47 replies to this topic

[Nev]

i already know mines not the quickest, but its no slouch either.. will take you out for a spin at national, feel free to make a sandwich and read the local newspaper as i go round

 

I'm not going to the National, but thanks for the offer any way.

 

I expect yours would be faster down some of the B-roads I go down.  

[Exmantaa]

Running (much) bigger injectors than you need to keep your IDC at max 60% is a bit stupid. Those big hoses most likely will screw up the idle behavior, as they need very tiny opening times for the required idle fuel amounts...

[Nev]

Running (much) bigger injectors than you need to keep your IDC at max 60% is a bit stupid.

 

That's nonsense mate, there are millions of OEM cars out there with big CC injectors, all with perfectly good idle. Just think of all the big Porches/Ferarris/Lambos (particularity the boosted ones with big VE ranges) that all have rock steady idling, all with big CC injectors. For example, I was parked up next to a Nissan GTR at the weekend, it was idling steady as a rock.

 

I bet my bottom dollar that OEM factory cars do not come out of the factory pushing their injectors to 80%. And with good reason, they'd be far more stressed on endurance tests and more likely to fail. And that is why something like the stock OEM Z20LET injectors only see a max of something like 65% duty cycle and have headroom for another 75 BHP if a mapper wanted to get more petrol out of them, proven time and again by mappers such as CS etc.

 

Yes bigger CC injectors make mapping harder, but if there is an idling problem, it usually lies in the 3rd party mapping of our own cars and the maper not spending enough time on the cells or the ECU not allowing enough granularity of the cells.  

Edited by Nev, 17 April 2017 - 07:21 PM.

[Exmantaa]

Injector designs can cope with 100% duty cycle, but normal practice is to limit to 80-90%, as near 95% the ecu can't control them correctly anymore due to the dead times and you also need to build-in some safety for different atmospheric conditions etc.

The Bosch 60lb injectors some of us run on the bigger powered Harrop SC engines are in fact stock injectors for a Porsche GT3.

Now the Bosch EV14's happen to be very modern injectors that can cope with very tiny opening times that we need on idling our meazle 2200cc engine, but on older injector designs the injector dead time and latency can play havoc with your idle AFR's when the required opening time is outside their linear behavior.

 

Buying bigger size injectors only to stay at 60-65% duty cycle is a waste; buy the correct injectors for the engine (spray pattern) and size them for you max power & rpm's around 80%.

[vocky]

I have always believed you should run injectors at around 80% and fit bigger injectors if you are at 90% or above (duty cycle)

 

Also worth remembering some injectors may not flow as much as they are supposed to, especially if you alter the fuel pressure. As an example; I bought some 370cc injectors and they turned out to only flow 310cc, quite annoying.

 

I still run 330cc injectors - rated at 3 Bar, but I use 4 Bar of fuel pressure which makes them 375cc (or something like that), they fire twice per cycle thus the engine gets 750cc. 

 

Which if you use an online injector calculator and enter 270bhp, 4 injectors, 85% duty cycle = 375cc

[fezzasus]

 

Running (much) bigger injectors than you need to keep your IDC at max 60% is a bit stupid.

 

That's nonsense mate, there are millions of OEM cars out there with big CC injectors, all with perfectly good idle. Just think of all the big Porches/Ferarris/Lambos (particularity the boosted ones with big VE ranges) that all have rock steady idling, all with big CC injectors. For example, I was parked up next to a Nissan GTR at the weekend, it was idling steady as a rock.

 

I bet my bottom dollar that OEM factory cars do not come out of the factory pushing their injectors to 80%. And with good reason, they'd be far more stressed on endurance tests and more likely to fail. And that is why something like the stock OEM Z20LET injectors only see a max of something like 65% duty cycle and have headroom for another 75 BHP if a mapper wanted to get more petrol out of them, proven time and again by mappers such as CS etc.

 

Yes bigger CC injectors make mapping harder, but if there is an idling problem, it usually lies in the 3rd party mapping of our own cars and the maper not spending enough time on the cells or the ECU not allowing enough granularity of the cells.  

 

The fuel system makes up about 30 % of the cost of the engine, so I can assure you that OEMs do size injectors very closely and will be pushing 80 % (quick backwards calculation shows that the Z20LET injectors are running at around 80 % stock, assuming they max out at 250 bhp).

 

You really don't want to be letting the duty cycle get too low as these high flow rate injectors get pretty bad at controlling very low flow. This is why many high power engines go for a mixture of direct injection and port injection - the direct injection is very good at low fuel flow which helps emissions and idle, while the port fuel injection puts a big slug of fuel in at high loads where emissions don't matter.

[Exmantaa]

And the port fuelling washes the carbon build-up from your DI intake valves...

[2-20]

In some cars they reduce idle fuel pressure to get longer duty cycles at idle