Today i though of a way to have a special large cam gear and make it advance with rmps using centrifigal force and have it adjustable via changing weights and springs. Im still learning about cams and im not shure if the engine will get significant, if any, low rpm torque and high rpm hp gains. Does retarding the cam make the car behave better on the street at idle and throtle response? How many degrees of change shoud there be from low rmp operating to after the system kicks in? ive seen the cam gears with +3*/0*/-3* setings so would 6* be a good starting point. it cna also be made with adjustable total degree change by making adjustable stops. Im planing on making this for my experimental turbo 267 chevy engine project im thinking of running other trick one off parts or systems like this and make a the ultimate gas sipping hi-hp street turbo engine. Thanks please someone help i would love to make the cam advance system if it will give me torque and hp.

 

not sure if this is right but.

avancing the valve timing should provide more low speed grunt. and retarding it should provide more high speed hp. from what i've been around thats how it is in general, but i think there are exceptions to that. and if i'm not mistaken valve timing is usually changed 4* at a time. i'm sure others will chime in. sorry if i'm wrong on things. all my knowledge came from 90-95 car craft and hot rod magazines when i was still unable to drive .


btw i've been trying to figure out how to operate the valves electronicly for awhile now. i think it can happen someday. but it will be very costly when it does. i dont think we possess the tech abilities to produce this in a realiable form yet.

by electornicly operate (motor on every valve)... think stock lt1 cam at idle with lift rates that blow away a solid roller. and at wot it acts like a huge solid roller cam at high rpms. just imagine this valve events that optimize power all across the powerband and sacrifice nowhere.

 

So is cam advance an engine specific thing, like i wont defenitly get make more power by advancing it at low rpm them retarding it alot for hi hp. It would have to be tuned to every engine combo.

 

i really think its more one of those things where your actual cam will make the difference. the hard ground in valve timing will make quite a difference. some cams respond like you wouldnt believe to adv/ret. others will only lose power.

i think if you gave more specifics about your particular combo on here, and the cam specs, how much boost etc. somebody would play with it in a simulation program and try to give you an idea. if you'll post your stuff i'll try it in desktop dyno. probably not the most accurate but some of the other guys have really high end programs for doing this.

 

If memory serves me correctly, back in the 1960's, there was a centrifugal cam sprocket available for the SBC that allowed variable cam timing.

Anybody else old enough to remember that piece?

 

Chevys new inline 6 4.2L to replace the 4.3 has 2 cams but is still a pushrod engine. As rpm is incressed the exhaush cam was retarded (i think) anywho it make's 280hp. I'll try to fine more info

 

The 4200 6 cyl is a dual overhead cam engine; no pushrods.

The exhaust cam is infinitely variable (programmed by the computer) over about 50 (crankshaft) degrees. That means the LSA can vary a total of 25 degrees! This is used for a number of purposes: emission control (no egr needed), fuel economy, and power production at full throttle or part throttle at all rpms. It moves a lot!

The engine gets 90% of it's maximum torque from converter stall to shift point at wide open throttle. No peakiness here.

You bring up an interesting point of two-cam pushrod engines. I think there is room designed into the LS1 for a second cam on top of the first one. Look at the front cover on the block. By driving the second cam (exhaust) off the first (intake)with a gear, and putting the variable system on it, you get variable LSA, and the same advantages as the 4200. It would be more complicated to have both cams variable, so I see that farther down the road.

 

Old enough? Yep, but memory is the second thing to go.

I recently saw a variable cam advance/retard system on a strong small block in the Pop Rod Engine Masters contest. It used a big solenoid which actuated an eccentric between the cam sprocket and the cam (I think). It was actuated by a MSD timer which used an rpm chip. The builder claimed he didn't get more out of the variable system, so he didn't use it in the contest. It was fascinating, however.

 

The engine im planing on use for the cam advance system is a 267 chevy v8 3.5 bore 3.48 stroke. a 300 hp 327 stock cam W/ .390 195 @.05 int .410 202 @.05 and lobe seperation of 112. I ported the stock heads fulley and matched the intake to the heads. The intake is a edelbrock performer (Dual plane). Im puting a 600 cfm vac sec holley carb with the secondaries ritchened up for turbo and modified the vacume actuator into a boost actuator. The turbo is a rebuilt t04b W/ .60 compressor and 1.15 turbine. I will be fabricating my own headers out of 5/8 mild steel with equal primaries length about 20" long. Im know much about header size and length so if anyone knows any better suggestions on length or diamiter for 2000-5500 rpm i will use them. i ran the engine on desktop dyno and it came up with ~260 hp without the turbo, i pluged it in witout the turbo because when you make an engine with turbo on desktop dyno 2000 the choice of intake manifold is no longer there and that makes a big diffrence in an engines output. and i looked at the cam specs on DD2000 and i dont kno whow to advance/retard the cam is it the intake center line and what is i measuring the degrees from TDC? Therefore acvancing the cam by increasing the centerline?

 

I remember it vaguely. Digressing a bit, but how about the 1/4 speed cam that came out in that time period. It had two lobes per valve. It was supposed to end valve float.

 

D'OH... i've been corected

 

1/4 cam what hapened to it? i guess the cam didnt have enough area to be 0 lift for long engough? I bet it would work with larger cam lobe circle thingamigiger whats its name? you know the diamiter on the lobe where there is no lift?(wow i feel stupid)

 

I'm in as good as shape you're in. I think it's called the base circle.

 

yea so ive figure out all the cam degrees thanks to grapeaperacing.com (great tech site and turbos) and i woul get about +5 ft lbs and stretch it out but of kickin in like v-tec or the cam thing oldsstroker that works in 2 postions hi and low rpms. I can try to design it so it slowly advances like a ferrari cam setup but they have the duration change too that would be awsome to have on a chevy. You could put it on where the the rockers would go and it would change the gearing and rockers via centrifigal weights or even better compuer for ultimate tuning. It would be altering lift and duration so you can get every cam imaginable at the rpm you want but the lobe center would have to stay. But now im geting too advanced and out of my budget range letst just start with the timing advnce for now

oo yea so.. making it advance per rmp slowly instead of at a set rpm go from seting ot setting. what this did on desktop dyno was allow me to take teh peak torque and as i rev the engine i can increase centerline (advangine the cam) and insted of the torwue droping i can keep it up and almost drag it across the rpm range and of course inceased torque at hi rpms mean higher hp and also i can stretch out the peak hp both ways too making the peak be across almost 2000 rpms. verry cool . and i figgured out a way to make it advance how you an it to you can hook it up to an motor that after gearing can get the timing gear to around 6000 rpm and hook it up with a flashing light thet flashes every rotation like when timing an engines spark and measure the advance curve and fool with the weights and springs till the curve is to your likings. . So i think i should give this gear a try, right?

 

thanks i thats it base circle wish i had a car dictonary every time i cant remember a name i have a choice search countless old mags for an article i read it car craft, or was it hot rod, (after digging through all the cc mags) or PHR, no... or i can feel a litle dumb