I would rather use a single .040" base shim, than the 2 pieces I have now. I don't like the aluminum shims either, but, remember, similar pieces were a stock item on the Type 4 engines from the factory. They do eventually give way, but the thinner cylinder walls will definitely hasten their demise. Wann sell me 4 good, matching base shims?
Mike B. ----- Original Message ----- From: "marc vellat" <[EMAIL PROTECTED]> To: "Air-Cooled Volkswagen Discussion List" <[email protected]> Sent: Wednesday, April 30, 2008 8:57 PM Subject: Re: [vintagvw] 40 horse expert 1961-1965 beetles > Oh, I see. You merely forgot to mention the .008" > paper gasket OR the .040" aluminum head gasket. Taking > those into account your calculation would be correct. > I wish you luck with the aluminum head gaskets, they > are a BAD idea. The narrow contact area of the > big-bore 40 cylinder wall is going to cut into it, > clamping force will be lost, compression leakage will > occur and it will melt down and burn away. Even steel > head gaskets fail eventually, aluminum are doomed. > You'd be far better off leaving those off and buying > some cylinder base shims. If you don't wish to do it > using one of the "right" ways I recommended before, at > least consider using thicker cylinder base shims > instead of the paper gaskets. .030" would give you > ~7.33:1. > > --- Mike <[EMAIL PROTECTED]> wrote: > >> There's nothing wrong with the Engine CR calculation >> spreadsheet I've been >> using. >> It is my piston/ cyl. deck hieght of .040", plus a >> stock .008" paper >> cylinder gasket plus a special .040" aluminum head >> gasket (to compensate for >> previous fly-cutting of the heads....total deck >> equals 2.25mm, so my CR calc >> is correct. >> >> Mike B. >> >> ----- Original Message ----- >> From: "marc vellat" <[EMAIL PROTECTED]> >> To: "Air-Cooled Volkswagen Discussion List" >> <[email protected]> >> Sent: Wednesday, April 30, 2008 2:24 PM >> Subject: Re: [vintagvw] 40 horse expert 1961-1965 >> beetles >> >> >> > Mike, I'd recommend that you toss that spreadsheet >> as >> > far as you can and do the math yourself. I don't >> know >> > where you got the idea that .040" = 2.25mm - >> either >> > that's a typo or it's where your error is coming >> from, >> > but either way you're FAR off. >> > >> > 83x64mm => 346.279cc >> > 1mm piston deck @ 83mm bore => 5.411cc >> > With 45cc chambers, that's (346.279+50.411)/50.411 >> > ...that's 7.87:1, not even close to 7.1:1... you'd >> > need another 6.35cc to bring it that low. That'd >> take >> > .045" more piston deck, which WOULD probably >> present a >> > problem with intake manifold fit. The intake >> manifold >> > can be tweaked enough to accomodate slight >> variations >> > in engine width, not likely to be difficult until >> you >> > get to +.050" or so - but you'd be +.090". >> > >> > You can safely run 87 (R+M)/2 octane fuel up to >> about >> > 7.4:1 with a stock cam at sea level...The way fuel >> > prices are these days I'd be inclined to go to >> ~7.7 >> > (that's about the max with a stock cam) and run >> > mid-grade gas, the cost-per-mile should be the >> same or >> > better. >> > Personally I don't like to run that low of piston >> deck >> > on an endurance engine - I would go with a minimum >> of >> > .045" for 77mm and .050" for 83mm. Keeping the >> deck as >> > close as possible to the lower safe limit will >> > increase the "quench" effect, promoting better >> > combustion characteristics and allowing a slightly >> > higher C.R. than on a "non-squish" engine. But >> > semi-hemi cutting also destroys the quench effect >> - >> > it's a quick & dirty way to gain chamber volume. >> Far >> > better to take the time to open the chambers up >> > manually by laying back the walls while leaving as >> > much of the flat quench surface as possible >> intact, or >> > mill a shallow dish in the center of the piston >> top. >> > I would run .050" deck which'd yield a C.R. of >> just >> > under 7.7:1 with 45cc chambers, and plan on buying >> > better gas. If you MUST run Regular, then stay >> with >> > the same deck and open the chambers up by ~2.5cc - >> > that'd bring it under 7.4:1. >> > Cylinder base shims ARE available, just not as >> common >> > as they are for later engines - and big-bore or >> not, >> > the shim I.D. is the same (nominally 86.25mm). >> SOME >> > 1200s had the larger 90mm opening found on >> 13/15/1600 >> > engines, but only late-model ones sold in other >> > countries. These engines have strange cylinders >> that >> > look like short 1300 jugs. >> > >> > I'm out-of-stock on all but .010" 40HP cylinder >> shims >> > ($7.50/set + shipping, [EMAIL PROTECTED]) >> > Chirco lists .010"/.020"/.030"/.040" for $8.95/set >> > >> > --- Mike <[EMAIL PROTECTED]> wrote: >> > >> >> I'm overhauling a 62/63 stale-air 40HP for my >> >> beetle right now. I'm >> >> installing later heads (square rocker bosses) and >> >> 83mm big-bore pistons and >> >> cyls. I found that my deck measured .040" >> (2.25mm) >> >> and my stock head has >> >> 45cc's combustion chamber volume. This results >> in a >> >> 7.1.1 CR, which >> >> requires 87 octane gas minimum. I'm installing >> >> black cool tins under the >> >> cyls, and have checked the thermostatic bellows >> for >> >> proper opening @ 150*. >> >> If your head CC is 40 to 43cc's due to >> >> fly-cutting, then semi-hemi >> >> cutting the heads and/or 'sinking' the valves >> will >> >> increase the volume to >> >> lower the CR. The 77mm stock cyls don't have the >> >> luxury of having shims >> >> available, but the 83mm big-bores will use the >> same >> >> shims as a stock 1600cc >> >> engine with 87mm cyls. >> >> Boston Bob told me that the limited length of >> the >> >> intake manifold won't >> >> allow you to shim the cyls very much, if at all. >> >> I'm sending you my spreadsheet in a pmail. >> >> Thanks for the reminder to use later rockers, >> >> Marc. >> >> >> >> Mike B. >> > >> > >> > >> > >> > >> > ____________________________________________________________________________________ >> > Be a better friend, newshound, and >> > know-it-all with Yahoo! Mobile. Try it now. >> > >> > http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ >> > >> > _______________________________________________ >> > vintagvw site list >> > [email protected] >> > http://lists.sjsu.edu/mailman/listinfo/vintagvw >> > >> >> _______________________________________________ >> vintagvw site list >> [email protected] >> http://lists.sjsu.edu/mailman/listinfo/vintagvw >> > > > > > ____________________________________________________________________________________ > Be a better friend, newshound, and > know-it-all with Yahoo! Mobile. Try it now. > http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ > > _______________________________________________ > vintagvw site list > [email protected] > http://lists.sjsu.edu/mailman/listinfo/vintagvw _______________________________________________ vintagvw site list [email protected] http://lists.sjsu.edu/mailman/listinfo/vintagvw
