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unleaded vs super unleaded

11K views 62 replies 21 participants last post by  Radrc51 
#1 ·
anyone notice a massive difference between using either of these on the rc51?
 
#6 · (Edited)
Yeah, in a pinch! till you can get more premium gas back into the tank.

wondering if it would smooth out my fuelling any, if i go up to super
I think the octane rating system may be different for Polarbear in Scotland?

Our gas in the US is pretty sorry compared to what Europe and Australia get, from what I understand. But if we're talking about US gasoline, the service manual says 91 octane. The highest we get is 91 here in CA. So that's what I run.
Don't run a lower octane than what the manual for your country recommends. Performance will definitely suffer, your engine is built to run premium gas.
That gets me wondering, what's the stock compression on our bikes?
 
#8 ·
As I recall stock compression is somewhere around 10.5, which isn't as high as it could be; but this depends on the cam durations too. The longer the duration (of open) the more compression - usually.

US & European Octane ratings are measured differently (I think it's detailed on Wikkipedia, etc. if interested), so the US rating show as lower than European, but the gap in resistance to pre-ignition isn't as much as most people think.
As an example I see Turbocharged performance cars that are meant to run in Japan on 100 RON & owned by US Military on bases here, be filled up with US 91 RON and they run just fine too.

But yeah, I still put in 100RON Japanese premium fuel in my bike all the time. It's about 6% more expensive but what the hell! The VFR & my other bikes run 95 RON regular. I believe the UK is 99-97 RON premium (Depends on where you buy from) and 95 RON regular.
 
#19 ·
As I recall stock compression is somewhere around 10.5, which isn't as high as it could be; but this depends on the cam durations too. The longer the duration (of open) the more compression - usually.
Compression ratio is based solely on the size of the combustion chamber relative to the cylinder displacement.

i.e. If the displacement of one cylinder is 499cc, and the combustion chamber volume is 50.9cc, then the compression ratio is (499+50.9)/50.9 = 10.8:1
 
#10 ·
I have run 87 92 and 100LL(av gas)

I didnt notice any difference between them! I run 87 pretty regularly, No problem!
 
#13 ·
I could be wrong but I thought I read the RC will make more power with lower octane but will have detonation problems... I was short on fuel the other day so I put in a few gal of cam 2. I had the LB'S corked and noticed heavy bogging. Even after 4 tanks of premium it still has that sweet smell. Now she looks good, sounds good and smells good:D
 
#15 ·
What...lol
Actually that got me thinking of something.. I spent the last 4 days at the drag strip. The guy pitted next to us was running his dragster on alcohol. With it being slightly cheaper than cam2 and very cool burning I wonder what would be needed to run it in bikes.. I think its just a few different gaskets in the carb to switch over from gas in our motor. Seems like it would be awesome for track bikes...
Oh I didn't think it was possible but smells way better than cam2.... ok I might have a problem:)
 
#17 ·
I'm lucky, I have about 4 stations here in town with 100% premium 92 octane. I only by ethycrap when I have no choice and then only premium for the bike.
 
#18 ·
The sticker on the bike says 95 RON which converts to 91 octane. the Sunoco stations around me only have 87, 89, and 93, so I get the 93. if I really needed good gas, I'd hit up one of the marinas that sell non ethanol blended stuff. No 10% blend there, but there are only a half dozen or so in the state.
 
#22 ·
This tangent all started because I said above: "the longer the duration (of open) the more compression - usually. "

Mike - with an N/A It's not just a matter of dropping in cams to get more power.
Look at it this way....If a valve is open for much longer (304-320 degrees, say as opposed to a normal duration of around 250-265) will longer duration cams allow compression of the mixture just as much, or less?

Think about it and imagine it in your mind.

The answer is less compression, because the intake valve was open for longer (We'll forget about valve overlap, etc to keep it simple).

This is why N/A race engines with long duration cams run higher than standard compression ratios, so the mixture is compressed to a maximum without detriment, or why other bikes with more modern engine designs run higher compression ratios and make so much more power, but at higher rpm.

By the same token, if you put in high compression pistons on an engine with short duration cams, you'll get too much compression and the result is ignition by compression (Which is very basically the principle of how a Diesel engine works).

Hope this helps make more sense.
 
#24 · (Edited)
Thanks for the more technical explanation. ;)

I love engines that have been properly put together, although not by me as I prefer to leave the expertise to those who have been doing this sort of work & racing for decades when it comes to building 'em. ;)

It's quite amazing how much more power & response comes from N/A engines that are put together by experts in their fields. I've seen roughly 35% increases in power without increasing capacity at all..
And the sound... Geez, really makes the hairs on my neck stand on end! :D

Here's the 4A-GE with said 304 degree cams. It's a 1.6 litre making just a hair off 200 bhp at 8,900 rpm (Standard is 127 bhp) and the car weighs 950kg. Doesn't make much below around 4,000 rpm, then the intake becomes very noisy...before acceleration goes ballistic. Also runs a TRD close ratio gearbox, TRD LSD & all sorts of other things for enhancement of fun :D



The engine lives inside this:

 
#25 ·
Very nice build Stig, Im diggin the ITB's lol.
Here are a few of our cars and builds :D
Girlfiends Camaro, Sisters Trans-am and gixxer, Dads Chevelle


My dads 67 SS chevelle, 565ci BBC AFR heads pump gas 850hp


Customers 55 chevy with a 496ci BBC


Sry for the thread jack
 
#26 ·
With a name ending in V8 - I'd have expected nothing less from you, Ricky. :D
OK, I apologise too for the thread hyjack -let's get back on topic.
 
#34 ·
No, Tesco do 99, but if i recall reading somewhere its 95 dosed up with bioethanol to make it 99

BP ultimate is rated at 102...The drift boys like using that

give it a try, remember higher octane fuel burns a little slower, but the knock resistance is higher, so you need to be running a more agressive tuning to make the most from it, ie another few degrees advanced timng
 
#33 ·
I believe Tesco's is 99 RON (Turbo car drivers tend to go for this). Shell's is maybe 99, I can't remember (but could find out)... I don't live in the UK.
 
#36 ·
Yeah, have heard BP Ultimate is quite high RON too. You don't need anything higher than 98 anyways and won't notice any difference in performance really (Japan is 100 - 102 for high octane). At least there's some choice. See what you can find near you. :)
 
#42 ·
Most of the stations here in Florida are 93 octane, although a few are 91.
The governor recently signed a bill where stations are no longer required to carry E10 ethanol diluted fuel, and are free to carry 100% gasoline if desired.
I for one can't wait for more stations to supply 100% 93 octane fuel.
 
#47 ·
...Sounds like it was a lot of fun. :)
 
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