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  #1  
Old 08-29-2013, 08:09 PM
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gearing & city hills

OK all, so i have a 2.88 ratio differential swapped along with the 617 into my 240D and its original manual transmission and rims. tires are 195/75-R14. i've been getting the engine running well, and it seems fine in most ways, but i can't start uphill well enough, so i think the differential swap is probably to blame. if i had kept the 3.69 diff presumably things would be easier on the low end.

specifically, climbing from a stop i can't get up enough RPMs to get any boost. the engine sort of chugs along at a very low speed, but i am pretty sure one of these days i'll be on a hill where i can't climb at all and have to bail out sideways.

i guess that without getting a getrag 5-speed my main options are another diff swap and/or smaller diameter tires. did i miss anything, or do you all have other suggestions? thanks!

(i am not worried about the speedo being off, i will fix that after figuring out the rest of this.)

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Old 08-29-2013, 09:24 PM
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Put a few turns into the alda until off the line acceleration is acceptable or remove it all together for a test drive.
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Last edited by tjts1; 08-29-2013 at 10:11 PM.
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  #3  
Old 08-29-2013, 10:03 PM
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Above, what he said, only quarter turns were effective in my experience
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  #4  
Old 08-30-2013, 06:47 AM
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I've driven in SF. Those hills are steep. If you're dead set on keeping the 2.88, get used to revving the engine higher and slipping the clutch more on takeoff. Clutch life will suffer, but probably not to an extreme degree. I have a 617/four speed with a 3.07 diff. Most hill starts are no problem, but the hills of Carson City, while frequently much longer, aren't as steep.
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  #5  
Old 08-30-2013, 06:59 AM
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3.69 will definitely improve your hill starts, but kill your top end. What's your usage, around town? Highway a lot?
Id consider a 3.07, or even a 3.46 out of a NA 300D. 3.07 diff is by far the most common though, might give you the added oomph for hill starts, while still giving you decent highway performance
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Old 08-30-2013, 08:46 AM
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Quote:
Originally Posted by JB3 View Post
3.69 will definitely improve your hill starts, but kill your top end. What's your usage, around town? Highway a lot?
Id consider a 3.07, or even a 3.46 out of a NA 300D. 3.07 diff is by far the most common though, might give you the added oomph for hill starts, while still giving you decent highway performance
X2 3.07 is probably the best long term solution to your hilly environment with an OM617a

But it does sound like engine health could also be an issue.

Whilst I haven't driven around San Francisco like a local might I didn't have any trouble - it was a bit like some parts of Devon actually minus the high hedges, cows, sheep, tractors and poobooters of course.
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  #7  
Old 08-30-2013, 09:18 AM
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The oversize tires are really hurting you. You need to go to standard diameter or one size smaller.
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  #8  
Old 08-30-2013, 10:04 AM
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This might be one of the rare occasions where a swap to automatic might be warranted. If most of your driving is in the city you could keep the 2.88 as a compromise for highway driving and the auto trans would make uphill starts a breeze. Maybe even the 722.4 with the high stall converter - again not the general recommendation but maybe an option for your particular, highly unusual driving profile.

Just food for thought.
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Old 08-30-2013, 02:18 PM
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I've spent some time in San Francisco with a 4 speed VW Fox. 81 hp and 93 lb-ft of torque, first gear ratio is 3.45 and final gear ratio 3.88 with 22.76 inch diameter tires. It was a bit of a struggle to get going for the car on some of those very steep hills. San Fran has quite a lot of steep hills that no other city has.

I think as a daily driver in city along with regular highway cruising, a 3.47 ratio diff may work out best for you with the 4 speed first gear of 3.90. Stock tire size with a diameter of 24.75 inches should improve with the 2.88, but not much. And going with a 3.07, will show a bit of improvement, but not as a comfortable daily in the city.



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Old 08-30-2013, 04:53 PM
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The 123 280 gassers came with a 358 too so that is an option. a 288 with a stick is never going to be comfy on a really steep hill though.
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  #11  
Old 08-30-2013, 07:24 PM
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I don't recall how the torque of the 603.96 compares with the 617.95. The 617 has about a third of an inch more stroke. My '87 300D AT is comfortable in and around Lombard despite it's 2.65 diff. It makes more smoke than power but still makes enough power.

How about slipping the clutch to hopefully get the engine rev to where the turbo kicks in?

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  #12  
Old 08-30-2013, 07:41 PM
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This is strange to me, and I'm thinking it sounds like power output is suffering. My '77 with turbo swap, 4-speed, and 3.07 rear end has zero trouble with getting up to speed on steep hills. Even at 700 RPM idling, I can let the clutch out on milder inclines without giving any throttle, and the car starts moving without effort. There is a bit more delay in boost kicking in on slopes, but I have never had a fear of not making it up any steep hill, even though there have been a few that were so steep and gravel/dirt covered that traction became a real issue.

It seems to me like either my car is a freak, or your car isn't putting down the low-end power that it should, over-sized tires, or not. What is the service history of your motor? Maybe it's the 2.88 rear end, but I'd exhaust the tuning options before doing gear swap. Having experienced a few gear ratios, and many underpowered 617's, I can't see the 2.88 becoming that much of a disadvantage. It's usually the motor that is the issue.
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  #13  
Old 08-30-2013, 08:58 PM
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^^^ In piggy backing on what KAdams4458 brings up, perhaps the throttle linkage is not adjusted properly. Maybe a direct simpler linkage is in order since you don't have an auto trans to control and other emissions stuff.


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  #14  
Old 08-30-2013, 09:21 PM
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Originally Posted by DeliveryValve View Post
^^^ In piggy backing on what KAdams4458 brings up, perhaps the throttle linkage is not adjusted properly. Maybe a direct simpler linkage is in order since you don't have an auto trans to control and other emissions stuff.


.
Oh my goodness, having the linkage monstrosity that the autos used is a giant pain. I. Have yet to simplify mine because I haven't yet sourced the parts, but does introduce about a billion places for things to go wrong. My set up is so horribly worn out that no matter what I do, absolute full throttle is not possible. I can get close, but not all the way there. If you still have that mess installed, I highly recommend upgrading to something simpler, even if it isn't yet an issue.
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  #15  
Old 09-02-2013, 02:21 AM
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so good to get input from all of you. this is more clues than i thought i would come back from the weekend trip to find. despite that my usage is mostly city. first of all, i really should have a better idea of how well my engine is running, right? i have not been able to find a road suitably flat, empty, and nearby to test my 0-60 time from a stop. i do think a number of you are right to say it's not putting out rated power yet. thanks all for chipping in. here are the details on each suggestion i got:

ALDA: yes. great idea. i have been putting off adjusting it but this is a good reason and i'll do it soon.

throttle: i do have a simplified one, thankfully, and have checked its motion before, but i'm sure it's worth looking at again.

overrevving (i just used that word cause i wanted to try to spell it): i either don't get how to do it, or my car really is running poorly; it didn't seem to help when i tried it this evening. while standing still, the boost doesn't start to build unless i really try to redline it. that didn't strike me as odd, but is it normal?

rolling stock: if i get some 15" wheels to accommodate the big brakes i could put on, say, 155/60s, which at 12.5% less circumference should be the equivalent of installing a hypothetical 3.24 differential. i'm not sure how much 12.5% more RPMs would matter, though.

automatic transmission: the only option i must rule out completely!

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