Best oil for use in COFS / SOHN setup

[350matt]

So then chaps
having recently fitted a COFS setup what oils are others using ?
reading up on it so far Castrol 2T keeps popping up

was using a Motul as premix before but apparently not recommended for direct oiling

also mineral or synthetic ?

thoughts please
and if anyone has ever done or found some actual testing with dyno runs please do tell all

[qwakers]

ive spoken to a couple of engine builders that dont think much of the castrol. its too cheap for my liking too..


motul 800 racing is good for everything, premix and cofs injection. recommended to me by rrp.

[goodeggbob]

Exol Optima, as recommended by LC Rotary for premix and sohn, that was 7 yrs and 42,000 miles ago on Lewis's rebuild with no problems whatsoever.

[warpc0il]

You'll not see any effects on a dyno.

The quality of oil may effect the lifespan of the engine but can't have any impact on power.

Some 2T oils are only certified for premix, as shown on the packaging.

Any 2T oil that is certified for direct injection should be suitable for use with a Sohn/COFS, this includes those that are described as "synthetic".

Some 2T oils are also labelled as "Catalyst complient," which could be a bonus but is probably irrelevant at the effective dilution of the OMP delivery rate.


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[RenesisRaceBuggy]

You'll see more difference from bumping up the rates on the dyno than you will from the brand so long as it's JASO FD.
But to put enough in to start seeing a difference you'll kill the cat in short order.

[Dove66]

I was looking at changing the 2 stroke oil I am using to Motul 800 but saw some conflicting information, so I emailed Motul.

Date: 27 November 2025 at 09:34:42 CET
To: Technical@uk.motul.com
Subject: Motul 710 or 800

Dear Sirs,

I have a Mazda RX8. I have been running a Sohn Adapter for about 13 years.

Currently I am using Motul 710 in both the Sohn adapter & for premix.

I was looking at using Motul 800 for both, but I have seen conflicting information as to whether Motul 800 is suitable for a Sohn Adapter.

Can you help?

Regards

Graham Dove


Hi Graham,

The 800 product is not suitable for oil injection systems and can only be used for premix applications. The 710 is suitable for oil injection systems and premix applications.

Kind Regards,


Technical UK & Ireland
Co-creators of performance
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[warpc0il]

It makes a change for an oil company to respond in that detail, and is a good example of the point I made above.

I always thought that someone at Motul had a great sense of humour, naming their product "710" - for those that put their OIL filler cap upside down

[MightyCondor]

Interesting discussion. Scott at RRP has me running the 800 for track and I've been using it through a COFS. Otherwise I normally use Optima racing for road driving.

Having read the above, I suspected that the reason it's not recommended for injection is its viscosity. AI search seems to back up the theory:

"Motul 800 2T is not suitable for oil injection systems primarily because it is too viscous (thick) and can clog the delicate injection lines and pump components, potentially leading to engine seizure. It is explicitly designed by Motul for pre-mix lubrication only."

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[350matt]

I've been on the Exol optima all this time, so far so good and quire reasonable when bought in a gallon can

[warpc0il]

Exol Optima isn't a single product, it's a branded product line
https://www.exol-lubricants.com/product ... gine-oils/

If you're running a COFS/SOHN then something like https://www.exol-lubricants.com/product ... w-40-m412/ should be fine in the sump.

Of their three 2-stroke options https://www.exol-lubricants.com/product ... ycle-oils/ only this is suitable for high-output, injected, engines https://www.exol-lubricants.com/product ... roke-m124/

[osman]

Does anyone run millers Kr2t ?

[osman]

That's another example of oil that is designed for premixing and not for injection, so shouldn't be used with Sohn/COFS
https://www.millersoils-shop.co.uk/moto ... engine-oil

If you want to use Millers, it should be this
https://www.millersoils-shop.co.uk/zfs-2t-two-stroke

[350matt]

I use the Exol optima racing 2 stroke, pours like water , JASO FD spec
https://www.ebay.co.uk/itm/350586223232

[hachiroku]

I have an RRP OMP adapter and an Epitroch Install kit that I've yet to fit.
One well known garage/rebuilder mentioned that he's seen little/no difference in the cleanliness of the engine internals between the stock setup (if well maintained) and and the Sohn adapter type of modification. My engine is just over 60k and healthy, so I'm in two minds as to whether to fit the adapter or not? Currently I use the Exol Optima 2T for premix.

[hachiroku]

The main benefit I get from having the Sohn is that the sump oil level doesn't move between changes.

I can set it at 3/4 Full, knowing that it won't need topping up again, so no chance of running low or, worse still, overfilling.

The side benefit is I know that the oil being delivered to the injectors is clean, rather than being, at best 60% clean and 40% mix of all the previous oils, as that's all that gets replaced on a change.

When I fitted the Sohn I checked the injectors and found one totally blocked and two partially. There's no way to tell how long they had been and I did manage to clear them. That was in 2010.

When I checked the injectors again in 2021, they were all still fine.

Having the separate 2T tank means I can monitor OMP usage, which in nominal when road driving and massive on track, as it should be.

I also premix, though this is nothing to do with having a Sohn or not, just for peace of mind, @ 100ml / tank, it's not going to do any harm, even to my original cat.

2004 car, in the family since 2006, still on original engine with good compression.




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[350matt]

Agree with Dave here, for me a sohn adaptor should be how the car came from the factory,
Advantages are:
far less chance of clogging a nozzle
able to run thin clean burning 2 stroke oil that flows well when cold
able to run proper synthetic oil in the sump so helping with the rest of the engine wear
2 stroke oil will leave far less carbon deposit in the chambers

do it, you won't look back

[warpc0il]

Of course, all the advantages of the Sohn apply to the COFS too, plus the COFS is better engineered, designed and built in the UK
https://www.ryanrotaryperformance.com/s ... of-adapter
https://www.ryanrotaryperformance.com/s ... mplete-kit