Rocker Ratio and Duration

[cpalma]

Hi there,

a hypothetical question on my part but maybe already tried out by the guru engine builders here...

i've heard it said somewhere that increasing rocker ratio also increases effective cam duration, is this correct? if so, by how much, is there a way of knowing this?

i guess what i wanted to know is will an fk10 with 268deg. dur @ 0.05 on 1.5 rockers for a total lift of 0.58" be "the same" as an fk89 with 282deg 0.05 duration on 1.4 rockers and the same total lift? was playing with the idea before i actually change parts...

thanks...

[Johannes Persson]

Hi cpalma,

You won't increase or decrease the cam duration by changing rocker ratio, the cam will always has the grinded numbers , but you will increase the valve duration by putting bigger rockers on.
The valve duration is actually more important when it comes to designing an engines output.
The valve duration is the timing the the engine breaths from, not the cam numbers.
An fk10 has about 276deg at the valve at zero lash with 1.5:1 rockers.
An fk89 has about 290deg at the valve at zero lash with 1.4:1 rockers.
Both cams has the same valve lift but 14deg diff in valve dur, this means that the fk10 has to open the valve to the same lift on less dur or time which results in a lot higher opening and closing acc than the fk89.
A high opening and closing acc needs a bigger valve spring and that is harmfull to the valve train.
Also what is interesting is the valve lash when the engine is running, a hot engine has about 0.4-0.5mm(0.015"-0.02")lash which reduses the real breathing duration with as much as 10-12deg.

Regards
Johannes Persson
JPM
Sweden

[cpalma]

Hi Johannes,

Thnks for the insight, became a fan of yours since i followed the thread on your mouse 1603cc motor, so nice to hear from the man himself....

Anyway, it makes more sense now that i think about what you say on valve duration - what's not clear yet is how you come up with the actual numbers for example on the fk10, i know it has 268 or thereabouts at 0.05, how do i convert this to the 276 @ zero lash and with the 1.5 ratio?

Also on acc ramp, i always looked at the advertised minus the durattion at 0.05 numbers and the bigger it is the milder the ramp? Is this an acceptable way of evaluating cams and is it true that higher valve opening/closing acceleration rates improve on overall torque/power?

Lastly, if lash when the engine's already at operating temp and running increases, does it make sense to set it to "zero" at hot if i want maximum lift out of the cam/rocker combo?

Rgds, Cris

[John Maher]

... if lash when the engine's already at operating temp and running increases, does it make sense to set it to "zero" at hot if i want maximum lift out of the cam/rocker combo?

Rgds, Cris

AS JP stated above, chromoly pushrods, even when set to zero cold clearance will have a hot clearance of at least .015".

Each camshaft is designed with a specific running clearance in mind. This figure is taken into account by the manufacturer such that the initial lift phase takes up lash gently - saving wear and tear on the valvetrain.

Check your Engle cam card and you'll see designed clearance is .008" for the FK10 intake (.010" on the exhaust) and .006" (inlet and exhaust) on the FK89.

Because you're likely to have in excess of .015" clearance on your fully warmed engine, the initial 'gentle' take up portion of the lobe has already gone past before the valve is subjected to any lift.
The greater the difference between actual valve clearance and the cam designers intended clearance, the harder the valve gets hit and the greater the initial velocity. You also have less duration than intended, less area under the curve and (usually) less performance.

Closing up the valve clearance when hot effectively increases duration and will accelerate the valve more gently off its seat (and sooner).
Depending on valve spring installed height (avoid coil bind) and valve to piston clearance, this could give good results but requires frequent maintenance if you want to avoid burnt seats.

On the dyno, adjusting hot valve clearance can be a neat way of checking cam selection (trying to evaluate lash changes on the track or street is almost impossible).
If the engine makes more power with tighter valve lash, you might conclude a cam with more duration should have been selected

Likewise, increasing lash reduces duration. If gains are made, it looks like the engine needs a milder cam.
Increasing valve clearance beyond the normal settings isn't recommended for regular use - excessive clearance is hard on parts.

You can't make one cam behave like another by playing with lash and different ratio rockers but you may get a hint as to whether your existing cam choice is the right one.

Camshaft duration is also a deciding factor with regard to compression ratio... switching from FK10 to FK89 requires an increase in static CR, otherwise performance will be flat due to a big loss in dynamic CR.

[Zach Gomulka]

Hmmm... wonder what will happen to the the valve duration when I swap from 1.1's to 1.4's on my stock cam

Good info here, guys. Thanks for sharing

[Jon]

As always great information, Thanks!  If "we" could keep down the clearances it would be easier do keep the cam/valves to doing exactly what you want them to, and more power would be the result.
Does anybody have any great ides for how to keep engine expantion down to a minimum? Either by simple things like better cooling or shorter barrels/stroke or fancy stuff like unobtanium cylinders?

