What's the most power you've been able to achieve?

[MikeH]

Mike, Even with 5 degrees advance at 9.3 to 1 the Dynamic compression is only 6.8. At 10 to 1 it is perfect at 7.3.

Your meaning here is that at 10:1 I would run the cam straight up, correct?

 

[260Alpine]

Mike, That was before I knew crank degrees, not cam degrees. 5.3 or 1 tooth on the cam is too much. it would be 10.6 at the crank. The more I think about it would be better to just grind 4 degrees advanced into the cam specs.

 

[260Alpine]

I found the cam specs for a stock cam on the replacement ones they sell. 206 duration @ .050 for both valves and .395 lift for both valves. My program with Offy intake and Holley 390 carb shows 150HP @ 5000RPM and 170TQ @ 4000RPM. 6.5 Dynamic Compression. 18 Inches of Vacuum. 120HP @ rear wheels.

 

[MikeH]

Mike, That was before I knew crank degrees, not cam degrees. 5.3 or 1 tooth on the cam is too much. it would be 10.6 at the crank. The more I think about it would be better to just grind 4 degrees advanced into the cam specs.

That might take blank or a meatier cam to do that, don't you think? What compression works with the cam straight up? I wonder how hard it woul be to have a hole drilled in the end of the cam and on the cam gear to use a pin to achieve the advance. That is if an offset key is not found.

 

[260Alpine]

Mike, You would be close with 10, comes out 6.9 Dynamic for Jose grind. I think when they regrind, it goes to smaller base circle. There is enough meat in an un ground stock core.

 

[todd reid]

What's the most power you've been able to acheive?

Jim,
1. I understand the theory of machining a second keyway, but is that really practical in the real world? At 4* (or 8*) it seems like the keyways would be practically touching and the resulting part would be weakened - or are you expecting us to be smart enough to weld up the first keyway without being told to do so?

2. I went back and looked for the picture of the pulley with 3 keyways. The keyways look really far apart - like close to 90* apart. What purpose would that serve, or am I missing something?

3. If it is not too much of a hassle, can you run numbers on the stock cam with the stock 2bbl carb? That would establish the baseline that more or less everyone started from.

Thanks in advance! I for one am learning a lot!

TR

 

[260Alpine]

Todd, if you draw a cross and move one line 4 degrees crank, 2 degrees cam one way you can visualize what they did. I also posted a link for a offset key. I'll run the stock 2 barrel. You gain over original by better exhaust flow and no choking emission control.

 

[260Alpine]

Todd, Here you go. Stock 2 barrel, stock cam, no emissions, headers. 139HP @ 5000RPM, 163TQ @ 4000RPM, 6.5 Dynamic Compression, 18 Inches Vacuum, 111HP @ rear wheels.

 

[MikeH]

Here's a cam calculator I found online. Plug in the opening and closing degrees.

http://www.wallaceracing.com/camcalc.php

And another article on cam basics.

http://www.tildentechnologies.com/Cams/CamBasics.html

 

[MikeH]

You sure 1 tooth is gonna be 8 degrees?

Remember that cam degrees double the crank degrees (which is what the engine simulator uses).

You want 4 degrees at the cam to make 8 at the crank. You may be able to get there with an offset key. Otherwise you may need to make a timing adjustable cam drive or a custom cam gear.

The more I read on this the more confused I get. Wouldn't this actually be the other way around. Two revolutions of the crank turn the cam one. So wouldn't one cam gear tooth be equal to 5.3/2=2.65?

Is the cam advance relative to the cam's position in the block or relative to the crank?

This doesn't clear it up either.

Lobe Separation Angle or Lobe Displacement Angle – The angle between the centerlines of intake and exhaust lobes, expressed in camshaft degrees. For timing 25-65-65-25, the lobe separation is 110 cam degrees (220 crank degrees).

Cam Advance - the position of the midpoint between intake and exhaust lobes relative to TDC. A cam with timing 25-65-65-25 has no advance and is said to be "straight up". If the same cam is advanced 4 degrees, its timing becomes 29-61-69-21. The intake and exhaust centerlines are now at 106 ATDC and 114 BTDC respectively.

 

[260Alpine]

Mike, Cam gear is twice as big as crank gear. Crank gear goes around twice for every time the cam gear goes around once. Open and Close are in crank degrees. ATDC= After Top Dead center. BTDC=Before Top Dead Center. Same for Bottom Dead Center. I think offset key 2 degrees for cam would be easiest. One way would be 4 advance crank degrees, flipped around would be 4 degrees retarded. Another thing to be careful about is, at 10 degrees advance the intake valve is closest to the piston. 10 degrees retarded the exhaust valve is closest to the piston. 10 to 1 or more compression, even at 4 degrees you should check piston to valve clearance.

 

[MikeH]

It all still goes back to why wasn't this an issue with past conversions.

Think I finally found something to clear it up.

Remember: The camshaft angle is half of the crankshaft angle, therefore the camshaft will correspondingly advance or retard 1°, 2°, 3°, or 4°.

So moving the cam gear one tooth (5.3 degrees) changes the timing 10.6 degrees at the crank.

Found in the article below.

http://www.compcams.com/(S(yyboabakneda22nutbxo1jvq))/Instructions/Files/COMP4-153.pdf

 

[V6 JOSE]

Hi Mike,

There hasn't been a problem with this cam, because there is nothing wrong with it. The problems are because of other reasons. I can't exactly diagnose the problem, because I'm not there to see it for myself, but I can tell you for a fact, the cam is not the problem. Rich Gordon told me a month ago, that he can actually idle his engine down to 600 rpm if he wants. He runs his at 800 rpm, because that is where it should idle.

I would venture to guess it is because of engine assembly.

It all still goes back to why wasn't this an issue with past conversions.

Think I finally found something to clear it up.

Remember: The camshaft angle is half of the crankshaft angle, therefore the camshaft will correspondingly advance or retard 1°, 2°, 3°, or 4°.

So moving the cam gear one tooth (5.3 degrees) changes the timing 10.6 degrees at the crank.

Found in the article below.

http://www.compcams.com/(S(yyboabakneda22nutbxo1jvq))/Instructions/Files/COMP4-153.pdf