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Old 02-06-2009, 11:50 AM   #1
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Default fuel injectors, pressure, power, and tuning

I'm going to the dyno hopefully for the last time tomorrow. Currently I'm at 67% duty at 12psi with 550cc injectors, walbro 255 in-tank and unknown fuel pressure...and not sure how much power thats making but not much. My goal is 250whp with some head-room, I'd like to see a 300whp pull so I can crank up the boost when I get the 6-speed in.

will I need more fuel pressure?

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Old 02-06-2009, 11:52 AM   #2
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You got a 190HP? If so, you got the fuel system for 300whp. But that's the upper limit. With rich AFR's, you may not hit 300whp. A RRFPR in conjunction may be needed.
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Old 02-06-2009, 11:52 AM   #3
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you should have enough fuel to see 300rwhp.
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Old 02-06-2009, 12:12 PM   #4
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Quote:
Originally Posted by Braineack View Post
you should have enough fuel to see 300rwhp.
I had a bad fuel pump that wouldn't go north of 200whp at 100% duty. I put the 255 in and duty dropped to 67% or whatever at 12psi (overboost)...the motor has loosened up but considering that 85% duty is actually 100% open, do you still think your assumption is reasonable? I'll take it up to 18psi or 301whp, whichever comes first. I'm considering upping fuel pressure tonight. I'm putting afr in boost at 11.5:1
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Old 02-06-2009, 12:16 PM   #5
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With injectors, it's like:

Duty cycle..... Actual duty cycle
0...................0
10..................10
etc....
75....................75
80....................80
83....................83
84.....................84
85....................85
86....................86
87.....................100
88.....................100
100.....................100

You reach a point where it can't open and then close, and it just stays open. 80-85 is the limit. I would tune for higher than 80% as to still have a spec of headroom. You don't want to tune it for 90% duty cycle (really 100%) and then on a warm day it runs 86% and fuel actually falls to 86%.
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Old 02-06-2009, 12:24 PM   #6
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Quote:
Originally Posted by patsmx5 View Post
With injectors, it's like:

Duty cycle..... Actual duty cycle
0...................0
10..................10
etc....
75....................75
80....................80
83....................83
84.....................84
85....................85
86....................86
87.....................100
88.....................100
100.....................100

You reach a point where it can't open and then close, and it just stays open. 80-85 is the limit. I would tune for higher than 80% as to still have a spec of headroom. You don't want to tune it for 90% duty cycle (really 100%) and then on a warm day it runs 86% and fuel actually falls to 86%.
thanks for driving that home. I won't go north of 85%...or should I drop it back lower? (shouldn't you be concrned with lower temperatures, considering colder air needs more fuel?) Its supposed to be 70* that day, what should I do for max duty?


I think I need to do some logs tonight because after about 500-miles on the new pump, idle AFR went from 14.7 to 12.8:1. Apparently there's a break-in period for Walbro pumps./
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Old 02-06-2009, 12:29 PM   #7
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i'm seeing ~85% duty on rx7 550's at 6800rpm, if that helps. thats at 320whp/325ft-lbs, mid 11's AFR.
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Old 02-06-2009, 12:33 PM   #8
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i'm seeing ~85% duty on rx7 550's at 6800rpm, if that helps. thats at 320whp/325ft-lbs, mid 11's AFR.
what fuel pressure?
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Old 02-06-2009, 12:37 PM   #9
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stock FPR, walbro 255 pump. if i prime the pump with the engine off it stays at 43 psi as it should.

i have a fuel pressure gauge on the rail, but i forgot to watch it when i had the thing on the dyno... so i dont know if it's running at exactly 1:1 but it seems to be. i'm running 23psi of boost.
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Old 02-06-2009, 12:46 PM   #10
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Quote:
Originally Posted by therieldeal View Post
stock FPR, walbro 255 pump. if i prime the pump with the engine off it stays at 43 psi as it should.

i have a fuel pressure gauge on the rail, but i forgot to watch it when i had the thing on the dyno... so i dont know if it's running at exactly 1:1 but it seems to be. i'm running 23psi of boost.
I have a gt2860rs, so I will most likely make 250whp at 12-16psi...so the regulator is not on my side. I guess I'm a little late to worry about it now.
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Old 02-06-2009, 12:56 PM   #11
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it also put down 275whp last fall at 18psi with a slightly less agressive timing map. the VJ23 is fairly comperable to the 2860... my compressor wheel is 65mm at the exducer. i dont recall the trim at the moment.

i think you will be just fine
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Old 02-06-2009, 01:17 PM   #12
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Quote:
Originally Posted by therieldeal View Post
stock FPR, walbro 255 pump. if i prime the pump with the engine off it stays at 43 psi as it should.

i have a fuel pressure gauge on the rail, but i forgot to watch it when i had the thing on the dyno... so i dont know if it's running at exactly 1:1 but it seems to be. i'm running 23psi of boost.
What year is your car?

Built motor?
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Old 02-06-2009, 02:18 PM   #13
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its a 95 escort gt with a 323 GTR motor. it's "built" from the factory, i'm sure most of you guys have heard of it?
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Old 02-06-2009, 07:56 PM   #14
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ok i remembered wrong...

i just opened up the logs from my dyno runs, on both runs i saw a peak of 74% duty cycle.
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Old 02-06-2009, 08:37 PM   #15
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258kPa gives me a boner.
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Old 02-07-2009, 12:34 AM   #16
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yeah, its a good time lol. i just desperately need a stiffer wastegate spring - as you can see in that log my wastegate control sucks even with an EBC.
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Old 02-07-2009, 01:10 AM   #17
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Quote:
Originally Posted by therieldeal View Post
yeah, its a good time lol. i just desperately need a stiffer wastegate spring - as you can see in that log my wastegate control sucks even with an EBC.
MBC. Get an external gate, dual port, and MBC. Win Win Win.
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Old 02-07-2009, 12:18 PM   #18
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i do have a dual port external gate (tial 38mm) with a greddy EBC
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Old 02-07-2009, 12:35 PM   #19
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Is it setup using the dual port? What spring you running? From my research, a dual port setup and stiff WG spring is the best setup for best spool.
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Old 02-07-2009, 12:50 PM   #20
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Quote:
Originally Posted by therieldeal View Post
i do have a dual port external gate (tial 38mm) with a greddy EBC
Some Greddy EBC's have a setting one for internal wastegate and one for external. Not sure if you were awhere of this.
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