Moparts
5.9 Magnum Pistons
Posted By: dfsmopars
5.9 Magnum Pistons - 10/07/10 02:47 AM
I am finding out that finding pistons for the 5.9 Magnum I am building is more difficult than I intially thought. I talked to a tech. rep. at KB today who told me since I am truing up the deck and the heads (~0.020" total) this would cause me problems with the piston being above the deck and not enough quench area. He said their pistons are designed to be zero deck and that I'd end up spending a bunch of money on custom head gaskets.
Please help me out here I know this can't be this difficult.
Posted By: Sick 660r
Re: 5.9 Magnum Pistons - 10/07/10 02:52 AM
My block was decked twice puting my pistons .015" out of the hole. Ended up going with thicker cometics.
Posted By: dfsmopars
Re: 5.9 Magnum Pistons - 10/07/10 03:01 AM
Quote:
My block was decked twice puting my pistons .015" out of the hole. Ended up going with thicker cometics.
I hope you don't mind me asking, how much did you have to spend on the Cometics gaskets?
Posted By: Sick 660r
Re: 5.9 Magnum Pistons - 10/07/10 03:18 AM
4.040 bore and .060" thickness cost me 250 shipped.
Posted By: dfsmopars
Re: 5.9 Magnum Pistons - 10/07/10 03:26 AM
That is crazy.
That is exactly what the KB guy told me to expect, or more. The 0.060" gasket is what he said I'd probably have to go with but he highly recommended mocking it up first with the pistons and crank assembled. Did you explore any other possibilities or were there none?
Posted By: BBR
Re: 5.9 Magnum Pistons - 10/07/10 04:25 AM
What height is he decking the block to?
Posted By: Duner
Re: 5.9 Magnum Pistons - 10/07/10 04:32 AM
I ran into the same thing. Decked block to get it square. My pistons were .006" out of the hole - so I had some Cometics made at .051" thick. Paid the same price.
realistically, if your going to do the job right, your probably either going to spend a little more for a better piston that has the correct deck height or your going to pay for the gaskets to get the piston to head clearance you need. sometimes there's just no way around it.
personally i'd rather use the better piston. looking on the upside, at least the cometics are reuseable if the need ever arises.
Posted By: Duner
Re: 5.9 Magnum Pistons - 10/07/10 04:58 AM
I got to experience the benefit of using "off the shelf" pistons for my hooptie. I hurt three of them and was able to just pick up the phone and get just the three I needed without waiting for anything to be made. I still had to get them balanced, but it was pretty convenient - if breaking parts can ever even be considered that. I put a set of Probes in mine.
Posted By: POS Dakota
Re: 5.9 Magnum Pistons - 10/07/10 10:46 AM
I came up .017 out of the hole with the KB/IC-745 piston and my magnum block. My static comp is about 10.3:1.
I used a felpro .054 thick gasket for a .037 quench. If you're not nitrousing it all the time, and not boosting it, it should be fine.
Posted By: dfsmopars
Re: 5.9 Magnum Pistons - 10/07/10 01:01 PM
Alright then. I appreciate all the great information. You know what they say, "It is what it is." I am looking at the KB362 piston which will be somewhere around 9.6:1 compression with the block decked somewhere around 0.010" This means the piston will be somewhere around 0.019" above deck.
Posted By: TheOtherDodge
Re: 5.9 Magnum Pistons *DELETED* - 10/07/10 01:32 PM
Post deleted by TheOtherDodge
Posted By: HotRodDave
Re: 5.9 Magnum Pistons - 10/07/10 05:14 PM
I am building a motor right now with KB 107s and with no block milling or squareing at all are all between .008 and .009 above deck to start with. I ran them in a stock 360 LA block and they were about the same amount under the deck and very un even. Fel pro makes a .051 gasket and I am going to use those and some aluminum closed chamber heads for a nice quench distance. I think the number is 8553 and should work good till pistons are about .015 out the hole, depending on how tight you want your quench.
Posted By: dfsmopars
Re: 5.9 Magnum Pistons - 10/07/10 09:26 PM
Quote:
I am building a motor right now with KB 107s and with no block milling or squareing at all are all between .008 and .009 above deck to start with. I ran them in a stock 360 LA block and they were about the same amount under the deck and very un even. Fel pro makes a .051 gasket and I am going to use those and some aluminum closed chamber heads for a nice quench distance. I think the number is 8553 and should work good till pistons are about .015 out the hole, depending on how tight you want your quench.
