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Old 06-27-2007, 04:22 PM
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Wormhole
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Default Motor Oil

I know there have been some discussions on this in the past and would like some more opinions.

Iím currently using Mobil 1, and changing it after every event in my 944T. Thinking about trying something less expensive. Not looking to substitute quality over price, but since I am changing it after every event Iím wondering if it would differ at all? If not whatís a good substitute?
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Old 06-27-2007, 04:43 PM
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kurt M
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Do you need to change it after each event? Is it contaminated or heat cooked? Other than heat breakdown track driving does not trash oil like street driving can. The oil gets hot enough to keep and or drive water and fuel contamination out. Heat damage will make the oil thinner as heat goes after the viscosity modifiers used to make the oil muti viscosity. They tend to get thinner with age until a point where contamination starts to affect the viscosity.
Just an opinion but considering the cost of a 951 motor and mods I myself would not lower to a lesser oil in a track driven 951. M1 or better considering that M1 can often be found on sale or in bulk. .
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Old 06-27-2007, 04:45 PM
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I know my Franky isn't a diesel, but I still use Rotella T 15w40 , changed after every event which is likely overkill (but it allows me to inspect for metal shavings).
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Old 06-27-2007, 04:56 PM
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I agree with kurt - do you really need to change after very event? Best way to answer that question is with an oil analysis. I use Balckstone Labs but there are others out there. For $20 they analyze a sample of the used oil. The results will help you decide if you need to change after every event.
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Old 06-27-2007, 05:17 PM
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Wormhole
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PHP Code:
Do you need to change it after each eventIs it contaminated or heat cookedOther than heat breakdown track driving does not trash oil like street driving canThe oil gets hot enough to keep and or drive water and fuel contamination outHeat damage will make the oil thinner as heat goes after the viscosity modifiers used to make the oil muti viscosityThey tend to get thinner with age until a point where contamination starts to affect the viscosity
I change it mostly for fear of fuel contamination, and with the rod bearing issues on these cars I try not to take a chance. It usually does have a rich smell and is rather dirty after I dump it.
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Old 06-27-2007, 09:45 PM
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Antonio
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I experimented with 20-50 conventional motor oil and I saw a noticeable drop in pressure when hot. Actually I switched from Mobil1 to Red Line and I've been pretty happy so far. Personally I would change the oil less often rather than compromise on quality.

From the sticker on the side of your car it looks like you run with SCCA. In a typical SCCA race weekend here in the Northeast you almost never get more than 1 hour of total track time. This is hardly enough to compromise your motor oil's lubrication qualities.
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Old 06-27-2007, 10:36 PM
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Use UOA's (used oil analysis) to judge the oil's condition. Changing oil after every event is probably not necessary. If you are using a high quality oil like Redline or M1 or Motul you are probably OK for at least 10 hours. A series of UOA's can show you a trend that will help you decide when it is time for a change. It will also spot fuel dilution issues or internal coolant leaks. These items will show up in a UOA. In my race cars I can run Redline 10w40 for 20 hours and it is still very capable of protecting the engine. For the street cars I use Rotella or Chevron 15w40 and these oils will easily go for 10,000 miles in a well tuned engine. I have found that the 50 weights were not giving me any better wear numbers and in one of the 911's it was causing a higher oil temp.

Last edited by bgiere; 06-28-2007 at 09:00 AM. Reason: sp
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Old 06-27-2007, 10:45 PM
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sweanders
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A 951 is a turbo car and it might be running pretty rich, would make sense to change the oil as soon as it starts smelling of gas. Which can be pretty quick if you are boosting a lot.
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Old 06-27-2007, 10:58 PM
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Oil that is severely diluted should indeed be changed...The question would be when is there too much fuel in the oil? By the time you can actually smell it in the oil it may be compromised and not protecting the motor. Again, a UOA will flag fuel dilution issues.
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Old 06-28-2007, 02:54 AM
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Mobil 1 turns to water at race temps. maybe not an issue for 911s, but in the 928 community, there are about 20 motor grenades all running mobil 1. i use amzoil and have a record number of race hours on an original engine made in 1986 that has never been apart.
running mobil one in another car i built, gave 1 bar less oil pressure at temp. dont know of the connection , but seeing that dramatic difference in oil pressure at temp is something i was concerned with. i think a good kendal 20-50 racing oil is fine if you change it more frequently.
my opinion.
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Old 06-28-2007, 11:40 AM
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Mobil 1 turns to water?!?!?! HUH? What temp is your oil getting to? Synth oil can stand higher temps than dino oils.
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Old 06-28-2007, 12:45 PM
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Wormhole
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Thanks for the advice guys. I think I will try to get a UOA done. I suspect it will probably be fuel contaminated. As Sweanders pointed out with the high boost and a rich mixture it probably doesnít take long.
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Old 06-28-2007, 01:52 PM
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I used to run Mobil 1 in my 944 NA race engine.

Due to oil pressure drops when it got warm I moved to AMSOIL 20w50 Series 2000 racing oil. It cost twice as much, but held pressure alot better. I change it every 3 or 4 events. It is quite expensive, but still cheaper than blowing up motors.
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Old 06-28-2007, 03:04 PM
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I have worked with a tribologist named Terry Dyson...he knows Porsche and racing engines...

http://www.dysonanalysis.com/

I have gotten some valuable advice from him over the years.
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Old 06-28-2007, 04:19 PM
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Joe Weinstein
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Pressure (above a minimum of about 10psi/1000rpm) is not what you want. Flow
is what you want. With too thick an oil, it can be pushing merrily past the pressure
relief valve in the filter, and your bearings getting starved and the pressure meter
reading 'nice and high'. You actually want to run as thin an oil as your manufacturer
recommends for the conditions. Formula 1 motors regularly use *very* thin oil.
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