USAsOnlyWay

How do the size of RRs you use affect things like where your power band is at?

Just kept reading this lately...don't honestly know why...anything else you want to throw in go for it! Thanks!

:seeya

scorp508

More lift = more air being sucked in = lower velocities at equal RPM as before = more RPM needed to get the party started.

USAsOnlyWay

So when you hear...if you go from 1.5RR on my car to a 1.6RR setup. The reason I get 10-15chp more is because I am allowing for more flow. But this also causes me to lose some down low even though the peak of the graph is 10-15hp higher? Right?

If yes...then...is that 10-15hp really worth the loss down low???

(Thanks again!!!)

Zix

Well, the problem is you can't just look at the rockers as a single component. You have to also factor in the flow numbers for the heads and the duration/lift numbers for the cam. All these factors work together to determine what power you will gain, and where. On a relativly stock LT1 though, you lose little, if any low-end power when switching to 1.6rr's...I'm not sure how the effect is on L98 engines.

65Z01

Actually 1.6:1 RRs increase the apparent cam "intensity", that is the valve opens at a more rapid rate up the cam slope so the lift all anong tghe slope is 1.067 higher. This means that the effective cam duration at .050" is increased by about 2deg.

Just adding 1.5:1 RRs has been shown to add about 10chp to an early L98, the explanation was due to several factors:
-it blue-prints the valve train, since stamped rockers can vary considerably from the assumed 1.5:1 valte.
-lower friction resunts in less wasted power

Then the addition of 1.6:1 RRs was shown to add another 5-8chp., over a stock cam.

Indeed most of the power is developed at higher RPM where better breathing is needed. But, usually going to 1.6:1 RRs doesn't cause any loss of low end torque since the LSA of a stock L98 cam realy doesn't have much overlap to start with.

With a stock L98 cam you should see a gain chp of 10-15chp with no loss of low end and a good idle from adding a good set of 1.6:1 RRs.

vader86

The RR dont affect the low-end so much, they lower the losses to friction everywhere, their affect is most felt at high rpm where the losses to friction become more important

USAsOnlyWay

Interesting....that is good to hear that it won't cut low end. Just seeing what my options are say...I suddenly can't afford to cam swap when I do a new heads and ported LTR TPI intake.

So in my situation....
Lets say I am putting on the new intake base....and worked over 113D heads. Now the compression ratio should raise along with the flow. Lets say I was going to throw 1.6 RR on.

Is this still going to have a positive effects?

ALSO,

The 113s have hardened guide plates in them currently...didn't the irons have non-functionals too....can I install the way they are?

Thanks again guys!!!!

JAKE

[SNIP]
ALSO,

The 113s have hardened guide plates in them currently...didn't the irons have non-functionals too....can I install the way they are?

Thanks again guys!!!![/SNIP]

I honestly don't understand the question.

Jake

65Z01

Especially with proted #113 heads & LT runners a set of 1.6:1 RRs would have a positive effect. If you later install a hotter flat tappet cam the 1.6:1 RRs will enhance that cam's profile.

Those #113 heads come with a set on "non hardened" guide plates that should be removed when you go to 1.6:1 RRs (check out Chuck88's posts on RR install). The stock stamped rockers on the #113 heads were self-aligning and the guide plates were not supposed to touch the push rods after the engine was assembled. Your stock iron heads didn't use guide plates, instead they used narrow slots in the heads to guide the push rods.

Also, since you will likely be doing a cam change in the future, it would be a good idea to install 7/16" rocker studs to enhance valve train stability at higher RPMs and a set of Ti retainers for increased RPM before valve float. With your mods you will likely push the useful RPM range to 6k RPM, give or take a few hundred RPM (with stock cam, heads & runners my L98 is now pullling pretty strongly through the 5,800rpm shift point. These items along with new valve springs will put the valve train upgrade in the $500 range.

George West

65Z01,
you said:

"Actually 1.6:1 RRs increase the apparent cam "intensity", that is the valve opens at a more rapid rate up the cam slope so the lift all anong tghe slope is 1.067 higher. This means that the effective cam duration at .050" is increased by about 2deg."

That is the best explanation of how rocker arm ratios will affect performance that I have ever heard. The additional lift is not the only effect, as you so nicely explained.

