3/4 cam
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Posting Guru
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From: San Antonio, Texas
3/4 cam
hey fellas, was wondering I have heard of 3/4 race cams, but can never find any specs on them. Is this just slang for a certain duration cam or is it a myth of some sort.
Thanks
Clint
Thanks
Clint
Postmaster
Joined: Nov 2002
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From: Littleton, CO
It's the difference between a 1/2 race and full race cam 
Yep, it's a slang term. Back when there were not many choices, you didn't have too many between the lines cams, hence the terms.
--Mike
Yep, it's a slang term. Back when there were not many choices, you didn't have too many between the lines cams, hence the terms.
--Mike
Post Fiend
Joined: Jan 2003
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From: Iowa
I could be wrong, but I think a 3/4 cam was where the base circle was ground to 3/4 it's regular size. The days of 3/4 cams and the like were well before my time, so maybe we could get an old timer in here? 
Postmaster
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From: Littleton, CO
What are you looking at, just to put us in perspective... Used to be that if you had a 3/4 race cam, you were carring a big(er) stick. It was of course a good selling point, or bragging issue, but only if you won of course 
--Mike
--Mike
Last edited by Mike G; Mar 16, 2005 at 10:06 AM.
Posting Legend
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It is just an old slang term used in the days when there were not many choices and cam specs were not compared closely. Every cam manufacturers 3/4 race cam was different. I don't remember that there were any 1/2 or 1/4 race cams either. Just 3/4 and full race.
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Lead Driver
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From: Oak Harbor, OH
Not sure of the spec's but what I remember is that the 3/4 was a nice street cam, while the full race was a bit too bumpy for street use.
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From: Peoria, IL (more or less)
According to some older guys I learned from in the late '70s....a 3/4 cam is called that because it would typically have 270 degrees of duration (advertised duration, although it wasn't called that back in the day..)
270 degrees is three-fourths of 360, the number of degrees in a circle, or cam revolution. (Although cams are actually described in crank degrees...but I digress.)
A typical fairly healthy street cam was about 270 degrees; most cam grinders' profiles back then were very similar or identical from one engine to another. 3/4; better than a plain 'ol stocker, not quite a race grind.
A full-race cam originally meant a cam that was all-out, race only; it later became just a term that conveniently fitted along with "3/4 cam" to describe them.
Dunno if any of this lore is true, but it sounds good!
270 degrees is three-fourths of 360, the number of degrees in a circle, or cam revolution. (Although cams are actually described in crank degrees...but I digress.)
A typical fairly healthy street cam was about 270 degrees; most cam grinders' profiles back then were very similar or identical from one engine to another. 3/4; better than a plain 'ol stocker, not quite a race grind.
A full-race cam originally meant a cam that was all-out, race only; it later became just a term that conveniently fitted along with "3/4 cam" to describe them.
Dunno if any of this lore is true, but it sounds good!
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From: Seattle
Well, here I am. An old-er guy, to help set the record straight on this.
Torque1st almost had'r right. This terminology all started back in the old flathead days when there were only a couple of cam grinders to be found.
These cam grinders marketed a 1/4 race, 1/2 race, 3/4 race, and last but not least, full race cam. The 3/4 race cam would typically exhibit a 290° intake duration, putting to bed the 360° × .75 = 270° myth that was previously mentioned .
Torque1st almost had'r right. This terminology all started back in the old flathead days when there were only a couple of cam grinders to be found.
These cam grinders marketed a 1/4 race, 1/2 race, 3/4 race, and last but not least, full race cam. The 3/4 race cam would typically exhibit a 290° intake duration, putting to bed the 360° × .75 = 270° myth that was previously mentioned .
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Posting Guru
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From: San Antonio, Texas
Well, fellas I got a chance too ask my grandfather about this, and he said that back in the old days, they decided on a fractional standard, along with what was said above by rocketscience.