Thread: 355 cam choice

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Originally Posted by SBC

Is there a rule of thumb as to how much timing can be added before everything is out of whack?? Seems like I have read posts suggesting as much as 36 degrees in some cases.

I'm not sure what your're asking, but if you're talking about how much you should advance or retard a camshaft to get the characteristics of the motor where you want them, a rule of thumb there is that if you have to advance or retard more than 4 degrees, then you have chosen the wrong cam.

Originally Posted by 1gary

The main reason why on my build I am not using KB pistons is the design promotes carbon build up on the ring lands.Seems to be just a bad design.I spoke to Mahle some more to find you can run those pistons at 4.029 vs 4.030,one thousands tighter that limits or eliminates cold forge piston slap because of the coating.One tip they gave me was to NOT use anything like carb cleaner to clean the pistons before the install of them.That kind of cleaner lifts off the coating.Of course they are making claims the coating last for the long term where on another thread I had concerns posted.The piston/ring design on the Mahle hands down seal without any carbon build up.They also told me they don't build cast pistons or pistons without the coating.Yeah I think in this case I found the age old saying.............."You do get what you pay for".The Mahle of course costs more.

well that s BS there telling you.... must of been the broom pusher grab the phone ? i have used there cast piston that had NO coating on them and they do or did make pistons for PBM and they are not coated as i have used a set in a 355. botom line is how are you going to run a coat piston 001 less if you can not messure it for size real size?? its coated . if there 2618 there going to move if 4032 you can fit them closer to the wall for what your doing

mahle made the cast pistons chevy used in 90s and maybe even now

No kidding guys.I just talked to them and was informed no cast pistons available.Check it out your self:1-888-255-1942.

i do not need to call them i bored a 351 ford out 040 so 4.040 last year PBM sent me mahle cast piston not coated in a mahle box NO Kidding .i mic the piston so i had a good look at them ..do they coat them now... well they may now.. BUT they own clevite now so hard to say whats going on thinking i did a 460 030 over as well with the mahles as well not coated casters

SBC has asked a question on PM about the cam we used above and the calculator on the Keith Black Pistons site. My answer is way too long for the PM, so I will publish it here on the board.

Originally Posted by SBC

OK - now I'm confused. if the cam suggested for the recent 355build discussion requires 15 degrees advance to get to pump gas SCR - I was think a cam with a later intake closing angle than 36 degrees would be a better recommendation (like closer to 50 degrees).

I am really liking the cam discussions on this forum - and trying to get a solid understanding as to what goes into the right choice - other than 'I want it to sound like "rump rump rump" at idle' .

I still have a long way to go - once I get a handle on cam choice - I'd like to work on stall selection. I finally got a better idea as to accommodating squish and quench through deck height/gasket selection.

Thanks for your effort to educate!

First off, rump-rump is the sound of the motor being inefficient. It's the sound that results from the speed of the motor being out of the operating zone for that particular cam. It's the sound of fuel/air mixture being blown back up the intake tract to confuse the venturis as the piston ascends with a still-open intake valve. Not that rump-rump is bad. It just indicates that the cam was not designed to operate at the rpm you are operating it at. Once the RPM's increase, the motor comes "up on the cam" and all is right with the world. Personally, I consider it "poser" to choose a cam based only on rump-rump without regard to engine efficiency or power.

The cam I used in the DynoSim was very close to the correct choice for the motor in my opinion. It's the....CALCULATOR....that requires the additional 15 degrees in order to make it work.

There is duration at 0.050" tappet lift and there is duration at seat-to-seat (On a hydraulic cam, usually shown as 0.006" tappet lift. On a solid cam, usually shown as 0.020" tappet lift. This is also shown as "advertised" duration.)

Let's say a theoretical cam has a duration @0.050" of 200 degrees. Let's further say that at 0.006", the duration is 230 degrees. (The difference used here is too radical to be a real-world cam, but I just need to do it this way to explain the calculator). We have 30 degrees of difference between 0.050" and advertised duration on the lobes of this cam. We are dealing with the intake lobe for use in the calculator. So, the lobe would have a difference of 15 degrees on the opening ramp and 15 degrees on the closing ramp of the same intake lobe. So the calculator is asking you to add 15 degrees to the 0.050" closing point that you have to enter into the calculator in order to get the valve closer to its seat position. As you know, we cannot begin compression in the cylinder until we close the intake valve. That's just the way the calculator is configured and something we have to work with to use the calculator.

