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Discussion Starter · #1 ·
I'm trying to figure out what cam I should use for my 383 build. I'm aiming for at least 400hp & 400 ft pounds of torque (preferably with great throttle response and acceleration)

My current parts and specs are as follows:

Compression Ratio is 10.27 : 1

Edelbrock Performer RPM Vortec intake manifold.

64 cc Vortec heads w/ beehive springs

1.6 rocker arm ratio

Rotating assembly:
Eagle Nodular Cast Iron 383 Stroker Crankshaft
6 inch rods
-12cc speed pro pistons

Engine block is a 1991 small block 350 bored .030 over
 

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okay, go for a solid roller with about 250/256 duration and around .600" lift, on a 108 LSA, installed on a 102 ICL. Should get you plenty of power, the rest of the combo (and the cost) well need to be built up as well. It shoudl run power brakes fairly well though if you use a big canister.
 

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83montess said:
ap72are you over the edge-vortecs hit a wall at apx 500 lift.

with a little SSR and bowl work you can get it over .550", and I do mean very little, like 30 minutes a port. Also, in MANY cases a cam goes a little past the stall point to get max power.
 

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10.27:1 cr with vortec heads will need a cam with around 280 degrees (seat to seat) to run pump gas.

then vortecs flow poorly on the exhaust so use 10 more degrees on the exhaust duration as compared to the intake.

No real need to lift past 0.500" with vortec heads. Make sure the heads can handle 0.500" lift plus 0.050" for extra clearance.

so, look for a cam with 280 on the intake , 290 on the exhaust, 0.480 to 0.500" lift with 108 to 112 lobe separation angle (lsa). Use higher lsa for a smoother idle and more top end power. And lower lsa for more mid range torque and a rougher idle. This cam should have 230 to 240 degrees duration at 0.050".

make sure to use zddp oil additive with your new cam. use at break in and at each oil change if you want your cam to live a long life. www.zddpluss.com. get a case.

finally this compression and cam setup will need a 3.55 to 3.73 gear with a 2500 to 2800 stall converter.
 

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Discussion Starter · #12 · (Edited)
W/ the beehive springs the max lift is 500-550 or so I've been told.
(Lol thank god I have a spare 2500 stall torque converter in storage. Didn't know if I'd ever get to use it haha....)

Now would this give me good low to mid end torque plus throttle response throughout the power band? What RPM range are we talking here? Im preferring that this thing operate in the 1500-6500 range.
 

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454C10 said:
10.27:1 cr with vortec heads will need a cam with around 280 degrees (seat to seat) to run pump gas.

then vortecs flow poorly on the exhaust so use 10 more degrees on the exhaust duration as compared to the intake.

No real need to lift past 0.500" with vortec heads. Make sure the heads can handle 0.500" lift plus 0.050" for extra clearance.

so, look for a cam with 280 on the intake , 290 on the exhaust, 0.480 to 0.500" lift with 108 to 112 lobe separation angle (lsa). Use higher lsa for a smoother idle and more top end power. And lower lsa for more mid range torque and a rougher idle. This cam should have 230 to 240 degrees duration at 0.050".

make sure to use zddp oil additive with your new cam. use at break in and at each oil change if you want your cam to live a long life. www.zddpluss.com. get a case.

finally this compression and cam setup will need a 3.55 to 3.73 gear with a 2500 to 2800 stall converter.
:thumbup: I agree.
 

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Discussion Starter · #14 · (Edited)
Is there a mathematical formula you guys use when figuring all this out or do you just have a feel from working with engines?

Also are there any cams off the top of your head that would match 454C10's description? It would certainly help cut down the searching time on my end.
 

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If you want a killer street 383 this cam will work GREAT for your application. Isky 201281-6.

280/280
232/232
.485/.485 lift with 1.5 rockers
106 LSA, install it on a 102 ICL.

This would be a killer street cam for combo. I'd run it with 1.6 rockers to get your lift up a little. more exhaust duration would give you a few more top end hp, a street car would run slower. So you can have a few more ponies, or have a little quicker car- your choice.
 

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atomicrockerdude said:
Is there a mathematical formula you guys use when figuring all this out or do you just have a feel from working with engines?
atomicrockerdude, love your screen name. :thumbup:
I'll put together a short primer to help you understand the workings of a camshaft. First, understand that lifter and tappet are the same thing. It's the component that changes the rotary motion of the camshaft to linear motion to drive the pushrod.

