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Old 05-26-2009, 01:19 PM   #1
Tgui
Scooby Specialist
 
Member#: 44771
Join Date: Oct 2003
Default Max PSI on 93 octane, conflicting results.

So out of a triad of tuning and theory books I've been reading, the reported max PSI on 93 octane in the higher RPMs (given still in efficiency range of turbo) is about ~20 PSI.

I did a few tests and have been running 24.5psi at 4K RPM tapering to 22.5 PSI at redline. Not smart from what I've read, but then again I always log.

NO METH!!

Timing is sane as well.
14.5 degrees peak torque, ~ 4K RPM
21 degrees at 6K RPM
23.5 degrees at 7.2K RPM

Tests run at 90F.

AFRs dip to ~ 11.0:1 at peak torque and hold about 11.3:1 tapering to 11.1:1 at redline.

Knock threshold for stock ECU has been upped, and tuner pro doesn't light up.

My basic modifications on my 04 STi:
- EL Headers
- UP Pipe
- FP Green 7cm^2 2.4"
- AEM CAI
- APS TMIC
- Catted DP
- Borla Hush

Granted not 90F, but representative of what I've seen. 4th gear.
Code:
Time	PEDAL	LOAD	RPM	FBKC	FLKC	IAM	KNCK	LD	PSI	WB02
9188	17.65	0.84	2217	0	0	1	0	0	-6.3	14.65
9391	28.24	1	2285	0	0	1	0	0	-5.5	14.65
9594	54.51	1.33	2256	0	0	1	0	10	-2.6	14.7
9813	91.37	1.47	2302	0	0	1	0	10	-0.4	14.11
10016	99.22	1.51	2321	0	0	1	0	10	0.6	13.03
10219	100	1.55	2392	0	0	1	0	10	1.1	11.93
10438	100	1.61	2424	0	0	1	0	20	2.3	12.34
10641	100	1.69	2503	0	0	1	0	20	2.9	12.68
10844	100	1.77	2522	0	0	1	0	20	3.5	12.81
11047	100	1.83	2616	0	0	1	0	30	4.1	12.81
11266	100	1.91	2629	0	0	1	0	30	4.9	12.68
11469	100	2.03	2695	0	0	1	0	30	5.9	12.53
11672	100	2.13	2802	0	0	1	0	40	7	12.42
11891	100	2.3	2870	0	0	1	0	40	8	12.23
12094	100	2.43	2977	0	0	1	0	50	9.6	11.96
12297	100	2.62	3040	0	0	1	0	60	11.3	11.65
12516	100	2.85	3171	0	0	1	0	70	13.3	11.3
12719	100	3.14	3259	0	0	1	0	80	15.5	11.17
12922	100	3.46	3412	0	0	1	0	90	18	11.17
13125	100	3.82	3574	0	0	1	0	100	20.6	11.11
13344	100	4.06	3713	0	0	1	0	100	23.5	11.02
13547	100	4.06	3898	0	0	1	0	100	24.1	11.02
13750	100	3.98	4016	0	0	1	0	100	24.3	11.2
13969	100	3.94	4190	0	0	1	0	100	24.1	11.43
14172	100	3.9	4306	0	0	1	0	100	24.1	11.62
14375	100	3.88	4483	0	0	1	0	100	24.1	11.68
14594	100	3.87	4604	0	0	1	0	100	24.1	11.58
14797	100	3.82	4822	0	0	1	0	100	24.3	11.52
15000	100	3.79	4864	0	0	1	0	100	24.1	11.45
15219	100	3.73	5000	0	0	1	0	100	23.9	11.34
15422	100	3.69	5152	0	0	1	0	100	23.7	11.3
15641	100	3.67	5272	0	0	1	0	100	23.3	11.33
15859	100	3.62	5484	0	0	1	0	100	23.3	11.33
16063	100	3.59	5622	0	0	1	0	100	23.1	11.37
16266	100	3.51	5670	0	0	1	0	100	22.9	11.34
16484	100	3.45	5804	0	0	1	0	100	22.7	11.3
16703	100	3.39	5904	0	0	1	0	100	22.7	11.33
16906	99.61	3.33	6032	0	0	1	0	100	22.9	11.33
17109	98.82	3.27	6165	0	0	1	0	100	22.7	11.3
17328	98.43	3.2	6250	0	0	1	0	100	22.7	11.27
17531	98.04	3.14	6440	0	0	1	0	100	22.5	11.24
17734	97.25	3.08	6465	0	0	1	0	100	22.3	11.24
What boost thresholds have you all (y'all) seen on 93 octane? What parts do you feel most positively/negatively impact knock with higher boost?
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Old 05-26-2009, 02:03 PM   #2
2.5racer
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Member#: 12482
Join Date: Nov 2001
Location: Lakewood, Co
Vehicle:
2000 RS w/ej20 & e85
94 RX-7 1/2bridge w/meth

Default

It's not really boost that determines it... its the air flow that does.

You can have a small turbo that pushes x amount of air at 20psi, and a big ass turbo that pushes the same x amount of air at 10 psi. The air flow is what determines if you're gonna run lean or not... not the pressure.

edit: fwiw I run e85 so I can't help you much with the 93 question.
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Old 05-26-2009, 02:14 PM   #3
Tgui
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Default

Quote:
Originally Posted by 2.5racer View Post
It's not really boost that determines it... its the air flow that does.

You can have a small turbo that pushes x amount of air at 20psi, and a big ass turbo that pushes the same x amount of air at 10 psi. The air flow is what determines if you're gonna run lean or not... not the pressure.

edit: fwiw I run e85 so I can't help you much with the 93 question.
I'm not concerned with running lean as the determining factor in how much pressure I can run as I am in full control of the AFRs.

The limit I'm talking of (and should have been more specific with) is this *magical* PSI limit that my books refer to that off the top of my head are a combination of engine compression ratio, PSI (with sane AFRs) and octane rating of fuel.

Was this just an arbitrary limit for the sake of not so skilled readers or are there some physics that I need to read up on that determine max PSI for a given octane? Rule of thumb and correlation and causation issue>
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Old 05-26-2009, 02:42 PM   #4
2.5racer
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Member#: 12482
Join Date: Nov 2001
Location: Lakewood, Co
Vehicle:
2000 RS w/ej20 & e85
94 RX-7 1/2bridge w/meth

Default

I think I know what you're saying. You're talking about detination do to pressure. We'll I guess you'd have to figure out what pressure causes 93 octane to spontaniously combust. Then you'd have to figure out the amount of pressure thats in the cylinder at it's max compression at atmosphere (14.7lbs). Then figure out how much more compressed pressure 20psi makes.

I'll see if I can't figure that out for yeah.
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Old 05-28-2009, 09:55 PM   #5
69subaru360
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I ran almost the same timing and boost on my 2.0 20G on 93 and it works fine.
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