Need help choosing forged pistons!!!

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duster360

duster360

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I am looking to get 9.5:1 compression on my new 340 build. I want to use forged pistons also. The block will clean up at .030", stock 3.31 stroke steel crank and 6.123 rods. I cc'd the heads and they spec'd at 65cc's. Cam is a VooDoo 60403. I don't want to push it much over 9.5:1 because I don't want to have to worry about detonation. I will be running 93 octane fuel and would like to be able to get the timing up around 34*. I have been looking at these pistons: SRP-142068, http://www.jepistons.com/Catalogs/SRP/Mopar/340-360_flat_inv.aspx, but not sure about calculating the actual compression ratio. From what I have read, most 340's come in around .016" -.018" above the deck. Does that sound right? I also would need a head gasket recommendation.
 
Diamond Pistons part# 51001. .030 over flat tops using the standard stroke and standard rod lth just like you are looking for. Look online and you can get them from Mancini Racing, Hughes Engines, Marsh Performance etc. Hope that helps.
 
Ok. I looked at the Diamond pistons and $700+ is a little too much for my engine build. I would rather keep it down around $500 or so.
 
Call SRP and find out what head gasket they're using to get 9.8 compression with a 65cc head and simply use a head gasket that's thicker and has more volume. Also, look at their block deck number. 9.586. That's below the stock 9.6. Remember too, that Mopar blocks are usually very generous when it comes to deck height. My bet is, if all you do is simply square the deck up and nothing else, you will be fine with compression.
 
I agree with Rusty - SRP are a good piston and you'll probably end up with less than 10.5 if the block hasn't been decked much. Probe is another good buy. Check Summit & others for price comparisons.
 
If you don't mind hypers KB 243 will get you there.
 
This one has never been machined before. I hope they don't have to do anything but a .030 bore. Hopefully the deck won't need machined. I would rather keep away from the 10.5:1. Anything above 9.8 I fear will be an issue.
 
the SRP compression height is 1.804, where as the stock high compression piston is 1.84...so they have a little less CH......
 
I am using Mahle forged pistons , lighter than the stock forged . So far 10,000 miles no problems . I can search for the part number if you need . they are 1O.5'1 .030 over
 
Locomotion said:
I agree with Rusty - SRP are a good piston and you'll probably end up with less than 10.5 if the block hasn't been decked much. Probe is another good buy. Check Summit & others for price comparisons.
Click to expand...

The only Probe pistons I saw was for a 360.
 
jerry6 said:
I am using Mahle forged pistons , lighter than the stock forged . So far 10,000 miles no problems . I can search for the part number if you need . they are 1O.5'1 .030 over
Click to expand...

That's a little more compression than I need.
 
duster360 said:
This one has never been machined before. I hope they don't have to do anything but a .030 bore. Hopefully the deck won't need machined. I would rather keep away from the 10.5:1. Anything above 9.8 I fear will be an issue.
Click to expand...

I can guarantee that your deck needs to be machined. It's a small block Mopar. It is not square to the crank from the factory. Every one I have every seen needed to have the block square decked. The T/A block that I built was off less than all of the others, but still needed to be square decked.

You can read about square decking here:

http://www.bhjproducts.com/bhj_content/products/blueprintfixt/bt1_intro.php
 
Keep in mind also that a heavy piston will need mallory added to the crank.
So a cheap heavy piston may cost you more in the long run after balance, then a higher qualilty lighter piston.
 
sireland67 said:
Keep in mind also that a heavy piston will need mallory added to the crank.
So a cheap heavy piston may cost you more in the long run after balance, then a higher qualilty lighter piston.
Click to expand...

A heavy piston will only need Mallory metal in the crank if it's heavier than the heavy OEM piston it's replacing. 340 pistons are naturally heavier than comparable 360 pistons because 360's are shorter (compression height) due to the extra stroke.
 
Yes,
That is why I suggested looking into the piston weight before making a final decision.
 
the L2316F pistons are no heavier then a stock 340 piston which weights a ton also....
 
What heads are you running. With a 63 cc closed chamber head and 0 deck the block, the comp cal came out to 10.44
 
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