Len Posted January 17, 2005 Share Posted January 17, 2005 Ok currently I'm working on rebuilding a 2 liter 4 cylinder 1979 fiat 124 spider engine. Normally they are about 8 to 1 comp. 86hp. I am installing 8mm. domed pistons and 40/80, 80/40 hot cams (twin overhead cam alumin head engine). I had a reputable racing machine shop do my heads. Before I gave the head to them I told them if they saw the head had any issues... I had an extra head they could use. Well got back the completed head...noticed scaring from something in #3 cylinder....didn't look that good...brought it back...they said it will do fine since none of the scaring was where the head gasket mates with the head. I wasen't satisfied...so just to be sure went to another reputable head shop...they said the same thing it was ok....well had some friends over we used a graduated burette and measured the cc's in each chamber. There was a 2.5cc difference in that "scarred chamber as compaired to the other three (53.5cc, 53.5cc 56cc, 53.5cc's). Using our figures that works out to 11.1 to 1 compression on three cylinders and 10.68 to 1 on the scared chamber. .... yea regular driving they are probably right saying no problem but for performance I don't know I just don't like it..this could not be good ... I was thinking of slightly smoothing out the scaring anyway....but then I thought what if I smooth out just enough on each of the other three combustion chambers to equal the 2.5 cc's. What do you think? am I playing with fire possibly disrupting the swirling effect of those scientifically developed hemi combustion chambers with my dremmel tool....I will also contact some more head shops showing them exactly where the trimming will be...but just wanted to ask what you guys thought? Quote Link to comment Share on other sites More sharing options...
Guest Magnum Rockwilder Posted January 17, 2005 Share Posted January 17, 2005 "Clearancing" the CC is fine as long as you don't create any sharp edges. I would build up a weld on the scarred cyl and grind it down until you get the same displacement as the rest of the cyls. ...or leave is as-is. Quote Link to comment Share on other sites More sharing options...
Clifton Posted January 17, 2005 Share Posted January 17, 2005 If you want to remove material I would only do it where it would be benificial. Like unshrounding the valves. You should be able to get it welded and then smooth it back down. That's what I would do if it was mine. Quote Link to comment Share on other sites More sharing options...
Len Posted January 17, 2005 Author Share Posted January 17, 2005 Good point...except I don't have the tools to weld alunium (never could spell that word..but you know what I'm talking about). I think I'll just smooth out the rough edges of the scarred area then as you mentioned smooth around the valves. I'll then re-cc it to see if I'm closer volume with all four chambers then leave it alone. Anyway 11.1 to 1 is pretty high compression for 93 octane (pump gas in OK). so evening chambers out to approx. 10.6 or 10.7 to 1 might be a good thing. I will also be running twin 40 IDF webers along with the better cams.. I would think that would help any possible detonation. Quote Link to comment Share on other sites More sharing options...
Clifton Posted January 17, 2005 Share Posted January 17, 2005 If you can find some one that can Tig weld, it wouldn't be that much. I would call around before starting plan B. Quote Link to comment Share on other sites More sharing options...
Guest 81na ZX Posted January 17, 2005 Share Posted January 17, 2005 Are taking into account the head gasket thickness in your CR calculations? Either way, sharp edges in the combustion chamber are a much bigger enemy than a 5% volume difference. Quote Link to comment Share on other sites More sharing options...
Len Posted January 18, 2005 Author Share Posted January 18, 2005 Yea...took in account head gasket volume, deck clearance, first ringland gap volume etc... Agree concerning what you mentioned concerning sharp edges...I am still working and gaining info....thanks guys Quote Link to comment Share on other sites More sharing options...
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