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AKRA clone cam question

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shoestring19

Member
Cam Question..AKRA clone



was checking the lift at the valve on my sons kart.. on the intake I believe your allowed .238 and on the exhaust.. .242. on the intake im only getting .230 and .232 on the exhaust.. haven't checked duration. my question is would it be worth the effort to try and get the extra lift? running locally in the purple plate class. Thanks in advance
 
I would think if the engine came from a builder that way, he would have called the builder about that issue. I would try to get the lift closer to the max, but leave yourself some room for wear. If it came from a builder that way, call your builder and ask him if that is where its meant to be or if you need to get it up to spec. Some use a cam that is actually designed with less lift, like the CL1-M cam that dyno cams sells, before we were allowed to file the tips of the rocker arm.
 
W5R said:
I would think if the engine came from a builder that way, he would have called the builder about that issue. I would try to get the lift closer to the max, but leave yourself some room for wear. If it came from a builder that way, call your builder and ask him if that is where its meant to be or if you need to get it up to spec. Some use a cam that is actually designed with less lift, like the CL1-M cam that dyno cams sells, before we were allowed to file the tips of the rocker arm.
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Zach, do you go through very many big name builder engines?
 
What Scott (Hothead) was saying is trying to get the extra few thousands lift will not help. I set the the lift on all our engines at .234 In and .238 Ex because I have seen as much as .003 more lift after the engine is run a time or two. If you set the lift right at the max you run a good chance of failing the lift check.
 
rebsfan4 said:
Zach, do you go through very many big name builder engines?
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Can we keep this on topic for once instead of dragging someone else's thread way off, just one time Bryan? The guy asked for help or opinions on what he should do, he doesnt care how many engines someone has been thru from a big name builder, im sure, because that is not going to help him any.

If it came from a builder, that builder is the one that this question needs to be asked to because he may have a reason for the lift being where it is. If its just a kit engine or one that the man has built himself, then getting the lift up closer to the max will help more than hurt performance most likely, especially with his lift being .008-.010" below the max. If a little lift didnt show any gains, we wouldnt have a max and min check on it would we?
 
W5R said:
Can we keep this on topic for once instead of dragging someone else's thread way off, just one time Bryan? The guy asked for help or opinions on what he should do, he doesnt care how many engines someone has been thru from a big name builder, im sure, because that is not going to help him any.

If it came from a builder, that builder is the one that this question needs to be asked to because he may have a reason for the lift being where it is. If its just a kit engine or one that the man has built himself, then getting the lift up closer to the max will help more than hurt performance most likely, especially with his lift being .008-.010" below the max. If a little lift didnt show any gains, we wouldnt have a max and min check on it would we?
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It's not off topic. You made a suggestion to him to do something. My question to you has to do directly with what I see ALL the time in the tech room. Hense my reason for asking if it came from a builder and if it did for him to leave it alone.

Also he stated he checked his lift "at the valve". There is no minimum measurement for that. That's check is off the pushrod.

I'd be willing to bet he doesn't see much compression on his engine when it's cold, if it's from a builder.
 
What most are figuring out now with help from technology from the cup guys is the right combination of valves and rockers will cut friction and make more horsepower in all classes with less lift. With the 10.8 springs your not touching the top of the lobe over a range at higher rpms. I've seen adult engines with much lower max lift than listed make great numbers on the dyno. I'll show some test on our webpage when I have time this week.
Www.racingcarb.com
 
Racingcarb.com said:
What most are figuring out now with help from technology from the cup guys is the right combination of valves and rockers will cut friction and make more horsepower in all classes with less lift. With the 10.8 springs your not touching the top of the lobe over a range at higher rpms. I've seen adult engines with much lower max lift than listed make great numbers on the dyno. I'll show some test on our webpage when I have time this week.
Www.racingcarb.com
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Glad you said it Eric. Seeing it all the time.
 
Yes the engine if from a well known builder. Junior Sands. Not downing the engine at all!! Its actually a beast for a purple plate, as long as you hit the rpm sweet spot.
 
shoestring19 said:
Yes the engine if from a well known builder. Junior Sands. Not downing the engine at all!! Its actually a beast for a purple plate, as long as you hit the rpm sweet spot.
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Don't change anything. He knows what Eric is speaking of. Some still do not though. :)
 
Shoestring,
I've dyno'd a couple of sands motors and they're good as I've seen so I'd leave it just as he shipped it. Jr stays on top of whats working.
 

It is a generally accepted engineering principle that in a poppet valve application the maximum flow coefficient is achieved at a lift-valve diameter ratio of approximately .25.

For our application, with a stock intake valve diameter of .982”, maximum flow would be achieved at around .245” lift. Since rules and cam design limit maximum lift to .238”, Stock class Clone engines never achieve the maximum flow coefficient lift (.245” +/- ).

As a side note, lifts greater than .25 valve diameter, actually result in diminishing returns of instantaneous flow capacity .... however the TOTAL flow through the valve will be greater due to the increased duration, or time the valve is above the maximum flow lift.


 
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