Magnum head swap compression increase

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Dragonbat13

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I'm not looking for exact numbers, just a general idea. This is low buck stuff here.

I already have a few sets of magnum heads. And an intake. I'm not bringing the heads to the machine shop, or the short block. I'm taking a free short block and bolting free magnum heads on it.

I have searched for this answer and all I read are eq this or machine shop that.. stuff I know but don't want to do right now.

Anyway, ABOUT how much compression can I expect from removing the open chamber heads on my mid 70's two barrel 360 and putting on some stock magnum heads?

Thanks.
 
I'm not looking for exact numbers, just a general idea. This is low buck stuff here.

I already have a few sets of magnum heads. And an intake. I'm not bringing the heads to the machine shop, or the short block. I'm taking a free short block and bolting free magnum heads on it.

I have searched for this answer and all I read are eq this or machine shop that.. stuff I know but don't want to do right now.

Anyway, ABOUT how much compression can I expect from removing the open chamber heads on my mid 70's two barrel 360 and putting on some stock magnum heads?

Thanks.
Only way to get an Idea is to know the exact chamber volume of the mag heads you have.

Stock 360 la motors on average had 72 cc chamber heads.
Do the work.
Do the math.


But if you're the lazy type, half a point is what you can expect to gain
 
IIRC, 63 cc's is typical for the Magnum chambers and 72 cc as stated above is typical for the LA open chambers. With a 9 cc change you can expect around
  • 0.75 CR increase with the Mr Gasket 1121G head gaskets at .028" thick.
  • 0.5 CR increase with the Felpro 1008 head gasket at .039" thick
  • 0.3 CR increase with the standard kit Felpro gaskets, PN 8553PT at .051" thick
These comparisons are to the original head gasket that reportedly was around .025" thick + or -.
 
I came at it from the other end;
the LA360s were advertised at 8/1 which requires a total chamber volume of~105cc;
(737.2+105)/105= 8.02cr
Assuming a 9cc gain, the total chamber volume drops to 96 and the Scr rises to;
(737.2+96)/96=8.68..... with no other changes.
Is it worth it?
Oh yes, those Magnum heads have other perks that the LA 360 might like.
And make sure you install the cam from zero advance to plus 4 degrees. Up to Plus 8* if you don't mind sacrificing some fuel economy, to get some pressure happening.
 
We have to buy a converter to put the engine and trans in. It will be some budget 2800 stall. Car has a 323 open rear. I've been eyeballing that comp xe262 cam.

Would I have enough compression for that cam? Dual plane and a Carter 650 on top. Shitty headers.
 
IMHO, that is the largest I would go. (But I am a low RPM torque junkie LOL) DCR numbers look to be in the low 7's and that is pretty good for that old low compression block and any sort of camming up.

BTW, if you go with those 1121G head gaskets, then check the heads and deck for flatness; those thin composition gaskets reportedly are more prone to leaks, and I suspect that is due to folks slapping them into engines with slightly warped head and or deck surfaces. So skimming the heads at the shop would be a good idea for this head gasket IMHO.

Or, if it is just slapping things together, then you could just go for it and see if it holds!
 
Enough compression- short answer is no
explanation- you can get hp up top with low compression but driveability sucks
Compression not exactly the change pistons thread but take a look at
NOT the usual cam advice...
especially post 5
later there is a discussion of cams
first- I agree with NM check the heads for flat and you could cut for a little more CR
but still no quench
on the CAM
UDHarold designed the Comp XT series- later the Lunati Voodoo series- he learned something on the way
in your case the Lunati 250 discussed in the above thread trumps the comp 262
The Lunati 256 or Howard 256 are also considerations
The comp xt line has the same limitations as the Crane cams discussed
 
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Son of a *****.....

I thought I had a pair of magnum heads. I got off my *** went outside and looked and I actually have one 308, or 302, or some closed chamber la head with a magnum head sitting on top.

I'm gonna say this right now. If I have the junk laying around to make a motor with an la head on one side and a magnum on the other I'm doing it.
 
This is unfortunate. Oh well....

Regarding cam timing. Can I advance the cam with the stock heads? I've never messed with advancing cam timing. I can still do a cam swap too with the smogger heads. Might even do a shade tree rebuild. But no machine work right now. We're talking ball hones and grindstones here. Cheap.
 
which cam are you thinking of advancing
stock cams are spread out so advancing the intake gives you more cylinder
however the exhaust open is already spread out and opening 4 degrees earlier starts to blow efficiency out the exhaust so gas mileage can suck and exhaust temp go up
with stock compression- well stock cams were designed for that
all the compromises built
 
late blocks are resonably hard so if you can find some higher compression pistons dingle ball, new rings and go
now what pistons would work that could be take outs
???
standard bore no machine work
 
Son of a *****.....

I thought I had a pair of magnum heads. I got off my *** went outside and looked and I actually have one 308, or 302, or some closed chamber la head with a magnum head sitting on top.

I'm gonna say this right now. If I have the junk laying around to make a motor with an la head on one side and a magnum on the other I'm doing it.

That only works if you run a manifold on the Magnum side and headers on the LA side, to even it out.

Run open exhaust and it'll sound like, and run like, a Hemi. Guaranteed.
 
somebody that put in new pistons and took the old ones out
I used to have a pile of them
but I can't think of a common take out that would bump his compression-
more compression height than he has
best to get the vehicle safe and road worthy
brakes, suspension, hoses, shocks, bushings etc can eat up that $ 800
 
I've got a speedmaster intake. Carter carb. The car came with headers. The front end will be safe. I gotta do brakes. I gotta do wipers, lights, fuel pump, radiator, stuff like that. But I got a free 360 and a free 727. Me and my brother just want to take the parts, put them all together, get this Mopar back running, get a title, and bam! Another Mopar back on the road. It's a good straight car and right now is a good time to get to putting it together for me.
 
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whats wrong with the heads that are on the 360
can you do a compression test where it is
else you have to come up with at least one head to match
what are the numgers on the heads you have
 
whats wrong with the heads that are on the 360
can you do a compression test where it is
else you have to come up with at least one head to match
what are the numgers on the heads you have
I'm starting to entertain a cheap rebuild just to clean up the motor and see what I'm working with. I don't have an issue with the la heads. I could invest a little money in some machine work in them if I really need too. I'm hoping to get a better look at it later this week.
 
looking to hear back from you
think about finding a mate to one of the later heads in your pile if you want to bump the cr
sorry about the phantom magnums
 
looking to hear back from you
think about finding a mate to one of the later heads in your pile if you want to bump the cr
sorry about the phantom magnums
The one magnum head is no good. The other is a 302 casting, which if I found another would be one to find a match for. Only because they go good with some 318 builds.
 
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