Hardt

In a situation in which you are starting from scratch with a rocker arm/camshaft design. Would there be any advantages or disadvantages to increasing the rocker ratio from say, 1.55 to 1.85 or even 1.95?

This is for a drag race application. Were going to make new roller followers anyway (different design than crane/ferrea) and have new profiles designed for them. The idea of changing the ratios came up, hence the thread and questions.

Im sure there are downsides to higher ratios, Honda did choose to go from a 1.85 ratio with the H23 down to a 155 with the H22. They also went from a 1.75 with the LS down to a 1.55 with the B series VTEC applications. Im sure there were reasons in doing so.

From the looks of it, there seems to be an advantage by going with a higher ratio. The higher ratio would require less lobe lift to generate the same gross lift. To me, that seems like an advantage.

Suck my DX

were cam profiles changed to accomodate the different ratio between the series?

i would assume theyd have to be

edit* after re reading the orginal post i realized my original question was irrelevant.. but would it (rocker ratio)have anything to do with the the engines RPM capabilites?

Hardt

Rocker ratio is one of the factors that determines gross lift.

lobe lift x rocker ratio = gross lift

Increasing the rocker ratio will increase gross lift with the same camshaft lobe lift.

Heres a quote from an old post:

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">Example 1 (1.55 ratio):

A cam with a lobe lift of .300/7.62mm and a rocker ratio of 1.55 (stock B/H series) would result in a gross lift of .465/11.81mm

Example 2 (1.85 ratio):

A cam with a lobe lift of .300/7.62mm and a rocker ratio of 1.85 (custom) would result in a gross lift of .555/14.09mm
</TD></TR></TABLE>

DonF

It also increases duration @ lift points, which you might need to know as you are designing them.

Furyof4

Would the higher ratio have more risk of cam/rocker arm wear at higher rpm's? Maybe thats why honda went with lower ratios for the vtec heads.

DonF

Not on a roller rocker.

Furyof4

I realize that but, I was thinkin more about the reasoning behind this:

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Hardt &raquo;</TD></TR><TR><TD CLASS="quote">Im sure there are downsides to higher ratios, Honda did choose to go from a 1.85 ratio with the H23 down to a 155 with the H22. They also went from a 1.75 with the LS down to a 1.55 with the B series VTEC applications. Im sure there were reasons in doing so.

</TD></TR></TABLE>

Fkned

Also dont forget a few things- it makes the valve speed faster w/higher ratios and may need extra spring pressure to compensate.- Along with the stress it imparts to the valves from the higher loading it causes on guides and harder/faster closing rates may be one of the reasons they have thicker stems on the ls heads.

Hows life been Ben,havent heard from you in a while how's the head doing?

Furyof4

Life's been good lately.
That heads running strong.