can someone tell me some more about this shim head gasket.


Thanks
-Brandon-

 

Well I havent used Shim gaskets in years...what seems to be the problem??

Russ

 

what do they do? boost comp ratio


are they any good? where can i get them if they do boost the ratio

what type of problems could this cause me?

whats the price?

 

Yes they will boost compression....But havent you allready checked you compression with your new pistons and piston to deck height...and your head chamber cc's and a .041" felpro head gasket?

Russ

 

nope not yet

I am putting the bottom ned together. maybe finish that up tonite

 

I used the .018" steel shim gaskets from DSC. They will definitely boost compression. How much depends on your specific setup. When you have all the data, you can run the compression calculation with the felpro gasket and with the steel shim gasket and see the difference for your engine. For my setup, it added about .2, giving me about 9.8 to 1.

 

how much is to much in a 390 street truck?

 

I don't know that there is a simple answer to that. Too many variables depending on your exact build. If I remember your build, the cam you are using (941??) is best optimized around 9.5 to 1 compression ratio. You can't run too high with today's gas....I think 10 to 1 is a good limit to stay at but that's just my personal opinion...other people here have alot more experience in this...I've done many engine builds but I haven't done alot of performance work.

 

how can i go about checking the comp ratio that i have now?

 

check out http://www.rbracing-rsr.com/compstaticcalc.html. The calculations are simple but it's even simpler to just enter your #'s in one of the online compression ratio calculators...there's several to choose from.

 

Here's how mine came out:

73cc chambers
7cc valve reliefs
.041" thick Fel-Pro head gasket, with a 4.4" bore
Pistons .012" below deck - .053" quench space, a little much, but still acceptable
9.74:1 compression

Had I used the .018" thick, 4.25" bore gasket, I would have had .030" quench space, and 10.35:1 compression.

As it is, this engine doesn't like a lot of timing. With a quick distributor curve you will get a low rpm ping. I am running 89 octane 10% ethanol gasoline, as it is the cheapest here. I do have it tuned correctly and the ping is eliminated. Runs great with lots of power. I had to change the distributor springs to a 10 degree per 1000rpm straight line advance curve. The initial timing is set at 8 degrees BTDC, which is just on the bleeding edge of pinging. I mean, one more degree and it's pinging. Also, I am running a Mallory Unilite vacuum advance distributor.

I do suspect I could have gotten by just fine with the thinner head gasket. The quench space will create more turbulence in the chamber, which will prevent pinging better. This will allow the increased compression the thinner head gasket gives you.

Remember, with the motor set up like this with a tight quench area and high compression, you can get by with lower octane gasoline and make more power. However, the motor will be VERY sensitive to timing. Get it right BEFORE you stomp the loud pedal if you want the motor to last.

Edit: FWIW, Crane lists the 941 cam as good to 10.75:1 compression. I could see that if you had a good quench area as mentioned above, and ran premium.