where to get a 175 cam

In very simple terms, duration is measured in crankshaft degrees of rotation. Meaning that if a cam has 200*@.050" lift of duration on the intake lobe, the crankshaft rotates 200* from .050" lifting of the lifter
to .050" from being closed.

Then there's valve lash adjustment to take into account and rocker arm ratio. So the first bit of lift is used up taking the slack out of the parts, then more is used to get the valve off it's seat to the point of it allowing air to start moving or in the case of the valve closing to allow air to stop flowing into the cylinder.

So if you have 180* of crankshaft rotation from TDC to BDC and your can has say 200* of duration @/.050 lift, then the valve has to be moving before the piston reaches TDC and it's still not closed after BDC right? This is where we take into account cam timing. For some math let's say that cam with 200* if intake lobe duration is timed with the intake centerline at 100 degrees ATDC that means that 5he can lobe is exactly half way through its movement when the piston is at 100* past TDC. So the post on still has to move down for another 80* of crank rotation, the valve is open for 100* or 20* past BDC.

The incoming air charge into the cylinder has inertia, it can overcome the post on heading in the bore some and still charge the cylinder for some time but eventuallyt the piston movements will cause a reversion.

There's typically 2 numbers for duration, one is advertised or seat duration measured as the lifter starts moving to the point of closing a few thousands and the other is measured at .050". The difference tells us how fast the can ramp is, or how aggressive it is.

That's all for now, but hopefully give a basic understanding.

Edited by wi50 - 26 Aug 2014 at 5:36pm

Wizard says intake closing point can be figured by advertised duration as follows 280 ÷2 =140 +LSA 112=252 - advance ground into cam along with 180=68 degrees abdc

mgburchard wrote: Wizard says intake closing point can be figured by advertised duration as follows 280 ÷2 =140 +LSA 112=252 - advance ground into cam along with 180=68 degrees abdc

You are doing a fine job reenforcing my point that a can with 280* of duration no matter how its measured is to much for the engine in question.....though for a highly boosted engine at high speeds it works fine.

As wizard said and has always said i
A cam tooth is more than six degrees your good at looking up his old post to see where you argued that it was six degree instead of more that you are now in agreement with the wizard that it is .

wi50 wrote: [QUOTE=mgburchard]   The morning crew will love this abomination of geometry....y.

And to "run fine" on 110 octane fuel, what exactly is your ignition timing set at for 2,000 RPM running???????

The isky cam you traded to Pankey didn't work for you . The cam Pankey gave you in the trade from what I gather did work for you. Is this correct Larry ? Did Pankey spec a working cam for you? . here's a anoalogy Pankey left me with last night . you have a swimming pool and are filing it with a garden hose . the time the valve is open to closed when the pool is full is duration now fill the pool with a fire house time hydren is open till valve is closed is duration . so when by Marty's account the intake port of allis is the garden hose . the question is why would you want less time for garden hose to be open

The wizard is full of wis-dumb.

280 degrees of exhaust duration won't burn exhaust valves, but slow ramps will. You see the numbers on a cam card are important there pank. Seat duration and @.050" tell how the beginning of the ramp is shaped.....but I've covered this before and you haven't quite picked up on it yet.

But what 280* of exhaust duration will get you is a real short power stroke and a lot of overlap. In fact on a siamesed port 4 cyl engine like the allis, you'd have 2 intake valves open at the same time on the same port, one opening and the other closing and one exhaust paired to the opening intake open also as well as one exhaust opening on another cylinder on the engine. The result would be a sonic crack transfered to the intake.....long story short, draw it out on paper for yourself pank. You really don't know what you're talking about. The engine wouldn't make enough power to drive across the yard.

Those numbers on a cam card mean something. Learn what they mean, how to interpret them and how they relate to the engine....again come back tomorrow and try to display some level on intelligence.

Marty you see Larry ran that isky cam so it had real world testing and not computer WiFi testing . so if it burned a exhaust valve in a low ci engine he will know ?

I'm certain you are not bright enough to know what you're trying to argue about. I'll outline it so your simple mind can understand it.

You are saying that you think a camshaft with 280* of duration on both lobes makes a good pulling camshaft in this siamesed port 4/ cyl engine. Though you don't know the other specs on the cam, and those with new found fascination of the internal combustion engine would only look at the big numbers.

I'm saying that there's no way a camshaft with 280* will work (in this application of course) unless of course the @.050" numbers are very low, in which case the ramps would be to slow to be any good, and that you have a poorly designed camshaft if it does work.....

At least you can go back to the drawing board now and make up some bs. Maybe you'll figure out why you were unable to move the pulling sled when you put the cam in your engine......