That all sounds right to me. I will certainly not do anything until I mock up the pistons. With a factory piston at 9.1:1 compression ratio what would be wrong with going with a stock piston, .01 off the deck and .01 off the head? This I think would be in the ball park of 9.5:1 which for my application would be good. Am I off base here?
Posted By: BBR
Re: 5.9 Magnum Pistons - 10/07/10 10:37 PM
SCE has thicker head gaskets. Not cheap, but not quite as spendy as a Cometic.
http://www.scegaskets.com/
Posted By: dizuster
Re: 5.9 Magnum Pistons - 10/08/10 12:46 AM
Depends on thickness, but the SCE's are still pretty pricy. Only the high end SCE Titans have fire rings in them. Everything else needs o-rings.
Posted By: POS Dakota
Re: 5.9 Magnum Pistons - 10/08/10 12:54 AM
Quote:
Depends on thickness, but the SCE's are still pretty pricy. Only the high end SCE Titans have fire rings in them. Everything else needs o-rings.
And they are NOT cheap.
Posted By: dfsmopars
Re: 5.9 Magnum Pistons - 10/08/10 01:12 AM
Somebody please tell me I am going to be really glad I built the Magnum instead of building my 318! Tell me that when I get this Magnum in my Charger I am going to be like a woman giving birth that soon all the pain will be erased by the joy!!
Posted By: Wedgeman
Re: 5.9 Magnum Pistons - 10/08/10 02:05 AM
Of course it will !!!
I am using a Magnum block with the 745 KB/Ic pistons, may be .15 out of the hole,....don't settle for anything less than cometic, you'll be saving money since they are re usable ...mine are .050 thick, 10.1:1 cr engine and using a 250/250* @.050 solid lifter cam, RHS iron heads
KB 745 for 408
KB 362 for 360
Grreat performance !
Dan
Posted By: joedust451
Re: 5.9 Magnum Pistons - 10/08/10 02:13 AM
Quote:
Somebody please tell me I am going to be really glad I built the Magnum instead of building my 318! Tell me that when I get this Magnum in my Charger I am going to be like a woman giving birth that soon all the pain will be erased by the joy!!
You will be VERY happy with it, me & a buddy are running "stock" bottom end 360 magnums in are darts with nothing wild by any means, I'm running 12.5s, he just went 11.79, he got his engine from a junkyard, mine was from a rolled 95 truck, factory pistons/rings/bearings ect. He runs alittle more comp (thinner head gaskets & i think his heads are 62cc)/gear/cam/stall then me, both of us run small carbs, his car has the factory interior & bench seat.
You should have no problem getting 9.5.1 with a stock dished piston without decking, just run a thinner head gasket & mill .020" off the heads, if you do deck the block, i'd say 10.1 shouldn't be hard to acheive, but i'd go with 9.5.1 so it will be pump gas friendly, i run on 87 octane.
Posted By: HotRodDave
Re: 5.9 Magnum Pistons - 10/08/10 02:14 AM
The stock pistons on this motor were .070 in the hole, you could have them mill that much off the deck and use stock pistons and the readily available 1008 fel pro and you will get good quench and compression.
Posted By: POS Dakota
Re: 5.9 Magnum Pistons - 10/08/10 02:18 AM
Quote:
Somebody please tell me I am going to be really glad I built the Magnum instead of building my 318! Tell me that when I get this Magnum in my Charger I am going to be like a woman giving birth that soon all the pain will be erased by the joy!!
Well, you won't feel violated! That's for sure!
Posted By: dfsmopars
Re: 5.9 Magnum Pistons - 10/08/10 02:28 AM
Phew! Thanks everybody I feel better. I'll keep plodding along and figure this combination out with the help of your input.
Posted By: joedust451
Re: 5.9 Magnum Pistons - 10/08/10 02:28 AM
Quote:
The stock pistons on this motor were .070 in the hole, you could have them mill that much off the deck and use stock pistons and the readily available 1008 fel pro and you will get good quench and compression.
This is true, & thats not counting the dish (its deaper then the edge of the piston itself). I think acheiving 10.1 out of them with the closed chambered head should be very easy, especially if you deck the block some, don't know how pump gas friendly they would be at that level with iron heads, maybe good .
Posted By: HotRodDave
Re: 5.9 Magnum Pistons - 10/08/10 02:31 AM
10 to one with iron magnums is fine even with pretty mild cams, they are very detonation resistant with good quench.
Posted By: forphorty
Re: 5.9 Magnum Pistons - 10/08/10 03:15 AM
Quote:
Somebody please tell me I am going to be really glad I built the Magnum instead of building my 318! Tell me that when I get this Magnum in my Charger I am going to be like a woman giving birth that soon all the pain will be erased by the joy!!
