Preferable Tuning RPM range

[Subomi Omowa]

Hello everyone, my name is Subomi Omowa and I am with Hebron motorsports from Covenant University, currently competing in the Class 2 FSUK section. I understand that it is not wise to tune the the engine at the original rpm due to the effect of the restrictor has on the engine, and so the question is how do I find a reasonable rpm to work with?




Omowa Subomi
Covenant University
Hebron Motorsports

[Jonny Rochester]

For people that don't understand engines, or know what the ECU controls, it's very easy to get mixed up with what "tune" means. To me it means at least 2 things. The first "tune" is setup of the physical things, exhaust/ intake, camshafts etc. And you may have an RPM in mind for this but the computer (ECU) can do very little about all that. Then the other meaning of "tune" is to setup your software to fill out the fuel and spark maps, aiming for best power/torque/fuel ratios at each and every RPM and load point. The ECU is tuned for ALL RPM points, even to high RPM points where the power is dropping (provided the engine is capable and won't grenade itself) and the resulting power is what it is.

I am guessing you are designing for best torque at a chosen RPM, to design your exhaust and intake lengths, and gear ratios. (I think our engine guy is thinking 10500rpm on a 4cyl as he says it reaches chocked flow at 11000rpm. But he maybe optimizing for lower than that, like 9000. -as a side note, not reliable info).

I think they figured max power would be near chocked flow around 11500rpm, and some of our team where thinking that would also be the hard rev limit. I am trying to convince them we need to tune (fill out all the RPM and load points in the ECU for factory rev limit of 15k) for lots of reasons. Thankfully the engine will be "tuned" by a professional on a good dyno. All our team have to do is select exhaust and intake lengths, plenum volume and throttle.

[Claude Rouelle]

Subomi,

1. Covenant University where?

2. What would be YOUR beginning of the answer to your question?

[Subomi Omowa]

Thank you John Rochester and Claude Rouelle for the quick resposne
1) Covenant University Nigeria
2) When I understand the method used to determine the value(or range of values) of the chosen RPM for designing best torque

[RenM]

You have 2 parameters:
- the air consumption of the engine
- the maximum restrictor air flow

Air Consumption:
For a naturally aspirated engine you can estimate a volumetric efficiency of 1. So for 2 Turns of the engine (4 stroke) you basically pump its displacement as air volume

Maximum Restrictor Flow:
With the Restrictor Diameter and ambient values you can calculate the maximum Restrictor Airflow

Calculating both parameters and plotting them in a diagram with mass flow over engine rpm will give you an intersection point. This is the point where the engine will reach choked airflow. (for a volumetric efficiency of 1)
Now you can think for yourself what happens when you rev higher and what happens when you rev lower? What effect does a "bad" gas exchange have on your volumetric efficiency, how does this affect the rpm at which you reach choked flow.

Thinking of this should give you an idea of the best usable rev range for your engine.