Camshaft lobe design

[Walter R. Malik]

I would think, but, it might not be true though, that getting the valve area open to be using the choke of the port for its flow velocity at the maximum piston/cylinder demand to maximum piston/cylinder volume is paramount.

[David Redszus]

I would think, but, it might not be true though, that getting the valve area open to be using the choke of the port for its flow velocity at the maximum piston/cylinder demand to maximum piston/cylinder volume is paramount.

I assume you mean that the valve curtain area should be of sufficient area so as not to impede air mass flow at peak piston air demand (or shortly thereafter). That would transfer the flow choke point to the port and not the valve.

But could not the same effect be accomplished by designing an asymmetrical intake lobe with a steeply fronted opening and a shallower closing? Or re-indexing the cam lobe?

But what about the exhaust cam lobe? Exhaust gas mass flow is not dependent upon piston velocity; how should the exhaust lobe differ from the intake lobe?

And...how do upstream and downstream ducting affect cam lobe design?

Remember, lift and duration are still held constant. Since some engine rules limit duration and lift, could not the shape of the cam lobe extract more power if properly designed?

[Walter R. Malik]

I would think, but, it might not be true though, that getting the valve area open to be using the choke of the port for its flow velocity at the maximum piston/cylinder demand to maximum piston/cylinder volume is paramount.

I assume you mean that the valve curtain area should be of sufficient area so as not to impede air mass flow at peak piston air demand (or shortly thereafter). That would transfer the flow choke point to the port and not the valve.

But could not the same effect be accomplished by designing an asymmetrical intake lobe with a steeply fronted opening and a shallower closing? Or re-indexing the cam lobe?

Exactly what I was thinking.

On the exhaust side ... whatever it takes to be "on the port" from just before BDC through maximum piston speed.

This certainly could be all wrong but, that is what I am thinking.

[Racer57]

And...how do upstream and downstream ducting affect cam lobe design?

My $.02 is telling me that up stream and downstream ducting has everything to do with cam lobe design. One would think on the exhaust side as you spoke of that the more restrictive the exhaust the faster you would want to be able to open the valve. You may then possibly be able to open the valve a few degrees later and let the combustion process work longer building more torque while still allowing enough time/area for the combustion gasses to sufficiently "blowdown" the cylinder and push the exhaust past the restriction. I am just thinking out loud here please correct me if iam wrong!

[Frankshaft]

I think the exhaust side is critical. Say you have a n/a spread port BBC, that makes 1300hp. And now you have a 900hp BBC, with a 400 shot of nitrous, for 1300 total hp. How different would the cam be? Assuming similar rpm levels.

[In-Tech]

I agree the exhaust timing is critical and once again is time sensitive vs mass flow. If you are in a limited lift/duration and RPM NA environment, shaping the lobe to tailor can make 3-4% hp, Intake or exhaust. The rest of the world deals with mass flow and time on the exhaust and it gets worse if you have packaging issues as well as a limited exhaust system. IMO

[Frankshaft]

I agree the exhaust timing is critical and once again is time sensitive vs mass flow. If you are in a limited lift/duration and RPM NA environment, shaping the lobe to tailor can make 3-4% hp, Intake or exhaust. The rest of the world deals with mass flow and time on the exhaust and it gets worse if you have packaging issues as well as a limited exhaust system. IMO

Right. I have argued that numerous times with guys that just don't get it. "Why do you have a nitrous cam in your n/a engine?" <<< I do that a lot.

[David Redszus]

The critical duration period for an exhaust cam is from EVO to BDC. At BDC, chamber pressure should be as low as possible in order to reduce exhaust pumping losses.

What defines a "nitrous" cam?

[Frankshaft]

The critical duration period for an exhaust cam is from EVO to BDC. At BDC, chamber pressure should be as low as possible in order to reduce exhaust pumping losses.

What defines a "nitrous" cam?

Right. That's my point above. Generally, most guys think it's wide lobe sep and a ton more exhaust duration compared to the intake side defines a nitrous cam.

[paulzig]

Right. That's my point above. Generally, most guys think it's wide lobe sep and a ton more exhaust duration compared to the intake side defines a nitrous cam.

Have you had something where using this approach on a naturally aspirated engine have achieved good results?

[Frankshaft]

Right. That's my point above. Generally, most guys think it's wide lobe sep and a ton more exhaust duration compared to the intake side defines a nitrous cam.

Have you had something where using this approach on a naturally aspirated engine have achieved good results?

Absolutely. 4.70's at 146+ at 3000 lbs on a 275 radial. N/A ultra street combo. Only one other guy in the country is faster NA than us, and he has literally 4x the money in it, and changes valve springs every 8 passes. We went 3 seasons on the same set. And I would argue we made a lot more passes. 7.20's at 190 in 3500+ ft of air, top sportsman C heads big block Ford, at 2520 lbs, NA, plenty of other examples too. The ultra combo above is apart getting updates. More head work, more intake work, single carb cast manifold. Carb is going back to the carb guy for a few tweaks. New Pistons, more compression, more trick ring stack, etc. Also, new Bullet custom grind 55mm to update the current Bullet custom grind, that was originally a LSM grind. The biggest difference? More exhaust duration and 1.5 degrees more lobe sep. Plus a little more aggressive lobe profile, that will probably drop spring life a little. Also possibly some oiling system changes. Right now, most guys can't believe it still has a melling select oil pump in the pan, wet sump. There is likely 25-30 hp easy in the oiling system without getting crazy. Remember, this is a budget deal.

Forgot to add, we have never been on one of those Super killer tracks at -400 feet like all the hero passes have been made. We will hopefully be in Georgia this fall. If the Pistons show up in time. Diamond screwed up the chamber mold and I had to redo it. That ate up a week and a half.

[Steve.k]

I was wondering as you add lift does this not inherently add duration? How do you control the amount of duration and as you get to a certain amount of lift you have to accept a set amount? Is that the case?

[Stan Weiss]

I was wondering as you add lift does this not inherently add duration? How do you control the amount of duration and as you get to a certain amount of lift you have to accept a set amount? Is that the case?

This is at the valve. The same cam lobe with 1.65:1 and 2.0:1 rocker arm ratio and valve lash adjusted for change. One would have to look at the change in velocity / acceleration / jerk at the valve to see if this is really able to be run.

Stan

_______I__N__T__A__K__E
Rocker_Arm_Ratio_=_1.650_________Valve_Lash_=_0.0210

VALVE_____Lift______Opens___Closes__Duration
_________________Deg_BTDC__Deg_ABDC_____________Area
_________0.00000____47.69_|__84.37_|_312.05_|__61.01
_________0.00600____44.55_|__80.80_|_305.35_|__60.99
_________0.01000____42.73_|__78.67_|_301.39_|__60.98
_________0.02000____38.71_|__73.99_|_292.70_|__60.91
_________0.04000____32.32_|__66.84_|_279.16_|__60.69
_________0.05000____29.68_|__63.94_|_273.61_|__60.56
_________0.10000____18.96_|__52.59_|_251.56_|__59.70
_________0.15000____10.52_|__43.84_|_234.35_|__58.68
_________0.20000_____3.06_|__36.19_|_219.26_|__57.27
_________0.25000____-3.97_|__29.07_|_205.10_|__55.41
_________0.30000___-10.85_|__22.20_|_191.36_|__53.71
_________0.35000___-17.79_|__15.20_|_177.41_|__51.04
_________0.40000___-24.96_|___7.98_|_163.03_|__48.74
_________0.45000___-32.52_|___0.38_|_147.86_|__45.30
_________0.50000___-40.80_|__-7.88_|_131.31_|__41.46
_________0.55000___-50.19_|_-17.26_|_112.55_|__36.16
_________0.60000___-61.45_|_-28.50_|__90.05_|__29.76
_________0.65000___-76.72_|_-43.55_|__59.73_|__20.32


_______I__N__T__A__K__E
Rocker_Arm_Ratio_=_2.000_________Valve_Lash_=_0.0255

VALVE_____Lift______Opens___Closes__Duration
_________________Deg_BTDC__Deg_ABDC_____________Area
_________0.00000____47.69_|__84.37_|_312.06_|__73.95
_________0.00600____45.08_|__81.38_|_306.45_|__73.93
_________0.01000____43.51_|__79.57_|_303.08_|__73.91
_________0.02000____40.03_|__75.53_|_295.56_|__73.83
_________0.04000____34.36_|__69.09_|_283.45_|__73.66
_________0.05000____31.98_|__66.46_|_278.44_|__73.52
_________0.10000____22.33_|__56.13_|_258.46_|__72.82
_________0.15000____14.78_|__48.24_|_243.02_|__71.81
_________0.20000_____8.21_|__41.47_|_229.68_|__70.34
_________0.25000_____2.17_|__35.28_|_217.44_|__68.90
_________0.30000____-3.62_|__29.42_|_205.80_|__67.45
_________0.35000____-9.30_|__23.76_|_194.45_|__65.82
_________0.40000___-14.99_|__18.02_|_183.03_|__63.55
_________0.45000___-20.81_|__12.17_|_171.36_|__60.97
_________0.50000___-26.79_|___6.13_|_159.33_|__58.09
_________0.55000___-33.11_|__-0.21_|_146.68_|__54.91
_________0.60000___-39.93_|__-7.02_|_133.06_|__50.26
_________0.65000___-47.47_|_-14.53_|_118.00_|__45.81
_________0.70000___-56.09_|_-23.13_|_100.77_|__39.68
_________0.75000___-66.47_|_-33.49_|__80.04_|__32.36
_________0.80000___-80.83_|_-47.59_|__51.58_|__21.44

[Steve.k]

Thanks Stan. Quite a difference indeed.

[Walter R. Malik]

Right. That's my point above. Generally, most guys think it's wide lobe sep and a ton more exhaust duration compared to the intake side defines a nitrous cam.

Have you had something where using this approach on a naturally aspirated engine have achieved good results?

NHRA "Pro Stock" engines seem to run pretty well with camshafts similar to that approach. They ARE naturally aspirated with no nitrous.
Again ... that is not what this thread was supposed to be about.