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Old 02-08-2007, 09:46 PM   #1
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Default boost vs fuel again i think

ok i looked but didnt find anything. i have the 305cc supra injectors and i want to know about how much fuel (psi) per psi of boost. that simple. i have no aftermarket computer or anything just injectors and begi.
thanks
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Old 02-08-2007, 09:50 PM   #2
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I'm using a 6:1 disc, probably be better off with only a 4:1. Really depends on how much boost/HP output.
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Old 02-08-2007, 10:15 PM   #3
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well around 12-14 psi of boost. is it possible without very high pressures.
also i was curious about the begi afpr. so its about 100psi of fuel for 10 psi of boost. but is this measured at redline and full throttle or how does it work. the problem is that i ahve the 1.8 inj and i adjusted to 105psi of fuel for 10psi of boost, and all of this occurs at 4000-4500k rpm. but as rmps go to redline the fuel pressure reads about 130 at 6500 and the car feels boggy so what should i do. i have added the restrictor or fuel pressure should rise like it does but doesnt make sense
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Old 02-08-2007, 11:11 PM   #4
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I remember seeing someone do:
((Disc ratio x PSI) + 48 = Fuel pressure
And using this table:
http://www.rceng.com/technical.htm#WORKSHEET
Assuming you set max duty cycle to 80%, 0.50 fuel consumption, and 4 injectors...

Using the linked table with 305cc injectors and assuming you want to be good for 250 bhp (roughly what 12 psi could give you with the BEGI kit) you need 80 psi fuel pressure.

So, assuming you want 80 psi fuel pressure:
(( Y x 12 ) + 48 = 80 where Y= 2.6
So... a 2.6:1 disc is the smallest you could run. But that is if you want to run at the max injector duty cycle. With a 4:1 disc you would get:
(4x12)+48 = 96 psi fp
With 96 psi you would only run your 305cc injectors up to 73%.
Or, looking at it another way, with a 4:1 disc and the 305cc injectors you can running the injectors up to 80% duty cycle allows you 275 bhp so you can even add HP a bit and be safely within your fuel capability.

Oh, all that means I'd suggest a 4:1 disc. 96ish psi is safe and allows a bit of room in the injectors.

-Ryan

P.S This is obviously assuming you have 305's. In your second post and your sig you say you are running 1.8 injectors which are smaller than that so then you would have to plug the 1.8 injector size (I think 240cc - correct me if im wrong) into the equations.
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Old 02-08-2007, 11:42 PM   #5
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Basically right now you have to tune to assumption....which isn't the best route. you can do so math and figure ok I have X HP and need X fp. but you don't know exactly for sure what's going on. What I suggest is finding a dyno that will let you rent it for an hour. This way you can make multiple pulls and adjust the FP on the fly and make sure you have exactly the right amount of fuel.

Your greddy will make around 220-250rwhp will that amount of boost. with that said it is a must you run the 305cc injectors. If you only see 100psi and then it rises, then you are making more boost. The bog is probably from overfueling as the ECU like to dump it in. I'd try to tune for 100-110psi at max boost.

BTW for the cost of the LC-1 it's worth it to skip the dyno and tune on the street and always be able to monitor your AFRs.
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Old 02-08-2007, 11:53 PM   #6
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so does this mean that the disk the Begi afpr is using is a 4:1 or a different one?

A note when i mean begi like previous post i mean BeGI AFPR
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Old 02-08-2007, 11:57 PM   #7
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ok i understand braineak but when you say tune for 100-110psi at max boost this means that the rpms are at redline or it does not matter. i had been tuning at 100-110psi but as revs went to redline holding the same 10psi the fuel pressure went to 120-130psi. basically i wanted to know if this was normal or i had to tune it back to 100-110psi at redline assuming 10psi boost constant
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Old 02-09-2007, 12:04 AM   #8
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If it all of a sudden rises, if might be that you are just making more boost and not constant.

try to make all things constant when you tune....get in third gear and make pulls from 2.5-3k each time @ WOT. that way you can monitor to FP and boost and make sure it's doing exactly what you want it to do, as you would on a dyno.



