Okay, so first a little background. Let's assume a person has 650CC injectors and intends to use it for a 250whp twincharge application. I'm pretty sure the 650CC injectors are oversized. However, I want to see what duty cycle the 650CC injectors would operate at. You can see my calculations and how I'm thinking about it below. Please let me know if I'm missing something.



In my mind, since the theoretical BSFC of the stock MCS is .5512, the twincharge application should have a higher BSFC. Now, my question is, is it okay to run a 650CC injector even though it is running at a theoretical 70%+? At what duty cycle is it unwise to run large injectors?

Thanks a bunch and thanks for reading the post.

 

I like your math....pretty complete. The biggest issue you will have is setting idle. I managed to get my idle to set around 760-800 rpm with little fluctuation with 550cc injectors. How are you planning to tune it? Apexi? if so running the 550's for me and I have my trims pulled almost all the way back, so you could run into an issue where you have just too much fuel being dumped even when pulled all the way back.

 

We generally run injectors up to 80-85% duty. ~70% duty will give you plenty of over head.

Keep in mind that most injectors are rated at 3 bar of fuel presure and if im not mistaken these cars run 3.5 from the factory. If you install a 650cc injector, it will flow more then 650cc's.

 

Yeah, I think apexi is the way to go right now, especially considering the lack of shops around this area.

I'm okay with running a bit rich at idle since I don't sit around in traffic very often... not fine with flooding the engine...

Interesting... Is this just an easy conversion (i.e. - 3.5 divided by 3 and multiply 650?)?

 

 

Okay, so applying the 3.5 bar vs. the standard 3 bar that injectors are rated, we get.... a little over a 700CC injector...

Edit: It comes out to be about the same result... the 650CC injectors will be running at about a 70% duty cycle since we also have to apply the conversion to the original fuel injectors, thus increasing the BSFC, etc...

 

honestly 650s are just too big... the math has been done... and the testing to boot... if you trim back the AFC the way you you would have to you are going to end up with a blown motor..

550s are the biggest you need/should use... but to achive 250 whp you only need 440s...

sing with me now "that just the way it is.... somethings will never change"

LOL

 

im with stupid ^ I mean Tuls

 

ha ha thanks dizzle...

 

I can understand not wanting to run 440's because you want the duty cycle to be lower. One thing I didn't notice anyone mentioning an adjustable FPR......I've used these on many applications and have had really good luck. If it was me, I personally would be doing larger then 440's because I don't like buying parts twice, that and the fact that I would need them down the road because I get bored easily with power and always want more....

 

returnless fuel system...

you could add a boost a pump...

 

Yeah in order to run the adjustable FPR you would need to run a return line. No real biggie...but a bit more work...

 

a boost a pump is also a very nice thing to have... plus you don't have to smell like gas for the rest of the day... just a couple of wires.. and a mount and you are D U N