Your pain will become more acute 
when you realize you could have had a 440. sorry,kidding(sort of).
Posted By: joedust451
Re: 5.9 Magnum Pistons - 10/08/10 03:32 AM
Quote:
Quote:
Somebody please tell me I am going to be really glad I built the Magnum instead of building my 318! Tell me that when I get this Magnum in my Charger I am going to be like a woman giving birth that soon all the pain will be erased by the joy!!
Your pain will become more acute when you realize you could have had a 440. sorry,kidding(sort of).
I race a guy at my track, he has a 440 in a dart with aftermarket lower components, more cam, more gear, & i think more stall, don't know what his problem is, but we run "dead on", he keeps accuseing me of running the nitrous , i told him flat out, you "WILL" know when i run the nitrous 
. & the funny thing is, he has another 440 dart that runs 11.0s.
Posted By: dfsmopars
Re: 5.9 Magnum Pistons - 10/08/10 03:48 AM
Quote:
Quote:
Somebody please tell me I am going to be really glad I built the Magnum instead of building my 318! Tell me that when I get this Magnum in my Charger I am going to be like a woman giving birth that soon all the pain will be erased by the joy!!
Your pain will become more acute when you realize you could have had a 440. sorry,kidding(sort of).
I have a 440! I am kinda partial to some nice handling to go along with some respectable power. I have 318, a 440 and a 360 Magnum and I chose the magnum for several reasons. I may have to sale everything else to finance my decision. 
Posted By: forphorty
Re: 5.9 Magnum Pistons - 10/08/10 04:16 AM
Quote:
Quote:
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Somebody please tell me I am going to be really glad I built the Magnum instead of building my 318! Tell me that when I get this Magnum in my Charger I am going to be like a woman giving birth that soon all the pain will be erased by the joy!!
Your pain will become more acute when you realize you could have had a 440. sorry,kidding(sort of).
I have a 440! I am kinda partial to some nice handling to go along with some respectable power. I have 318, a 440 and a 360 Magnum and I chose the magnum for several reasons. I may have to sale everything else to finance my decision.
In spite of my above comment, i've been considering a 5.9 myself. I own two B bodies with big blocks, but a couple years ago i bought a 72 duster with a 318. Been fooling with it on the cheap. I have been doing the stuff that needs to be done regardless of the engine choice . Suspension,brakes frame connectors,etc. I have been following Joedust451s progress and have been pretty impressed. Also been reading everthing i can about the RHS heads. I now have the opportunity to buy an old 380 hp crate engine , incomplete(no lifters,pushrods)and condition unknown. So... in the future i may be a member of the 5.9 brigade myself. 
Posted By: joedust451
Re: 5.9 Magnum Pistons - 10/08/10 04:39 AM
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Somebody please tell me I am going to be really glad I built the Magnum instead of building my 318! Tell me that when I get this Magnum in my Charger I am going to be like a woman giving birth that soon all the pain will be erased by the joy!!
Your pain will become more acute when you realize you could have had a 440. sorry,kidding(sort of).
I have a 440! I am kinda partial to some nice handling to go along with some respectable power. I have 318, a 440 and a 360 Magnum and I chose the magnum for several reasons. I may have to sale everything else to finance my decision.
In spite of my above comment, i've been considering a 5.9 myself. I own two B bodies with big blocks, but a couple years ago i bought a 72 duster with a 318. Been fooling with it on the cheap. I have been doing the stuff that needs to be done regardless of the engine choice . Suspension,brakes frame connectors,etc. I have been following Joedust451s progress and have been pretty impressed. Also been reading everthing i can about the RHS heads. I now have the opportunity to buy an old 380 hp crate engine , incomplete(no lifters,pushrods)and condition unknown. So... in the future i may be a member of the 5.9 brigade myself.
Thanks for the props forforty, I will say this, i'm a BB A body builder by heart, i can pretty much make/build a 440 dart/duster with little of nothing & it'll run the #s, but i'm sooooo impressed with this 360 "magnum" that i'm stoked, for a very very mild stock/used shortblock to run like this is amazing, & its damn near in the 7.9s in the 1/8 shifting at 5100, what that tells me is its a torque monster 
.
Posted By: forphorty
Re: 5.9 Magnum Pistons - 10/08/10 06:39 AM
My goal for the duster is to have a mild comfortable driver that gets driven on the highway a lot. Will probably end up with 3.23s once i get a 8.75 built for it. Ac and stereo are in the plans also. A build similar to yours would work well . I can get the crate motor pretty cheap. Will probably get it and tear it down to see what is useable. The cam is a little hotter than i want and i would probably trade off the single plane. Since it has no lifters, are the factory replacements expensive? I think the spider is still there. Wondering if i might be better off just getting a good complete truck motor as you did, instead of the incomplete crate motor.
