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Old 09-24-2004, 12:22 AM
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Another Cam Question: What To Use?

So I'm about to purchase a cam. I've asked a similar question of this sort before, but just want to be 100% confident of the choice that I make. Thanks in advance for any input.

Chevy Pickup 4x4: 4800lbs
TH 350 Tranny
3.42 rear gears
Stock Converter

350 ci .60 over
Vortec Heads
Edelbrock Vortec Performer RPM
Stock Crank and Rods: Should they be balanced?
Flattop Pistons- I realize compression will be high. Around 10.3:1
Quadrajet: Gotta Love Em

Ok, which cam to use?

Comp Cams XE 268: 224 intake 230 exhaust- .477/.480
lsa- 110 degrees
or

Comp Cams XE 4x4: 218 intake 226 exhaust- .462/.480
lsa- 111 degrees

I've been told before that the 268 would be an excellent cam and should make the truck to be a real sleeper. However, the higher duration makes me worry it will be a dog off the line with not a lot of low end torque. I want the truck to be pretty quick despite its heavy weight. Can i get away with using this cam?

On the other hand, the XE 4x4 is known for making great torque with this combination which is what it needs. However, I dont want to lose top end hp. I want to get the max power out of this combo. Which cam should I go for?

I mainly drive this truck on the street and like to surprise people when they want to line up next to me in their 3500 lb car. It see's some occasional pulling time too with a trailer.

Is there any noticeable difference between the lobe seperation angles on these cams? 110 degrees vs. 111 degrees.

Also, are there any good books on rebuilding performance small block chevy's that anyone could recommend? I enjoy learning new chevy knowledge every day.

Well there is my question or questions i shoud say. I know there are some very experienced builders and mechanics out there so a wide variety of input is appreciated to help make my choice easier. Thank you.

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Old 09-24-2004, 12:36 AM
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I have an XE 268 in my car. I think it would work good in your truck. That would be the biggest (duration wise) I would go. You need at least that much duration to bleed down some of that compression anyway. Also, the comp cams XE line has pretty steep ramps for a flat tappet. Some guys have had excessive wear issues. I don't have any problems with mine, but it does "tick" a little. If you do get an XE, install a set of Crower Camsaver lifters. They should make it last.

BTW, the XE 268H has a nice lope at idle.
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Old 09-24-2004, 07:46 AM
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268H with a cruise RPM of 3000
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Old 09-24-2004, 08:46 AM
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I was in your shoes about 2 months ago, I couldnt decided on which cam I wanted. Finally after months of research I realized, camshafts are not permanent, you can change them out
All motors are different and its not uncommon to try a few cams before you find one that suits your needs. I would try your first cam and see how it reacts. From there you can evaluate where to go in your cam needs.


Ben
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Old 09-24-2004, 09:18 AM
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Ben,
I have to disagree. With the right info a camshaft is black and white. Spending an extra $100 on a custom cam designed for your engine is much cheaper then putting in 2 or 3 camshafts.

I think Rogers/K-star/ and Tom will back me on this one.


Chris
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Old 09-24-2004, 09:28 AM
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Chris,

If its one thing I have learned about cams they are not black and white, I wish they were.

There is more to cams then just the numbers they give us. unfortunately we have things such as ramp speeds, ect, ect, that are not listed on cam cards. Im not saying you cant get close to what you need but its not an exact science, there are too many variables involved. Im not trying to say he is going to have to change cams, I think that cam will work for him, I am mearly saying if it doesnt work, its ok, you can change it out.

if it was black and white then over caming would be such a common problem

Ben

Last edited by brainsboy; 09-24-2004 at 09:56 AM.
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Old 09-24-2004, 10:00 AM
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Ben,
I am not saying most can do it. But there are guys out their, Buddy Rawls/Ed Curtis to name a few that for the extra $50 or $100 they charge to run your combination through and grind the right cam for. . . .its cheaper in the long run. To me the camshaft is the most important part of the engine and I see way to many times the wrong shaft going into an engine.

