Moparts
Zero deck or not to zero deck on 340 build
Posted By: tee-john
Zero deck or not to zero deck on 340 build - 12/22/09 08:14 PM
Hey guys I am to the point of the build where I am getting suggestions from Chevy guys on my block. It's a 340 block that I am trying to get good running street motor (375-425 hp) with good torque. I don't know any technical stuff like all the clearances. One guy tells me to zero deck the block and the other says leave the pistons 10-20 in the hole. Does anyone have Mopar suggestions? I have a set of J heads 2.02 1.60. Not sure of the chamber size or even how to find out.I want to run pump gas. Any info is appreciated, thanks.
Posted By: topside
Re: Zero deck or not to zero deck on 340 build - 12/22/09 08:26 PM
Need more of that pesky "technical info", but overall:
For 91 octane with iron heads and ANY advance curve, you're limited to about 9.0:1 unless you run a cam with a fair amount of overlap to bleed off cylinder pressure; downside to that is soggy throttle response.
Don't machine anything until you have pistons and some plan for the motor. You should have the heads measured to see what you have for chamber size.
You may well end up zero-decking your block, but that's not where a build, or a plan, starts.
Posted By: tee-john
Re: Zero deck or not to zero deck on 340 build - 12/22/09 08:34 PM
Hey Topside I'm trying to get a plan together but I have no help being that all my friends are
chevy people and they are not sure of Mopar builds. Do you know where I can find info on build specs?? Thanks
Posted By: 540challenger
Re: Zero deck or not to zero deck on 340 build - 12/22/09 08:42 PM
What heads do you plan on using this makes a bit of a difference. To gain the benefits of Zero Decking a block you need a closed chambered head. That leads you with either late model magnum heads or an aftermarket ALUM. head.
Like said before need more info.
What stuff are you using for the build or willing to buy???
What heads you have now??
Do you have a crank, pistons and rods???
Posted By: patrick
Re: Zero deck or not to zero deck on 340 build - 12/22/09 09:13 PM
Quote:
Need more of that pesky "technical info", but overall:
For 91 octane with iron heads and ANY advance curve, you're limited to about 9.0:1 unless you run a cam with a fair amount of overlap to bleed off cylinder pressure; downside to that is soggy throttle response.
Don't machine anything until you have pistons and some plan for the motor. You should have the heads measured to see what you have for chamber size.
You may well end up zero-decking your block, but that's not where a build, or a plan, starts.
huh...my 9:1 (actual measured) 318 with a 33 degree overlap roller cam (259/259, 208/208@.050 on a 112 LSA, installed at 108) runs fine with a quick advance curve (all in by 2000 RPM, no appreciable quench (.055" in the hole with .028" head gaskets and magnum heads), and 87 octane.
I'd build the short block at 0 deck with flat tops, that makes setting up future head options much easier if you're looking for tight quench. with typical open chambered heads, that'll net you 9.5:1 compression with a thin .028" head gasket, which coupled with a cam like a comp XE268 should run fine on 89 octane and get you in the 350-375 HP range depending on the quality of the head work.
then if you ever want to upgrade the heads, with a .039" head gasket and typical 63cc closed chamber (magnum heads, or eddie heads) and .039" gaskets, you're looking at 10.1 compression with tight quench, which should allow the engine to run on similar, if not lower octane than it did previously.
Posted By: Crizila
Re: Zero deck or not to zero deck on 340 build - 12/22/09 09:43 PM
John, you really do need a plan going in before you do any milling. Your open chamber J heads ( not a bad head by the way ) are typically 68 - 72 CC's. You can use 70CC's when computing your CR. You will probably end up with zero ( or close to it - I always like to leave myself a little room - .005 to .010" down in the hole )deck height. Much of the info out there is based on zero deck height. 9 - 9.5:1 are good numbers to shoot for.
Posted By: 70AARcuda
Re: Zero deck or not to zero deck on 340 build - 12/22/09 09:48 PM
off the shelf pistons only come in two compression heights for 340s...
1.84 for the 68-71 high compression 340s
1.74 for the 72-73 low compression 340s
the high compression piston will be out of the hole about .008 depending on the actual deck height of the block....
the low compression will be down in the hole about .090 depending on the actual deck height of the block.
so unless you are going to special order pistons you will need to accompdate the compression heights of the pistons available...
either out of the deck or milling around .090
I would use the KB 243 pistons and adjust the head gasket to get your quench...plus the KB piston is ALOT lighter then the old trw/seal power piston...
