There was a rare factory option called Turbo+ which functions similar to
APC and nearly doubles boost for a short period of time under WOT,
adding over 20 horsepower. It's very rare, and not as good as the APC
system.
Stock 740 Turbos do have a knock sensor which retards ignition timing,
which is supposed to save the motor from pre-detonation, but I've still
seen cars with bad wastegates or wastegate lines destroy motors, despite
the knock sensor.
The APC system can be pulled from a Saab in the junkyard and installed
on any turbocharged gasoline car. It's a popular mod on Volvos
(especially 240 Turbos without knock sensors), since you can set it to
automatically adjust boost to the maximum possible to prevent
pre-detonation- so the amount of boost you're running will change
dynamically depending on the quality of your fuel! This is still a bit
risky though...
It's amazing that Saab was running over 2 bar with the stock turbo-
about 29psi! The motor probably could handle that if the fuel system and
turbo were upgraded to maintain a rich fuel mixture and cool intake air
at that boost level to prevent piston destroying pre-detonation. The
stock turbo and fuel system probably can't handle over 14-15psi safely.
If I ever see an intact APC system in the junkyard, I'll grab it and
install it on my 740.
Tyler
Mitch Haley wrote:
Did Vulva ever put a system like Saab's APC on the 740 turbo?
I replaced a piston in a 1981 900 Turbo once. (APC came out in 1982)
Never seen a Mahle piston broke like that before.
My boss took it out for a test drive and asked if the boost gauge (no
numbers) was supposed to swing off scale. First line past neutral is
1/2 bar, max boost. 2nd line is .75 bar, right about where the safety
switch is supposed to kick in.
Last mark is 2 bar, and it was going past that. I found the hose to
the overboost protection switch under the dash, unhooked and plugged.
I plugged it back in and readjusted the wastegate for 7psi. My boss
drove it home for the night, complained it was slow compared to the
way it was before. Well, duh, it only made 150hp, just like it was
supposed to.
We compromised. I lengtened the wastegate rod until the safety switch
killed the fuel pump, and then backed off 1/2 turn. Told Vic that was
absolutely the most power the car would make without bypassing the
safety and breaking pistons. He sold it a while later, and AFAIK the
buyer had no problems. At least it never landed in my shop again.
I'd love to know how many psi it was running when the moron previous
owner blew it up. At least he shut it down immediately and the block
was still usable.
Mitch.
_______________________________________
http://www.okiebenz.com
For new and used parts go to www.okiebenz.com
To search list archives http://www.okiebenz.com/archive/
To Unsubscribe or change delivery options go to:
http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
