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IMO, for a flat-tappet cam, nothing thinner than the 10w40 you're proposing changing to.

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IMO, for a flat-tappet cam, nothing thinner than the 10w40 you're proposing changing to.

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So would 5W-30 RP be ok for a roller cammed engine?

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Accord to the RP tech, you should base the viscosity you choose on oil pressure for a particular engine. For their racing synthetic oil, they recommend idle pressure in the 15 lb range, and 7 lbs for every 1000 rpm. I can't bring myself to run pressures that low, but that's what the guy said. I do believe that with the quality of synthetics these days, you can run tighter clearances and thinner oil - and make more HP. JMO.

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Like was mentioned above, the "correct" oil viscosity is a factor of oil clearance, oil temps, application (short-duration vs. endurance), etc. Spending some time on the Joe Gibbs oil web site looking through their oil application guidelines may help improve understanding of this.

I also have some concerns about using oils that IMO are too thin for extended street use, especially when it comes to flat-tappet cams. I look at things like the HTHS (High Temp High Shear) ratings for different oils because that is a good indication of how the oil should handle heavy-interface loads such as cam & lifters.

You'll have trouble finding any Xw30 oil w/ a HTHS rating much higher than 3.5, whereas you can get as high as a 5.x HTHS rating w/ heavier oils. In that respect, oil viscosity can be (like so many other things) a compromise.

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Damn Brad, you`ve got too much time on your hands. Some people love to over-complicate things and oil along w/all of the other subjects beaten to death is another one of them. I have to question how many actually try stuff instead of asking others who may not know what works and what doesn`t. I keep doing things that "experts" say can`t/shouldn`t be done again like the 8" vert on the street, spool thin oil etc. My clearances are bigger than most and even w/a high volume pump and only 6-quarts of oil, I still see 20-25 hot at idle and 65+ above 7000 rpm`s and never a problem EVEN street driving as in LOTS of desert miles and even dirt roads occationally.............just do it!

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... Some people love to over-complicate things...

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Guilty as charged!

FWIW (serious note), if you're still running Mobil 1 10w30 as I recall from the past, I really don't believe what they sell now is a "beefy" enough oil for the power level you're making. I know you're all about bang for the buck and not over-spending (I try to be, but often fail miserably at it), but that stuff is about one step above horse p!ss now from all the info I can find on it.

I've stopped running it in my '02 WRX, if that's any indication of my loss in confidence w/ Mobil 1's street oils.

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Brad, would you know if the RP 5w-30 falls into the same category as M1?

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I'll rephrase that and point out that it's not just M1; all the standard light-viscosity (5w30 and under) passenger car oils out today have been "watered down" w/ respect to their anti-wear additive packages that can mess w/ the cat converters. The stuff on the shelf of the local parts store these days is intended for my Honda mini-van, not a 700 HP street car.

It sounds like you've had good luck w/ what you've done to date. Just be aware the latest API standards have applied yet another "hit" to passenger car oils in the name of the saving the environment.

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As usual, this thread has gone slightly off target. The OP is presently using a race oil, designed for race engine applications. The point is that in the past race oils usually included high viscosity oils, like 20/50 stuff. Todays race only oils are a lot better than they were 20 years ago and there is less "linkage" between "thick oils" and "race oils" than in the past. As an old conservative engine builder and racer, I have turned the page on this one - and aint lookin back!

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Brad ,everyone
thanks for the replies and feedback.
this saturday will probly be my last meeting till February,except possibly T&T.
i will run the 20/50 and over Xmas dyno the motor back to back with the 10/40 .
i guess my biggest worry is daily driving/highway use particularly when hot.the last 2 weekend of racing temp has been high 20's and into the 30's Celcius.and its not summer yet.

Tex

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Tex, I use Valvoline 5W20wt non synthetic in my Duster, limited street and a lot of strip My bearing clearances are pretty loose, .0035+ on the rods and mains , My oil pressure reads right at 20 lbs at 850 RPM in gear with oil temps at or above 180F on the street 1200 RPM makes the oil pressure go up to 35 lbs and it has 50 lbs at 1500 RPM, 65 lbs at 7000 RPM There is some HP gains with low oil temps with the lightweight oils is what I found years ago, just what most bracket racers need

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"you bracket racers that see your cars pickup when hot lapping, what type and weights of oil do you use"

Yes my car will pick up but I do not think it is oil temps. You have trans temps- rear end -wheel bearing-motor get heat in it and burns fuel better. I run 15-40 wt oil. all these things together make it pick up.

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My first pass of the day is always a bit slower...
thats with driving it around to warm it up