# 1.9 TDI crank in 1.8 8v?



## antdagreat (Feb 26, 2003)

i heard that it is possible to put the crank from a 1.9 TDI in the 1.8 8v. i was wondering if anyone ever heard of something like this? is it true? if so how much good would it do?















i did a search and didn't see anything.
i appreciate the help.


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## Knappsterx (Feb 18, 2003)

*Re: 1.9 TDI crank in 1.8 8v? (antdagreat)*

why?


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## kickster (Aug 15, 2000)

*Re: 1.9 TDI crank in 1.8 8v? (antdagreat)*

it is possible. It will increase your displacment = more torque but your car wont rev as high.


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## EDV (Feb 15, 2003)

*Re: 1.9 TDI crank in 1.8 8v? (kickster)*

Does this mean peole with Oeittinger 99mm cranks won't rev high either??


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## kickster (Aug 15, 2000)

*Re: 1.9 TDI crank in 1.8 8v? (EDV)*

by increasing the length of stroke you are slowing down the engine. trucks use very long stroks and high reving engines use short stroke.


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## EDV (Feb 15, 2003)

*Re: 1.9 TDI crank in 1.8 8v? (kickster)*

Just curious because Oettinger guys with 99mm cranks must still rev pretty high. Anyone on this board have a 99mm crank or 95.5mm that can chime in here?


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## milkman (Apr 21, 2003)

*Re: 1.9 TDI crank in 1.8 8v? (EDV)*

I'll just clear up a few things here.
The revvability of a lower assembly (crank, rods, and pistons) is primarily a function of three factors:
1) Piston speed
2) Crankshaft design
3) Rod and piston design
I'll cover each below.
1) Piston speed is really only useful as a comparison tool because there are a number of different methods for calculating it and there's really no way to determine which way you're using.
We'll assume an 86.4mm stroke (Reference) from a 1.8l 8v engine. We'll also assume running at 6500rpm.
Average piston speed can be calculated with this formula: (S*R)/6, where S is stroke in inches and R is RPM. The result is in ft/min (FPM).(Ref 1, Ref 2). This formula is an approximation that ignores the impact of connecting rod length.
For the stock 1.8l crank, we'll be seeing an average piston speed of 3685FPM.
The TDI unit, with a 95.5mm crank, runs at 4073FPM.
For the Oettinger 99mm crank, we're looking at 4222FPM.
As a comparison, the rev-happy Honda B18A (Ref) motor at 8000RPM runs at 4200FPM. (3412FPM at 6500RPM)
The S54 in the E46 M3 (Ref) at the 8000RPM redline is running at 4776FPM (3881FPM at 6500RPM). I've heard rumors that this piston speed, at 8000RPM, is around that of some F1 cars.
2) This is where crankshaft design comes into play. Here we're seeing that the piston speed, even with the 95.5mm and 99mm crankshafts, is lower than what Honda runs in a production motor and what BMW runs in a tuned production motor.
Of the five parts covered above, (stock VW 1.8l crank, stock VW TDI crank, Oettinger 99mm crank, Honda B18A crank, BMW S54 crank), there aren't many similarities. They're made by a handful of different manufacturers and for a number of different applications. Thus, we can't that just because Honda runs at X FPM, we can run at that same speed without any problems. We also can't say that although BMW starts having problems at Y FPM, we shouldn't go any faster.
3) In addition to the crankshaft, we need to consider the weight and strength of the pistons and rods. If you're sticking with stock VW pistons and rods, you _really_ need to consider this fact. I'll extrapolate below.
Given this information, what we can't really do is demonstrate situations where a certain crankshaft will work just fine. I'm sure you can find some stock crank out of a old pickup truck and rev it to 9 grand without any problems. This is not really what we're looking for.
What we _can_ do is make some guesses as to the impracticality of certain applications. It's probably not the best idea to use that truck crank at 9000RPM because the piston speed is probably astronomical and would _likely_ be a serious danger. Making this type of determination requires an analysis of the raw FPM numbers, as well as the build quality and intended design of the component.
Let's consider the situations above.
a) Stock 1.8 crank
The redline isn't a terribly useful number, because the valvetrain can stand less abuse than the bottom end. However, I've heard of people with beefed valving systems running around 8-8.5kRPM, at the most. 8000 seems like a safer point, although I probably wouldn't run anything much past 7.5k. We'll use 8000.
b) TDI crank
Because your pistons will be moving faster, this number will necessarily be lower than that found in (a). Calculating against piston speed puts this at 7200RPM. Also, bear in mind that the TDI crank has a redline of around 4500RPM in the TDI engine. This crank may be designed with this in mind.
c) Oettinger 99mm crank
Maintaining the same piston velocity as the stock unit requires this crank to be revved no higher than 7000RPM. Now, this crankshaft can _likely_ take more abuse than a stock unit, so as long as you have upgraded (i.e. lighter and stronger) pistons and connecting rods, pushing this setup faster is reasonable.
So, now that we have all this information, what the heck does it all mean?
If we're talking about performance, this is a much trickier question. Going with a bigger crank is likely to increase power across the whole rev range, but if you're sticking with stock pistons and rings, it'll seriously decrease the redline. This is probably not much of a concern for anyone with a stock valvetrain, because that's the limiting factor.
Additionally, the Honda and BMW numbers quoted above imply that a high-revving engines can be built with production components, but bear in mind that both are designed with this in mind, and low-end power and reliability sometimes suffer as a result.
Conclusion:
I) If you're looking for more power across the stock rev range, investigate the TDI or Oettinger cranks.
II) If you're looking for more power at higher revs than stock but don't want to spring for new pistons and rods, stick with your current crank.
III) If you're looking for more power at higher revs than stock and will be buying lighter pistons and rods, the Oettinger is probably the best bet, just because the stroke isn't significantly more than the TDI but it's likely a stronger unit. I'd be wary of revving a diesel crank really high unless there was significant evidence that it can handle the speed.
Hope this helps!


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