7000 RPM valve job

[mr_sunshine]

I know we are all extremely limited by our diesel illpotential to rev higher than 5K. So I was thinking maybe I could do a spring job and reset the rev limiter. Before I do it, I need to know if anyone has ever tried it before, if so, what resulted? The other thing I need to know is what the spring tension rates are stock. Does anybody know? Or should I go looking for a technical data sheet?

I've been driving the newer benz passenger CTDI's and the tach's all go up to 7K, so I believe the potential is there for our TDI's.

 

[Variant TDI]

Diesels don't rev higher than 5k because of the slower burning nature of the fuel, not the nature of the engine.

The internals aren't much different than those in a 2.0, and they can easily be spun out to 7k with just a software change.

 

[Oldman]

the tac goes that high but what is the redline of the engine
clearly max HP is at 4200 rpm and max torque is 1800 to 2600 rpm, meaning that you should shift at or below 4500 rpm. The common rail can have good control of the injector so you will see a few hundred more RPM, my TDI red line is like 4500 rpm.

Now to your question, if you could rev the diesel that high it would produce almost no HP as the flame front could not reach the piston moving down. If you tried to go that high the rods would fly out of the block as the applied load would go through the roof trying to compress the burning fuel at such a high RPM.

 

[VWRacer1]

[ QUOTE ]
...if you could rev the diesel that high it would produce almost no HP as the flame front could not reach the piston moving down.

[/ QUOTE ]
Well, that's not really true for diesels in a technical sense (though it might be in actual practice with a computer-controlled TDI somehow revved to 7000 RPM -- such as jamming it into 1st gear at 40 MPH). In fact, the only significant difference between the speed of combustion events in compression versus spark ignition engines is the delay interval in diesels, which is generally considered independent of engine speed. However, even this limitation can be accommodated by advancing the injection timing in a manner analogous to spark advance in gas engines. All other compression ignition events are essentially proportional to piston speed, just as they are in spark engines. This is being exploited in some drag racing diesel engines, which are now approaching 8000 RPMs.

[ QUOTE ]
If you tried to go that high the rods would fly out of the block as the applied load would go through the roof trying to compress the burning fuel at such a high RPM.

[/ QUOTE ]
Actually, peak cylinder pressures in normally operating diesels are quite similar to those in gas engines, but occur over a greater number of degrees of crank rotation (a big factor in the generally greater torque of diesel engines). But since dynamic loads tend to be heavier in diesels compared to similar gassers at the same engine speed due to heavier rotating assemlies, it is fair to say that loads are somewhat heavier in diesels. Still, it is nothing that should send the rods out through the block.

 

[Peter Cheuk]

[ QUOTE ]
The internals aren't much different than those in a 2.0, and they can easily be spun out to 7k with just a software change.

[/ QUOTE ] The main difference that I can think of are the lowered spring rates for the valve springs. That means that you would probably get valve float above 5000 RPMs. Going to heavier springs and lighter moving components (titanium retainers, etc) would decrease the likelihood of the valves floating, though. They went with the lighter springs for economy's sake.

 

[mr_sunshine]

I'm well versed in the internal workin's of compression ignition engines, and 7000 rpm is well within reach, it is not so fast that the igntion timing will cause misfire. Nor is it high enough that it would produce little or no power. All it would do is stretch the power band a few hundred rpm's further. I have been informed that the CDI is infact capable of 7K however it's shift points are significantly lower for fuel efficiency reasons. So. whats left on the plate now? valve spring weight, and valve spring compression rate, plus hypothetical ignition timing changes. I think that the latter will be unnessacary because of the fuel pump in use, the bosch VE distributor pump. this pump by nature has very little tolerance for play in the Start of injection and end of injection, leaving the only injection issue wether or not the pump itself can spin 7000 relational RPM.

 

[mojogoes]

Not to mention the injection window being so small no time to ignite our fuel

 

[KERMA]

The rpm is not limited by speed of the burn. Tractor pullers regularly go over 7k rpm even with old school indirect injection diesels.

(maximum available)timing advance is proportional to the internal pressure of the injection pump, which depends on the rotational speed of the feed pump. The whole rotating assembly of the injection pump turns at half crankshaft speed. There is also a mechanical limitation in the maximim advance in the timing device, but there's ways around that if you want it (nothing easy that a backyard mech can do we're talking custom fab stuff) In our ve-edc pumps timing control is two-stage- advance is mechanical until about 2500 rpm when the soleniod duty cycle takes over. "but what about chips, dont they change timing?" all chiptuning changes is the requested, can't do anything about the actual in low rpm.

