[Fot] SU oil/refurbishing race suit?

[Phil Gott]

Correct: The purpose of the oil is to retard the rise of the piston. Why do that? If you can watch the fuel flow out of the orifice, you’ll see that slowing the piston rise gives a temporary enrichment, similar to the accelerator pump in a fixed- Venturi carburetor. 
This is needed because opening the throttle raises the pressure in the manifold ( remember it is running as a vacuum) and so raising the pressure makes the fuel condense onto the walls of the manifold ( like rain!) and so you temporarily need more of it in the air stream  to compensate.
Unlike street engines, race engines are tuned extra-rich to begin with, so they are less sensitive to this phenomenon. You can get away with no oil in the carbs sometimes. 
I run 10 W (when I can get it) or cheap ATF. Why? I find the engine is more responsive under part throttle conditions such as when I am feathering the throttle in controlled oversteer conditions (I run a welded diff so the throttle is part of my steering mechanism.)
Try it both ways and see how it works in your car at the altitude you run. It’s more about driveability than absolute power.
Phil Gott


Sent from my iPhone

> On Nov 24, 2020, at 3:20 AM, Rocky Entriken via Fot <fot at autox.team.net> wrote:
> 
> 
> Re Oil:
> I once did a race at Woody Creek Raceway, Aspen, CO (8000 feet) and could not get the car to rev over 5000 rpm. A friend diagnosed the problem ... got out his wire cutters and snipped the posts off the rods in the SU caps. Never had a problem again!
>  
> He about gave me a heart attack when he did it. Thing is, the purpose of the oil in the SUs is to retard the piston going up and down, mostly up. It was explained to me, you don’t WANT to retard the carb piston on a race engine. You hit the gas you want it WOT. RIGHT NOW! Street car, sure. Race car, no.
>  
> But a tip: Clean the inside of the carb, piston & cylinder, regularly. Before each race. Brakleen. Fuel residue will gum it up if you don’t.
>  
> --Rocky
>  
> From: Henry Giffin via Fot
> Sent: Tuesday, November 24, 2020 12:58 AM
> To: fot at autox.team.net ; fot-bounces at autox.team.net
> Subject: [Fot] SU oil/refurbishing race suit?
>  
> FOTs, I have two questions for the knowledgeable ones.
>     Do you use light oil in your SUs on your racing engines?  I have heard both sides of this.  I have not been using any oil, but have heard from friends I should be. 
>      A number of years ago when my son-in-law started racing we sent my old racing suit to someone to be refurbished.  It came back in great condition.  My current suit could use some work.  We lost the name of the company who did the work.  Can anyone recommend a source for refurbishing my suit?
>      Thanks, Hank
>  
> Hank Giffin
> 757-375-1491
>  
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