Robbie (Forum Supporter)
Robbie (Forum Supporter) MegaDork
12/28/20 4:23 p.m.

I'm planning to do some dyno tuning this offseason on the challenge car. I've got some software that allows me to update the settings in the factory hardware, similar to HP tuners. It is for a challenge car so while I'd like more power, I need to minimize buying new parts (like fuel pumps or injectors, etc). 

Engine is a 600cc honda CBR engine. Factory HP rating is like 107 or something. I believe the factory fuel spec is 91/93 octane. I can confirm if useful. High compression, high rpm, naturally aspirated. The engine has 8 fuel injectors, a primary set of 4 and a secondary set of 4 that kick in above 4000 rpm and 10% throttle. The engine has a knock sensor, but no O2 sensor. Only real modification from stock is a 'race' exhaust system that doesn't have a cat and doesn't have the exhaust throttle valve. 

I looked up the minimum fuel flow spec for the fuel pump, and it works out to be about 250cc/min per cylinder. Fuel pressure spec is 50 psi, regulated at the pump (no return line). If the internet is to be believed, the primary injectors are 199cc/min and the secondaries are 205cc/min.

So, how do I determine what will be my best choice for fuel to make the most power? I don't really mind paying more for race fuel because the car doesn't use much and I'm not endurance racing. I know e85 can make more power even in a naturally aspirated engine, but I'm worried that the fuel pump won't be able to keep up - according to internet calculators 130 HP requires about 250cc/min x 4 cylinders on e85. 

I know you all may not have much bike-specific knowledge, but I'm sure we can do better than most sportbike forums, which seem to either say "e85 will melt all the o-rings in your fuel system and burns clear so no one will know when you are on fire" or "I just put 1 gallon of e85 in my 4 gallon tank - bike is running much smoother and has lots more power now". Not much in between. 

Ranger50
Ranger50 UltimaDork
12/28/20 7:02 p.m.

I'd only entertain e85, IF you have a fuel system that can handle the additional 30% of volume needed. Beyond that I'd run a racing 100UL and call it a day.

David S. Wallens
David S. Wallens Editorial Director
12/28/20 7:54 p.m.
Robbie (Forum Supporter)
Robbie (Forum Supporter) MegaDork
12/28/20 8:34 p.m.

In reply to David S. Wallens :

Thank you! I remembered that second one and was going to go looking through my stack of back issues to find it, but you saved me a ton of time. Looks like I probably should get after e85 if I can. 

David S. Wallens
David S. Wallens Editorial Director
12/28/20 10:08 p.m.

Rock on. 

Robbie (Forum Supporter)
Robbie (Forum Supporter) MegaDork
1/1/21 9:51 p.m.

Well, I made some what I believe to be pretty good challenge parts trades this weekend, but as a bonus I ended up with a duplicate fuel system (pump, lines, two rails, 8 injectors). So, I may be rigging up an injector testing station to see how much fuel I can actually get to see of e85 is possible.

Does this seem like the right track?

frenchyd
frenchyd PowerDork
1/1/21 11:47 p.m.

In reply to Robbie (Forum Supporter) :

I've been a solid fan of E85 ever since the politicians made it such a deal. I've had to drill bigger jets ( carb guy ) until I got my pickup with Flex fuel. 
     One of the nice things about alcohol is how flexible it is. You can be pretty rich and it will still run decently. Same with going lean.  Gas if you are lean it will start popping back through the carb and  not too long after that start hurting the motor.  Alcohol just makes the engine weak.  
     Once the computers understood how to adjust, wow! It feels like a really serious power boost. 
Plus it doesn't kill the fuel mileage as much as internet rumors would have you believe.  Commuting to and from work I lose about 2 MPG  from the 22 MPG I normally get. 
    Realize though that pump E85 can be anywhere from 85% down to 51%  you won't know unless you have the test equipment. ( I got mine from Kinsler )  

The  only sure way to get 85% is buy it from the fuel suppliers. 5 gallon cans and 55 gallon drums.   Your plugs, heck your whole engine will stay cleaner.  But it's really only good for about a month once you open it.  I can dump unused in my pickup. But if you don't have a flex fueled car you'll have to mix a lot of gasoline in to use it in your daily driver.  Anything after 2000 can safely run on 15% alcohol. Or if you have SU's about six flats will allow you to burn 15%. 
 I buy non alcohol fuel because then I can know exactly when I'm at 15% based on how much fuel I have. 

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