I've been told by more than one VW head guy that the TDi valve springs are stronger than any of the gassers and in fact the gassers sometimes use tdi springs as an upgrade.

The rpm limit is set by the maximum timing advance available in the injection pump and nothing else. If your fuel was of known quality (known burn rate) there would be more leeway possible with the range of advance before you could no longer be certain that you were staying in the right crank angle for the burn.

You want 7k rpm get a different car. Or, I know a guy who can modify your injection pump to acomodate it if you really want to badly enough ($$$$).

 

[TDIfreak]

I don't know about max timing advance of the VE37 pump, but the timing can be advanced several degrees from the stock value at 1500 or 2000 rpm with VAG-COM adaptation, no problem.
So one would think that it can be done with programming, too. /images/graemlins/rolleyes.gif

 

[MikeZ]

It's all possible to be done via the programming in the ECU but I’m not sure my self that it will be possible to rev to 7000rpm, i know that on my engine it can reach 5500 rpm at the max, but I keep it below 5000 for safety reason.

Here is a dyno sheet recently done in Europe with AFN engine.
Injectors Bosch .216
Pump 10mm stock
Turbo PD130

(HP are at the crank not wheels)
We can see that it still keeps the HP at 5000rps pretty high and there is almost no power lost even after the redline.

My self I would like to be able also rev the higher possible , but for now I have to relax little bit because I had speand too much money up to now.

/images/graemlins/grin.gif

 

[Oldman]

the engine shown is producing max HP at about 3800 rpm, so even though the cut off is at 5000 rpm or so there is no more HP to be found, so why rev it higher.

The poster was asking about a production car diesel and RPM, which my point is valid. You can talk race diesel all you want which IMO is not the topic. Don't forget the 50 to 100 PSI of boost to get all the air flowing though the RACE diesel so that it can work at that RPM /images/graemlins/eek.gif

 

[Oldman]

Mike I like the way you moved the torque on this 10mm / .216 injector engine up and 170 BHP with less of a spike over a much broader hump. All good things.

 

[MikeZ]

OK boss /images/graemlins/cool.gif


[ QUOTE ]
the engine shown is producing max HP at about 3800 rpm, so even though the cut off is at 5000 rpm or so there is no more HP to be found, so why rev it higher.

The poster was asking about a production car diesel and RPM, which my point is valid. You can talk race diesel all you want which IMO is not the topic. Don't forget the 50 to 100 PSI of boost to get all the air flowing though the RACE diesel so that it can work at that RPM /images/graemlins/eek.gif

[/ QUOTE ]

 

[Oldman]

also the race diesels, continue to throw huge amount of fuel into the engine before, during and after TDC to continue the burn rate, leading to massive amounts of heat and BLACK smoke. So I guess yes flame front is not an issue.

 

[VWRacer1]

[ QUOTE ]
The rpm is not limited by speed of the burn. Tractor pullers regularly go over 7k rpm even with old school indirect injection diesels.

[/ QUOTE ]
That's right. Most folks think that diesel's slightly slower burn rate than gasoline acts as a limit on engine RPM. Yet it's burn rate in an engine is essentially the same as gasoline...i.e., it is proportional to piston speed. Therefore, in any practical diesel engine the fuel will continue to provide superior thrust on the piston to as high an RPM as the engine can physically rev.

The guys who are drag racing high-revving VW's (7000 - 8000 RPMs) are using the old 1.6l and 1.9l TD mechanical injection pumps. These pumps can have their speed limiter springs shimmed or even replaced with solid links to effectively eliminate rev limiting; their advance mechanisms adjusted to give all the advance required to sustain operations at that rpm level; and fueling increased far enough to provide 400% of stock fuel flow at 6000 RPM (before starting to drop off). With proper engine development and tuning a 1.9lTD can make 300 hp and 450 ft-lbs in drag racing mode. Endurance mode is lower, but there is still plenty of potential.

The TDI has at least as high a power potential as a TD, but it is considerably more difficult to achieve the high revs in a TDI that are possible in a TD, due to the difficulty in re-programming the TDI's computer.

[ QUOTE ]
I've been told by more than one VW head guy that the TDi valve springs are stronger than any of the gassers and in fact the gassers sometimes use tdi springs as an upgrade.

[/ QUOTE ]
That may be true for the TDI springs, but one diesel pump shop I am familiar with which builds high revving TD pumps says that the TD springs test out the same as the mid-80's GTI gasser springs, and that the diesel valve springs are perfectly good to at least 7000 RPMs.

