While investigating options as I add mods (I recently posted the related ECU tuning options/more mods post), I now have the following question:

If adding the lightweight 2% plus crank pulley to a 15% sc reduction pulley car, is there a reason or benefit to adding the larger 380cc injectors?

 

We do not find it to be necessary. I had them in for awhile and was running too rich as well as getting really bad gas mileage. Our opinion and of course there are many others is that up until you have a reduction of 19% or more you can get by with stock injectors. I have been running our 16% SC and our 2% CP with stock injectors for about the last 11,000 miles with no issues.

Randy
M7 Tuning

 

a 340 cc injector can support about 67 HP. We have four, so that's 260 HP. But remember, it takes a bunch to spin the SC. I went to the Eaton site, http://automotive.eaton.com/product/...argers/M45.asp The stockers shouldn't run out of steam until somewhere north of 200 HP. Depends on what duty cycle you start to worry at.

FWIW, the JCW 380 support 76 hp per injector. With losses, these should get you to a bit over 250 HP.

Matt

 

so if ur hitting around 200whp u should be getting bigger injectors?

 

I am at that mark and have not switched back to the larger ones.I am still running safely rich and in some cases too rich. Your results may vary.

Randy
m7 tuning

 

Latest book I've been reading: How to Tune and Modify Engine Management Systems, bu Jeff Hartman. As injectors get bigger and bigger, they have more issues delivering very small amounts of fuel, needed for good idle control. The fact that the car is boosted means that the required dynamic range is larger.

Also, there are some rules of thumb (different rule for each thumb ) about what the max duty cycle one should allow is. Corky Bell was reccomending staying below 85% duty cycle, a different Bell (A. Graham) said stay away from over 65% or so. Seems that the injectors will heat up too much as they approach 100%, and the lifetimes will shorten or they will fail. But I haven't tried all of them, and I sure don't have the experience of others here. The right way to go is data log what you've got, and run the smallest injector that will not starve the motors fuel demands at full load and WOT at red-line, using the duty cycle limit that is your rule of thumb. Clear as mud, right? Also, seems that Lucas is making disc based injectors (As opposed to those that run with a plunger) that are faster acting at low flows. But I don't know of any part numbers that are drop in replacements for the Bosch units we run.

There's another method of fuel tuning, like done by Dinan, where they play with the fuel pressure regulator, and up the fuel pressure with boost more than stock, and this will deliver more fuel at the high end, and will still allow the good idle afforded by the stock unit.

Like all good tuning subjects, it's a mess. The best thing to do is get some logging software, so you can measure when your system is running out of steam, or can let you know that it will run out of steam with the next set of mods.

Sorry, but there's no exact answer here. Also the numbers I quoted above were for one fuel pressure. If the Mini runs higher pressures, then each injector will MAY support more HP. The pressure is really the fuel rail pressure vs the manifold pressure (what it has to squirt against!).

Matt

 

Since the total parasitic losses on our cars is pretty much unknown, that will really be the tell when they start running out of steam....

Matt

 

im goign to be honest.. dr obnxs all that stuff u jus sed went way over my head !!

 

I do not know the duty cyles at this point but we have something new coming that will tell me that and a LOT more

Randy
m7 tuning

 

I've read the A. Graham's book and it didn't make sense. Because %65 is too low. If you have 240hp in your mini 240 X 5.6 / 4 = 336cc. That means you need min. 340cc injectors and it will work %100 duty cycle. Than if you want to use them %65 duty cycle 336 X 100 / 1 X 65 = 517cc. It comes up to 517cc??? This part I don't get. Has the injectors changed over years and this book coming from behind or what?