Thread: My Chevy 355 has little real power - looking for suggestion on CAM change

Tweet

Once you've figured the static compression ratio, you can use this handy calculator from KB pistons to figure the dynamic compression ratio....

http://kb-silvolite.com/calc.php?action=comp2

Where it asks for the intake closing point, take the info from the Crane spec page for the cam you're looking at. It will give you the figure at 0.050" tappet lift. Add 15 degrees to that figure and that is what you'll enter into the KB calculator. Crane shows the cam I suggested to have a closing point of 35 degrees ABDC. When I calculated your DCR with that cam, I entered 50 degrees into the calculator.

You know, it just is that simple. You look through the list of cams and pick the characteristics you want from the upper right hand corner of the cam description (Crane), then use the KB calculator to see if you have a match. Try to get the DCR between 8.0:1 and 8.25:1. Any less and you won't have much of a motor and any more than that and you won't be able to run pump gas without detonating. Of course there are exceptions to every rule. If you have a very tight squish, combustion chamber polished, spark plug electrodes de-burred, no overhanging head gasket, no PCV and no EGR, you will be able to get away with more on pump gas.

One more thing about Crane. They will give you the LDA too, although they don't list it that way. Go all the way to the bottom of the cam spec card and add up the two cam timing figures at max lift, then divide by 2. Here's a for-instance.

http://www.cranecams.com/?show=brows...tType=camshaft

This cam reaches max intake lift at 105 degrees AFTER top dead center and max exhaust lift at 115 degrees BEFORE top dead center. Adding the two together gives you 220, then dividing by 2 gives you 110. So, this cam has a lobe displacement angle of 110 degrees. Cams with a higher LDA (112 and up) will make more power higher in the rpm range and will tend to be very smooth at idle, making excellent manifold vacuum. Cams with a shorter LDA (110 and under) will make power lower in the rpm range, but will tend to peak sooner. They will also exhibit a choppy idle and low manifold vacuum. (You will need about 18" of mercury to operate power brakes properly).

You asked if it is necessary to degree the cam in. It's just like anything else. Once you learn how to do it, it's easy. And YES, I would urge you to learn how to do it and to degree this cam in. How else are you going to know that everything is optimized for performance? Go here and click on Degreeing a cam.....the easy way.

http://www.cranecams.com/?show=insta...t%29#Camshafts

OK, I'm out of breath. Any questions?

Thank you very much. I have some reading and work to do.

In order to calculate the CR, there are pieces of information I do not have such as eyebrow volume. Do I simply estimate? I don't want to tear apart the engine to make the decisions on what to buy.

Originally Posted by techinspector1

Once you've figured the static compression ratio, you can use this handy calculator from KB pistons to figure the dynamic compression ratio....

http://kb-silvolite.com/calc.php?action=comp2

Where it asks for the intake closing point, take the info from the Crane spec page for the cam you're looking at. It will give you the figure at 0.050" tappet lift. Add 15 degrees to that figure and that is what you'll enter into the KB calculator. Crane shows the cam I suggested to have a closing point of 35 degrees ABDC. When I calculated your DCR with that cam, I entered 50 degrees into the calculator.

You know, it just is that simple. You look through the list of cams and pick the characteristics you want from the upper right hand corner of the cam description (Crane), then use the KB calculator to see if you have a match. Try to get the DCR between 8.0:1 and 8.25:1. Any less and you won't have much of a motor and any more than that and you won't be able to run pump gas without detonating. Of course there are exceptions to every rule. If you have a very tight squish, combustion chamber polished, spark plug electrodes de-burred, no overhanging head gasket, no PCV and no EGR, you will be able to get away with more on pump gas.

One more thing about Crane. They will give you the LDA too, although they don't list it that way. Go all the way to the bottom of the cam spec card and add up the two cam timing figures at max lift, then divide by 2. Here's a for-instance.

http://www.cranecams.com/?show=brows...tType=camshaft

This cam reaches max intake lift at 105 degrees AFTER top dead center and max exhaust lift at 115 degrees BEFORE top dead center. Adding the two together gives you 220, then dividing by 2 gives you 110. So, this cam has a lobe displacement angle of 110 degrees. Cams with a higher LDA (112 and up) will make more power higher in the rpm range and will tend to be very smooth at idle, making excellent manifold vacuum. Cams with a shorter LDA (110 and under) will make power lower in the rpm range, but will tend to peak sooner. They will also exhibit a choppy idle and low manifold vacuum. (You will need about 18" of mercury to operate power brakes properly).

You asked if it is necessary to degree the cam in. It's just like anything else. Once you learn how to do it, it's easy. And YES, I would urge you to learn how to do it and to degree this cam in. How else are you going to know that everything is optimized for performance? Go here and click on Degreeing a cam.....the easy way.

http://www.cranecams.com/?show=insta...t%29#Camshafts

OK, I'm out of breath. Any questions?

Yes,I have a question.What drew you to northern Wisconsin?

Originally Posted by techinspector1

You asked if it is necessary to degree the cam in. It's just like anything else. Once you learn how to do it, it's easy. And YES, I would urge you to learn how to do it and to degree this cam in. How else are you going to know that everything is optimized for performance?

I agree I need to learn. If the extra 4 degrees makes so much of a difference, why don't they just grind that into the cam (possibly differences between each engine setup)?

Originally Posted by pnut

I agree I need to learn. If the extra 4 degrees makes so much of a difference, why don't they just grind that into the cam (engine differences)?

Comp. cams does on some of their grinds.
What I do on some of the performance engines is "degree" the cam and then start the engine get it broke in or at least get it to operating temp. for a few cyles and then go back and re-degree the cam again.
Most of the chains I have used will loose about two degree' or maybe a little less.

Originally Posted by DennyW

You can buy the pre-stretched sets for 32.95, for small block chevys.

COMP Cams Magnum Double Roller Timing SetsPerformance and reliability for the street.
Building a really high performance street vehicle? COMP Cams Magnum double roller timing sets are built for maximum performance on the street. They have heat-treated, pre-stretched, large-pin, double-row chains for extra strength and reliability. They also have crank sprockets with three keyways, which allow you to set cam timing at 4 degrees advanced, 4 degrees retarded, or normal. In addition, all Magnum double roller timing sets are dynamically balanced for smoother operation.

http://store.summitracing.com/egnsea...1&autoview=sku

What Denny say's is true.
One thing I might add is "crank timing" is not the same as "cam timing" in other words I would check all piston to valve clearance's and re-degree the cam when or if you decide to move the crank sprocket around.

Originally Posted by DennyW

I like to check them both ways. Example: I may advance the crank sprocket 4º. And retard the cam gear 1 to 2º. You can work it, and dial it right in. Get a descent dial indicator, and timing (degree) wheel, and just work it to where you need it. Double check it until all your marks repeat. Instructions come with the degree wheel, and tells you syep by step how to check things out. That, along with the cam specs, and you can do it.

I do the same thing.
When I was drag racing I could move the cam timing one way or another 1/2 a degree at a time on the belt drive.
In other words if I thought my 60 ft times where to slow I might advance the cam 1 degree to make it pull a little harder on the bottom.Well you all get the general idea.