Rebuilding engine/ head gasket compression question

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mopar_1974

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alright... i am rebuilding a 360 for my duster and have a few questions. I want to keep it cheap, but keep it so it will run strong for a good 5+ years until i am out of college and finally get some money to pull it and build it the way i want. I am sticking with the stock pistons and am planning on having the machine shop re ring them and put new bearings in. clean and test the block and rework the crank if neccisary. i'm also going to have the valves back cut and bowl port the j heads to increase flow a little bit. I have heard of getting thinner head gaskets to increase compression a little bit. What am i looking at for an increase and any suggestions on size? will the thinner gaskets be much less reliable? any other suggestions on how i can build a better engine? I am looking mostly for suggestions that will be affected while at the machine shop.
 
you can gain a ton of HP with machining...factory tolerances were pretty wide, so everything is not neccasarily where it should be....deck heights, deck angle, line bore, cam bore, piston bores, lifter bores, etc.

They say Richard Petty gain 25 hp alone by properly align boring/honing the cam and crank bores in relation on the 426 hemi

stock pistons are not a great idea unless the motor is very early 70s or before because you will lose a large amount of compression
 
YES! The year of the 360. The pistons are low in the block. The factory used the thin gaskets regularly. You can't go thinner, only thicker.
IMO, I really realy suggest a new set of pistons. Fed-Mougal makes a nice 9.5-1 coated skirt piston and KB makes a few as well.

Increaseing the compresion ratio will make the roatating assmebly lighter so it can spin faster, easier. The increased ratio will add some power. Zero deck the pistons with a .039 gasket with the big chambered "J" heads will get you 9.8-1. .054 gaskets will drop it a tad more to approx. 9.5-1.

Zero gap piston rings are expensive, but worth the price. Extremely low leak down rates.

And what was said above. Just tell your machinest you want a million mile engine when your done.
 
sorry...forgit to say... 1972 360. do you have any specific pistons you reccommend and any part numbers on them? Thanks
 
Theres to many to chose from. You really didn't say much about your motor or the performance goal. If your thinking of the flat top zero deck pistons I mentioned, KB107's I have used before without problems. There about $190 with pins.
I do not remember the part number for the Fed-Mougals I have. But no problems ethier.
 
The 107's worked great in my 360. I would also look at using a cam like a comp cams 280H cam. I used a stock converter with it and drove it everyday on the street. It was a great set up and ran like a bat outta hell. One thing I would make sure that I did is put a good set of rod bolts in it and have fun. I had alot of maching work done on my motor and spent very little in parts. The car would run (leaving in second gear) 13.94 @104 in the 1/4. I don't care who you are on pump gas and street tires and no posi that is not bad at all.
 
ok i've looked at the kb107's before actually. What is the advantage to flat over dome and dish? If my memory serves me correct, you have answered a few of my engine questions before, rumble. I was planning on building a streetable motor with 350+ hp. I've so far managed to gather an air gap intake, 650 holley, mopar purple cam and lifters 429"/.444" lift 268/276 duration pn4452782, proform roller rockers, oh and some nice shiney chrome edelbrock valve covers :) should i get new valve springs? what pushrods? man this whole engine thing is spendy. i havnt even touched the brakes, rear end and tranny yet. Thanks a ton for the info
 
Well the pin location on the piston puts the piston further up in the hole and the small dome on it will help to raise the comp. ratio. I noticed that you were going to use the Proform rockers. I would stay away from them. There is a reason they are the price they are. for what you are trying to do I would look into a little more cam that what you have listed.
 
BJR I know a couple of guys running the Proform rockers with success but they changed the adjusters out for some from Crane. From what I have heard the adjusters are the only bad thing about them. Here is the P/N for the Crane Adjusters: crane p/n 99802-16

I personally run Harland Sharpes but for a budget build if you upgrade the adjusters these are okay.
 
Flat tops, in general, should weigh less. No extra meat in a dome. The flat top will help promote flame travel. When used with a close chambered head, it should burn the mix very well with less timing. In the open chamber of the older "J" head, it will not matter to much.

The dished pistons are designed to lower the comp. ratio in any engine. This does not mean there not performance pistons. There very good to run in very samll chambered heads for lower ratios that will be OK for pump gas and super/turbo charged applications. These should weigh less than a flat top. But not allways.
You will have to check if it is a needed to know thing.

Once you have selected a cam to use, you should most certainly get the springs that are matched to the cam. This is extremely important.
I believe the cam you listed is the OE 340 cam. If you run over 9.5-1 with this cam, you might run into a octane problems. If you don't have the cam yet and are running a higher comp. ratio engine, look to the replacement 340 cam. It has a tighter centerline/overlap that will run better without pining.

If you have milled the deck of the block and/or the cylinder heads, you'll need to shorten the pushrods the like amount from there stock length.
Also, if you use a thicker head gasket than stock, you'll need to lengthen the rods by the like amount.

You have a total of .100 lifter plunger movment and the last .010 is not to be traveled in. This leaves you with .080 total room.

In example, you mill the block surface .010 and the heads .010, your down a total of .020. If you then get a gasket @ .040 (Fel-pro has a .039) your back to where you should be. Becaused you raised the head away from the block the same amount you milled off that made it closer.

Understand the plus and minus's gong on here?

Spendy ? Yes. But when it is all done correctly and the assembly is balanced well, you'll be very happy you did it right so you only do it once.
No engine build is a cheap thing to do. No matter what brand. Machine work is machine work and the machinest has to be paid.
 
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