340 Pistons with 10.5 CR with X Heads???

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SheSaid

SheSaid

Mopar/Jeep Guy
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Hello FABO,

I feel like I am missing something here...

Does anybody make a replacement 030 over 340 piston with 10.5-1 CR with 72 cc X heads??? I want to at least be able to compare the costs for the different options of this rebuild. However I have not found a direct replacement.

I don't want 9.5-1 or 13-1 CR, I just want a 10.5-1 piston that is lightweight and somewhat affordable? Does such a thing exist? Or would this be a special order$$$
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I was getting that with Ross Racing pistons for my 340
 
No I have the 99625 piston. When we punched in the numbers it worked out to 10.Something (don't remember because I changed out to Closed chamber eddy 60779 head)

That said if you can't find the pistons your looking for, you can always that the 99626 pistons, milled down to your specs.
 
sealed power is whats in my demon 340,there cast 10.5 :1....i don't know the part # though.
 
when they advertise 9.5 cr you need to know the piston to deck height and head gasket thickness etc.. they used to calculate. Most I have seen are using a thick multi-layer head gasket at .040+, and they do make a gasket .020 thickness.

Keith Black makes a silvolite 1267 but they are 10.2 - closer
 
If you do not already know you have to do all the math as mentioned above.The factory 10.5 engines were really around 9.5 actual compression when you tear them down and measure everything.There are alot of factors such as gasket thickness,deck height,piston and head cc etc that are need to know things to pick a piston for a specific compression.Wih all that you should still be able to achieve the compression you want easily with some keith black 243's and either slight block mill,head mill or both and or playing with gasket thickness,all easy to do.
 
The 2316s will get you 10.5:1 w 65cc heads and a fel pro .039 head gasket. These are what I usually use. They are not light though.
 
swinger340 said:
The 2316s will get you 10.5:1 w 65cc heads and a fel pro .039 head gasket. These are what I usually use. They are not light though.
Click to expand...

Yeah I ahve seen a few of these TRW 2316s floating around the FABO For Sale ads. Seem like they might work. But I have 72cc heads so I would need to do a little milling thinner head gasket ect. I would really like a piston at 10.5-1 comp without any milling. Then I can adjust gasket thickness and cam to get my dynamic comp ratio in that danger zone area of 8.4-1.
 
lead69 said:
If you do not already know you have to do all the math as mentioned above.The factory 10.5 engines were really around 9.5 actual compression when you tear them down and measure everything.There are alot of factors such as gasket thickness,deck height,piston and head cc etc that are need to know things to pick a piston for a specific compression.Wih all that you should still be able to achieve the compression you want easily with some keith black 243's and either slight block mill,head mill or both and or playing with gasket thickness,all easy to do.
Click to expand...

Doing some math on the Keith Black 243's

Bore 4.070
Stroke 3.31
Head Gasket .040
Deck Height -.018
Piston Volume 6cc
Comp Chamber 72cc
= 9.53-1 Comp ratio
with a .023 Gasket = 9.92-1 getting closer

How much could I mill the block and heads without having to also mill the intake and create a nightmare of valve train geometry?
 
Did you cc your heads? My 69 untouched X heads measured 68 ccs. I realize they do very a little.
 
SheSaid said:
In the process of setting new valves then going to cc them. At that point I will have to decide if I need to mill.

Forum on them here.
Click to expand...

If they were to cc 68 the 2316s would give you 10.2:1 I have the 2316s, stock lightened rods w ARP bolts, and a stock .010/.010 forged crank in one of my 340s with OOTB closed chambered edelbrock heads and it dynoed 428 HP @ 5800 w a solid flat tappit cam. Not to shabby for a 340 ci May have port work and install a roller cam later on to see if I can get 450 + out of her.
 
So running some numbers on Dynamic Comp ratio with a cam that I might use. The Comp Cams XS274S 236/242 @.050 536/546 with 1.6-1 Rockers, Intake closes at 63* ABDC. Specs here.

