LA360 compression

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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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So that leads me to ask how does he know you need new ones? If its just based on his opinion of the strength of stock components then sure (and they are fine for your build if they are good) but you'd have to disassemble and measure things to find out if they are out of Spec. cracked or off in some way.

At this point ask yourself, do I run with the used short block I have or redo the whole things from the ground up from who is being represented as and back up as a quality engine builder? Just based on the piston information being possibly incorrect from what you we're told you we're bough I'd go through it all. Building engine isn't inexpensive anymore, do it right the first time. Whats his opinion on the heads?
 
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 FRAKKIN WAY they are in the hole .100" or more. NO WAY. I just figured it on the United Engine web site and the KB107 sits .012" in the hole with the stock 9.6 block, 6.123 connecting rod and the KB107's 1.675" compression height. Something is WRONG somewhere. If the piston really is in the hole that much, it's NOT a KB107.
 
KB107s should drop in at around .012 below deck of an LA
I think something is wrong
IMO, you need to get your combo up to at least 9.8.
at a bore of 4.03, that would be 85cc@sealevel. It doesn't much matter how you do it.

But I just don't see how KB107s can be .100 down, that should be impossible.
My KB107s measured 1.675 on the nose and everyone exactly the same.
My guess is that if you had the crank reground then she ain't no 3.58 stroke any more. But if the crank is ok, then the stinking rods are short, by a whole big bunch.
Kb makes pistons with raised Q-pads for open-chamber heads. KB 190/191s

I know yur gonna hate me, but IMO, I would back up the bus. I would NOT assemble it with the parts you have, unless yur running an exceptionally light car, an exceptionally high stall, or exceptionally deep race gears, or just don't much care about low-rpm power. Otherwise, the bottom end is gonna be exceptionally boring.
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Here's what I know works, cuz I built it
KB107s at ~ plus .005 above deck = 4cc
closed-chamber alloy heads @63cc
FelPro 1008s at .039" =8.6cc
The total chamber volume was thus 75.6cc
the bore was 4.045=753.9cc of swept
The Scr thus was 10.97
A cam with an Ica of 61*.
At sealevel, this calculates to a Dcr of 8.99 and a predicted Cylinder pressure of 190.34psi
The Q was .034
I ran this on 87E10 at 930 feet elevation at 34* of power-timing and at 3650 pounds, for 4 years Car went 106mph on it's only run; with 3.55s, 245 street tires, and a 4-speed.
Oh yeah, and it got phenomenal fuel economy. This was my DD at that time.
Had my Scr been 8/1
The pressure is predicted to have been 126psi, and this combo at low rpm would have felt like a 2bbl 273
 
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You could just put it together as is, then find a pre magnum roller block have it built over the next few years, then pull your engine refreshing the heads for the new short block 360 or 408 and drop it back in. Would be my plan.
 
I used the KB107 back in the mid 90s in a 360 I had in a 65 Valiant. I zero decked the block and milled the heads to achieve right at 12:1 compression. I am guessing that you don't have the KB107 pistons.
 
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.
View attachment 1716094189
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Matt, can you get us a picture of the pistons? We can tell you real quick if they are KB107s or not. I'm bettin they're not.
 
AJ/FormS said:
KB107s should drop in at around .012 below deck of an LA
I think something is wrong


I know yur gonna hate me, but IMO, I would back up the bus. I would NOT assemble it with the parts you have, unless yur running an exceptionally light car, an exceptionally high stall, or exceptionally deep race gears, or just don't much care about low-rpm power. Otherwise, the bottom end is gonna be exceptionally boring.

Here's what I know works, cuz I built it
KB107s at ~ plus .005 above deck = 4cc
closed-chamber alloy heads @63cc
FelPro 1008s at .039" =8.6cc
The total chamber volume was thus 75.6cc
the bore was 4.045=753.9cc of swept
The Scr thus was 10.97
A cam with an Ica of 61*.
At sealevel, this calculates to a Dcr of 8.99 and a predicted Cylinder pressure of 190.34psi
The Q was .034
I ran this on 87E10 at 930 feet elevation at 34* of power-timing and at 3650 pounds, for 4 years Car went 106mph on it's only run; with 3.55s, 245 street tires, and a 4-speed.
Oh yeah, and it got phenomenal fuel economy. This was my DD at that time.
Had my Scr been 8/1
The pressure is predicted to have been 126psi, and this combo at low rpm would have felt like a 2bbl 273
IMO, you need to get your combo up to at least 9.8.
at a bore of 4.03, that would be 85cc@sealevel. It doesn't much matter how you do it.

