camshafts

[C Z]

has anyone used high performance cams in an f4/f4i? if so what succeses/failures have you experienced. Also, what company did you get them from? And if you're not to stingy with the deails, maybe some lift & duration #'s of what you used. Thanks

chris

[C Z]

Yes, I agree that most of the performance cams available don't work for our application. I have been looking at www.megacyclecams.com, (http://www.megacyclecams.com,) they have a couple of cam grinds that have roughly the stock duration but more lift. I think it's a large expense for a minimal return but would be nice to have done something to the motor to tell the judges.

[gug]

maybe someone can give me a bit of a lesson here.

high speed air => low pressure, as in bernouli's, so is the reverse true? does low pressure air move faster than atmospheric?

so therefor, do the standard cams on a 600cc inline 4 give the cylinder a full charge of air at 10000rpm? where is the benefit in increasing the lift or duration?

like i said, im asking for a lesson here. i only know some basic fluid mechanics, and have little experience with engines.

- if it isnt coming, you need a bigger tool.

[Angry Joe]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by C Z:
Yes, I agree that most of the performance cams available don't work for our application. I have been looking at http://www.megacyclecams.com, they have a couple of cam grinds that have roughly the stock duration but more lift. I think it's a large expense for a minimal return but would be nice to have done something to the motor to tell the judges.<HR></BLOCKQUOTE>

I hate to preach, but don't make more work for yourself just to impress the judges. If you think there is a real need then go for it, but remember: testing time is worth more than a couple HP from camshafts.



Lehigh Formula SAE Alumni
Team Captain 2002-2003

www.lehigh.edu/~insae/formula (http://www.lehigh.edu/~insae/formula)

[Jackson]

I know our engine guy is looking into it.

Since our engines generally suck (literally...) above about 8Krpm because of the intake restrictor, a cam with less duration and possibly less lift could be beneficial, since the volumetric efficiency goes up as rpm goes down.

I'm sure it won't be cheap either.

Gug; you are trying to infer odd things from the bernoulli equation. You have to look at things in terms of pressure drops, not absolute pressure-- (like how voltage has no definition except when it is referenced) Smaller tubes shoot higher velocity air, but they cause more pressure drop (higher shear stress between the laminae) Bigger tubes shoot lower velocity air, and give less pressure drop.

It isn't just how much air you are getting, you need to have good swirling (mixing) which generally requires a higher velocity when the fuel/air mix enters the cylinder.

Will any cam let your engine have 100% intake charge (of Volumetric Efficiency, VE) at 10,000 rpm? Hell no. But longer duration and higher lift can help increase VE. Of course longer duration can mean overlap too, which is why the high performance NA V8 engines usually idle like absolute CRAP.

For lower revving engines you generally need less lift to keep the air velocity higher (intake air going through a smaller hole) and less duration since VE will be higher at lower RPM's. It is all about finding the balance, and of course I really have no idea where that balance lies.

Brian
WSU Formula

[gug]

thanks Brian!

- if it isnt coming, you need a bigger tool.

[clausen]

How about vernier cam gears as a cheaper, more experimentable alternative?

Regards

Paul Clausen
Uni of Adelaide

[Jackson]

Vernier cam gears?

Vernier in relation to the old (non dial) way of reading calipers?

Intrigued--

Brian
WSU Formula

[Jarrod]

a simple slotted drive gear works fine, very little torsion load on a camshaft. Just back the bolts off a little, turn the cam on the gear, tension it back up, cam timing adjusted.
In the process of having camshafts ground at present, will have some testing done as soon as we (Monash) get another motor for the dyno. (two trashed cranks due to oil surge. wings +wet sump = not good)

[Ryan Schoffer]

what about camshafts with more overlapping duration - it would lope pretty bad at low rpm, but you would get more air packed in there at high RPM

Vehicle electronics leader

www.ucalgary.ca/fsae (http://www.ucalgary.ca/fsae)

[Scott Wordley]

You may flow better through the head but you cannot get any more air "in" because your limitted by the restrictor. What you may do though is flow more air through the engine without actually burning it, which is not ideal considering that the amount of power you can produce is limitted by the amount of air you have available. Optimising your usage of this air is what may result in more power, or so we hope.

Regards,

Scott Wordley

http://www-personal.monash.edu.au/~fsae

[eon]

Pretty much how i percieve the situation as well .. in changing the cam profile you can only hope to more effeciently (i.e. intake timing, pulses etc ) tune the engine.

If your plenum etc is all of a tuned length/volume you should be able to make gains in the torque curve and better fuel efficiency. Im not sure what a lot of overlap would do in this case.. hi lift cams with overlap generally don't idle because you have trouble creating stable vacumm at idle.. traditionally a reservoir (see vacuum tank) is added to overcome this but we already have one in place i.e. the volume tween the restrictor and the valves (albeit a variable one due to the throttle interaction) but still???

eon in da gong

"Tell them an they'll forget
Show them an they'll remember
Let them do it and they'll understand"

Founding member of "DNA" the National Dislexics Association.

You think you've got it hard !? .. try spreading vegemite on rice bubbles!!

"Do not meddle in the affairs of dragons - because you are crunchy and taste good with ketchup."

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