I'm considering having my roller cam reground.

I am running an Isky single pattern mechanical roller now and was thinking about having the exhaust side reground for a little more duration and lift.

Current cam: 290/248@.050/.602" lift
New cam :290/290 /248 & 252 @.050/.602"&.646"

I know that on the exhaust side that I will automatically reduce my v-p clearance by .044",(.646-.602) but how much reduction will there be with the additional 4 degrees?

I am a little limited on how much v-p I have so I want to make sure before I regrind the cam.
Thanks in advance.

Don't know but I think you are confusing max. lift with the piston down in the hole at max. suck vs. tdc v/p clearance.

B/c I really don't think it will change at all if you don't advance or retard your cam so that you actually change it's lifting movements vs. the pistons. Use say 30 degrees both before and after tdc if you check timing vs. lift between there.

And I see you are only changing the exhaust by 4 degrees which increased it 2 degrees which to me isn't much... You should be picking up the other 2 degrees on the closing side..

Anybody around that knows more then this, please jump right in!!

pdq67

Yes please others jump in. When in comes to talking about camshaft operation in detail, the old brain gets a little overloaded. :confused: graemlins/clonk.gif

Originally posted by 71454Chevelle:
I'm considering having my roller cam reground.

I am running an Isky single pattern mechanical roller now and was thinking about having the exhaust side reground for a little more duration and lift.

Current cam: 290/248@.050/.602" lift
New cam :290/290 /248 & 252 @.050/.602"&.646"

I know that on the exhaust side that I will automatically reduce my v-p clearance by .044",(.646-.602) but how much reduction will there be with the additional 4 degrees?

I am a little limited on how much v-p I have so I want to make sure before I regrind the cam.
Thanks in advance. ==
Darren,
Max lift has nothing to do with p/v clearance other than the lift may be a bit more during valve opening & closing.
Duration & lobe seperation are far more important than total lift.
The more duration and or the tighter the separation angle the further the valves are open around TDC overlap.
The valves get close to the piston at overlap when the exhaust valve is closing & the intake valve is opening.
Unless you are very tight now changing the exhaust lobe by 4 degrees should not cause a problem unless it is all on the closing side of the lobe.
Do you know what your clearance is now?

Mike,
The only thing that I would change would be the exhaust lobe. When I installed the cam the v-p clearance was .110" intake and .160" on the exhaust.

I seem to be a little slow, but I guess I don't really understand why if you increased the lift by .044" why the v-p clearance would not decrease the same amount?

I have not yet called Ron (at Isky) on a price and I thought that you delt alot in Isky stuff, do you know what they may charge to regrind a cam?

It's because the piston is "chasing" the exhaust valve as it's closing. The minimum clearance on the exh valve occurs before the piston reaches TDC. With .160 exh valve clearance you should be plenty good only changing duration 4 degrees. I have .110 exh clearance which I consider close to the minimum for a street engine. You can advance the cam more to get more exh valve clearance if necessary. This closes the exh valve sooner and "gets it out of the way" more as the piston is rising. Right Mike? Sorry if I butted in.

The .160" clearance is where I am at now with 248 deg and .602" lift. So with the added lift of .044" and 4 degrees (252 deg and .646" lift on the exhaust) you think I would be okay?

The cam is ground with a 110deg lobe sep and 4 deg advance. I don't know if I want to advance it any more, I have always heard (except for Harolds cams) that you don't want to go more than 4 deg advance.

When is it too much advance?

I don't think you'll have anywhere near .044 less piston to valve clearance. You shouldn't have to advance it. I've always heard from .100 to .120 is the minimum on the exhaust side. I'll guess you'll end up with around .135 with the new cam specs. I wouldn't advance it any more than recommended unless you want more bottom end power at the expense of top end. I'm sure Mike has much more experience at this though.

Thanks Von smile.gif

Darren,
The reason total valve lift isn't as important is because it is 180 degrees away from where the valves get close to the piston.
The pistons & valves get close right around TDC overlap when you are on the opening part of the intake & the closing part of the exhaust lobes & not any where near max lift or highest part of the lobe
And Von is right with that much clearance you should be fine.
I have never had a cam reground by Isky so I don't know what they charge. Never even asked if they did it ;)