.042 deck with no shims, CR of 11.3. Cam is C20 with 1.4:1 rockers. Heads are 044 castings, no port work and I think 40x35.5 valves with single high rev springs. I figure I'm going to add barrel shims to get the CR down a bit. I'd like to build this thing with the parts I have on hand but if a cam change would make this thing run on US 87 octane I could scrounge up a few bucks.
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Type 3 small stroker build
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Thenoj
- Posts: 17
- Joined: Tue Nov 17, 2015 5:37 am
Type 3 small stroker build
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Thenoj
- Posts: 17
- Joined: Tue Nov 17, 2015 5:37 am
Re: Type 3 small stroker build
This is a street engine and the carbs are dual 40idf's.
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66brm
- Posts: 405
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Re: Type 3 small stroker build
Keep the tight deck and open the chambers up, can that cam run with 1.4s?
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Thenoj
- Posts: 17
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Re: Type 3 small stroker build
Yeah, the C20 is supposed to work well with 1.4 rockers. If I could add 10cc's to the chambers, that would bring the CR down to about 9.5:1.
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Marc
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Re: Type 3 small stroker build
Take the piston deck up some - .042" is scary-tight for a 90.5 bore, and with a little more you'll still have good "quench".
I'd go with .055" and 55cc chambers (or .050" and 56cc), that'd give you 8.4:1 static and a chance of getting away with 87 (R+M)/2 gas.
Even better, mill a shallow flat dish in the piston top and remove less from the head. For example, a 2" dia dish .060" deep would add ~3cc unswept volume and still leave a >3/4" wide quench pad around the perimeter.
I'd go with .055" and 55cc chambers (or .050" and 56cc), that'd give you 8.4:1 static and a chance of getting away with 87 (R+M)/2 gas.
Even better, mill a shallow flat dish in the piston top and remove less from the head. For example, a 2" dia dish .060" deep would add ~3cc unswept volume and still leave a >3/4" wide quench pad around the perimeter.
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Thenoj
- Posts: 17
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Re: Type 3 small stroker build
Old configuration of this engine had 5.7 rods and .054 deck for 9.6:1 CR. As you can imagine, it ran hot.
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Thenoj
- Posts: 17
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Re: Type 3 small stroker build
I was able to get the chambers up to 50cc and put a .020 shim under the barrel to get down to 8.8:1 static. The cam and long(ish) rods get the dynamic down to 7.9:1. The engine should be running this week.
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Thenoj
- Posts: 17
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Re: Type 3 small stroker build
4K miles on this engine and it runs great except needs 89 to not ping. Not a terrible situation but missed my goal. Marc was probable spot on with .050" and 55cc but I wasn't comfortable removing any more material from the heads I had and I thought more deck would kill quench and cause other issues.
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sidemarkers
- Posts: 124
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Re: Type 3 small stroker build
hemi cut or flat chamber?
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Thenoj
- Posts: 17
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Re: Type 3 small stroker build
I hand shaped the chambers mainly unshrouding the valves. Most of the flat area on the spark plug side is intact.