Can someone explain to me [a complete mechanical moron] how "cams" make such a dramatic improvement in HP/torque?

 

I'll have a go! But first read this link, then ask questions.

 

Wow! Great link. I think I get it. Conceptually, I understand that lengthening the duration of a valve being open allows more air to enter the cylinder, thus increasing HP and/or torque. [I suppose that is the benefit of "turbocharging"?] I'm unclear how making that happen earlier or later affects the engine, but I do understand that the entire process is a compromise. So what is it that makes many of the after market replacement cams [S&S?] that many members speak of on this Forum superior to the stock cams? How close does an open valve come to the piston crown? Are we talking inches or millimeters? To a trained eye, can one look at a camshaft and determine if the shaft is stock or "high performance"? If tolerances are as tight as I suspect, with the cam "nudging" the valve open thousands & thousands of times per minute, don't the contact points wear, thus changing [shortening?] the opening? How is changing cams different from changing the air/fuel mixture with a device such as a Power Commander? Sorry for the ignorance. I'm sure if I saw a breakdown and rebuild of an engine it would make more sense to me. Thanks for the link.

 

A turbo-charger, or super-charger, is an external pump used to shove air under pressure into the engine. It's a separate aspect of engine tuning with it's own 'rules' and science! We have a dedicated Tech section of HDF where you can learn more if interested.

In essence they open the valves sooner than stock and hold them open longer. Just to tease you, it is routine in a tuned engine for the exhaust valve to open while the inlet valve is still open, so that some fresh air/fuel mixture is drawn through the cylinder and into the exhaust. The inlet valve is then closed, but the exhaust kept open, so that a pressure pulse in the exhaust system can push that extra mixture back into the cylinder, hence over-filling it. That is why choice of exhaust system is so important when building a tuned engine.

The design and cams of any current engine has to comply with EPA regulations, as well as meet the wishes of the manufacturer, and both these tend to provide modestly tuned engines. Which leaves plenty of scope for the aftermarket to play with!

Fractions of an inch. The precise clearance will depend on the level of tune of the engine. High performance tunes and racing engines will actually be trial built to check valve clearances with the piston, before finally completing the build. The piston valve pockets may actually be hand-finished so if they hit a valve it is not bent or otherwise damaged as a result.

Yes, a stock cam will be 'egg' shaped, compared with a high performance cam, which is likely to be more 'oval' in shape.

Cams have been manufactured for well over a century and used in far more demanding applications than road vehicles. So no, they don't wear, except after exceptionally high mileages, or with extreme performance.

An engine is an air pump, so changing cams will usually significantly increase the amount of air it pumps and fuel will need to be adjusted to suit. Changing cams will definitely require use of a tuning device to provide optimum performance.

On a stock engine the air/fuel ratio has to comply with EPA regulations, which are lean compared with optimum figures. Hence a tuner can give improved performance over stock, if optimum tuning is used.

No need to apologise! We're here to help. There are bound to be on-line videos showing an engine build, which may help.

 

Ahhhhh! In my feeble mind I always assumed that if one was willing to tolerate the noise, straight, open pipes would provide the best performance in an engine; if I understand the above statement correctly, my assumption is incorrect. The engine requires some back-pressure to operate at peak performance?

Thanks for your help and suggestions. I will indeed be checking a few YouTubes for an engine build and maybe also follow along with a cam installation.

 

There's a bit more to it than just back pressure. A tuned exhaust will send a pressure pulse down the pipe, caused by the exhaust valve opening, then send back a reflection of that pulse. The reflected pulse is what stuffs the fresh mixture, drawn into the exhaust, back into the cylinder.

A tuned-length drag pipe, with a square-cut tip, will do just that, although it is only operational over a short rev range. A suitable system for a road bike, such as a good brand-name 2-into-1, will give a wider and more useful effective rev range. I have a SuperTrapp Supermeg on my Glide (with S&S 107" engine), which is just great!

 

Air = Power...end of story...

 

2017 RG Stage 3 Vance and Hines Titan 4.5 and Power Duals. TTS Tuner and High Flow Breather. Almost forgot... Woods 777 cam


https://www.hdforums.com/forum/the-d...l#post16698446

 

2011 ultra 96"
Rev perf 107 kit with balanced and trued crank. Rev perf stage 2 heads. Woods cams 7H . H beam rods. Dyno tuned twice
V and H pro pipe- 108 HP 114 tQ
Magnaflow 2-1-2 with 4.5 top gun muffs-98 hp 120 tq
Still not happy with Magnaflow. Perhaps a change over the winter.... Can you say Fuel Moto 117"?

 

Thats where I want to be