1988 760 turbo (w/plus kit)

Is it normal to be in slight boost cruising around at 85-90mph? or can you get it to stay at neg pressure usually? Just trying to see what it's like for all the rest of you (turbo) folks...if there's anything for me to be looking at or not.


Thanks!
-Matt

My car doesn't need boost to just cruise at those speeds.
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1988 760Tic - electric fan, HD radiator, boost gauge, a/f gauge, remote start, NGK plugs, MBC@10psi - 157,800 1966 M-B 230 sedan - 98,000 1982 Rx-7 - 201,000

It is normal, due to the nature of the transmission... when cruising at such speeds (which I recomend highly) the engine is at about 3000 rpm, and so, with the higher RPM rate, the rate of combustion is higher, so as soon as you open the throttle, it will pull the boost right in.
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Robb R, 1989 740 Turbo 177,xxx

With both my 945T's, you'd be running slight boost at those speeds. I think it's normal.

Jeff Pierce
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'93 945 Turbo ( one kickass family car ! ), '92 Mercedes 190E (my daily driver), '53 Willys-Overland Pickup (my snow-plow truck/conversation piece)

This is a great question. It opens up all kinds of topics for debate.

It seems you already recognize that it doesn't feel normal to be under boost at cruise. This is a good instinct to have. It can be a sign of a mechanical problem with the engine, transmission, even brakes...or it can be normal.

I live in Colorado, and most of my cruising is done at elevations of 7000+ feet above sea level. Up here, the air is so thin, boost is required to maintain anything over 75MPH. Depending on where you live, if the air density is greater, you may not notice this as much.

It's likely not a problem on your car though, and likely not going to cause damage either. Volvo engines, at least in factory condition on the 700s, are Light-Pressure Turbos (LPTs) so even if your boost gauge is half way between the center and the maximum it ever reaches, you're only under a couple of pounds of boost. Just watch your gauges, especially temp and oil pressure! Propellor-driven aircraft will often employ a LPT configuration similar to this to allow them to operate more efficiently and at higher altitudes. Other turbocharged engines, however (like my roommate's 1999 Mitsubishi Eclipse GS-T) operate at much higher pressure (~16 PSI) and should not normally be much above 0 PSI at cruise.