Hey guys i have my 1968 383 block at the machine shop to have the bores checked to see if i am able to re ring the std size pistons and hone the bores.If i have to bore the cly what is a good stock piston to use? The car is a 68 cuda formula S 383 4 speed matching number car so i want to keep the car as origanal as i can. And should i use the stock rod bolts or replace them with ARP rod bolts? Thanks
1968 383 piston replacement
- Thread starter Darren
- Start date
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EL5DEMON340
Well-Known Member
Replace the rod bolts,
There are no stock style 10 to 1 exact replacement pistons.
There are no stock style 10 to 1 exact replacement pistons.
Challenger340
Well-Known Member
Like Demon said... no EXACT replacement available.
However,
You could try the KB162 as about the closest thing to a stock replacement Piston as you will find ?
It is pretty close to the same height as the stock Piston, but the KB162 has Valve Reliefs(add 6CC's) which lowers the Compression Ratio to 9.2:1, and if you are using 906 Iron Heads(88CC's) not a bad idea for Todays Pump Gas on a stock Cam ?
Then,
if you decide to start adding a bigger Camshaft...you can always get your Machine Shop to deck the Block(.020" room to zero Deck) and bring it up to 9.5:1. which should still be fine on 91 Octane with Camshafts in the mid 220's @ .050 Duration.
However,
You could try the KB162 as about the closest thing to a stock replacement Piston as you will find ?
It is pretty close to the same height as the stock Piston, but the KB162 has Valve Reliefs(add 6CC's) which lowers the Compression Ratio to 9.2:1, and if you are using 906 Iron Heads(88CC's) not a bad idea for Todays Pump Gas on a stock Cam ?
Then,
if you decide to start adding a bigger Camshaft...you can always get your Machine Shop to deck the Block(.020" room to zero Deck) and bring it up to 9.5:1. which should still be fine on 91 Octane with Camshafts in the mid 220's @ .050 Duration.
Well the machine shop got back to me and said to be safe the need to bore the bores to 0.30. the car will be street driven and remain as stock as possable. Is the KB 162 my best bet. I would prefer to not deck the block or shave the heads, will i notice a difference in performance due to these pistons resulting in a lower comp ratio? Thanks
..............Probably not notice any difference as the factory comp ratings were not exactually spot on.........kim......
EL5DEMON340
Well-Known Member
the decks could be way off i would true them up so this engine runs good. one side of my 383 the pistons sat at about zero other side they were under front about .009 to rear .015. Also your stock head gasket was most likely .020 thick and the felpro will be about .040 i would mill the head .030 to keep a little compression.
moper
Well-Known Member
I would replace with somethign with a valve relief. With stock heads, the gaskets available, and pistons available you will struggle to get past 9:0 without having some blueprinting work done on the block and heads. But that being said - if basically "stock with a little cam" is your goal - I would say don't worry about it. Use the KB-162s, use the MP thinner head gaskets, and let the other numbers fall where they may. Assuming the machining is good and the cam choice is good - it will make at least what it made new, and depending on the valve job and parts used, probably more.
The speed pro 2315 forged pistons are a better choice as they have a 1.920 compression height , were the KB162 are .012
shorter at 1.908. This will make your compression higher, and they are flat tops, no valve relief. Check your math on those for compression ratio.
shorter at 1.908. This will make your compression higher, and they are flat tops, no valve relief. Check your math on those for compression ratio.
moper
Well-Known Member
The lack of valve reliefs worries me with modern cams but keeping the cam small will help avoid that.
80fbody
Well-Known Member
Balance weights come to mind here. You want the piston as close to your stock weight as possible. To me, that would be the most important factor in a budget build where you're not re-balancing.
moper
Well-Known Member
The only question in terms of effect on balancing would be is the crank cast or forged? Forged would work with either piston. Cast may be light for the TRWs.
Regardless of piston choice I would never replace pistons with anything other than factory type replacements for that specific block without re-balancing.
Regardless of piston choice I would never replace pistons with anything other than factory type replacements for that specific block without re-balancing.
You may be in luck. My original stock block for my GTS had .030 forged TRW pistons. I ended up having to go to .040 so I had to buy new pistons.
Thanks i will keep that in mind
80fbody
Well-Known Member
Dome piston, zero decked? Better mock up first. Could hit your heads if you're not careful. I would also think that it would put you well above pump gas range although some heads (mine) have huge 90cc+ chambers.
Note: Found a 383 piston weight on the web (770 grams). If correct those KB400's are really close to the factory balance.
Note: Found a 383 piston weight on the web (770 grams). If correct those KB400's are really close to the factory balance.
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