George

BTW I went from stock stamped rockers to roller type 1.6:1 ratio rockers, and here are the results. The big spike is the torque coverter slingshot at the 1-2 shift:


[Modified by George West, 9:27 PM 11/28/2003]


[Modified by George West, 10:58 PM 11/28/2003]

scorp508

George, there are some serious variations in power there where the line is swooping what it looks like 20hp between RPM. Were you losing spark or fuel pressure on those runs?

flyersfan1088

I believe it's 3 hundreths.

George West

:iagree: I was working with a total lift of .050, so the increase in lift due to the ratio change was the surprisingly small figure of .003, as I stated.

But.......... .050 is not much lift!!!!! DUh!!!! :_dupe:

What's an order of magnitute between friends?

Gee, I hope you don't mind if I go and change it to 30 thousandths, before everyone else catches on that I am more than capable of being stupid!!

The graph I posted is HP vs. TIME - not HP vs. RPM. I shifted late in both cases, and so the major HP roll off. The overall increase in HP when the X-axis is TIME is real, and all cars exhibit this on such a graph. It is caused by the power consumed in rapidly changing the inertia of the rotating assemblies - including the tires. As soon speed becomes stable, this effect is gone.

You can also see both plots start out very much the same - it takes a second for any difference to become apparent. That is because I cannot do full throttle launches. The gain from the rocker arms is only there at WOT, of course.

Sorry - it is an unusual way of displaying HP, I should have mentioned it. I like it because it is easy for me to see how a change affects the motor in the first few crucial seconds.

George

scorp508

I'm not exactly following you. For a second I think I do, but when I look at my own graphs I become lost again. Perhaps you could explain in in a different manner?

Here is one of my dyno pulls. The first graph is SAE RWHP vs. TIME and the second one is SAE RWHP vs. RPM. Both of them have smoothing turned off completely. You'll have to click on it to see them better. My car is also a stick so you don't get the shift whackyness.




You can see that both charts show the same overall very smooth trend with no major loss in power in successive frames.


[Modified by scorp508, 10:40 PM 11/28/2003]

George West

My data is collected while actually driving the car at WOT, not while stationary on a chassis dyno. Losses from wind resistance and frictional losses are removed by subtracting HP loss data - collected while coasting down from high speed.

Both methods of collecting HP data are valid, although accelerometer systems are not as popular. Chassis dynos display more appealing numbers, as you can see.

I love my accelerometer system. I have 130 data sets collected, including 10 1/8 mile 8.6 second runs. The repeatability is suburb. Looking at your car's mods, I would say that my car on a chassis dyno would look very much like yours - and yours would look similar to mine on an accelerometer system. But your shift points would become very obvious - just like mine are.

When you shift into 2nd gear, the engine is screaming one moment, and back to lower revs the next. The energy stored as RPMs is suddenly released to the rear wheels through the clutch. Why a chassis dyno does not see this, I do not know.

Scorp - that is a nice web page that you have, BTW.

If you are interested in reading more, see :
http://www.mrdyno.com

My "Mr Dyno" is the most useful tuning tool that I own

-George

USAsOnlyWay

I have been out of it recently and this computer is not my home one and the pictures won't load. But this looks like some great info . I can't wait to look at the graphs along with the words!
:flag

TIMSPEED

Since we're on the subject of roller rocker arms..if I swapped from stock stamped's to 1.6 RR's would it make my car sound more "cammed"? Or would the difference be unnoticable?

JAKE

From my experience and what I've read from others' comments, the difference is definitely noticable; both in sound and power.

Jake

BIG JIM 54

Larger rocker arms don't do anything different than stock R's except use up more room under the valve cover.

Rockers with more ratio definitely will however.

BIG JIM

George West

Roller rockers can be expected to add at least 10HP from reduced friction. The 1987 Corvette advertised 240 HP, up 10 from 1986. The reason? - roller rockers!

Factory stamped rockers do not usually make the 1.5:1 ratio, so there is some additional HP gain to be had. Simply put, roller rockers will give you horsepower.

From:
http://www.chevyhiperformance.com/te...148_0207_rock/

"To prove this point, we tested several supposedly 1.5:1 small-block rocker arms and discovered rocker ratios between 1.30:1 and 1.49:1. We also found that the ratios changed throughout the lift curve, increasing the ratio as lift increased. This reduced ratio means lost valve lift and potentially lost torque and horsepower."

George