Ok cam just arrived,was using 236 248 114 solid rollor 1'' base circle. Checked new cam 224 236 114 it looked a little smaller its .9'' mad: will the .1 really mess up geometry of rockers originally perfect I set them up with the litlle plastic checker and bought the right pushrods. I don't want to buy another set unless I have to but now they are 0.10 too short should I worry

John Carpico

 

You definately need to check the pushrod length now.

You might also want to look at 3/8 pushrods with a SR cam.

Bret

 

I am using comp cams magnum pushrods, problem is I know even If I use thinner head gasket the pushrods are .09 shorter than ideal length: is this acceptable.

John Carpico

 

Um...

..what Bret said...

 

Surprised no one said this, same as Bret said though, ALWAYS check the pushrod length no matter what, valvetrain geometry is a vital part of engines performance, off a little bit wont "hurt" anything, but you could be missing out on quite a bit of power.

jon

 

Thanks Jon always do check, just sometimes the only way to get perfect geometry is with a custom pushrod right now using an 8'' comp cam pushrod, next step up is 8.150. So with shelf pushrods I am at least .065 to .090 to short or .085 to .060 to long if I tep up to 8.150.

The question I was asking is is this OK or should I buy custom pushrods. Most guys buy an aftermarket cam and never check the base circle, so there must be a + - to optimum.

John

 

I think I would go custom. Just MO, but seems like that would be the smart thing??

 

John: I'm confused. If you haven't checked the new combo how do you know what the exact length you need is? Comp Cams catalog shows the "Hi-Tech" PR in 8.000", 8.025", 8.050", etc. These are better than the "Magnum" line and are ~$40 more expensive/set.

Rich Krause

 

I know my old combo and I was just doing math with new parts.
Guess I should have known comp would have a pushrod somewhere that would be right.

Is .09 to .065 to far off has anyone run into problems or broken anything being this far out, just didn't want to spend any more money on this short since I will probably run hyd next shortblock.

John

 

How do the lobe lifts compare on the 2 cams? To get more lift you may need the smaller base circle. The lobe can't stick above the cam journal! Most custom cams I've seen have the top of the lobe very close to journal diameter to keep the base circle as large as possible.

2 times (lobe lift + half the BC) would be the max "diameter" of the cam lobe. Examples:

2 (.330 + .500) = 1.660

2 (.380 + .450) = 1.660

In other words, that extra .050 lobe lift requires a .100 smaller base circle diameter.

My $.02