"...I think my sig line really fits here ;-)" Yes it does.. analysis to
paralysis!
Don't forget overlap. When it gets right down to it, all the guess work
(mathematics) has been done.
Larry Macy wrote:
> OK I got a question. As most of you know I am in the process of doing a
> rebuild on a 1500 Midget engine. I have been thinking about putting a cam
> in the engine, for a bit more performance. I have run into some
> questions I have no idea about. All of the rebuilds I have ever done have
> been stock. Whether it was a 7490 cu. in. Waukesha, a D-9 Caterpillar
> diesel, or the 1500 that is now coming apart on me, it was always stock.
>
> I am getting a lot of info on cams that I do not know how to interpret. I
> am looking for a mild street cam. I understand that for the most part a
> cam shifts the powerband, while adding a bit more ponies. (at least I
> think that is what I understand).
>
> There seems to be 3 relevant things on a cam, but I don't quite get what
> they mean, or how they relate to performance. Now bear with me.
>
> We have duration, which is how long the valves are open.
> We have lift, which is how far the valves open.
> We have cam lobe lift, which I don't know what the hell it means.
>
> For instance I have an Kent cam that has
> 295 duration
> .382 in lift & .378 exh lift
> .261 cam lift.
> Power range 2500 - 6500
>
> An APT cam that has:
> 278 duration
> .256 lobe lift
> 231 cam duration @ .050 lift
> Power range 2000 - 6500
>
> And Ted Schumacher that will grind a cam for me, but I forget the exact
> specs.
>
> And Elgin Cams, Which Mike G posted the other day, but I don't have handy.
>
> I know that all that stuff is supposed to make the engine breath better,
> but what the hell does it all mean??
>
> I know that the longer the duration the longer the valves stay open, I
> know that the greater the lift the more fuel/air charge gets into the
> cylinder. I know that if the lift gets too much you need stronger
> springs. I know that there is such a thing as valve overlap that is
> supposed to make the charge mix a bit better. (for those of that don't
> know, that is when both valves are open at the same time, one closing and
> the other opening, I think it happens on the intake stoke when the
> exhaust valve is not quite closed and the intake is beginning to open,
> but I forget a lot of the theory as to why that is a good thing).
>
> Ok put it in simple layman's terms for me. I want a cam that will give me
> a bit more oomph, but that I can tolerate in a car that is still a daily
> driver. I do spend a bit of time at stop lights so the less "lumpy" idle
> the better. What cam do I choose, and why should I choose that one, or
> should I stay with the stock one??
>
> I am going with the 9:1 pistons, balancing, and debating lightening the
> flywheel. I do not want a race car, I want a daily driver with a bit more
> oomph. I have a Weber DGV (water coke) and headers. Someday I will do the
> dual SU's but not today.
>
> Remember this is a street car, not a race car.
>
> Help
>
> Thanks
>
> Larry
>
> BTW I think my sig line really fits here ;-)
>
> Larry Macy
> 78 Midget
>
> Keep your top down and your chin up.
>
> Larry B. Macy, Ph.D.
> macy@bblmail.psycha.upenn.edu
> System Manager/Administrator
> Neuropsychiatry Section
> Department of Psychiatry
> University of Pennsylvania
> 3400 Spruce St. - 10 Gates
> Philadelphia, PA 19104
>
> Ask a question and you're a fool for three minutes; do not ask a
> question and you're a fool for the rest of your life.
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