[ QUOTE ]
If your fuel was of known quality (known burn rate) there would be more leeway possible with the range of advance before you could no longer be certain that you were staying in the right crank angle for the burn.

[/ QUOTE ]
I think you mean ignition delay here, Kerma. The actual burn rate of hydrocarbon fuels in piston engines varies very little from the heaviest diesel compounds through the lightest kerosenes, and is proportional to piston speed. What is critical to high RPM diesel operations is good fuel to minimize the ignition delay, and large capacity injectors to ensure all the desired fuel is injected during the available time on the power stroke. If those two conditions are met, and adequate injection timing advance is provided for, a diesel engine is capable of making as much or more power than an equivilent gas engine.

For decades diesel engine have been designed and manufactured as low-RPM, high torque utility engines, and that has conditioned us to think of them solely in those terms. However, with the right combinations of factors it is entirely possible to embarrass more than a few unsuspecting Hon-duhs and other "performance" cars. /images/graemlins/grin.gif

 

[TDIMeister]

Actually, the R-TDI's development team set a limit of 2.5 Bosch smoke numbers, which for all intents, is barely visible. This goal was set so as to not propagate the reputation of Diesels as smoky.

 

[KERMA]

[ QUOTE ]
I think you mean ignition delay here, Kerma.

[/ QUOTE ]

Correct. I did mean ignition delay. /images/graemlins/blush.gif

 

[mr_sunshine]

It's good to know that I've sparked a debate that should lead to some serious discussion about engine capability. However only people to have even hinted on the 2 real issues has been kerma and vwracer1 . He brings up an intresting point about the only weak link in the TDI engine, the half mechanized VE pump. This pump was built with durability in mind, not sustaining a power band for as long as possible. In my IDI the pump lost it's lubrication from a manual timing advance,thumbscrew set, and rev limiter reset. the end result was snapped timing belt when the pump lost an o-ring, spraying fuel all over the engine compartment. So unless the pump itself has been seriously redisigned with better seals at higher comparitive pressures, this remains one major issue.

I can tell you from first hand expeirience that the valve springs from the 80's GTI and 80's IDI are both shyte. I have floated the valves on my GTI numerous times, and the same with my last IDI engine. with the rev limiter hashed up to 5K+ it was easy to float the valves.so if those are supposed to be stronger than the current TDI spec valve springs, they will have to go.

 

[mojogoes]

Very sorry i did'nt realise it was a test or Quiz how many goes before i'm the weekest link /images/graemlins/eek.gif

 

[Oldman]

I give up change the valve springs lets us know when you do 7000 rpm OK, lot of advice here

 

[Oldman]

see above

 

[Oldman]

see above

 

[robnitro]

Not only valves and flame front affect max revs. The actual speed of the piston should be below 4000 ft/min, otherwise the rings don't hold and the hot gasses blowby into the crankcase!
The TDI with 95.5 mm stroke does about 6400 rpm at 4000 ft/min. A cummins with 120mm stroke does 5069!

> I copied this from a post on the BMW list. I don't know who did
> itSorry
> if you know who you are:
>
> <quote on>
>
> 1. Normal Condition
> Gas pressure in the upper cylinder holds the ring down
> against the bottom of its groove and out against the
> cylinder wall, forming a seal.
>
> Gas Pressure
> :
> :
> \| :
> \| v
> \| :|----------------------------|
> \| v| .
> \| :| Left . Right
> \| v|------- Cross-section . Side of
> \| :.v.... | of Piston . Piston
> \|[[[]] <: |\ . (not shown)
> \| |-\----- \ .
> \| | \ Ring Groove .
> Cylinder \| | \ .
> Wall \| | Piston Ring .
> \| | .
> \| | .
> \| | .
> \| |----------------------------.
> \|
> \|
>
> 2. Too Much Piston Acceleration
> Piston acceleration lifts the ring, shutting off pressure
> behind the ring and breaking the seal. The ring groove
> is damaged by constant mechanical pounding. Hot
> combustion gases get past the ring, overheating it and
> the piston.
>
>
> Gas Pressure
> :
> :
> \|:
> \|:
> \|: |----------------------------|
> \|v | .
> \|: | Left . Right
> \|v |------- Cross-section . Side of
> \|:[[[]] | of Piston . Piston
> \|v \ |\ . (not shown)
> \|: |-\----- \ .
> \|v | \ Ring Groove .
> Cylinder \| | \ .
> Wall \| | Piston Ring .
> \| | .
> \| | .
> \| | .
> \| |----------------------------.
> \|
> \|
> \|
>
> <quote off>
>
> The result? Increase wear on the piston, piston ring, rods, crank,
> etc.
> etc. etc.
>
> Thanks whoever made the great diagrams!
>
>
>
> Okay simple enough. Now comes the question of determining at what RPM
> this occurs. I turn to an article out of Gordon Jenning's "Two Stroke
> Tuner's Handbook". True we have a four stroke, but the principle
> should
> remain the same. Anyway, the formula is as follows to determine the
> maximum speed allowable before things turn bad:
>
> Cm = 0.167 x L x N
>
> Cm = mean piston speed in feet per min
> L = stroke in inches
> N = crankshaft speed in rpm


