LA360 compression

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RustyRatRod said:
Why would you return the heads?
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Because the engine builder won't do a simple piston swap. I'm not going to throw these heads (68CC) on the 360 short block I have. Compression will be dismal. I am going to rebuild the late 80's swirl port heads I have on my 318 and save up for a better build later.
 
RustyRatRod said:
My money says they are Silvolite stock replacement pistons.
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God I hope you're not right. Unfortunately, the build's not coming apart because the builder won't just change the pistons. Mabcco is supposedly looking into the build. They list the rebuild as having "high compression pistons", but I asked the brand and model and they didn't have it listed in the computer so they are going to let me know. I asked how they can be high compression sitting .100 below deck; no straight answer.
 
Matt68 said:
God I hope you're not right. Unfortunately, the build's not coming apart because the builder won't just change the pistons. Mabcco is supposedly looking into the build. They list the rebuild as having "high compression pistons", but I asked the brand and model and they didn't have it listed in the computer so they are going to let me know. I asked how they can be high compression sitting .100 below deck; no straight answer.
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It does not have high compression pistons.
 
There would have been no way I would have sent those heads back. Those were that engine's only chance at any decent power using those pistons, IMO. Flow trumps compression in "that" particular instance, IMO. But it's your deal, so carry on.
 
RustyRatRod said:
There would have been no way I would have sent those heads back. Those were that engine's only chance at any decent power using those pistons, IMO. Flow trumps compression in "that" particular instance, IMO. But it's your deal, so carry on.
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Can the 714 casting swirl port heads be machined to have better flow?
 
On Mabco’s website they list a piston upgrade with a sku# of 1273
92A8002D-F83C-4D75-BE1E-0B21E03F7287.png

That is a part number for a silvolite cast replacement piston. Wouldn’t you know it, looks just like yours.
AB676473-058C-41E3-83CC-AC1D72B3C2A0.png
 
I'd have stuck with the aluminum heads if you already had them. There are plenty of good running low compression engines out there. Just don't over-cam it and advance the cam a bunch. Or go with a cam designed for low compression engine. Or strip it down and zero deck the block. Or just replace the pistons. There are plenty of options.
 
Compression distance
Kb107=1.675
Silvolite1273=1.576
.099 difference.
Learn to assemble your own engines and this will never be a problem again. I’d buy a set of rods with floating pins, a set of kb107s, and a ball hone and go to work. That’s assuming the bores measure ok and Mabbco’s machine work is ok, Which is questionable. You could be up and running in a weekend.
 
318 heads on a 360 to gain 1/2 point or cr to gain 3-6hp and lose 60+ cfms of head flow probably lose 50-80 hp on this build big hp difference .

Just put it together probably will make 280-300 hp and dig up another 360 for a propper build.
 
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TT5.9mag said:
On Mabco’s website they list a piston upgrade with a sku# of 1273
View attachment 1716097323
That is a part number for a silvolite cast replacement piston. Wouldn’t you know it, looks just like yours.
View attachment 1716097322
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The piston "upgrade" is not an upgrade at all. There are two main pistons for the 360. Flat top and dished. The dished has a taller compression height and basically has the same compression. Although it sits higher in the bore at TDC, it has a dish, which reduces compression. The flat top has a shorter compression height and no dish. There are essentially different types of pistons that achieve basically the same thing. Different year model pistons. There WAS a 1971 only piston from Chrysler that was a flat top and near zero deck height that had an actual 9:1 compression for the 71 only model year, but those pistons are impossible to find in the aftermarket now. You DO NOT have a high compression piston, so stop digging for it. I don't understand your reasoning for returning the heads at all, as you've been told time and again that a low compression engine can be built to run and run strong. You're just not listening. It's your baby though, so have at it.
 
273 said:
318 heads on a 360 to gain 1/2 point or cr gaij 3-8hp , lose 60+ cfms of head flow big hp difference probably lose 50-80 hp on this build.

Just put it together probably will make 280-300 hp and dig up another 360 for a propper build.
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It would HAVE made more than that had he kept the aluminum heads. I can see close to 1HP per cube with a good hot ignition curve and a good tune. But oh well. lol
 
RustyRatRod said:
It would HAVE made more than that had he kept the aluminum heads. I can see close to 1HP per cube with a good hot ignition curve and a good tune. But oh well. lol
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I havent returned them yet. I have the return bar code ready to go, but am still at work. I was going to return them today; now I'm not so sure.
 
Matt68 said:
I havent returned them yet. I have the return bar code ready to go, but am still at work. I was going to return them today; now I'm not so sure.
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You said before you got a short time frame to get it ready for the shop doing the engine swap.
I'd would put it together with the aluminum heads and call it a day.

What gears are going with the rear end swap ? A set of 3.55 would be good compromise but 3.23-3.91 will work and are you adding a stall? like a 2800-3500 rpm.
 
Here's @318willrun 12 second duster low cr 360 with speedmaster heads small cam header stock gear and stall so basically same engine as you ask him how it works and if the low cr is or isn't tolerable.

 
273 said:
You said before you got a short time frame to get it ready for the shop doing the engine swap.
I'd would put it together with the aluminum heads and call it a day.

What gears are going with the rear end swap ? A set of 3.55 would be good compromise but 3.23-3.91 will work and are you adding a stall? like a 2800-3500 rpm.
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yes, doing a 3.55 suregrip swap.
 
Matt68 said:
I guess that's their "high compression" piston. The Mabbco rep keeps telling me it will get at least 9:1 compression.
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Ok, then take his word for it. I'm tired of typing.
 
Ok, I'm spending way too much time on this but that piston sits .111" down in the hole at TDC using Silvolites own numbers. Taking that info and using UEM's own calculator to figure compression, I got 8.4:1 using a .039 thick and 4.250 bore head gasket and a 68cc chamber. All those are only guesses since I have not measured chambers or have the compressed thickness or gasket bore info.
 
BUT remember, unless the block's been decked, it's very likely tall from the factory so that will lose a little more compression. I still stick by my original recommendation. Build it with the aluminum heads as is. Just because everybody on the forums and magazine articles run them with compression on the ragged edge doesn't mean you have to, OR that it's necessarily a good idea. But, you HAVE all the parts. That in and of itself is the biggest decision maker to ME. It's your project. Build it like you want to.
 
Like mopowers said;
your Mabco block,
Your S master heads,
A small cam, ( smaller than factory 340 #’s),
Small 4 b,
Heck, even manifolds will work!
You will be able to fry the tires at the light with what you have.
Even a 360 2bl cam will accept a small 4 bl or a sb tq and not lose bottom end torque.( if you don't over carb )
Remember, 360 have a different stroke than a 318 so they came factory with bottom end torque.
Build what you have and it will work on reg fuel also.
If you want to have fun on the street it sounds like you have almost everything you need.
If you want to 1/4 mile then do what your engine builder is suggesting.
I’m sure he can build a honkin motor but we just don't want to see you spend more money when you can get in plenty of trouble with the law with what you have to work with.
Less is more.

…So excited for a big red X
 
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