1964 383 Pistons

[dryheat]

I'm shopping for all of my parts to rebuild the 383 in my Polara and need a little insight/advise.

It is a 1964 engine with stock heads and all of the books that I have indicate a 10:1 CR on this motor yet I can't seem to locate any suppliers for pistons @ 10:1 ... most of them indicate a 8.4:1

So ... I was wondering if the 10:1 is truly accurate ... seems a little on the high side to me.

Thanks in advance for your help.

 

[Cranky]

That I can't answer but I have these for sale.....but seems like the factory advertised their engines a bit on the high side imo.
http://www.forbbodiesonly.com/moparforum/showthread.php?t=14611

 

[dryheat]

Thanks Cranky ... I don't know what oversize I need just yet ... perhaps the .040 will be just perfect. I will let you know as soon as I have the machine work complete.

 

[dryheat]

Somebody help check my measuring ... I'm using a Harbor Freight dial caliper.

Internal pin diameter is .750

Distance from inside of pin to top of piston is 1.535

add 1/2 of pin diameter .375

Compression distance is 1.910

 

[lewtot184]

compression distance for that piston should be around 1.90. '68 and later around 1.92. i'd use the KB 1.902 piston. actual compression was around 9.5 with a '516 head. don't use the "8.4:1" piston.

 

[Garys1969RR]

I think Compression Height is important. That is centerline of pin to top of piston.

 

[Garys1969RR]

Checked the K B Catalog, and the KB 162 piston has a comp. ht. of 1.908" To have 0 deck height you would need a C/H of 2.032" . This means the 162 would be .124" below deck. Then you can use the KB Compression calculator to determine final C/R. Will need to know head CC volume, gasket thickness, and final bore size. Plug all these #s into the calculator and it will show you static C/R. Then you can change the figures around to see what it would take to get 9.5/1 C R.

 

[lewtot184]

Checked the K B Catalog, and the KB 162 piston has a comp. ht. of 1.908" To have 0 deck height you would need a C/H of 2.032" . This means the 162 would be .124" below deck. Then you can use the KB Compression calculator to determine final C/R. Will need to know head CC volume, gasket thickness, and final bore size. Plug all these #s into the calculator and it will show you static C/R. Then you can change the figures around to see what it would take to get 9.5/1 C R.

this isn't correct. zero deck is close to 1.93 compression height. the '68 1.92 piston is very close to zero deck but will probably yeild too much compression for pump gas. the kb 162 piston is very close to the '67 and earlier piston. actual compression with this piston and a steel shim gasket should be close to 9.5:1, and close to 9:1 with a .040 fel-pro.

 

[dryheat]

Using this calculator

CR Calculator

I plugged in these values -

Bore 4.25
Stroke 3.38
HG Bore Diameter 4.25 (guessing)
HG Thickness .020
Head CC's 73.5cc (516 heads)
Dome Volume 0 (flat tops)
Deck Clearance .028 (guessing)

I got this result ... 10.25

 

[Garys1969RR]

Ok, I stand corrected. The 383 crank centerline to deck is 9.980" . Deduct rod length of 6.358, gets you to 3.622. Then 1/2 of stroke so deduct 1.690" gives 1.932 to zero deck. So a piston with a C/H of 1.908 gives .024 " piston top below deck. So your pretty close at .028. These are all factory specs, so actual dimensions can vary a little. I am going to run 11.5 to 1 C/R in my 451, but I am at 5200 feet and will mix 93 octane with 100. This should take care of potential pinging problems.

 

[lewtot184]

Using this calculator

CR Calculator

I plugged in these values -

Bore 4.25
Stroke 3.38
HG Bore Diameter 4.25 (guessing)
HG Thickness .020
Head CC's 73.5cc (516 heads)
Dome Volume 0 (flat tops)
Deck Clearance .028 (guessing)

I got this result ... 10.25

unmilled '516 heads will probably be 80+cc's. .020 gasket about 4.5cc's. .039 fel-pro around 9-10ccs. a kb162 with an 80cc head should be around 9.5.

 

[Garys1969RR]

If you use the KB 162 piston, you have a deck height of - .024 piston top below deck. With a .020 thick head gasket you get .044 quench distance, using the 516 heads, which is good for detonation resistance and chamber turbulence. My C/R calculator says with these figures and a 78 cc head, you would have 10.02 to 1 C/R. Which is what the factory states it should be. In reality, the heads check at about 80 cc, which gives a C/R of 9.8 to 1. A 73 cc head would give a C/R of 10.5 to 1. This is with a totally flat top piston with no valve reliefs. So your pretty close with the 162 piston and the 516 head. This is an old thread, so you probably already have the engine running by now! Let us know of your progress, thanks