Direction on cam choice..............sbc

[statsystems]

let us know statsystems
on those steep seat builds I'm curious
if you went to an IR with say 8 degrees less seat timing and about the same at 200
or
same seat timing and fatter at 200 (would the steep seat still be able to kill the reversion)
or
split the difference and try a 4 degree shorter seat to seat cam
the "wheelbarrow of cams approach"
or
methodology would be to plot the intake opening to see where the reversion starts (lift and degree wheel) then grind the cam to the max to match
an approximation would be to take the head flows and simulate
Randy is on to something and I appreciate his sharing as much as he does.
I would think that mike's computer program would cut down the number of cams in the wheelbarrow

I'm just putting the carb together now, so I plan on beating the hell out of it soon.

I'm not sure I have ever seen a SFT cam with an IR but I may be wrong.

Mike, can you do an IR for a SFT cam?

[wyrmrider]

FT oops for you
but if you get your flows , valve weights, springs rockers, max lifts, rod length and all the other questions he asks answered he can maximize your cam
Krooser is running a HFT - ask him Mike said that that master is designed to maximse what the lifter can take without collapse and even a change to 1.6 rockers would upset the applecart
Mike pays attention to little details like that
there is also a thread- maybe even this one, where Mike comments on using a slightly shorter cam, in that case a SFT
have you filled out his cam request form yet on his website?

[Stan Weiss]

let us know statsystems
on those steep seat builds I'm curious
if you went to an IR with say 8 degrees less seat timing and about the same at 200
or
same seat timing and fatter at 200 (would the steep seat still be able to kill the reversion)
or
split the difference and try a 4 degree shorter seat to seat cam
the "wheelbarrow of cams approach"
or
methodology would be to plot the intake opening to see where the reversion starts (lift and degree wheel) then grind the cam to the max to match
an approximation would be to take the head flows and simulate
Randy is on to something and I appreciate his sharing as much as he does.
I would think that mike's computer program would cut down the number of cams in the wheelbarrow

I'm just putting the carb together now, so I plan on beating the hell out of it soon.

I'm not sure I have ever seen a SFT cam with an IR but I may be wrong.

Mike, can you do an IR for a SFT cam?

How would the solid tappet be able the follow the IR?

Stan

[Stan Weiss]

15 or 20 hp for $200 would be the best bang for the buck I have ever heard of.$10 per hp; sign me up, but I down need any more pie in the sky.
Also other cam companies are not claiming 50hp gains.

I think that it is all about the combination that someone has. I have seen people post up their combination and specs for a cam they have laying around, and Mike said that is close enough to what I would do just run it.

Stan

[statsystems]

let us know statsystems
on those steep seat builds I'm curious
if you went to an IR with say 8 degrees less seat timing and about the same at 200
or
same seat timing and fatter at 200 (would the steep seat still be able to kill the reversion)
or
split the difference and try a 4 degree shorter seat to seat cam
the "wheelbarrow of cams approach"
or
methodology would be to plot the intake opening to see where the reversion starts (lift and degree wheel) then grind the cam to the max to match
an approximation would be to take the head flows and simulate
Randy is on to something and I appreciate his sharing as much as he does.
I would think that mike's computer program would cut down the number of cams in the wheelbarrow

I'm just putting the carb together now, so I plan on beating the hell out of it soon.

I'm not sure I have ever seen a SFT cam with an IR but I may be wrong.

Mike, can you do an IR for a SFT cam?

How would the solid tappet be able the follow the IR?

Stan

That was my question. How the hell would a SFT follow the profile? I never saw a IR SFT lobe, but that didn't mean someone didn't do it.

[cgarb]

I made an inverse radius lifter once...lol.

[MadBill]

I'm just putting the carb together now, so I plan on beating the hell out of it soon.

I'm not sure I have ever seen a SFT cam with an IR but I may be wrong.

Mike, can you do an IR for a SFT cam?

How would the solid tappet be able the follow the IR?

Stan

That was my question. How the hell would a SFT follow the profile? I never saw a IR SFT lobe, but that didn't mean someone didn't do it.

It can't. rewguy didn't specify what kind of lifters he was currently running and we all ass-umed (correctly I'm pretty sure) it was a solid roller. The flat tappet reference came from statsystems as highlighted above..

[wyrmrider]

I can't tell if poster is being serious of factious or devils advocate or what
I tend to answer as if it's a serious question
I have no idea at what level a poster is coming from
there are always exceptions like mushrooms, keyed radius tappets or followers etc
Hmmm wonder if we could do an IR for a radius tappet flathead...
back to reality
what are you trying to do OP?

[MadBill]

..there are always exceptions like mushrooms, keyed radius tappets or followers etc.

Ah, but they wouldn't be flat then, would they? (Of course neither are what we call 'flat'; the just have a very large radius...)

