have to mill the intake,  so get a cheap one and be done with it.
9.2 compression will get you a reasonable performer.

[Chryco Psycho]

Well if it was me I would put your car back in the garage you have for it , sell this short block , build a stroker using a cheap 360 block as the parts to do a stroker vs a stock rebuild the cost is very similar , save the heads & use them . yes it may take a year but will be worth it !

If you decide to push through with this short block you need to disassemble & deck the block use cheap heads & intake , no need for a roller cam but you need a high lift short duration 112* lsa cam to help build compression , but you are throwing away good $$

Roller cams are a lot of expense with minimal gain in any engine .

[HP2]

Lets all keep in mind that he took the car to a a service garage for engine replacement and the engine to a machinist/builder, so I'm assuming owner ability to do work complex precision work is very, very limited.

Did you get the flex plate with this engine? I recall looking at it in the classified and wondering if it was internally balanced since it has a neutral balance dampener. Seller said it had the offset balanced flex plate instead of the offset dampener so this is an imperative to use to make sure it is balanced. Might also verify this with your builder.

Looked up the Speedmaster heads. While they have a fairly large chamber, they are a heart shaped chamber, so they do have the ability to generate some quench/squish, IF you can get the the piston within range. To get quench, you need to be within .030 to .050 of the head. See the heads here; https://www.speedmaster79.com/Mopar-Chrysler-SB-318-360-190cc-68cc-CNC-Hydr-R-Complete-Aluminum-Cylinder-Heads

So your slugs are .100 in the hole. A portion of your combustion chamber is over this hole at zero. If you use a shim style gasket (.020) then you can have your piston down .030 to still be within .050 quench. This is the large end of reasonable, tighter would be better. This would necessitate milling the block .070 on the head surface and a corresponding  .105 on the manifold rail (double check me on this everyone, .015 intake to every .010 head surface).

So, to the membership here, can we cut that much off the block? You don't want to mill heads this much because then they become specific to this engine only and can't be used anywhere else. If the .070 is possible,  ask your builder if he is willing to do this.

The other option, and your builder may refuse this, it to bolt it together, live with a relative dog (relative because many mid to late 70s engines were this low on compression), or later on drop a super/turbo charger on it to  increase the cylinder pressure because the low compression is very boost friendly.

[Chryco Psycho]

No way I would add boost to a junk Hyper piton unless you lke grenades .

[Filthy Filbert]

Holy smokes those pistons are deep!!!   

Hyper pistons are perfectly ok for mild NA builds.  You're not spraying or boosting are you?  The problem people have with hypers is that they put more heat into the rings, and require higher ring gaps than people are used to.  I've built several small blocks in the 375-400 hp range with hyper pistons and not have a problem.

Options that would be cheaper than a whole new build:

Tear the motor down and deck it for zero deck.  Cost should only be couple hours labor and couple hours machine time.  I'd guess maybe cost around $500

Tear the motor down and replace the pistons with one that has higher compression height.  Cost would be couple hours labor and cost of new pistons and re-balance the crank. That may push $1000 depending on cost of pistons

Change the cam.   Contact Hughes.  They have several cam grinds designed for mopar lifters (many mopar cams use Chevy lobe designs. They also have lobe separation angles and built in advance that make for fun peppy drivers on low compression motors.    I have their 'whiplash' cam in my Dakota.  I don't recall the specs exactly, I seem to recall 220/230 duration @ .050 (ignore advertised duration. Pay attention to the @ .050 numbers). .544" lift with 1.6 ratio rockers, a 107 LSA on 104 Centerline.  I have stock low compression bottom end, edelbrock heads, mopar m1 single plane intake, mid-length headers....   Truck puts 330hp to the wheels and runs mid 13s at 100-ish mph.   
Changing cams to one with an earlier closing of the intake valve will help dynamic compression and low end pep driving on the streets. 

A cam change would likely be the cheapest path. 

[Matt13]

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.

@RUNCHARGER  I am thinking this is the way to go. Unfortunately, the engine builder will not do this. He won't even agree to just change the pistons. I can tell my shop is going to end up taking the block back and start over again. Lots of wasted time. Basically he doesnt want to touch it unless I stroke it. That or he doesnt want to be a part of it. Im thinking of grabbing some heads with 63cc or less chambers, throwing them on and running it. Money is adding up very quickly. I also might just sell this short block and get something already built. From what the builder quoted me today to stroke it and balance it, I'm about $2,000 away from a really nice completely built 340 or 360. Problem is I'd need to sell this 360 short block first...

[YellowThumper]

Sounds like your engine builder has already forced your hands.
Bite the bullet and build it their way. Or accept where you currently are and "live" with it for now. Motor compete and running is worth $$$ that could be sold to offset future build cost.
Tough spot. Good luck with your final decision.

[70 Challenger Lover]

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.

@RUNCHARGER  I am thinking this is the way to go. Unfortunately, the engine builder will not do this. He won't even agree to just change the pistons. I can tell my shop is going to end up taking the block back and start over again. Lots of wasted time. Basically he doesnt want to touch it unless I stroke it. That or he doesnt want to be a part of it. Im thinking of grabbing some heads with 63cc or less chambers, throwing them on and running it. Money is adding up very quickly. I also might just sell this short block and get something already built. From what the builder quoted me today to stroke it and balance it, I'm about $2,000 away from a really nice completely built 340 or 360. Problem is I'd need to sell this 360 short block first...

I have a set of 302 heads and the closed chambers measured 56ccs. That plus gaskets that compress down to .027 will give you back a lot of the lost compression. On a 318 I almost used them on, it would have taken my 7.4 motor to 8.7. That's a pretty decent increase. These 302 heads are not hard to find. And you could mill them a little and do even better. My original 318 heads cc'd at 70 so getting it down to 56 is huge.

Your engine builder is being more difficult than most. I suspect what he's really not telling you is that he doesn't want to touch any short block that he himself didn't build. And you can understand that attitude. He can't guarantee that it was built properly unless he did the entire thing himself.

If it was me, I'd get the smaller chamber heads and thin gaskets. Then calculate the exact compression ratio you will have. Easy to do with all the online calculators out there. Then call a cam company such as Hughes and use what they recommend. You might very well find that you end up with a nice motor in the low 9s on compression and coupled with the right cam and intake, it should be a respectable street motor. Sure it won't win races but it's a $500 solution and not a $5000 one. And you can do the final assembly yourself in an evening and not have to deal with your builder any more.