Rockers to suit cam

[maldotcom2]

Hello. I have a cam ready to install into a project engine (ecotec V6), now i'm looking for some higher ratio rockers to suit. Here are the cam specs, please advise what is the highest ratio rocker i can use with this cam on a standard crank with high comp pistons. Also what springs and pushrods will be required.

[acarmody]

I wouldn't go any bigger than 1.8:1. You will need 105lb springs and modified retainers and oil seal I think. Give Steve from MACE a call, he can fix you up. Sells all these parts at very reasonable prices.

[immortality]

.520" max lift stock heads
.540" with slim valve stem seals
.550 with modified retainers
.570 with modified retainers and new slim valve stem seals

for total valve lift greater then .570 you need to machine the top of the valve guide off.

push rods depend on how much you have machined of the deck and heads, head gasket thickness etc

the cam supplier should really suggest a appropriate CR but i'd suggest a little more then stock will be a good starting point. maybe 10:1

you will also need suitable springs

.294 and 1.7 rockers = .4998" lift
.294 and 1.8 rockers = .5292" lift
.294 and 1.9 rockers = .5586" lift

personally i'd go for the 1.9's with new seals and retainers, you will need new springs so you will need new retainers, may as well get the ones with the extra .030 clearance and the new seals. MACE sell all of these

[MACE]

"Hello. I have a cam ready to install into a project engine (ecotec V6), now i'm looking for some higher ratio rockers to suit. Here are the cam specs, please advise what is the highest ratio rocker i can use with this cam on a standard crank with high comp pistons. Also what springs and pushrods will be required."

Assuming you're running a double row timing chain, shorter retainers, shorter stem seals and 130lb springs then I would recommend a set of 1.9:1 ratio rockers. This is also assuming that the piston to valve clearance is ok at this level of lift.

Cheers
Steve

[maldotcom2]

Hi Steve. That is essentially the crux of my question, if I use 1.9's am i gonna smash a valve through a piston? Is there a calculation i can do? I know how to do it with the rockers in place but obviously i need to know what rockers to buy.

I have the double row timing chain, everything else i'll probably buy from you shortly.

[chargedvx6]

Hi Steve. That is essentially the crux of my question, if I use 1.9's am i gonna smash a valve through a piston? Is there a calculation i can do? I know how to do it with the rockers in place but obviously i need to know what rockers to buy.

I have the double row timing chain, everything else i'll probably buy from you shortly.

You will need to measure the piston to valve clearance with some ratio of rocker. Maybe start with a stick rocker and plot the PTV through out the combustion cycle, especially the exhaust valve as the piston is very good at playing catch up when the ex is closing.

Looking at the specs of that cam I'd suggest not going crazy with lift. It doesn't have a crazy duration and the LSA is tight. Looks to be a very efficient grind so I wouldn't go messing with that by having un needed lift. Keep in ming your engine is N/A and would not out flow that cam with stock rockers.....................that is unless you are running heavily worked heads and some kind of more efficient fuel like E based.

What ratio did the cam manufacturer state?

[maldotcom2]

I was under the impression you can never have enough lift. I figured some more lift from rockers might help low down without adding duration. The heads are ported and polished, but nothing crazy.

Once i work out the PTV clearance with stock rockers how to i work out clearance for higher ratio? Measure clearance, divide by stock ratio, times by new ratio and add the difference to the PTV measurement?

[MACE]

You can calculate the PTV clearance theoretically if you plot everything out, but if your not handy with a calculator and geometrical equations then your best bet would be practically determine what that is. You can use dial indicators to do this however the cheapest easiest method (considering the engine is apart) would be to use the plastacine (spelling?) or clay method for the job as shown in the link below.

FORDMUSCLE webmagazine: Fundamentals - Checking Piston to Valve Clearance

As for going higher ratio rockers on a roller cam, it’s not a problem provided the spring seat pressure and stiffness is there (to stop valve float). Assuming that the cam itself still has a hardened layer on the surface (which can be compromised with heavy regrinds unless they’ve been nitrided after regrinding) then they’ll be able to with stand the contact stress associated with the increase in seat pressure with no local deformation of contact surfaces (chewed lobe, roller bearing on lifter etc). The “theoretical” forces acting on the various valve train components can be worked out here.

valve train dynamics

In saying this though in, very rare cases, where an engine has done many many km’s or where the contact stresses are very high using extremely stiff springs (as found on NASCAR engines), fatigue cracks can occur on the contact surfaces as shown in the link below.

www.mechanicsupport.com: Some thoughts on camshaft lobes

In saying all of this though it would be best to contact cam supplier, as they may have removed .100” off the base circle for the job which would certainly have an impact on the forces in the valve train, or haven’t re hardened the cam after a regrind etc. For the cams we supply though this isn’t a problem nor are the springs which are designed to be used with aggressive LS1 cams (same spring we use for the eco 6’s) as has been proven time and time again.

If it was a flat tappet cam then I would definitely say no, as they’re much harder on the cam lobes as it is LOL.

As for going higher lift here are my thoughts on the matter as cut and paste from another forum…

Going higher lift even a little beyond the flow capability of the heads, is as close to one will ever get to achieving a "free lunch" with a cam. By that I mean will have minimal impact on low end performance, unlike going a narrower LSA or greater duration which can. Show in the link below is a good example of the impact that going a set of higher ratio rockers can have on power production

V8 Performance Parts

It's for this reason our 2.15:1 ratio rockers or an standard ecotec cam are very drivable even with a standard tune, though valve lift has increased by around .130"!

Yes people may say that it's pointless going past a certainly valve lift on a cylinder head as as there are no peak gains in flow rates, however the average flow rate per given amount of time and duration at .05" would most certainly have increased! So ramp rate is also something to consider.

At the end of the day it depends on what you want, however if your after a more streetable cam, best to err on the side of less duration with more duration and more lift

My 5 cents

Cheers
Steve

[delcowizzid]

just have to watch with big cams the lifter acceleration rate is allready huge then you add rocker ratio and the valves accelerate and close even faster slamming on the seats and wanting to bounce.ide stick with the lowest ratio possible the cam is ground to suit stock ratio.with higer ratio youll change the 50 though lift duration as well

[maldotcom2]

Hmm, maybe it's a bit risky to go with high ratio. I do after all want to play with the cam timing as well. It just pisses me off that i have to pay the same for stock ratio and get no added performance.

[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.

Book 283.jpgBook 284.jpgBook 285.jpgBook 687.jpgBook 693.jpg

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

[MACE]

The term valve float is a bit ambiguous of which I've been guilty of using loosely. As mentioned in the articles valve jump and valve bounce, are clearer more technical descriptions IMHO.