VW 1835cc vs 1915cc: Why is the 1835cc more popular?

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Vigilant1

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When we talk about "small" VW aero engines (those with a 69mm stroke), I get the impression that most folks go for the 1835cc (92mm bore and 60HP) rather than the 1915cc (94mm bore and 65HP). Since the cost of the parts is the same, the weight is (virtually) the same, and boring the case for a 94mm cylinder is no more trouble than for a 92mm cylinder--why don't more folks take the "free" 5 extra HP? Scott Casler only charges $25 more for the 1915cc engine than the 1835--$5 per HP is a deal that is hard to beat!

I'm guessing that the relatively small amount of metal between the cylinders in the case and the heads with 94mm cylinders might be the reason folks prefer the 1835cc with its 92mm cylinders. Is it that, or is it something else/additional?

Thanks
 
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Hot Wings

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It's about power and reliability.

The thin wall 92s don't make as much power as the 90.5s and the 94s don't make as much as the thick wall 92s. The thin walls just distort too much over time.
 

Pops

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It's about power and reliability.

The thin wall 92s don't make as much power as the 90.5s and the 94s don't make as much as the thick wall 92s. The thin walls just distort too much over time.
Thanks for the answer. Like I always say, the 1835 cc VW engine is the "Most Bang for the Buck". Most HP, reliability, low cost, with the lightest weight for the money.

Weld and fill in the area at the flywheel end of the case behind #3 cylinder, bore for 94 mm pistons and jugs and then use the heavy wall 92 mm pistons and jugs.

https://www.appletreeauto.com/92-X-69-PISTON-KIT-THICK-WALL/

CB will weld, machine, etc for what you want at extra cost on a new case.
http://www.cbperformance.com/product-p/043-101-003.3.htm
 
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Vigilant1

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Thanks. So, I assume the same reasoning ("don't go above 92mm cylinders") would be the same for the engines of even longer stroke. That would mean avoiding the Revmaster R2300 (94mm bore x 84mm stroke) and the Hummel/Casler "2400cc" engines (94mm bore x 86mm stroke). 2180 cc would be as big as we go, then. Nobody seems to bother making kits or complete aero engines in 2234cc (92mm bore x 84mm stroke) or 2287cc (92mm bore x 86mm stroke). I guess there's not much point anyway. If we are limited by the ability to shed heat from the head to approx 75 HP, going larger than 2180ccs just let's you hit 75hp at slight lower rpm/higher torque.
 

Pops

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Thanks. So, I assume the same reasoning ("don't go above 92mm cylinders") would be the same for the engines of even longer stroke. That would mean avoiding the Revmaster R2300 (94mm bore x 84mm stroke) and the Hummel/Casler "2400cc" engines (94mm bore x 86mm stroke). 2180 cc would be as big as we go, then. Nobody seems to bother making kits or complete aero engines in 2234cc (92mm bore x 84mm stroke) or 2287cc (92mm bore x 86mm stroke). I guess there's not much point anyway. If we are limited by the ability to shed heat from the head to approx 75 HP, going larger than 2180ccs just let's you hit 75hp at slight lower rpm/higher torque.
That is the way I see it. Revmaster makes there own heads that cool a little better and advertise 80 HP continuous. Last time I checked they were $995 a set. Remember stock stroke (69mm) pistons are not the same a stroker pistons. The stroker pistons have the wrist pin higher up towards the top of the piston to keep the CR down to reasonable values where you can set the CR where you want. I like 7.5 CR. Just right for the local 90 octane non ethanol auto gas.
 

Pops

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I would snap up a Revmaster in a heart beat
Yes, I like the engine. There are two things that I don't like, one is I don't like a carb with no reservoir , an air bubble could mean an engine stoppage. I would put a Zenith carb on it. Second, I don't like how you get to the lower spark plugs. Have to take the valve cover pans off and then remove a cover with a gasket. Just another place for an oil leak. Guess I could live with that, but I would change the carb.
 

Pops

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Pops and all, what do you think about just taking the CB "Gas Saver" 1902cc engine as a basis for a DIY aero conversion?

http://www.cbperformance.com/product-p/1179.htm
Not much. Just marketing to boost sales. Slightly stroked engine for more torque and used in a late model transaxle with a higher gear ratio for increase mileage. Some parts they use are not helping with higher mileage, like stiffer valve springs than stock, larger oil pump than needed,(not building a high rpm race engine). etc.
As a base for an aircraft engine. No, waste of money for more expensive race parts than you need.
 

cluttonfred

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Good to know, thanks. Are there any off-the-shelf, turnkey engines or assembled long blocks that you would recommend?
 

Pops

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Just a quick observation: You get 4 pistons (with rings and wrist pins) and 4 cylinders for $225. ...I can't think of any other areo-conversion that has parts the cheap.
The cheaper set will have cast pistons and the more expensive set will have forged pistons. I have always used the cast pistons and have never had any problems with all the engines I have built. But I buy the more expensive cast pistons set, but I don't know if they are any better than the cheaper cast piston set. Works for me.
Here is a cheap set of thin wall 92 mm pistons and jugs for a stock 69 mm crank for 1835 cc. https://chircoestore.com/cast-piston-and-cylinder-kit-fits-big-bore-vw-engines-1835cc-92mm-x-69mm.html

My 1835 has a little over 200 hours on it now and has never missed a beat and starts on the first blade 95% of the time and uses about a cup of oil in 25 hrs between oil change and check valve adjustment.
 

Pops

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Aren't those prices per cylinder?
NO-- Its for a set of four of pistons with rings, a set of four cylinders and a set of four wrist pins with clips. You can do a MOH to new specs on a VW for $500 of parts.
 
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