How do you decide what cam you want

[marks73]

After reading through c9zx's post on head flow data it occured to me to ask the question:

How do YOU decide the specs of the cam your about to purchase?

I was always taught to chose the engine parts around the cam. Sort of a build it from the heart out theory. How do you decide what cam to buy when you do your build? Just curiouse!

 

[droptop73]

I would recommend giving the fine folks at Comp Cams a call. Describe to them what you have and what you want.

 

[c9zx]

A. What fuel octane limitations, if any are there? (This is a big deal)

B. What idle speed/quality and vacuum limitations are there?

C. What gear will be used?

D. If automatic, what is the convertor stall speed?

E. What type of exhaust system will be used?

F. What cylinder head will be used (flow numbers help here)?

G. What type intake will be used?

H. How will the vehicle be used?

I. At what RPM do you want peak power to occur and Max RPM?

J. What lifter type will be used?

K. What is the static compression ratio (SCR)?

L. Aim for an effective CR that matches the octane requirements.

The effective CR is set by the SCR, cam timing events (overlap and intake valve closing point, and rod ratio. Getting accurate and complete cam information is not as easy as it should be and usually requires speaking to the "right guy" at the cam company. VERY few 351C "right guys" out there. a cam that is right for a 351C 2V is not right for a 4V. A quasi-custom cam for your particular setup is usually not much more money than an off the shelf cam. I've had good luck with Crane, Schneider, Lunati, and others who are no longer around. See, nothing to it.

 

[Don65Stang]

^^^^^^^^^

What Chuck said.

Chuck is to engines like Scott is to body work.

 

[marks73]

Yeah but if all I'm after is that "pocketa,pocketa,pocketa"?

 

[73vertproject]

Chuck is right on the money, but the easy way is to follow Jeff's advice. I emailed Comp Cams, then talked to them on the phone, and it worked out great. If you want the sound of a fire breathing dragon and 4 miles per gallon, they can grind the right cam for you.

If you can figure out exactly what you want to do, that will help. Give them a call.

 

[Don65Stang]

Chuck is right on the money, but the easy way is to follow Jeff's advice. I emailed Comp Cams, then talked to them on the phone, and it worked out great. If you want the sound of a fire breathing dragon and 4 miles per gallon, they can grind the right cam for you.

If you can figure out exactly what you want to do, that will help. Give them a call.

That's funny...the fire breathing 4mpg grind. It's all about the overlap. Lol

 

[will e]

M. Are you going carb'd or fuel injected?

N. How much money can you spend? (roller vs non-roller)

O. How much time are you willing to spend maintaining the car (solid vs hydro)

I went with the comp cams. I was in a pinch to get the car running again and I had messed up a lifter/lob so I had to swap out the cam. This one had a little more duration. I offset that somewhat by going with rhodes lifters.

It's about the combination. One thing I missed was a higher speed converter.

 

[droptop73]

Yeah but if all I'm after is that "pocketa,pocketa,pocketa"?

Comp's Big Mutha Thumper it will give the choppy idle, maybe not much else...

 

[TommyK]

A. What fuel octane limitations, if any are there? (This is a big deal)

B. What idle speed/quality and vacuum limitations are there?

C. What gear will be used?

D. If automatic, what is the convertor stall speed?

E. What type of exhaust system will be used?

F. What cylinder head will be used (flow numbers help here)?

G. What type intake will be used?

H. How will the vehicle be used?

I. At what RPM do you want peak power to occur and Max RPM?

J. What lifter type will be used?

K. What is the static compression ratio (SCR)?

L. Aim for an effective CR that matches the octane requirements.

The effective CR is set by the SCR, cam timing events (overlap and intake valve closing point, and rod ratio. Getting accurate and complete cam information is not as easy as it should be and usually requires speaking to the "right guy" at the cam company. VERY few 351C "right guys" out there. a cam that is right for a 351C 2V is not right for a 4V. A quasi-custom cam for your particular setup is usually not much more money than an off the shelf cam. I've had good luck with Crane, Schneider, Lunati, and others who are no longer around. See, nothing to it.

Great guidance.

I have one comment. I think "H" should be "A". If you answer H first, many of the other blanks are much easier to fill in.

 

[Mister 4x4]

Comp Cams has an online utility that can help with this. It's not all-inclusive, nor is it the best method, but it certainly helped me out (especially since I didn't know squat about cams at the time - still know very little compared to Chuck and others around here).

Also after hearing what Doc (73vertproject) picked out for his cam, I wound up going a similar route with mine (not quite the same, but very close).

 

[woodsnake]

Is it a street car, or a race car? over drive transmission? Are you concerned about "big end" performance only, or do you have to live with the car around town, as a daily driver?