There are basically 4 different tappet types you can use in a motor.
1. Solid flat tappet. Cheapest cam/lifters you can use. No hydraulic function, strictly mechanical, requiring periodic adjustment of valve lash clearance of the rocker arm tip to the valve stem tip. Normally used in a motor where rpm's will exceed the capabilities of a hydraulic tappet. This would typically be, for instance, a smaller displacement motor that you would have to wind to the moon to make power. Any motor out there is just a big air pump, so to move the same amount of air through a smaller motor that you would move through a larger motor, you have to wind the smaller motor tighter. For instance, a 383 wound to 6000 rpm's will pass 665 cubic feet per minute (CFM) of air. Comparitively, you'd have to rev a little 283 to 8125 to pass 665 CFM and you'd need a solid tappet (either flat or roller) to reach that RPM level. Hydraulic tappets would have ceased to function properly far below that 8125 level.
2. Solid roller tappet. Much more expensive than a solid flat tappet camshaft, but used in the same applications. Cam lobe profiles can be much more agressive with a roller tappet than they can with a flat tappet, so comparing these two types of tappets at the same duration and lift, you can get the valve open quicker and close it quicker with a roller because you can use a more radical opening and closing ramp on the cam lobe. Another advantage to a roller is that you don't have to worry about the lifter going south and taking out the cam with it. The oil manufacturers have taken extreme pressure lubricants out of the oils they make because those elements clog up catalytic converters, so using any flat tappet camshaft with off-the-shelf oils available locally are little more than a crapshoot. Personally, I'll never build another flat tappet motor. Too much risk.
3. Hydraulic flat tappet. From 1955 through 1986, 99.9% of all small block Chevies came from the factory with this type tappet. They're relatively cheap and reliable when used with low to moderate valve spring pressures, if you use proper break-in procedures and add extreme pressure lubricants to the oil. Once you adjust them initially, they're pretty much maintenance-free through the rest of their life. They are still the choice of most amateur engine builders because of the low cost and relative lack of maintenance. The problems arise when these builders fail to follow proper break-in procedures, use valve springs with excessive pressure and use locally available oil with little or no extreme pressure lubricants. The other main mistake is breaking in the motor with stiff valve springs. You can't expect to start the motor initially for break-in with, for instance, valve springs that have a 300+ valve-open pressure. Do the break-in with old, worn-out stock valve springs, then change them to your "double-throw-down" killer springs after the cam is broken-in.
4. Hydraulic roller tappet. These are the current "sweethearts" for use in a street or street-strip motor that will be RPM-limited to a little over 6000. Slightly higher revs can be had when using a "rev kit" available from the cam manufacturer. These tappets do not require break-in. You just wash the preservative grease off with solvent, oil them with engine oil, drop them in, fire the motor and drive. Chevy began using hydraulic rollers in 1987 in car motors and a few years later in truck motors. The hydraulic roller cam/lifter combo costs more than a hydraulic flat tappet combo, but it's pretty much bulletproof and maintenance-free once the initial adjustment is done.

Now, back to your original question about choosing a cam. Best way is to get all your information together about your motor/converter/transmission/differential/vehicle-use and call the cam grinder of your choice for a recommendation.

Many of the fellows on this board have built enough motors that they can pretty much choose the grind they want to use in the motor for the expected results.

Any camshaft you bolt into the motor will have an effective power range of 3500 rpm's. For instance,...... idle to 4250......1500 to 5000......2500 to 6000......3500 to 7000......4500 to 8000 and so forth.
The cam should be the next-to-last item chosen, following rear gear, transmission, static compression ratio and rpm range. The last item is the converter.

The main point will be the static compression ratio. Any cam you use will have the intake closing point ground into the cam at the time of manufacture. Compression cannot begin in the cylinder until the intake valve closes, so you want to use an intake closing point that coincides with the static compression ratio you will use. For instance, if you had a SCR of 9:1 and used a cam with a power range of 4000 to 7500, the duration of such a cam would have the intake valve closing very late in relation to the piston position in the cylinder and the motor would make insufficient cylinder pressure, because there would be TIME for the piston to push some of the mixture back up the intake tract with the valve still off its seat. The motor would be a turd. This is the biggest mistake made by newbie builders. Just bolting in a killer cam will not make a good motor. All components have to be matched to each other.

On the other hand, if you had a SCR of 11:1 and used a cam with a power range of idle to 4250, the intake valve would close very early, trapping a tremendous amount of fuel air mixture in the cylinder. This would result in extreme cylinder pressure and the motor would require alcohol or race gas to operate without detonating.

Overlap. On the exhaust stroke, with the piston approaching top dead center, there is an overlap period where the exhaust valve is still open and the intake valve also begins to open. This is the only time during the 720 degree cycle in a 4-stroke motor when both valves are open. The intake/exhaust lobes on the cam have a point of max lift. This is the "nose", or centerline of the lobe. The intake lobe centerline will be shown by the grinder at some point before top dead center (BTDC). The exhaust lobe centerline will also be shown at some point before TDC, but on the other side of a timing circle. These are shown as Intake Centerline (IC) and Exhaust Centerline (EC). If you add these two points together and divide by 2, you arrive at the lobe separation angle (LSA) also called by some as the lobe center (LC).

