82 300d switch over valve

[nevremj]

I've had this 300d (1982) for about 6 years. It has no switchover valve. The line from the intake manifold goes directly to the ALDA. PO must have had it taken out.

Should I consider putting a switchover valve in? Car has 268K miles, don't know when swover was taken out - it was before I bought it.

It doesn't appear that replaceing the swover valve would be very difficult (once I got the valve and attached it to fire wall).

Does any one recommend this? Leave it alone? Any experience w/out this valve?

[Brian Carlton]

It's one of those situation that is sinister.

Nothing bad happens if every other system functions properly.

But, say the wategate hose develops a crack (it sits in an unbelievably harsh environment) and the wastegate can't open.

The boost climbs to over 22 psi pretty quickly and you'll blow a head gasket or melt a piston in short order.

The overboost protection valve would have saved you.

[libbybapa]

I am new to MBZ having acquired my first one within the last two months, but have extensive experience with VW IDI turbo diesels. Are the MBZ headgaskets really so weak as to blow at 22 psi??? The VW fiber gasket doesn't seem to blow until 30 psi or more coupled with the VW 23:1 compression ratio, and the metal one will go higher. Also, does the ALDA on the MBZ pump keep adding fuel up to the 22+ psi quoted above? If not, then fueling would drop off, boost would stabilize in an underfueled situation, EGT's would decrease with the added air and "lean" running, and unless the injectors were junk (peeing streams) or the injection timing was overly advanced, then there would be virtually no risk of piston melting. If the ALDA does keep up with fueling then woo-hoo, I look forward to doing a few more mods on mine...

22 psi with a 23:1 CR in the VW IDI TD world is more on scale with a sporty daily driver than a grenade waiting to happen. I find it hard to believe that the MBZ is a weaker construction than the VW IDI. My switch is gone and I am not concerned. It reminds me of the BOV originally fitted to the VW TD engines. They dispensed with that in 1990 and no newer ones are fitting with the redundancy. I maintain that boost alone will not kill an engine. Boost and enough fuel, maybe...

Andrew

[Brian Carlton]

Originally Posted by libbybapa

I am new to MBZ having acquired my first one within the last two months, but have extensive experience with VW IDI turbo diesels. Are the MBZ headgaskets really so weak as to blow at 22 psi??? The VW fiber gasket doesn't seem to blow until 30 psi or more coupled with the VW 23:1 compression ratio, and the metal one will go higher. Also, does the ALDA on the MBZ pump keep adding fuel up to the 22+ psi quoted above? If not, then fueling would drop off, boost would stabilize in an underfueled situation, EGT's would decrease with the added air and "lean" running, and unless the injectors were junk (peeing streams) or the injection timing was overly advanced, then there would be virtually no risk of piston melting. If the ALDA does keep up with fueling then woo-hoo, I look forward to doing a few more mods on mine...

I can't guarantee that you'll blow one, but 22 psi is well over the limit that M/B has set for the overboost valve........15 psi. That's 50% more pressure in the cylinders which certainly won't do the head gasket any good.

Don't think we have enough data of folks who took the risk for an extended period of time.

No, the ALDA can't do much above about 14 psi or so. Folks have tried with additional boost and the vehicle did no better. The extra boost just causes higher exhaust temperatures.

[libbybapa]

Well, it's certainly not 50% more peak pressure. It may be significantly more initial pressure, but unless the fuel is there to burn with the added air, the peak cylinder pressure will not increase proportionately. Odd that folks found increased EGT's with added air above the fueling threshhold, as typically that will "lean" it out and on a diesel will greatly reduce EGT's. Perhaps there was not an intercooler added in the mix ()?? When EGT's are too high, rule of thumb is either reduce fuel or increase air to lower them.

Andrew

[Brian Carlton]

Originally Posted by libbybapa

Well, it's certainly not 50% more peak pressure. It may be significantly more initial pressure, but unless the fuel is there to burn with the added air, the peak cylinder pressure will not increase proportionately. Odd that folks found increased EGT's with added air above the fueling threshhold, as typically that will "lean" it out and on a diesel will greatly reduce EGT's. Perhaps there was not an intercooler added in the mix ()?? When EGT's are too high, rule of thumb is either reduce fuel or increase air to lower them.

Agreed.

The increased EGT's apparently come as a result of the increased charge air temperatures caused by the higher boost pressures. Fuel remains the same.........just operating the engine at higher temperatures and pressures.

I don't believe you can increase air to lower the EGT, if the air is provided at an elevated temperature. With an intercooler, you'd be all set......more air......at the same.......or lower temperature.

[libbybapa]

Originally Posted by Brian Carlton

I don't believe you can increase air to lower the EGT, if the air is provided at an elevated temperature. With an intercooler, you'd be all set......more air......at the same.......or lower temperature.

Yes, unintercooled air won't gain you anything. I can't see not adding an intercooler even if not messing with boost or fueling levels. Longer lasting motor, better performance, better for the environment, better MPG... I certainly can't see fussing with boost or fuel prior to adding an intercooler. Cart before the horse...
Mine will be going into the bumper. Very convenient how MBZ put the grilles in the bumper just for me.

Andrew

[Brian Carlton]

Originally Posted by libbybapa

Yes, unintercooled air won't gain you anything. I can't see not adding an intercooler even if not messing with boost or fueling levels. Longer lasting motor, better performance, better for the environment, better MPG... I certainly can't see fussing with boost or fuel prior to adding an intercooler. Cart before the horse...
Mine will be going into the bumper. Very convenient how MBZ put the grilles in the bumper just for me.

Agreed on all points.

Most of us have been reluctant to go that route due to the cost and the plumbing issues, especially with the modifications required to the manifold due to it's proximity to the turbo.

If I could find a decent set of parts that wouldn't take weeks to cobble up, I'd do it on the 617.

Post some photos and hardware utilized if you get it done.

You might consider adding the vehicle to the signature.........I realize that we don't know which engine you've got????

[libbybapa]

The intake scroll can be reindexed so that it's proximity is not much of an issue. A good FMIC can be had for $100 or so. Add another $150 or so for plumbing needs and a day of mucking about. I think it's worth it. I will not be staying with the stock turbo setup anyway, so adding an intercooler will certainly not be the biggest challenge.

Andrew

[libbybapa]

Oops, '82 300SD. 617.

Andrew