On a real-world camshaft, the difference between 0.050" and advertised might be anywhere from 70 degrees (35 degrees on each side of the lobe) down to as tight as around 40 degrees (20 degrees on each side of the lobe) and even a little less on some radical flat tappet roundy-round cams. If you think about this, you can see that there comes a point when the lift is so radical coming off the base circle of the cam (where you set lash) up to 0.050" lift, that the edge of the lifter could dig into the ramp of the lobe. Back in the day, the fast guys introduced special aftermarket mushroom lifters for a Chevy that you had to insert from the bottom (the cam bore). I'm told that a spot-face operation was also performed on the bottom of the lifter bore. This presented a wider footprint for the lobe to work on so that the lobe had no lifter edge to contend with. Today, it is common practice to enlarge the lifter bore and use larger diameter lifters, such as perhaps a 0.904" diameter Chrysler lifter in a SBC motor instead of the stock 0.842" lifter diameter.

I was surfing and came across this post on www.chevelles.com by Harold Brookshire, known as UDHarold (world-renowned camshaft engineer and designer). It's the first time I have ever seen a chart outlining the limits of rate of lift compared to lifter diameter.....


"UDHaroldMar 31st, 05, 3:42 PM
Since if there's anything I know, it's History, here goes.....
Prior to the widespread use of computers, very few mushroom cams were made. The earlier designers had enough trouble making cams follow their normal lifters, much less an extra-wide one.
By the mid-70's, NASCAR racers had learned enough to know that the Chrysler .904" tappets allowed more aggressive lift curves than the .842"-.874" tappets. NASCAR's compromise?---Let everyone use a Mushroom lifter. Chevrolet went to .960", and NASCAR settled on that, even though Chrysler had some 1.000" ones. Those were used in drag racing.
In 1978 I designed the Comp Cams' 310/318 mushroom cam, 268/276 at .050, .390"/.410" lobe lift. In 1980 Buddy Baker won the 1980 Daytona 500 with this cam, and it is still the fastest Daytona 500 ever run. NASCAR went to restrictor plates, and then to .874" max tappet diameter.
Cams with flat-bottom lifters, either hydraulic, solid, or mushroom, are design-limited by velocity. Here are the max safe velocities(more or less) for the various lifter diameters:
.842" .00705"/°
.874" .00733"/°
.904" .00759"/°
.960" .00808"/°
There ARE tricks around these numbers, but not all cam designers know them, or else how to use them right.....
Cams with rolller lifters, either hydraulic or solid rollers, are design-limited by acceleration and base circle diameter. A peak acceleration rate that may be un-makable for a .900" base circle may be usable for a 1.100" base circle.
There are obviously tricks around these limitations, also. The hard part is knowing the tricks, not the basic theory, and when and how to use the tricks....
UDHarold"


If you'll go to the calculator and play with it, you'll begin to get a sense for what works and what doesn't. Start by using the same static compression ratio, rod length and stroke, changing only the cam timing by 5 degrees each time you run a new calculation. If you run a few dozen of them, you'll begin to see the effects of less cam and more cam. For instance, start with a 350 Chevy. 3.480" stroke, 5.703" rod length and a generic 9.0:1 static compression ratio. Start with a very short cam that closes at 20 ABDC and add 15 to see the results. Then use a cam that closes at 25 and add 15, then 30 and add 15 and so on. After you have run the range with those figures, change up the static compression ratio to 9.5:1 and run through them again. Then 10.0:1, then 10.5:1, then 11.0:1. If you are writing down the results, you'll begin to see a pattern. Like I'm saying, the more you use the calculator, the better feel you will have for the relationship of static compression ratio to cam timing, what works and what doesn't.

In the final determination, it is probably best to consult with the tech guy at the cam grinder of your choice and discuss the details of your vehicle and your engine build before you pull the trigger on a choice. But it most certainly helps for you to have an idea of where to start. We see fellows all the time on this forum and I'm sure it's the same on a hundred other forums where they come on to tell us their tale of woe about the car not having any power after their world-beater rebuild and change to a "double-throwdown, John Force camshaft" in their 8.00:1 small block Chevy. You realize right away that they have chosen the wrong cam without having a clue as to how things work in the motor. You also know that they used short, cheap rebuilder pistons and have a squish somewhere around 0.080" to 0.100". The only thing keeping the motor from detonating itself to death is the fact that they used too much cam for the static compression ratio and the cylinder pressure is zip.

