Another Cam Question
Thread Starter
Tech Contributor
Joined: Aug 1999
Posts: 15,135
Likes: 3,939
From: Connecticut, USA
Another Cam Question
What are the differences between 110* and 112* lobe centers on idle and driving? I reread the magazine ad from Crane comparing the xe262 to their PowerMax 272A and the centers are 110* vs 112*.
Thanks,
Gary
Thanks,
Gary
Le Mans Master
Joined: May 2000
Posts: 6,493
Likes: 6
From: Bloomington MN
Cruise-In II Veteran
Re: Another Cam Question (gtr1999)
The wider lobe seperation seems to make the motor idle slightly better. My Crane Powermax 288 has a 114 LSA and idles better than my old Speed Pro cam which had smaller lift and duration, but only a 110 LSA.
AC
AC
Thread Starter
Tech Contributor
Joined: Aug 1999
Posts: 15,135
Likes: 3,939
From: Connecticut, USA
Re: Another Cam Question (A C)
Thanks AC, so the only difference is a smoother idle? There wasn't any rpm range changes? If that's the case then do the Comp Cams give more of a "lopey" idle then the Cranes?
Gary
Gary
Race Director
Joined: Oct 2000
Posts: 14,997
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From: central FL, near the beach.
Re: Another Cam Question (gtr1999)
if you can believe the ad, in a stock motor the crane makes 10hp more. it might idle smoother, might not because 230 exhaust, 6 more than CC.
But with great heads, a single pattern cam may put out more power, there are numerous exceptions.
The only way to know for sure is to try both cams on the dyno/street. They don't cost much; cam changing is a great hobby :yesnod:
some suys want a rough lopy idle. don't have to change the cam to get that :rolleyes:
But with great heads, a single pattern cam may put out more power, there are numerous exceptions.
The only way to know for sure is to try both cams on the dyno/street. They don't cost much; cam changing is a great hobby :yesnod:
some suys want a rough lopy idle. don't have to change the cam to get that :rolleyes:
Safety Car
Joined: Feb 1999
Posts: 3,631
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From: Fountain Hills AZ
Re: Another Cam Question (gtr1999)
At a given duration and lobe design, closer lobe centers increase overlap and it's overlap that affects idle quality. If you took two otherwise identical cams, one with 270º duration and the other with 280º and they both had the same LSA, the 280º cam would have more overlap. If you gave the 280º cam wider lobe separation, you could get it's overlap down to the same as the 270º cam's. The reason they use tighter LSA is to increase the amount of time the valves can be closed on the compression and power strokes, which helps make more torque at higher rpm. Keep in mind that there are only 720º of cam timing to work with so as you increase the time (duration) that the valves are open to let more mixture in and out, the amount of time that the valves can be closed is reduced. In the case of tighter lobe centers, they are giving up some low rpm torque for more high rpm torque. Race engines don't race at idle so it's no big deal but too much overlap can take away a lot of the enjoyment from a street engine.
