RPM-Redline

[texplorer1994]

Okay..all of this in one message...what makes the redline. If you build a race engine with a different crank, cam and timing chain system you can have huge red lines...8,000-10,000. What contributes most to the redline? The valves can float...what causes this? What is the science that explains why OHC produce their power at higher RPMs and use less gas at the lower RPMs? Why is OHV so great at producing low-end EVERYTHING? I know it is a lot of questions, but I have never understood this. Also, what is the story with high-torque cams? I understand bigger lift and longer duration is more gas and more power but what do the numbers mean and how do they affect torque? Any info is appreciated.

 

[94WhiteEB]

...And whoever is going to rely to those questions, could you also explain the differences between horsepower and torque?

 

[WakeBoarder]

horsepower gives your top speed and the more torque you have the faster you get to your top speed

 

[texplorer1994]

Think of diesels..that's how I understand torque and horsepower. I think it has to do with moving and now moving motion...and twist. Diesels have ALL torque and no horsepower (yes there are exceptions). Diesels can pull a house and are argued to be better for wheeling. Horsepower can cause wheels to spin and torque is the twisting force. Horse power is the application of the twisting force and how effective it is...maybe.

One more question...why is the redline on diesels low...like 3,000 or 4,000 RPM?

 

[Iggy flywheel]

Diesels are built for low rpm range to last longer with closer tolances. Torque happens at the lower rpm range.
The most important part is they have to limit or it will keep accelerating until it self destructs

 

[izackary]

one thing i learned from one of the car shows on tnn saturday was that diesels have no spark plugs. they generate ignition from the piston moving so close to the top of the cylinder, compressing the air and getting it so hot it ignites by itself. perhaps the low redline is partly to prevent this from becoming uncontrolled.

There's a saying i saw on the mark viii club a couple other guys here and i are on:

"Horsepower is how fast you can go. Torque is how fast you get there."

 

[SteveVB]

There are many things that go into the "redline" of an engine. Generally it has to do with reciprocating mass and valve train length/weight. 4 cylinders usually rev higher than 6's or 8s since they dont have as much weight to rotate. Cam Shafts with pushrods wont rev as high as a Overhead cam with no pushrods to move/bend.

Other factors also like valve timing, headflow, size of valves (4 smaller valves rather than 2 large etc.) go into the upper rpm limit of an engine. More info could be found in an engine blueprinting book where lightening componants(valves,rods,pistons, pushrods), and increasing valve spring pressures will allow higher rpm potential.

Remember HP increases as a function of rpm.

 

[rocklaurence]

High revers have in general: short stroke cranks, slightly advanced timing of stark, overlap of the exhaust and intake valves, larger higher volume intake and exhaust systems. "Red line" is determined when the motor can no longer increase the speed that air enters and exits the cylinders.:redexp: That's a very general discription and applying the opposite features make "Torquers"

 

[455 Jet]

SteveVB pretty much got it right. Floating valves are cused by not enough valve spring pressure to close the valve soon enough before the next stroke. A higher spring rate slams the valve shut, however requires more HP to open the valve.
The overhead cam eliminates the need for pushrods and rockers. OHC, not necessarily needed to be able to create higher revs; however, fewer parts needed to move, less drag on components, more reliability in the higher rpms.
OHV is kind of like blowing into a Pepsi can with the bottom cut out. If you blow into it, you have to divert the air into the can (top of cylinder) and make it escape back at your mouth, you have to move the air in different dierctions (up and down). If you have a valve (OHV) at the top of the can (pop open the tab), the air is already moving in that direction (piston travelling upward on exhaust stroke) allowing the air to escape more efficiently.
The shorter the stroke, the more revs you can get out of an engine. My jetboat engine has a stroke of 4.25". It takes a lot of rotating mass (torque) to move it, and a lot more to stop it. A motorcycle engine has a stroke of less than 2" and can rev to 10,000, but has no torque, no mass. A diesel engine redlines at 2300, 470HP, 1000#lb/tq, but strokes at over 8". Torque is needed to get things rolling, but the HP is needed to make it go faster.
The more air you can move through an engine, the more power it can create. Port heads, performance intake, carb. Or force air...blowers and turbos.
I hope I didn't ramble and I hope this helps.