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Old 04-24-2013, 12:31 PM
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help with proper cam selection

Got this 010 stamped block, two bolt. .030 over Trw piston, piston stamped trw 1801..... domed piston .100, from what I read a 11:1 piston with 64 CC heads. I have 3973497x heads.2.02, 76 CC. So I would guess that's probably 10:1. Wieand intake 1500-6000 range, and 650 edelbrock. Single plain intake. What cam can I use to get the best power?

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Old 04-24-2013, 12:43 PM
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Buddy-if it sounds like I'm coming down on you hard,I kind of am.It's frustrating to see this kind of question all the time when the info is right here.

http://www.crankshaftcoalition.com/w..._compatibility
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Old 04-24-2013, 01:38 PM
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Proper Cam Selection

Buddy, I would call Comp Cams and talk to a rep telling them all info that they ask for and be truthful. There are so many variables to picking a cam to work with all the other components for the best power output that rather then trial and error use a person that makes a living suggesting the right cam. I've been there and done that!
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Old 04-24-2013, 03:06 PM
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Comp cams 265DEH-10 or 275DEH-10 Ditch the single plane manifold.
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Old 04-24-2013, 03:08 PM
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Quote:
Originally Posted by 1Gary View Post
Buddy-if it sounds like I'm coming down on you hard,I kind of am.It's frustrating to see this kind of question all the time when the info is right here.

http://www.crankshaftcoalition.com/w..._compatibility
Picking a cam with compression as the primary determining factor...

That article should be banned, not linked to.
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Old 04-24-2013, 03:39 PM
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I know there's a lot of material out there, but I'm bad at math. But I was gonna go with lunatic, but comp has a lot more packages that flow together. So thanks. I don't wanna go real fast on top end. Just fast enough to make stock sports cars drivers feel dumb. What do u think is a street able stall on that set up. I'm using a aluminum power glide.
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Old 04-24-2013, 03:55 PM
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You don't give any info on the car details and purpose.

2000++ stall

You can use up to a 3500 stall 10" converter with either of these cams.
The higher the stall, the harder the launch.
Put some gear in it if you want acceleration, especially with a glide.
usually a th-350 swap works better than a glide.
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Old 04-24-2013, 04:03 PM
How fast is fast enough?
 
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Just fast enough to make stock sports cars drivers feel dumb.

Depending on what sports car and what year you'll have a pretty hard time doing that.
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Old 04-24-2013, 06:40 PM
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Quote:
Originally Posted by ap72 View Post
Picking a cam with compression as the primary determining factor...
That article should be banned, not linked to.
That's twice you've said that. Do you have a better alternative or is it that you just can't get your head wrapped around it?

I said several places in the tutorial that it is not the end-all of choosing a camshaft, but if you don't match the intake closing point of the cam timing to the static compression ratio, how else are you going to choose a cam that works? Are you one of those guys on here who doesn't believe in DCR?

I also included a blurb from the Crane engineers that reads thusly:

"Why is it necessary to know the Compression Ratio of an engine in order to choose the correct cam?
The compression ratio of the engine is one of three key factors in determining the engine's cylinder pressure. The other two are the duration of the camshaft (at .050" lifter rise) and the position of the cam in the engine (advanced or retarded). The result of how these three factors interact with one another is the amount of cylinder pressure the engine will generate. (This is usually expressed as the "cranking pressure" that can be measured with a gauge installed in the spark plug hole.)
It is important to be sure that the engine's compression ratio matches the recommended ratio for the cam you are selecting. Too little compression ratio (or too much duration) will cause the cylinder pressure to drop. This will lower the power output of the engine.
With too much compression ratio (or too little duration) the cylinder pressure will be too high, causing pre-ignition and detonation. This condition could severely damage engine components."

Now, AP72, either step up to the plate and offer an alternative or stop bad-mouthing the stuff I write.

Last edited by techinspector1; 04-24-2013 at 06:45 PM.
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Old 04-24-2013, 07:08 PM
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OK, after spending a little time on the web, I have found that the pistons are more than likely -2.4 cc's, whereas most flat or dished pistons are in the +5cc's to +18cc's range. Now that we know the negative displacement of the domes, we can deduct that number from the combustion chamber volume and begin to find the static compression ratio of the motor.

We have a 0.030" over 350 motor with 76cc heads, so let's begin.....
(.7854 x 4.030 x 4.030 x 3.484 x 16.387 = 728.24 cc's in the cylinder
~76 cc's in the chambers. We will deduct the dome volume (2.4 cc's) from the chamber volume, leaving us with a 73.6 cc chamber and a zero piston.
Assuming the block deck height is stock at 9.025" and that the stack is 9.000", that leaves the piston deck height at 0.025". We will figure that volume thusly:
(.7854) x 4.03 x 4.03 x 0.025 x 16.387 = 2.09 cc's
Not having a clue what head gasket you used, I'll estimate it at 9cc's.
Now, we will total all the values.....

