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3/4 race cam ?

38K views 29 replies 23 participants last post by  bowtie488 
#1 ·
I've heard of it before and recently told my 55 year old uncle about the Velle and he said "Ya gotta put a 3/4 cam in it."
Any one know about the origins of this term?
I've always wondered.

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The ongoing saga of the MALIBRUISER 70 SS fake
MALIBRUISER
 
#3 ·
I think it is a cam that only moves 12 out of the 16 push rods in a V8, isn't it ??


Actually I will be interested in some serious replies on this as, because of my age, I grew up in the era when all the gear heads used terms like "3/4 and full race cams". I have to be honest, I just shook my head and said "Oh Yeah?" but never really new what it meant. My suspicion is that it is a phrase that evolved based on some kind of lift/duration calculation.

I wonder, has this been discussed before? If so a search may produce something on this.

'Da Mouse



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67 SS396 350HP 4 sp 3:55 Posi Butternut Yellow w/Black Vinyl
68 RS Z/28 302 350+Hp? 4sp 4:10 Posi, Euro Red on Black
70 SS396 350HP 4 sp 3:55 Posi, Black on Black

Mytmouse A.K.A. Robert Stacho
ACES Member # 04359
 
#6 ·
The term originated in the days when the Ford flathead was king. Before cam specs were used widely as they are now, an engine might have a "1/2 race" to "full race" cam depending on how the rest of the engine was built. Anyone using the term "3/4 race" in reference to cams these days is a little behind the times (IMO).

Mark

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1965 Buick GS HT 4-speed
1966 Impala 396/TH400/12 bolt
 
#8 ·
I believe 3/4 race refers to the size of the track.Where talking roundy-roundy tracks here.I know Comp Cams makes 3/4 cams..that's what you end up with after a few miles with the way their grinds wear out!


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1970 Chevelle SS396/M20/4.10 My 70 SS396
Engine pic
1970 Chevelle SS454My 70 SS454
1968 Oldsmobile Cutlass convertible
1982 Oldsmobile Cutlass 350 Olds,TH350(daily driver)
Chris Corwel,TC Member 785

[This message has been edited by mr 4 speed (edited 11-30-2001).]
 
#10 ·
I had intentions to post this question, but I kept forgetting


A friend of mine always used to call his cam a 3/4 race cam when people would ask what he was running. I always used to tell him "dude that's old school, get with the new school." Oh, he also claims he has 2.56 gears even though he tachs at over 3200RPM @ 60 mph. I told him to get with the program cause you facts are wrong. It's funny to hear the 3/4 race cam phrase though


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1971 Chevelle
1994 Impala SS
1996 Schwinn when both are torn apart :)
The Silver Bullet
"If you don't have extra parts after a rebuild..you did it wrong"
 
#13 ·
Asked an od gear head at work that used to race in the 60's and 70's and his explanationis that the phrase grew out of the 50's. When asked for a technical explanation..."a real radical lopey cam (high lift/duration) = full race, a moderately lopey cam (moderate lift /duration) = 3/4 race cam....." (but I need to qualify this to some extent because he said that the stock 30/30 cam in the Z/28 Camaro was considered a full race cam back then and the lift on that is either .455 or .485 and by todays standards that is not very radical. So what are some of the radical grinds used on the street today considered to be " greater than full race cams?


So where does that leave us with the original question of this post?? So far no real technical explanation of the difference between full race and 3/4 race cam as were the legendary phrases used in the olden times. But that is OK, I never could find those chrome muffler bearings back then that were so pupular and that my gear head freinds told me about either.


Mytmouse

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67 SS396 350HP 4 sp 3:55 Posi Butternut Yellow w/Black Vinyl
68 RS Z/28 302 350+Hp? 4sp 4:10 Posi, Euro Red on Black
70 SS396 350HP 4 sp 3:55 Posi, Black on Black

Mytmouse A.K.A. Robert Stacho
ACES Member # 04359

[This message has been edited by Mytmouse (edited 12-01-2001).]
 
