Some 360 engine improvements

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1973dusterkid

1973dusterkid

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Ok so right now here is my setup


71 year 360
.508 purple shaft cam
340 J heads 2.02 1.60 valves Casting number (3418915)
340 intake casting number (2531915)
Stranded bore with no valve relief flat top pistons
Long tube headers 3in collector
Holley 750 carb
Stock mopar electronic ignition

First thing is to get a sure grip under it so it will hook.


My question is what do you guys think the comp ratio is now as it sits as for as I know no machine work has been done to the engine.
 
8.5 if you are lucky most likely lower.
 
1973dusterkid said:
Why do you say so low
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because the pistons are so far down in the hole. these engines were built to be work horses and the gas crunch had them by the balls. they were in no way performance engines. if its stock bottom end i bet your slugs are .050-.080 down in the hole. it is what it is man. my 383 has about 8.5:1 compression. next engine i will build with a game plan going in.
 
you really have to properly calculate it to be sure.
early 340's had pistons that were .022 above the deck and they were only about
9.6:1.
 
Besides milling the hell out of the head for only a modest amount of gain..

The KB-107's should the you close to a 9.0-1. The problem being they may still sit in the hole a bit. Once you deck the block for a zero deck piston, with the 72cc J heads and a .039 head gasket, this will yield a 9.8-1 ratio @ a standard bore.

I'd rebuild the lower end with new lighter and stronger rods. It'll be way worth it!
 
Even if you were to get a sure grip you'd need a 3.91 and a 3500 convertor to justify that cam you have. But since we're on the subject of cams. That's a lot of cam for any compression you may be getting. That's even at 9:1. Which you may very well have. A lower compression piston would most likely have a dish in it so I'm not real sure on the compression. I therefore won't guess at it.
 
Just an educated guess when you asked for a piston to give you 10.1 without boring reality says you have no budget to work with.

Spend the money making your car hook, handle and be safer.
Brake upgrade, limeted slip rear, better gears, shocks etc.

Buy a project motor and build it, while keeping your car on the road.
 
there is a guy who does have some kb107si think there .030 tho but worth it for 200.00set some perfect circle rings and bore it now it will be ready for next year
 
If it is truly a 1971 360 the compression is probably smack on top of 8.5:1. The 71 had more compression than any of the rest because the pistons used had a taller compression height than any other year. You can get 9.1 real easy by milling the heads about .030" and running thin head gaskets. The .025" ones are on Ebay.
 
This^^^ .Also Mr Gaskets 1121 head gasket.Compressed.028" ,possibly a good choice.
 
RustyRatRod said:
If it is truly a 1971 360 the compression is probably smack on top of 8.5:1. The 71 had more compression than any of the rest because the pistons used had a taller compression height than any other year. You can get 9.1 real easy by milling the heads about .030" and running thin head gaskets. The .025" ones are on Ebay.
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True,
Dont forget to mill the intake.

Rusty how do you remember all this???????
 
sireland67 said:
True,
Dont forget to mill the intake.

Rusty how do you remember all this???????
Click to expand...

I honestly don't know. Kitty keeps telling me that I need to write a book or something. lol
 
dusterkid, my advice to you would be to put your money in the heads. The short block seems sound. Yes, technically it is over cammed. But, if you put some money in the heads, put 2.02 and 1.60 valves in, have them professionally ported (PM me if you are interested, my guy is VERY reasonable), get them milled no more than .030 and run the thin head gaskets.

Then you will be all over 9.1 and have some great flowing heads. It will make all kinda power then. It's all in the heads. You will be sorry if you go to 10.1 with an iron head motor on a street car in the Georgia heat idling in traffic in 99 degrees with 75% humidity.

It will SUCK BALLS. Take my advice. Stop readin all the forum horse crap that says you gotta have gobs of compression because it's simply not true AND it can get you in trouble in hot weather. PLUS you gotta run the best gas you can find. Spend your money in the heads. Leave the compression down. It will run on pump swill and make all the power you will ever need or want on the street.
 
What was the ICL that your cam was installed?

That single factor will make an engine like yours a dog or a scalded cat.
 
He can get a 9.5-1 ratio with milling. It would be a lot. But doable. That woe be OK for the cam he has. Lots of converter and gear wll get going Ok.

What is Ga.'s best octane? 93 right? That's good for what he's doing.
 
(Evil laugh)
He he he he he, yeaaaaa buddy! Fun!
 
9.1 will be fine and he doesn't have to mill half the engine off to get there.
 
I was planning on changing cam to I have good brakes and good driveline.

The reason for wanting to get the comp up without boring I figured if you can get the comp ratio up with lesser work the better.
 
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