Posted By: POS Dakota
Re: 5.9 Magnum Pistons - 10/08/10 10:50 AM
Quote:
My goal for the duster is to have a mild comfortable driver that gets driven on the highway a lot. Will probably end up with 3.23s once i get a 8.75 built for it. Ac and stereo are in the plans also. A build similar to yours would work well . I can get the crate motor pretty cheap. Will probably get it and tear it down to see what is useable. The cam is a little hotter than i want and i would probably trade off the single plane. Since it has no lifters, are the factory replacements expensive? I think the spider is still there. Wondering if i might be better off just getting a good complete truck motor as you did, instead of the incomplete crate motor.
The factory replacement rollers are good stuff and only about 140 bucks for an entire set.
nothing wrong with them at all. They will be perfect for you.
Posted By: joedust451
Re: 5.9 Magnum Pistons - 10/08/10 01:12 PM
Quote:
My goal for the duster is to have a mild comfortable driver that gets driven on the highway a lot. Will probably end up with 3.23s once i get a 8.75 built for it. Ac and stereo are in the plans also. A build similar to yours would work well . I can get the crate motor pretty cheap. Will probably get it and tear it down to see what is useable. The cam is a little hotter than i want and i would probably trade off the single plane. Since it has no lifters, are the factory replacements expensive? I think the spider is still there. Wondering if i might be better off just getting a good complete truck motor as you did, instead of the incomplete crate motor.
Like bignozzle said, the lifters aren't exspensive, & you can run chevy style roller rockers so you can save there too, If you can find a good used Magnum from a truck with fairly low miles & don't spend more then 4-500.00 then grab it, the only weak area with them is in the magnum heads, they tend to crack in-between the valves in the chambers, the end chambers are the worsed, what all comes with this crate motor your looking at & what do they want for it?
Posted By: StrkrDart69
Re: 5.9 Magnum Pistons - 10/08/10 01:28 PM
If you are not in a big hurry and shop around at salvage yards, you can find magnums fairly cheap. I picked up a complete 5.2 magnum, complete with wiring harness, and everything on the engine, including alt. for $150.00 And it was in the shop on a pallet, I did not have to wait for them to pull it.
I also found a 5.2 magnum in the local paper out of a 95 dakota with 40k miles on it for $250.00 And it came with the A518 trans! I thought about putting the trans in my Dart, but instead put it on craigslist for $250 and it sold the same day. The guy had wrecked his Dakota and planned on using the eng. and trans. and never did. Wanted it out of his garage. Also I have several sets of magnum heads and none of them are cracked. On my stroker in am running RHS X heads.
Posted By: StrkrDart69
Re: 5.9 Magnum Pistons - 10/08/10 01:57 PM
Quote:
10 to one with iron magnums is fine even with pretty mild cams, they are very detonation resistant with good quench.
I have 10.5 compression with .544 int lift .568 ex and no detonation on pump gas.
Posted By: Duner
Re: 5.9 Magnum Pistons - 10/08/10 02:08 PM
I wouldn't be in a big hurry to trade off that single plane intake. These Magnum engines really like those.
Posted By: HotRodDave
Re: 5.9 Magnum Pistons - 10/08/10 03:50 PM
I have to agree on the single plane, the eddy air gap is a little better but I have the M1 single plane on mine and even with a comp XE268 cam stock converter and 2.76 gears it lacks nothing in the TQ department. If you stomp the gas right off idle it twists the body pretty good, feels like the tire is gonna come off the ground (it don't but it feels that way).
Stock magnum heads crack on 9 out of 10 heads but I have never ever seen it cause any problems. They just don't go into the water ports. I have even seen cracks on brand new castings.
Posted By: forphorty
Re: 5.9 Magnum Pistons - 10/08/10 08:51 PM
Sorry if i might have gotten this thread a little off topic. I do appreciate the info guys. Nice to know that the single plane is a pretty good intake for a mild street engine. Looks like i can get the engine for $200. Includes the intake and the finned alum valve covers, headers and some other misc. no lifters.
Posted By: patrick
Re: 5.9 Magnum Pistons - 10/08/10 10:15 PM
another option, look at diamond pistons PN 51420, they're stock 9cc dish 360 pistons, with a 1.667CH (.008" lower than the KB's)