Pulling the 'throttle' on an OM616
Pulling the 'throttle' on an OM616
As I thought, this TB is a big restriction. Never seems to open fully, it's a restriction even if it is open fully, and at best should be closed only when there's no throttle input, instead it's the reverse. I wasn't expecting much - you don't usually get much out of a sub 3.0 liter engine without doing some kind of major work, especially an NA diesel - but this thing drives like a real car now. It's not a 'well, screw putting an OM617a in' kind of difference, but what a difference it does make to make a car with one of the worst power to weight ratios I've ever driven (beaten only by an NA diesel Rabbit and an old flathead powered Studebaker) a more livable daily driver experience. I actually managed to pass someone on a two lane without needing essentially a deserted lane going the other way to accomplish it. Throttle response is way up, on both sides. It doesn't feel like you're telegraphing throttle inputs across the Atlantic when you lift now.
Speaking of that old Rabbit, that was my inkling that MB might have compromised quite a bit on power in order to get the smooth idle that I think is really the only reason for the TB to even be on there in the first place. The cold idle is noticeably worse, though I don't have a functioning fuel adjuster for that right now so it might be easily dialed out from behind the wheel. I'll probably have to put it back on once it gets cold out but for now it's staying off. Big deal, I'll have to give a little more fuel at startup. As a matter of fact, that's an indication that the fuel mixture might have leaned out from the extra air intake.
The Rabbit's intake manifold, in contrast with the 616's, looks like a folded over phone book with a filter stuffed into the mouth. There is no throttle body, it's just a wide open 'horn' going to the intake ports. It's a contemporary design that compares favorably with the Benz - 1.5l making 50 hp vs 2.4l making 72. It would probably be a more swapped motor if not for the small displacement and FWD setup (and the fact that the TDI came later). Most NA diesels have a similar intake setup, which is why it's 'common knowledge' that NA diesels are essentially un-tunable. Most of them do have a 'wide open' intake that's free of restrictions to help with an IDI's shitty intake flow, so in most cases this would be true. However, for a 240D, I think there are options. One is to do as I have done and get rid of the damned throttle body and live with a little bit of cold idle nastiness (idle's fine at operating temp).
Another option that I might pursue (since the 616 will be kept around to find another platform to power should I ever get the 617a swapped in) would be to get a junkyard manifold and - wait for it - saw the goddamned end off of it. I don't think, from what I can tell with it attached to the motor, that the intake sees any engine coolant at all. If this is so, then there's little keeping someone from opening up the end of the manifold and fabbing up a little sheetmetal adapter for it, seal and add cone style air filter. Even with the plate and shaft removed the motor is still breathing through a golf ball sized opening, then the airflow has to pull a 180 to head to the ports. Opening up the end would allow for a straight shot to the ports and even some flap wheel work if one felt like it (probably way overkill). This won't make for a turbo killer but I think you could get to NA five cylinder territory with it.
This would also work for someone with the NA five cylinder, but I don't have to deal with an automatic so it might not work as well for NA 300D owners, although I personally have my doubts as to whether a long runner intake would make a difference in the low end torque of a diesel. I might be wrong. Certainly getting rid of the TB on that motor would work, at least in summer, without any compromise on low end torque (possibly could improve the off-idle torque response). It's something to tide over those of us who want the OM617a but either can't afford to do the swap, or don't have the time or space to do it in at the moment. I'd like to start the new year with a turbo five under the hood, but I'll have to see if that happens. In the meantime, I'll enjoy being slightly less slow, for now.
CID Vicious
10-04-2009, 01:38 AM #1Well, after taking care of my ball-bearing-shooting axles and getting my power steering working again (I was getting a tweak in my left elbow after wrestling with this thing for the past few months), I decided to experiment and I pulled the 'throttle body' (I'm sure it's called something magnificently MB, but it is what it is) and pulled the plate and shaft out, sealed up the resulting holes with tape for now, and gave it a drive.
As I thought, this TB is a big restriction. Never seems to open fully, it's a restriction even if it is open fully, and at best should be closed only when there's no throttle input, instead it's the reverse. I wasn't expecting much - you don't usually get much out of a sub 3.0 liter engine without doing some kind of major work, especially an NA diesel - but this thing drives like a real car now. It's not a 'well, screw putting an OM617a in' kind of difference, but what a difference it does make to make a car with one of the worst power to weight ratios I've ever driven (beaten only by an NA diesel Rabbit and an old flathead powered Studebaker) a more livable daily driver experience. I actually managed to pass someone on a two lane without needing essentially a deserted lane going the other way to accomplish it. Throttle response is way up, on both sides. It doesn't feel like you're telegraphing throttle inputs across the Atlantic when you lift now.
