How do you calculate fuel flow in lbs/hr with MFI ?

I use spuds calculator at fie.com

Before you can calculate with any accuracy you have to know the actual flow numbers of your pump, not the advertised GPM the actual from a flow bench

quote:

Originally posted by Big Steve:
Before you can calculate with any accuracy you have to know the actual flow numbers of your pump, not the advertised GPM the actual from a flow bench

When I sent this late 1980’s 0 pump back to Rons in 2013 to be flowed, the older gentleman that called said it flowed slightly more than a brand new 0 pump. That’s 2.74 gpm @ 6000 and 3.44 gpm @ 8000 . I assume this is actually engine rpm and pump rpm would be half of that as they are geared 2-1 from the crank drive.

When he called, I told him to look at the pump, it’s plumbed backwards. He said “Yep, but the pump don’t know it”.

quote:

Originally posted by BJs Wild Ride:
I use spuds calculator at fie.com

Says you have to register to access calculators. Not me.

quote:

Originally posted by markemark:

quote:

Originally posted by BJs Wild Ride:
I use spuds calculator at fie.com

Says you have to register to access calculators. Not me.

It's a safe site, dont worry about registering.
I have used his calculator in the past, its good for getting some and playing with flow numbers but I would not tune with it.

The other thing you have to remember is all the different brands of pills and nozzles flow differently. Also barrel valves are very different even tho wide open they should flow 100%. I think his calculator has you specify what your using, don't believe any of Ron's stuff is a choice

^^^^^^^^^ Ok, Thanks Steve. Maybe I’ll contact Killer Rons and see if they can offer something.

I’ve ised that calculator to tune multiple combos. Not saying it’s a good idea, just giving you an option.

I get a conservative baseline BASED on the numbers (don’t match it exactly), put it in the converter to make sure it’s close, then go as far as I feel comfortable with on the first pass.

The only problem I’ve had is when I failed to realize that boost pressure + port check pressure was less than pump pressure on the converter.

X2 on the Fuel Injection Enterprises calculators, been using them since being introduced to them back in 2015. Not an absolute, but definitely a tool you can use to refine and better your tuning. Should give you VERY accurate flow numbers if you know all the specifics of your pump, number of nozzles, nozzle jet sizes, pump drive ratio, and main pill.

quote:

Originally posted by markemark:
How do you calculate fuel flow in lbs/hr with MFI ?

What are you really asking here? It's just math to go from lbs/hr from GPM.

Flowing a MFI pump just gives you a flow curve based on rpm. From that you can determine if that pump is too small/large or correct for the motor combo you want to use it on.

quote:

Originally posted by markemark:

quote:

Originally posted by BJs Wild Ride:
I use spuds calculator at fie.com

Says you have to register to access calculators. Not me.

Why. You enter name and pass word. Calculator is great gives you lots of ideas using various nozzle sizes and even alt changes..

quote:

Originally posted by TOP38:

quote:

Originally posted by markemark:
How do you calculate fuel flow in lbs/hr with MFI ?

What are you really asking here? It's just math to go from lbs/hr from GPM.

Flowing a MFI pump just gives you a flow curve based on rpm. From that you can determine if that pump is too small/large or correct for the motor combo you want to use it on.

you know lbs/hr from GPM would work as long as the density of the fuel never changes from a change in temperature.

Joe

-Calculate the total area of all the nozzles.
-Calculate the total area of all of the bypass pill(s)
-With the above info find the ratio of the amount of fuel going to the engine.
-Multiply that by the pumps output at any given rpm. In general the gear pumps product a linear fuel curve. Since the pumps are rated in gpm the result is in gpm
-To convert to lbs per hour mulitiply the above result by 6.6 (general weight of methanol) then multiply by 60 (minutes in an hour).

-As Joe mentioned earlier... The above doesn't take density changes with temperature into account. Since the density of the fuel doesn't change a whole lot in the temperature ranges we race in it doesn't make much difference. The above also assumes the same brand nozzles and pills are being used throughout the system. Mixing brands can effect the result as not every brand flows the same for a given orifice size.

