Box Stock

thoughts on a cam grind

S

subbietjw

Member
.275 lift 230 duration with a high lc... Im wondering with a short duration and a high lc would exel/torque pick up? I want to think the short duration but a high lc would have a high vaccume level? It would snap open hold there longer then slap closed like a drag stile cam with out the high rpm... What's your guys thoughts?
 
High Lobe Centerline?... As in how high? If you're talking about a high lobe separation, I ground one at 115 to see what it would do. It was pathetic to say the least. No power at all.
 
Yes the center line on the lobe... At least I think it would be referred to as center line? (The top of the lobe where the valve is held at max lift) to make that area larger...
 
subbietjw said:
Yes the center line on the lobe... At least I think it would be referred to as center line? (The top of the lobe where the valve is held at max lift) to make that area larger...
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That would be the nose of the cam.
some take the 356 and flatten the nose for that effect.
dyno cams would be your best source for info on that effect.
 
I'm just wondering what a cam like that would run like being a short duration and a longer time frame at max lift? I love my bm Jr! Fits my rpm range spot on. But it could still use more power for me... I know isky does it in a .310 lift... But wonder how it would run with more time at max lift?
 
What you're describing sounds to me like the NR 274-0207. It is a square lobe cam that has a lot of duration at max lift. It's notorious for being a hard pulling cam, well suited for short tracks.
 
I have the .252 lift from NR and it is ground that way and I did well with it this year on short track. It does pull hard.
 
mater said:
I have the .252 lift from NR and it is ground that way and I did well with it this year on short track. It does pull hard.
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That's a great little short track cam NR252-0207 . Power comes in early . If U like the 252 try the NR274-0207 or throw some ratio rockers on that 252 bad boy. ..
 
Just remember, a big ole fat lobe is aggressive, and will need a good spring package to turn rpms.. and if you put ratio rockers, it makes it more aggressive..
 
That's the catch I'm not running a short track... I'm running it on a sprint course with a 18-60 gear set... It's fast! But because of the large gear set a box stock will out pull me off a corner... But not once I have momentum.. I'll walk away! Trying to find a way to keep rpms down but have enough force/tq to twist a big gear...
 
Keep in mind a box stock will be on a 15-60 something gear set. So its easier for then to get off the corner but fall off on the straight. Where I just get going! It's tough to build around a stock rod. Limited rpms but you can lay down some power on a budget
 
subbietjw said:
That's the catch I'm not running a short track... I'm running it on a sprint course with a 18-60 gear set... It's fast! But because of the large gear set a box stock will out pull me off a corner... But not once I have momentum.. I'll walk away! Trying to find a way to keep rpms down but have enough force/tq to twist a big gear...
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Where is the intake center position on the cam you have in it.. move it down 4 to 6 degrees.. (I wouldn't go under 101 tho)
 
subbietjw said:
I'm just wondering what a cam like that would run like being a short duration and a longer time frame at max lift?
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The cam you're describing isn't really a short duration cam. It could be kinda low @ .050, but it's going to be high @ .200". That means fast ramp rates and square lobes.. Which like youngengines already mentioned is hard on the valve train and requires a good spring to control.
 
Even with the black mamba Jr I have now. I think the 37 lbs springs would be a better fit over the 26lbs springs isky calls for... In my build the cam will run 6500-6700 but the springs go soft after 2 or 3 days..
 
Having such a short rpm range and such a big gear set I have to make the most out of each explosion. Granted I could still do port work and easily see more power! But in prevous build like this I've seen more power an had to compensate with a larger gear to stay in the rpm range. So the power just turned into more top end... The only think I can think of would be a different stile cam? My thought is it would rase the amount of fuel/air allowed in and still keep rpm down with the over all short duration? But I could be wrong? With the high duration at .200 and over it may just move the power higher and into an rpm range out side of what the stock rod will handle? Idk...
 
Bigger valve? More flow at a given lift and duration? IDK?
A clone slapper. Push rod containment. ?? Valve stops in the retainers? Over rocker springs?
 
Since you have a flat faced follower (lifter) you are acceleration limited on the cam by the diameter of the follower face. You will end up reducing max lift in order to max out the acceleration of the cam. By doing so you put more emphasis on the low and mid lift ( 1/3-2/3 max lift) flow of the head. Big valves and seats taliored to low loft help here. Lobe separation in the 112-ish range is fine with decent amount of overlap and an early IVC. This is really what you want if you need a stump pulling engine, especially with no induction tuning. Keep the valvetrain light and stiff.
 
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