728.24 + 73.6 + 0 + 2.09 + 9 = 812.93 cc's
Deduct 728.24 from 812.93 and find 84.69 cc's
Divide 812.93 by 84.69 and find 9.5988:1 static compression ratio (call it 9.6:1)

Now, referring back to the tutorial which AP72 takes such a dim view of, we find that a camshaft with a 0.050" intake duration in the range of 214 degrees would be the right place to start looking. If you begin looking at cams here on page 58 (see the link below) and reading the static compression ratios written at the left side of the page, you'll read the static compression ratios recommended by Crane engineers for these particular cam durations that are in the middle of the page and you'll begin to see that the tutorial which I wrote is right on the money. Holy lizard crap, Batman, can it be true????????
http://www.cranecams.com/56-67.pdf

Last edited by techinspector1; 04-24-2013 at 07:30 PM.
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Old 04-24-2013, 08:29 PM
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Quote:
Originally Posted by ap72 View Post
Picking a cam with compression as the primary determining factor...

That article should be banned, not linked to.
I cant believe you said that. I have seen you post some really stupid stuff.

Not only stupid, disrespectful also.
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Old 04-24-2013, 09:26 PM
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lunatic cam?

Quote:
Originally Posted by buddy6350 View Post
I know there's a lot of material out there, but I'm bad at math. But I was gonna go with lunatic, but comp has a lot more packages that flow together. So thanks. I don't wanna go real fast on top end. Just fast enough to make stock sports cars drivers feel dumb. What do u think is a street able stall on that set up. I'm using a aluminum power glide.
best description Ive ever heard of those cams yet,,,
lol

but seriously,a cam is just one part of the recipe and you tell us what you want the engine to do and Tech and others will give you the combination
as many details as you can think of and questions/expectations and the parts list(s) will appear
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Old 04-25-2013, 12:00 AM
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Quote:
Originally Posted by ap72 View Post
Picking a cam with compression as the primary determining factor...

That article should be banned, not linked to.
I'm fully supporting that article.Why??. Because it works.There are also runs and builds that matter......................

So let's not derail another post with this stuff.If you don't agree,say so, and let the info you provide prove your point/advise.
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Old 04-25-2013, 08:09 AM
How fast is fast enough?
 
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Quote:
Originally Posted by techinspector1 View Post

Now, AP72, either step up to the plate and offer an alternative or stop bad-mouthing the stuff I write.
I already have given you a much better alternative many times. And that is picking one based on application. Displacement, target use, and induction and exhaust are ALL more important than compression.

DCR means what exactly? It's a fancy way of renaming cranking compression. Hell your target DCR is again dependent on loading and fuel so any "target DCR" is void as soon as I suggest changing fuels, cylinder heads, or in some borderline cases even induction and exhaust.

DCR is a RESULT that can be checked to help provide assurance- it is NOT the starting point.


I know you attempted to simplify things, but you not only over-simplified it but also used one of the worst metrics as a scale. A more common set of metrics would be RPM and displacement which is more accurate than your approach but still leaves a lot of room for problems.

The plain and simple truth is that you CANNOT simplify cam selection by that much and still claim to have valid results.

From what I understand your "research" came from the cam catalog of Comp, you gathered your results by selecting the target static compression ratio listed in the cam descriptions. You also chose to throw away anything they listed about RPM, induction, exhaust, usage, etc. Interesting that your argument is that their recommendations are to be trusted because of their experience yet you started by throwing away 80% of what they recommended as you deemed it irrelevant.

My "alternative" is to simply use the traditional methods of cam selection and throw away this silly idea that there is a singular trend that can be followed in cam selection, especially a trend based on such an irrelevant parameter.

DCR is a CHECK, not a target.
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Old 04-25-2013, 05:08 PM
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Well I'm trying to build something just to drive on Friday night. Just something to cruise with. I would have figured with the 71 lt1 having pretty much the same piston just with 64cc chambers and the 72 having flat pistons and 76 CC chambers. The 71 being 11:1 and 72 being 9:1. I would have figured mine to be in the middle at 10:1. Not considering the .030 over. But I planning on running it on an octane booster, as for gears I have a 9". Ford rear end. It has 3.50 gears. I really just want a quick 0-100 nothing more. And maybe a good set of breaks. I've got a 78 elcamino. But planning on buying a different. Car to put this in after its done, so I don't rush it. Ready to roll and then drop it in
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