How often does your 617 diesel see 4400 RPM? - Page 4 - PeachParts Mercedes-Benz Forum

85chedeng300D · #46 08-02-2007, 05:25 PM

Quote:

Originally Posted by Brian Carlton

No, of course not.

To get those times, I shift it manually at about 4400 rpm for the 1-2 and 2-3.

For some reason, the '87 runs out of breath up there..........need to see what that's all about.

Just wonderin. I try and most of the time shift at 3K and my 0-60 averages 15-17 secs and from what I read on this thread, RPMs beyond 3500 are not beneficial to gain more HP due to the curve drop. So I thought yours can do 10-12 secs at rpms below 3K.

ConnClark · #47 08-02-2007, 05:57 PM

Quote:

Originally Posted by Brian Carlton

I think you can redesign forever but cannot overcome the limitations of the burn rate for diesel fuel. It takes a certain amount of time for the flame to propagate and once you get over 3800 rpm or so............torque starts falling off in a big hurry.

Upping the boost will increase the burn rate and reduce the ignition lag.

Edit: I suppose upping the compression ratio would do the same thing too.

larry perkins · #48 08-02-2007, 06:22 PM

did you high revers ever think of what it happening at the top side of your cyl walls as the piston and rod assy stretch at these high rpm's? every one i take apart has a ring groove formed at the top and as the components elongate it would seem to me that you are forcing the piston rings to a position where the bore is at origional demensions and doing damage to rings and pistons.
larry perkins lou ky

Brian Carlton · #49 08-02-2007, 07:14 PM

Quote:

Originally Posted by 85chedeng300D

Just wonderin. I try and most of the time shift at 3K and my 0-60 averages 15-17 secs and from what I read on this thread, RPMs beyond 3500 are not beneficial to gain more HP due to the curve drop. So I thought yours can do 10-12 secs at rpms below 3K.

Beyond 3500 or so is where the engine runs out of torque.

However, HP is completely different. The 617 runs out of HP at about 4400 rpm. You need to shift at this point if you want minimum ET's.

In reality, most gassers would straddle the HP peak when they shift. But, the falloff on this diesel is so severe that straddling the peak would result in longer ET's.

Hatterasguy · #50 08-02-2007, 07:17 PM

Quote:

Originally Posted by Brian Carlton

0-60 times are usually in the 12 second range. Nobody does 10 seconds unless they've turned up the fuel..........including you.

The '86 will run about 10.7 on a good day. The '87 has yet to crack 12.5. It's got a fueling or an exhaust problem..........don't know which just yet.

Well I didn't say it was totaly stock, the fuel is turned up a bit.

I found I lost maybe a second at most with the AC. I think because it takes a moment for the Kilma to dump the compressor?

Brian Carlton · #51 08-02-2007, 08:23 PM

Quote:

Originally Posted by Hatterasguy

Well I didn't say it was totaly stock, the fuel is turned up a bit.

I found I lost maybe a second at most with the AC. I think because it takes a moment for the Kilma to dump the compressor?

You went into the IP?

You never mentioned it??

How much did you turn it up?

EGT gauge??

Hatterasguy · #52 08-02-2007, 08:34 PM

No I cheated I turned up the ALDA for more midrange. I'm not messing with the IP.

#53 08-02-2007, 08:40 PM

Quote:

Originally Posted by Hatterasguy

Diesels in boats typically run at 80% of max RPM. So whats max rpm for a 617? About 4,500? If it were in a boat then I would run it at about 3,600, for thousands of hours.

I do, 3600 rpm is about 80 mph and the engine is very happy there. I tend to drive in the 3000 to 3500 range for hours at a time. I'm driving from WA to CO tomorrow (about 1100 miles), so that's about 14 hours at 80 mph.

Brian Carlton · #54 08-02-2007, 08:43 PM

Quote:

Originally Posted by Hatterasguy

No I cheated I turned up the ALDA for more midrange. I'm not messing with the IP.

.......you're not at 10 seconds........

Brian Carlton · #55 08-02-2007, 08:48 PM

Quote:

Originally Posted by Craig

I do, 3600 rpm is about 80 mph and the engine is very happy there. I tend to drive in the 3000 to 3500 range for hours at a time. I'm driving from WA to CO tomorrow (about 1100 miles), so that's about 14 hours at 80 mph.

You really ought to find a 2.88 diff for that vehicle.........or, if you're really bold.........a 2.47.........but, climbing hills is impossible in 4th gear.

You're well above the torque peak at 80 mph with the 3.07. The engine will thank you for it. You can do the swap in an afternoon.

#56 08-02-2007, 08:50 PM

Quote:

Originally Posted by ConnClark

Upping the boost will increase the burn rate and reduce the ignition lag.

Edit: I suppose upping the compression ratio would do the same thing too.

It may increase the burn rate slightly, but not enough to change the peak torque rpm significantly. The important parameter is the piston speed, if you really want a higher rpm diesel, design a diesel engine with a shorter stroke.

Brian Carlton · #57 08-02-2007, 08:52 PM

Quote:

Originally Posted by Craig

It may increase the burn rate slightly, but not enough to change the peak torque rpm significantly. The important parameter is the piston speed, if you really want a higher rpm diesel, design a diesel engine with a shorter stroke.

I'm not sure that a shorter stroke will get you that much more rpm. With a given burn rate, you're limited by time. Sure, you can get a bit of a benefit, but, I don't think you'll find any diesels with a torque peak much above 3500 rpm. There is just insufficient time for the fuel to burn.

Anybody know the torque peak for the new CDI's? Presumably, they've pushed this envelope as far as current technology will allow.

#58 08-02-2007, 08:57 PM

Quote:

Originally Posted by Brian Carlton

You really ought to find a 2.88 diff for that vehicle.........or, if you're really bold.........a 2.47.........but, climbing hills is impossible in 4th gear.

You're well above the torque peak at 80 mph with the 3.07. The engine will thank you for it. You can do the swap in an afternoon.

I've thought about a 2.88, but I do drive up some significant hills. It would help my mileage a bit and be easier on the engine, but I do like being able to cruise up 6% grades.

#59 08-02-2007, 09:07 PM

Quote:

Originally Posted by Brian Carlton

I'm not sure that a shorter stroke will get you that much more rpm. With a given burn rate, you're limited by time. Sure, you can get a bit of a benefit, but, I don't think you'll find any diesels with a torque peak much above 3500 rpm. There is just insufficient time for the fuel to burn.

I theory a shorter stroke will give you more rpm at the same piston speed, which should raise the rpm corresponding to peak torque. However, I believe you also need to keep the bore/stroke ratio pretty square in a diesel. I guess that means you would have to go to more cylinders to get higher rpm from the same displacement engine. Does anyone know the specs on the audi tdi racing engine, I think it runs about 6000 rpm.

DslBnz · #60 08-02-2007, 09:40 PM

Quote:

Originally Posted by Craig

I theory a shorter stroke will give you more rpm at the same piston speed, which should raise the rpm corresponding to peak torque. However, I believe you also need to keep the bore/stroke ratio pretty square in a diesel. I guess that means you would have to go to more cylinders to get higher rpm from the same displacement engine. Does anyone know the specs on the audi tdi racing engine, I think it runs about 6000 rpm.

No less than 6600 rpm.

http://www.exoticcarsite.com/pages/audi-r10-2006.htm