Isky cam (VPW) specs

[Guest 57plymouth]

Here is the cam card for the Isky cam from Vintage Power Wagons.

[james curl]

Someone clue me in on how a mushroom tapper can give a 1.5:1 lift ratio. I understand how an overhead valve with rocker arms that pivot around a shaft and one side is longer than the other side to gain lift but how does a tappet multiply movement?

[Normspeed]

I can't figure how you would get a 1.5: 1 lift ratio with flat tappets either.

[Suddensix]

Here is the cam card for the Isky cam from Vintage Power Wagons.

Thanks for the info 57.

Cheers

Gary

[Guest rockabillybassman]

Unless the chart is generic to all motors. What interests me is that it specifies at the top that it's 3/4..... presumably to mean it's equivalent to the old 3/4 race grinds. That would seem to be a strange thing for a cam in a truck, where the emphasis should be on low revs and low end torque. All very confusing.

[Plymouthy Adams]

that card is very very messed up..it is not a 3/4 cam..as it would have to be 270 degrees...what you have there fall in the RV series if compared to todays general specs

this will have a marked improvement in performance..should not have adverse effect on idle..maybe cut into the vacuum a tad...

[Guest 57plymouth]

Hey, I just scanned the card.

It does not have a noticeable impact on performance. It sounds bone stock and idles like a stock motor. I do not think the car has more power than before I added the cam. Of course, I added the cam during a total rebuild of the motor. It is stronger than before, but since it has been rebuilt I don't know if it is this cam or if it is having good rings, a good timing chain, etc.

Take it for what it's worth...

[Plymouthy Adams]

The performance you will most likely see with this cam will be in added torque while pulling a heavy load. As the lift is stock the only added breathing is in the duration of the valve opening..that timing tag is very poorly done and I am very shocked and amazed that a company would tag a cam as such...As written they are calculating values in terms of lift according to an OHV six ..not the flathead. Seems a real waste of time to undercut a stock cam just to change the ramps and not take advantage of some degree of lift for to change the ramp a sufficient amount of material has been removed from the base circle thus automatially giving the toe an increase in lift at the valve..(they cut the toe to return to stock lift) the marking of 3/4 is also way off from 270 degree a true 3/4 cam and therefore the implied name. With a 3/4 cam in this engine and especially in smaller cubes the idle quality would be a tad choppy and suffer up to about 5 inches of vacuum loss at idle. Base line idle speed would also have to be altered to establish a somewhat smooth feel due to the "lope" and even with the cam installed in a fresh engine with stock intake a noticable increase should be felt but with a true 3/4 cam one should improve the intake by going to the duals or at minimum a larger carb as the CFM requirement with a deep breather is now required. (this can be argued as most carbs can flow more than the engine can suck in stock form...possible rejet will suffice) Now that the engine is breathing better it now must have the ability to exhaust the increased volume of air which translates to heated gases therefore dual exhaust will be nice and at miminum here would be a larger diameter exhaust pipe through a low restriction muffler. Again if going with a performance cam, go all out for the dual carbs and the dual exhaust IMHO

[Don Coatney]

I have always thought that a 3/4 cam should have 270 degrees duration or something close. Others have expressed different definitions in the past.

Like others I do not understand the 1.5/1 rocker ratio where there is no rocker. The advertised cam lift and valve lift numbers reflect this 1.5/1 ratio also.

As Tim mentioned there may be a very slight lope at idle and a vacuum drop using this cam. It would most likely require a dyno to measure the horsepower gain.

I am using a Earl Edgerton reground cam in my Desoto long block engine. The specifications given me are 260 degrees duration @.410 lift. I measured the valve lift and it is exactly .396 plus .014 lash for a total of .410". With this cam I do have a slight lope at idle and a vacuum loss. Some of this vacuum loss is due to the dual carburetor setup I am running.

