Boost 'struggle'??

[winnas13]

Originally Posted by pwpanas

11.5psi is the oem boost spec.

If you raise your boost, it depends on the octane of fuel that you run. With an otherwise-bone-stock* 2jz-gte, running 93 octane gasoline (calculated via (R+M)/2) you should never exceed 16psi. If you do so, your engine will be damaged in direct proportion to the amount you exceed this limit. For example, at 17-19psi, your 2jz-gte may survive for several years, but your compression numbers (and horsepower) will decrease gradually. Regularly hitting 20psi and above on 93 octane fuel, your 2jz-gte will likely die within months or even weeks. Keep it at 14 or 15 psi and your 2jz-gte should last just fine. When you want to 'play hard', fill the tank (don't mix) with 100+ motor octane unleaded race fuel, and feel free to boost to about 21 psi safely (ideally you'd monitor the oem knock sensors to find the exact limit).
Disclaimer1: all this assumes proper maintenance (eg. keeping your fuel filter changed, your cooling system regularly flushed, regular synthetic oil changes, etc., etc.).
Disclaimer2: Temperature and atmospheric density are also factors. High boost on very hot days is more likely to produce detonation. Near sea level the atmosphere is more dense, so cylinder pressures may be higher...which may be more likely to promote detonation, everything else being equal.

*When I say otherwise-bone-stock, I'm primarily referring to the timing and fuel curves in the oem ecu. In general, I mean no modifications other than those specified by "BPU" (with as many plusses "+" as you want that do not affect the oem fuel and timing curves). Anything that affects these curves (eg. a 'piggyback' ecu (eg. PHR MAP ECU II) or 'standalone' ecu (eg. AEM)), your max boost with any specific octane of fuel will depend on the (extensive) tuning required to properly configure these devices.

Oh nice... I run it on 98 octane every tank. So basically what your saying is, i could run my supra at 14 or 15 psi, (on 98 octane) and it should be fine?

How do i change the PSI? Boost controller install? (real newbie)

EDIT: My boost gauge looks like this

By phuzion123 at 2011-09-06

- Am i right to say that if when i gun it, and the boost gauge shoots upto 1.0 that i am running around 14 psi?

Thanks

[pwpanas]

Originally Posted by winnas13

Oh nice... I run it on 98 octane every tank. So basically what your saying is, i could run my supra at 14 or 15 psi, (on 98 octane) and it should be fine?

How do i change the PSI? Boost controller install? (real newbie)

- Am i right to say that if when i gun it, and the boost gauge shoots upto 1.0 that i am running around 14 psi?

Thanks

Is that 98 *motor* octane, or 98 *research* octane?

To raise boost, install a boost controller OR do one of the simple mods on mkiv.com
http://www.mkiv.com/techarticles/clamp_mod/_clamp.jpg

1 bar is about 14.503773800721814 PSI

[winnas13]

Originally Posted by pwpanas

Is that 98 *motor* octane, or 98 *research* octane?

To raise boost, install a boost controller OR do one of the simple mods on mkiv.com
http://www.mkiv.com/techarticles/clamp_mod/_clamp.jpg

1 bar is about 14.503773800721814 PSI

just 98 Octane BP unleaded

[pwpanas]

Originally Posted by winnas13

just 98 Octane BP unleaded

You need to find out the motor octane of that fuel from BP. I'm quite sure it is not 98.

Oh, when you raise the boost, you'll hit fuel cut. You need to install a GReddy BCC to avoid this.
http://www.mkiv.com/techarticles/bcc.../bcc_intro.htm
http://www.mkiv.com/techarticles/bcc...GReddy_BCC.htm

[winnas13]

Originally Posted by pwpanas

You need to find out the motor octane of that fuel from BP. I'm quite sure it is not 98.

Oh, when you raise the boost, you'll hit fuel cut. You need to install a GReddy BCC to avoid this.
http://www.mkiv.com/techarticles/bcc.../bcc_intro.htm
http://www.mkiv.com/techarticles/bcc...GReddy_BCC.htm

Thanks mate.

If my boost gauge is correct, then i am already running around 14 PSI. So if this is true i should have a greddy BCC installed already? I'll have a look.. What happens when the fuel cut kicks in? Maybe this is my problem?

[pwpanas]

Originally Posted by winnas13

Thanks mate.

If my boost gauge is correct, then i am already running around 14 PSI. So if this is true i should have a greddy BCC installed already? I'll have a look.. What happens when the fuel cut kicks in? Maybe this is my problem?

Fuel cut is very distinctive... it feels almost like you drove your car into a wall, and only right at 14.5 psi (never below that). You may be right - 2nd gear may go by too fast to hit the fuel cut boost level.

Try this as a test :
http://www.mkiv.com/techarticles/ffcd/freefcd.htm
Don't use it long-term or the longevity of your turbos can suffer.

[winnas13]

Originally Posted by pwpanas

Fuel cut is very distinctive... it feels almost like you drove your car into a wall, and only right at 14.5 psi (never below that). You may be right - 2nd gear may go by too fast to hit the fuel cut boost level.

Try this as a test :
http://www.mkiv.com/techarticles/ffcd/freefcd.htm
Don't use it long-term or the longevity of your turbos can suffer.

Okay, Supra is back on the road ($700 later)... Now that i've paid more attention, the boost gauge hits about 0.7 bar, So i reckon I'm running the stock boost still. It hasn't played up so far either, nice smooth boost apart from 1 time, in 3rd gear, it boosted nicely, then stopped for 1/2 second then kept going even though my foot stayed flat. It seems the 2 week rest in the garage has fixed some of these problems.. weird.

Another question i have is, From cold start the idle is perfect, sitting at about 1k rpm. When i drive a short distance (4km or so), stop the engine and start it about 15 mins later - The rpm at idle is down at around 400 - 500 and jumps up and down. It might go down to 350 or 400 and almost stall, then jump to 500 - 600 then back down again. Any ideas what might be causing this?