But I just don't see how KB107s can be .100 down, that should be impossible.
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Here's a low cr 360 build, your telling me the 277hp stock cam 4bbl headers will be stronger than the cam upgrades 339-387hp with lower DCR, the lower DCR even makes more torque even down low, I don't get this, 318willrun has proved cams will work on low cr 318/360 with e.t.'s even though your maths says otherwise. I'm not saying what your saying no importance but you seem to give it too much importance like a car with low V/P index can't perform even though people build low cr engines all the time that do well. Obviously cr would make them all better.

 
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RustyRatRod said:
Matt, can you get us a picture of the pistons? We can tell you real quick if they are KB107s or not. I'm bettin they're not.
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@RustyRatRod
KB107ss.jpg


KB107.jpg
 
Here's the KB107.
www.summitracing.com

KB KB107.030 KB Performance Pistons | Summit Racing

Free Shipping - KB Performance Pistons with qualifying orders of $109. Shop Pistons at Summit Racing.
www.summitracing.com www.summitracing.com
I know you're probably wondering how they can have more compression than a true flat top. That's in the compression distance. The KB107 comes way up in the bore at TDC. Rather than the .100 plus, the KB107 only sits down in the bore around .012".
 
But look man, run that ***** like it is. It'll run great. Plenty of people have built respectable stock compression engines. It's all in the tune. One thing's for sure. It will run on regular pump gas.
 
The good news is, if the bore is fresh, you can order kb107s (or any piston that gets you where you need to be compression wise), have your builder hone the block for the skirt clearance and press the new pistons on. Bobs you uncle.
 
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.
View attachment 1716094189
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Matt68 said:
@RustyRatRod
View attachment 1716094288

View attachment 1716094289
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If somebody sold you that short block assembly saying it had KB107 pistons, they lied.

The good news is the engine builder you have now is NOT screwing you. He is correct about the pistons being low compression. But, if he does not want to deal with this unless you get another rotating assembly just use another builder. There is a likelihood he is expecting a **** show if he opens up the bottom end, to help move it along he says start over. That is reasonable.

If you want this short block with more compression, you just need actual KB107 pistons, possibly a new balance job since the KB107 may be much lighter, and then you are good to go.
 
Looks like UEM 1273 piston, about .120 in the hole. net result about 8.25 to 1 with 68cc head and .042 gasket
 
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.
View attachment 1716094189
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I didn’t read all the replies but you should be able to mill the cylinder heads and the deck height of the block. Quench is PRECISION measurements and timing-at that close, there is a risk of valves kissing pistons.
 
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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Replacing the piston and balancing the assembly is literally right up his alley, his forte, HIS JOB. Tell him you want some KB-107 +.030” (or Speed Pro H116cp pistons) pistons and rebalance it-you will have everything you want.

It’s your engine/money, wtf does he mean “No.” (to replacing the piston.)?
 
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StreetSleeper said:
Replacing the piston and balancing the assembly is literally right up his alley, his forte, HIS JOB. Tell him you want some KB-107 +.030” (or Speed Pro H116cp pistons) pistons and rebalance it-you will have everything you want.

It’s your engine/money, wtf does he mean “No.” (to replacing the piston.)?
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It’s time to get your property and find another machinist/engine builder.
SOME business owners are disagreeable when they don’t want to do something-I’m hoping this is your problem and not ignorance/greed-w/dishonesty.
 
Using the United Engine compression calculator and .100 in the hole and 74cc chamber with a .039 gasket I get 8.2:1. If it was ME, I would cam accordingly, run a decent intake, headers, put a hot timing curve in the distributor and hold on. It'll be a tier melter if done right. You do not HAVE to have high compression to run well. People have been dispelling that MYTH for decades.
 
Then, I went back and lowered the chamber volume to 68 and .019 for the head gaskets and boom, 9:1. So it's really not terrible. I'd build it.
 
RustyRatRod said:
Using the United Engine compression calculator and .100 in the hole and 74cc chamber with a .039 gasket I get 8.2:1. If it was ME, I would cam accordingly, run a decent intake, headers, put a hot timing curve in the distributor and hold on. It'll be a tier melter if done right. You do not HAVE to have high compression to run well. People have been dispelling that MYTH for decades.
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A decent cylinder head helps.
 
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