If you swap out for a high flow air intake, fuel moto headers and slipons, can you retune the bike via PC5 to run on regular fuel instead of the high ocatne??

Have not made the changes yet but will soon. Need to know opinions please.

thanks in advance!!!!

 

octane reflects the ability of the fuel to resist ignition.

High octane fuel allows higher compression ratios and more advanced ignition timing ( which is good for economy and a little power)

in a high compression mtor, low octane fuel may self ignite like a diesel motor, before the sparkplug fires, resulting in lost power and gasses expanding while the piston is still coming up on the compression stroke.

so- fuel octane requirement is more a function of compression ratio

You should stay with high octane fuel ( and carry octane boost if you are going into areas where supplied fuel is low octane... like Texas- http://www.consumeraffairs.com/news0...e-content.html )*

the older H-D motors ran compression ratios more like 8.2 or 8.5 to 1, the Twin Cam 103 is at 9.6:1

- Compression ratios are "nominal" and are affected by cam profile and rpm. Nominal compression ratios are calculated by the volume of the cylinder with the piston all the way down, then the volume of the remaining area when the piston is all the way up- at normal atmospheric pressures.
Certain cams at certain rpms with a tuned exhaust system may get more than 100% cylinder fill due to velocity of the incoming air charge-- ( this is sometimes called scavenging and is really the art of tuning, calculating the inter-performance of parts to get extra gains at specified rpms)
-turbo and superchargers also increase the cylinder fill beyond 100% by boosting the pressure of the air entering the intake

mike

* this is a joke, Texas has good gas, mostly--the link is to an article about a Texas convenience store chain selling regular as premium in 143 of their pumps

 

Yup, good way to explain it. We help our Bikes run better with free flowing air and exhaust but that doesn't change the compression ratio and timing and the need for high octane gas.

 

Stay with minimum 91 octane and run 93 when you can get it.
Why cheap out on the gas?
Why would you cheap out on the gas and retard the timing just to loose power?

 

Yes. I'd imagine FuelMoto has a regular fuel tune. If not, it'd just be a matter of reducing the timing curves to tune out any detonation.

With that said, I wouldn't recommend it. You're going to spend over a thousand dollars on a Stage 1, then eliminate the power and efficiency benefits by chopping the timing. Doesn't seem worth it to me in order to save what, 15-20 cents a gallon when you fill up.

The exception to my recommendation would be if you were planning on a road trip into Mexico or up the ALCAN where premium fuel is scarce. Then that's a helluva idea.

 

9.6:1 is NOT a high compression engine and fuel type does not change engine compression, Heard it all now. The HD engine is a LOW compression and low tech engine and does not need higher octane except for HD to try to meet the EPA crap. I have been using 87 and actually get better MPG than with premium and don't waste money. It also does not ping and runs just fine. Feel free to waste your money with premium, the only down side for you might be carbon build up in the heads from incomplete combustion.

You are going to see people on this forum swear that premium octane fuel is required because HD says so then recommend an octane booster when the owners manual specifically states that is is NOT recommended. They just cherry pick what they want to believe and use.

 

For an air coled motor, 9.6 is "high"; when the air/fuel charge is compressed it creates heat(before it gets sparked), in an air cooled motor there is already a significant amount of heat present before the compression stroke begins. Isolating and comaring compression only in different types of engines, without factoring other operating parameters is off balance. If new passenger veheciles were air cooled, they would not be designed with "high" compression. Besides the inheirent heat, you have to factor in the OEM EPA compliant cam profile also, which imacts corrected compression. I run 89 usually, I tried 87 this summer as a test, it ran fine with no pinging until I got slowed down and the engine got hot, after that it was prone to ping under load until I let it cool down for a while. Compression is a mechanical source of heat, so ultimately heat is why the Twin Cam needs higher octane fuel, to resist predetonation.

 

If it does not ping it's fine. However depend a lot in how you drive it. Say you're crusing at 2300 and 60 mph and you desired 70mph. Someone is going to hit throttle all the way. Someone else is going to do it easy and pick the 10 mph up in the next 1/8 mile. Number 1 will surely need premium fuel. Number two will get away with mid-grade 89. If it runs fine on the lower grades (not cheap since running premium when it's not necessary is foolish and wasteful) use it. Lowering compression will probably be only way to run regular.

 

I am lucky in where I live and ride. I rarely do any in-town riding, and mostly on open road with plenty of air moving across it. Trust me, if there was pinging I would hear it and change fuel. Interestingly enough, the worst fuel economy and performance came from mid grade, accidental button push on my part. The station had the mid button on the far left as a way to boost that grade sales I suppose. I don't lug the engine and do wind it up from time to time to keep the combustion chambers from carbon up. I don't waste money on fuel or oil types just because HD says so. Also don't buy their chinese shoes.

Heat is also, let's say excessive heat, created with an EPA tune and stock components. Open it up, get rid of the CAT, do some fuel mapping, and it runs cooler, read less hot, and fuel requirements change.

To each his/her own on his/her own bike.

 

For the purpose of this discussion, the catalyst is downsream of the combustion chamber, it does not impact the total amount of heat in the heads that effect octane requirement. Mild enrichment cools the exhaust and ultimately the rider, it doesn't cool the engine enough to reduce pinging and the lower octane requirement. If you are experiencing carbon build up, that indicates significant enrichment, and that causes a gradual increase in compression which will eventually lead to pinging also, no matter what octane fuel you use. If you run a rich tune, "winding it up" occasionally won't clean the carbon out of your heads, but it might blow some soot out of the muffler, the extra throttle used to wind it up puts you into an even more enriched sector of the map, so it really just adds to total acumulation of carbon.