advancing cam

[ZIGGY]

Athomp, whatever you decide to do, let us know how it works or doesn't.

[randy331]

randy
how about your dyno test #'s at 3000 rpm? he needs to come out of a corner faster than the competition.
i agree that a dyno test would be needed on HIS CAM to find out for sure...
thanks for your experience as i do find it interesting.

Matt, like I said earlier the 3000-4000 rpm range was almost identical from one position to the other, but with each move back with the cam it made a little more peak power, at a little higher rpm, and hung on to the power past peak way better.

Randy

[dwilliams]

If the cam is too small, the gain in cylinder pressure will require backing off the spark, which can lose more power than you gained.

I've seen this on a couple of mild street engines that ran better with the cam straight up than 4 degrees advanced - and one had the time slips to prove it.

[cjperformance]

Where is its strongest rpm area now? Im guessing its best between 2500 and 4600rpm??

Is all of your race run between 3k and 5k? - what max rpm do you run?

[athomp]

Where is its strongest rpm area now? Im guessing its best between 2500 and 4600rpm??

Is all of your race run between 3k and 5k? - what max rpm do you run?

I haven't run this particular cam before and to be honest I don't spend much time looking at the tach. I never look at it coming out of the corner so I'm just guessing at 3000. I do sometimes glance at it just before I let off and it's at 5800rpm. I blew up a couple of years ago at just over 6000 so I keep it under that now.

[cjperformance]

Where is its strongest rpm area now? Im guessing its best between 2500 and 4600rpm??

Is all of your race run between 3k and 5k? - what max rpm do you run?

I haven't run this particular cam before and to be honest I don't spend much time looking at the tach. I never look at it coming out of the corner so I'm just guessing at 3000. I do sometimes glance at it just before I let off and it's at 5800rpm. I blew up a couple of years ago at just over 6000 so I keep it under that now.

I would definetly try retarding 2 to 4 degrees for a start point. As Randy331 noted above, you wont loose any notable Hp/Tq in the low end,(up to a point of course until you retard it too far.) it will stay pretty much the same but make a little more peak and rpm over peak a little freeer. Advancing that cam will pick up some low end TQ but it will peak lower Hp/rpm and will fall off earlier after peak.

[ZIGGY]

Sounds like you need to put an adjustable cam drive & quick access cover on it.

[franklstoner]

advancing the cam means your intake valve will close earlier compared to the piston therefore building more cylinder pressure which means more power. So unless you have excellent scavaging heads that's were I would run it. Ptv clearance is the only thing to check. With a small cam it's probably fine.

[randy331]

advancing the cam means your intake valve will close earlier compared to the piston therefore building more cylinder pressure which means more power.

If this statement was even remotly true, why not just keep advancing the cam and gaining more power?
Why not close the intake valve right at BDC? With your theory that's where you'd get the most cylinder pressure and therefore the most power.
And then why would any engine need more than 180* of intake duration? I mean if you have more than 180* of duration you either open the valve before TDC or close it after BDC.

Randy

[franklstoner]

you have to fill the cylinder before you can build cylinder pressure. You should know that randy331. The key is to get as much of a charge as you can get before compressing it. But if your motor doesn't benefit from scavaging than you have to compromise. If he had really good cylinder heads than retarding the cam would be benefitual because he could reap the benefits of scavaging. You got to use what you got.

[randy331]

you have to fill the cylinder before you can build cylinder pressure. You should know that randy331. The key is to get as much of a charge as you can get before compressing it. But if your motor doesn't benefit from scavaging than you have to compromise. If he had really good cylinder heads than retarding the cam would be benefitual because he could reap the benefits of scavaging. You got to use what you got.

So my engine benefited from scavaging because of those really good 882 casting heads flowing 200cfm, and that's why it gained power when the cam was retarded?
It wasn't because the cylinder was still filling at IVC, so leaving the intake valve open latter helped?
How does retarding the cam benefit scavaging?

Randy

[Matt Gruber]

as the facts have changed, i'm more with randy!
1. now up to 5800
2. 2bbl
i seem to recall 2bbl circle track cams typically in the250-262 range.... is my memory correct?
so this weenie cam probably will work better straight up or retarded.

[franklstoner]

you have to fill the cylinder before you can build cylinder pressure. You should know that randy331. The key is to get as much of a charge as you can get before compressing it. But if your motor doesn't benefit from scavaging than you have to compromise. If he had really good cylinder heads than retarding the cam would be benefitual because he could reap the benefits of scavaging. You got to use what you got.

So my engine benefited from scavaging because of those really good 882 casting heads flowing 200cfm, and that's why it gained power when the cam was retarded?
It wasn't because the cylinder was still filling at IVC, so leaving the intake valve open latter helped?
How does retarding the cam benefit scavaging? What size cam was you running with those 882 heads? Keepin the exhaust open later allows for a longer draw on the intake side as compared to the piston. If your heads flow well enough the benefits can out weight the extra cylinder pressure. Rpm range will change as well. If your after long rpm runs than maybe your better off straight up or retarted. If your cam is to big you can also benefit from it by advancing. It really depends on what your trying to accomplish.

Randy

what size cam was you running with those 882 heads?

[franklstoner]

sorry randy. Some of my post ended up at the end of your post. Advancingthe cam in a mild chevy is generally the rule but not always the exception.

[KnightEngines]

Intake restricted engines with smallish cams almost always like a bit of retard, I'd wind it back 4 deg & see what happens.

All the motor has going for it is intake velocity, which can be pretty good on this style of engine - take advantage of that & hang the intake open a little longer after BDC, provided you've got enough velocity (& you should do) the cylinder will keep filling after TDC if you hang the valve a little longer.

Is the cam a spec item? - if not a new cam with single pattern or even more intake than ex duration & tighter lobe centres can often make a big difference on an intake restricted engine.

If you have the time & $ try something like a 236/230 on 104 centres, dialled in on 108 intake centre line, that should wake it up.