[Toyman]

Currently I have a 355 in a 1970 Chevelle. The 355 is built to the following specs: Stock/refurbed bottom end, flat top hypereutectic pistons, Edelbrock Performer RPM cam, intake & 70cc heads, roller rockers, Holley 650 dbl pumper, Holley red fuel pump, dual electric fans, 3.08 posi rear, th350 tranny, Hughes 35 convertor. I am running 13.7x @ just under 100 mph. I acquired a virgin 400 sb last year, which is on a stand. I am going to build it right when I do, but now is not the time. Anyway, I am a little low on compression on the current 355, approx 9.3:1. My block was decked .010 at the machine shop, which leaves me .015 to 0 deck. I plan on pulling the motor, installing a Crane 114681 solid cam that I already have,and also installing new, thinner, head gaskets. The choices are: GMPP 10105117/.028 compressed thickness, steel shim, or GMPP 14096405/.028 CT, graphite coated steel shim, or Felpro 1094/.015 CT steel shim. I believe that all three can be used with aluminum heads, and my quench will be .030-.043. I realize .030 may be tight, but it does get me to 9.8:1 compression. According to DD2000, this should pick me about 50 hp & tq with these two changes. Looking for opinions & suggestions on the head gaskets, combination, & anything else.

[DoubleVision]

According to my info the GM gasket won`t work with a overbored block.
By looking at your combo, what you need the most is gears.

[spinn]

well tune your gear to get the engine rpm to max as you cross the finish line. if its a race car.

or if its a cruiser tune the gear to the rpm you want to cruise at, in final drive. like 2000rpm with a 1:1 @ 70mph. no one cruises in the right lane anymore so, with a 26" tire at 70mph with the 3.08 your at 2800 rpm(max cruising rpm). if you have OD somewhere around 2200rpm, not to much room if you want to keep it roadworthy.

the third choice is to make a compromise

recommended crusing RPM for the smc is 1800-2800rpm. contact a trans or differential place and have them explain it to you.

[Toyman]

Ok- I probably should have left the rear end info off in the first post I realize that the rear end is somewhat limiting. This car is a cruiser with about 10 timeslips per year. With racing in mind, if I can get this car into the low 13's and keep the 3.08s for cruising, that would be my compromise. Anyway, my main question really has to do with .030 quench. Is it too tight, would I have to blueprint my block & heads to determine if it's usable? The Felpro gasket will pick me up .4 compression ratio as compared to .2 for the GMPP. Are neither of the GMPP gaskets usable on an overbored block?

[johnsongrass1]

Why not a steel shim?


.030 is close but not tight with a close piston. Don't turn more than 6 thousand with stock rods.

[spinn]

yes your .030 quench should work. the end gases should cool? right? they wont be too thinned out! with that cam it should be fine

i dont know about the gmpp gaskeys. what, they dont offer oversizes?

what is the best setup for a 3.08 gear?

[roy383ci]

hi toyman you have the edelbrock heads
sins you want to replace your head gaskets
take also a closer look at your heads
maybe you can find a Little more gain from them TO by
cleaning them up (porting)

i got the edelbrocks to and found that the
short side radius on the in en ex ports where not that
good especially the ex ports some where almost 90 degree of angle
whit very sharp edges
i also did a littel valve unshrouding (bad for compression) but
the chamber is now 73cc
there is also work to be done on the valve guide area
you can see some pictures in my photo album these are not quite ready
but its a good start

good luck

[Docs91RS]

Anytime you make changes in the distance between your head and piston you should check your piston to valve clearance. Especially when your dealing with decked blocks, milled heads or both.

When you start approaching quench areas of .035 or less you really need to know that your short block was put together right. Things like bearing and piston to cyl. wall clearance have to all within spec.'s. Even with the shortblock being within spec's I set quench no tighter than .035-.040". If you want more compression get the heads milled abit and go with the .028" gasket, but be sure and watch that piston to valve clearance. When you start gettin things in the combustion are this tight it gets to be more of a concern. Also watch your valve train geometry when you start changing things this much. You may need to get shorter pushrods to maintain the proper rocker arm to valve stem geometry.

Doc