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Author Topic: P-38 engines left/righ  (Read 1380 times)

Offline GScholz

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« Reply #15 on: September 05, 2004, 10:08:08 AM »
You're right that the documents only list a 0.2 difference in compression ratio, but that difference is just an effect of either a difference in stroke or volume. I'm guessing stroke.
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Offline mora

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« Reply #16 on: September 05, 2004, 10:10:06 AM »
Quote
Originally posted by Staga
Are you sure about that?



Taken from USAF museum:
http://www.wpafb.af.mil/museum/engines/eng1.htm


Oops, my bad.
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Offline mora

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« Reply #17 on: September 05, 2004, 10:11:59 AM »
Quote
Originally posted by GScholz
You're right that the documents only list a 0.2 difference in compression ratio, but that difference is just an effect of either a difference in stroke or volume. I'm guessing stroke.


How would have this been done, eccentrically located crankshaft?
« Last Edit: September 05, 2004, 10:20:40 AM by mora »
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Offline GScholz

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« Reply #18 on: September 05, 2004, 10:13:54 AM »
You don't see how what is possible?
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Offline MiloMorai

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« Reply #19 on: September 05, 2004, 10:17:36 AM »
Quote
Originally posted by GScholz
You're right that the documents only list a 0.2 difference in compression ratio, but that difference is just an effect of either a difference in stroke or volume. I'm guessing stroke.


You add more to the piston crown, which is not desirerable(weight), or shave some off the heads to increase the cr.

This pdf on the DB605 has the same bore and stroke, 154mmx 160mm for all models.

http://mitglied.lycos.de/luftwaffe1/aircraft/lw/DB605_varianten.pdf

To increase the stroke, the throw of the crankshaft has to increased, on one side for what you suggest. These long crankshafts were bad enough to balance without upsetting the balance by 2 throw lengths.
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Offline GScholz

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« Reply #20 on: September 05, 2004, 10:21:37 AM »
Quote
Originally posted by MiloMorai
You add more to the piston crown, which is not desirerable(weight), or shave some off the heads to increase the cr.


Then volume would be different. You can't have different compression ratios without having different volume, stroke or both.
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Offline mora

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« Reply #21 on: September 05, 2004, 10:23:00 AM »
Quote
Originally posted by GScholz
You don't see how what is possible?


How one cylinderbank has different stroke than other.
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Offline GScholz

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« Reply #22 on: September 05, 2004, 10:26:14 AM »
Quote
Originally posted by mora
How one cylinderbank has different stroke than other.


Why is that impossible?
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Offline MiloMorai

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« Reply #23 on: September 05, 2004, 10:43:00 AM »
:rolleyes:

The compression ratio is defined as (Swept Volume + Clearance Volume) / Clearance Volume

Shave some off the heads and you change the clearance volume. Very simple to do.

Until you show up with the DB,s throw dimensions(stroke),........


Mora, one has to have different crankshaft throw dimensions.



here is a web site to help explain, how shaving(milling) the heads changes cr, http://www.nightrider.com/biketech/hdhead_compression.htm

Notice that shaving the heads increases the cr by ~0.3 with a 0.020" cut. Yet Scholz would have us believe that the Germans would go to the hassle of making a crankshaft with different throws and all the hassles that involves.
« Last Edit: September 05, 2004, 10:49:54 AM by MiloMorai »
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Offline GScholz

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« Reply #24 on: September 05, 2004, 10:50:57 AM »
Quote
Originally posted by MiloMorai
:rolleyes:

The compression ratio is defined as (Swept Volume + Clearance Volume) / Clearance Volume

Shave some off the heads and you change the clearance volume. Very simple to do.

Until you show up with the DB,s throw dimensions(stroke),........


Mora, one has to have different crankshaft throw dimensions.



here is a web site to help explain, how shaving(milling) the heads changes cr, http://www.nightrider.com/biketech/hdhead_compression.htm



If you shave some off the heads you change both clearance volume and total volume. The top of the head would travel farther down the cylinder since it is shorter.

... And what's with the ghey rolleyes emoticon?


Edit: fixed swept to total.
« Last Edit: September 05, 2004, 10:58:00 AM by GScholz »
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Offline mora

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« Reply #25 on: September 05, 2004, 10:51:04 AM »
Quote
Originally posted by GScholz
Why is that impossible?


If you change the diameter of the crankshaft it will affect the stroke on  both cylinder banks. In a V-engine there are 2 connecting rods attached to each crankshaft lobe, one from each side.
« Last Edit: September 05, 2004, 10:55:02 AM by mora »
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Offline GScholz

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« Reply #26 on: September 05, 2004, 10:56:04 AM »
Quote
Originally posted by mora
If you change the diameter of the crankshaft it will affect the stroke on  both cylinder banks. In a V-engine there are 2 connecting rods attached to each crankshaft lobe, one from each side.


True if the connecting rods aren't independent. V engines are designed with both paired and staggered cylinder banks, but I don't know about the DB.
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Offline MiloMorai

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« Reply #27 on: September 05, 2004, 11:09:46 AM »
Forgot about the forked and blade con rods, Mora.:)

-------------------------

Explain this then Scholz

Mill Heads  -   Compression Ratio

.000"     8.50
.020"    8.77
.040"    9.07
.060"    9.39
.080"    9.73
.100"    10.01

----------------

DB601 with fork and blade con rods.

« Last Edit: September 05, 2004, 11:14:51 AM by MiloMorai »
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Offline GScholz

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« Reply #28 on: September 05, 2004, 12:46:24 PM »
Explain what? If you file down the crown of the piston you decrease compression ratio, but increase volume. What is difficult to understand?
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Offline MiloMorai

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« Reply #29 on: September 05, 2004, 01:29:28 PM »
Quote
Originally posted by GScholz
Explain what? If you file down the crown of the piston you decrease compression ratio, but increase volume. What is difficult to understand?


File??:rofl :rofl :rofl  How long will that take? And, can you guarantee that it will be the same depth of material removed in the x and y axis?:rolleyes:  No waves allowed. The heads are over 1m long.

You remove metal from the head (you know, the part that has the valves, camshaft, valve springs, etc, etc) that is contact with the block. Is that so hard to understand?
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