Valve Timing

[Rustkolector]

I have a small 4 cylinder, 4 stroke project started (1" x 1.125" bxs). I want it to run well in the 300-400 RPM range. All other slow running issues aside for now, what kind of cam design and valve timing would be best? I will be using roller type rocker arms riding on the cam. I am thinking of basic slow speed design with intakes opening 0-5 degrees ATDC, closing about BDC, and exhaust opening at 30-35 degrees BBDC, and closing ATDC. All comments, or experience greatly appreciated.
Jeff

 

[gbritnell]

Hi Jeff, that's really lazy cam timing. On my Holt which has the same bore and stroke my cam timing is IO 20 BTDC, IC 30 ABDC, EO 30 BBDC and EC 20 ATDC. More important is having enough flywheel weight. I can now get my Holt to idle down to about 450 rpm. I won't say that 300 can't be done but that's pretty darn slow. Here's the link to my Holt. It runs slower now than when this was taken.
gbritnell
[ame]http://www.youtube.com/watch?v=4ooTq2xF2pw[/ame]

 

[Rustkolector]

George,
My engine prototype is a 200 RPM engine. I am trying to come as close to that as reasonably possible. I got the cam timing figures from a builder of the Pacific Design Fairbanks-Morse engines, and those engines I am told will run at 200 RPM. Granted, they are a little larger displacement, and have fairly large flywheels. I also looked at some old engine reference books from the 1911-1919 era, and they were using similar valve timing to what I stated. It is also similar to that of Briggs and Stratton 1800 RPM engines of the 1920's. What I don't know is if that timing will work as well in a model as it did in the prototype engine. I am considering using larger than scale flywheels, and a relatively low compression ratio of about 3.5:1.