Can tightening up the LSA on a cam help compensate for heads that have a poor I/E ratio, or have a poor flow intake runner?

Thanks
Jeremy

 

I'm trying to remember what Vizard says in his book about SBC Cams and Valvetrains.

I believe he says that for engines with poor exhaust flow (and that can mean either exhaust port or the entire exhaust system), you want to trend toward less overlap (generally meaning a wider LSA on a given cam) to minimize exhaust gasses dilluting the intake charge.

So basically if you have poor exhaust flow, then exhaust velocity is likely not going to be very good, and therefore the scavenging effect of overlap is not going to work very well. Overlap is more beneficial with a good flowing exhaust. So if you have a big difference in I/E ratio I would say first of all you need a healthy split duration on your cam, at least 10 degrees more exhaust duration... If you do that and you have full headers/catback, etc. then you can probably run the LSA you want to.

 

Sounds good to me.