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Old 06-17-2015, 09:59 PM   #21 (permalink)
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The engine can't do over 4,500RPM. I'm some what afraid to go any higher with the compression ratio. According to any VW guru, I'm nuts for having more than a 7.5:1 CR. (This is what all your typical air-cooled VWs have become thanks to all those VW gurus, 7.5:1 CR or less (one of them recommends 6.5:1 or less) with a 13:1 AFR or richer across the board along with a mechanical advance distributor.) I think I can pull off a 9.5:1 CR. If I can control pinging good enough at that CR I might take the heads off and have them fly cut a little more than what I've cut them so far (on air cooled VWs you fly cut them to raise CR).

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Old 06-17-2015, 10:07 PM   #22 (permalink)
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Originally Posted by Isaac Zackary View Post
7.5:1 CR or less (one of them recommends 6.5:1 or less) with a 13:1 AFR or richer across the board along).
Sounds like a lawn mower.
I say think out side the box. Bump the compression up to whatever you think it will take make you smile when you punch it.
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Old 06-17-2015, 10:26 PM   #23 (permalink)
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when in doubt, emulate. older Porsches are easily the closest design to the VW boxer(and for good reason), but Subarus are a close second, they certainly had fun options.
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Old 06-17-2015, 10:27 PM   #24 (permalink)
Full sized hybrid.
 
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LOL! Since the old VW engines are air-cooled there are a lot of myths about them. For an example, that you should only run single grade oils in them, or 50 weight because of the belief the oil runs much hotter than in a water-cooled engine. Interestingly enough, this myth is untrue since the typical running oil temperature in an air-cooled VW is between 180 to 210*F (less than 100* C) which is the same or even lower than many and most water-cooled engines.

I wish Mythbusters would do an episode on air-cooled VWs.
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Old 06-17-2015, 10:46 PM   #25 (permalink)
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Quote:
Originally Posted by RobertISaar View Post
when in doubt, emulate. older Porsches are easily the closest design to the VW boxer(and for good reason), but Subarus are a close second, they certainly had fun options.
I think I can do fine with the VW engine. I'm not in this for power. The magnesium case on a VW engine is 2/3 the weight of aluminum. Calling it alawn-mower engine isn't too far fetched. I can pick it up by myself with just my arms and hands. The whole vehicle has a curb weight of 1,900lbs. I might cut a lot of that off if I go with fiberglass fenders and hoods someday.
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Old 06-17-2015, 11:28 PM   #26 (permalink)
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Quote:
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I wish Mythbusters would do an episode on air-cooled VWs.
They are really running out of ideas. I think they make one episode about every 4 to 6 weeks now.
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Old 06-18-2015, 04:57 AM   #27 (permalink)
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Oh lol, 4500rpm max, that sounds like a good candidate for a compression ratio increase + lean burn haha. 9.5 plus a detonation prone design will help the mix actually burn at 17 or 18+ AFRs and advance should be easy to dial in since there's only a small range of speeds.
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Old 06-18-2015, 09:21 AM   #28 (permalink)
Full sized hybrid.
 
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Quote:
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Oh lol, 4500rpm max, that sounds like a good candidate for a compression ratio increase + lean burn haha. 9.5 plus a detonation prone design will help the mix actually burn at 17 or 18+ AFRs and advance should be easy to dial in since there's only a small range of speeds.
According to the owner's manual the engine shouldn't be run at that RPM for over a minute. 3,800 is about the highest constant RPM. Not that these engines can't be modified to do more. With the right modifications, this little engine can push a Bug down the 1/4 mile in less than 10 seconds! I think the record in a Bug is something around 6 seconds! But the original design was "the car that costs the same as a used car new." It also was rated to get mid 30's in MPG. Not bad for a 1930's design!

When you say "detonation prone" do you mean it'll be pinging all over the place or do you mean it would be pinging all over the place with a rich AFR?

Of course I have that fully adjustable distributor with a 31 x 31 fully custom spark table. I plan on doing a very thorough tune on both jetting and ignition timing, basically as close to a dyno tune as possible.
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Old 06-25-2015, 08:25 PM   #29 (permalink)
Full sized hybrid.
 
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I thought it was interesting in that article I mentioned earlier how some pilots run wide open throttle and then regulate power by leaning it back, which puts it leaner than peak exhaust temps. Interestingly enough, that's a lot like a diesel. Of course the problem with a gasoline engine is you can only lean back so far, and then you have to cut back air too or it'll missfire.

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