Clearing up some of the myths regarding engine compression

Useful hints, tips that you think will help other drivers and owners. (No questions)
User avatar
DanBass
Club Member
Club Member
Posts: 14152
Joined: Tue Apr 24, 2012 8:18 pm
RX-8: PZ
Colour: Galaxy Grey
Location: Rogerstone, Gwent
Has thanked: 19 times
Been thanked: 157 times

Re: Clearing up some of the myths regarding engine compressi

Post by DanBass » Mon Mar 04, 2013 6:37 pm

To be honest I fitted it for both of those reasons. I like the idea that the oil I'm burning in the chambers is clean 2T designed for the job, and the fully synthetic is offering better bearing protection for longer, plus I'm using 5w40 grade, which offers (in theory) the best of both frequently recommended grades. I will still perform regular oil changes, as I've always done, but it was the combined advantages for me, not one in particular.
'96 NA8 MX-5: MeisterR, and soon to be choo-choo'd
'56 Galaxy Grey PZ: sold

'54 Brilliant Black 192: sold
'54 Titanium Grey 192: rebuilt, sold
'53 plate Velocity Red 192: being rebuilt...still

‘67 Sunset Orange BMW 335D MSport Touring
'01 Topaz Blue BMW 330ci convertible

User avatar
Phil Bate
Spin Doctor
Spin Doctor
Posts: 8908
Joined: Thu Mar 22, 2012 12:49 am
RX-8: 231
Colour: Sunlight Silver
Location: South Wales
Has thanked: 26 times
Been thanked: 144 times

Re: Clearing up some of the myths regarding engine compressi

Post by Phil Bate » Mon Mar 04, 2013 11:08 pm

From what I have learnt (and I am in no way accomplished in oil knowledge) proper synthetics are able to have a higher shear resistance and can stay in grade at higher temperatures for longer. It makes sense to me that this may be an advantage in our engines once you don't have to worry about burning it.

Phil
Phil's subtle sunlight silver - stronger, faster, with added red bits and stuff
The pimped out Glacier White XE - quintessential British motoring from Jaguar

User avatar
Dadiodude
Former Member
Former Member
Posts: 2329
Joined: Sun Dec 25, 2011 8:02 am
RX-8: 40th Anniversary
Colour: Crystal White
Location: Peterborough

Re: Clearing up some of the myths regarding engine compressi

Post by Dadiodude » Mon Mar 04, 2013 11:33 pm

Phil, the advantage of higher shear resistance is that you can run a lighter grade. With something like Royal Purple (arguably one of the highest) you should be able to confidently return to 5W30 and get reduced resistance and friction therefore a performance gain over a mineral/semi 10W40 offering similar characteristics. It's a molecular shear not a mechanical shear that's referred to and it means the oil will not increase in viscosity beyond its stated spec when hot, whilst a mineral oil would. Rather than cold as on a piston engine its quite possible that much of the bearing wear on a rotary is when the engine gets very hot and the bearing oil film breaks down. Cold the oil is thick and at quite high pressure.
"very funny Scotty - now beam down my clothes"


2008 40th Anniversary in Crystal White Pearl
Mazda Aero Kit, Coded Rear, Custom Cat Back, Vent Pod and Depo Gauges, Pipercross, Redline Trans Oils, Blue Calipers, Eibach 20mm Spacers, Rays Wheelnuts, LEDs, Leather Gaiter, Oh! and a Dangly Air Freshener

To Do: What's cheap?

User avatar
Phil Bate
Spin Doctor
Spin Doctor
Posts: 8908
Joined: Thu Mar 22, 2012 12:49 am
RX-8: 231
Colour: Sunlight Silver
Location: South Wales
Has thanked: 26 times
Been thanked: 144 times

Re: Clearing up some of the myths regarding engine compressi

Post by Phil Bate » Mon Mar 04, 2013 11:56 pm

Do you mean will not decrease in viscosity beyond it's spec when hot?
Phil's subtle sunlight silver - stronger, faster, with added red bits and stuff
The pimped out Glacier White XE - quintessential British motoring from Jaguar

User avatar
Dadiodude
Former Member
Former Member
Posts: 2329
Joined: Sun Dec 25, 2011 8:02 am
RX-8: 40th Anniversary
Colour: Crystal White
Location: Peterborough

Re: Clearing up some of the myths regarding engine compressi

Post by Dadiodude » Tue Mar 05, 2013 7:49 am

No mate. If an oil gets too hot it can start to break down and become too thin. The perfect oil would be a single grade that wasn't affected by temp but they all become more viscous as temp falls and less when it rises so every engin oil is a compromise. A fully synth is more consistent at high temp and is less prone to weakening and vaporising.

Its similar really to a standard grease. It works fine until it gets warm then it starts to liquefy and becomes useless. If you synthesise it by adding something like PTFE it'll continue to perform at temps where the non- synth grease has dribbled all over the floor.

Edit: Sorry Phil, just realised why you'd asked if I meant "decreases" and yes I did :).I should really plug the laptop in and not rely on the micro mobile screen. Anyway, your Sohn let's you use better sump and OMP oil and I can't see any downsides to them.
Last edited by Dadiodude on Tue Mar 05, 2013 6:43 pm, edited 1 time in total.
"very funny Scotty - now beam down my clothes"


2008 40th Anniversary in Crystal White Pearl
Mazda Aero Kit, Coded Rear, Custom Cat Back, Vent Pod and Depo Gauges, Pipercross, Redline Trans Oils, Blue Calipers, Eibach 20mm Spacers, Rays Wheelnuts, LEDs, Leather Gaiter, Oh! and a Dangly Air Freshener

To Do: What's cheap?

