What is the most boost you can safely run on a stock N18 motor?
I hear everywhere mixed results.
14-15psi. 16-18psi. 18-20psi.
Anyone know the answer? I peak at 18.5psi and Terry from Burger Motorsports said I should turn it down to 15-16psi. What do you guys think?

 

Boost is half the equation. The other half is advance. And octane is the major determining factor for how far along that boost/timing scale you want to slide. Using 91 octane fuel, definitely keep it below 15-16psi in 70 degree weather IMHO.

 

Yea that does make sense. I will bring it down a bit before I cut my turbo life in half.

 

Turbo life is another issue all together. The car has great knock sensors but going too aggressive could hole a piston worst case.

 

I don't know about anyone else but I've seen my boost rise from a max of 14 psi pre JB+ incrementally over the course of 300 miles to:

Today 57 deg F and pulled 17.5 psi peak in fourth gear, I think somewhere around 5000-5500 rpm. I am extremely surprised. Every time I think I've hit the top end and been satisfied on boost it's bested the next day. As Nigel is quoted in Spinal Tap "This one goes to eleven."

Using 93octance Shell V-Power 10% ethanol blend. Measured with a Craven Speed Vac/Boost gauge with electronic sending unit and peak recall. In Chicago area (about 750 ft above sea level).

Terry does this sound reasonable and safe for my vehicle on 93 octane or should I back the dial down?

 

Boost will increase as IAT increases so 17.5psi during a longer pull sounds OK. If it's hitting 17psi early in the run though I'd probably lower it a tad.

 

Thanks for the quick reply Terry,

The boost comes on quickly at starting at 12 psi and then climbs gradually with the engine through the rpm range which is nice as it helps minimize torque steer. I have not made any adjustments to the JB+. I'll keep an eye on it and continue to provide feedback. The car is almost "scary fast" now. I don't need a dyno to tell me your JB+ topped the total gains of my bolt on upgrades at about 1/7 the total investment. That being said I do think that they complement each other nicely however and would particularly recommend one of the various stepped intercoolers as a must first upgrade followed closely by an exhaust.

 

Jim, u need to drive a fast car.......

 

Are you also asking what boost levels can bend a rod?

 

Just asking what the max psi you can run safe on a stock car without messing stuff up. Like would the car handle 22 psi bone stock? Just curious.

 

Sure you can. The question is how long it will last

Like Terry said, it's not as simple as boost.

 

There is a billion variables to what an engine can handle.

15psi on a mini with stock turbo is different than 15psi with a fp green turbo. Fp green turbo will flow waaaay more air.

Psi is just a measurement of pressure in the manifold.

Also, 15psi with intake air being 100 degrees is different that 15psi at 50 degrees. When you compress air a by product of that is heat, when you spin a small turbo to a higher psi, at some point it produces enough heat were its no longer worth it to raise boost.

Then when you start throwing in timing, octane, outside temp, fuel quality...ect

In the end..there isnt a perfect answer to your question...but if a tuner is telling you to back it down, I would just listen to him.

 

I've added a pair of FCD's and have my MBC set to about 25PSI. OEM crank, rods, and pistons. Using a custom remote AP tune for 91 octane. Don't get on it much, but say a couple prayers every time I do. Been running this configuration for about 6 months / 6K miles --- no problems, YET! Still trying to find a good dyno tuner with Mini AP software, anywhere west of the Mississippi River.

Don't even think about doing something your tuner doesn't approve of --- tuning is everything!

 

"...but if a tuner is telling you to back it down, I would just listen to him."

Best quote ever!

 

I was peaking at 22psi on a JCW turbo....ultimately ended up with a blown piston...

My advice, don't go above 18. And adding water/meth injection would be wise as well...

 

From what I've read on here, it isn't the rods that are the problem it's the pistons themselves. They tend to break ring lands.

 

That's the case with most OEM motors. Cast pistons even high quality ones can't stand up to much knock. Lucky for us Siemens timing advance systems are pretty solid.

How many of you have damaged a factory piston and at what boost/timing/octane level was it at?