Remember the formula Pankey gave for maximum lifter acceleration . a allis 1.250 mushroom lifter will always have a faster ramp to .050 than a automotive .904 roller lifter .call Charles at cam craft

wi50 wrote: mgburchard wrote: The wizard says ramp rate or lifter acceleration depends solely on lifter diameter not duration. In fact the math for maximum velocity goes like this example he gave me lifter diameter 1.250 x 3.14 or pie divided by 360 gives you inches in degrees so .0109 inches in degrees is a fast as a 1.250 diameter mushroom lifter can be accelerated . The wizard went over this with you when you was arquing that 60 teeth in 360 degree was a 6 degree timing change but now your agreeing with wizard that its more . the allis 226 can gear tooth is about .400 thick a 8 degree eccentric cam bushing has .090 more material on one side . if .090 is 8 degrees how much is .400 ? The morning crew will love this abomination of geometry....you boys have a lot to learn. If a gear has 60 teeth, there's 6 degrees per tooth, if its a can gear driven at half crankshaft speed, then 12/degrees per tooth. Basic math boys and girls. If you place an offset bushing in it, the offset would depend on the bushings placement from the center, or in other words its radius....again basic geometry. When we get to a more complex geometrical shape such as a cam lobe, lifter acceleration is controlled by a combination of cam profile and lifter diameter. Part of this can profile is the difference in duration from one lift compared to another lift. Advertised duration and @.050" duration are a result of the ramp profile of the cam, thus controlling the lifter. You should have listened to me earlier and taken the whole day to use Google, it appears a few hours weren't enough for you to learn enough.

Edited by Butch(OH) - 27 Aug 2014 at 10:10am

If advertised duration is measured at .004 lifter rise then the duration will be greater than it would be if measured at .015 lifter rise .

Think of it this way Mike, with all things being equil other than the .050" duration the lesser duration cam has to rotate further from advertised duration to get to the .050" of lifter rise, the lifter accleration is slower.

If I have a 270 / 220 duration lobe the cam rotates 25 degrees of engine rotation or 12.5 degrees of camshaft rotation to achieve .050" lifter movement.

If I have a 270 / 240 duration lobe the cam rotates 15 degrees of engine rotation or 7.5 degrees of camshaft rotation for the lifter to move .050"

I bet you've found out what to much duration does....the engine hits a wall and the torque goes flat, trim the duration back and they'll run like crazy.

So in this case if we use that 280 degree cam that pank thinks is so great, we simply can't have per say a 240 degree @ .050" duration, we would have rapid lifter accleration, but again for the siamesed port 4 cyl engine will not tollerate 240 degrees of .050" duration, the exhaust is pushing out the intake upon opening and on closing the piston is to far up in the bore pushing air back into the port.  It may tolerate 220 degrees for example,  but to get from 280 to 220 there's 30 degrees of engine rotation on each side of the lobe, hence me saying that the ramp would be very slow or lazy.  Typical lobe @.050" durations used in the 4 cyl antique pulling engines we would see 190 on the mild side, 210-220 is pretty common and sometimes into the mid 220's on the bigger engines if they are going to run some RPM.   It's typical to see 35*-45* advertised duration than .050* duration numbers.  Most of the cams though for these Allis and Farmall will be between 195 and 215 @ .050" in order to work well for a pulling application, with some a slight bit on both sides of those numbers depending on if the engine is larger or smaller, carb, head and manifold limitations and RPM range. 

So again, in order for an advertised duration of any reasonable lifter lift say (.006-.012) (as some grinders use a different number) to work, the ramp would be very slow to get to a reasonable . 050" duration with these engines...... and by going to a shorter advertised duration, with the same .050" duration, the engine would gain torque through it's operating range.  In Larrys case, the cam was passed around the neighborhood for a good reason and he's much happier (I'd assume by the wording of his post) with something Barney sent him which would have a .050" duration in the range I posted above.  I know some of the low RPM cams coming from Barney were in the 195* @ .050" range and the higher RPM or bigger engines had a tad more.

I'd be willing to bet that the 280 seat duration cam was around 230* @ .050", maybe even a tad more, 234* maybe.  We know how well it works and how much happier pullers are when they drop to a more reasonable range, and have a faster ramp....of course pank can't tell us, he blew his engine (governer failure coupled with a connecting rod made for a 15hp per cylinder engine)  with no proof of it working well and refused to show up at the dyno challenge he requested.  Though he claimed to build an engine, to date no one's seen the Tennesee Stud make an appearance.

Marty you didn't read Larry's post did you ?