User avatar
Phil Bate
Spin Doctor
Spin Doctor
Posts: 8908
Joined: Thu Mar 22, 2012 12:49 am
RX-8: 231
Colour: Sunlight Silver
Location: South Wales
Has thanked: 26 times
Been thanked: 144 times

Re: Clearing up some of the myths regarding engine compressi

Post by Phil Bate » Tue Mar 05, 2013 9:24 am

Are you sure about which way around you have viscous, or am I having an arse-backwards moment here? I understood more viscous = more resistance to flow (thicker) - oils lose viscosity as they warm up (the 10w and 40 not being ratings of the same scale).
Wikipedia wrote:The viscosity of a fluid is a measure of its resistance to gradual deformation by shear stress or tensile stress. For liquids, it corresponds to the informal notion of "thickness". For example, honey has a higher viscosity than water.
Phil's subtle sunlight silver - stronger, faster, with added red bits and stuff
The pimped out Glacier White XE - quintessential British motoring from Jaguar

User avatar
fernandofan08
Former Member
Former Member
Posts: 3076
Joined: Fri Feb 10, 2012 1:34 pm
Location: Mansfield, Nottinghamshire
Been thanked: 7 times

Re: Clearing up some of the myths regarding engine compressi

Post by fernandofan08 » Wed Apr 03, 2013 5:09 pm

im fixated as mines 5.4/5.2 basically. but i think when shes running again 2 stroke oil and my usual checks should keep her going
February 2009- June 2010: Fiat Punto 60S Baby Blue

June 2010- June 2011: Renault Megane Coupe Dynamique+ Ink Blue

June 2011 - August 2012: Citroen C4 VTR+ Rouge Lucifer

September 2012- August 2014: Mazda RX-8 Evolve phantom blue

August 2014- Present: Renaultsport Megane 250 Oyster Grey

super
Former Member
Former Member
Posts: 30
Joined: Sat Aug 17, 2013 7:41 pm
RX-8: PZ
Colour: Brilliant Black
Location: South Ockendon, Essex

Re: Clearing up some of the myths regarding engine compressi

Post by super » Wed Aug 21, 2013 9:50 am

Good thread this. I took a similar opinion to the OP.

I paid 4200 quid for a mint car, even if I have to pay 2.5 - 3k for a rebuild, the car is still good value compared to other similar cars on the market.
It felt good on the test drive, and had no visible issues.
Guess I'm a glass half full type of guy.... ;)

Cheers,

John

User avatar
Soul
Former Member
Former Member
Posts: 4729
Joined: Tue Jan 27, 2009 2:50 pm
RX-8: Import
Colour: Galaxy Grey
Location: Maidenhead, Berks.
Has thanked: 1 time
Been thanked: 7 times

Re: Clearing up some of the myths regarding engine compressi

Post by Soul » Wed Aug 21, 2013 10:25 am

Let's face it, even if you had to rebuild every 4 years, that's still a lot cheaper than shelling out for a new car :D
'09 Mazdaspeed Galaxy Grey JDM
^^ Lots of mods ^^ AEM, AgencyPower midpipe, HKS Legamax......

User avatar
ChrisHolmes
Events Team Member
Events Team Member
Posts: 11619
Joined: Sun Jan 29, 2006 10:04 pm
RX-8: 231
Colour: Velocity Red
Location: Cheltenham
Has thanked: 1935 times
Been thanked: 641 times

Re: Clearing up some of the myths regarding engine compressi

Post by ChrisHolmes » Sun Apr 05, 2015 11:52 pm

Just read all this and thought it worth bumping to make it visible to more people again.
Toyo SS Catback
SS Strakes
Custom Sat Nav 3 Gauge install
Meister Zeta R Coilovers
Whiteline ARBs F&R
Slotted & Dimpled Discs F&R
Mintex 1144 Pads F&R
Full OE Aero Kit
Revolution Alloy Front Strut Brace
Lockwood SS Grills
Passenger Footrest
Lambo doors
Original engine 86000 smiles (169.7 rwhp) and then it died!
Own build Steet ported engine fitted Feb 2018 and running sweet as nut

User avatar
Shagrington
Forum Moderator
Forum Moderator
Posts: 30727
Joined: Tue Sep 12, 2006 1:54 am
RX-8: 192
Colour: Sunlight Silver
Location: Surrey (in the urban bit)
Has thanked: 517 times
Been thanked: 630 times

Re: Clearing up some of the myths regarding engine compressi

Post by Shagrington » Mon Apr 06, 2015 12:01 am

It is a sticky, so stays at the top of the page ... but yes, I guess it wouldn't be on the 'recent/new posts' or the 'active topics' lists for people who view the forum that way.
'Grington.
former Club Treasurer 2010-18 (now finally retired - just need to get rid of hand over the bank stuff etc)
Silver 192 green interior LEDS, Nordic Green hoop spoiler, roof inserts and wheels Silver Stripes

Post Reply

Return to “RX8 Hints and Tips”