I think it was more of a point of going from semi to fully synth and a lower viscosity that made the difference in the Clio Cup. It didn't use any oil and was a very fast example, run in to the book and then gently buit up the revs.

 

Certainly the car should feel noticeably responsive on the correct oil, 5w-30 or 5w-40 as there is less oil drag.

Tests have been done on dyno's, I've seen the Silkolene ones and there is roughly a 3% gain in BHP at the wheels between 15w-50 and 5w-40 of the same basestock composition. I would guess that this would be slightly more dramatic comparing a 10w-60 with a 5w-30 as this is a wider viscosity difference.

I posted the Silkolene tests here before but can again.

My main concern is the difference between an sae 60 and an sae 30 in viscosity throughout the temperature range

If the WRX STi 05 is set up to run on an sae 30 (tolerances and design elements) then an sae 60 is just madness!

The centistoke viscosities at operating temps are completely different.

Visc.............10degC......20degC.......40degC.. .....60degC........100degC.......120degC

SAE30...........1600..........315............95... ..........38.5............11................7.....

SAE60...........7865.........1218...........303... .........105.............24...............14....

I can only conclude that Dealers know about servicing cars but didly squat about oils and their properties.

Cheers
Simon

 

Quite dramatic difference. I WILL be changing at next 5000 mile servuce to 5/30 fully synth to release all those bogged down horses !!!

 

I don't feel that the viscosity of oil is the be all and end all of power figures - surely friction modifiers must be looked into to tell drag on engines?

Shamelessly stolen from Forced Induction Performance Tuning by A. Bell (not the same one who made telephones though!) to illustrate my point!

Synthetic Oil Horsepower Comparison
RPM........Mobil 1........Shell Helix........Castrol RS........BP Visco........Amsoil
.............5W-50.........5W-40............10W-60...........5W-40...........10W-40
3000.......143.2..........144.8.............140.5. ..............139.8............141.2
4000.......202.9..........201.3.............203.6. ..............202.3............203.2
5000.......263.1..........262.5.............262.4. ..............261.5............262.5
5700.......290.4..........290................293.3 ...............289.9............290.7
6200.......304.3..........303.5.............306.5. ..............303.6............305.6
7000.......280.7..........278.9.............282.7. ..............279.1............281.4

The test engine was a Subaru Liberty RS Turbo, and oil and water temps were controlled at 95-97degC and 85-87degC respectively

Mobil 1 0w-40 made the most power (311.2bhp) but I didnt have room to post that up (plus, as the book states, it will allow slightly more engine wear - so perhaps not the best oil to use!)

As you can see, the oil temp was kept at around 100degc, to compare the sae30 and sae60 oil bhp figures, see the table below:

RPM........Royal Purple..Castrol SLX.....Castrol RS
.............0W-30(*1)...0W-30............10W-60
3000.......140.7..........138.6.............140.5
4000.......202.5..........201.2.............203.6
5000.......262.8..........260.8.............262.4
5700.......294.0..........289.7.............293.3
6200.......308.7..........305.1.............306.5
7000.......284.5..........282.4.............282.7

*1 Royal Purple does not state a viscosity rating, although lab testing shows it to be in 0W-20 or 0W-30 range

If we were to believe there is such a huge difference in drag between the oils, would we not see an equally huge difference in BHP outputs (I would tend to trust an independent test rather than one done by a manufacturer!)


As you can see, Castrol RS outperforms the SAE30 oil, and is not far behind the SAE20/30 Royal purple (although, TBH, the differences between all 3 are not huge)!

 

Royal Purple is great! I used to be a Mobil 1 fan till I found out they arent really a true synthetic oil any more. Of course now I pay quite a bit more for the RP over M1. Now if I could just get their 75w90 and 75w90ns so I can fill the tranny and diff.

 

Mobil1 IS a true synthetic!

Royal Purple will not state what's in their oils so who knows.

Cheers
Simon

 

What basestock does M1 use? I bet its Polyalphaolifins instead of real synthetic oils polyalkyleneglycol!

Just thought I would add this:

Polyalphaolifins = 'synthetic' oils that are mineral oil based. (Mobil 1, Castrol Formula RS etc)

polyalkyleneglycol = 100% pure synthetic oils. No carbon breaking process or mineral oil.

 

oilman, or indeed anybody else that has some insight into this, any idea about the question below?

Thanks

 

Depends, alot of high performance engines come factory filled with synthetic oil. Some say synthetics are too slippery and dont allow engines to develop a wear pattern on the freshly machined parts.

All I can say is that my '02 WRX got its first oil change (with conventional oil) then at 3k & 6k. Once it hit 9k miles I switched to fully synthetic oil. I know the FSM says oil changes are every 7,500 miles but I just cant seem to convince myself thats ok. So mine gets changed every 5k miles.

Everyone has their own opinion and way of doing things. You have to find whats comfortable for you.

 

I ran the first 1000 (text book) and then went fully synth. Used a little oil for the next 1000 miles while I gradually built up the revs and was tight higher up the rev band till I had done abott 2000 miles. Done 5700 miles now (another oil change done at 5000 miles (fully Synth again)) and oil level remains pretty constant and it revs freely. I get good low down torque as well so compression must be ok too (even off turbo it starts to pull). I was concerned at first when I went fully synth at 1000 miles and some people on here were saying not good and some no problems. From my experience it has done no harm, if anything a nice slow final polish after initial 1000 miles seems a good idea to me. Think of when you polish anything, to get a perfect finish you use a very low abrasive.......that's exactly what you get with fully synth as opposed to semi

 

It's been known, seem to remember someone saying they supplied their dealer with some Silkolene Pro S which has a slightly redish tinge to it only to find on checking the dipstick that something else entirely had been used

 

Yes, sadly this does happen.

Remember though.

Pro S 10w-50 = Red.
Pro S 5w-40 = Golden.

Cheers

Simon.