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OS 91 VRDF - care and feeding

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Old 03-28-2013, 11:42 AM
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MJD
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Default OS 91 VRDF - care and feeding

The classified ads will be the death of me yet, financially and matrimonially speaking.

I just picked up a NIB small head OS .91 VRDF. No instruction sheet, but I assume it contains the usual assortment of barely relevant info.

My goal of course is a prop application.

I need to pick up a bolt on header and pipe for it. I could go to Macs but notice that there were options available for the DF crowd, as in JMP header/pipe systems. But they are OOP and hard to find it seems.

1. Anyone have a recommendation for the most effective pipe system out there for this engine?
2. OS lists max hp at 23k so I will assume that is the in flight target rpm. I have a variety of CF D speed props so will look for something that runs in the 21k range on the bench open header. Sound about right?
3. I believe the head design and compression ratio are set up for up to about 30% nitro - yes/no? I'll probably end up using 15% fuel with 22-23% total oil content syn/cas blend.

In other words, anyone on this forum have hands-on running this engine in prop applications? If so I'd appreciate any input.

As soon as the ground dries up a bit I'll be out with the test stand and ear protectors.
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Old 03-28-2013, 01:13 PM
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Default RE: OS 91 VRDF - care and feeding

Sometimes I search thoroughly first, sometimes I don't. This time I didn't.

A bunch of info here.. and I posted on this thread.. but I didn't own an OS .91 at the time so I forgot about it.

[link=http://www.rcuniverse.com/forum/m_11296981/tm.htm]OS 91 vrdf thread[/link]
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Old 04-09-2013, 10:22 AM
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Default RE: OS 91 VRDF - care and feeding

In the DF world, we ran these on 5-10% nitro with the stick head shim package. You may also want to clearance the big end of the rod to get .003". If not the bearing could peel out of the rod at high rpm. I have seen that and the results are ugly.
I had one that the sleeve was tapered on the outside up to the ports to in effect create more flow behind the port. That made a difference in topend but also consistency.
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Old 04-10-2013, 06:12 PM
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Default RE: OS 91 VRDF - care and feeding

If I have to open up the big end, can I do a decent job of it with simple tools? I'll check out the clearance. That other thread had warnings about the rear bearing only lasting a few flights.. should I stock up with Boca?

I need to order a header and pipe. Snow's nearly gone and I want to get this out on the test stand and play vroom vroom.

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