1991 RS 305

I'm removing the 305 because I have a few mods planned this winter. Since I am going to have it out I want to freshen the engine up a little. I'm looking at at this rebuild kit: http://store.summitracing.com/partde...0&autoview=sku

Questions: I'm assuming the stock connecting rods are press fit, does anyone know if this is correct? Another issue I have is that these pistons are +5 cc's. This raises my compression too much over 12:1, even if I go back to the stock head gaskets... FYI, my heads are 56cc's. Anyone know of a good stock replacement piston that has the same or similar dish? I'm guessing the stock piston is around -11 to -13 cc dish... I get this from some reverse calculations I've done. Anyone know different from this

I know I could get a thicker gasket yet, but I don't want to mess up the quench.

Thanks for any help, Matt

rocko350

i ran the numers in dd2000 and came up with 10.74:1 with piston.0005 down in hole, .030" overbore, flat top . you might find a blower piston with a dish not in the quench pad area, not eyebrows. mill the deck to .005 and use an .041 head gasket and it ends up to be 10.5 i think. slightly less compression but better quench. any one care to verify please. i would have the rotating assembly balanced after mockup to ensure a smooth engine regardless.

all in all it seems like the kit you need. left to itself it would work out to a 3.795" bore (.060" over), probably .007 down in the hole with flat tops is like 10.69:1 with you 56 cc head

1991 RS 305

thanks for the help roco350, but I'm only planning a hone to the walls, no bore. I had the heads off recently and could still see the factory hone marks. It's just the fact that it had 140K miles and I would like to freshen up the bearings and what not. I don't want to dump tons of money into it. Maybe being I can see the factory cross hatch marks I should leave it alone?? Any input?

Thanks!!

Fast355

iTrader: (2)

I always just leave the piston .025 in the hole and run a .016" compressed steel shim head gasket. The only exclusion to this is if I am going to run Aluminum Vette heads. Then I deck the block .010 for .015" in the hole and run GMs .028" L98 type thick compressed head gasket.

I can tell you this was GMs logic on my LE9 that was in the van. Flattop pistons with 6cc worth of valve relief. The pistons were .025" in the hole. The heads were 14022601 castings with 53cc chambers. The head gasket was a steel shim style that comes out to .015" compressed or so. What that means is my stock 305 was 10.40:1 compression or there about. Even with the tiny stock cam, 700r4, and 3.08 gears, it never pinged a lick on 87 octane.

Damon

Not sure why that kit would include domed pistons???? The picture of the kit shows domes, but the kit contents says they are 4-relief flattops. And if they're 4 relief flattops that would be about 5cc worth of DISH volume. Different companies use the plusses and minuses in different ways. Trust me, it's 5cc worth of DISH due to the valve reliefs. Change the + sign to a - in your compression calculations and you'll get much more "sane" results.

With flattops it shouldn't be a problem to bring in the compression in the mid-high 9s somewhere, dpending on your head gasket.

Yes, stock rods are press-fit on the wrist pin.

1991 RS 305

Thank You Damon!! That makes way more sense!! Appreciate it!!