How much boost can I get on a stock engine NB8C - Page 2 - Miata Turbo Forum - Boost cars, acquire cats.

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DIY Turbo Discussion greddy on a 1.8? homebrew kit?

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Old 11-10-2008, 04:03 AM   #21
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Originally Posted by paul View Post
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.
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?
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Old 11-15-2008, 09:43 AM   #22
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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.
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Old 11-15-2008, 10:02 AM   #23
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<- 19 psi stock engine on 93.
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Old 11-15-2008, 10:48 AM   #24
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<- 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!
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Old 11-15-2008, 11:09 AM   #25
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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
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Old 11-15-2008, 12:34 PM   #26
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i have 12psi on a stock 1.6 and its fine all day
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Old 11-15-2008, 07:06 PM   #27
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Are the octane ratings different in New Zealand or something? I thought 98 was odd until I saw the location.
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Old 11-22-2008, 04:39 PM   #28
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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
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Old 11-24-2008, 01:38 AM   #29
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Default 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.

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?
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Old 11-24-2008, 01:49 AM   #30
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Quote:
Originally Posted by Poison View Post
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.

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.
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Old 11-24-2008, 02:15 AM   #31
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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.
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Old 11-24-2008, 02:24 AM   #32
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Quote:
Originally Posted by Poison View Post
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 her 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 blobked off the fuel return at the tank. I'm confused as I thought the NB is returnless. Where would the FPR be fitted?

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 220. So I should be OK as long as I don't end up lean on my fuel supply.
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.
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