Guys!! my first time here!! thank you thank you thank you... hey! do not bow untill yer told! (grin, jest kidding guys) any way, I love this website and I have like a zillion questions.. Personally I kneel down infront of Injuneer (I am not worthy..) I have seen his web page...errr oops... grin. Ok on a serious note, Guys why is it that I ran the fuel injector size calculations at the MSD website and I always come up with a way bigger injector size than what you folks are running consistenly here?? is like for a 400hp (crack err not I mean cranck) the injector size I come up is a 48lbs or so? that is using the 80percent on time and standard fuel pressure?? I am only a beginer mod-ulator type a guy but I want to start with enough fuel capable system so I dont hafta buy injector twice.

Many thanks folks... thank you for such a wonderful site.

Marvin

 

Most of the formulas recommend an "NA" brake specific fuel consumption (BSFC) of 0.50 pounds/hour/HP. They also recommend a duty cycle of 0.80.

That is what gives you the result of

400HP x 0.50#/HR/HP / 8 injectors / 0.80DC = 31.2#/HR

When I ran my stroker on the engine dyno, after tuning, the BSFC was in the range of 0.43 - 0.44. On a huge hit of nitrous, BSFC was 0.53.

If you just drop the BSFC down to 0.45, you reduce the injector size by 10% from what you calculated at 0.50. If you decide you can live with 85% or 90% DC, then the injectors get smaller yet.

My guru convinced my to go the other way.... use a large injector, boost the fuel pressure to make it an even larger injector, and then run it at less than 70% DC so you can actually start setting injector pulse width timing with respect to valve events, rather than running the injector wide open at max power. I run Bosch 64's at 58psi (4 baR), making them "75's". Even at close to 800HP with dry nitrous (all the fuel through the injector), my DC is about 70%. It helps to run a "quicker" low impedance (peak & hold) injector, in order to turn them down to allow the engine to idle at 800rpm, and then using a computer with 0.0001 second pulse width resolution and good injector drivers to control them.

I guess its just a matter of who you listen to and who you choose to trust.

 

Like I said.... Injuneer is the MAN! Thanks injneer I will save your reply in my files. Also what about Injector response time? do I need to worry about it when choosing a larger injector size?

My goal is a NA 400hp street machine that is docile enough to take my GF for a Spin without having her fly off the window on a slow turn. I also believe in always allowing some breathing headroom on any machine design. meaning if 400hp is the goal the injectors will be capable of at least 20 percent more than that. I think is called overdesign. I believe is cheaper in the long run. Kinda makes me think of Military specs if you get my drift.

Oh by the way.... Eagles may soar but weasels dont get sucked into jet engines (grin) I love that quote.


Marvin

 

i have the exact setup, LE heads, xe 224/230-112, bryan at pcmforless told me set the fuel pressure at 58psi and he would program the injector constant accordingly, stock injector, pump

 

From my personal experience with a similar cam and better heads the stock fuel pump is not good enough to keep up. I maxed out the regulator to get the pressure up to 43# and and when you rev the motor the pressure drops. So im droping in a walbro. Steven