Sale ends todayGet 30% off any course (excluding packages)

Ends in --- --- ---

Speed Density versus Alpha-N

General Tuning Discussion

Forum Posts



Tech Articles

Discuss all things tuning in this section. News, products, problems and results. 

= Resolved threads


I am new to tuning and find myself stuck with Alpha-N as the ECU I have does not give me a choice. This is on a restricted motorcycle engine. If you can please make a pros and con comparison between Alpha-N and speed density? Some "tuner" expressed concern with Alpha-N for my application, do you?


You should use Alpha-N in case when you can't tune the engine via Speed Density because the following reasons:

1) No reliable source for map sensor (no intake plenum after throttle body or dramatic air velocity makes map signal not realistic)

2) Small angle change of throttle butterfly makes big change in VE of the engine even if MAP signal remains the same.

If you are using ITB's it's a reason for tuning via Alpha-N

We have been tuning the engine via speed density with a single throttle body and the map sensor connected via a hose to the bottom of the plenum. I suppose I could get a MAF sensor and data log those readings with TPS and MAP to determine which one would be best?

Could you give us some more information on the engine itself and manifolds?

the reason I ask is because I have worked on a Formula SAE car before and they were running a single cylinder quad bike engine which lead to a few issues when it came to refinements.

A few things to consider are:

Are you getting pulsations in the MAP value?

Is fuel economy one of the areas they test?

Is the power smooth an consistent once tuned?

The engine is from a GSXR 600; four cylinder and 600cc. Custom intake manifold with venturi restrictor into plenum with four equal length runners. Fuel efficiency is important and I will have to look at some data of the MAP sensor. The power starts out slow than takes off at higher engine speeds, not the easiest to control.

The reasons why you'd typically use alpha-n have already been stated. Typically I'd always use MAP as the load input on any engine with a single TB and plenum unless the cam profile means I have insufficient vacuum at idle/low rpm to get good resolution.

That being said you can use alpha-n with great results and I purposely did this as one of our worked examples in the Practical Dyno Tuning course despite the engine having a plenum/single throttle and great vacuum, just to demonstrate.

One aspect that's worth considering though is if the MAP signal is ignored completely you will get some fluctuations in lambda depending on engine load - ie if you go up a slight incline vs down a slight incline at the same TPS, the actual MAP vs TPS will be slightly different and this in turn will mean the engine goes rich/lean.

We usually reply within 12hrs (often sooner)

Need Help?

Need help choosing a course?

Experiencing website difficulties?

Or need to contact us for any other reason?