the afr verses horsepower test

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wistech · #11 Post by **wistech** » Fri Aug 22, 2008 5:53 pm

QUOTE (jinx44 @ Aug 22 2008, 12:33 PM) <{POST_SNAPBACK}>

Dyno HP and useful HP are too different things.

Im going to have to disagree . I think the dyno is a good measuring device to see where your usefull hp is. Thats how we know how to build engines for different applications.

peterock · #12 Post by **peterock** » Fri Aug 22, 2008 5:54 pm

Of course it has an effect on horse power. Your title of this post is AFR vs Horsepower Test and your AFR lines are all over the place. The red is the best one and it still shoulld be better coming from a fuel injected motor. It just really isn't a good test is what I'm saying. Half the runs have a different RPM they cut out at?

wistech · #13 Post by **wistech** » Fri Aug 22, 2008 6:05 pm

QUOTE (peterock @ Aug 22 2008, 12:54 PM) <{POST_SNAPBACK}>

Of course it has an effect on horse power. Your title of this post is AFR vs Horsepower Test and your AFR lines are all over the place. The red is the best one and it still shoulld be better coming from a fuel injected motor. It just really isn't a good test is what I'm saying. Half the runs have a different RPM they cut out at?

The cut out rpm are because of changing the rev limiters.It has no effect on the powerband except for overrev. How can it not be a good test . An afr that is way lean in one spot and crazy rich in another should show up as a major difference in power and torque than another afr or why else would we bother to measure it?

wistech · #14 Post by **wistech** » Fri Aug 22, 2008 6:09 pm

The rev limiter may have given away a clue as to the tuning results. Maybe even who or what was used for tuning.

kdeal · #15 Post by **kdeal** » Fri Aug 22, 2008 6:17 pm

The red one was the highest....right before the motor melted!!!!

jinx44 · #16 Post by **jinx44** » Fri Aug 22, 2008 6:30 pm

QUOTE (Wistech @ Aug 22 2008, 05:53 PM) <{POST_SNAPBACK}>

Im going to have to disagree . I think the dyno is a good measuring device to see where your usefull hp is. Thats how we know how to build engines for different applications.

I didnt' say a dyno isn't a useful tool, but its not the end of tuning. Put any of those maps in the bike, put it on the ground under the load of a pass, and watch your AFR change.

The highest HP on a dyno doesn't always mean that it will go down the track the best either. There were several times I would dyno my banshee, then take it to the next TT race and the thing not pull worth a **** around the track. I could throw a little more jet to it and it was fine. When it would be one the dyno with that jetting, it would be 2-3HP under the top numbers.

My car is the same way. I have seen over 730HP out of it, but the AFR graph was as unstable as the ones you posted. Stabilize the AFR and lost over 20HP. On the tune that put up the highest dyno numbers, the car went 108.0 MPH in the 1/8th. The stable AFR tune went 110 and change.

cannondale27 · #17 Post by **cannondale27** » Fri Aug 22, 2008 10:30 pm

Its called drivability.

Wistech given a long enough pull to clean out the terrible mapping the AFR could very well be right at point of max hp.Thats all.Doesnt mean it is going to start,Idle,pull smoothly up to that point.

wayneschofield · #18 Post by **wayneschofield** » Sat Aug 23, 2008 11:17 am

The power output from a motor has a lot to do with the DISTRIBUTION of mixture withing the cylinder, in particular the concentration of fuel around the plug when it fires. (look up 'stratified charge engines').

An engine that tends to concentrate the fuel around the plug will be happier and give more power on an overall leaner mix.

However, because the density of fuel is very different to that of the air in a cylinder you tend to get different mixture concentrations around the plug at different rpms. Because of that you can often get an engine giving better power when the mixture varies through the range rather than following the 'textbook correct' mixture profile.

There's a lot goes on in a cylinder and what comes out of the tailpipe is only a guide to what is happening.

There is absolutely no substitute to a good dyno with absolute repeatability.

jinx44 · #19 Post by **jinx44** » Sat Aug 23, 2008 1:17 pm

QUOTE (Wayne Schofield @ Aug 23 2008, 11:17 AM) <{POST_SNAPBACK}>

There is absolutely no substitute to a good dyno with absolute repeatability.

Yes there is. Real world testing under a full load. You even said it yourself in regards to mixture at different RPMs. The acceleration rate of the piston and swirl in the chamber varies the air charge as well. A dyno can not offer a real world load so the acceleration rate is different. The exception to this would be Mustang brand dyno's can put a load on the tires based on weight and even wind resistance as RPMs increase. They are the only dynos that get close to real world.

BTW, don't get me wrong guys. I use dynos to initially tune everything, but that is not where tuning stops.

thedeatons · #20 Post by **thedeatons** » Sun Aug 24, 2008 12:06 am

Our engines have shown us the best numbers between 12.5:1 - 13:1... Therefore on our dyno charts the red line would be making the most power at that particular point.

Not to get into a huge arguement, but I agree that the smoothest (flattest) AFR has always produced a nice linear power curve for us.

There are all sorts of ways to tune an engine though, depending on what the rider wanted. As long as the AFR is in the safe zone, then make the power hit the way you want it. Otherwise we are argueing personal preference...