I have heard it mentioned before, that specific standard or large base circle cam durations change when the same cam profile is applied to small base circle cams. I am thinking in terms of circumfrence, circle is smaller , does the lobe become more agressive to compensate this smaller circle? Anyone ever notice or witness this? Did I express this term correctly?

Don, as I understand it, the max lift rate on a flat tappet cam is dependant on both the lifter diameter and the base circle of the cam.

The bigger either is, the faster the valve can lift without the cam running onto the edge of the lifter.

That's why some racers run "mushroom" lifters, and other who must run stock size lifter drill thier smallblocks for big block sized cam bearings.

I don't know if or who any of this affects roller cams.

Remember that the nose of the lobe is always ground just below the bearing size, and the actual lobe lift # is achieved by changing the diameter of the base circle.

You need to go over to Big Brother's, (Team Chevelle's), site and do a search for UDHarold, b/c he has explained this great in past posts!!

He is one GREAT CAM GUY!!!

Read everything he's ever posted and learn MORE than you will remember!!

He's that GOOD, imho!!

pdq67

You need to go over to Big Brother's, (Team Chevelle's), site and do a search for UDHarold, b/c he has explained this great in past posts!!

He is one GREAT CAM GUY!!!

Read everything he's ever posted and learn MORE than you will remember!!

He's that GOOD, imho!!

pdq67

Big Brother is the one who mentioned it to me and is cutting a small base circle for me. But I am having doubts about it as I am thinking this is not the thing to do, but I am sure he would not steer me wrong. I placed my order about a month ago and he was having core availablilty issues. Hope he has gotten on the other side of that now. I just got an email from dacaman over on chevelle board, he said he did the grinding for Harold, he said he would check into the issue. Lucky me.

Look, Harold is NOT Big Brother here, only that I call Team Chevelle that b/c their cars are bigger than our cars so YOU got that straight!!

pdq67

pdq, what?

Don I think Jim did a good job of answering your question. I will only add a few things. Coarse you know me, it'll take a few paragraphs:)

This is part of "why" they are doing all the 50 and 55 mm cores. But the other bigger part of that "why" is cam twist. Cam twist is probably not a concern for your average hotrod. It's a Big Boys deal IMO.

Small base circle is not a power killer. Think of how many badass 383's are out there with small base circle cams.

As for the interaction with a roller, my opinion, it is not as severe as on a flat tappet because you theoretically have only a line at your intersection of the lobe and roller. Versus a tappet which as we all know rides the entire flank of the lobe intersecting at whatever may be the highest point below it's plane. Like Jim said, they try to keep the edge of the tappet away from the lobe. That distance from the edge of the lobe is what creates the circle we see on the bottom side of our flat tappet, and the smaller that wear circle the higher the load on the cam lobe and that's what smears cams.

They don't have that concern with a roller. Rollers are acceleration limited if I remember right, and flat tappet are velocity limited but you need to do some UDHarold searches at the other TC or better yet at Speedtalk.com for the straightup cuz I could very easily have it backerdz:D. Nah, I got it right I just checked.

ft velocity limited= How fast it can go. Expressed in inches per degree... .00705" per °
roller acceleration limited= how fast it can increase velocity

Thanks Tim , Jim, pdq, just recapturing this issue. I have the comp 853 rollers and was running 160# closed pressure on the cam. I need to check to see how close the roller lifter body is ,( the edge) to the cam , when I get it. I am sure all this has been thought of long before I came along.

Don,

I call Team Chevelle's site "Big Brother" only b/c their cars are bigger than our 1st Gen. Camaro Cars is all.

Harold is UDHarold, not "Big Brother".. Unless I miss-read you.. Didn't mean to come on so strong, sorry if I seemed to..

pdq67

PS., and imho, Harold WON'T steer you wrong!

I do question max wanted lift's and the valve spring and guide problems that seem to creep in over time, b/c imo, lift is a secondary power producer. That and you make the cams base circle shaft size smaller and then use Mongo springs on it, I can see torsional twist playing heck w/ the last cylinders lobe timings!! That as well as our oil pump and dizzy both being driven back there too probably don't help matters either.

No thorns here, I am on your page, just need to get cam and trial fit. My cast comp roller is 1.180 id on the lobe base circle, before the ramps. The smaller base circle cams I would guess are .050 smaller? Maybe some where in the .900 range?
All this tells me that my retro link bar lifters will set that unidentified id, lower into lifter and also impact push rod length . I was also concerned about the new angle of the roller lifter body to this new id.
As I said, I just need to get this puppy in my hands and start checking. I did run across a man by Chevelle name, dacaman12, that said he grinds cams for Harold. He was going to check up on the delay and I would bet dollar to donut, that is a 8660 core shortage.
Guess I worry too much.

I was also concerned about the new angle of the roller lifter body to this new id.
Guess I worry too much.



Be same angle huh? Still on the same centerline. Or am I missing something?

Naw you don't worry too much. Heck, thinking ahead is what it's all about.:hurray:

Be same angle huh? Still on the same centerline. Or am I missing something?

Naw you don't worry too much. Heck, thinking ahead is what it's all about.:hurray:

I think this cam will be a 107 ICL . Harold said :

{Don,

I have been replacing the XR282HR with a 282/290 at .006, 231/239 at .050, 156/162 at .200, and .552"/.552" valve lift cam on 110 or 112 LSA.
It has more bottom-end, and more top-end.
The cam would be a CMC 8660 steel billet with the EverWear Gear, which has given us no trouble since 2003.
Cost is $350, and this would be a small base circle cam, unless you have stock 400 rods, which clear regular base circles.}

So , I will go with it and just have to check stuff , like I normally do.

Is this going in the 306 in your signature Don?

si, guess that will have to change, but at least I have the ce block .