I will NEVER recommend an Edelbrock cam to anybody, if I like them or not!

 

[cazsper]

Is it a street car, or a race car? over drive transmission? Are you concerned about "big end" performance only, or do you have to live with the car around town, as a daily driver?

I will NEVER recommend an Edelbrock cam to anybody, if I like them or not!

Why don't you like the Edelbrock cams? I'm just curious. Is it their quality?

Mike

 

[woodsnake]

Correct.

Readers digest version, is that when I was going to school a few years ago, I built the engine in my 68 Cougar as part of my shop project. (Auto tech school BSU) Simple plan- .030 over, +.010 over and under on the rods and mains. I looked at all the catalogs, and decided that the Performer RPM (.496/.520) looked like a nice performing, yet streetable cam for a 4 speed car.

I bought all the parts from Summit, and had the machine work done at a shop recommended by a friend who did a lot of mechanic work.

First cam lasted about an hour and a half of run time. Coil bind.

Second cam, lasted about 3 yrs, after new roller rockers, and three sets of push rods. Ran great once I figured out all the things that other people had told me that were wrong before. So, another year or two rolls by, a few more miles on the car, and then it's time to go ahead and put on the Edelbrock aluminum heads that I had been sitting on for a few years. Another trip to a new machine shop to verify the springs that were on the heads would fit the bill. They did not.

New springs on rebuilt aluminum heads to meet installed height and compression properties as called for in the Edelbrock catalog for the cam that I had. That cam (2nd) lasted 10 miles. So I am on my 3rd copy of that same POS camshaft.

The first cam, I freely admit that I played a good role in its early demise. I didn't know about measuring for push rod length, installed height, coil bind, et al for the stuff that will kill a cam. However, the 2nd copy should have lasted MUCH MUCH longer than it did.

Lest you think it was just my inability to follow procedure, after 22 years in the military, and 2 yrs in school, I absolutely can read an instruction and follow a procedure. When the book says zero lash, plus 1/2 turn, that's EXACTLY what happens. So now, on my 3rd copy, it seems that the latest failure may also have gotten some material into my main bearings, as I now have low oil pressure once the car warms up. (sorry the windy short version!)

Next I'll share my experience with Trick Flow heads!

 

[cazsper]

Nice.. Thanks. Personally I always use Comp and Crane. Also, thanks for your service. I actually just retired from the Air Force after 21 years.

 

[marks73]

Correct.

Readers digest version, is that when I was going to school a few years ago, I built the engine in my 68 Cougar as part of my shop project. (Auto tech school BSU) Simple plan- .030 over, +.010 over and under on the rods and mains. I looked at all the catalogs, and decided that the Performer RPM (.496/.520) looked like a nice performing, yet streetable cam for a 4 speed car.

I bought all the parts from Summit, and had the machine work done at a shop recommended by a friend who did a lot of mechanic work.

First cam lasted about an hour and a half of run time. Coil bind.

Second cam, lasted about 3 yrs, after new roller rockers, and three sets of push rods. Ran great once I figured out all the things that other people had told me that were wrong before. So, another year or two rolls by, a few more miles on the car, and then it's time to go ahead and put on the Edelbrock aluminum heads that I had been sitting on for a few years. Another trip to a new machine shop to verify the springs that were on the heads would fit the bill. They did not.

New springs on rebuilt aluminum heads to meet installed height and compression properties as called for in the Edelbrock catalog for the cam that I had. That cam (2nd) lasted 10 miles. So I am on my 3rd copy of that same POS camshaft.

The first cam, I freely admit that I played a good role in its early demise. I didn't know about measuring for push rod length, installed height, coil bind, et al for the stuff that will kill a cam. However, the 2nd copy should have lasted MUCH MUCH longer than it did.

Lest you think it was just my inability to follow procedure, after 22 years in the military, and 2 yrs in school, I absolutely can read an instruction and follow a procedure. When the book says zero lash, plus 1/2 turn, that's EXACTLY what happens. So now, on my 3rd copy, it seems that the latest failure may also have gotten some material into my main bearings, as I now have low oil pressure once the car warms up. (sorry the windy short version!)

Next I'll share my experience with Trick Flow heads!

2 things stand out to me. First is your oil pressure which is an indication of cam bearings. Second, I always used the zero plus a 1/4 turn as a starting point on new builds. You can always dial it in later using good gaskets.

 

[woodsnake]

I used Joe Gibb's break in oil this time, to avoid any chance of wiping a lobe. Oh well. The car is in Colorado now, and I am in NY for a while longer. Thread hi jack over....