need help choosing 360 pistons and cam

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TomSchichtel

TomSchichtel

73 Duster
Joined
Jul 3, 2010
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Location
Newcastle, CA
Hi there I have a 75 360 at the machine shop right now which is 20 over which the machinist is going to take to 40 over. He is going to line bore it and turn the crank and recondition the rods. He is completely redoing my j heads (I plan on using stock rocker arms) , and he will balance everything.

The build is going into a 73 duster with 3.23's and an 883 tranny. I want to use a split duration cam and am going for street/strip application. What compression ratio should be my goal? I am going to be meeting with him on friday what are some specs I should find out from him in order to start matching up my cam and pistons.

Also I will be bringing him my flywheel for balancing reasons and i need to purchace a harmonic balancer. I'm looking at either the summitracing, mopar performance or dorman brands for the balancer because of their price range. Which do you recomend? I wouldn't mind just buying the Dorman because it is so cheap but I would like to know what you think of that first.

I feel like the output of my motor will be night and day with the selection of correct pistons and cam so if there is any advice on which combo to buy I would be very grateful!
 
A true 9 to 1/zero deck setup,would be ideal.You want .043" to .050" piston to top of head gasket clearance.This sets up ideal measurements for "quench",makes the engine more detonation resistant.Check out Federal Mogul,Keith Black hyperutectics,or Icon forged pistons. As for cams,Comp's 262 or 268 grinds are sweet.Consult the machinist,on brands and cost of labor.
 
funny, just got a 360 in my 73 duster as well.

so. i ran kb 107 pistons, bored 30 over which with my heads was around 9.4 compression. perfect for mid grade and half cheap at the pump. with your heads tho im not sure what your compression would be post the cc's of your heads. also a lot of people run kb 107's

running a comp 20-222-3. (262 grind)you can use stock rockers (like me), but i recomend using their new springs and push rods (i got trick flows). cam works awesome and isnt a crazy cam so sitting at a stop light it has no problems. also starts easily in cold

as for balancer i used my stock one so i would say more money the more nicer its gonna be
 
Good info ,Wild. Always conservative on that,unless building/blueprinting from scratch. Cool to know,thanks.
 
well youre not gonna have any quench with J heads unless you mill them to closed chamber or get a piston with a quench pad.
 
The MoPar unit is inexpensive and a really nice quality part made in Canada. Total thumbs up for this part.

The KB-107's or the Federal-Mougal equal which has coated skirts are excellent slugs. The block will most likely need to be decked to fit the piston in at zero deck. Use these slugs at zero deck with a .039 gasket for a 9.8-1 ratio. Thicker gaskets will drop the ratio slightly for an ideal pimp gas range engine with a small cam like mentioned above.
You can get gaskets off the shelf at .050/.055 thick.

As far as a cam goes, so run a split duration cam if you run headers or not. This helps breathing. Thus, the engine becomes more Efficent making more power.
Cam companies rate there cam by RPM band. They also often suggest a stall conveyer if need be and gear ratio to run.
 
KB 107's seem to be very popular on this forum, so I'm leaning towards using them. I told my machinist that I was thinking about using KB's and he mentioned that they need to be file fitted something to the tune of filing the top ring or around the top of the piston, I can't remember which it was. Is this true?
 
TomSchichtel said:
KB 107's seem to be very popular on this forum, so I'm leaning towards using them. I told my machinist that I was thinking about using KB's and he mentioned that they need to be file fitted something to the tune of filing the top ring or around the top of the piston, I can't remember which it was. Is this true?
Click to expand...
you gotta set the top ring gap the pistons come with instructions on this issue....:read:
 
Baxter61 said:
well youre not gonna have any quench with J heads unless you mill them to closed chamber or get a piston with a quench pad.
Click to expand...

If u have the piston .019 -.020 out of the hole and use a .025-.039 head gasket ..then mill the head to end up around .022-.030 deep on the shallow side of the chamber... Suprise...you have quench. You can mill the heads just to closed, but the chamber will be in the 48-52 cc range. I have seen where some guys have milled beyond just making the closed chamber and end up finding a thin spot and making a hole out of it. But I have j heads that are at the .030 deep shallow side and they run great and spec to 60 cc's
 
1wild&crazyguy said:
If u have the piston .019 -.020 out of the hole and use a .025-.039 head gasket ..then mill the head to end up around .022-.030 deep on the shallow side of the chamber... Suprise...you have quench. You can mill the heads just to closed, but the chamber will be in the 48-52 cc range. I have seen where some guys have milled beyond just making the closed chamber and end up finding a thin spot and making a hole out of it. But I have j heads that are at the .030 deep shallow side and they run great and spec to 60 cc's
Click to expand...