Keith Black 243's
Assuming that after my valve job my chambers are 70 cc's
using a .040 Gasket
@ about 700ft above sea level

Static 9.74
Dynamic 7.70-1

So I still think I would need to do some milling to get the compression that I want.
 
best to get an actual measured cc on the combustion chambers. then maybe speak to a/the machine shop to find out how much can be milled to achieve the desired compression ratio. you need to know what gaskets your going to use because they will already account for +/- .020 that they will need to factor in before facing intake manifold etc.
I just checked using your above factors. IF you do have 67cc heads you will be 10.469 with thin head gasket w/gasket vol of 4.180
 
swinger340 said:
If they were to cc 68 the 2316s would give you 10.2:1 I have the 2316s, stock lightened rods w ARP bolts, and a stock .010/.010 forged crank in one of my 340s with OOTB closed chambered edelbrock heads and it dynoed 428 HP @ 5800 w a solid flat tappit cam. Not to shabby for a 340 ci May have port work and install a roller cam later on to see if I can get 450 + out of her.
Click to expand...

That is what I am aiming for. Hope port and flow the X heads up to around 250 cfm at 500 lift. I think I can do it with mild pocket porting gasket match and the 2.08 intake vale with 5/16 stem diameter. Then top it with a gasket matched air gap intake. Stock steel crank with lighter rods and pistons. Hope to get up to 450 HP with a torque curve as broad as possible. If that means higher comp ratio and maybe rough street manors I am ok with that. Not like I even have the time to drive it every day. I want the car to scream like a bat out of hell but still look as stock as possible.

Thanks for all the info. I think I need to get my heads done first. Then CC them before deciding on milling either head or block. But if I come across a good enough deal on a KB 243 or similar piston I might pull the trigger and make them work.
 
Rocky_JS said:
best to get an actual measured cc on the combustion chambers. then maybe speak to a/the machine shop to find out how much can be milled to achieve the desired compression ratio. you need to know what gaskets your going to use because they will already account for +/- .020 that they will need to factor in before facing intake manifold etc.
I just checked using your above factors. IF you do have 67cc heads you will be 10.469 with thin head gasket w/gasket vol of 4.180
Click to expand...

Right on man. I am hoping to use the gasket thickness as a final adjustment to either go up or down once the heads are cc'd and I have the exact pistons figured out.
 
I think every .005 milled = 1cc .020 = 4cc and about 1/2 point in compression. problem is there are only a couple different gasket thicknesses to play with, argh...
 
SheSaid said:
That is what I am aiming for. Hope port and flow the X heads up to around 250 cfm at 500 lift. I think I can do it with mild pocket porting gasket match and the 2.08 intake vale with 5/16 stem diameter. Then top it with a gasket matched air gap intake. Stock steel crank with lighter rods and pistons. Hope to get up to 450 HP with a torque curve as broad as possible. If that means higher comp ratio and maybe rough street manors I am ok with that. Not like I even have the time to drive it every day. I want the car to scream like a bat out of hell but still look as stock as possible.

Thanks for all the info. I think I need to get my heads done first. Then CC them before deciding on milling either head or block. But if I come across a good enough deal on a KB 243 or similar piston I might pull the trigger and make them work.
Click to expand...
My OOTB edelbrocks flowed 255@ .550 Im running an XE282S w/ 10.8:1 compression. 428 HP @ 5800. Im thinking you may fall shy of 450 HP. 400 sounds more likely w your combo unless you go more compression, more cam or get them heads to flow a little better. JMO
 
swinger340 said:
My OOTB edelbrocks flowed 255@ .550 Im running an XE282S w/ 10.8:1 compression. 428 HP @ 5800. Im thinking you may fall shy of 450 HP. 400 sounds more likely w your combo unless you go more compression, more cam or get them heads to flow a little better. JMO
Click to expand...

Hey if that's what it takes then that's what I'm going to have to do!

Thanks for all the info man! Thanks FABO
 
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