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Old 03-31-2005, 08:36 AM
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Please Critique Cam and Combo for 383

1969 Chevy C/10 Pickup
2 wheel drive
Weight-???
Muncie 4 speed

97 Chevy Hydraulic Roller Block
Eagle 5140 3.75 stroker crank
-18cc Speed Pro Hyperuetic Pistons
Stock-rebuilt PM connecting rods
9.6:1 compression ???
Vortec Heads- all modifications done (springs, etc.)
Self-Aligning Full Roller Rockers
Vortec Air-Gap RPM
Holley 770 or 670 Street Avenger
1 3/4 headers


Now for the cam:

Cam 1: XR 276 Hydraulic Roller
224/230
110 lobe sep.
.502/.510 with a 1.5 ratio rocker

Cam 2: XR 282 Hydraulic Roller
230/236
110 lobe sep.
.510/.520 with a 1.5 ratio rocker

Cam 3: GMPP Hot Cam Hydrualic Roller
218/228
112 lobe sep.
.525/.525 with a 1.6 ratio rocker

This pickup is going to be driven quite often and I want to feed it the max amount of cam as possible without making it a pain in the butt to drive. Also, I am aware the vortecs drop off flow at about .500 lift, but I figured I could get away with a little more duration with running a 4 speed. How much of a difference will there be between the 110 lobe sep. and the 112 lobe sep. as far as the "rough" idle sounds. I just basically want this thing to run like a beast while still being able to "drive it". Any other cam suggestions or constructive criticism on the combo is appreciated. Thank you.

chevy21

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Old 03-31-2005, 09:25 AM
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cam critique

The wider the lobe separation, the broader the power curve, while the narrower the lobe separation, the higher the peak power, as a general rule.
The 218/228 cam would be great for your vehicle if it had a narrower lobe separation, say around 110, in my view, but even with the 112 lobe separation, Im inclined to think its probably the best cam for your application.
Remember this, you can always ring out a cam with higher RPM than its actually designed for, but you cant underwind one that is too large.
The 218/228 cam will take you well up to 6000 RPM, and from what I gather from your posting, the occasions that it will ever see that kind of RPM, is very very seldom. Most typical American V-8 engines very seldom see more than 4500 RPM in their lifetimes, unless they are dedicated race engines.
You are pulling a heavy load with a Pickup (close to 5000 lbs) and bottom and mid range grunt are far more important than hi RPM horsepower.
As for carb, I would opt for the 670, for better street driveability, as well as gas mileage. The 670 will very well feed your engine way past 6000 RPM, and to add more carburation than what is needed to supply your engine within its power curve, is in my view, a waste of time and money.
A little bit is good but a lot isnt always gooder.
You will realize the majority of your gains, going with the more conservative setup.
As far as a nice lumpy sounding cam, you will have enough to let the world know you arent running a stock one.
Combining your this cam and carb with the heads, intake, and exhaust you have, I think you will find it to be a very pleasant package.
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Old 03-31-2005, 01:14 PM
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combo

With a .525 cam your rod bolts are most likely going to hit the cam.
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Old 03-31-2005, 02:00 PM
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Well lets see hmmmm. First off your trucks pretty heavy and secondly its your daily driver. You neglected to mention the rear gear ratio but no matter.

The hot cam is not a good choice at all. It was designed primarily for an EFI application hence the wide lobe seperation. It will widen the power band on your engine causing the torque curve to be too wide and the engine will feel flat. With the longer stroke and Vortech heads your engine would be more suited with a cam that feeds its desire to build torque. With that said if max HP was your choice then I would run the XR282. Given that fact that your trucks a stick shift and I imagine has a decently high rear end ratio (3.73 or more) I would think it could benefit from the longer duration. My only concern would be the valve springs. If it were me I would compare the specs on the springs you have now with the ones comp cams recommends for that cam. If your springs are weaker I'd replace them with the comp springs. If drivability and Idle quality as well as gas mileage were more of a concern then the XR276 would be the way to go. Being rollers and given the size of your engine both cams will have enough Vaccum at idle for your needs

The horsepower you gain from the XR 282 will be more than the amont of torque you will be losing by not using the XR276. So the choice is yours more torque at lower rpms, better idle quality, and gas mileage from the 276 or the added exspense of better valve springs and about 10-15 more HP from the 282.

Last edited by Docs91RS; 03-31-2005 at 03:24 PM.
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Old 03-31-2005, 02:10 PM
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Even with the smallest of his cam choices the .502 lift will contact a couple of the rods...#1 & #6 cylinders if I remeber right. As with any engine ya have to mock it up first and clearance what needs to be clearanced. .050 is typically enough clearance between rods and cam for most any application.
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Old 03-31-2005, 04:07 PM
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I would say go with the 276, I think it matches those heads perfectly. It will give you great low and midrange power, which is what you would want in this combo because of the weight, and also, that is what the Vortec heads are good at. The Vortec heads are much better suited to a lower RPM motor.

Adam
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Old 03-31-2005, 08:07 PM
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lobe lift

Something I think a lot of you missed on this is the fact that hes looking at running 1.6:1 Rocker Arms on the GM 218/228 cam, which will have the lowest lobe lift of .328".
the 276 cam has a lobe lift of .340" on exhaust side.
the 282 cam has a lobe lift of .347" on exhaust side.
wasnt aware that Chevy cams had that tight of clearances in them between the cam and rod bolt caps.
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Old 04-01-2005, 12:50 AM
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They have that tight of clearance when ya start using non factory bore and stroke combinations.
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