Btw does engines make more power from cold with certain cams?
 

[Udo]

Hi there,

a hypothetical question on my part but maybe already tried out by the guru engine builders here...

i've heard it said somewhere that increasing rocker ratio also increases effective cam duration, is this correct? if so, by how much, is there a way of knowing this?

i guess what i wanted to know is will an fk10 with 268deg. dur @ 0.05 on 1.5 rockers for a total lift of 0.58" be "the same" as an fk89 with 282deg 0.05 duration on 1.4 rockers and the same total lift? was playing with the idea before i actually change parts...

thanks...

I think you first think about what you want to do with the engine ! Racing, Street ? What engine size and heads ? The K10 is a good street cam , K89 is more a race cam... You can run both with 1,5 or 1,4 rockers

Udo

[cpalma]

x2 on the great info here, as always, that's why i keep coming back...

thanks John for the tip on watching out for burnt valves when running such tight valve clearance but since i'm leaning more toward using the engine for weekend racing than high mileage street use, heating the engine up enough for that to be a problem will be remote.

good advise also on assessing a cam if it's too small or too big for the engine making use of valve lash adjustments. i think i got matching the cr to cam duration covered - right now the k10 gets 10.5:1, maybe 11.5 for the fk89 w/ pump gas?

Udo, this car has been mostly street in the past and i want to see now how quicker i can go - 2.2L with 044 wedgeports, 44x37.5, k10 w/ 1.4 rockers and 10.5:1cr. best time so far is 12.8 @ 104. I want to go low 12's maybe 12.3 or better so i'm thinking about changing the cam and raising the cr...

[John Maher]

If you decide to tighten up lash when the engine is hot, the valves won't close once everything has cooled down.
Combustion gases will travel past the intake seats and backfire out through the carbs.
Exhaust valves can't dissipate heat if they don't make contact with the seat.

When the engine cools you need to back everything off so it will run smoothly from a cold start.
Then once warm and everything has expanded you can close up lash again. And so on....

Like I said, a lot of work but the price you pay for running pushrods that don't expand at the same rate as the engine 

[Felix/DFL]

Does anybody have any great ides for how to keep engine expantion down to a minimum? Either by simple things like better cooling or shorter barrels/stroke or fancy stuff like unobtanium cylinders?

Very good Infos in here! I always set lash to zero with chrom molys!, as I once measured the lash at warm engine (The push rod should turn free without play at the rocker).

The better way to compensate the engine expansion would be with very strong alu pushrods, as the alu expands more than the chrom moly one`s.
Thermal expansion:
Alu=23
Steel= about 11-16 (depends on composite)
Maybe Alu one`s with a loose steel core?

[SlingShot]

Thermal expansion:
Alu=23
Steel= about 11-16 (depends on composite)
Maybe Alu one`s with a loose steel core?

What about the other way around? Say a 5/16 alum pushrod with a 3/8 steel sleeve over that? The alum could still expand end to end, and the steel could help reduce deflection.

[JS]

Or what about one of JPM´s newly designed cams that has very nice ramps that require very low spring pressure so you can run alu pushrods without sleeving?
Any test results Johannes?

[Jon]

The big problem is perhaps the expanding case? Not the cylinders as I first thought. What can be done to limit the case expanding?

[Johannes Persson]

Cris,

There is no good way to check valve numbers if you don't have the cam in the motor and measure at the valve or have the possibility to run your cam in a "cam doctor".

I have fortunately both, that is way I could give you the numbers.

Yes, you could get a hint of how long the ramp is by doing the calculation you mentioned.

A fast opening and closing of the valve is normally what you want, to see good numbers, but you will come to a point when the spring pressure needs to be so high that the valvetrain starts to flex and you lose power.

Every type of valvetrain has it owns limitations on positive acc and spring pressure.

For a year ago I started to work with my "Single cyl type 1 engine(69x94)".One of the most interesting R&D has been to improve the valvetrain and to design new valve lift profiles(cams).
I started to put light parts in the valvetrain like ti valves, Alu retainers, just a single OTEVA75 spring, JPM 1.55:1 rockers, GB 160000 psi pr, Schubeck lifters and a Fk87.Dyno pulls was from 3000rpm till valvefloat.The Fk87 did float, severe, at 7500rpm, not bad with just a single spring, 70lbs installed and 175lbs at full lift approx 15.5mm.After a pull I put the lash to zero and picked up another 150rpm before float, that tells you the importance of a good ramp.
I use the latest computer soft ware to design the Valve Lift Profile.On the two first cams small changes was made to the ramps, no improvements over the Fk87 because the Fk87 has a good ramp if only the valve lash is kept small.The third cam had the same Dur and lift as the Fk87 at 0,05" but more area under the curve and optimized acc, improvements was huge 8450rpm before valve float and 10% more power and torque.

