Recommended Boost on stock internals

Novice1 · Postby **Novice1** » Mon May 12, 2008 7:39 pm

Have just fitted a turbo to my 99 model NB mx5.

Did 120kw atw on 7 psi. Has heavy duty clutch, lightened flywheel.

What sort of boost can I run on stock internals ?

Is there any correleation between boost increase and power increase, ie

increasing boost to 9 psi would yield ? how much power gain?

Cheers Ron

jules · Postby **jules** » Mon May 12, 2008 8:30 pm

9 would be a very safe bet I would imagine.
UA's gets up around ten. The engine's fine, but the clutch wasn't happy.

I have heard of up around 12psi being the threshold.
If it were me, I'd be shooting for 9-10 and keeping an ear on the diff and clutch.

Jules

Novice1 · Postby **Novice1** » Mon May 12, 2008 9:01 pm

Thanks Jules:

Clutch as already been upgraded XEDE heavy duty.

Diff and radiator are next on my agenda.

Cheers Ron

Juffa · Postby **Juffa** » Mon May 12, 2008 9:36 pm

There a lot of different factors around the amount of boost a stock engine will take. I believe some members of this forum have run some pretty high numbers, as well as members of the miataturbo.net forum. Foremost would be ensuring you are supplying sufficient fuel to ensure you don't lean out on full boost, but you also don't want to run so rich that you loose power.

Whats injectors and fuel management are you using?

I'm running 9 pounds, with 330cc injectors and a full standalone ECU. I have no idea on how much power I'm putting out as she is yet to see a dyno and/or fully tuned.

Just my 2.2 (Including GST) worth.

J

Novice1 · Postby **Novice1** » Mon May 12, 2008 9:42 pm

Juffa wrote:There a lot of different factors around the amount of boost a stock engine will take. I believe some members of this forum have run some pretty high numbers, as well as members of the miataturbo.net forum. Foremost would be ensuring you are supplying sufficient fuel to ensure you don't lean out on full boost, but you also don't want to run so rich that you loose power.

Whats injectors and fuel management are you using?

I'm running 9 pounds, with 330cc injectors and a full standalone ECU. I have no idea on how much power I'm putting out as she is yet to see a dyno and/or fully tuned.

Just my 2.2 (Including GST) worth.

J

Thanks Juffa:

Running Walbro fuel pump, 500 cc injectors, Haltech E8 management system.

Ron

maxmx5 · Postby **maxmx5** » Tue May 13, 2008 12:23 am

I am running my SE on 13-14psi.. using a 460cc rx7 injectors and Haltech Interceptor. runs fine on a Stock SE.. but to be safe I am using 100 octane fuel,,, I am getting around 165rwkw...

PS: on stock Clutch and flywheel... the car feels great but I do have a flat spot..but I am upgrading to a E8 soon.

btw how is your E8 going?? did you ran into any problem at all on tuning ???

NMX516 · Postby **NMX516** » Tue May 13, 2008 9:17 am

There is no real tangible measure between boost pressure and power. Higher boost can be more of a hindrance to power if it creates too much heat and back pressure. The best turbo setups get their power at lower boost pressures. I.E it is much better (more efficient and safer) to get say 140kw on 9psi than 140kw on say 13psi. Heat is the enemy with turbo's and also power. More heat also = shorter component life.

16bit · Postby **16bit** » Tue May 13, 2008 9:58 am

It sounds like your fuel system is capable of handling around 210 - 220 wkw pending the afr. I have about 9psi with my supercharger setup with just on/over 160wkw and an afr of about 12-12.5. Its different but is an nb8a too so that boost level should be ok for you as you have a more capable fuel system. I run stock injectors with a 42 pound 5th injector and a standard fuel pump. I have an exede processor from chiptorque so I am not sure how it compares to your computer but i would say yours would be as tunable if not more. Just a quick question what kind of injectors do you have?

16bit · Postby **16bit** » Tue May 13, 2008 10:05 am

NMX516 wrote:There is no real tangible measure between boost pressure and power. Higher boost can be more of a hindrance to power if it creates too much heat and back pressure. The best turbo setups get their power at lower boost pressures. I.E it is much better (more efficient and safer) to get say 140kw on 9psi than 140kw on say 13psi. Heat is the enemy with turbo's and also power. More heat also = shorter component life.

Not only as the turbo will be spinning faster and probably glowing thus increasing under bonnet temps but higher pressure air is hotter as well which puts more stress on your intercooler system.

Garry · Postby **Garry** » Tue May 13, 2008 11:03 am

Flyin Miata have some recomendations on their website. They say 10lbs max for an NB8B. You should be able to go higher on an NB8A because of it's lower compression ratio. But remember the MX5 motor has a tendency to bend/break rods under prolonged high boost conditions.

Changes in boost levels produce different results for different setups but in my car an extra 1lb boost results in about 10rwkw more power.

Steampunk · Postby **Steampunk** » Tue May 13, 2008 4:03 pm

Ron sent me a txt before:
147.6kW@wheels on 10Psi.
Gotta be happy with that!

jules · Postby **jules** » Tue May 13, 2008 4:36 pm

That's where she should live!

Jules

Novice1 · Postby **Novice1** » Tue May 13, 2008 9:15 pm

Thanks all for the replies.

As IRED5 said , car made 147.6kw atw on 10 psi. Will post up dyno tomorrow.

Overall, I am stoked with the performance. Will fit boost controller this

weekend and drop her back to 9 psi for daily running.

Cheers Ron