Yes, I can adjust accordingly, but it does affect peak torque. ...then of course HP.

Yes, for example, you can take away 5% of the lift, and give it 5% more duration and the power will change very little, 3 or 4 #/ft.

Slower stuff lends to making better power on a combination that is over headed or well matched for the CID and RPM range. Aggressive stuff for poor flowing heads mated to a CID, under headed combos for high rpm, or restricted inlet stuff such as 2 barrel engines. It's not that I prefer one or the other, I use what maximizes my customers combination. Now I am a firm believe in asymetrical lobes.

Chris

 

Ah yes. I can relate. I only got 6 pistons notched this weekend 'cuz the chickens needed a coop

 

Whoa... whoa... whoa there Nelly...

Stop it Chris...

You're stepping on some thin ice here with that info....

Next you'll be talking about reducing rocker ratios and varying the ramps speeds on intake and exhaust lobes...

Site sponsors may get upset with you...

BTW... check the cylinder head discussion on HC50. A lot of flow bench myths are being busted by our buddy Jay... Some people are just finding out that flow numbers are only a small part of cylinder head and engine performance.. Image that!

Sorry Denz... Back to the cam discussion....

Rump.. rump...rumpety.. rump...

Ed

 

You mean kinda like my 1.2 ratio rockers run on some .425lobe lift profiles for .500" rule classes? Hell Ed BMW has been doing it for years, wear do you think I cam up with it.
Mr. Allen, I have tried to get a hold of him. . .what site?

Chris

 

A little history--

We wrote the app around the calculations/formulae that a physicist buddy of mine uses during engine building for creating piston velocity and acceleration curves. It was easy to toss max CFM into the mix. We're now in the process of polishing the GUI, adding calculations for average cfm, and adding the mass to the rotating assembly.

 

J-Rod, tell me when you want me to discuss the negatives of CNC's profiles. . .that's a hole another ball of wax. . .you better PM me on that one.

Chris

 

I had another thought on the whole "how do you tell an engine is overcammed?" question. This isn't directly related, but close. Just another part of analyzing performance.

If you look at a dyno sheet, engine or chassis, you'll notice that eventually torque begins to drop off. Not necessarily before the 5252 rpm crossing point, but at some point the torque ceases to rise and begins a slow or sometimes sharp descent.

As soon as your torque begins to decrease, you are no longer sufficiently filling the the cylinder with air. Cylinder pressure drops and less force is pushing down the piston. Consider this when you're looking at any dyno sheet. It can tell you a whole lot.

 

One of the things you guys are hung up on is the 279CFM flow rating. You are assuming that that is what is flowing through the port. It isn't, the 279 CFM is determined at a 28"H2O constant pressure drop across the port. (Flowing ports at 28" H2O started years ago due to limits of flow on inexpensive flow boxes that became available at reasonable prices to raceers.)That means that (Assuming atmos. press. is 30.00" Hg) your manifold pressure at WOT would be less than 28"Hg of manifold pressure. It isn't and can't be as you approach 100% VE. At 100% VE manifold pressure is 30.00"Hg. Average pressure drop at WOT across the port is on the order of 8"H2O giving a manifold pressure on the order of 29.6" Hg. With only a small amount of suck across the port on average, actual airflow will be on the order of your 80-85 CFM. Keep in mind that I am using both H2O measurements and Hg measurements and I'm talking about manifold pressure (ga) not manifold vacuum.

 

I'm glad you're here Tahoe. Good input as always!

Welcome again.

 

Hey DenzSS, the torque curve dropping off could be any number of things such as bad cylinder head flow,poor exhaust,too weak of valvesprings,intake restrictions,poor tuning, ignition timing,a bad combination of performance part chosen, also it could be a poor camshaft design.I don't follow your last comment, usually a smaller cam will produce more torque at lower RPM's say peak at 4200 RPM'S a larger cam will usullly make less torque down low but the torque curves of each cam will cross probably above the peak4200 RPM of the first cam.A lot of bigger cams will never match the torque of the smaller cam but carry less torque to a higher RPM,I mean they have more torque than the smaller cam does at a higher RPM but the torque peak will still be less than smaller cam.Bigger cam makes more HP because torque x RPM=hp .So explain what you meant?

 

I think this is an excellent thread but I would really appreciate it if someone shared the formula that shows the ~280 cfm in required for the cylinder head at 6800 rpm.

Thanks

 

An awesome thread. I'm really monitoring this one

 

Well, I should have stated my assumption.

Assumption: The engine is correctly tuned.

Correct. If you'll notice, all of those result in decreased cylinder pressure. If you have a loss of torque, less force is pushing on the piston. Since the only thing we have to work with is cylinder pressure (combustion), a decrease in torque is caused by a decrease in cylinder pressure. The decrease in cylinder pressure may be caused by a number of things, including those you mentioned. A good camshaft design takes all intake and exhaust limitations into consideration and works around them as much as possible.

Which implicitly states: If ft-lb of torque is constant, if you double rpm you double the horsepower. If rpm is constant, if you double ft-lb of torque you double horsepower.

Your statement isn't necessarily correct. It needs a few assumptions as well.

 

Me too 99BlackbirdT/A,I calculated that it takes around 85 CFM to fill one cylinder at 6800RPM I think someone else did too, so I don't know how DenzSS came up with 280 but I think it has to do with cam and valve timing.Thanks for info on intke, I'll call Steve today!

 

What part is not correct?

 

We're going to try to get up the formula this week. I'll probably have to write it out by hand and scan it in.

That is the part that is incorrect. Bigger does not equal more horsepower. Correct size = more horsepower.

You can cost yourself more power by having "too much" camshaft that you can by having "too little". The current very large camshafts on engines with stock heads produce high amounts of peak horsepower because they are "camming around" the cylinder head restrictions. I don't agree with their approach, because they basically dyno queen camshafts. To be successful at the track, they have to be used in lightweight cars with a hefty gear in them that are willing to spin some rpm. Tight power band and a lot of gear to get them off the line because they make little in the way of torque. They make horsepower by dropping the cylinder pressure at a slower rate than the rpm increase.

A correct camshaft for the application will make horsepower and torque throughout its entire range.

 

Maybe we should state a "Custom Matched" camshaft= More Power. But don't get hung up on HP, its theory, torque is what is measured. HP just sell parts.

Chris

 

Yup.

We could always get into the arguments against using HP as a measurement. I know Stahl and other have written volumes about that.

Technically, any significant change in the intake or exhaust profile dictates a camshaft change. 99% of us aren't going to do that with a street car, but technically it should happen. As an example, switching from LS6 intake to LSX.

 

FASTONE,

I didn't hear the cell last night. I'll give you a call from home tonight.

 

One other thing, if you degree your camshaft in to where it is suppose to be. Dyno the engine, then you advance or retard the camshaft and pick up power, you have the wrong camshaft. . .it is not correct for the engine.

Chris