Regards
Johannes

[Rasser]

After a pull I put the lash to zero and picked up another 150rpm before float, that tells you the importance of a good ramp.

The third cam had the same Dur and lift as the Fk87 at 0,05" but more area under the curve and optimized acc, improvements was huge 8450rpm before valve float and 10% more power and torque.

Regards
Johannes

I had no idea, that the beginning of the ramp had THAT much effect on valvecontrol/power!   
Amazing R&D

Thanks for sharing!!!

With the early state of the ramps beeing so  damn important - could you then say that alu pushrods will make your valvetrain live longer (if they are strong enough for your valvetrain offcourse), compared to steel pushrods? (both used in street cars, and therefore adjusted cold)

[cpalma]

Hi Johannes,

Really appreciate you taking the time to answer questions from newbies like me, and off course sharing your knowledge to fellow speed freaks. I hope you don't mind more   Q's       

No need for "cam doctor" software when the r&d is done for us by experts like yourself, i think most can do the lift at valve measurements and together with a degree wheel can also determine duration.

Very interesting points you raise on lash where keeping it close like in your example made 150 more rpm before float on the fk87, also the detail you gave on the same lift as fk87 but bigger area under the curve cam. I was under the impression that the bigger area under the curve scenario meant higher duration and therefore higher "top end" power and torque due to the higher rpm? Is this correct....but that i stand to loose torque down low if i go bigger area under the curve / duration - do these 2 terms mean the same? I mean in your example where it made 10% more power (which is "huge" for just a cam change) with the much higher rpm, was this only at top end or across the board?

Lastly, in your 1603cc mouse motor, i noticed u used a 1.5+ rocker ratio with the fk45 - this will increase more the valve acceleration on the already high intensity cam, did you sleeve the lifter bores?

Thanks again...

[Johannes Persson]

Hi again,

You can get more area under the curve without making the 0.05" dur and lift bigger.
Let's say that you increase the dur at lifts above the 0.05" then you still have the same opening and closing points at the valve, this will give more area under the curve and power and torque improved all over the power band.When changing a cam in this way an eye has to be kept on the acc so they don't get too high.As long as you don't close the intake valve too late and open the ex valve too Early the power band will be kept at about the same rpm but the cyl pressure will increase.

The peak power with the third cam was at the same rpm as the fk87 but thanks to the optimized acc numbers the valvetrain could hold all the way to 8450rpm without floating.No other changes was made to the valvetrain like bigger springs or lighter parts.

The acc numbers on fk45 with 1.55:1 rockers is abnormal, I wouldn't go with that choice today after all the R&D I have done on modern thinking on valve lift profiles.It is possible to deign a cam with more area under the curve than the fk45 without changing the 0.05" dur and lift, using lighter springs coming down in friction, temp and releasing some hp a win win situation.

After what I experienced, when I switched from fk46 to one of my own cnc grinds in my own street car, every fk4.... needs a good quality sleeve in the lifter bore.

No, I did not sleeve the mouse motor lifter bore.

Rgs
JP

[71CALRIPPER]

Just reading this thread and thought how lucky we are to have some of the real big name of our hobby/passion answering our questions.

Very interesting and great reading at work

Ty
Rob

[Rasser]

What´s your thoughts on using alu pushrods to better "control the lash" between hot/cold (aircooled.net sells HD ones). As I understand the problem with steel pushrods is that they have more lash when hot, and the alu pushrods don´t have the same tendency - correct?

If using alu pushrods, then you would have an easier ramp, because of the lash beeing smaller (when engine is hot!  (lash initially set at cold engine))?  Thus making the valvetrain live longer? And the weight difference on the pushrods will also help the valves not to float, and be easier on the valvetrain.

With your newly designed cam that can get away with only single springs, then Alu pushrods could be a possibility?

Am I completely wrong here, or does it make sense?

After a pull I put the lash to zero and picked up another 150rpm before float, that tells you the importance of a good ramp.

The third cam had the same Dur and lift as the Fk87 at 0,05" but more area under the curve and optimized acc, improvements was huge 8450rpm before valve float and 10% more power and torque.

Regards
Johannes

I had no idea, that the beginning of the ramp had THAT much effect on valvecontrol/power!   
Amazing R&D

Thanks for sharing!!!

With the early state of the ramps beeing so  damn important - could you then say that alu pushrods will make your valvetrain live longer (if they are strong enough for your valvetrain offcourse), compared to steel pushrods? (both used in street cars, and therefore adjusted cold)