True, but given that most 360 decks are tall from 9.6 to begin with, and the tallest self flat top piston Im aware of has a compression height of 1.675, and you need a compression height of 1.687 to get to 0 deck in a 360 (given your rods are actually 6.123 and your stroke is actually 3.58) that means you need to take your deck to 9.6, then take another .012 off that plus .020 to get the piston proud. And most J heads Ive seen the quench side of the chamber is .120 deep so you gotta take .090 off the heads. to get to .030 deep which depending on where your located may cost a pretty penny. Not impossible to do, very possible to do in fact, maybe just not practical for many, unless theres a shelf piston im not aware of that would fit the build.
 
Baxter61 said:
True, but given that most 360 decks are tall from 9.6 to begin with, and the tallest self flat top piston Im aware of has a compression height of 1.675, and you need a compression height of 1.687 to get to 0 deck in a 360 (given your rods are actually 6.123 and your stroke is actually 3.58) that means you need to take your deck to 9.6, then take another .012 off that plus .020 to get the piston proud. And most J heads Ive seen the quench side of the chamber is .120 deep so you gotta take .090 off the heads. to get to .030 deep which depending on where your located may cost a pretty penny. Not impossible to do, very possible to do in fact, maybe just not practical for many, unless theres a shelf piston im not aware of that would fit the build.
Click to expand...

Your right in that it would take machining to do, that's what the op is having done..machining. if we were talking 340 stuff, it would be simply milling heads or at the most a shave of the block/square deck which is very commonly needed to start with.
Yes its true now j heads and or stocker stuff starts out around .100 deep, it just takes .060-.070 off both and int face and ur there.
I'm always into making something better and its no sweat off my brow
 
70aarcuda said:
cheaper route...dont deck the block...use mopar head gasket P4120094


http://www.monicattichrysler.com/comersus/store/comersus_viewItem.asp?idProduct=247


unless you are going to run a close chamber head...which J heads are not....zero decking the block is a waste of money...you can get the same compression with the thinner head gasket...
Click to expand...

Glad to see these in stock somewhere. They were hard to find for a while. I disagree about the decking though. Not a waste of time or money. It'll insure that a zero deck is what he gets and with the heads in use (to be used) a popular gasket from Fel-Pro is always available. The slugs can be deep in the hole. Deep enough that the thin head gasket will not make up for the distance. Moper has had a good run with the KB-107's being a bit deep. I myself have had a 50/50 with where they sit in the block.
 
KB107 pistons are generally about .018 down in the bore on a uncut 360...take the .026 head gasket...you got .044....zero deck the block and use a .038 head gasket....which are twice the price as the MP thin...and you gain .006....for couple hundred dollars total cost.

and does the machine shop have the proper equipment to SQUARE a block...or is he just cutting based on where you measured the piston in the bore...

and if you are spending money to square the block...make sure you have the stroke equalized and indexed on the crank...and make sure you spend money on having the Center to Center blueprinted on all 8 rods.....
 
I use 107's in my 360, .030 over, decked the block to 9.58, the pistons are .008 out of the hole. Using a non-tuliped valve in the heads will tighten up chamber volume for a compression boost. Depends on what you want.


Paper is cheep, write it out, it helps to understand what's going on.
 
70aar; now your just getting silly and spending money that may not have to be spent in order to get to the goal. If we follow your last line of thought, the. We should all be dining that.

Glad to hear that your slugs were "only" .018 in the hole. This may not be the case for his or any other block out there. It sure want for my last one. That's for damn sure!
 
I prefer the speed pro 116 pistons. Use the summit compression calculator and keep the ratio below 9.5 for pump gas. The Lunati voo doo series has some real nice choices.
 
rumblefish360 said:
70aar; now your just getting silly and spending money that may not have to be spent in order to get to the goal. If we follow your last line of thought, the. We should all be dining that.

Glad to hear that your slugs were "only" .018 in the hole. This may not be the case for his or any other block out there. It sure want for my last one. That's for damn sure!
Click to expand...


Isnt that we all do here..spend other people money....tell them they need to do this or that...like deck a block went a cheap set of head gasket will do the same thing....

unless production tolerances for the rods and crank are corrected....then you going to have deck heights all over the place...so why did you deck the block again?...lol

especially went he is using an open chamber head.........
 
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