jadedvette

The stock ratio rocker arms for a 1986 coupe is 1.5. If I change them to 1.6 I know it will give me more cam lobe lift, but why do I want that. Is it more horsepower, or more torque, or both. Will I feel it seat of the pants. I know this sounds like a dumb question because I know what it does. I just don't know if it helps. What will raising the lift without changing the duration do?
Thank you,
Joe

siggy_freud

Getting more lift for the same duration, is in a way getting free horse power/torque. I say that because, in a sense, your not changing anything else about the engine or its powerband. You aren't really sacrificing power at a certain range to gain it somewhere else. Some argue that it does change duration, however thats impossible since duration is dependent on the cam lobe itself and short of regrinding the cam, duration wont change. It can change duration when measured at a certain lift.

Realize that by going to 1.6, the valve is staying open for the same amount of time. However, the valve is also lifting further, thus allowing more air in, during the same amount of time. That translates into more torque and horsepower. If the valvetrain can handle it, I dont see any reason not to do it. Just be sure to keep valve geometry in mind.

CFI-EFI

It will not change your, "cam lobe lift", but it will increase the amount of lift at the valve. By it's self, a rocker arm ratio change should be good for 5-10 horse power.

RACE ON!!!

redbullapril23

also you gain hp just by the rollerized tips because it has less frictions than your stock rockers.
your friend
Sean

jadedvette

Thanks for the answers, but of course I have one more question. Why do people split the ratios (1.5 on exhaust and 1.6 on intake). I would think that if you add more fuel mixture you would need more exhaust opening to get rid of it.
Joe

siggy_freud

That and less side to side movement and strain on the valve stems. But if your going to rollerize it . . . go full roller, not just roller tips. Just my opinion anyways.

bogus

I have wondered that myself...

VAHROOM

It has also been said that the stock rockers aren't all created equally. I have heard that the ratio between a set of stock rockers vary within the set. You may be getting parts that make each cylinder work equally and smooth out the engine even more.

65Z01

Going to 1.6:1 RRs increase valve lift by 6.7% and increase duration at .050" lift by 2deg, though of course they do not change advertised duration (i.e. at .004"). This is because at every point along the cam lobe the valve now opens 6.7% higher so the .050" valve opening point comes earlier in degrees or cam rotation and the .050" valve closing point comes later. If you plot a typical cam profile with 1.5:1 rockers and then add 6.7% to the lift at every point you will see how this works.

Years ago TPIS installed 1.6:1 RRs on an '85 L98 and found that 1.6s on the intake gave about a 15chp peak power gain but that installing 1.6s on the exhaust brought no more power but a rougher idle. So they recommended splitting the RR ratio. You might also want to split ratios to keep valve lift within the bounds of the springs when going to a new cam.

I now run 1.6:1 RRs on both intake & exhaust of my '88 L98 (with #113 Al heads) and idle is even smoother than with stock stamped rockers.

Also, with the iron heads the push rods are guided by slots in the heads which can interfere with 1.6:1 rockers. So it might be necessary to machine iron heads to accept the 1.6s.

If your '86 has iron heads and don't want to bother with the possible needed machining, you could still gain about 10chp at peak power by going with 1.52:1 RRs. This gain comes from reduced friction as well as reduced side thrust, which allows the valve to track the cam profile more accurately.

Yellow95

Only down side is engine wear. You lower mechanical advantage with the increase in lift. The cam/lifters/push rods/rockers/springs have to work harder. You go to rollers to manage the additional forces.

neat

If the heads work well witht he cam shaft design to promote good scavenging, you can get away with less lift on the exhaust side. Using a smaller ratio rocker is easier on valve train components, especially the springs. It also allows you to use a spring with less pressure on the exhaust side. Less pressure means less force is required to open the valve, so the engine will put that power to the tires instead of losing it internally by opening a stiff valve spring.

Popular hot rodding did an article awhile back called "Horse power shootout" or something like that. 10 of the best engine builders in the world built NA small block V8's. One of the top 3 made over 600 CHP, and had a 1.3 rocker on the exhaust side. They tried all the way 1.6 with no gain in power.

CFI-EFI

This is a small factor IF one goes to roller rockers. jadedvette didn't specify or address rollers. Not ALL 1.6:1 rocker arms are rollers.


The RATIO of the rocker arm has no effect on the "side movement" or "strain on the valve stems"

RACE ON!!!

red88L98convert

The RATIO of the rocker arm has no effect on the "side movement" or "strain on the valve stems"

RACE ON!!![/QUOTE]


uh.......if you use a lever to pry or force something open, you apply pressure, or strain, on whatever you are trying to move or pry. if you use a bigger lever, you exert more pressure, or strain, with all else being equal.