Speaking of that old Rabbit, that was my inkling that MB might have compromised quite a bit on power in order to get the smooth idle that I think is really the only reason for the TB to even be on there in the first place. The cold idle is noticeably worse, though I don't have a functioning fuel adjuster for that right now so it might be easily dialed out from behind the wheel. I'll probably have to put it back on once it gets cold out but for now it's staying off. Big deal, I'll have to give a little more fuel at startup. As a matter of fact, that's an indication that the fuel mixture might have leaned out from the extra air intake.
The Rabbit's intake manifold, in contrast with the 616's, looks like a folded over phone book with a filter stuffed into the mouth. There is no throttle body, it's just a wide open 'horn' going to the intake ports. It's a contemporary design that compares favorably with the Benz - 1.5l making 50 hp vs 2.4l making 72. It would probably be a more swapped motor if not for the small displacement and FWD setup (and the fact that the TDI came later). Most NA diesels have a similar intake setup, which is why it's 'common knowledge' that NA diesels are essentially un-tunable. Most of them do have a 'wide open' intake that's free of restrictions to help with an IDI's shitty intake flow, so in most cases this would be true. However, for a 240D, I think there are options. One is to do as I have done and get rid of the damned throttle body and live with a little bit of cold idle nastiness (idle's fine at operating temp).
Another option that I might pursue (since the 616 will be kept around to find another platform to power should I ever get the 617a swapped in) would be to get a junkyard manifold and - wait for it - saw the goddamned end off of it. I don't think, from what I can tell with it attached to the motor, that the intake sees any engine coolant at all. If this is so, then there's little keeping someone from opening up the end of the manifold and fabbing up a little sheetmetal adapter for it, seal and add cone style air filter. Even with the plate and shaft removed the motor is still breathing through a golf ball sized opening, then the airflow has to pull a 180 to head to the ports. Opening up the end would allow for a straight shot to the ports and even some flap wheel work if one felt like it (probably way overkill). This won't make for a turbo killer but I think you could get to NA five cylinder territory with it.
This would also work for someone with the NA five cylinder, but I don't have to deal with an automatic so it might not work as well for NA 300D owners, although I personally have my doubts as to whether a long runner intake would make a difference in the low end torque of a diesel. I might be wrong. Certainly getting rid of the TB on that motor would work, at least in summer, without any compromise on low end torque (possibly could improve the off-idle torque response). It's something to tide over those of us who want the OM617a but either can't afford to do the swap, or don't have the time or space to do it in at the moment. I'd like to start the new year with a turbo five under the hood, but I'll have to see if that happens. In the meantime, I'll enjoy being slightly less slow, for now.
ForcedInduction
10-04-2009, 02:20 AM
#2
Swap in an intake manifold and air filter housing from a non-egr 240D. It has no bend in it, plus, the end has a plug pressed in that can be cleanly removed.
This intake has the four runners coming out perpendicular to the block, with the TB in the center of the 'square' it makes from up top. It has a couple of 'freeze plug' looking plugs in the fat end closest to the wheel well. As far as intake manifolds go it's flat as a board. I'd take a picture but I'm all out of batteries for my camera at the moment. I've not seen another 240D manifold so I don't know what they look like; I know that the NA 617 intake you guys have been swapping in to the turbo motors looks nothing like it. I've seen a 'stretched' version of the same (240D) intake on the NA 300D from later years, though (same style intake but for a five cylinder). My car is an 82.
CID Vicious
10-04-2009, 03:03 AM #3I don't think my car has one. It came from Oregon, though I never did a full title history so it could technically originally be from Katmandu for all I know. Were EGRs California only?
This intake has the four runners coming out perpendicular to the block, with the TB in the center of the 'square' it makes from up top. It has a couple of 'freeze plug' looking plugs in the fat end closest to the wheel well. As far as intake manifolds go it's flat as a board. I'd take a picture but I'm all out of batteries for my camera at the moment. I've not seen another 240D manifold so I don't know what they look like; I know that the NA 617 intake you guys have been swapping in to the turbo motors looks nothing like it. I've seen a 'stretched' version of the same (240D) intake on the NA 300D from later years, though (same style intake but for a five cylinder). My car is an 82.
ForcedInduction
10-04-2009, 03:30 AM
#4
All 240D models 1981+ had an EGR and intake butterfly. Any intake from a 76-80 240D will bolt on.
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