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Old 09-24-2007, 11:41 AM   #1
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Default How much boost?

Using the info in the DIY thread I figured out that for 220 hp at 80 psi of fuel at 80% duty cycle I need 293cc min injectors . My question is how do you figure out how much boost you need in corolation to injector size and fuel pressure?
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Old 09-24-2007, 11:44 AM   #2
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there are formulas that will get you close, but it's still a variable.

a small turbo will have to run more boost to match the HP at redline of a larger turbo due it it's inefficiencies.
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Old 09-24-2007, 12:17 PM   #3
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So how do I figure it? I would like to run 10 psi.
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Old 09-24-2007, 12:27 PM   #4
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220BHP x 12:1 AFR x .00916 = 21.18 CFM
BHP x AFR x BSFC/60 = REQ CFM

(CFM x CONSTANT X (460 + AIT) / VE X RPM/2 X CID) - 14.7 = PSI
21.18 x 639.6 x 550 / 3500 x 97.7 = 21.78psia - 14.7 = 7psi

like i said, it gets you close, but there are many other factors involved.
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Old 09-24-2007, 12:33 PM   #5
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lol, is there a thread in here where I can learn what all the abreviations mean?

I should just buy a wideband, shouldnt I?
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Old 09-24-2007, 12:38 PM   #6
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yep. then you just log, turn up the boost, see how much fuel you have.
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Old 09-24-2007, 12:43 PM   #7
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Ok, so just so I know, when I get a wideband and I get my fuel pressure correct with my 1.8's at 7psi. Which it should be already. When I swap to larger injectors like 330's this should cause me to go rich right? and then i could just turn up the boost to correct the afr?
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Old 09-24-2007, 01:12 PM   #8
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In theory yes. What FP are you gonna run an dwhat rate on your FPR the rate might overrichen you on tip in and cause you to lose power. with a rrfpr and a healthy pump capable of 80 psi 220whp should be doable on a mid to small size t28 before you hit 10psi if you have the right cooling and timming in place. If not you can blow to 15 psi and you still won't make the power you want just a bunch of silent knock.
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Old 09-24-2007, 01:15 PM   #9
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Quote:
Originally Posted by levnubhin View Post
and then i could just turn up the boost to correct the afr?
No. With a rising rate fuel pressure regulator setup, you would have to turn down the pressure rise per psi in order to have the same fuel flow rate at a given boost level. Remember, with a RRFPR, increasing the boost also increases the fuel pressure up top.
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Old 09-24-2007, 01:22 PM   #10
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No. With a rising rate fuel pressure regulator setup, you would have to turn down the pressure rise per psi in order to have the same fuel flow rate at a given boost level. Remember, with a RRFPR, increasing the boost also increases the fuel pressure up top.
That makes sence. So when I install 330 injectors and turn the boost up to say 10psi, I will have to lower the pressure on the afpr until the wideband is happy?
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Old 09-24-2007, 01:27 PM   #11
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yes
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Old 09-24-2007, 01:30 PM   #12
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Phil!!!

The stock ECU can idle 330's? Wow..... something tells me the exhaust gasses at idle will be flammable lol
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Old 09-24-2007, 01:32 PM   #13
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Originally Posted by DropTopDrifter View Post
Phil!!!

The stock ECU can idle 330's? Wow..... something tells me the exhaust gasses at idle will be flammable lol
Adjust the AFM to get a better idle mixture.
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Old 09-24-2007, 01:34 PM   #14
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Quote:
Originally Posted by DropTopDrifter View Post
Phil!!!

The stock ECU can idle 330's? Wow..... something tells me the exhaust gasses at idle will be flammable lol

the AFM has an idle-mixture screw. you can still achieve a perfect 14.7:1 AFR at idle.

...then you start to get into the realm of open loop mode with higher fuel pressures
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Old 09-24-2007, 01:38 PM   #15
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Yeah i got 460's to idle just fine with a safc and rx7 afm 300's is easy. Given you have a 1.8 and run 265 cc/min injectors anyway the change will not be as drastic for you as it is for us 1.6 guys at 212 cc/min.
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Old 09-24-2007, 06:08 PM   #16
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Jesus, just buy a megasquirt. I don't know why anyone would dick with FPRs, RRFPRs, lean/rich tip-in, trying to idle injectors, new fuel pumps, and then trying to figure out how to correct the timing in all that mess.
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Old 09-24-2007, 06:28 PM   #17
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Originally Posted by Savington View Post
Jesus, just buy a megasquirt. I don't know why anyone would dick with FPRs, RRFPRs, lean/rich tip-in, trying to idle injectors, new fuel pumps, and then trying to figure out how to correct the timing in all that mess.
+1.

Bandaids ******* suck. Never again.
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Old 09-24-2007, 06:44 PM   #18
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wheeheeehee... i had my megasquirt for about 3-4 months now and STILL didnt install it
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Old 09-24-2007, 07:56 PM   #19
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Originally Posted by Savington View Post
Jesus, just buy a megasquirt. I don't know why anyone would dick with FPRs, RRFPRs, lean/rich tip-in, trying to idle injectors, new fuel pumps, and then trying to figure out how to correct the timing in all that mess.

Any donations will be gladly accepted.
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Old 09-24-2007, 08:41 PM   #20
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Quote:
Originally Posted by levnubhin View Post
Any donations will be gladly accepted.
Sell your Bell AFPR. That alone should get you halfway to MS. Then you can run 440 injectors and make all the power you need without putzing around with AFM adjustments and FPR tweaks.

You can probably make the 330s work on the stock ECU if you are so inclined. However it's a bit like kissing your sister- you can do it, but why on earth would you want to?
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