Chris
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Old 09-25-2004, 01:01 PM
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In my oppinion, some of what i've read and learned about makeing a cam choise is, every one has there own oppinion about what work's and dont work. But if you go to the Engle cam's web page, there some really good info on cam's on there, some of witch state's that a performance engine will have an intake valve closeing some whare in the range of 50 to 75 deg. ABDC. and the closer you get it to 75 the more you start to lose your bottom end. For instance my Comp 268H High Energy cam has an intake closeing of 60 deg. ABDC. and the EX 274 has 74 deg, ABDC closeing witch mean's the EX 274 would have less torque in the lower end. And what your try'in to bleed down is your cylinder pressure because if it get's to high like say over 200 psi with iron head's your in trouble, you want to have it around 160 to 180 psi to run pump gas. I also have a 4,000 lbs 1/2 ton truck that i'm try'in to beef up, the engine is a 350sbc the would of had had over 10.0:1 C/R with S/R torquer head's and dome piston's, but i'm switching to a set of KB flattop's to get it down under 9.5:1. With your C/R you could look at a Crane Enigiser cam part# CRN-100132 in the summit mag, you also have to watch how much lift your head's can handle.
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Old 10-26-2004, 11:39 AM
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Ben, and the rest of the guys out there reading this post:

Cams are an exact science, a very exact science. An engine is ruled by the laws of physics and thermodynamics just like any other man-made deal. It will respond according to those laws just like anything else. All you gotta do is figure out the science behind an internal-combustion engine and you can figure out the ramp rates, valve timing events etc etc. I'm not saying that many people know how to do it, because most don't. The reason why you see people switching out cams is because they don't know the calculations and formulas and science behind camshafts. A smart guy can put the variables into the equation, just like any formula, you can account for just about anything.

BTW, Chris Straub is one smart guy and I would listen to the stuff he says.

Aaron

p.s. Chris, I'm sitting here looking at those trophy stock parts in my house wondering if I should put them on a car one day or just sell it and get out of racing. I would like to put them in something so I can get the confused looks when I run a second or two faster than I should.
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Old 10-26-2004, 11:56 AM
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Quote:
Originally posted by 89WhiteGT
Ben, and the rest of the guys out there reading this post:

Cams are an exact science, a very exact science. An engine is ruled by the laws of physics and thermodynamics just like any other man-made deal. It will respond according to those laws just like anything else. All you gotta do is figure out the science behind an internal-combustion engine and you can figure out the ramp rates, valve timing events etc etc. I'm not saying that many people know how to do it, because most don't. The reason why you see people switching out cams is because they don't know the calculations and formulas and science behind camshafts. A smart guy can put the variables into the equation, just like any formula, you can account for just about anything.

BTW, Chris Straub is one smart guy and I would listen to the stuff he says.

Aaron

p.s. Chris, I'm sitting here looking at those trophy stock parts in my house wondering if I should put them on a car one day or just sell it and get out of racing. I would like to put them in something so I can get the confused looks when I run a second or two faster than I should.
I disagree.

The problem with cam "science" is that its near impossible to predict "exactly" what a motor is going to do when you put a specific cam in it. There is no exact measurement! This is why cam technology is ever-changing and why cams of 30 years ago are a night and day difference from today's cams! If cam sceince were exact, why would cam manufacturers even bother doing dyno tests? They should be able to plug in formulas, because they're "smart guys" and know exactly what's going to come out right? No, they don't know exactly what's going to happen. You don't know exactly what the measurement of density of the air is that day, the quality of your fuel, exactly how your carb is going to atomize said fuel, variability in ignition, plugs, wires. Variability in intakes and runners! If you've ever taken a statistics or calculus class, you'll realize (and I'm not suggesting you have or haven't btw, no disrespect) that with this many variables the best we can get with cam science is "ballpark." If comps cams has a "pretty" good idea in a controlled enviornment what kind of power they're going to get from cam A and cam B, we at home have a "fairly educated" idea what is going to come from our choices, but again, I don't believe that it is by any means exact. I have a 280 comps cam in my motor, but I could get very similar results by any number of other grinds. True, they'd have to be in the same range, but there's certainly no way to lay a calculator on your hood, punch in some numbers like a "smart guy" and crap out results with your motor!

K
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Old 10-26-2004, 12:55 PM
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It all depends on what you want the engine to do. The "Right" cam for me could be the "Wrong" cam for someone else even in the same vehicle.

Now back to the regularly scheduled program.

If this were my truck I would go with the second cam you have listed. The truck is heavy and you have a small engine. You didn't mention tires size but, since it is a 4x4 I would guess the tires are fairly tall. This along with 3.42 gears tells me you need some torque from idle on up to ~5000-5500. You said you have a stock converter as well. The smaller cam will probably out perform the larger cam in this application. You are not going to be RPM'ing this engine anyway you need low RPM torque.

