im going to ask a noob question but i was looking at sharkracing.com and found the cams, i was wondering what the diferent durations and cam lifts mean exactly? i know it changes how it idles, but what would be good for a basic upgrade?

Hyundai 2.0 Stage 1 Cam (Tiburon 97-01, Elantra 97-00) Specs: Duration: 214, Valve Lift: 0.335 $380.00
Hyundai 2.0 Stage 2 Cam (Tiburon 97-01, Elantra 97-00) Specs: Duration: 222, Valve Lift: 0.351 $380.00
Hyundai 2.0 Stage 3 Cam (Tiburon 97-01, Elantra 97-00) Specs: Duration: 236, Valve Lift: 0.353 $380.00

[ November 16, 2002, 04:39 AM: Message edited by: xxxmonoxidechild ]

 

Well duration is the amount of time that the valve is open measured in degree's a full rotation of the cam is 360 degree's so the stage one will be open 214 out of 360. Lift is the max distance that the valve opens and is measured directly at halfway through the duration cause it is not open that distance through the entire duration. Hope this makes sense. Normally the larger the duration and lift the more low end tourqe you will lose but you will gain top end horsepower, that is why they make stall converters for automatics so the engine will rev straight to it's peak torqe output. there are other factors in the desighn of a cam that have to be considered as well, such as the centerline and lobe seperation but I won't get into that right know. Just be sure if you buy one of these cams that the stock valve spring's will hold up to that much lift, the stage one should work with them but two and three I'm not to sure, they may require an aftermarket spring and another thing that might have to be checked is the piston to valve clearance, they might require a notched piston as well. Hope I answered your question.

[ November 16, 2002, 07:30 AM: Message edited by: MAXXTIB ]

 

very well said, maxtib.

 

MAxxtib,you're almost right...
duration is calculated in crankshaft degrees
and max lift isn't always in the middle of the cam lobe,some lobe are grinded in differente configurations

Denis

 

thanks you for the info. now i know what i should be looking at.

 

but to further complicate your decision, consider that the longer the valve is open, the smaller your effective compression ratio is. unless your running boost and revving high, you don't want one of those cams. basically, the cam will be open farther for a longer amount of time, so your piston will be be further up its stroke before the valve closes.

 

Umm, how do you figure the compression will be lower? This may be true at lower rpm's, but with the EXTREMELY high speed of the piston at high rpm's, this factor is negated. You're still squishing just as much, its just at lower rpm's there is more time for the intake charge to escape. Compression will stay the same, however the amount of air being compressed changes.

This is one of the reasons long duration cams are bad for street cars that have to pass emmissions. You have all of this unburnt fuel going out the tailpipe at idle, and your gonna have a crappy/high idle. Big durations are for big power at big rpms; are you willing to sacrifice bottom end/around-the-town power for all out top end horses?

 

Read This

It explains the differnce between dynamic compression ratio and static compression ratio. It explains why/how long duration cams can alter dynamic compression ratio based on RPM/cam duration.

[ November 18, 2002, 12:07 AM: Message edited by: Random ]

 

Yeah, i realized that after i posted and feel dumb now, lol. I was just too lazy to go back and edit.