[Plymouthy Adams]

Don...cam specs are very misleading in todays market as most are now expressed in degrees at .050 lift...this will translate to roughly in the 220-225 area in a "advertised" 270 duration (3/4) cam. There is a formual for calculating this but I don't have it at my finger tips. This however is was not the case in the Isky timing tag. When you get up to above 292 duration the compresion ratio has to be increased in numbers to retain an accepatble CR due to compression loss in overlap. This is what makes the 3/4 such a hot street cam...basically a drop in from stock for added gain.

The rocker issue is just an advertise lift if applicaple..sonfusing as we all know the cam is direct valve push..they are just taking be baseline lift time the multiplier of a ratio rocker and giving the specs..you be surprised the number of folks that do not take into account the multiplier of the rocker in an OHV engine.

The cam grinder that irks me to no end is the straight grinder where the lift and duration is equal intake and exhaust..give me a break..want to see the secret of the 340...look at its cam profile...

[Guest 57plymouth]

Hmmm... Maybe I should post up the cam in the truck. It's much more noticeable.

[Normspeed]

Here's my cam profile. I guess the duration would qualify it as a 3/4. I get a nice lope at idle, more grunt at low rpms, and really good roll-on power from 50 to 70 mph. That's with stock valve springs, 2 carbs, a less restrictive exhaust plus supposedly the Flowmaster muffler has some amount of scavenging effect. It's still a low rpm motor though. Winding it up tight in low and second doesn't get you much more than shifting at lower rpms.

Bottom line, a 218 is a 218, and I never expected it to be a fire breather. When the machine shop did my motor, I just said "make it lope" and they delivered. I'm real happy with it.

[Plymouthy Adams]

Now that cam is more in spec..and is a 3/4 cam for sure..the addition of the dual in/out take full advantage of the cam..I notice you have .013 increase over stock lift..with that being said, there is really no need for heavier springs..this combo ought to have longevity built into it.

[Normspeed]

I did lose some vacuum though. Performance wise, Darin's wolf whistle has mine beat hands down.

[Plymouthy Adams]

Are you saying Darin's car sucks more than your own? Get yourself a vacuum cannister and a check valve and whistle all you want.

[Normspeed]

LOL. I did install a canister in the right fenderwell, but the tire creased it, and it collapsed under vacuum. Worked great up til then.

[blueskies]

Anyone know what the stock specs are off hand?

Here's what the cam grinder had to say about my cam... Cams are a bit of a mystery to me, so I don't really know if what they did makes any sense...

250 duration advertised, 226 duration from .050 thousands

.366 lift

112 deg lobe seperation

I had the shop that did my block work send out the cam to a grinder in the region, someone that they trusted but unknown to me. I had to call the grinder to get the specs, and this is what they told me, but I don't really know what I got. I ran these numbers by a few folks on the old forum, and they seemed to think that they didn't add up.

Wish now that I'd had Edgerton grind the cam, and make it a bit more radical that it is. It runs great, but not really what I was after...

What say you, Tim?

Pete

[Plymouthy Adams]

.I am not certain but for some reason 230 duration and .375 lift is what sticks in my head as stock. Now specs for the slant 6 are easier to come by and thier original cams were 232 duration with only .400 lift..and the overall best cam for the street was produced between 71 and 77 and guess what..the magic number for the engine was 244 duration. (that be you Pete) again in true MoPar power maker the duration is staggered and the exhast is a bit greater than the intake (remember, exhaust valve is smalller) I had a 73 Slant 6 Windsor QRS and that sucker would crank pretty good..even on an automatic shift under full throttle would chirp second gear. The cam they gave you is a not opening the valve as much as stock and the duration is increased enough that it is probably a tad more than stock but not by any great amount. Your engine should idle smooth as silk, and have excellent vacuum..by looking at the specs the greater benefit you have is the dual intake, exhaust and ignition upgrade..

I know just enough about cams to hopefully keep out of trouble..I studied this subject in depth about 16 years ago when building my Tiger engine trying to find out what was wrong with the sucker..lets say I will never ever have a cam ground by this comapny. I learned a lot and for those that are interested go the the Crane web site..this did not exist online and I had to did it all out of book years ago. Makes for an interesting read.