Engine differences and fuel?

Hi all,
Can anyone explain the differences between an over-the-counter Mazda crate motor for an RX8 and the PFM spec motor? Are there any internal differences below the intake?

Follow on question, can the PFM spec motor run safely on pump gas if it is 93 octane no-ethanol? Sunoco 98 GTX has to be ordered in advance if you're not going to a track with fuel and it is very pricey when buying in 5 gallon pails (more than $14/gallon). Can get it for $9.50 at certain track pumps which is more reasonable but I could buy 93 no-ethanol at a local pump for about $4.50.

I'm not racing, I'm just playing at track test days, so I'm only concerned with not hurting the motor and not some rule book.

Thanks,
Mike

I believe some run two stroke oil mixed in the gas to help lube the internals. Someone far more knowledgeable will soon chime in.

Yes, I run Idemitsu and will continue to do so regardless of what gas goes in it..

No idea about the PFM engine. I would suggest calling Drummond as he is the one who seals them I believe. I would guess they are the same internals as they come from Mazda. I can't see PFM engines using non-stock rotors. The Rx8 is already 10:1ish compression, and with a rotory anything above 10:1 is not advantageous. Even the 787B was using 10:1 compression IIRC. I'd bet you would be fine with premium pump gas.

To Racerdad's question; Premixing oil is typically done when the oil injection system is disabled. The oil injection pump siphons oil from the oil pan, meaning the lube oil is the same as the injection oil. Since synthetic oil doesn't burn cleanly, you can't run synthetic oil in the engine if the oil injection is still functioning without loading the rotors with carbon. So, you disable the oil injection, put synthetic in the crankcase, and two stroke premix in the gas tank. Depending on the RX model, you need to trick the ecu to read the oil metering pump is still functioning or it will not run, or go into limp.

No internal differences unless you order the ceramic apex seals. Except dry sump system of course.
Premix or ordering fuel with lube is absolutely required.
I would think that 93 octane would be fine, especially for track days. You may need to adjust the mixture knob. Ethanol should not be an issue. (Pro Series fuel has ethanol).

Thanks guys - I got a response from Jay Horak at Star Race Cars as well. It seems the motors are pretty much same as OEM stock RX-8, but of course dry-sumped and the oil injector is removed so we pre-mix in the fuel and run synthetic in the sump. Speed source motors are put together with ceramic bearings.

The biggest difference is the MoTeC ECU and fuel mapping, it reportedly won't be very happy on 93 octane because it is a pretty aggressive mapping. I suppose I'd need to schedule some dyno time to test fuels.

A partner of the original owner of my PFM, who also had one of his own, claimed "naw, just run the cheapest fuel you can get.. I ran 87 in mine - the further left on the pump the better" The fellow seemed genuine enough in all other conversation, but I'm quite dubious on the soundness of that suggestion.

Quote:

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Originally Posted by mikey

Speed source motors are put together with ceramic bearings.

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Interesting info, thanks for adding that.

As for the ceramic bearings, I think they meant ceramic apex seals. Stock they are steel.

https://encrypted-tbn1.gstatic.com/i...AlqDS_LQh4b6Vw

Sppedsource does not use ceramic bearings. They do use ceramic seals.

It is the seals that are ceramic as noted, but Star Mazda referred to them as bearings. I have seen them called both in technical documentation.

Definition of bearing (among other definitions):
a part of a machine that bears friction, especially between a rotating part and its housing

Thus it is correct to call it a bearing! Same could be said of piston rings in other motors..

Cheers,
Mike

It appears Sunoco GTX is Ethanol Free. So, what's the verdict? Pump gas ok to use for track days?

I've stuck with GTX 260 thus far. Based upon the discussion with Star Race Cars and the MoTeC tune being specific to that fuel. I'm pretty sure you won't hurt it on pump 93, but would definitely stick to no ethanol. In FL, we have lots of places that offer no ethanol at the pump. Will probably give it a try later this year.

The fuel you choose has to with the map that's in the ECU, The Pro Series now use's Sonoco. Before it was VP there is a difference in the mapping for the two different fuels. If you have any questions feel free to e mail me @ cer-performance@centurylink.net We are a Approved Scca engine rebuild facility for the PFM. Also I used to do the engines for Star Race Cars.

Mike Williams