Buying a custom cam is not for everyone, while I agree you can get close to if not exactly what you want if you order a custom grind. For most basic combinations such as this truck it is just not needed to buy a custom. I did go with a custom grind for my last build (from Engle cams, can't say enough good things about them), they nailed it exactly. The reason they were able to get it exactly where I wanted it is because I gave them very accurate info and I knew exactly what I wanted. Now just because it is the perfect cam for me, someone else will probably say it's too rough, wild, etc... With that being said this is why I say cam choices are not black and white they are grey at best. There is a factor that can't be measured, and that's "opinion" or "preference".


Royce
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Old 10-26-2004, 01:33 PM
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CAM CHOICE

I feel that cam choice is 100 % black and white for the professional engine builder with the skill and experience to pick them. The problem is there are not a lot of people with the time involved to get to this point.. Excluding an all out racing engine changing cams will usually gain you very small amounts of hp/torque, unless you are way off right from the begining. I think back to the begining of my engine building time and the cam choices i made. Most of them were so far off it wasn't funny, but the engines still ran and performed well, maybe not to 100% of what they could have been but they still worked. I feel i am much better at picking cams now then i was back then but still call the pros for help. I agree with every engine needing a different cam per application but the point is the cam professionals armed with all the correct info can get the cam spot on for all the different intended uses.......If the are given this info....IMO

Keith
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Old 10-26-2004, 04:43 PM
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Quote:
Originally posted by killerformula
I disagree.

The problem with cam "science" is that its near impossible to predict "exactly" what a motor is going to do when you put a specific cam in it. There is no exact measurement!K
If an internal combustion engine is controlled by the laws of physics then it can be measured. It might be more complicated to account for all variables but it IS a "quantifiable entity and should be treated as such" - Buddy Rawls

Quote:
Originally posted by killerformula
I disagree.This is why cam technology is ever-changing and why cams of 30 years ago are a night and day difference from today's cams! If cam sceince were exact, why would cam manufacturers even bother doing dyno tests? They should be able to plug in formulas, because they're "smart guys" and know exactly what's going to come out right? No, they don't know exactly what's going to happen.K
A cam manufacturer is only as good as the engineer designing the cams. Most people's cams from mainstream manufacturers probably aren't optimum because they're getting specs from a $7 an hour phone jockey reading from a catalog.


Quote:
Originally posted by killerformula
You don't know exactly what the measurement of density of the air is that day, the quality of your fuel, exactly how your carb is going to atomize said fuel, variability in ignition, plugs, wires. Variability in intakes and runners! If you've ever taken a statistics or calculus class, you'll realize (and I'm not suggesting you have or haven't btw, no disrespect) that with this many variables the best we can get with cam science is "ballpark." If comps cams has a "pretty" good idea in a controlled enviornment what kind of power they're going to get from cam A and cam B, we at home have a "fairly educated" idea what is going to come from our choices, but again, I don't believe that it is by any means exact. I have a 280 comps cam in my motor, but I could get very similar results by any number of other grinds. True, they'd have to be in the same range, but there's certainly no way to lay a calculator on your hood, punch in some numbers like a "smart guy" and crap out results with your motor!

K
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Old 10-26-2004, 04:56 PM
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I would drop the compression ratio one full point and use the smaller cam.

The XE268 is not designed for your application and power range.

The smaller camshaft would be great, except for the fact that you are using tall gears, heavy vehicle, automatic with stock converter,

Bud, it's gonna spark knock.

The engine will be working right off of idle trying to pull your big truck around, and cylinder pressure is going to out run pump fuel.

No need to expound about physics, etc. This ain't rocket science in this instance.

Brian
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Old 10-26-2004, 05:22 PM
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This discussion is precisely why I've always felt a fella should pick a cam first, then build his engine to suit it

Personally, I always overcam. I rarely build anything I'm driving on a regular basis (who wants to pay that gas bill, eh?) so it doesn't matter a great deal. If, however, you're slapping a .509 lift, 301 duration Isky into the family grocery-getter, you might be overdoing it a tad. A duration in the neighborhood of 265 (your choice fits in nicely) will make for a very drivable vehicle that will have a decent amount of excess power. You won't be pulling those low 12's in the 1/4, but you also won't be worrying about your bottom end giving it up because you chose too much bumpstick for the iron you have under it to handle. And your fuel economy won't even be that terrible.

EDIT
Just noticed your compression ratio....unless you're going to either use premium fuel, or a mix of avgas and pump gas, or use a high quality additive, I'd seriously consider reducing that to 9.5 to 1. The guy above who said "Dude, you're gonna detonate" knows exactly what he's talking about.
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