I've read a few articles on what rockers can do (both good and bad), and issues you can run into.

However, many of these articles make some assumptions that the person reading them has a fairly good idea of how these mechanics work. Which I don't.

What I do (think) I understand, is that if rockers with too great of a ratio are used, the pushrods will rub and obviously impact the operation of the engine, and hurt power.

Now, how do you tell what the maximum "safe" ratio is? I don't see a "suggested" or "maximum" rocker ratio listed for my cam (or I'm completely overlooking it, also possible).

Right now I'm running the Comp Cams Pro Magnum 1.5 rollers. Part 1301-16. My cam is listed in the subject line.

Since the engine will (hopefully) be coming out later this year for the EFI swap, I figured it might be a good time to get the heads checked/upgraded, and wanted to ask about the rockers.

I say "checked" because on my left bank, when the throttle is blipped to over 4k and let off quickly, I get an exhaust-back fire. Always just that one bank, and it happens through the entire spark-timing range. I always run 92/93 octane. So I think my exhaust port is floating just a hair. So I might need to step up from the standard Beehive springs that AFR includes with their 1040 heads.

Any thoughts, suggestions, recommendations would be greatly appreciated!

 

1.6 rockers are for guys who want more valve lift without having to swap the cam out

Impact being the operative word ; things BREAK

You are not looking at the rocker ratio as such ; you are looking for the max lift the valve springs on a particular head will handle and work back from there.

You could say get .600 valve lift off a cam with 1.5 rockers ( no binding problems ) or use a smaller lift cam and 1.6's
Same end result ; .600 lift
But if you have the engine out easier to fit a cam with the lift you want and use stock 1.5 geometry

 

Hi Vetteoz,

Thanks for the insight, I guess I knew *a little* more than I thought, I knew it would change lift, essentially giving me a "virtual" bigger cam.

While the engine will be out, it won't be near the place that did the engine work - where-as with the heads, I can have the guy doing the EFI pop them off and ship them to the guy who did the engine work, to have them done.

I guess the question becomes, will more lift, with my head/cam combo, provide worthwhile results?

And again, I'd like to have the heads checked for that possible float issue, so that's why I thought it'd be a good time to get the heads done.

Unless there's more to this than I thought, and the builder would likely need to get his hands on the engine anyway.

Thanks for the input!

 

Dont the lift/duration numbers of the xfi cams assume 1.6 ratio rockers?

 

The max valve lift spec on XFI cams is calculated using 1.6 ratio rockers, I believe (somebody double check me on that).

AFR heads should have AMPLE pushrod room to prevent binding. Valve spring coil bind distance, too.

 

InfernalVortex, Damon - thank you both. I wasn't sure about that either.

I tried looking up the information, but wasn't have much luck on "definitive" information - save for trying to contact compcams, which of course is always something I could do.

I guess ultimately the question is... if your components can support it, and you don't want to bother with a cam swap, is "bigger always better"?

This will be for a naturally aspirated car with a manual transmission, and eventually running a modest amount of nitrous.

Thanks guys!

 

That is correct. I've had 2 XFI series cams and they are calculated based on 1.6 ratio rockers.

 

Great! Thank you for the confirmation. I'm putting that on the list! I appreciate it everyone!