Naturally Aspirated methanol engines need approximately 1 to 1.1 lb per hour per hp.

*** edit... The 1.1 to 1 lb per hr is only approximate.
Simple math can make it confusing. As the engine loses efficiency after peak torque sometimes a hi speed leanout is needed to flatten the linear fuel curve of a mfi belt driven pump. Engines dont exactly follow a linear fuel curve accross all rpms. Below my original words were quoted. I wasnt trying to say the lowest bsfc occurs at peak hp. I chose the wrong way and words to say what I said in the previous couple sentences. ***

Scott

This message has been edited. Last edited by: 358T,

quote:

Originally posted by 358T:


Naturally Aspirated methanol engines need approximately 1 to 1.1 lb per hour per hp. Generally peak torque is closer to the 1.1 while the peak hp is closer to the 1.

Scott

What is the difference with blown motors?

quote:

Originally posted by Curly1:

quote:

Originally posted by 358T:


Naturally Aspirated methanol engines need approximately 1 to 1.1 lb per hour per hp. Generally peak torque is closer to the 1.1 while the peak hp is closer to the 1.

Scott

What is the difference with blown motors?

Mildly blown motors (10 psi or less) are about the same as NA (just lean towards the richer side). After that as the boost goes up the number goes up also since the engines need much richer air/fuel ratios in comparison.

Also, as the boost goes up, a person has to take into consideration the method of boost and where the nozzle is along with any aeration the nozzles may have. Things like does the fuel pressure have to overcome boost pressure. Or, if a roots style supercharger, are the nozzles above or below the blower and if above the blower are they vented.

Scott

Interesting. I’ve always seen more like 1.8 - 2.0 lb/hr/hp at 25 psi+ with a roots blown bbc (I think Hemis tend to run a little lower). I didn’t realize the lower hp setups could get away with that much less fuel.

Also surprised to see a bigger number at peak torque. I thought everything was most “fuel efficient” at peak torque?

The reason I ask is because is because I think the Lbs fuel/ Hour could give an indication how much the blower takes to drive?

quote:

Originally posted by BJs Wild Ride:
Interesting. I’ve always seen more like 1.8 - 2.0 lb/hr/hp at 25 psi+ with a roots blown bbc (I think Hemis tend to run a little lower). I didn’t realize the lower hp setups could get away with that much less fuel.

Also surprised to see a bigger number at peak torque. I thought everything was most “fuel efficient” at peak torque?

I tried to stay vague about the boosted stuff. Most definitely the fuel needs change dramatically as the boost goes up. Cylinder heads, type of boost, type and flow of the barrel valve, type of nozzles etc etc all play roles also. This is just mathmatical calculations we are discussing. Flow differences of all of the things can mean that the simple math being used here and on spuds sight does not match actual or that one persons calcs will match anothers.

Regarding my general N/A numbers... IMO, it relates to why sometimes engines like a hi-speed leanout. As the rpms go up and the efficiency of converting air/fuel to hp goes down (or gets wasted) then they want/need less fuel.

Scott

Scott

This message has been edited. Last edited by: 358T,

quote:

Originally posted by Curly1:
The reason I ask is because is because I think the Lbs fuel/ Hour could give an indication how much the blower takes to drive?

I am sure that plays a roll too. More boost created usually means more drag on the engine (if belt driven supercharger) therefore the engine actually makes more hp than observed at the crank therefore possibly higher fuel requirements than the HP would indicate.

Scott

quote:

Originally posted by 358T:

Naturally Aspirated methanol engines need approximately 1 to 1.1 lb per hour per hp. Generally peak torque is closer to the 1.1 while the peak hp is closer to the 1.

Scott

Scott

you have the numbers reversed, the lowest BSFC numbers occurs at peak torque (or right after).

Joe