I would urge everyone reading this post to also read through (several times) this tutorial written by Dimitri Elgin, one of the old-time cam grinders....
http://www.elgincams.com/campaper.html

Originally Posted by techinspector1

SBC has asked a question on PM about the cam we used above and the calculator on the Keith Black Pistons site. My answer is way too long for the PM, so I will publish it here on the board.





First off, rump-rump is the sound of the motor being inefficient. It's the sound that results from the speed of the motor being out of the operating zone for that particular cam. It's the sound of fuel/air mixture being blown back up the intake tract to confuse the venturis as the piston ascends with a still-open intake valve. Not that rump-rump is bad. It just indicates that the cam was not designed to operate at the rpm you are operating it at. Once the RPM's increase, the motor comes "up on the cam" and all is right with the world. Personally, I consider it "poser" to choose a cam based only on rump-rump without regard to engine efficiency or power.

The cam I used in the DynoSim was very close to the correct choice for the motor in my opinion. It's the....CALCULATOR....that requires the additional 15 degrees in order to make it work.

There is duration at 0.050" tappet lift and there is duration at seat-to-seat (On a hydraulic cam, usually shown as 0.006" tappet lift. On a solid cam, usually shown as 0.020" tappet lift. This is also shown as "advertised" duration.)

Let's say a theoretical cam has a duration @0.050" of 230 degrees. Let's further say that at 0.006", the duration is 200 degrees. (The difference used here is too radical to be a real-world cam, but I just need to do it this way to explain the calculator). We have 30 degrees of difference between 0.050" and advertised duration on the lobes of this cam. We are dealing with the intake lobe for use in the calculator. So, the lobe would have a difference of 15 degrees on the opening ramp and 15 degrees on the closing ramp of the same intake lobe. So the calculator is asking you to add 15 degrees to the 0.050" closing point that you have to enter into the calculator in order to get the valve closer to its seat position. As you know, we cannot begin compression in the cylinder until we close the intake valve. That's just the way the calculator is configured and something we have to work with to use the calculator.

On a real-world camshaft, the difference between 0.050" and advertised might be anywhere from 70 degrees (35 degrees on each side of the lobe) down to as tight as around 40 degrees (20 degrees on each side of the lobe) and even a little less on some radical flat tappet roundy-round cams. If you think about this, you can see that there comes a point when the lift is so radical coming off the base circle of the cam (where you set lash) up to 0.050" lift, that the edge of the lifter could dig into the ramp of the lobe. Back in the day, the fast guys introduced special aftermarket mushroom lifters for a Chevy that you had to insert from the bottom (the cam bore). I'm told that a spot-face operation was also performed on the bottom of the lifter bore. This presented a wider footprint for the lobe to work on so that the lobe had no lifter edge to contend with. Today, it is common practice to enlarge the lifter bore and use larger diameter lifters, such as perhaps a 0.904" diameter Chrysler lifter in a SBC motor instead of the stock 0.842" lifter diameter.

I was surfing and came across this post on www.chevelles.com by Harold Brookshire, known as UDHarold (world-renowned camshaft engineer and designer). It's the first time I have ever seen a chart outlining the limits of rate of lift compared to lifter diameter.....


