Premixing and cats

[R1DSO]

I’ve done a lot of website and forum searching, but can’t find a clear and definitive answer on the viability of RX-8 premixing whilst using a cat. Maybe there isn’t one...

Ideally, I would like to premix the street recommended 4mil of Idemitsu 2-stroke synthetic blend racing premix per litre of fuel when I pick up my 2009 R3 next weekend. I’ll be refuelling with 97+ RON whenever possible.

Although the R3 has the extra oil injector (and there doesn’t seem to be a wealth of tangible proof backing the benefits of premixing), from everything that I have read about the engine, providing further clean and high quality lubrication into the Renesis seems like a good idea.

However, I would like to keep the cat. The hassle of MOT swapping etc aside, I’d rather not have to put up with noxious exhaust fumes. I have never experienced a de-catted RX-8, but if the fumes are as bad as a piston-engined classic car or a 2-stroke outboard, then this doesn’t particularly appeal.

A lot of people are saying 2-stroke oil will clog the cat, ultimately leading to overheating and a potential source of engine failure. However, RX-8 cats of course fail without pre-mixing due to poor ignition. And, there seems to be a contrary opinion that, if your ignition system is healthy and you’re using a high quality ash-less premix, then pre-mixing is cat safe.

I will be replacing the ignition system with RRP coils + new plugs and leads, but cannot find anything that says Idemitsu is ‘cat safe’, although it appears to be what most people are using.

Can anyone who has premixed with a cat provide any guidance on this + what brand of pre-mix oil they’ve used? And would a high flow 200 cell cat like the one Racing Beat sell make any difference to the equation vs the OEM part?:

https://www.racingbeateurope.com/mazda- ... 2288-p.asp

Many thanks in advance...

[warpc0il]

I’ve done a lot of website and forum searching, but can’t find a clear and definitive answer on the viability of RX-8 premixing whilst using a cat. Maybe there isn’t one...

A lot of people are saying 2-stroke oil will clog the cat, ultimately leading to overheating and a potential source of engine failure.

You're looking at the wrong websites and reading the wrong forums, if this is the fake news that you're seeing.

Premixing with a quality 2T oil won't do your cat any harm at all.

[350matt]

I premix on mine and have a 200 cell cat and have since done about 30K miles since fitting the cat
a recent inspection showed no issues with ash formation at all - I think the 2T oil burns pretty cleanly and the CAT gets so hot there's not much left

the only thing I do still get with mine is a rare P0420 code ( cat not functioning within range) this tends to pop up every 5-6K miles
So i erase it and carry on

[Essex2Visuvesi]

I’ve done a lot of website and forum searching, but can’t find a clear and definitive answer on the viability of RX-8 premixing whilst using a cat. Maybe there isn’t one...

A lot of people are saying 2-stroke oil will clog the cat, ultimately leading to overheating and a potential source of engine failure.

You're looking at the wrong websites and reading the wrong forums, if this is the fake news that you're seeing.

Premixing with a quality 2T oil won't do your cat any harm at all.

This is the important bit

[R1DSO]

That’s re-assuring to hear. Thanks guys .

Most of what I could find specifically on the subject of premixing and cats was on rx8club.com/rx7club.com, r/RX8 on Reddit and YouTube channels such as Driven By Madness and The Slip Angle. There seemed to be a lot of voices advising to de-cat if premixing. And I couldn’t find anything on Idemitsu product pages confirming it was ‘cat safe’.

On the cat clogging point, my nearest point of reference was an old 2-stroke marine outboard I used to have, which (with a 50:1 premix), used to spit unburnt oil out the exhaust at idle. Aware that that’s a very different (and rudimentary!) engine vs the Renesis. But, with the content I had read on the subject, I had images of unburnt 2-stroke oil coating the honeycomb in the cat!

Now knowing that that isn’t the case, I’ll order some Idemitsu or similar for next week. I see forum members are using Castrol Power 1 and that can be bought from Halfords, so I may default to that for ease.

[350matt]

bear in mind most folks don't premix anything like that sort of 50:1 ratio of a old 2 stroke

I typically add roughly 50ml to a 25ltr fill

so 1:500 ratio

[R1DSO]

viewtopic.php?f=25&t=50814

[R1DSO]

bear in mind most folks don't premix anything like that sort of 50:1 ratio of a old 2 stroke

I typically add roughly 50ml to a 25ltr fill

so 1:500 ratio

Interesting, so as little as 2mil per litre.

Yeah, I guess you need more premix in a 2-stroke where that’s the only form of engine lubrication. And an outboard is running much lower temps than the Renesis.

I remember getting my leg splattered with a load of unburnt oil after walking in front of my outboard exhaust. The engine was running out of the water with hose muffs (to keep it cool).

With what I’d read elsewhere, that was my vision of what the inside of a pre-mixed RX-8’s cat might look like .

[R1DSO]

viewtopic.php?f=25&t=50814

Don’t know how I missed that sticky. Thanks .

[delta0]

I have a high flow Milltek cat and I also premix about 100-150ml per tank in an R3. Zero issues and have gone through the last 2 MOTs without problems.

[acegeezer]

RX8club.com is not where I'd be looking for info, they still recommend revving to 4k before switching off a hot engine .. so lots of misinformation spouted by that US site

[Honkytonk]

Not to distract from being redirected to the sticky post, but just as a further reassurance I run the OEM cat on mine and premix with no ill effects other than the odd 2 strokeywhiff every now and then (particularly if I've just started the car and am reversing out of a car parking space, for obvious reasons).

If you're using a racing one designed to burn cleanly then at the concentrations we're talking about (150/175mls per 60L) you won't have anything to worry about. Castrol Power 1 racing 2T (gold bottle)is what I use and is the most widely available and cheapest to get hold of unless you buy in bulk. You can get all fancy with royal purple idemitsu etc. but the good old gold bottle works for loads of us round here.

[warpc0il]

What is it with those guys that they won't let the facts get in the way of "a good story"?
Do they think that it somehow makes the RX-8 more "special"

[Markl17]

Hi
I have just started premixing and found an oil that is cat tested (no animals were harmed) and does not smell bad.

[R1DSO]

Great stuff. All good to hear, thank you. Looks like everyone here is mixing 2-3mil per 1 litre rather than 4, so I’ll start there. Nice to see Motorex staying they’re cat safe also .