04-16-2004, 09:53 AM
(Modification du message : 04-16-2004, 09:56 AM par PetruSeven.)
Excellent apport par Bob Cord (ingénieur développement chez Cosworth). Confirme ce que j'ai eu l'occasion d'écrire dans le passé.
<i>
--------------------------------------------------------------------------------
Also... the oil continues to get runnier as it heats up further and further. If you run a max temp in the gallery of 130 you will probably see 150 in the big ends (somewhere in between for the mains). A 0W40 oil thins less with temp than a 15W40. Therefore at 150°C the 0W40 will have a higher viscosity and provide a thicker bearing film event though they have the same visc at 100°C.
The HTHS (high temp high shear) viscosity can vary a lot. This isn't quoted so often. A modern 0W30 such as Castrol SLX(stock Audi fill)will have a HTHS of 2.9 groats but the special oil for the RS4 (which is still classed as 0W30) is 3.5. Mobil 1 0W40 has an HTHS of 3.6 and 15W50 is 5.1. Castrol RS 10W60 is 5.7. The trade off using oils with high viscosity is that even though they protect bearings at high speed they will increase friction and sap power. Looking at the Mobil website it claims they supply Maclaren Mercedes with 0W30 racing formula. Not very thick at all.
I guess it comes down to what the designer has specified during the bearing calculations. Rover use 10W40 usually and most Caterhams have run on similar grades until recently (Comma Syner Z 5W40 was OE fill wasn't it?) but now they use their own (Comma underneath) 5W50. I guess this is to protect the highly loaded big ends of the R500.
I think as long as you use a reputable synthetic oil there is no need to go above a 40 weight oil, you'll just lost power and make heat unless you have an R500 or similar rated engine when the 50 wts will be over benefit. If Caterham are satisfied with 50 then I'd stick with that.</i>
<i>
--------------------------------------------------------------------------------
Also... the oil continues to get runnier as it heats up further and further. If you run a max temp in the gallery of 130 you will probably see 150 in the big ends (somewhere in between for the mains). A 0W40 oil thins less with temp than a 15W40. Therefore at 150°C the 0W40 will have a higher viscosity and provide a thicker bearing film event though they have the same visc at 100°C.
The HTHS (high temp high shear) viscosity can vary a lot. This isn't quoted so often. A modern 0W30 such as Castrol SLX(stock Audi fill)will have a HTHS of 2.9 groats but the special oil for the RS4 (which is still classed as 0W30) is 3.5. Mobil 1 0W40 has an HTHS of 3.6 and 15W50 is 5.1. Castrol RS 10W60 is 5.7. The trade off using oils with high viscosity is that even though they protect bearings at high speed they will increase friction and sap power. Looking at the Mobil website it claims they supply Maclaren Mercedes with 0W30 racing formula. Not very thick at all.
I guess it comes down to what the designer has specified during the bearing calculations. Rover use 10W40 usually and most Caterhams have run on similar grades until recently (Comma Syner Z 5W40 was OE fill wasn't it?) but now they use their own (Comma underneath) 5W50. I guess this is to protect the highly loaded big ends of the R500.
I think as long as you use a reputable synthetic oil there is no need to go above a 40 weight oil, you'll just lost power and make heat unless you have an R500 or similar rated engine when the 50 wts will be over benefit. If Caterham are satisfied with 50 then I'd stick with that.</i>
![[Image: icnecatapetrusrm3.gif]](http://img147.imageshack.us/img147/1927/icnecatapetrusrm3.gif)
