New Cams New Thread

[Claviger]

 

[Claviger]

Bad news, cranking compression too high, guess who's doing it a 6th time now lmfao

 

[Claviger]

Where I'm calling it a day (night). Garage is still a disaster area, lol, that'll come once the bike is right!!

Also... This is NOT what you want to see:

The pic is 230, but two subsequent tests were 240 and 240, probably pulsed it one time too few on the 230.

 

[Joesmoe]

For the laity among us, what is the cause of that measure, and what is expected, and how to correct it ?

 

[Claviger]

The short version, I set the cam timing to the wrong timing (though it is exactly where I intended to put it).

I was hoping my static compression was really closer to 12:1 than 13:1, well, no, it's much closer to 13:1 after all.

Also... its the same cranking PSI as I had with my Carpenter setup, and it started on ONE battery, something the old setup simply wouldn't and couldn't do. 1st indicator all this work has been worth it and that I'm heading in the direction I intended to.

 

[Jvheli]

Where I'm calling it a day (night). Garage is still a disaster area, lol, that'll come once the bike is right!!

Also... This is NOT what you want to see:

The pic is 230, but two subsequent tests were 240 and 240, probably pulsed it one time too few on the 230.

Rob, curious how much pressure you think you can drop by changing cam timing? Since this is largely dependent on duration, wouldn’t you have to make a pretty significant change to the intake cam closing?

 

[Gerald]

Rob, curious how much pressure you think you can drop by changing cam timing? Since this is largely dependent on duration, wouldn’t you have to make a pretty significant change to the intake cam closing?

Would think with two cams, and two different gears, you could change the overlap and ramp open and closing times.

 

[Jvheli]

Would think with two cams, and two different gears, you could change the overlap and ramp open and closing times.

Well in this case, we are talking about too high cranking pressure. Which in this case is the intake cam closing too early on the compression stroke (more air volume to compress). The cam gear Rob has (me too) are slotted so it’s easy enough to advance or retard each cam. Ramp rates and duration are the cam grinders domain. All we can do is advance or retard what’s been ground.

What I’m curious about is how much can be dialed out and still make good power.

Robs reading is pretty close to what I’m seeing(not quite as high).

Just curious, I’m no motor expert!

 

[Claviger]

TLDR:. Yes, a small change can have a big effect. Below is my understanding, I know there are people on these boards who understand cam theory a hell of a lot better than I do.

Small changes show up as big effects on cranking compression and DCR (dynamic compression ratio). Debatably the most important timing event is IVC (intake valve closing), aside from setting compression values it has a large effect on what RPM peak power and torque will arrive. By closing it later, you're allowing more EGR from reversion, effectively making the engine smaller until you hit the RPM where air column inertia stops the reversion and gives filling action the whole time it's open. 90 degrees ABDC @ .006" is often as far as you can go, but some exceptions exist. This is why a cam can be under/over sized for an engine, if it has too little duration, setting it too late to establish power at a high RPM will open it too late resulting in no scavenging effect and too little overlap.

The other valve events are important, but none has quite as much effect as intake valve closing. IVO (intake valve opening) and EVC (exhaust valve closing) obviously both contribute to overlap, IVO being the more important, it is a large contributor to throttle response because IVO is ideally what you use to set exhaust scavenging period, cracking open just before peak cylinder vacuum occurs. EVC then can be used to ultimately establish the overlap period, overlap being largely important at raising peak torque RPM, but also raising it's value, too much and the engine is a dog below 3000 RPM, too little and it's a diesel like power band, all below 3000 then nothing up top.

So now you have IVC known, IVO known, EVC known, then it's just EVO.

EVO is the least critical event, 90% of combustions is done long before typical EVO, however certain engines like specific EVO because of rod/stroke ratio effects on piston position, speed and acceleration. The rocket has 1.8:1 rod/stroke ratio, so, it has pistons that hang out at the top and bottom for a long period, then shoots them down the bore at very fast speeds.

Lift is a factor of geometry of the valve train "how high can you go?" and valve size/flow. There are a few classic guidelines to determine what the ideal peak lift is for a given valve size. The R3 engine cannot accommodate the "ideal" lift for it's intake valve size, as a result more is always better on this engine.



Reset it last night out of frustration.

 

[Claviger]

Regarding high CCP, the Carpenter setup uses high cranking compression to preserve bottom end torque as much as possible, then uses large duration over the nose to get top end power. It's what's classicly refered to as a "cheater cam". They get away with it because the chamber is highly ping resistant by design. Equal values on a V8 would need well over 100 octane.

As a result they have VERY high ramp rates between .200 and .450 lift compared to a traditional egg shape cam. That's exactly why I dislike them, because I feel the rates are excessive and are the reason for the excessive valve spring pressure.

Delaying your Megacycle cams a few degrees would bring cranking compression to more normal levels, but it'll cost you bottom end power and provide little added top end because now overlap is too low and IVO is too late to scavenge right.