Larger fuel injectors for the XX (and busa)

(Updated with current info 12-18-03)

Thought you guys might find this interesting.

I had my XX injectors tested and they have a static flow rate of 335cc/min @43psi. This equates out to a max horsepower of around 260 (done mathmatically so results may vary somewhat) before the injectors start malfunctioning caused by excessive duty cycle. This is to say they may not allow enough fuel at high RPMs and boost levels in a turbocharged application. So if we are trying to make HORSEPOWER what we need is an injector that flows more fuel than stock without having to do modifications of any sort and with a PCIII and fuel pressure regulator we can adjust down to compensate for the higher flow rate when at low RPMs. This will allow more horsepower at a reasonable duty cycle, without any fear of running out of fuel causing a lean/heat condition because an injector failed.

After some research I found that Keihin, the company that made our injectors, also made six other flow rates for the same style injector. If you look at the Keihin-us.com website (under OEM/products/fuel injectors/english) they show 6 different fuel delivery rates for the KN4 style, which is what we have, at two different fuel pressures.

Keihin Drawing#.........KN flow%....Max Flow.......Pressure

D30NA-AY4-0200-------25%-------=13.99lbs/hr @ 42.7psi

----------------------------------------=15.27lbs/hr @ 49.8psi

D30NA-AY4-0300-------STD--------=18.58lbs/hr @ 42.7psi

-----------------------------------------=20.28lbs/hr @ 49.8psi

D30NA-AN1-0101------+30%-------=24.17lbs/hr @ 42.7psi

-----------------------------------------=26.36lbs/hr @ 49.8psi

D30NA-AN1-0200------+60%-------=29.71lbs/hr @ 42.7psi

-----------------------------------------=32.37lbs/hr @ 49.8psi

D30NA-AY4-0400------+90%--------=35.26lbs/hr @ 42.7psi

------------------------------------------=38.45lbs/hr @ 49.8psi

Reference--------------+156%-------=47.32lbs/hr @ 42.7psi

The tricky part was no one knew what they were used in. They can tell you the Honda part number but not the keihin number and only if you know which car. By chance I stumbled across part of the puzzle while searching ebay. An individual was selling injectors for a 2000-2003 Honda S2000 car and lo and behold they match ours. So I then searched the web for S2000 forums and found http://forums.s2ki.com/forums, After doing a search on injectors I found out the ones in the S2000 flow 360-380cc/ 38lb per hour depending on who you ask and fuel pressure used at time of test. I had the ones I bought tested by Marren Fuel Injection (injector.com) and they had a static flow rate of 390cc/min @43psi.

After some searching for phone numbers I managed to get in touch with Paul Rodgers of Keihin USA. He was able to answer some of the questions I had regarding the KN4 injector.

First off he said the letters and numbers on the injectors don't signify specific models or flow rates but rather manufacturing date and batch codes. Therefore all the speculating I did regarding the ABS-E vs. B that are marked on the injectors is out the window. He said there is no way he knows of to differentiate between the different flow rates by looking at the injector. Removing an injector from a specific application or getting the number off the parts bag with the Honda label are the only ways aside from having it tested of knowing what the flow rate is.

I asked him about the chart on the Keihin-us.com site that showed different flow rates and he said those are the standard sizes offered by his company but that a customer like Honda can call up and have the injectors made for a specific flow rate. This means our injectors may or may not be one of the standard flow rates listed. Another aspect about the chart he clarified was the area under the Q=mm3/st. It has to do with the dynamic flow rate. How much fuel is flowed at 2 milliseconds, 6 milliseconds ect.

He also mentioned that the spray patterns would be the same no matter the flow rate for that style injector and that variation in the static flow rates between injectors of the same size would be no greater than 1-2%.

That's about all I was able to get out of him that didn't fall under proprietary information.

So looking at the keihin chart it appears we have the 60% model or something close to it and the S2000 has the +90% model or something close to that. They are the same physical dimensions and impedance, just different flow rates. Next quest will be to find out what applications the others were used on. The PCIII should compensate for the increased flow at low rpm since it's only a 15% increase. Today I talked with RC engineering (rceng.com) and managed to find out the new Civic SI has 310cc/30lb per hour injectors. Oddly enough the Suzuki Hayabusa which uses the exact same style is quoted as having a flow rate of 280 cc/min. I can't verify that for certain, but that's what they reported on suzukihayabusa.org.

This gives us a number of choices.

Because the S2000 guys want more power/fuel too they go for after market injectors at $90.00 a pop. This means they have some perfectly good injectors sitting on their shelves collecting dust which they might part with. Elixxer posted an ad on the S2K forum and scored four for $100.00. You can do like I did and search ebay every few days for Honda injectors until some go up for auction, I got mine for $50.00 for a set of 4 new in bags, or you can stroll down to the Honda auto dealer and ask for the injectors for the S2000 at $120.00 each.

The fuel pressure changes after the '00 model and so there is a different part number for the fuel pressure regulators on the '01-'03 models..

'99-'00 has a fuel pressure of 43 psi

'01-'03 has a fuel pressure of 50 psi

The part numbers for all the stock XX injectors are the same irregardless of year.

Kind of long winded I know but I hope this helps.

CBR1100XX injectors flow 335 cc/min @ 43 psi fuel pressure

S2000 injectors flow 390 cc/min @ 43 psi fuel pressure

Forrest

Here is a picture of the CBR1100XX injectors nexxt to the S2000 injectors.

That's the Honda S2000 part number in the lower right hand corner.

Here is a picture of the Hayabusa injectors

Ignore the numbers and letters on the injectors they are manufacturing date and batch codes.

Below are the test sheets I received from Marren Fuel Injection.

The cost for having four S2000 injectors and one CBR1100XX injector tested for static flow (max flow rate) as well as a dynamic 6 millisecond flow rate was $48.00 which included return shipping.