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  #1  
Old 02-02-2018, 11:46 PM
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Increasing W123 300D top end power

Alright, so the 300d's turbo kicks in around 2200rpm or so, and power doesn't really do much past 3500rpm or so...

So what's needed to have power increase a little past 4k rpm?

What's restricting what? I want a stronger top end.

I feel like the stock power band is basically 2k - 4k rpm, and thats generous... with it falling off toward 4k. I want the power to build to 4k+ then fall off.

Im willing to experiment and see what happens.

Ive got a healthy, stock, daily driver 1983 300d that makes good power and sounds good, but id like it to do more without upgrading to take more boost or replace it with a om606 or small block Chevy. i dont want to degrade the engine either.

Yes i know the om617a isnt built for speed, and has many things against it in that pursuit. But a healthy om617a certainly has potential, and doesnt need an upgraded/rebuilt fuel pump to yield modest top end gains. There's got to be inherent restrictions that can be addressed.

Thoughts?
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  #2  
Old 02-02-2018, 11:49 PM
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FWIW peak power for the 617A is 4350 RPM. So if you feel yours dies off you may have turbo issues?

Nothing stopping you going for a proper turbo swap and tweaking your IP.
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1978 300D, 373,000km 617.912, 711.113 5 speed, 160cc superpump, HX30W turbo...not yet legal
1984 240TD>300TD 121,000 miles, *sold*
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1977 280> 300D - 500,000km...Daily

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  #3  
Old 02-02-2018, 11:55 PM
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Ive seen turbo rebuilt kits, but should I throw my effort toward a VNT?

Power progression toward 4500rpm would be great.
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  #4  
Old 02-02-2018, 11:56 PM
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Start with the basics. Make sure your valves are adjusted, your compression is good, and your timing is correct. Hook up a boost gauge and make sure you're building 12PSI. If not, adjust your wastegate until you do. You should be able to pull all the way to 4300RPM or better before you feel the power start to drop off.

Check your ALDA line routing and make sure you don't have a split or a clog somewhere in the pathway. Leaking boost pressure or a restriction in the line to the ALDA will result in a lack of fuel and a reduction in power.
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'83 500SL Euro - "The Money Pit" 116K
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The Diseasel Thread - Everything You Didn't Know You Wanted To Know
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  #5  
Old 02-03-2018, 12:20 AM
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Valves are adjusted and compression is good across all cylinders, but despite me having a Mighty Vac or whatever its called, I havent verified turbo boost.

Assuming all is well, what can I do to improve pull past 4500rpm?
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  #6  
Old 02-03-2018, 12:40 AM
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The governor starts to pull fuel out past 4600 RPM and cuts off fully at 5200. So you can't get anything above that. On top of that, the 617s have a really crappy VE at high RPM. So I don't think there's much you can do.
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1978 300D, 373,000km 617.912, 711.113 5 speed, 160cc superpump, HX30W turbo...not yet legal
1984 240TD>300TD 121,000 miles, *sold*
1977 250 parts car
1977 280> 300D - 500,000km...Daily

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  #7  
Old 02-03-2018, 01:13 AM
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the most effective thing with stock parts beyond verifying everything is working as it should ( boost at 12psi, alda adjusted right, fuel filters, valve job, timing, ect, ect) would be to advance the timing slightly to around 26* adjust or remove the alda to prevent fuel limiting and finally adjust the governor in the pump. the max speed governor is easy to get to once you get the cover off. that will limit it pulling fuel till later in the rpm. i can say from experience that while the stock VE falls off a cliff after 4K with a bit of port work they pull hard to 6000 RPM.
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  #8  
Old 02-03-2018, 11:21 AM
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Check pedal to IP throttle linkage and make sure you have good fuel supply. You might not have enough fuel to rev properly to the governor limit under load. If there’s a safe way to test, it should go to 105-110mph with a couple of people aboard.

My ‘83 SD would get to 85mph with AC relatively quickly and be happy there for miles. I would have liked it to get off the line with more spirit but I didn’t miss the 603 for freeway cruising.

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  #9  
Old 02-03-2018, 11:48 AM
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A fresh set of injectors and verifying boost would be in my top few things to do. Uzi I could also pull the intake manifold and clean all of EGR crud out of it and out of the inlets on the head. Take the opertubity to block off the EGR valve while your at it.
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1992 BMW 525i -traded in
1990 Silver 300TE -Sold Loved the wagon, hated the M103
1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
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  #10  
Old 02-03-2018, 12:48 PM
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I should also mention that a previous member here found that by only installing a VNT he freed up a few more hp, which showed that the stock turbo is restricted at higher speeds....
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2003 Volvo V70 5 Speed
1997 E290 Turbo Diesel Wagon -traded for above, an amazingly comfortable car to drive, great drivetrain, but the rust, oh my god the rust
1992 BMW 525i -traded in
1990 Silver 300TE -Sold Loved the wagon, hated the M103
1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
1979 Silver 300D "The Silver Slug" -Sold
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  #11  
Old 02-03-2018, 12:57 PM
Shadetree
 
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What is a VNT?
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  #12  
Old 02-03-2018, 01:02 PM
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Variable nozzle turbo - https://en.m.wikipedia.org/wiki/Variable-geometry_turbocharger

Sixto
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  #13  
Old 02-03-2018, 07:28 PM
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If someons has not already mentioned it go over to the superturbodiesel forum. There is lots of suggestions on boosting power there.
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  #14  
Old 02-03-2018, 08:43 PM
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Basically the best you can do is to make sure your engine is as close to stock as possible.
What is really restricting your high rpms is the length of your stroke...
which of course is that gives you your compression ratio.....
For high rpms engines are designed as ' over square' meaning the surface area of the piston is bigger than the length of the stroke... plus those engines are subject to increasing the fuel supply , wasting fuel , in exchange for more power..
A Diesel MUST have excess oxygen to function properly... so unless the amount of air provided is increased along with any fuel increase you will not get extra power..
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  #15  
Old 02-03-2018, 10:30 PM
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Quote:
Originally Posted by Diesel911 View Post
If someons has not already mentioned it go over to the superturbodiesel forum. There is lots of suggestions on boosting power there.
X2!!!

Std is where u will get your real answers... Not just your valve adjustment, compression, linkage, etc comments... That's pretty dang close to all the help your gonna get on here. Lol no offense guys...
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