#14 ·
It's from back in the day when it was all, as Smokey used to say, "monkey see, monkey do." If you wanted a fast car, you called the speed shop and got a 3/4 or full race cam. A full race cam was what the NASCAR boys would run and the cam specs varied wildly from cam to cam. It was whatever the manufacturer thought was good for max power. 3/4 was just a little milder and so on down the line. To use terms like that when every cam comes with a card that lists the specs is just telling every one, "I have no idea what is in this engine."
 
#15 ·
Wish I could give a technical distinction between 3/4 and full race, but I can't even though I began my love affair with wheeled conveyances in the early 50s...That was just a few days before I discovered the REAL difference between boys and girls.
Frankly, I'm not sure there are many people that knew the technical difference in the cams. I don't remember seeing references to actual cam specs until sometime in the 60s.

I know that the terms originated with the flat head Fords...I had 3-4 of those...but for me, the distinction between the cams came with the advent of the small block. A mild cam with a small lope using hydralic lifters was the 3/4. The heavy lope full race cams were those with solid lifters.

Yep, 3/4 and full race cams are outdated terms, but ya gotta remember that technology and the knowledge thereof didn't happen overnight. For example: Most of you think of a fax as sticking a sheet of paper into a machine and a few seconds later it's gone. My introduction to facsimile was back when it took 4-5 minutes to transmit a single page. If it was a picture, it took much longer. The PC you use to make these posts has a memory capacity measured in gigabytes. I was teaching computer related stuff in the 60s when the memory capacity was measured in single bits...several years before the term "byte" came into common usage.

Outmoded terms they may be, but those were the terms used for performance cams in the beginning of the common folk's need for speed. We had to start somewhere.


I keep telling myself I'm not getting old. You guys keep bringing up subjects that prove me wrong.
 
#17 ·
<BLOCKQUOTE>quote:</font><HR>Originally posted by Argus:
Vettefella:

I keep telling myself I'm not getting old. You guys keep bringing up subjects that prove me wrong.

I say AMEN to that!!!
<HR></BLOCKQUOTE>

TC forums tend to do that, don't they
Anyone remember Clay Smith Cams w/the Woodpecker logo? I remember "3/4" and "full race" cam-talk back in high school (early 60's). To most of us then 3/4 meant any cam other than stock that wasn't in a full out race car. I always wondered though, 3/4 of what? I think Mytmouse and vettefella have about the best explanation...just an old racers term.



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Dale McIntosh
TC Gold #92/ACES #1709
67SS & 67 Elky
http://www.dalesplace.com
 
#18 ·
<BLOCKQUOTE>quote:</font><HR>Originally posted by Big Block Dave:
Crane still has cams that are marketed as 3/4 race cams<HR></BLOCKQUOTE>

Dave's right. When I rebuilt my 355 in the summer of 2000, I got a Crane with the rebuild kit. The specs are .470/.470, 226* @ .050. On the end of the box, it says "3/4 Race Cam"...



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Nick Pratt,

TC #1442

Proud owner of a 66 Malibu -
355, four speed, 3.08 pegleg

14.94 @ 93.75

<A HREF="http://www.public.iastate.edu/~amcarthu" TARGET=_blank>
Andy and Nick's Muscle Car Half-way House</A>
 
#19 ·
Nick, I put that same cam into an L69....a 305 Z28 motor.....ran pretty funny!
 
#21 ·
Here's the scoop. (I think) Back in the olden days about the only place to get speed parts was the Chevy dealer. There were three cams available, a stocker and two high perf grinds. The middle cam was the Duntov 350hp/350cid cam. The other high perf was another very lumpy solid lift Duntov job. You walked up to the dealer parts counter in your cool buckskin jacket and shades and announced "Gimme a 3/4 race cam." What you got was a 350/350. I'm still looking for the PN's.
It's history. Cool history.


