I took a digital caliper and measured my old stock cam and my new custom ground cam. I measured each lobe down the middle for both base circle and max lobe height. I'm a bit concerned with the amount of variation I am seeing compared to the stock cam, so I thought I'd ask for your expert opinions.

The stock 2002 cam's base circles were all within .0005" of each other (1.548-1.5485), and the lobe lifts were within .001" for both the intake & exhaust. A noticable pattern shows the different intake & exhaust lobes, granted they have a more significant difference in lift (.274 versus .280) than my custom @ 0.597 / 0.598.

I measured the new custom cam, and am seeing base lobe variations from 1.4440 to 1.4545, and max lift variation from 1.7965 to 1.8075. Is this normal, or how should I compensate if at all?

Assuming the lobes are concentric and using stock rockers, the range in pushrod lift is from .597" to .603". With LS7 lifters, the preferred preload is 2.09mm (0.0822"). Any worries with the +-0.10mm variance?

Measured in pairs from the end with the cam gear dowel (in pairs, not by cylinder):

Pair L/R Base Max
1 L 1.4545 1.8075
1 R 1.4470 1.7990
2 L 1.4500 1.8040
2 R 1.4540 1.8060
3 L 1.4510 1.8020
3 R 1.4475 1.8000
4 L 1.4485 1.8000
4 R 1.4510 1.8030
5 L 1.4520 1.8030
5 R 1.4440 1.7965
6 L 1.4485 1.8030
6 R 1.4495 1.8030
7 L 1.4490 1.8010
7 R 1.4475 1.8000
8 L 1.4490 1.8020
8 R 1.4475 1.8000

As a reference, here are the 70k mile stock cam's lobe lifts (the last lobe had visible wear):


1.8225
1.8280
1.8285
1.8225
1.8230
1.8285
1.8285
1.8225
1.8230
1.8290
1.8290
1.8225
1.8230
1.8285
1.8285
1.8215

I do have a PR checker and intend to measure once assembled. Any input is appreciated.

Todd

 

You need to understand what specs/tolerances the cam supplier is manufacturing to. Untill you know that, all you have is a disparity between the stock and aftermarket cam. I would give the cam vendor a call.

 

All depends on WHO is the cam grinder--Is it a re-grind or a new billet piece ?---Re-grinds are cheaper but you get what you pay for---You can't go wrong with anything from Comp--
Comp also grinds 75% of other smaller manufacturers cams anyway--major cam companies like Crane Lunati all do there own stuff--Shops that specialise in LS engines with their own custom grind were most likely ground by Comp as well----
As far as variances there isn't much you can do to compensate And I doubt it makes much differance anyway unless you are building an all out race only car with engine rule limits---

 

I'd be interested to know what the variation is from the center line of the cam to the base circle for each lobe.

 

Fine

Buy 4 identical cams, measure all of them. Pick the one with the best or least variance

Send the other three back

 

Sent message to Comp for their tolerances. Will post back when I get their response.

Brand new, ground by Comp for EPS. It's not a race build, just a fair weather DD. I'm just looking for opinions from other people that have ordered custom cams, and if this variance is to be expected. Considering the OEM is pretty much nuts-on.

I laid a straight-edge across the journals, then used a depth gauge to compare the distance to the base circles of 1L and 1R. The difference is somewhere in the 0.006-0.008 range, roughly half the variation since I was really checking radius.

Todd

 

I had this conversation with Geoff @ EPS and Patrick Guerra. You would be supprised at the torrerance they (Comp) use. If you want to know what you got find someone with a cam pro like Geoff and have it measured. I had a custom cam ground then had it ran on a cam pro to see what I got. I remember being very supprised in the results. Guys like these two know this and figure this in when they spec a cam.

You might have a bad cam but you need to have Geoff measure it.

 

Thanks for the feedback guys. I guess it is par for the course.

Patrick responded and said he rarely sees more than 0.005 lift variance from Comp.

Comp replied, and lift tolerance is +0.003", -0.004". The base circles have no range, as they will vary based on the amount of grinding they have to do to achieve lift.

I asked Geoff about measuring before sending it to me, and he said rarely 1:1000 were bad and that it was a waste of time.



One other quote while reading the Comp faqs (http://www.cpgnation.com/forum/comp-...made-3981.html):

 

what I liked about having it run on his cam pro was it allowed me to dial in the valve timing when I installed the cam to exactly the way Patrick designed the cam. I used the Cloyes adjustable timing set so this made it easy.