As the manufacturer of Yella Terra shaft type roller rockers we have read with interest the discussion last week regarding our rockers and others having been fitted and tested by various users.

We appreciate the positive feedback expressed by a number of users and this reaction is fairly general amongst the hundreds of users who already have our product in Australia and the U.S.

The dyno figures presented in this discussion on 1.7, 1.8, 1.85 and 1.9 rockers created some comment. The question was raised regarding why a factory (OEM) style 1.85 rocker would not exhibit a similar drop off in power as the Yella Terra and Jesel extruded alloy arms at over 5500 revs.

The explanation given was that the factory style arms might have less flex than the extruded arms thereby giving some power advantage at high rpms. Our own testing on LS1 rockers undertaken some years ago during a project for (believe it or not!) Rolls Royce, and reconfirmed in testing this week actually shows the factory (OEM) LS1 flexes (deflects) considerably more than the Yella Terra extruded arm.

The test used a light checking spring as a base line then a mild performance spring with 290 lbs. at .460” valve lift. The lobe lift at the point where valve lift was checked is .272” Results where as follows

Arm tested, valve lift light spring, effective ratio light spring, valve lift heavy spring 290lbs, deflection, and effective ratio heavy spring.
Effective 290lbs Deflection Effective
Spring Ratio rocker Ratio

1.7:1 LS1 Factory .451” 1.66 .439” .012” 1.61:1
1.7:1 Yella Terra .464” 1.71 .456” .009” 1.68:1
1.8:1 Yella Terra .484” 1.78 .476 .008” 1.75:1
As you can see the Yella Terra 1.7:1 arm deflects considerably less and by design is much closer to a true 1.7:1 ratio under normal spring loads (.017” more lift under 290lbs pressure)

The theory that additional rocker flex in the extruded arms caused the power drop is unfounded. The more likely explanation is that because the extruded Yella Terra and Jesel rockers actually generate greater net lift, they are more likely to send an engine equipped with inadequate valve springs for these revs into valve bounce earlier- thereby showing an earlier drop off in power.

Testing on Yella Terra LS1 rockers by GM Australia’s performance division on various OEM and performance cam profiles with both conical and straight performance springs has not shown any drop off in power above 5500rpm.

Hopefully this information may shed some light on these discussions.

In answer to some other questions about our rockers raised during these discussions.

1/ Rockers are available in 1.7:1 ratio (part number YT6624) and 1.8:1 ratio (part number YT 6614)

2/ The sets are non-adjustable – IE they are designed to suit all hydraulic roller cam applications.

3/ Both sets will fit under all standard LS1 rocker covers without spacers and no machining is required.

4/ The rockers are designed to fit larger diameter straight valve springs and retainers without machining.

5/ We have dealers stocking this product throughout the United States, Canada, United Arab Emirates, Australia and New Zealand for your nearest dealer email sales@yellaterra.com.au

 

Wow, very thorough response. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> Thanks. <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

 

I have heard nothing but good things about your rockers....

Mostly what I hear is that after switching to your rockers, guys with high lift cams (.560" and larger) claim that their valve train quiets down considerably.

Could you shed some light on this. What other benefits, other than getting a true 1.7 ratio, does switching to Yella Terra offer.

Thanks a million.

 

Good info!

 

MY CAR SOUNDS LIKE A SEWING MACHINE
If these quiet down the valvetrain, wouldn't Jesel's or comps do the same?

what's the price on these and where can I get them?

thanx

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by muscratmauler:
<strong> MY CAR SOUNDS LIKE A SEWING MACHINE
If these quiet down the valvetrain, wouldn't Jesel's or comps do the same?

what's the price on these and where can I get them?

thanx </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Go look in the GP section. Raging Motorsports has them for <500$.

The 'Search Function' is your friend.

 

Here's a link to a few pictures showing the Yella Terra's (at the end of album)

yella terra's

<small>[ March 30, 2003, 10:14 AM: Message edited by: C5Corvette ]</small>

 

so how do these compare to Jesel or comps?

thanx

 

Are these rockers adjustable? ... I notice they have a roller tip..