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weight vs. fueling requirements?

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simple

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May 29, 2001
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how much of a difference in fueling will there be between a mid 10sec 3700lb combo vs. the same combo in a 2900lb vehicle?

i know with my LT1, @ 3400lbs with a Walbro 340HP intank and 36lb injectors @ 39psi, i was @ 82% duty cycle under WOT

would that pump be able too keep up with the requirements on a TE45a/GN1/60lb/3600stall combo @ 24psi of boost in a 2900lb car? with more fuel pressure
 
avg rwhp=197 * weight going down track (car+driver) / et^3,
so if your weights include the driver, then 197*2900/10.5^3=494 hp and 197*3700/10.5^3=630 hp. You can inflate those by your favorite auto trans fudge factor, usually 15-25%, to get flywheel hp. However, just looking at the ratio, 630/494=1.28 so the heavier car needs 28% more hp and thus 28% more fuel at the same bsfc as the lighter car. Remember, fuel pump output falls with increasing pressure so the more boost you run the higher the wot fuel pressure and thus the lower the pump output. Your LT1 (assuming it was n/a; you didn't say) fuel pressure at wot was still 39 psi, while on a turbo motor at 25 psi boost and a typical 43 psi base pressure the wot fuel pressue is 68 psi. There are curves online that show the output of a 340 vs pressure, my fuzzy memory says the pump will be down maybe 10-15% at 70 psi vs 40 psi. You can bandaid a smaller pump to some extent by running larger injectors and keeping the base fuel pressure low (say 30-35 psi), but somewhere between low 11's and high 10's most normal weight TR drivers go to something more than a single 340 pump. Obviously the hp calculation shows you could push that well into the 10's for a lightweight car; just how close to the edge do you like to keep your motor?
 
simple said:
how much of a difference in fueling will there be between a mid 10sec 3700lb combo vs. the same combo in a 2900lb vehicle?

i know with my LT1, @ 3400lbs with a Walbro 340HP intank and 36lb injectors @ 39psi, i was @ 82% duty cycle under WOT

would that pump be able too keep up with the requirements on a TE45a/GN1/60lb/3600stall combo @ 24psi of boost in a 2900lb car? with more fuel pressure

Maybe.......
I have a TA-62, and 60s and (off the top of my head), at ~60%DC started running out of fuel pump, and went to a double pumper setup.

The answer is mounting a pressure guage in the return line and make sure you see like 4-6 PSI there. That way you know the regulator is facing fuel, and not running out of volume at max pressure (see Carl's comments). Not to mention that under some conditions, what works for a Drag Car maynot for a streeter. While a Drag Car might just run for secs atta time, some *street* cars run for minutes in boost, and they need a *reserve* capacity to live under those conditions.
 
thanks for the replies and the math :) that will definately be helpful information

keeping the motor on the ragged edge of lean (possible destruction) isnt what i have in mind at all for this project

i did find some of those graphs for the pumps and you are correct about how much they drop off as FP increases, give or take a little bit

now what if Alky injection is added into the mix?

some of the fuel systems (Aeromotive externals or dual Walbro in tank setups) i've been looking at for this mustang are into the $1200+ price range.
where as single pump setups like racetronix combined with alky injection will run me about half that. plus it makes more sense for me too go that route as i would only (90%) of the time be getting into the alky at the track. i'd keep the boost levels conversative for street duty

Bruce, what is your cars weight with you in it?

Steve
 
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