Cams and the effects of different lift and duration

[dan filipi]

The 75-77 cams have 3 mm more lift than the 1200 cams.
I'll have to track down what the opening and closing degrees are of the 1200 and compare the difference but my first question is, what effect does less lift have on performance? or put another way what effect does more lift have on performance?

 

[AApple]

An internal combustion engine is nothing more than an air pump. The more air you can get in, the more work it can perform. So....if you have a cam with more lift, you will be able to draw more air into the cylinder on the intake stoke. More air + more fuel = mo power.
Cam lift, duration, rocker arm ratio, intake/exhaust port size/shape/volume, stroke, and cylinder diameter ALL have an effect on how much air can get into the belly of the beast.
In theory, a higher lift cam will produce more work(horsepower/torque), but you also have to figure in the duration of that lift...or how long the valve is open at a usable lift. The higher the lift, and longer the duration, the more power can be made to a point. Static compression is very important in regard to that.
A 3mm higher lift at the cam lobe is not the same as the corresponding lift at the valve. The rocker arm will change the lift ratio. ON an overhead cam engine, where the cam directly moves the valve is different, since there is no ratio change due to rocker arm ratios.

Are you sorry you asked now? :smilie_happy:

 

[dan filipi]

Are you sorry you asked now? :smilie_happy:

No, not at all lol.
The more K nowledge the better!

I hadn't considered the rockers themselves, mmm.
Then there's the volumetric space of the valve, ports etc. etc.

My brain is starting to hurt.

 

[dan filipi]

So Imma thinkin in my usual stupid is as stupid does fashion, a cam that has THAT much less lift with all else being equal I should feel a severe reduction in power. Looking at a caliper how much 3 mm is that's a lot!

 

[AApple]

You can have a cam with less lift, but more duration, and have the same power...it would just be in a different RPM range. :mrgreen:

 

[dan filipi]

You can have a cam with less lift, but more duration, and have the same power...it would just be in a different RPM range. :mrgreen:

I gotsta find specs on the 1200.

 

[joedrum]

it gose like this im pretty sure hot est to mildess cams 75-77 1000 cams 371.....1100 463 cams ....78-79 1000 431 cams ....1200 cams ....the milder cams will probably give better low speed power and softer more forgiving mechanics.....and the hotter cams will stuggle some at low rpm and give good power on top with non forgiveing machanics that need to be in top shape :mrgreen:

 

[dan filipi]

The manual shows a very tiny difference in the lift of 75-77 cams compared to the 80 on cams.
Is this small difference what makes them hotter or is it the small difference in duration?

 

[dan filipi]

I spoke too soon so I take that back :grin:

After looking at a 1000 cam and 1100 cam ends it's easy to see the 1000 lobe is much wider so the valve stays open longer.
So the hotter is in the length of time the valve stays open.

 

[joedrum]

yep its about 8degrees longer duration thats a bunch my 82 proves it ....its the best tool to calculate with :smilie_happy: :mrgreen: but thats why if your going to use that cam in something you have to have to bring everything up to par and then some to have confidense in it ....that where im at anyway ....its a wide ride for the valve with the 1000cams :whip: lota whip times eight :hihihi: :ahem: :mrgreen:

 

[slabghost]

I'm wondering if rockers differed any over the years? Maybe the 1200 rockers have a longer push on the valves enabling the lower lift cam lobes to accomplish the same valve opening?

 

[joedrum]

the 1200 maybe different...but i dont think so in stroke but they could be ...someting i dont realy know yet :mrgreen:

 

[dan filipi]

Say Joe, can you pull one of the 1200 rockers out and compare?

 

[joedrum]

im pulling the heads on the 1200 right now ...i will look at them and see... :mrgreen:

 

[joedrum]

the rockers are totaly different but they seem to be the same leanth so i dont think there any gain in valve movement... :mrgreen:

 

[slabghost]

Length is only part of the equation. Placement above or below center from side to side can affect motion length.

 

[joedrum]

all that seems the same vince ...the valve end is not adjustable was the big differense...i didnt measure it with anything ...but the blots for the cam carrier and rocker shafts are in the same place and valves to :mrgreen:

 

[dan filipi]

all that seems the same vince ...the valve end is not adjustable was the big differense...i didnt measure it with anything ...but the blots for the cam carrier and rocker shafts are in the same place and valves to :mrgreen:

blots?
Uh, do you mean slots where the rocker shaft slides into?

 

[joedrum]

i guess in my world at that moment ...that spells bolts :smilie_happy: :smilie_happy: :mrgreen: