4 replies to this topic

[knightec]

I'm interested to know information about the basic principles employed when designing a camshaft for a normally aspirated race engine that runs air restrictors.........an f3 engine would be a fine example...........my thinking is that overlap is generally to be avoided, because the depression in the intake (due to the restrictor) could potentially pull the exhaust gasses back into the combustion chamber during the overlap period - this in my mind would be a bad thing........I'm thinking a good set of restrictor camshafts would be much like a set of turbo cams, whereby turbo cams also have no overlap, otherwise the excessive pressure in the intake manifold during overlap, would blow too much air out of the combustion chamber - which is a tad inefficient.

[AndrewD]

knightec

i think your on the right path, however typically with turbo applications, emap is much higher than imap (or just map) hence then same reasoning for your restricted na engine applies for the turbo camshaft. i.e. reversed flow during overlap.

ps. map = Manifold air pressure (e = exhaust, i = intake)

[McGuire]

Right, like a "trapper" cam on a turbo combination. The idea is to minimize pumping losses.

[Halfwitt]

Originally posted by knightec
I'm interested to know information about the basic principles employed when designing a camshaft for a normally aspirated race engine that runs air restrictors.........an f3 engine would be a fine example...........my thinking is that overlap is generally to be avoided, because the depression in the intake (due to the restrictor) could potentially pull the exhaust gasses back into the combustion chamber during the overlap period - this in my mind would be a bad thing........I'm thinking a good set of restrictor camshafts would be much like a set of turbo cams, whereby turbo cams also have no overlap, otherwise the excessive pressure in the intake manifold during overlap, would blow too much air out of the combustion chamber - which is a tad inefficient.

Hey there knightec. There is a company very close to you who could help. They reckon they can design / develop LMP900 and LMP675 engines, so they must be very well informed on this sort of thing I expect. Their website is http://www.knightecengineering.com/ and their postal address is, I think, the same as your own. Perhaps you can pop downstairs and ask them for advice.

[knightec]

I openly admit to knowing nothing about restrictor camshafts - thats why I posted the subject........in truth NOT many engine design companies design their own cams - they always sub-contract it out to specialist cam companies......because its exactly that - a VERY specialist subject......not to mention the manufacturing know-how.......hence people like you and me put posts on places like this to find out more........

now if you dont have anything usefull to say please stay under your rock - very apt name by the way.......although I could easily swap the "half" word for another word beginning with F