[SchmidtMotorWorks]

How would the solid tappet be able the follow the IR?

Stan

He was describing something else.

If you have a flat tappet lobe with flanks that are flat or slightly concave (whatever the grinding wheel allows), the acceleration and jerk are very high in the lower lift range.
If you duplicate the same motion on a roller it will sometimes have a concave flank.

Remember if a roller and a flat are run on the same lobe, the motion of the roller is slower in the lower portion of the lift range.

All that said, there is a lot of variation possible withing the range of concave designs, they are not all alike.

It might be helpful to think of it this way.
Generally (with some exceptions) the curvature of the lobe is an indication of the acceleration:
The more the flank is in the direction of concave the higher the positive acceleration in lower lift.
The smaller the radius of the nose (top lift), the greater the negative acceleration.

[CamKing]

That was my question. How the hell would a SFT follow the profile? I never saw a IR SFT lobe, but that didn't mean someone didn't do it.

My flat tappet profiles don't have an inverse radius, but they are designed the same as my inverse radius rollers.
I design the valve lift curve, and then work back through the valvetrain to generate the lobe shape. When I take my valve lift curve, and generate the lobe for a roller follower, or finger follower, it comes out with an inverse radius. When I generate the lobe for a flat follower, it comes out looking like a normal flat tappet cam.
If I took any of my flat tappet cams, and generated a roller profile to have the exact valve lift curve, it would have an inverse radius.

[statsystems]

That was my question. How the hell would a SFT follow the profile? I never saw a IR SFT lobe, but that didn't mean someone didn't do it.

My flat tappet profiles don't have an inverse radius, but they are designed the same as my inverse radius rollers.
I design the valve lift curve, and then work back through the valvetrain to generate the lobe shape. When I take my valve lift curve, and generate the lobe for a roller follower, or finger follower, it comes out with an inverse radius. When I generate the lobe for a flat follower, it comes out looking like a normal flat tappet cam.
If I took any of my flat tappet cams, and generated a roller profile to have the exact valve lift curve, it would have an inverse radius.

Hmmmmmmm,. I'll have to read this over a few times to let that sink it.

[MadBill]

It's probably an over-simplification (if not just plain wrong), but as I understand it, a flat tappet/lobe can have very high acceleration if desired but is velocity-limited (lift per degree) by the lifter diameter. A conventional roller is acceleration limited in the early going by the grinding wheel diameter precluding the ideal contour. Both it and an IR lobe are limited by the maximum usable pressure angle but they can sustain that acceleration and so reach higher velocity. With shorter duration low lift lobes, acceleration is the predominant factor and so a flat tappet can have more 'area under the curve' than a conventional roller but as the duration (and lift) goes up, the velocity factor becomes more important and the roller starts to shine. I think the benefit of being able to generate an inverse radius is in allowing the roller version to more closely mimic the initial acceleration of a flat tappet while preserving the other benefits of a roller. Of course the same factors are in play on the closing flank, giving more latitude for lots of area under the curve while still providing a soft landing for the valve.

Under this scenario, there is no inherent 'parts breaker' aspect to an IR roller; it just combines much of the best attributes of flat and roller designs. Just as a bad FT profile can be a total failure by say initially slamming into the lifter at almost the OD, creating huge accel and jerk, so a bad IR roller can wipe out parts by for example maxing out the pressure angle at well over 30° and snapping the axle or punching the lifter out the side of the bore.

[DaveMcLain]

It's probably an over-simplification (if not just plain wrong), but as I understand it, a flat tappet/lobe can have very high acceleration if desired but is velocity-limited (lift per degree) by the lifter diameter. A conventional roller is acceleration limited in the early going by the grinding wheel diameter precluding the ideal contour. Both it and an IR lobe are limited by the maximum usable pressure angle but they can sustain that acceleration and so reach higher velocity. With shorter duration low lift lobes, acceleration is the predominant factor and so a flat tappet can have more 'area under the curve' than a conventional roller but as the duration (and lift) goes up, the velocity factor becomes more important and the roller starts to shine. I think the benefit of being able to generate an inverse radius is in allowing the roller version to more closely mimic the initial acceleration of a flat tappet while preserving the other benefits of a roller. Of course the same factors are in play on the closing flank, giving more latitude for lots of area under the curve while still providing a soft landing for the valve.

Under this scenario, there is no inherent 'parts breaker' aspect to an IR roller; it just combines much of the best attributes of flat and roller designs. Just as a bad FT profile can be a total failure by say initially slamming into the lifter at almost the OD, creating huge accel and jerk, so a bad IR roller can wipe out parts by for example maxing out the pressure angle at well over 30° and snapping the axle or punching the lifter out the side of the bore.

That's right. Also I think that just about any roller profile will become inverted if the base circle is reduced far enough from the size where it had a positive flank.

[MadBill]

Here's a cam that's not at risk for that problem!