which is it- dished or flat?

[dixchief]

As i am trying to increase my Stude info base, I am confused about pistons. I read how the supercharged motors must have a lower compression ratio, 7:1, and use the dished pistons. the non SCed motors could use a higher CR 9:1 and used flat pistons.
SASCO has flat pistons advertised for R1 and R2 289's.
I need to rebuild a 289 and need good info. Not sure if I will use the SC I have or keep the AC unit (live in FL)
Richard

[Kurt]

R1 and R2 engines both used flat top pistons. The Compression ratio was reduced on r2 engines by using a different head. Actually R1 engines had 10.25:1 Cr and R2's were 9:1. As for pistons on 289's I believe you have 3 choices standard dish, flat top and semi dish. I used semi dished pistons on my 289 project with a steel head gasket and R1 heads. That dropped the compression enough that I have not had any problems with detonation

66 Commander R1 Clone
51 Commander 4dr

[GTtim]

Cup style (semi dish) pistons with a standard head will give about 9.2 compression ratio. Works great with the super.

Tim K.
'64 R2 GT Hawk

[dixchief]

Do you have this setup? Earlier posts say the SC needs a lower CR (around 7:1). Haven't read anything about what CR higher octane gas will allow/
Richard

[GTtim]

Yes, that's what's in my car. I didn't have an R2 engine to replace the original that had gone missing. Jim Pepper advised using the standard heads with cup-style pistons. I also used Ted Harbits R2+ cam. Everything else is standard R2 equipment. It works great with 93 octane running about 26 to 28 degrees advance. 91 requires it to be set back a little.

Tim K.
'64 R2 GT Hawk

[2R2]

Studebaker produced two different versions of the supercharged engine (we'll ignore the R3, due to it's rarity). The '57-'58 versions had around a 7.5-1 compression ratio, while the '63-'64 R2 had a factory 9.0-1 ratio.

Eric DeRosa

'49 2R-5 (original Survivor)
'63 R2 Lark (barely surviving)