Put It To The Test
In the Bangin' Gears column of the Feb. '14 issue, you stated that a high specific output is not about the engine's efficiency as measured by brake specific fuel consumption or, said another way, fuel economy. I believe that a good brake specific fuel consumption number (low BSFC number) is required to win the AMSOIL Engine Masters competition. I would expect to see numbers well below 0.4 centering near peak torque in order to do well in this competition. Fuel economy, per se, is a part-throttle design objective. Most published BSFC numbers are at wide-open throttle. The kinds of things that impact BSFC include combustion efficiency, mechanical friction of the engine, pumping losses, and compression ratio. Improved combustion efficiency, reduced friction and pumping losses, and increased compression ratio all will improve horsepower. So I believe that engine efficiency over the specified rpm range of the Engine Masters Challenge is an important objective in producing a winning entry. BSFC is not just about fuel economy as we normally think of it in terms of mpg. It is also about the efficiency of using fuel to make power.
You bring up good points, Robert. It certainly would seem intuitive that a low BSFC number would help the score, but, in fact, it has no bearing on the outcome. (And by the way, peak torque rpm is normally where you'll find the lowest BSFC.) At the Challenge, an engine's fuel intake does not have any sway on the competition score, other than the fact that lower BSFCs tend to be a marker for well-designed engines. It can chug as much—or sip as little—VP100 fuel as needed. It's an established fact that each engine is going to demand a unique amount of fuel per unit of power, and BSFC is not something that can be dialed-in like jet size or ignition advance. One final clarification: BSFC does have a profound impact on efficiency (and yes, economy). It is most often measured at full throttle, but it's also important at part throttle, particularly at the OEM level. Don't take our word for it though. If your belief about BSFC is so strong, you ought to enter the AMSOIL Engine Masters Challenge and try out your theory!
With regard to the "Feeling Fuelish" piece on setting up the fuel system for the project Cougar, I offer a word of caution. I've used a competitor's version of the fuel hose you chose (Earl's Pro-Lite 350) when replacing the fuel system on my car. When used with modern fuels (gasoline plus alcohol), the smaller hydrocarbon molecules came right through the fuel line in a gaseous/vapor form. No liquid leaks mind you, but the smell of gasoline fills any enclosed space the car is parked in. If this happens with your lines routed inside the passenger compartment, well, it will be interesting. I ended up having to replace all of it with aluminum hard line to eliminate my garage reeking of gasoline. If the fuel line itself is of rubber-type compounds, it needs to be rated to meet or exceed the SAE30R9 spec (high pressure EFI hose) or have the PTFE liner in order to keep all of the hydrocarbon fuel inside the line. Many of the braided lines don't have the liner, and I haven't found any of the braided rubber lines that have the SAE rating. There are lots of examples out there of people who have encountered the same problem with both stainless and textile braided lines. I thought a well-intended warning might keep other readers from finding out the hard way, as many others and I have.
Editor Johnny Hunkins responds: Michael, very well put. I had this exact conversation with Tech Editor Christopher Campbell in the planning stage for this story, and he says as a race car, the Max Effort Cougar will have its fuel lines replaced at the prescribed intervals. Your experience is identical to two other projects I've had over the years, and I learned my lesson about using "race" fuel line on a garaged street car. You are right—those fumes coming from braided stainless race fuel line will knock you flat out! An EFI-spec rubber hose using push-lock–style fittings is a solution I've had great luck with. It's less expensive, and won't have to be replaced every three to five years when traditional braided stainless steel race line begins to get brittle and fume out. Additionally, Earl's and many other companies offer PTFE-lined hose, such as Earl's Ultra-Flex 650. If in doubt about the fuel additives, many of which can cause premature fuel line deterioration, a PTFE-lined hose is a good option, as is the aluminum tubing you mentioned.