Rockers to suit cam

[Immortality]

the cam in question isn't a big cam by any measure. the ramp rates aren't that intensive either. to not run a higher ratio rocker would be a shame in my opinion. i don't think PTV clearance is going to be a issue.

maybe some of the members with similar (or larger) cams can assist when PTV clearance becomes a issue on the V6

 

[delcowizzid]

rockers will not only increase lift they will also increase force on the lifters pushrods cam cam bearings etc which will result in drag .say you have springs with 105lb seat pressure and 240lb open pressure the difference of force on the engine componants between 1.6 and 1.9 rockers is 29.6Lbs more to get the valve off its seat and 72Lb's valve fully open.times that by 12 valves equals 864Lb's of force extra on the valve train in a revolution thats 391Kg of extra force.thats on top of the extra force of higher rated springs.now on top of that is extra friction from all that extra force exerting on all moving parts in the valve train.more on the rocker tip, rocker shaft, pushrod ends (will be minimal),lifters againts there bores due to more side loading,the roller pin of the lifters,the roller to the cam lobe,the cam in its bearings,the timing chain rollers then finally the crank bearing/s.if i hadnt lost my frictional engine modeling software in the last PC crash i could tell you pretty closely how many %hp you could loose but since i dont have it its unknown.you need to toss up weather the extra lift will out do the extra drag on the engine.thats why i would go a reground cam with lift over a cam suited to high lift rockers .there is a point where you cant get the same amount of lift as cam and high ratio rockers without fitting a cam with bigger cam bearing journals like they did on the formula holden V6's but that is no real biggy just costs and extra $600ish for a new cam billet on top of the $280 to get a regrind.just food for thought and my theory behind getting the extra Hp from an engine build

 

[Immortality]

to get as much lift with just a cam and 1.6 rockers you would need to have a sizeable increase in duration, coupled with a reduced base circle. one of the other members has such a cam. .600+ valve lift, however it has 238*@.050 that puts the power band a lot higher in the RPM range with peak power above 7000rpm i'd imagine. fine if you build a engine to suit but i'd imagine some serious $$$ are involved

i completely agree that higher ratio rockers increase the load through the pushrods onto the cam/followers. however using high ratio rockers have always shown a increase in power output, so the increase in lift (and therefor flow) must be greater then the increase in friction otherwise you would not see a increase in power @ the rear wheels.

you also gotta remember that not all valves are open at the same time, some are opening, some are closing and some are obviously fully closed. if you examine this you will see that these forces tend to cancel each other out to some degree. a valve that is opening is increasing the load on the cam lobe so is trying to stop the cam turning, however a valve that is closing is trying to turn the cam faster because of the high load from the compressed valve spring pushing on the closing ramp of the cam lobe.

to run a big cam with stock rockers that spins faster then your stock engine your still gonna need springs with increased pressure. so increased friction is unfortunatly a by product of any performance engine. fact is that internal combustion engine is a rather in-efficient piece of equipment. in fact , in a good engine only about 25% of the potential energy from the fuel burned is turned into useable power at the flywheel. the rest is wasted and a lot of that is seen as heat/friction.

the trick with valve springs is to run a spring that is just enough for the rpm that you want to spin the engine and no more. and of course don't over rev and then you won't suffer from lifter pump up and associated problems

 

[delcowizzid]

yeah effects are probably low really .but it does make you think where you can get the extra few ponies from every one counts and logevity of your engine if its a daily.

 

[MACE]

to get as much lift with just a cam and 1.6 rockers you would need to have a sizeable increase in duration, coupled with a reduced base circle. one of the other members has such a cam. .600+ valve lift, however it has 238*@.050 that puts the power band a lot higher in the RPM range with peak power above 7000rpm i'd imagine. fine if you build a engine to suit but i'd imagine some serious $$$ are involved

i completely agree that higher ratio rockers increase the load through the pushrods onto the cam/followers. however using high ratio rockers have always shown a increase in power output, so the increase in lift (and therefor flow) must be greater then the increase in friction otherwise you would not see a increase in power @ the rear wheels.

you also gotta remember that not all valves are open at the same time, some are opening, some are closing and some are obviously fully closed. if you examine this you will see that these forces tend to cancel each other out to some degree. a valve that is opening is increasing the load on the cam lobe so is trying to stop the cam turning, however a valve that is closing is trying to turn the cam faster because of the high load from the compressed valve spring pushing on the closing ramp of the cam lobe.

to run a big cam with stock rockers that spins faster then your stock engine your still gonna need springs with increased pressure. so increased friction is unfortunatly a by product of any performance engine. fact is that internal combustion engine is a rather in-efficient piece of equipment. in fact , in a good engine only about 25% of the potential energy from the fuel burned is turned into useable power at the flywheel. the rest is wasted and a lot of that is seen as heat/friction.

