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What fuel to use

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I know this has bee discussed but I need the opinion of someone who really knows what they are talking about.

I currently run Renegade SX4. Can I run Renegade 110 safely. I use the 110 in my 2 stroke mixed 50/50 and I can get it for $7.50 a gallon which is a lot cheaper then SX4.

 

I have 2012 Honda CRF 250r with heavy mods. Here is list:

 

1. Cp platinum high compression piston 14.1

2. Carrillo long rod

3. ported head

4. 1 mm bigger exhaust valves

5. xceldyne valves

6. psi valve springs

7. webb +3 grind cam

8. polished transmission

9. ceramic bearings

10. polished and lightned crank

11. full Yoshimura exhaust system

12. full hinson clutch set up

13. moto tassinari air boot

 

I know I can't run pump, nor would I want to. (Crap Gas) What are my options if the Renegade 110 is no good.

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The only things that will affect what octane of fuel you need are your dynamic compression ratio and your ignition timing. From the list of mods you have it looks like your ignition timing will only be slightly changed do to the longer rod, but otherwise your ignition is stock. Your dynamic compression ratio is increased slightly with the higher compression piston, but is decreased with the cam. Which web cam grind exactly are you running? Cam timing has a huge effect on the dynamic compression ratio.

 

You have also altered the combustion chamber with the larger valves, so without knowing how much this changed the combustion chamber volume, nobody can really tell you what you are looking for here. Realistically, you do not need 110 octane fuel, but it will not hurt to run it (other than hurting your wallet). I have had similar set-ups that would run fine on 93 octane fuel. The larger cam tends to counteract the higher compression piston, which is why a high compression piston is recommended whenever going with a larger cam (just to get the dynamic compression ratio back up to where it was stock).

 

If you are worried that 110 octane fuel is not enough for your motor, don't worry, that should be more than enough to prevent detonation.

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93-94 octane pump gas is likely fine for that motor as the cam might be big. I can easily run pump with a 14:1 piston, porting and big camshaft. Stock piston in the new 2014 is 13.5:1.

Your Renegade SX4 fuel is oxygenated so you'll need some big fueling changes if switching away from that fuel!!! You didn't mention it, but who reprogrammed your ECU for you? Are you running the stock ECU or an aftermarket one?

Edited by Eddie8v

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The R+M/2 octane number of SX4 is 97.  If the engine does what you want it to on SX4 then switching to 110 and even mixing 110 with 93 50/50 will most likely be ok.  There is only one way to know for sure, try it.  If you hear detonation at low rpm, heavy load (like 3rd gear, about 6,000 rpm, at better than 90% throttle angle) then you know you need more octane. 

 

In my experience with these engines you will notice detonation in the form of noise long before you do any major damage to the engine.  The key is to not allow it to detonate for long periods of time.  Once you hear it, to be safe, put more octane in it asap!

 

This is deff. not rocket science.  These engines will tolerate a lot more than most people think. 

 

The other thing I failed to mention and I did not notice on your list is an aftermarket ignition or aftermarket ignition and fuel map.  You certainly could modify the map to tolerate a lower quality or lesser expensive fuel.

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It has stock ignition and was mapped by engine builder with Honda programmer. So if I run the 110 or even cut it I would have to remap? I don't know about all this stuff. I thought it might just run a little richer.

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If you're going from oxygenated fuel to a non-oxygenated fuel you'll typically need to lean the mapping out quite a bit, I would bet your engine guy would remap your ECU for free for you.

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Ok thanks guys. I will try cutting it if you think that will be ok. I will have it remapped also. Cutting will save me a ton of money, just don't want to damage motor.

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