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B20 Compression Ratio Target: R Cam

hensh_ma

hensh_ma

Member
Joined
May 20, 2024
After "cheaping out" on Tinus Tuning for now, I pulled the trigger on an R cam from VP Autoparts for cheap. Head has adequate supporting mods, will be running double valve springs, forged pistons, Weber DCOE 45's, etc etc. Block has been zero decked and I plan to use a Cometic .030" head gasket. I'm going to be running premium pump gas.

One thing I'm unclear on is my target compression ratio for this camshaft. Seems like the consensus is 11:1. Highest i've seen is 11.2:1 mentioned in different threads, but looking for something more concrete.

See screenshot below of R Cam build with specified 11:1 compression ratio. Looking for thoughts.

Screenshot 2025-11-24 at 2.36.10 PM.png
 
Intended use?
Fuel octane availability?
What other head mods?
Header or manifold?
Give me some lift at valve and duration (specify the checking height) and i will make an assessment.
 
I agree with Mike P, I wouldn't want to run less than 10.5:1 with an appropriate amount of piston to head clearance. I'm sure it'd live happily at 11:1.
 
I am in agreement with folks here as well. 10.5-11:1 will probably work well. Just make sure you hit tight squish in the 0.030" to 0.040" range. Remember to knock the sharp edge off the rim of the combustion chamber after the head is shaved to its final thickness lest it get a hot spot there and develop run on.
 
I eeked out 12:1+ on a b20 b18 build, but that was with squish dialed in tight. Fun "DD" commuter for a friend that sees 75+mph freeway commuting as well as ripping back roads.
 
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Thanks all. Sounds like 11:1 is the consensus. I will stick to that number. Squish will be set to .030.

@cwdodson88 re: rockers -- I looked into this but from what I saw it seemed the cheapest available option was a 1.55 ratio thru Tinus @ €599 , and 1.65 ratio @ €1060 (link). Other options like YellaTerra are more expensive...if anyone knows a cheaper method that is still "easy" to do, I'm all ears... don't think I trust myself enough to execute the DIY 'drilled angled adjuster' method.
 
hensh_ma said:
Thanks all. Sounds like 11:1 is the consensus. I will stick to that number. Squish will be set to .030.

@cwdodson88 re: rockers -- I looked into this but from what I saw it seemed the cheapest available option was a 1.55 ratio thru Tinus @ €599 , and 1.65 ratio @ €1060 (link). Other options like YellaTerra are more expensive...if anyone knows a cheaper method that is still "easy" to do, I'm all ears... don't think I trust myself enough to execute the DIY 'drilled angled adjuster' method.
Click to expand...
I’m currently working on a prototype set of 1.65 and 1.7:1 roller tip rockers. I have a set being printed in stainless steel and a set going on the mills in 6061. These should be tea for a test dummy in January. If you’re down to be a test dummy, send me a pm.
 
@culberro you have a video of that thing running and driving? Would be interested in seeing what it sounds like w/ R Cam and 38/38. Limited media with R Cam floating around, and all using DCOE (which I plan on running anyway, but just curious)
 
hensh_ma said:
@culberro you have a video of that thing running and driving? Would be interested in seeing what it sounds like w/ R Cam and 38/38. Limited media with R Cam floating around, and all using DCOE (which I plan on running anyway, but just curious)
Click to expand...
First start with the new engine, before any tuning was done. Open exhaust in the vid as well, so it sounds a lot for aggressive/rough than it actually is.

 
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