(I'm using a vortech which uses discs to set a static rise ratio, you'd just have to do some math [rise x boost + 50] to figure out your rise)
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Old 02-09-2007, 12:16 AM   #9
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sounds good, i will work on it and bring back results
thanks
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Old 02-09-2007, 02:57 AM   #10
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For the record, I completely misread your post and should have read your sig - I thought you meant you had the BEGI turbo kit... but duh, obviously not because you posted this in the Greddy section!
Anywho, that's why I figured 250 bhp - the greddy kit at 12 psi won't put that much out so figure less.
-Ryan
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Old 02-09-2007, 03:03 AM   #11
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How can he fine tune the fuel pressure if its a disc-tuned FPR? Aren't there only a few choices available for discs, like 2:1, 4:1, 6:1, etc.? If thats the case I'd suggest the 4:1 but is there a way to actually fine tune the pressure?
-Ryan
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Old 02-09-2007, 08:53 AM   #12
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No, there is no fine-tuning method with the Vortec, disc-tuned AFPR.
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Old 02-09-2007, 09:36 AM   #13
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Quote:
Originally Posted by ThePass View Post
Anywho, that's why I figured 250 bhp - the greddy kit at 12 psi won't put that much out so figure less.
-Ryan
A greddy holding 12psi should be making 210-220rwhp.

Quote:
Originally Posted by ThePass View Post
How can he fine tune the fuel pressure if its a disc-tuned FPR? Aren't there only a few choices available for discs, like 2:1, 4:1, 6:1, etc.? If thats the case I'd suggest the 4:1 but is there a way to actually fine tune the pressure?
-Ryan
You can't but we're talking about a BEGi AFPR here.
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Old 02-23-2007, 06:24 PM   #14
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so i installed the yellow top supra injectors. i had a problem with one injecvtor which wasnt working well because for some reason the resistor didnt provide the current. but i fixed this and started the car. there was no problems. idles fine. i have stock 1.6 afm and leaned two ticks on it. because i thought there was a need to tune this too. but nevertheless i took it to the freeway and feels much stronger. it pushing around 12-14 psi of boost and feels fast.
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Old 02-23-2007, 06:46 PM   #15
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It "feels fast?" Are you monitoring AFR?
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Old 02-23-2007, 07:00 PM   #16
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Quote:
Originally Posted by Braineack View Post
for the cost of the LC-1 it's worth it to skip the dyno and tune on the street and always be able to monitor your AFRs.
Check that please.



With your current situation, you've probably leaned out your A/F ratios somewhat with the AFM fiddling. This will somewhat help your current situation (with the fuel pressures shooting to 130) on the top-end, but how are your mids? Safe, lean? Any idea?

It has been shown that one of the limitations of using the AFPR is achieving a "good" A/F ratio across the RPM band. If your top-end is perfect, your mid-range might be too lean. I'll see if I can find a thread..

At any rate, I'd be cautious with adjusting A/F ratios when you're not able to monitor them.
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Old 02-23-2007, 07:16 PM   #17
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Based soley on my own screwing around with the afm tensioner with the car strapped to a dynojet, I didn't get any meaningful changes in afr resulting from adjusting the flapper. The only changes were in idle afr. With the car under power, closed loop afr was regulated despite flapper setting. The afr log from a pull didn't change at all (open loop ignores the afm right? ie pegged isn't meaningful).
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Old 02-23-2007, 07:32 PM   #18
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closed loop. I have not adjusted mine. With the AFM changes not affecting anything meaningful, I'm curious regarding the result.

Quote:
Originally Posted by ngarcia1983 View Post
i have stock 1.6 afm and leaned two ticks on it. because i thought there was a need to tune this too. but nevertheless i took it to the freeway and feels much stronger. it pushing around 12-14 psi of boost and feels fast.

edit: Anyway, I think I misunderstood the post. I was assuming he had the supra injectors in already. I think he just switched them from a set of 1.8s, and thus the AFM adjustment. The boost in performance, no pun intended, was from the larger injectors, not the adjustment. I'll go back to my corner

Last edited by UofACATS; 02-23-2007 at 07:39 PM. Reason: edit:
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Old 02-23-2007, 08:17 PM   #19
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i used to have the 1.8's but changed to the supras. also before with the 1.8 the car felt it needed fuel with the supra inj. it now feels fine. yes the two clicks i did on the afm was to lean out at idle. but under boost if feels fine. i have not checked pressures but will do it soon. for now it feels ok i guess.
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Old 02-23-2007, 11:55 PM   #20
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Quote:
Originally Posted by UofACATS View Post
Check that please.
what's wrong with that statement? I'd rather spend $170 bucks for an Lc-1 and datalog whenever I want and monitor my AFR, then to pay $75-100 for three pulls, then go home and make changes and have to go back to the dno to monitor the AFR again.


ngarcia1983, I'd suggest putting the tension on the flapper back to OEM. Instead, back the air idle mixture screw back 3/4 to one complete turn. I see a perfect 14.7:1 idle when I do that.
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