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Old 09-30-2021, 02:18 PM   #33
blakemcelroy2000
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Join Date: Oct 2017
Location: Portland OR
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Originally Posted by 142 guy View Post
If you want a slightly dated overview of B20 cams (some may no longer be available), go here:

http://www.1800philes.com/ianr/_superlist_grinds.html

If you are looking for low overlap, the Volvo A, B and C grinds appear to be the winners. If you want to up the lift you could consider some high ratio roller rockers from Yellaterra.

The D cam probably represents the limit for SU carbs in terms of getting a reasonable idle at a normal idle speed. The C grind was the stock cam for the B20B. At an idle speed of 850 RPM the D cam on my B20E results in a MAP of around 55 kPa and on Tuner Studio with a high Res tach wheel you can see that the idle is definitely irregular, particularly if you try to run the idle AFRs at 14.7 or leaner.

The K cam showed up in 1972 or 1973. As noted, it just has slightly less advertised duration than the D cam, lift being the same (the measured duration at 0.05" is the same for both cams) . I don't know that the cam change was related to the drop in compression ratio associated with the F engine. I suspect that the reduced duration may have been more of an attempt to clean up the emissions at idle or improve idle quality.

As noted by others, do not drop the compression ratio by increasing head gasket thickness. This is an invitation for detonation of end gasses in the combustion chamber. If you don't want to fork over the additional $ for a custom MLS head gasket, a head gasket meant for the B20 B engine is your best choice (Elring lists them). The B and E head gaskets both had a compressed thickness of 0.028". However, E head gaskets are no longer available. All head gaskets listed for use on the B20E and B20F are now the thicker B20F gasket which is not the hot ticket for controlling detonation. True B20 B head gaskets will fit just fine on a B20 E or F head. When shopping for head gaskets, be sure to check the compressed thickness. As vendors rationalize their supplies for these older engines they may just start listing the thick B20F gasket for all B series engines.
That camshaft site is super helpful, thanks! Those Yellaterra rockers are pretty sweet, looks like running those with the stock C grind or Isky VV61 would be a fast setup. What do you feel is more important on a supercharged application? Limiting overlap as much as possible but sacrificing some duration and quite a bit of lift? Or picking a cam with a little higher overlap but with a little more duration and a whole lot more lift?
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