CFI-EFI

The spring provides the resistance to the valve opening. The rocker arm ratio doesn't change the pressure required from the tip of the rocker arm, to open the valve. Besides, the operative phrase, here is, "SIDE MOVEMENT

RACE ON!!!

red88L98convert

not to be tied up on terms......but, ive seen valve tips snap clean off of stems from too much rocker ratio--with the same set of springs. now, these were high spring rates, but point being, there is indeed added strain on the valve tips, which is what i was referring to. not the side to side movement. but on that note, take a look at the wear patten on a set of valve tips prior to changing to a different ratio, run the rockers for a while (50-100 miles) then recheck the wear pattern. youll see a difference. at least i did.

cv67

Some guys that run a single pattern cam like to run those in search for a "little" extra depending on the seat timing.Changing from a 1.5 to 1.6 can also tell you if the motor would repond to more cam or not. Yours has a dual pattern cam. Most guys here seem to be happy with 1.6 on both

mean8t

By going to a bigger cam you lower your engine's dynamic comprassion ratio. The longer the intake valve stays open ABDC the less cylinder pressure (dynamic compression ratio) the engine will have. I agree completely with what 65ZO1 said, 1.6's will increase duration at .050" lift, but frankly that doesn't matter, two degrees is a drop in the bucket. You however are not changing the total duration which is where you get dynamic compression ratio. The dynamic compression ratio is way more important than static compression ratio b/c it determines how the engine will perform. You can make all the compression in the world, but if it is bled off by a cam that is too large then it is all wasted.

CFI-EFI

What your referred to was my reaction to a post that said, "...side to side movement and strain on the valve stems". You even quoted my post that cited that post. I maintain that the rocker ratio does NOT increase the side movement of the rocker arm or the SIDE strain on the valve stem.

When you go to a greater rocker arm ratio, the rocker arm travels through a longer arc to attain the additional lift. This will cause a different wear pattern on the valve stem, but that wear will be in line with the rocker arm, not SIDEWAYS causing side strain.

By the way, a higher ratio rocker arm is a SHORTER lever, not a longer lever.

RACE ON!!!

65Z01

Take the cam in LPE's book for example:
268/268=int/exh, advertized duration (at .006deg)
218/218=int/exh, duration at .050" lift
110, LSA

With 1.5:1 rockers this cam has an overlap of 24deg at .006" (268/2 - 110 = 24) and no overlap before .005" lift (218/2 - 110 = -1).

Going to 1.6:1 rockers will not change the advertized (at .006") lift much but it will add about 2deg to duration at .050". This now brings overlap at .050" lift to 220/2 - 110 = 0.

Since dynamic CR depends on the area under the curve from advertized druation to the point on the cam profile where there is no overlap, 1.6:1 rockers indeed change dynamic CR.

There are several sources of friction in the valve train 1) rotation of the rocker about the fulcrum, 2) sliding of the tip across the valve tip, 3) sliding of the valve stem in the guide. We will neglect the slight rotation of the push rod tip within the rocker cup. At high RPM there are significant side forces on the rocker stud, which deflect the tip of the stud and increase the motion of the rocker tip across the valve stem tip. This not only increases friction at the valve tip but imposes additional side thrust on the valve stem, increasing friction with the guide. Of course this lateral motion of the rocker stud also reduces effective valve lift, which is why we upgrade to 7/16" studs or even to stud girdles.

So, when upgrading to 1.6:1 RRs there are a number of factors to consider if you want to spin your motor safely to higher than stock RPM (and this is really what upgrading the valve train is about). These can take a $300 upgrade to over $600 in a hurry (e.g. adding Ti retainers at $150/set).

Don't let the above frighten you away from this useful mod though, consider the LS7 with 1.8:1 Rollers.

CFI-EFI

I disagree that the overlap period has any influence over the dynamic compression ratio. The overlap takes place when the intake valve starts to open before TDC at the end of the exhaust stroke, and the exhaust valve closes past TDC into the intake stroke. The compression stroke doesn't start until 180* PAST the middle of the overlap period. Since the intake valve stays open past BDC, in to the compression stroke, it is the point of the intake valve closing that has the greatest effect on the dynamic compression ratio. Actual compression can't start to take place in the compression stroke, until the intake valve closes. The overlap period has nothing to do with dynamic compression.

We may not have a "meeting of the minds" as to the definition of "side thrust". I agree that the thrust of the valve stem in the valve guide will be greater at higher lifts, whether due to the rocker arm ratio or the cam profile, But that thrust is in line with the rocker arm and not to the side. It may just be semantics, But I would call that lateral loading rather than side loading. What I hear as "side loading" would remain pretty much unchanged.

RACE ON!!!