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The ongoing saga of the MALIBRUISER 70 SS fake
MALIBRUISER
 
#22 ·
The terms 3/4 race and full race predate the sbc by a quite a few years. I remember hearing the term "full race" around 1950 relating to a built up flathead in a '35 Ford coupe.

Cam grinders only made a few different cams. They were handmade, and the grinder reset for each lobe. Just a few cams per day. Ed Winfield actually ground different profiles for some lobes on the flathead Ford cams to make up for differences of flow from port to port. This would have been his "full race" cam. It was meant for nothing but competition. High compression, ported and relieved [flatheads], multi carbs, open exhaust stuff.

The 3/4 race cam would be a hot compromise cam. Sort of "hot street" in todays terms. It would work best with higher compression ratios and multi-carb manifolds, but could get you away from a stoplight ok.

As the market for hot cams got better, cam grinders would have more "full race" cams available designed for different kinds of racing, but all without compromise for street use. They added more street cam profiles under the 3/4 label. Even Sears had cams listed in their Catalogs, and I bought a 3/4 cam from them for my first car. There was no real science to our choices. Pretty much pot luck. I decided I needed a 3/4 cam, and Sears sold one for 10 bucks.

Things change. When the "Duntov" cam was released in '56, it was a "full race" cam in our eyes. With .400 lift, it allowed us to crank a 265 or the new 283 over 6 grand with ease.
 
#23 ·
Hoffman, the old Duntov stuff preceeded the 350/350 camshafts by well over a decade. There were at least a couple of different solid lifter profiles available from GM for the SBC before the 350/350 which was a hydraulic first delivered in 68. I always thought the 3/4 designation was a loose description for comparison, probably coined in the 50's, but maybe earlier since I never fooled with flatheads which were before my time. I know that the old mail order hot rod houses like Honest Charley and JC Whitney widely used the descriptions 3/4 and full race in their catalogue to loosely describe the comparisons. Now days there are so many possiblilities I'm surprised that Crane would still use the designation on one of their boxes.

Mr. 4 Speed, maybe I've just been lucky, but I've been using Crane repro, or blue printed camshafts in all my old Chevy restos for over 25 years and I've never lost a lobe or had a problem. I've got Cranes in both my LS6's, 4 435 cars and a number of solid lifter high perf small blocks with the 30 30's. I've also got a fairly radical solid lifter Crane in the 540 in my boat and even though it is prone to sitting for long periods without being started, and I don't prime it each season, it's been trouble free for 5 years now.

Someone at GM told me a long time ago that they use a variety of suppliers including Melling and TRW for their parts and that the cam specs could vary a good bit within a given part # as to specs.
 
#24 ·
<BLOCKQUOTE>quote:</font><HR>Originally posted by 2BlueLS6's:


Mr. 4 Speed, maybe I've just been lucky, but I've been using Crane repro, or blue printed camshafts in all my old Chevy restos for over 25 years and I've never lost a lobe or had a problem.
<HR></BLOCKQUOTE>

My comment said Comp Cams,NOT Crane.Just wanted to clear that up
 
#26 ·
Originally posted by vettefella:
For example: Most of you think of a fax as sticking a sheet of paper into a machine and a few seconds later it's gone. My introduction to facsimile was back when it took 4-5 minutes to transmit a single page. If it was a picture, it took much longer. The PC you use to make these posts has a memory capacity measured in gigabytes. I was teaching computer related stuff in the 60s when the memory capacity was measured in single bits...several years before the term "byte" came into common usage.
I'm just wondering what kind of dinosaur you had as a pet when you were a kid.........

JUST KIDDING !!!! ;)


My 11 year old daughter askes me questions like that..... drives me nuts


I remember all of us BIG BAD RACERS in high school throwing that 3/4 cam term around all the time (early '70's) and I just now realize that NONE of us had any clue as to what we were talking about. :D :D
 
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