Can advancing a cam hurt low end?

[travis]

I know this is counter to what most recommend in this situation...

If you have a big tight lsa cam, relatively low compression combination that already probably has a ton of low speed reversion, could advancing the cam more hurt the bottom end response even more? Or would the earlier closing intake and the slightly increased cylinder pressure more than compensate for that?

I’m working on something that has a Crane 302H06 cam in it...246/246@.050, .500/.500” lift, 106 lsa ground +4. Best guess is around 9.2 to 9.5 compression, but possibly less (I didn’t build it).

[Truckedup]

I'm far from an expert, but a different cam might be best...

[F-BIRD'88]

Yes if you want more torque and sooner you can try that cam a bit more advanced and test for effect.
Try a 100- to 102 intake C/L. Degree it first and move it accurately.
Also try locking out the diz mechanical adv curve.
It won't make a big cam into a small cam but usually adds a bit of torque in the low end 3000 ish.
You will need to drag test to know if it helped. Or...

Also if I think the cam is too big I try loosening the valve lash a hair on the intake rockers. .002"-.004" for temp testing for effect.
If it responds you need a shorter duration cam.

This cam will want a 3500+ stall and some gearz.
It really likes 10-10.5:1 cr.

[BigBro74]

What is the cranking psi?

Usually an engine like this has less compression than most people estimate - so probably way more duration than you want- try the 274 HO6 grind instead.....

[travis]

It’s cranking 155-160 on the couple cylinders I checked.

The owner doesn’t know much of anything about it. It sounds pretty nasty but it is all bark and very little bite.

I locked out the timing at 32*, wired up a switch to the HEI power wire so he could spin the engine up before energizing the ignition, fixed a couple of vacuum leaks, readjusted the valves (they were way too tight), and tweaked the idle mix screws a bit. This all brought it up to about 9” of idle vacuum at 1000 rpm vs the 5-6” it had before. Now it will haze the tires punching it from 3500rpms in 1st, where it wouldn’t before. Plus now it will actually idle instead of loading up and dying. I could probably fine tune it better, but I don’t have time...and I don’t want to.

This stuff is easy when everything is wrong

[GARY C]

It’s cranking 155-160 on the couple cylinders I checked.

The owner doesn’t know much of anything about it. It sounds pretty nasty but it is all bark and very little bite.

I locked out the timing at 32*, wired up a switch to the HEI power wire so he could spin the engine up before energizing the ignition, fixed a couple of vacuum leaks, readjusted the valves (they were way too tight), and tweaked the idle mix screws a bit. This all brought it up to about 9” of idle vacuum at 1000 rpm vs the 5-6” it had before. Now it will haze the tires punching it from 3500rpms in 1st, where it wouldn’t before. Plus now it will actually idle instead of loading up and dying. I could probably fine tune it better, but I don’t have time...and I don’t want to.

This stuff is easy when everything is wrong

On my Elcamino motor I used 1 light and one medium spring for the weights, set the total at 36 and then used an adjustable vac advance to get around 20 to 22 initial it brought to vac up about 6 points.

Big cam low compression is hard to overcome, sounds like you probably have as good as it gets... unless it turns out the cam is installed retarded.

[CamKing]

Can advancing a cam hurt low end?

Yes. If the issue is reversion, opening the intake valve sooner, will just put more exhaust charge back into the intake.

[SchmidtMotorWorks]

What is the exhaust system?

[travis]

What is the exhaust system?

Looked like basic 1 5/8” long tubes with 3” duals dumped at the rear axle. Flowmaster’s of some sort

[dfarr67]

I had a CC extreme series flat tappet that was ground 4 deg advanced in a GM TBI, tried advancing it- very happy with the enhanced low end- but it broke up on the higher end. Went back to straight up install.

[digger]

Why would it automatically exacerbate reversion? The overlap phase is just shifted w.r.t tdc does that inherently make things worse? Is it because the piston comes even less into play ?
The question was "Can it", not "Does it always"
Reversion is caused by the pressure below the intake valve, being higher then the pressure above the intake valve, when it starts to open.
If this issue is caused by a restrictive exhaust port, header, or not enough lift/duration, opening the exhaust valve earlier will not help lower the pressure during overlap. In this case, opening the intake sooner will just cause more reversion, until the piston drops the pressure in the cylinder(after TDC)

[BOOT]

Maybe try a shear plate