T&D 572-13 rockers, how high on intake ratio?

I am looking at going to -13 heads, 2.35 stainless valves, and am considering just how high a ratio I can go with them . 1.8 intake ratio would put me at . 900 net lift. My Jesel rockers are 1.7, so I will be increasing the net lift by . 051. Cam is a stock core size inverted flank from Jones. Your experiences?

For a race engine you should use the rocker arm ratio that most race lobes are designed for. That way you are in the "sweet spot" when it comes time to spec a race cam. Talk to Dwayne or flip thru some cam lobe catalogs and you'll see that 1.70 or 1.80 are probably the best choice for a big race engine. At least on the intake side. You should be able to get by with less ratio and less spring on the exhaust side.

I ran Jessel 1.7 ratio on my -13 Heads

The cam was spec'd for 1.7 ratio. 1.8 would be a 6 percent increase. Too much, just right, or not enough?
Wish I had a spintron!

What lift did you have? Many runs before maintanance?

I would be talking with Mike Jones. He designs his desired valve motion curve and works backwards. If you've told him you are running a 1.7:1 rocker, he would have worked it all around that.

I had the 572-13's on a 572" alum 91 pump gas street friendly motor, and I believe it had JESEL 1.7's with a soft kitty-kat baby cam; everything worked together as a unit for the best outcome; built by Best Machine and making about 760HP/7-something TQ IIRC. Checked lash once and never had to touch it again while I owned it. Put over 3k street miles on it and about 15-20 passes.

It's about finding what you can do with the architecture you're given. There's no X+Y=Z in this. A particular ratio and lobe design will run really good in one engine, and in the other completely unravel. I experienced this first-hand with my dry-sump alum 412" Yates headed Windsor from years ago. It was a nightmare until I spent some time in conversations with Billy Glidden who helped me get things changed around and finally resolved. After that I had no further issues at 9200 RPM....and.....it was ridin'..........with minimal maintenance.

So while discussing what might be best, high ratio/low lift or low ratio/high lift, on first-hand ratios are just numbers by themselves. What might be considered low is high for someone else's experiences, design and operating conditions and vise versa. With that said, to simply grab some numbers toward the extreme of one end or the other is possibly going to lead to disaster, or potentially no improvement vs some kind of noticeable performance gain. Sometimes gains do not overcome the control issues they create. I would suffice to say most high end engine builders tend to walk the middle ground of lobe lift that retains a decent base circle and a ratio that provides the max lift the engine needs based on valve diameter, rpm etc. Controlling valve events and enhancing area under the curve while maintaining valve train stability are big factors in maximizing engine performance.

In the end, race engines are all about compromise, top to bottom. The real job is to manipulate the compromise to the limit and turn it into success. But like Alan (LA360) said, contact Mike Jones.

Wes

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Hey Wes, how ya been? And thanks for bringing some clarity to my situation.

Hey Greg. Doing well for the most part. About to launch the new car shortly. I can’t wait! Hope all is well with you/family. I’ll give you a shout soon to catch up! It’s been a minute buddy!

Two major considerations come to mind. First as you increase the ratio, you're going to decrease the strength of the back side of the rocker. This would be a good question to ask the rocker manufacturer. Also, the stock size cam cores have a point where they become flexy and can/will break. Maybe Jones can shed some light on where the limits are for you.

Sean, your comment and others have led me to stay with the ratio the cam is cut for. .510 intakes, 1.7 ratio . 019 lash. Net lift . 848, right at the point Indy said to end up. They actually said . 825 would get it done. Others may have gone to more lift, but the stock diameter bearing cam I have shows lash change on the base circle of . 006 as checked by checking every five degrees around the base circle. I would like to see this at 7500 rpm. I am sure it would be considerably worse.
WES, looking forward for a chance to catch up!