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

All of it.

400 psi

1.367 psi

Well shit dude, he's already blowing that number out of the water with 12 PSI...must have one of those factory blueprinted motors...:giggle:

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.

If you have a 2 bar MAP sensor, you will be out of sensor at around 14psi (= 1 bar over, or 2 bar absolute).

Spooky, this thread is 3 weeks old and the OP hasn't logged in since the 14th. Just so you know.

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.

I just know he's going to check back in :)

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.

put another shrimp on the barbie!!!

I haven't heard of anybody leaving the forum due to any cost. Maybe they were being a jackass.

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.

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.

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 ass numbers.

The daily is running 15psi but he asked about NB 1.8.

I run 15-ish on an '04 and it works fine.

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)

eh! You're right!

How much would you expect to adjust your duty targets?

I don't know Jersey but say 75-90 ambient summer and way <55 winter, what kind of changes would you make to your table to maintain a given boost within seasonal extremes?

Thanks for all the reply's. So you guys running 12+PSI, is this on a stock engine? Did you lower the compression? Also what octane gas do you run? The best we can buy at the pump is 98.

<- 19 psi stock engine on 93. :)

Poison, don't forget that your 98 octane is measured differently than Apex's. If I'm not mistaken you are both running about the same octane.

About the shrimp remark; don't ever call a Dominican a Haitian! ;)

At 12 psi you should never even shorten the life of the motor. After 12psi is when boost starts effecting the motor. How long it will last after that is a guessing game. How good is the tune, how often do you get on it, do you track it, street it, drag it. Aot of varibles.

As long as you don't have knock, or cylinder wash alot, your 12psi should be golden.
I'm pushing the envelope and going one psi over. Hahahha

i have 12psi on a stock 1.6 and its fine all day

Are the octane ratings different in New Zealand or something? I thought 98 was odd until I saw the location.

just FYI, 98 RON is roughly the same as 93 ( (RON+MON)/2) assuming a typical 'sensitivity' or difference of 10.

In theory and according to this handy-dandy graph which IIRC is from solomiata, you'd aim to run about a couple less psi of boost on a 9.5:1 engine vs a 9.0:1 engine to get the same dynamic compression
http://lh5.ggpht.com/_T84_A-CR80w/R0...tcompRatio.gif

And what about the NB fuel pump.....
 

Hi Jif, from all the world the answer comes from someone I know.... lol. Not sure why but your graph has gone, (or at least I can't see it). Luckily I donwloaded it before.

I have made 2 postings on this foum (to say thanks for the info everyone), they also had links to other forums articles but my posts have all disapeared so maybe they don't allow web links. :mad:

I think some people missed my real question being that the NB having a higher compression ratio than the NA is more prone to pre-ignition. And what power/boost people have managed on a stock engine. A few good answers though thanks, great to know 12 PSI is attainable without destruction (on a good tune).

I forgot to ask... are you guys with 12 (or more) PSI on the NB (Please NB only, as it's running higher fuel pressure and CR) still on the stock fuel pump? All the performance fuel pumps seem to just list the NA , does anyone know what the difference is? Can I just buy an NA one?

The NB fuel system sucks. It's a returnless system that's not as good as the NA's return style. NB's loose fuel pressure at high load from the factory. It takes a 255HP Walbro to fix it. Even then, it's still not great. A few have converted to the NA style return setup, or added an atermarket FPR to the car under the hood and blocked off the return inside the gas tank. This is what I will be doing. I bought a 30-100 PSI adjustable FPR, a Mallory unit out of Summit Racing. It's also got a 1:1 vac/boost reference. I'll run ~70 PSI base pressure and use a Walbro 255HP for a fuel pump. I already added a return to the stock sending unit. Your best bet is to buy a used NA sending unit as it will not have a return to bypass and will already have a return line built into the sending unit.

Also, looking at total boost is NOT the only thing to look at. Different turbo's produce different levels of HP at the same boost. It's better to look at HP than boost. 250 is rather safe with a good tune. Higher numbers have been done reliably. Paul, who posted in this thread, is making over 300whp on a stock 99' engine. I'm planing to make 350whp or more on a stock 99'. The trick isn't "how much boost". It's making sure everything is capable of supporting the power. And very good tuning.

Thanks heaps PatsMX5, isn't the NB running 60PSI anyway? And what is the difference between the NA and NB fuel pump kit? all the Walbro kits I can find here in NZ just list them as for the NA. Will the NA one fit the NB??

You say a few have added an FPR, and blocked off the fuel return at the tank. I'm confused as I thought the NB is returnless. Where would the FPR be fitted?

And what is a sending unit? Do you mean fuel rail? I had mine out recently but it seemed to have some vacuume device mounted on the end so I did not modify it. Also any trick to un-attaching the wores from the back of the fuel rail?

Can you also explain the 1:1 vac/boost reference please?

Yes I agree HP is what it's all about, I was just interested about the effect of the higher compression ratio limiting boost. My target is 220RWHP. So I should be OK as long as I don't end up lean on my fuel supply. That's a beefy clutch and diff.

Yeah, factory FPR is set to run 62PSI. It's called "returnless" but it still has a FPR, and techinically, it has a return. The FPR is just inside the tank, and it "returns" in the tank. So you never see it.

99% sure NA and NB fuel pumps are all the same, even though all the kits are listed for NAs.

The regulator I bought to install one day has a 1:1 boost/vac reference. It has a little nipple that you hook a vacuum hose to and hook the hose to the intake manifold. Now it will change fuel pressure as to always maintain the same pressure difference between the fuel injectors and the intake. For example, on our "returnless" system where base pressure is always ~60, when we boost 15 PSI, we're now actually seeing a 45 PSI delta between the injectors and intake manifold. Loosing flow when we need it most. Definitely NOT ideal.

With mine I'll set it to idle at 70 PSI with the vac line unhooked, then hook up the vac line. Fuel pressure will drop to ~60 at idle, but when I go WOT, it will jump to 70 to maintain the 70 PSI delta. Then, when boost comes on, it will push fuel pressure up 1PSI per 1 PSI boost so that even when I'm running 20 PSI, I'll still have the 70 PSI delta. (70 base + 20 from 1:1 reference = 90 PSI). This is of course assuming the fuel pump is up to the task. Walbro 255HP will certainly be required for my setup and power goals.