Trying to figure out lift numbers?

[Anonymous]

So I am confused on one hand I find that the stock 200 can handle about .500 lift before trouble starts....

But then if I use a hipo cam number like .453 and Roller ratio numbers like 1.60/1.65:1...

I start to get numbers like = (.453 X 1.65 = .747)?????

How can I have that much lift.....
And how will this affect getting a 9.4cr?

I am not trying to make decisions or anything I am just trying to learn..


Thanks for the help....

Jim

 

[MLINE]

Jimbo,

The cam lift .453" advertised has a 1.5 ratio (stock rocker arms) figured into it.

So the cam actually has a .302" lift (.453"/1.5).

With a 1.6 ratio rocker it would be .483" (.302"x1.6)

(I think that's how it goes)

 

[CobraSix]

Jimbo,

Mline is right...with a 4.5 lift, you can usually use a 1.6 ratio roller rocker, but you will be very close. Recommend you verify valveiston cleareance.

Also, as far as CR, your lift has nothing to do with it. In only has to do with the full volume size (piston down) of hte piston and combustion chamber compared to the fully compressed (piston up) volume. Your lift has nothing to do with it.

Slade

 

[addo]

Valve events do affect CR - not lift, per se, but duration with respect to TDC/BDC. That was why Az made his comment. But the CR he referred to was the static, calculated one.

It's still a healthy lift with full roller gear! The old modelling clay and scalpel trick (or the poor man's version - the cigarette packet) might be a good move. If the lobes had a knob that big, they'd likely not clear the first bearing!

Regards, Adam.

 

[Anonymous]

Hi Jimbo65,

Mline's post is correct. Divide stated lift by 1.5 to get lobe lift them multiply by 1.6. Increased lift will improve CR as the improvement in flow will allow more air into the cylinder, but not by enough to worry about. 1.6 rockers will also impact duration as the valve will stay open a few degrees longer. But again, not to worry. As for the cam, be sure to think through the way you plan to use your car B4 you buy that cam. A car that has no torque below 3500 - 4000 rpm is no fun to drive around town. And, such a car would idle like c..p. The 2V head with a 5200, good ignition, a good header, and a cam with .05 duration fo 206 / 208 and 1.6 valve lift of .440 - .450 would be have a strong torque curve starting at about at 2000 rpm and a 5000 rpm HP peak. HP guess - 160/165 flywheel, 120/125 rear wheels. If there is a weak point in this set up it would be the carb. A 5200 is rated at 270cfm. Assuming this engine would produce an 85% VE the car will need 250cfm at 5000rpm. Should work just fine but the next step in the progressive carb line (I would stay with progressive for bottom end) would be the Weber 32/36. Flows 320cfm and mounts on the same pad as the 5200.

There's my 2 cents - Steve

 

[Anonymous]

By the way - those HP number I quoted are very interesting when you consider that a stock 289-2V is 300 pounds heavier and has 154 net at the flywheel. And that's a fact!!

Steve

 

[Anonymous]

My carb plans are more in line with a 2300 either the 350cfm or the 500cfm....

As for the rest, I am using a 9" flywheel.
And I am unsure about my rear gears, I am trying to find the ratio.

This will be a daily driven car, lots of in town, as I am downtown. But tons of highway, as Atlanta is a Highway city with average 70-85mph.

My goals for this rebuild are to get a touch more low end, I was always pleased with the 200 torque even on my old leaky stocker. I want to improve mid-range and dramtically increase top end.... Adding the 5 speed gears of 3.97/2.34/1.46/1.00/0.79. Lets assume I am running between 3.00-3.20 rear with 15" wheels. with that 3.97 first gear I should stay below 3.50 at best.

 

[Anonymous]

Remember, the 2300 is not progressive. Could be a little boggy off the line but the 5spd will help that a bunch. The 350 cfm is plenty. The 3.20 gears with the 5spd would be my choice. Great fun.

Steve