So here's the deal with the recent accident its going to cost too much to fix the body on the 87 300SDL, I found a 91 350SDL with bent rods for a good price so I went ahead and bought it as this car is very clean and rust free. The plan is to take the engine and trans out of the 300SDL and put it in the 350SDL body. My questions are what are the differences in the wiring and what will I have to do to make it work? Will the 350SDL head bolt onto the 300SDL block without any modification and is it worth swapping the heads?

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OBJECTS IN MIRROR ARE CLOSER THAN THEY APPEAR, ONLY IN A BENZ

89 560SEC
90 350SDL (Rudolph)
91 350SDL (300SDL drivetrain)
87 BMW 635CSi (Swanhild)
89 BMW M6 (euro)
99 Suzuki Hayabusa (Only the fastest thing ever)

The 350 has afterglow which means you need a wire from the temp sensor (in the head?) to the glow relay. Or don't use afterglow. Everything else should be fine as is.

The 350 head is a direct replacement for the 300 head except for a couple of bolts into the timing chain cover. Match the head gasket to the block. If the 350 has an extra belt idler by the fuel filter, you can keep it on the 300 block.

You have a choice of 300 or 350 IP. Keep the 350 injector lines with the 350 head.

Do you know if the 350 has a 50 or 55 trim turbo? 55 trim turbo will work with the reduced displacement.

Sixto
87 300D

Keep the oil pan with the block unless you swap the oil pump and windage tray as well.

I'm 99% sure the 350 cross member has room for the 300 side sump but better to be that extra 1% sure before you proceed.

Sixto
87 300D

Thanks for the reply, I'm thinking of keeping the 300 IP because from my understanding I will need to recalibrate the 350 IP if its swapped. I'm not sure about the turbo I haven't looked to see whats in there yet. I will be starting this on September 1st I will post updates as I go along.

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OBJECTS IN MIRROR ARE CLOSER THAN THEY APPEAR, ONLY IN A BENZ

89 560SEC
90 350SDL (Rudolph)
91 350SDL (300SDL drivetrain)
87 BMW 635CSi (Swanhild)
89 BMW M6 (euro)
99 Suzuki Hayabusa (Only the fastest thing ever)

I ran a 3.5 IP with 3.5 injectors on a 3.0 block in my 93 SD and got better mileage than I'm getting in the 87 300D. Go figure. The 3.5 IP governor steps in a few hundred rpm earlier than the 3.0 IP but I don't venture that deep into the pedal to care.

Sixto
87 300D

whats the 603 3.5liter horsepower rated at? The ip must push somehwat more fuel than the stock 603 pump. Why not put that on a 603 with the 3.5 head and give it a little more air

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1981 300SD 512k OM603

Barrett says the .960 is rated at 143hp @ 4600rpm/195lbft @ 2400rpm, the .970 at 134 @ 4000rpm/229 @ 2000rpm, the .971 at 148/229. Maybe the .970 has the same 50 trim as the .960. You feel the torque of a 3.5 even without boost. A 3.0 with boost can't get itself off the line as quickly.

Sixto
87 300D

It does, my '91 had the side sump.

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Gone to the dark side

- Jeff

My '91 had the 55 trim.

The .970 (1991) IP should deliver more fuel vs RPM because of the power curve, but I haven't verified. The down-side is the lower RPM limit of the .970.

I'd keep the .970 IP on the car, because the limits will match the transmission shift points. If the engine were going in with the '87 transmission and it's higher RPM shift points, I'd either turn up the .970 or fit the .960 IP.

__________________

Gone to the dark side

- Jeff

I was planning on taking out the engine and transmission out together, the transmission in the 87 300SDL was bought from the dealer 2 years ago so I would rather use that one.

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OBJECTS IN MIRROR ARE CLOSER THAN THEY APPEAR, ONLY IN A BENZ

89 560SEC
90 350SDL (Rudolph)
91 350SDL (300SDL drivetrain)
87 BMW 635CSi (Swanhild)
89 BMW M6 (euro)
99 Suzuki Hayabusa (Only the fastest thing ever)

Then keep the '87 IP, it matches the shift points. I would prefer the '87 trans if I were putting in a 3.0 / 603.96x for that reason.

Install the '91 head complete with glow-plugs and injector nozzles, and the injector hard-lines from the '91. As Sixto mentioned, the two (longer) bolts in the chain cavity should stay with the '91 head also.

You will use all of the existing wiring and plumbing in the '91, will connect to the temp sensor on the '91 head and use the '91 afterglow-rated glow plugs that are already there. Perfect.

Your '91 turbo should stay in the '91, it doesn't have the ARV but it does have the pressure-wastegate, exactly what you want regardless of which trim wheel it has. The '87 turbo won't physically fit because of the ARV IIRC, longer on the compressor intake side.

If you're considering re-sealing the front (chain) cover, consider the front cover from the '91, I believe that it is the later (stronger around the tensioner bolt) design.

Either pan should work, I'd stick with the '87 pan as windage wasn't a significant problem with the 3.0L crank.

If you end up with an extra belt tensioner or good extra vacuum pump let me know, I'm interested.

__________________

Gone to the dark side

- Jeff

If the head on the 300 shows no signs of having overheated, I'd say there's as much reason to keep the head as to swap. As it is you haven't noted whether the 300 has an original or later head. Defnitely keep the 350 head as a spare.

If you keep the 300 head, transfer the combination gauge and afterglow temp sensor from the 350 head. And of course you'd keep the IP and injector lines. Jeff knows more about turbo compatibility but you should be able to make either turbo work by using the corresponding inlet pipe. Jeff, is it more complicated than that?

Sixto
87 300D

I don't know whether the ARV will fit, not sure whether anything else was altered in that area on the engine. If not, then the 3L inlet (rubber) tube should be able to be transferred over from the '87, and the ARV just not hooked up (vacuum line).

I have one of each turbo sitting in the garage, and other than the size difference I think everything else is in the same place pre-'92.

I guess I understand the draw to keep the engine as-is and not swap heads and turbos, saves a minimum of $150 in gaskets alone and a half-day's work (even with the engine out), ... but I'm a "while I'm in there" guy (which gets me in trouble).

If you do that, you will want to use the '87 glow-plug relay (use the plastic plug mold from the '87, snap it around the existing wire harness minus the temp-sensor wire) or swap the glow-plugs out for afterglow-rated ones (I think '90-'93 300D 2.5 turbo glowplugs Dave/Sixto?).

I was running my '87 style glowplugs on an afterglow relay, have lost 4 of 6 in 2weeks, ... kind of wierd. Not a good shortcut.

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Gone to the dark side

- Jeff

I've been using non afterglow plugs with an afterglow relay for considerably longer than 2 weeks. I have a dedicated afterglow temp sensor rather than the violet wire mod so it doesn't necessarily glow the full term on cold starts. IMO afterglow time is somewhat offset by shorter hot start glow times.

Sixto
87 300D

I'll be pulling my glow-plugs tonight, see what I had in there. Lost 2-5 in a very short period, doesn't start very well on 2.

I wanted to wait until I had time to swap heads, oh well.

__________________

Gone to the dark side

- Jeff