K Series Injector Flow Rates

[revilla]

I've been looking into K Series injector flow rates.

I've been trying to help someone who is fitting TF135 camshafts and an aluminium plenum with 52mm TB to a Freelander 1.8. The only ECU can find that works happily with the other Freelander systems is from a Rover 25, so he wants to copy the fuelling and ignition tables from a TD135 map into the Rover 25 map to correct it. However, there's a problem with injector scaling. If he uses the black injectors that the map was written for, they won't flow enough to be safe at the top end. If he uses the blue VVC injectors, the map will be scaled wrongly as the injector flow rate will not match.

So I needed to look into exactly how he could update the injector scaling in the map. There was a table which I had previously identified as loosely "injector flow rate compensated for battery voltage (pump performance)" but I hadn't been able to consistently match the numbers in the table with actual injector flow rates in any sensible units.

The VVC/TF135 injectors are widely quoted on the internet as being 191.8 or 192 cc/min.

This has always made me feel uneasy because if you work out the peak BHP that they can support, they shouldn't be capable of delivering the 160bhp of the VVC engine.

So today I went back to the Bosch data sheets to get the original specifications for the injectors. These are quoted in g/min, based on a test fluid of n-heptane at 3 bar. From these I used the density of heptane 0.684 g/cc to convert to cc/min using heptane. The injectors tend to flow a bit better using petrol than heptane (but heptane is easy to standardise for tests where petrol formulations vary) so it is generally recommended to multiply the mass flow rates by 1.035 to convert to petrol. I then also converted the petrol mass flow rates to cc/min based on a representative density of 0.750 g/cc.

As you can see, I came up with a rather different number of 207 cc/min at 3 bar using petrol for the VVC injector, rather than the usually quoted 192 cc/min.

This makes a lot more sense.

As a final check, I then compared these numbers to the flow rates found in the ECU tables:

 

As you can see, they are an almost perfect match (if I assume that the ECU tables are in units of 0.1 g/min - the ECU only works in whole numbers).

These ECU tables are always consistent across engines with the same injectors and I'm now confident they are flow rates in g/min, and that I can easily rescale a map to allow for different injectors by copying in the appropriate table.

And I'm fairly sure that the value of 192 cc/min is a miscalculation that has since been propagated widely around the internet - unless someone can point out a mistake in my logic?

[7SW]

Hi Andrew,

Thanks for this information.

If I have well understood, if injectors are changed from black to blue, the Injector Flow Rate table has to be updated accordingly?

 

 

[revilla]

Yes, I think that's right.

There are three injector tables that I've found, identified as Flow Rate, Dead Time and Base Scale Factor in the latest version of MEMS3 Mapper (version 5.70 on the website here: https://andrewrevill.co.uk/MEMS3ToolsIndex.htm). These tables are consistent across all ECUs mapped for the blue injectors, and across all ECUs mapped for the black injectors.

The ECU works out the fuelling from first principles taking into account the injector calibration, so I think just swapping these tables from the black ones to the blue ones should leave the fuelling correct after an injector swap.

[revilla]

PS: If you need copies of the data for these tables for the blue injectors, or just want me to update your file with them for you, just let me know.

[Toby S]

I suppose I'm most  surprised at the flow rate on the Cream injectors on the MPI/VVC EU2 which mainly would have gone into the 1400/1600 K series I guess - seem very high (certainly for a 1400)

[oilyhands]

TBH, I take the injector absolute capacity with a pinch of salt, the notional capacities are only ever used when rescaling maps if changing injectors or trading injectors up when engine capacity changes. Their relative capacities are then used.

Dave