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Old 09-10-2008, 07:24 PM   #1
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Default How much boost can I get on a stock engine NB8C

Does anyone know how much boost I can safely run on my stock engine NB8C? I ask this as most of the guys on this forum seem to have NA’s, which have a lower compression ratio, and I see some have been running over 12PSI for a few years. Does having a higher compression ratio limit my boost? My car is a weekend only toy so it will not be doing high miles.

From what I have found the NB8 compression ratio is 1.8 is 9.5:1 and the NA8 is 9.0:1 so I assume this will limit my boost? I have no idea about the 1.6 compression ratio’s.

99 NB8C Jap spec as imported from Japan
T25 & I/C
Injectors - green tops @ 305cc/43PSI (bench tested at 330cc/43PSI) and of course the NB is around 60PSI
Emanage with;
AEM wideband (wired into throttle position)
And a 2 Bar (absolute) GM map sensor
O2 clamp
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Old 09-10-2008, 07:43 PM   #2
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All of it.
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Old 09-10-2008, 07:47 PM   #3
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400 psi
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Old 09-10-2008, 08:07 PM   #4
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1.367 psi
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Old 09-10-2008, 08:09 PM   #5
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Quote:
Originally Posted by bryantaylor View Post
1.367 psi
Well **** dude, he's already blowing that number out of the water with 12 PSI...must have one of those factory blueprinted motors...
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Old 09-10-2008, 08:17 PM   #6
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Ok, guys. Lay off the newb. He's at least done some homework.

Poison, disregard the peanut gallery.

The reason folks are being somewhat vague in answering (well, other than the fact that we've answered this exact question 7,973 times so far and that you could have found the answer by searching and reading the FAQs and Stickys) is that it's not so much about PSI as it is about power. Different turbos will actually make different amounts of power at the same pressure ratio, owing largely to differences in efficiency. And beyond that, boost is relative. A person running 12 PSI at sea level is flowing a lot more air than some poor bugger running 12 PSI at 2,000 meters.

As a very broad generalization, 200-225 HP (measured at the wheels) is well within the range of "Safe" operation, assuming that your fuel and spark are well sorted and that temperatures are under control. With something like a Garrett GT2560, this might happen at 10 or 11 PSI on a 1.8 NB.

Last edited by Joe Perez; 09-10-2008 at 08:33 PM.
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Old 10-01-2008, 09:08 AM   #7
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If you have a 2 bar MAP sensor, you will be out of sensor at around 14psi (= 1 bar over, or 2 bar absolute).
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Old 10-01-2008, 10:01 AM   #8
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Spooky, this thread is 3 weeks old and the OP hasn't logged in since the 14th. Just so you know.
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Old 10-01-2008, 10:03 AM   #9
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My motor is an 02 bottom end with a head thats been decked. Ill be running a sr20 t25. Ill let you know what I dyno at.

Last edited by leatherface24; 10-01-2008 at 10:05 AM. Reason: LOL I just realized the date of the OP's last log on
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Old 10-01-2008, 10:21 AM   #10
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I just know he's going to check back in
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Old 11-01-2008, 05:51 AM   #11
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Hi and thanks to those who made helpful reply's especially Joe. But KP and BT…WTF… get over yourselves.

Anyway I must have got my forum settings wrong as I was expecting an email notification of a reply. I had heard from two former members a lot of people had left the forum due to some cost??? Not that I got asked for any cash. So assumed my thread had died. Glad to see it’s alive and well. I do apologise I have poor success with the search feature. I read the FAQ and the comp ratio left me hanging so I thought I’d ask specifically.

Currently I am running only 5 PSI with a F-con mini piggy back. And I have just installed an emanage and the injectors. I was concerned that 8PSI would be my limit because of the higher compression ratio resulting in pre-ignition. My ideal would be 10-12PSI as I am aiming to just get past the 200HP mark and from what I have read here it may be do-able if my fuel hangs in there.

Hey Spooky, thanks for the faith!!! Yeah I’m back. yes it’s 2 Bar absolute as my target was under 14PSI boost I can get the best resolution over this range.
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Old 11-03-2008, 03:35 PM   #12
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put another shrimp on the barbie!!!
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Old 11-03-2008, 03:56 PM   #13
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I haven't heard of anybody leaving the forum due to any cost. Maybe they were being a jackass.
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Old 11-03-2008, 04:12 PM   #14
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Paul is running 14psi on his with a GT2560.

Everyone kept talking about psi and efficencies. It didn't make sence to me psi is psi.

Then some smart cookie made sence. Psi is a measure of back pressure from the turbo compressor wheel.

If you have a bigger wheel, more air can pass by. Therefore more air per psi.

So there is the answer for psi. Bigger turbo more air per psi. Simple and easy.

If you get a good tune, I'd push 10-12.
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Old 11-03-2008, 04:18 PM   #15
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Quote:
Originally Posted by Toddcod View Post
Paul is running 14psi on his with a GT2560.

Everyone kept talking about psi and efficentcy's. It didn't make sence to me psi is psi.

Then some smart cookie made sence. Psi is a measure of back pressure from the turbo compressor wheel.

If you have a bigger wheel, more air can pass by. Therefore more air per psi.

So there is the answer for psi. Bigger turbo more air for psi. Simple and easy.

If you get a good tune, I'd push 10-12.
He also said he's running 15psi on his daily with spikes to 18psi. Basically if you don't have knock you're okay. I'm running 15psi on mine with no issues so far.
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Old 11-03-2008, 04:25 PM   #16
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Quote:
Originally Posted by johndoe View Post
He also said he's running 15psi on his daily with spikes to 18psi. Basically if you don't have knock you're okay. I'm running 15psi on mine with no issues so far.
That's a fun Daily driver.
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Old 11-03-2008, 04:59 PM   #17
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While racing a Turbo Cayenne on the parkway last weekend up to 150+mph my girlfriend was watching the gauges in MT and said I was at 17-18psi. That was in the Machine. I spanked him every time he tried to pull even though I let him have the jump, first was about 80mph, then 100, then 120, and we did it a final time from 140. The reason my boost is up is because I haven't bothered to adjust the boost duty targets since the summer and temps are much lower now. I plan on taking it to dyno day (along with the daily driver) and having my boost DC set to give me 17-18psi as early as possible and out to redline just so I can throw down some big *** numbers.

The daily is running 15psi but he asked about NB 1.8.
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Old 11-03-2008, 06:37 PM   #18
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I run 15-ish on an '04 and it works fine.
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Old 11-10-2008, 01:45 AM   #19
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Quote:
originally posted by hustler
put another shrimp on the barbie!!!
Wrong Country mate!!!!!!

Thats as offensive as saying a Canadian is American! (nothin against Americans, just that Canadians get quite touchy about this subject - hehe)
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Old 11-10-2008, 01:53 AM   #20
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Quote:
Originally Posted by ogwazza View Post
Thats as offensive as saying a Canadian is American! (nothin against Americans, just that Canadians get quite touchy about this subject - hehe)
eh! You're right!
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