LA360 compression

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Matt68

Matt68

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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.
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If you know all the specs of your engine, ie pistons/compression head cc’s (which you already know) than you should be able to figure your compression, there are a few online calculators out there to give you a fairly accurate idea of what your 360 is capable of.
Summit has one I know of.
Unless your block and crank are pooched, it shouldn’t be overly expensive to build that block.
If you are looking to drag race then throw more money at it but if you just want to have fun on the street I think you have some healthy parts to start with.
The parts you have should be adequate to get you moving (not a dog) especially in a 360.
Not sure what KB’s you have but I cant see why those parts wont make that engine come to life in an A body!?

Do some homework on the piston part number to figure out what you have but I think KB pistons usually bring the compression up, from stock anyway.
My 360 pistons are about .025 below and it calculates out to around 9.1-9.4 comp.

A friend used that same cam in a stock 360 short block with 1.88” valves in a Valiant and that car moved!
 
If you got high cr pistons and closed chamber heads no way it's gonna be an 8:1 engine, might not be able to achieve quench with the thinnest gasket but still should make decent cr, all you need to do pull it apart mill the deck a bit to zero and put back together for quench and a bit higher cr.

Sounds like you got a decent engine quench or not.

You sure about the pistons though?
 
QUINN FORBES said:
If you know all the specs of your engine, ie pistons/compression head cc’s (which you already know) than you should be able to figure your compression, there are a few online calculators out there to give you a fairly accurate idea of what your 360 is capable of.
Summit has one I know of.
Unless your block and crank are pooched, it shouldn’t be overly expensive to build that block.
If you are looking to drag race then throw more money at it but if you just want to have fun on the street I think you have some healthy parts to start with.
The parts you have should be adequate to get you moving (not a dog) especially in a 360.
Not sure what KB’s you have but I cant see why those parts wont make that engine come to life in an A body!?

Do some homework on the piston part number to figure out what you have but I think KB pistons usually bring the compression up, from stock anyway.
My 360 pistons are about .025 below and it calculates out to around 9.1-9.4 comp.

A friend used that same cam in a stock 360 short block with 1.88” valves in a Valiant and that car moved!
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@QUINN FORBES Yeah, he showed me the calculator he used to estimate the compression. He just feels that .100 is too far below deck and I'm letting go of a lot of quench using this set up. He wants to stroke it, basically changing all the internals. That's a wasted brand new cam, crank, rods and pistons. He says I definitely want a roller cam if the car isn't driven daily, because that cam will get bone dry and ruin lifters. I don't want to argue with this guy as he is a professional (at engine rebuilds and prostock racing), and I'm sure he doesn't need my business as his shop was full of engines waiting for rebuilds and ones already rebuilt. He just doesnt want to finish it as is because he says I'll be pretty unhappy with the performance. He is Alan Prusiensky of Arc Racing Engines so he's a Mopar guy.
 
Matt68 said:
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.
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Do you have pictures of the pistons? Do you know the part number of the pistons? Did this well known builder tell you how far down below the deck the pistons are sitting?

Even if the pistons are lower compression KB pistons, why wouldn’t he simply suggest a piston upgrade without new rods?

Your 68 CC chamber Speedmaster heads; are those the CNC ported version?
 
273 said:
If you got high cr pistons and closed chamber heads no way it's gonna be an 8:1 engine, might not be able to achieve quench with the thinnest gasket but still should make decent cr, all you need to do pull it apart mill the deck a bit to zero and put back together for quench and a bit higher cr.

Sounds like you got a decent engine quench or not.

You sure about the pistons though?
Click to expand...
@273 Yes, they are Keith Black (KB107) flat top hyperuetectic for LA360 .30 over. They are sitting below deck at least .100".
 
Matt68 said:
@QUINN FORBES Yeah, he showed me the calculator he used to estimate the compression. He just feels that .100 is too far below deck and I'm letting go of a lot of quench using this set up
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If it's .100 you got stock type piston and basically need/should upgrade them as for stroker that's up to you if you want the additional expense, then if you go stroker you'll probably want more cam etc... It will still make power with low cr but definitely not ideal, 3-10% less depending the differences in cr.
 
Bobzilla said:
Do you have pictures of the pistons? Do you know the part number of the pistons? Did this well known builder tell you how far down below the deck the pistons are sitting?

Even if the pistons are lower compression KB pistons, why wouldn’t he simply suggest a piston upgrade without new rods?

Your 68 CC chamber Speedmaster heads; are those the CNC ported version?
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@Bobzilla They are KB107's. Flat top hypereutectic. Alan said they are .100" below deck. Speedmasters are Speedmaster PCE281.2149 CNC-Machined, Assembled, Aluminum, 68cc Chamber, 190cc Intake Runner, for Hydraulic Flat-tappet Camshaft
 
Matt68 said:
He says I definitely want a roller cam if the car isn't driven daily, because that cam will get bone dry and ruin lifters
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Oh. Is that so?

Did he quote you a price to make that work too?

