I seen this article recently & thought it was worth sharing.

http://www.enginebuildermag.com/Arti..._criteria.aspx

 

That's a good one. Thanks for posting it.

 

I agree and it further backs up my reason for doing custom cams. Not only are they not much more but then you get what will really work best.

I normally reduce lobe sep as the article says. That coupled with a bit less overall duration does 2 things. Gives you the idle you want (something you can hear) and makes the cam more efficient in the rpm range most used for the street, 2000-4000rpm. Also solidifies my many statements about Mondello/Engle cams. Their Olds grinds are no different than their ones for Fords or Chevys. Which do you think they still sell more off? They didn't optimize the grinds for Olds, I assure you of that.

IMO spend the extra $15.00 or so and have one done if you can't find the one you need off the shelf.

 

I guess that is the reason I had really good luck with the Mondello/Engle cams with my SBs. All had 108 LCAs with a little less duration and more lift than other companies. I saw this theory work very well in a 460 Ford. That thing was a real monster on the street. The Comp Cam in my stroker has a 108 LCA Some builders would go with a 110 or 112. As I'm sure you know Mark, a guy can't just look at "on the surface specs". You have @.050 specs, some are @ .006 and etc. Then you have specs at .200. It all has how long the valve is open and when in the cycle. Then how fast it opens and closes and the list goes on. So anybody out there should talk to a cam grinder when doing a motor. Joggs and Scummit just don't cut it.

Ooops I kinda got carried away

 

Agreed. I think most would go with the 110 or 112 because of the reasons given in the article, and maybe cuz they just don't know any better.

The point here is just what Nick said. Talk to the cam grinders themselves, the guys who are at the track, that talk to the racers and have the knowledge you need. Those are the guys I talk to. They'll talk to all of you too.

 

Oops my cam is a 108, not a 106. I corrected it in that last post.

 

I did not realize that the difference was that small. Where do you get yours ground?

 

The last one I did was from Lunati and they charged $15.00 extra. Had it in a week.
I think Comp charges about the same and they claim 2 day turn around.

The lower lift/duration stuff is probably fine but once you get to a hotter street or street strip for these prices why buy one off the shelf?

 

tx for that --I looked at who was commenting on this and tucked it away in "my favorites."
MIKE

 

I'm happy to help out in any way. It is hard being an engine builder to watch people make the same mistakes over & over. Knowledge is power & after all we ALL want more of that -- right. HAPPY MOTORING

 

Thanks for posting, Very interesting

 

It's an okay article, but you'll find that the guys most successful at specing cams look at LCA (or LSA) as the last parameter they calculate. You optimize the 4 valve timing events, and then look at the big picture.

When we did a custom cam for mine, I talked to BTR on the phone several times about where EVO and IVC was going to be. EVO has been tagged as the most important event by several cam grinders. IVC tends to be right up there with it. Bill explained a lot about his philosophy in the exhaust timing that makes sense.

If you hold intake lobe centerline (ICL) constant and change your LSA, you are really just moving exhaust valve timing events. Need to consider what the motor wants/needs for what you are trying to accomplish.

 

I like my exhaust duration to be 5 points higher than my intake duration. On a small valve iron head.

The idea is to get 100+% volumetric efficiency. I don't care if your heads flow 400 cfm.
If your events are not right, your efficiency goes down.

 

Why 5?

 

I think it's a good starting point to begin optimizing an Olds motor's valve events at.
No concrete mathematical reasoning, just my own personal hunch.
I had a 9:1 455 with Ga heads that I put a comp270H into that went 13.48.
I switched it out for a 262XE, and it went 13.17
It's my personal belief that the cylinders filled more efficiently with the difference of valve events.
It's all about the perfect valve timing for the best efficiency. Unfortunately, every motor is it's own entity, and will need to be tweaked back and forth to get the most efficiency.
Every little thing can be figured out with mathematics, but since there are so many variables and unknowns, I tend to use the trial and error method.

I wish I could grind 25 cams for each motor I put together, and try them all to get the maximum output for the application, but I'd have to win the lotto first.

 

Until you have over 100% volumetric efficiency, there's always more in it.