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Discussion Starter · #1 ·
I have recently acquired a 91 MR2 Turbo and while it runs very well, I am curious about two things:

1. When operating at full throttle and full boost, where should the needle on the boost gauge be pointing? The Gauge has a "-" and the bottom to indicate vaccum and a "+" at the top of the scale to indicate boost. There is a thicker white bar about 1/3 from the bottom of the scale which I assume?? is the transition point from off boost to on boost? How high up the scale should normal full boost be? and about what rpm would you expect to see it. I know this will vary with altitude, temperature, load, etc. Just looking for about what you owners would call normal.

2. When under load at partial (approx. 1/4) throttle, just as boost is coming on, I often hear a honking, woofing sound coming from the engine bay. If I open the throttle or back off, it goes away. This sounds like the BOV? Is this normal? The car is stock.

Irish
 

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JG26_Irish said:
I have recently acquired a 91 MR2 Turbo and while it runs very well, I am curious about two things:

1. When operating at full throttle and full boost, where should the needle on the boost gauge be pointing? The Gauge has a "-" and the bottom to indicate vaccum and a "+" at the top of the scale to indicate boost. There is a thicker white bar about 1/3 from the bottom of the scale which I assume?? is the transition point from off boost to on boost? How high up the scale should normal full boost be? and about what rpm would you expect to see it. I know this will vary with altitude, temperature, load, etc. Just looking for about what you owners would call normal.

2. When under load at partial (approx. 1/4) throttle, just as boost is coming on, I often hear a honking, woofing sound coming from the engine bay. If I open the throttle or back off, it goes away. This sounds like the BOV? Is this normal? The car is stock.

Irish
1: The stock boost gauge is very inaccurate. Anywhere between the 2nd thick mark and the top should be normal. To be more accurate, both my friend's 91 and my 91 (and many others Ive heard over the board) boosted around 7 PSI stock, although the max is supposed to be 11.8 PSI (some have been able to reach that before).

2: That is the BPV closing when transitioning to boost. The BPV is open during idle and cruise for better off-boost response and efficiency because air can go around the compressor when entering the engine.
 

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Get a real boost gauge!

"Normal boost", per the BGB, is 7.1 to 11.8 psi. Based on manay, many postings, actual boost covers the whole range. Most cars run ~ 8.5 to 10. My pristine '91T would make 11.8, even more on cold days.

The OEM "gauge" is only capable of reading about 8.3 psi. When it is maxed out, past the + mark, that's 8.3 psi.

po' kid's response on the BOV is correct.

bill
 

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Discussion Starter · #5 ·
Normal Boost

Thanks guys, I suspected the noise was the by-pass valve (BOV/BPV) but it was louder than other turbo vehicles that I had owned/driven.

My stock boost guage is usually about 1 or 2 hash marks below full scale when at full boost. The car seems to run pretty good, but I was just seeking to understand what a stock unaltered MR2 should do.

I have owned turbo'ed vehicles since 1985 and really like the 2. Maybe after doing some TLC, I can work on some more performance oriented tweaks. I want to make certain that it is right in stock trim first.

Irish
 
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