the trick with valve springs is to run a spring that is just enough for the rpm that you want to spin the engine and no more. and of course don't over rev and then you won't suffer from lifter pump up and associated problems

I was going to write up a long winded techincal explanation, elaborating on what I've already written but this will do

"the trick with valve springs is to run a spring that is just enough for the rpm that you want to spin the engine and no more. and of course don't over rev and then you won't suffer from lifter pump up and associated problems"

This is very true! The main reason is to stop valve float which will kill a valve train quicker then anything else, as the uncontrolled pounding causing a huge spike in contact stresses running the risk of causing localised plastic deformation. This can occur on even a standard engine if you drop back down to many gears at high speed exceeding the engine rev limit. Just check out the link below to see what I mean.

YouTube - Valve Float

From experience though, with the V6's alone (let along the LS1's) there are many aggressive cams with even higher lifts around the place which are perfectly fine. Valve train problems usually tend to rear their ugly heads very early on in a build usually through sub standard components, otherwise roller cams are very forgiving.

 

[delcowizzid]

YouTube - From Inside a Working Petrol Engine now thats a good video inside an engine during combustion.roller cams normally run a heavier spring standard than a flat tappet cam its probably why most of the v6's on here never get valve float in the first place with sub 5800rpm limiter in stock tunes

 

[Immortality]

whilst we are on the subject of valve float. can we clarify exactly what valve float is. since i believe a lot of people confuse valve float with valve bounce.

my understanding is that valve float is when the valve continues to increase lift even when the follower has reached the highest point on the cam lobe. i believe that it is also known as lofting

valve bounce is when the valve closing rate is very high, the valve hits the valve seat and bounces .

the fix for the first is more "over the nose" spring pressure, the fix for the 2nd is more seat spring pressure

 

[maldotcom2]

I thought valve float was the valve not closing when it should, like it skips part of the cycle and then picks up on the next cycle.

So basically i think i'll be looking at 105lb springs. It's unfortunate that mace doesnt sell roller tip rockers. Are better valve locks neccessary or will standard ones do for less than .500" lift?

 

[MACE]

whilst we are on the subject of valve float. can we clarify exactly what valve float is. since i believe a lot of people confuse valve float with valve bounce.

my understanding is that valve float is when the valve continues to increase lift even when the follower has reached the highest point on the cam lobe. i believe that it is also known as lofting

valve bounce is when the valve closing rate is very high, the valve hits the valve seat and bounces .

the fix for the first is more "over the nose" spring pressure, the fix for the 2nd is more seat spring pressure

Fair question immortality,

I too have been bamboozled myself at times with these terms myself, as there are many people who refer to these differently the same or other.

However referring to “Introduction to the internal combustion engines, by Richard Stone” which is indorsed by the society of automotive engineers (SAE) and “Design of machinery, Robert L Norton” a high end dynamics book, in summary they state the following.

Valve float (valve jump) is when the force required during the spring operated motion, is greater then what the spring can supply. This can cause the cam follower to float off the cam lobe, impacting the cam once contact is remade (bad)

Valve bounce is basically when the valve head itself, bounces off the valve seat (worse) This will occur if the seating velocity (extremely aggressive valve train arrangement) or there isn’t enough valve seat pressure.

I thought valve float was the valve not closing when it should, like it skips part of the cycle and then picks up on the next cycle.

So basically i think i'll be looking at 105lb springs. It's unfortunate that mace doesnt sell roller tip rockers. Are better valve locks neccessary or will standard ones do for less than .500" lift?

I'm quite happy not to be selling roller tipped items, as the non roller tipped items are more suitable for the vast majority of builds around for the various techincal reasons I've mentioned in the past. As for the valve locks, as long as the standard car has never been overheated (as is can weaken material hardness) you can get away with the factory items. In saying this though, for the price, it's a little piece of mind to change them I guess, unless you were will to truly make a budget corner cut build

Cheers
Steve

 

[Immortality]

Fair question immortality,

I too have been bamboozled myself at times with these terms myself, as there are many people who refer to these differently the same or other.

However referring to “Introduction to the internal combustion engines, by Richard Stone” which is indorsed by the society of automotive engineers (SAE) and “Design of machinery, Robert L Norton” a high end dynamics book, in summary they state the following.

Valve float (valve jump) is when the force required during the spring operated motion, is greater then what the spring can supply. This can cause the cam follower to float off the cam lobe, impacting the cam once contact is remade (bad)

Valve bounce is basically when the valve head itself, bounces off the valve seat (worse) This will occur if the seating velocity (extremely aggressive valve train arrangement) or there isn’t enough valve seat pressure.


Cheers
Steve

thanks Steve. that reflects my understanding of the 2 terms.

the first image is a perfect representation of that information

people unfortunatly seem to use term valve float to cover all scenarios