My understanding is a roller cam isn't necessarily a drop in on an LA.
 
Matt68 said:
@273 Yes, they are Keith Black (KB107) flat top hyperuetectic for LA360 .30 over. They are sitting below deck at least .100".
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there's no way, (Fits SB Chrysler 360, Bore 4.030, Stroke 3.580, Rod Length 6.123, Flat Top 5cc, 2 Valve Relief, Compression Height 1.675, Set of 8 Pistons) thats 9.588 stroke/rod/piston, deck height should be around 9.59-9.60+ thats .002-.012+ bellow.
 
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Uncle Bob said:
Oh. Is that so?

Did he quote you a price to make that work too?

My understanding is a roller cam isn't necessarily a drop in on an LA.
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@Uncle Bob , no quote yet, but he wants to change the crank, cam, rods and pistons. As far as the roller cam, he said that if the car is going to sit for periods, it's better to have a roller cam than potentially tear up lifters. Like I said, this guy builds engines all day long, and given his experience I don't want to doubt he's just making suggestions that will benefit me. He definitely doesnt need my business from what it seems. He's not going to be making a ton of money on me even if I do go with a rebuild.
 
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What is it that YOU want the engine to do? If you told him you wanted a 700hp small block he may be telling you that you can’t get there with your combination of parts. Alan Prusiensky is well know in pro stock and doesn’t build junk. If you told him you just want a 300hp street engine his opinion might change. How in the hell are KB107s .100 below deck?? That seems strange to me. Are you sure about that measurement?
 
I question the request for new crank and rods if you bough an assembled long block. Did they disassemble the engine to check everything?
 
dano said:
I question the request for new crank and rods if you bough an assembled long block. Did they disassemble the engine to check everything?
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@dano , no he didn't take anything apart, but I know he's been doing this for a long time. I do trust his judgement, but I just can't afford the money to change everything and stroke it out.
 
Matt68 said:
@dano , no he didn't take anything apart, but I know he's been doing this for a long time. I do trust his judgement, but I just can't afford the money to change everything and stroke it out.
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Then don't, enjoy as is, upgraded later down the road in a couple of years if you want more.

To me sounds you didn't get what you paid for with that short block, sounds like stock piston, if there .100 in the hole.
 
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TT5.9mag said:
What is it that YOU want the engine to do? If you told him you wanted a 700hp small block he may be telling you that you can’t get there with your combination of parts. Alan Prusiensky is well know in pro stock and doesn’t build junk. If you told him you just want a 300hp street engine his opinion might change. How in the hell are KB107s .100 below deck?? That seems strange to me. Are you sure about that measurement?
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@TT5.9mag I told him I definitely didn't want a dog, but I also don't need crazy hp. I would be happy with anything close to 400 hp with good torque. We spoke for a while about it, and he suggested the stroke to take advantage of all the lost quench I'm giving up. As for the .100 below deck, he brought the motor to TDC and the piston was at least .100 below. I asked about just changing the pistons but he said no.
 
273 said:
Then don't enjoy as is, upgraded later down the road in a couple of years if you want more.

To me sounds you didn't get what you paid for with that short block, sounds like stock piston, if there .100 in the hole.
Click to expand...
Problem is, I have the car sitting at a full service shop and it has been for 3 weeks. They are waiting on the engine to be finished to install as they are pulling the 318 and also changing the rear diff. Lots going on and at this point I just need this 360 ready.
 
A stock stroke, standard deck 360 +.030 with speedmaster heads and kb107s is a 400-430 hp combo and that’s enough to put a 3000lb a body in the 11s even with janky suspension. Alan builds top notch stuff and an $20,000 engine to him is cheap. You may want to find a builder that’s more suited to the type of engine you wanna build.
 
Matt68 said:
@TT5.9mag I told him I definitely didn't want a dog, but I also don't need crazy hp. I would be happy with anything close to 400 hp with good torque. We spoke for a while about it, and he suggested the stroke to take advantage of all the lost quench I'm giving up. As for the .100 below deck, he brought the motor to TDC and the piston was at least .100 below. I asked about just changing the pistons but he said no.
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Dog is a relative term, you'll probably make 350-375+ hp as is 375-400+ hp with 10.5:1 cr

here's a step by step low cr 360 build starting stock 2bbl 225-375 hp

 
I was heading toward the ledge too but a friend grabbed me by the back of the shirt and pulled me back. My build's going to have H116 speed pro pistons, stock stroke, e-heads and intake, and a relatively short duration high lift hydraulic FT cam. That same friend had access to a good simulator and found there's easily 400 hp there.
 
Matt68 said:
Problem is, I have the car sitting at a full service shop and it has been for 3 weeks. They are waiting on the engine to be finished to install as they are pulling the 318 and also changing the rear diff. Lots going on and at this point I just need this 360 ready.
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If you can afford the piston swap to zero deck it I do that if not just put it together and enjoy.
 
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Either learn to do it yourself so you know what you're looking at or find a new shop.
 
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