I have two questions...
What is the sensor grommeted to the bottom of the battery tray?
what is the action of the switch in the blow off valve

and has anyone tried a 'G-valve /Dawes device' to increase boost rise rate? in this or similar car? results? cautions?
Anyway, i had a look inside the motor and it all looks pretty sound, so I think I'll try to spice it up a wee bit.

Car is an 85 745 GLE w/stick.

I'm working on a write up of how i replaced the VWAudi water leaky oil cooler with the gas style thermostatic air cooler ; )

Many of the 700 series Volvos came with a temp sensor mounted to the battery tray. This sensor was hooked to a variable output controller built into the alternator. The idea behind this was that the alternator could recharge the battery at an increased rate, until the battery was overcharging and extra power was being dissapated as heat. (at which point the alternator would back off and charge at a normal rate)

While this idea works in theory, it didn't work very well in real world applications. Many Volvos got their batteries cooked by the hyperactive alternators that were getting a green light from the temp sensor in the battery tray. If I remember correctly, Volvo ended up issuing a Technical Service Bulletin to the dealerships and mechanics that instructed them to unplug the battery temp sensors whenever they worked on a vehicle that was equipped with one. This is not unlike the Technical Service Bulletin that was issued to tell all the mechanics to remove the flame traps from the PCV system whenever they came across one. (the flame traps were doing more damage than help since quick-lube oil change facilities weren't cleaning them and the engine would blow oil seals after they clogged up)

God bless,
Fitz Fitzgerald.
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'87 Blue 240 Wagon, 246k miles.

YOU HAVE FOUND A BATTERY OVER HEAT SENSOR I JUST PULL ONE OFF MY 1985 740 TD AND THE SWITCH ON THE INTAKE CUTS OUT THE CAR IF THE PRESSURE IS TOO HIGH I BELIEVE MAYBE IF YOU ARE IN EUROPE YOU COULD ADD AN INTERCOOLER TO GET MORE POWER THEY CAME ON THE LATER MODEL 940 AND SOME 760 DIESELS IT WOULD GET MAYBE 20% MY FRIEND IN GERMANY HAS A 780 TD INTERCOOLED

The blow-off valve is nothing more than a poppet valve with a contact to light the "TURBO" warning in the dash cluster, there is a screw in the center sealed with a brittle locking paint. Screwing it to the bottom locks the blow off diaphram and leave all the pressure requlation to the wastegate and is worth nothing in terms of additional boost unless you have changed the wastegate/exhaust scroll on the turbo. You can however bore out the little oil return fitting on the front of the turbo and wastegate diaphram to increase boost slightly, say an additional 009" however don't get crazy with it. The best way would be to get the proper intercooled intake, radiator and intercooler and make it a real TIC as this is worth about 30%!!! of real output without stressing the motor provided you know how to adjust the injection pump to take advantage of the intercooler without hitting the fuel limiter or smoke density issues.
Another consideration would be to change turbos all together and go with something more suited for the engine, this 2500 boost point is a bit to high for most people and kills off the line. Recommended turbos include small TO-4's, Warner/Ishi, Schweitzer and Garrets from say something smallish like under 2 liters gasoline displacement. Looking at the inlet/exhaust A/R, diameters of the wheels the D24T turbo is better used with a 3.5 liter diesel who runs from 1500 to 3000 RPM at 1.21 GPH BSFC and 140 bhp, a bit oversized. Remember the D24T was designed for vans/trucks in the 7500 pound relm in europe and not a little 760 at 3500 pounds max weight. It would be much happier with the properly sized turbo making 12 pounds boost at a lower crankshaft speed.

988

In the long run...I will probably have to modify my intake for intercooling, or make one from scratch. I have a stash of extra stock manifolds, and know a few TIG wizzards around here. I presently am not looking to increase boost, merely bring it in sooner as you suggest. With the 3.3ish rear, off the line performance is a little weak, but im pleased with 2nd and 3rd gears. would the Chrysler 2.2 turbo be a good donor? There are a million of those in the pick n pull, as well as Subaru turbos. I even see the occasional Chevy 1.6 Turbo Sprint! I also have a good spare stock turbo to play with if I want, and have begun a collection of intercooler piping.

I guess I'll have to test that turbo warning light, It never comes on...kinda redundant with 2(numeric and stock) boost guages anyway.

And a battery overheat sensor! wow what a marvell of engineering.

Smallers turbos eh? That leaves a lot of choices stateside.. in Volvos even.

The 90 and newer RWD turbos primarily got fairly small Mitsu TD04 units, some got Garrett T25 ones. The turbobricks crowd seems to like the 850 turbos as well (big TD04) because they'll spool up reasonably and are able to produce more boost than the smaller TD04s in the RWD cars.

Some of the earlier 700 turbos did get Mitsu turbos, TD05-12B or somesuch, but they're about the size of the T3.

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alex

You are right on the turbo choices in terms of availability however the D24T used a rectangular mounting pattern for the exhaust manifold so the Mopar 2.2 unit is out of the question. I wonder how that little sprint 1.6 turbo would do, if I had wheel diameters and area ratios I could give you a very good idea of how it would fit the D24T. That Subaru turbo I know nothing about but the Mitsubishi would be a nice choice as well from say a 760 Intercooled.

D24T intercoolers. Well the intake inlet is actually a bolted joint with rectangular flange on the back side spanning #4 to #6, bolted so one can access the cam cover without a fight. The non intercooled intake looks to be a nightmare to plumb up and I gave it a thought myself for.... maybe 5 minutes! I paid Gholmer here on the forum to pull and mail me a real intercooled intake with pipes and goodies. Dont know where he went however.

A word of caution on disconnecting the wastegate. You will seriously increase the output of the engine to the point of competing with a SVO Mustang in warm trim and waste just about every rice rocket around however it may last only a few passes in this configuration. Boost pressures approach 20 PSI and not only is this off the compresser map for the turbo itself it also puts you and your motor in a dangerous position should the compresser wheel decide to let go. With that turbo doing 20 PSI pumping 2.4 liters at 4500 RPM it is hovering around 185,000 RPM with the tips of the turbines way past the supersonic point, killing efficiency and your motor. I would say a safe point would be a realistic 15 PSI of boost, ramping up from say 5 pounds at 1200 RPM and leveling off at 3500, the large DT04(P) with a .54 A/R on the exhaust would put you into that ballpark, mounting however is beyond me.

Brandon-988