Max boost?

[redheddude222]

So I decided the stock 9psi was just too wimpy and made my own boost controller. It's consistent and works well, but the lowest it will go is 18 psi.

My question is, is 18psi too much boost for a stock N/A BP bottom end? It's got less than 10,000 FACTORY miles on it, so fatigue on any of the parts isn't a problem.

[yunvmyegt]

detonation isnt mileage dependant....lol.....

[redheddude222]

detonation isnt mileage dependant....lol.....

No detonation. If the AFR was remotely lean I wouldn't leave it on. The wideband was showing 12.2:1 under boost, so all I'm worried about is bending something.

[yunvmyegt]

oh ok atleast you have a wideband, what turbo are you running tho?if its a vj20 is 18psi neccessary, i thaught they ran out of usable cool air around 14psi?

[jay]

Yeah you might get to 18psi on a vj20 on a wicked midrange spike but it's all hot air and no more hp than what you get at 14. I can categorically state that 20 psi with a GT28R and a decent frontmount is... Too Much for stock BPT rods. (doc holiday, from tombstone)(val kilmer was *great* in this)
"Ah'm afraid the strain was moah than he could beyah"

So if you're getting constant 18psi on some other turbo it's only a matter of time before one of your rods gets bored by the view and decides to take a peek outside the block for a look around at the big wide world.

[Lex]

I'm with jay on this one. If it's a VJ20, 18psi is a lot of hot air. If it's a decent sized turbo, 18psi is getting a little bit on the borrowed time side. A small fluctuation in cylinder pressures can cause mayhem on rods that are at the limit.

[redheddude222]

It's a Subaru vf turbo, which is capable of around 21 max to be efficient, but I'm for sure taking the boost controller off. I only want to run between 12 and 15, I didn't expect it to turn it up so high before adjusting it.

What's the highest you can run (safely) on a stock bottom end?

[jay]

12, maybe 15.

[trailrider098]

i bent a rod very slightly at 15 with decent A/F ratios

[deadly_sleeper]

I wouldn't go over 13-14 on a stock N/A BP block. If you upgraded the rods, and possibly pistons, you would be good. But you're just asking to join the zoom-zoom-boom club at that psi.

AND let me state this, at that psi, it's not a matter of "IF" you will blow it, it's a matter of "WHEN" you will blow it.

[Lex]

Also remember that a larger turbo will generate a lot more airflow for the same psi compared to a small turbo.

I ran 15psi on the VJ23 on a GTX for a year or 2 and it was fine but I was nice to it.

Now I'm at 18psi on the same turbo but the motor is built. I'm worrying about the tranny at this point. More power is definitely not needed.

[yunvmyegt]

what vf are you using? vf10?

[redheddude222]

Thanks for the info guys, the boost controller came off last night. I plan on turning it up to 12, but not for a while.

I'm not 100% sure on which vf turbo it is, but it's off of my buddy's '07 WRX T/R Model.

[roymacavoy]

cant you just cut the spring down a little and then have the boost level you want?

[redheddude222]

cant you just cut the spring down a little and then have the boost level you want?

I can get softer springs too, but I don't ant to mess with it yet. I was just bored and decided to see what I could do woth it. The first autocross of the year is this weekend, so I want to be perfectly used to the car. I don't want to turn the boost up and end up spinning through the whole course.