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Old 10-01-2021, 11:53 AM   #35
142 guy
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Join Date: May 2014
Location: Saskatchewan, Canada
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Originally Posted by blakemcelroy2000 View Post
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?
I have no experience with forced induction on a B20.

That said, as an observation forced induction may be effective at dealing with flow restrictions on the intake; but, you need to be able to get the spent charge out the exhaust and the supercharger / turbo does nothing to help that. The B20 has a particularly crippled exhaust port (lots of threads discussing the problem) in terms of flow. You may find that you need overlap to help you scavenge spent charge out of the combustion chamber. The amount of overlap that is beneficial will probably depend on the boost level. A low boost application may do better with less overlap. More boost may need more overlap to achieve the maximum volumetric efficiency at the expense of poor low RPM operation and poor fuel consumption. So, optimum cam specs will likely depend on the maximum manifold pressure that you are planning for.

As a related observation, you don't necessarily have to trade off lift against duration. If you put high ratio rockers on a C cam the duration and overlap remain the same; but, the lift is increased. However, more lift without more duration typically means faster acceleration on opening and closing which can present some durability issues for the B20 valvetrain. The other thing to consider is that a lot of lift may not be of much value with stock ports. Turbobricks member Canuck did a lot of flow measurements on the B20 head and I think it was he who identified that increasing lift much beyond 0.45 " had exceedingly low returns in terms of flow improvement on a stock head.

The super list of cam grinds did not include any cam grinds from Tinus Tuning (www.tinustuning.nl). It has been a while since I looked at his offerings; but, I recall that he did have one or two B20 cams that were suggested for use with forced induction. If you email him he may be able to provide advice on the best cam for your planned level of boost or advise on what additional head modifications are required to support the level of boost that you are looking for.

Edit:

Unless you are wedded to using a supercharger, you may want to look at what Volvo did with the B230FT engines as a starting point. The B230 has a head design that is not exactly light years ahead of the B20 (its aluminum, has an overhead cam to reduce flailing parts and noise and Volvo finally figured out that having the intake preheated by the exhaust was probably not optimal); but, the ports and combustion chamber shape are still dated - almost as good as the ones on my Honda lawnmower. In turbo + configuration it was good for around 180 claimed hp. If you look at the B230FT cam profiles mixed with the boost level, intercooling, ignition timing and compression ratio you have a starting point that can probably be translated to the B20. Or you could do what other people do and just exchange the B20 for a B230FT which will be much cheaper and then you can start tweaking the B230FT.

Last edited by 142 guy; 10-01-2021 at 12:09 PM..
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