"UDHaroldMar 31st, 05, 3:42 PM
Since if there's anything I know, it's History, here goes.....
Prior to the widespread use of computers, very few mushroom cams were made. The earlier designers had enough trouble making cams follow their normal lifters, much less an extra-wide one.
By the mid-70's, NASCAR racers had learned enough to know that the Chrysler .904" tappets allowed more aggressive lift curves than the .842"-.874" tappets. NASCAR's compromise?---Let everyone use a Mushroom lifter. Chevrolet went to .960", and NASCAR settled on that, even though Chrysler had some 1.000" ones. Those were used in drag racing.
In 1978 I designed the Comp Cams' 310/318 mushroom cam, 268/276 at .050, .390"/.410" lobe lift. In 1980 Buddy Baker won the 1980 Daytona 500 with this cam, and it is still the fastest Daytona 500 ever run. NASCAR went to restrictor plates, and then to .874" max tappet diameter.
Cams with flat-bottom lifters, either hydraulic, solid, or mushroom, are design-limited by velocity. Here are the max safe velocities(more or less) for the various lifter diameters:
.842" .00705"/°
.874" .00733"/°
.904" .00759"/°
.960" .00808"/°
There ARE tricks around these numbers, but not all cam designers know them, or else how to use them right.....
Cams with rolller lifters, either hydraulic or solid rollers, are design-limited by acceleration and base circle diameter. A peak acceleration rate that may be un-makable for a .900" base circle may be usable for a 1.100" base circle.
There are obviously tricks around these limitations, also. The hard part is knowing the tricks, not the basic theory, and when and how to use the tricks....
UDHarold"


If you'll go to the calculator and play with it, you'll begin to get a sense for what works and what doesn't. Start by using the same static compression ratio, rod length and stroke, changing only the cam timing by 5 degrees each time you run a new calculation. If you run a few dozen of them, you'll begin to see the effects of less cam and more cam. For instance, start with a 350 Chevy. 3.480" stroke, 5.703" rod length and a generic 9.0:1 static compression ratio. Start with a very short cam that closes at 20 ABDC and add 15 to see the results. Then use a cam that closes at 25 and add 15, then 30 and add 15 and so on. After you have run the range with those figures, change up the static compression ratio to 9.5:1 and run through them again. Then 10.0:1, then 10.5:1, then 11.0:1. If you are writing down the results, you'll begin to see a pattern. Like I'm saying, the more you use the calculator, the better feel you will have for the relationship of static compression ratio to cam timing, what works and what doesn't.

In the final determination, it is probably best to consult with the tech guy at the cam grinder of your choice and discuss the details of your vehicle and your engine build before you pull the trigger on a choice. But it most certainly helps for you to have an idea of where to start. We see fellows all the time on this forum and I'm sure it's the same on a hundred other forums where they come on to tell us their tale of woe about the car not having any power after their world-beater rebuild and change to a "double-throwdown, John Force camshaft" in their 8.00:1 small block Chevy. You realize right away that they have chosen the wrong cam without having a clue as to how things work in the motor. You also know that they used short, cheap rebuilder pistons and have a squish somewhere around 0.080" to 0.100". The only thing keeping the motor from detonating itself to death is the fact that they used too much cam for the static compression ratio and the cylinder pressure is zip.

I would urge everyone reading this post to also read through (several times) this tutorial written by Dimitri Elgin, one of the old-time cam grinders....
http://www.elgincams.com/campaper.html

Outstanding post.Thanks.

Originally Posted by techinspector1

SBC has asked a question on PM about the cam we used above and the calculator on the Keith Black Pistons site. My answer is way too long for the PM, so I will publish it here on the board.




There is duration at 0.050" tappet lift and there is duration at seat-to-seat (On a hydraulic cam, usually shown as 0.006" tappet lift. On a solid cam, usually shown as 0.020" tappet lift. This is also shown as "advertised" duration.)

Let's say a theoretical cam has a duration @0.050" of 230 degrees. Let's further say that at 0.006", the duration is 200 degrees. (The difference used here is too radical to be a real-world cam, but I just need to do it this way to explain the calculator). We have 30 degrees of difference between 0.050" and advertised duration on the lobes of this cam. We are dealing with the intake lobe for use in the calculator. So, the lobe would have a difference of 15 degrees on the opening ramp and 15 degrees on the closing ramp of the same intake lobe. So the calculator is asking you to add 15 degrees to the 0.050" closing point that you have to enter into the calculator in order to get the valve closer to its seat position. As you know, we cannot begin compression in the cylinder until we close the intake valve. That's just the way the calculator is configured and something we have to work with to use the calculator.

Hi tech, thanks for the links to UDHarolds post. He is a wealth of knowlege. There is a small typo in your post above you may wish to change to avoid confusion, no disrespect intended.

Cheers

Originally Posted by Rimmo

Hi tech, thanks for the links to UDHarolds post. He is a wealth of knowlege. There is a small typo in your post above you may wish to change to avoid confusion, no disrespect intended.
Cheers

Thank you. I swapped the 200 and 230. Now it makes sense....I think