# Potential Problem 1.85 roller rockers



## gawexp (Nov 13, 2007)

I built my 06 GTO auto and changed to custom Lunati cam (555/571 lift)

Ran into a VERY STRANGE problem - a mechanical REV LIMITER

After 4 hour of DYNO time could not go past 5900 rpm - even though the computor was still sending the right info. (fuel, spark, etc.)

The graph went up very smoothly (like normal) then *STOPS* at 5900 rpm

NO ONE I knew or could consult with had a clue or had ever heard of this. The springs are good to 580 and have seat pressure of 135lbs.

I took the last resort and did some advanced geometry and discovered the springs were not tall enough by .0600

I HOPE THIS HELPS SOMEONE

FYI - Complete SLP exhaust (headers back), Prof. Products intake, Ported and hand polished heads (flow 300cfm), 1.85 roller rockers, hand ported and polished 90mm throttle body, 47lb injectors, Lnati new bee hive springs, titanium push rods, MSD wires, iridium plugs, K&N air intake, carbon fiber tall valve covers, and custom Lunati cam -- OH Yes .0600 tall spring locators


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## Rukee (Feb 8, 2007)

So, did you change the springs and did it help? Were they the stock springs in there to begin with that gave you the mechanical rev limiter?


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## 05GTO (Oct 6, 2004)

IMHO, 1.85 rockers should add 10-12 % to your Lunati cam's lift of 555/586 giving you a lift somewhere around 615/650. I would suggest going with a higher rated/stronger spring.


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## gawexp (Nov 13, 2007)

1st Stock springs are not good to 580, but to 550. I used livernois custom springs, then after the problem I changed to just released Lunati bee hive springs rated to 600 lift and to be sure I added the spring locators

2nd 555/571 is after factoring the 1.85 rockers

Just for everyones information (I figured it wrong for quite some time)
You take your present rated lift and divide it by the ratio it is rated at - this gives you actual lift you then mulitply this number by your new ratio

Example my custom cam was built for 1.85 lift - but out of the box the lift was rated 510/525 at 1.70 - So you divivde 510/525 by 1.70 to equal 300/308.8 and now multiply by 1.85 to get 555/571 true lift.

THANKS ALOT FOR THE REPLIES -again hopes this helps




b


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