For instance, if the IC is 106 degrees and the EC is 114 degrees, adding them together and dividing by 2 will yield an LSA of 110. As you decrease this LSA (108, 106, 104), you add bottom end to the motor, but diminish power at the top of the range. The motor will peak early and make less power at the top. The shorter the LSA, the worse intake manifold vacuum you will generate, so if power brakes and other vacuum-operated accessories are important to you, you will want to think about this. As you increase LSA (112, 114, 116), power picks up in the higher rpm range but gives up some at the bottom. Intake manifold vacuum increases.

A fairly happy medium is 110/112. You'll notice that most grinders will offer 110/112 LSA for most motors used on the street. With proper ignition advance/curve, manifold vacuum will be adequate for power brakes.

Advance/Retard. It is possible to alter cam characteristics by installing the cam relative to piston position either advanced or retarded. You can do this at the cam sprocket or at the crank sprocket on the timing set. There are 4 camshaft timing events, intake open, intake close, exhaust open and exhaust close. These events cannot be changed relative to each other because they are set when the cam is ground at the manufacturer, but the events as a whole can be changed relative to piston position. Advancing the cam will add to low end power at the expense of top end power. Retarding the cam will add to top end power at the expense of low end power. Advancing the cam will close the intake valve earlier, increasing low-rpm cylinder pressure and low end power. Retarding the cam will close the intake valve later, lowering cylinder pressure at low rpm's, but adding power at the top.

Cylinder pressure can be measured with a pressure gauge inserted into a spark plug hole and cranking the motor over with the starter. Understand, however, that this is cranking pressure, not dynamic pressure seen in the cylinder at the torque peak with the motor running. Engineers at Crane Cams published information that outlined a cranking cylinder pressure of 165 psi as the limit for a pump gas motor. Pressure would be much higher than that with the motor turning at the torque peak (generally 3500-4500 rpm's on a street motor).

I'll list a few cams and their characteristics so you can begin to get an idea of what cam works where and how. I'll show duration @ 0.050" tappet lift rather than advertised duration. Some of these are split duration, more exhaust duration than intake duration. That is not meant to confuse you, it is just that I have these cams on file and am using what I have.

SCR 7.0-8.0, 184/194 duration, 112 LSA, intake closes 19 degrees after bottom dead center (ABDC), range idle-3200 rpm's. You might build this motor to tow with if you had to run on REALLY crappy pump gas.

SCR 8.0-9.5, 204/204 duration, 110 LSA, intake closes 27 ABDC, range 1000-4600. Excellent low end torque. Smooth idle. This is representative of a cam that most newbies should use if they have not gone into the motor to change internal components.

SCR 8.5-10.0, 210/210 duration, 110 LSA, intake closes 30 ABDC, range 1400-5000. Close to the high end of the range for a stock motor with stock converter and numerically low rear gear (2.73 for instance). 3.1-3.7 rear gear recommended.

SCR 8.75-10.0, 216/216 duration, 110 LSA, intake closes 33 ABDC, range 1600-5400. Good low and mid range torque. A slightly looser torque converter might make this work better (2000 stall for instance). Also time to consider some rear gear. 3.70-4.10 advised.

SCR 9.5-10.75, 222/222 duration, 110 LSA, intake closes 36 ABDC, range 2000-5800. 2500 converter and 3.70-4.10 gear.

SCR 9.5-11.0, 228/228 duration, 112 LSA, intake closes 41 ABDC, range 2800-6200. 3000 converter and 3.90-4.10 gear.

SCR 10.25-12.0, 234/242 duration, 110 LSA, intake closes 42 ABDC, range 3000-6600. 3000+ converter and 4.10-4.56 gear.

Notice that as duration increases, the intake valve closes later and later.

The reason you need a looser converter with a longer cam is that as duration increases, there is more and more of a dead spot between idle and the lower end of the operating range of the cam. You must be able to get past this dead spot in order to accelerate the vehicle, so you use a converter that allows engine revs to go past the dead spot on ititial acceleration.

This was not meant to be the do-all, know-all list. It was included in this post ONLY to help you begin to understand the relationship between static compression ratio and intake closing point, what cam is used for what purpose and how to get a handle on cam choice along with converter and gear choice. You should ALWAYS telephone your favorite cam grinder for a recommendation before you purchase a cam.
 

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Discussion Starter · #20 ·
83montess said:
atomiccrc-look at lunati 60103 if you entertain comp xe274h the one that everyone laughed at was a little vega wagon with a x4270h until the end

In order to use the lunati 60103 cam would you need to do any machining to vortecs already equipped with beehive springs using 1.6 rocker arms?
 
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