Posted By: can.al
Re: Zero deck or not to zero deck on 340 build - 12/22/09 10:22 PM
..my 340 has L2316 pistons(old style TRW forged)which stick about .022 above the deck.
my deck was squared and my X heads(70 -72 cc) had a clean up cut.
i did the math and i think it was less than 9.5:1
Posted By: RapidRobert
Re: Zero deck or not to zero deck on 340 build - 12/22/09 11:22 PM
what octane are you going to run and what cam (or how mild/wild of cam) do you have in mind. Here is a very user friendly CR calculator.
http://kb-silvolite.com/calc.php?. As said .040" quench will let you run a much higher CR (& CR is squeeze and squeeze is power) but will take (alot)more machine shop labor to machine/equalize the open chamber recesses on your current heads then if you switched later to a closed chamber head it'd require a custom Cometic gasket but I am a firm believer in getting it right for your CURRENT combo as opposed to what you might do in the future. Stay close to us (& away from the chebby boys)
Posted By: can.al
Re: Zero deck or not to zero deck on 340 build - 12/23/09 01:27 AM
..70 Duster,91 octane,comp.xe-268,
Shaun built me a nice 9 1/2 converter.(Dynamic)
..you may recall my vac. advance thread back in late summer....you helped me dial it in
..timing 12/35,...it's a little Rocket,
..very pleased
Posted By: RapidRobert
Re: Zero deck or not to zero deck on 340 build - 12/23/09 01:49 AM
Quote:
you may recall my vac. advance thread back in late summer.
I sure do.
Posted By: Baxter61
Re: Zero deck or not to zero deck on 340 build - 12/23/09 04:14 AM
Quote:
..my 340 has L2316 pistons(old style TRW forged)which stick about .022 above the deck.
my deck was squared and my X heads(70 -72 cc) had a clean up cut.
i did the math and i think it was less than 9.5:1
on a 340 unless you cut those j heads down a bunch, if you dont have the pistons sticking .010 to .020 out of the hole your not gonna have 9:1 comp. Even at 10:1 and a decent cam your motor should be fine on pump gas and make plenty of power.
Posted By: ademon
Re: Zero deck or not to zero deck on 340 build - 12/23/09 06:59 AM
shoot for 10.0 to 10.5 to 1, that will give you the torque, J heads are good do a little bowl blend ask the machinest to backcut the valves, and gasket match the heads and intake, use a rpm intake if you don't have one yet, Block the exhaust heat crossover using a thin steel shim behind the gasket on the head side. i would use a cam in the range of 224 to 230 @.050. and a 750 dp holley. that should get you right around 380 to 400 hp.
Posted By: tee-john
Re: Zero deck or not to zero deck on 340 build - 12/23/09 11:47 AM
The heads that I have are a pair of 70' 3418915 J heads. When I got these, they were a fresh rebuild with S/S 2.02s & 1.60s. I don't much more on them. I do have the stock forged crank and rods, no pistons. The machine shop guy will make suggestions on pistons and cam setups. The block is .040 over.
I am willing to buy whatever it takes to make this motor run like it's supposed to (within the budget). Throttle response, torque and even great sounding exhaust system is what I am after. Specific part and tech info will help. Like I said before, I am not an engine guy, but I do understand terms. All that I need is more info to compare what other guys are telling me here.
Thanks
Posted By: moper
Re: Zero deck or not to zero deck on 340 build - 12/23/09 12:37 PM
tee - What are you planning to do with this car? What trans and gearing do you have planned?
Posted By: patrick
Re: Zero deck or not to zero deck on 340 build - 12/23/09 01:17 PM
I'd use the KB hypers, and a comp XE268 with comp 906 springs.
Posted By: Challenger 1
Re: Zero deck or not to zero deck on 340 build - 12/23/09 01:30 PM
I'd use the KB 243 with open chamber heads. Your J heads would be fine. Like what was said, decide which pistons your gonna use long before any machining get's done. With the KB pistons there's no need to deck the block. IMO I've used the KB pistons.