or cm= 0.00657479 x L (in mm) x N
>
> This gives you the actual piston speed in feet per minute. Then you
> go to
> this handy little table (I don't know how the determined it, but they
> did)
> to figure out where your engine stands.
>
> Mean Piston Speed Result
> ------------------ ------
> Under 3,500 ft/min Good reliability
> 3,500-4,000 ft/min Stressful, needs good design
> Over 4,000 ft/min Very short life
> Okay, this is all good and well, but how does it apply to our car
> Well
> let us see:
>
> VR6 Engine
>
> Stroke = 90MM (out of technical manual)
> 90MM = 3.54 inches (courtesy of handy HP 19BII
> Calculator)
>
> Okay so plug this stuff into the formula:
>
> First with stock rpm
>
> CM = 0.167 x 3.54 x 6500 (I think this is stock redline)
> CM = 3,842.67 ft./min
>
> Okay that isn't SO bad. We have already determined the VR6 is a
> fairly
> robust motor and is quite well built. Now let's figure it out for two
> tuner chip rpms (6900 my P-Chip, 7300 Garrett's)
>
> P-Chip
> CM = 0.167 x 3.54 x 6900
> CM = 4,079.14 ft./min
>
> Garrett
> CM = 0.167 x 3.54 x 7300
> CM = 4,315.61 ft./min
>
> Okay now it is true these speeds are reach for only a few seconds
> (providing you don't hang at the rpm) but there can be no doubt that
> revving above the stock redline can, and will, be harmful to the life
> or
> your engine. Even if the rings float just once, hot gases would
> escape to
> the bottom end. Figure this, let's say you hold the engine at 7,300
> rpm
> for 2 seconds.
> 7,300RPM = 121.67RPS (Revs per second, 7,300/60)
> Divide by six to figure out the revs for each cylinder
> 121.67/6 = 20.28.
>
> That means that each cylinder has its rings float and gases escape to
> the
> bottom end 20 times (providing the rings are indeed floating). Or a
> total of 121 times for the whole engine! All in the space of 2
> seconds!!!
> I don't care what anyone says, if the rings are floating damage and/or
> increased wear is happening.
>
> Now these formulas are just the opinion of people, but I think that
> even
> if you add a bit of safety into the formula even then 7,300 rpm would
> seem
> to cause extreme wear on your car. Here are some examples of other
> cars
> with what would be considered OVER BUILT engines.
>
> Redline Stroke Piston Speed
> Engine (rpm) in, mm (ft/min)
> -------- ------- -------- ------------
> BMW E36 M3 6,800 3.38, 85.8 3,838
> BMW E28 M5 6,900 3.31, 84 3,814
> BMW E34 M5 7,200 3.39, 86 4,076
> Just for comparison
> CBR600 (bike) 13,250 1.78, 45.2 3,939
>
>
>
> Okay, I know they are all BMW engines, but they are ALL M engines.
> And
> not one of you, even Wally

, can argue these are not well built
> engines
> built to take a load of stress. Hell the rumor is that BMW picked
> old M3
> four cylinder engine blocks right off the factory line to make F1
> engines
> out of them. I find it funny that only one of them goes over the
> danger
> zone (barely), but even then it's at ridiculous RPM and not even
> close to
> what the VR6 pistons are doing at that speed. Plus this is with a
> Dinan
> Chip that STILL recommends maximum constant engine speed be limited to
> 6500 RPM ">
>
> What's the point of all this?
> Now will this reduce the life of your engine noticeably? Maybe yes
> Maybe no.
> One thing, I am not an expert so I would like some responses from the
> group.
>
> Thanks,
> Kris,
> '93M5
>