Radical Fuel Question

I am trying to understand what's the right fuel for 1500cc radicals. The manual calls for “Super unleaded 98 octane , or 100 octane race fuel”. Since these are UK octane ratings they are based on the RON (Research Octane Number) standard. In the US everybody seems to use 100 octane race fuel. US octane ratings, however, are based on the AKI (Anti-Knock Index) standard so they aren’t directly comparable to UK (RON) ones. In fact, 98 RON octane = 94 AKI octane. I know that’s not what people here do, but shouldn’t US owners be using 94 US (AKI) octane fuel. What am I missing?

100 Racing fuel is the correct fuel.

Charley

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Originally Posted by CharleyH

100 Racing fuel is the correct fuel.

Charley

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Yes, everybody in the US says that but I don’t understand why. 100 octane fuel in the US should correspond to ~105 octane in the UK and there they use 98 octane for the 1500cc engine...

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Originally Posted by nis1973

Yes, everybody in the US says that but I don’t understand why. 100 octane fuel in the US should correspond to ~105 octane in the UK and there they use 98 octane for the 1500cc engine...

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You are asking a great question. But for me this was a simple decision to use 100. When I purchased my car from Spring Mountain they recommended using 100 octain and I figured they operate more Radicals than just about anyone in the US so it makes sense to follow their recommendations. Also in California Our best gas is 91 octain.

Octane levels are all about preventing pre-ignition due to high pressure and temperature in the cylinder, otherwise known as "ping". The higher the compression of your engine the more octane you need. Higher octane is not a more powerful fuel, in fact the opposite. All other qualities of the fuel being the same, then use the lowest octane that doesn't ping in your engine (or cause the ECU to retard the engine). So it all depends on the compression ratio of your engine.

Of course, all other qualities of the fuels are not the same, and you may use a higher octane racing fuel than you really need just because it is better quality or has higher energy content.

It would be best to call George Dean to get a definitive answer for your specific engine. http://georgedeanracing.com


Greg

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Originally Posted by holmberg

Octane levels are all about preventing pre-ignition due to high pressure and temperature in the cylinder, otherwise known as "ping". The higher the compression of your engine the more octane you need. Higher octane is not a more powerful fuel, in fact the opposite. All other qualities of the fuel being the same, then use the lowest octane that doesn't ping in your engine (or cause the ECU to retard the engine). So it all depends on the compression ratio of your engine.

Of course, all other qualities of the fuels are not the same, and you may use a higher octane racing fuel than you really need just because it is better quality or has higher energy content.

It would be best to call George Dean to get a definitive answer for your specific engine. http://georgedeanracing.com


Greg

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This seems like a good idea. I’ll call him.

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Originally Posted by CharleyH

100 Racing fuel is the correct fuel.

Charley

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In my SR3 1500 I use the fuel that Spring Mountain recommends (Sunoco SS100) which is readily available from my trackside supplier (and has the additional benefit of being legal in California since it's unleaded if I head across the border).

Not sure what the point would be in experimenting with anything other than the known good and available stuff. If you're motivated to save a few pennies on gas, then the SR3 1500 might not be the ideal platform.

Knut

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Originally Posted by ksgrimsr

In my SR3 1500 I use the fuel that Spring Mountain recommends (Sunoco SS100) which is readily available from my trackside supplier (and has the additional benefit of being legal in California since it's unleaded if I head across the border).

Not sure what the point would be in experimenting with anything other than the known good and available stuff. If you're motivated to save a few pennies on gas, then the SR3 1500 might not be the ideal platform.

Knut

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I am not and won't be experimenting. I'm simply trying to understand what appears to be an inconsistency between the official Radical manual and what's done here in the US.

The manual says "Powertec Suzuki 1340 engines may run on 98 octane regular unleaded fuel. The Powertec Suzuki 1500 engine should only be run on Super Unleaded 98 octane, or 100 octane race fuel.". Again, octane is measured differently in the US and UK so 98 octane in the UK is about 93-94 octane in the US. Spring Mountain appears to recognize this when it comes to 1340cc engines - they apparently run them on 93 octane (US). They stick to 100 octane (US) for the 1500cc engines, however.
It's very possible that there is more to fuels than simply the octane rating and that could be the key here. Could it be that all the ethanol that's now in regular fuels in the US is ok for the smaller engine but damaging to the more highly stressed 1500cc? if that's the case then the ethanos-free 100 octane race fuel seem like a natural choice. I'm curious to understand...

There are many threads here on apexspeed about fuel chemistry in general and racing fuel specifically. If you're curious to understand fuel, then do a search, and you'll find them.

Greg

I use the 98 octane ethanol free - 260GTX I think. In my opinion, the lack of ethanol and overall greater stability of the fuel is more important than the extra 2 octane. Also, I was told 98 by Francesco at Team Stradale.

Reviving this thread. I am new to the Radical scene, SR3 RS 1500. So I have called around and called distributors VP and Sunoco looking for pump not the expensive 5 gallons cans. So here are my local options. When I say local its still 1.5 hours from where I live. Sunoco 260 GTX which is 98 octane or Sunoco leaded 110. Those are my options aside from buying in cans. I have AV gas in my town but obviously that is discouraged. I could do 110 and mix with pump 93 which we have at every gas station. Suggestions. Not racing just using for track days. I know the last post above used the 98 with no issues.

What has been touched on here but not properly, explicitly stated, is the difference between RON and MON octane ratings... Research Octane Number vs. Motor Octane Number... IIRC in the UK the RON number is used exclusively. The MON number is usually lower, for a given fuel. In the US, we label with the average (shown on the pump as (R+M)/2 )... which is also lower than RON.

So as noted, our 93 or so octane is comparable to RON 100 UK fuel.

Poor form on the manual for not clarifying what rating is used.

As I believe the Radicals, in production form, are using stock street bike motors (be they 1000 or 1300 or such), they're designed to run on pump gas - so I'd have trouble believing they'd need more than 93 pump gas. Of course, then you get into the debate on ethanol content, or how screwed you are if you live in the People's Republic of Kalifornia where proper premium fuel kills trees faster than wildfires, so 91 is all you get at the pump... ;)

Anyway, I know I ran my stock GSXRs on 93 pump gas from Costco without detonation etc issues (with stock bike ECU maps) for some time. Now I've switched to built motors with higher compression, and run 100 octane (US, so R+M/2) race fuel per George Dean. Which is typically 260GTX, IIRC. I have done the mix of 50/50 93 pump gas and 110 leaded race gas, since that's actually available locally, but I hate it, it's messy and kills O2 sensors...

I should absolutely expect your 1500 should handle street pump gas... if it's running essentially the original bike engine cal? Perhaps a call to Radical to clarify their octane ratings is in order?

So what’s wrong with running lead?? I’ve yet to find an answer that’s negative except if you have cats.

Also O2 sensors... and your own health...

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Originally Posted by 924RACR

Also O2 sensors... and your own health...

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Yes cats..o2. But honestly what else? I’m trying to learn. I’m not drinking it

...but you can get it on your skin, and inhale the fumes...

I believe it also burns dirtier vs. unleaded...