# VW conversion economics

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#### Vigilant1

##### Well-Known Member
Supporting Member
I know that this is off-topic, but would you be able to share a list of the books and DVD's about aircraft VW engines that you mentioned?
This thread has many useful references (recommended books, DVDs, blog, etc):
Steps to scratch build a VW

Posts 4, 11, 22, 28,, 37, and 40 seem most responsive to your request.

There's a lot of info out there. Some of the info on VWs for performance cars/racers is interesting, but aircraft use requires high reliability and good output at moderate RPMs (3400-3600 and below). That's different enough from street racing that it's a good idea to pay closest attention to sources (including people) that are focused on flying Type 1 VWs.

#### curious

##### Member
Definitely seems to have increased oil flow to the top end, which would carry some heat away, and help lubrication
"seems ... help lubrication"

let me quote from the blog: "Auditing the engine’s lubrication system we found that all of the oil for both heads came through a single 5mm drilling. In theory, a hole that size should have provided more than enough oil. And it did, but only for the left-hand head."

what does that mean? so we need another 5mm drilling to the right case half and hence the case drillings?
in a late model case that 5mm drilling is 6mm and the drillings to and from the oil cooler are 8mm.
oil flow pressure loss is related to the velocity through the drilling (darcy-weisbach). so 2 - 6mm drillings is like having a single 8.5mm drilling. comparable flow velocities. my "audit" of the oil system shows that in "theory" hoover is trying to put more oil to the heads than is actually available.

#### Martti Mattila

##### Well-Known Member
My aviation buddy died and I salvaged (payd a real money) some of his stuff. Two Limbach converted case where I havent studied yet if something is done for routing lubrication and unused typ 4 case and opened heads for 103mm. cylinders. But why Im here is the VW conversion that someone dit a while ago. It was really narrow VW done by using shortened stroke camshaft. That time when I was reading it I tauhgt theres nothing for me, but now I have played with "what if idea" that coes like this. A wery short stroke crank, 1200 has 64mm. that can be reduced with 51mm. conrod journals to 61 mm. With some large diameter cylinders where we might have to use some heavier case. For example one that is made from modified Wasseboxer case, that takes in a big cans.
Next and most expensive thing would be the heads, might need to go to a Scat sigle unit heads, expensive. Now we would have a engine thats displacement would still be close two liters with short stroke and low piston speed. Is there a any sense to make sutch engine for aircraft use. Long ago in SA. magazine there was a comparison with engines and performance and they totally ignored displacement, they only count a piston tops area. Type 4 is there almost already and maybe cheaper to make, but heavy.

#### curious

##### Member
Seriously? Why the hell not?
asked and answered as i got an email from casler a few days ago. in a nutshell: not applicable to low rpm/compression motors.
i thought that was an interesting response. i figured it was liability but i was wrong. however, he avoids liability by not doing it.

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#### curious

##### Member
economics is the thread topic. how about making better use of the fuel being consumed?
let air and auto engine manufacturers show the way. some topics for you think about.

do any of you do anything with your cams, cam timing, cam gears? what sort of cams seem to work well? have you looked into dual pattern or asymmetric cam profiles? cams for use with high ratio rockers? methods for indexing? i have found next to nothing on cams in this forum. it's not all that expensive to have a custom cam made with modern features.

#### challenger_II

##### Well-Known Member
Fuel price is les important and avoiding a cornfield is numero uno.

I do not have any cornfields... I gots mesquite thickets. I have a vested interest in my little Dub to keep happily humming along!

Regarding heat dissipation/avoidance I will toss this concept in the mix, and see if my tail feathers get singed:
For an application that is happy with the 1835cc, propped to turn 3100rpm, what if One were to build a 1915cc or a 2180cc, use the prop from the 1835 and turn the engine at 3100revs? Yes, the engine would be underloaded, as compared to the 1835. Would this not reduce the workload on the engine and reduce the heat generated at the heads?

#### Marc W

##### Well-Known Member
If you are making the same HP you are burning the same amount of fuel and generating the same amount of heat. Cylinder pressures will be lower but the loads on the engine parts are the essentially the same.

#### Vigilant1

##### Well-Known Member
Supporting Member
I do not have any cornfields... I gots mesquite thickets. I have a vested interest in my little Dub to keep happily humming along!

Regarding heat dissipation/avoidance I will toss this concept in the mix, and see if my tail feathers get singed:
For an application that is happy with the 1835cc, propped to turn 3100rpm, what if One were to build a 1915cc or a 2180cc, use the prop from the 1835 and turn the engine at 3100revs? Yes, the engine would be underloaded, as compared to the 1835. Would this not reduce the workload on the engine and reduce the heat generated at the heads?
Well, if you turn the same 3100 RPM, your new larger engine will be capable of producing slightly more power (since more air and fuel will be moving through it) and you'll also have slightly higher CHTs (assuming everything else remains unchanged: compression ratio, etcl). BUT, since you say you'll use the same prop, and assuming nothing else changes (same airplane, same weight/induced drag, altitude,etc), then the only way that bigger engine will turn the same RPMs is with less than full throttle. In theory, the slightly bigger engine pulling air through a more fully closed throttle might have slightly higher pumping losses than the smaller engine.
If you bought a slightly longer prop for the bigger engine and turned it slightly slower to make the same thrust as the smaller one, you might reduce CHTs and also burn a little less fuel (all due to the slightly more efficient propeller).
Things would be different if the bigger engine also had a larger head with more fins, etc. Then it would stay cooler if it burned the same amount of fuel. But, it doesnt work like that, it's usually just the same fins regardless of bore size.

The bigger engine would give you more available power for takeoff, etc which might be handy.

Mark

ETA: Oops, cross posted with Marc W.

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#### Pops

##### Well-Known Member
Supporting Member
Steve at GP said that going from a 1835 to a 2180 with the same prop will increase the WOT rpm by 200.

#### challenger_II

##### Well-Known Member
Certainly it would. But if One were to reduce the throttle to 3100rpm, I would believe, as the engine isn't laboring as hard, the temps would be reduced.

#### Vigilant1

##### Well-Known Member
Supporting Member
It takes a certain HP to turn that particular prop at 3100 RPM. Whether we make that HP with an 1835cc engine or a 2180cc engine we'll burn approx the same amount of fuel and put the same amount of heat into the cylinder head. If it has the same "finnage", oil flow, etc we should expect the head to reach the same temp.

IOW, both engines are "laboring" just as hard. The bigger engine is laboring at a lower percentage of its max, but that's not relevant to the situation.

#### TFF

##### Well-Known Member
You have to pick what you are testing. You can’t float all sides. Are you locking RPM, horsepower, temperature, manifold pressure, or displacement? You can’t let them all float for a comparison.

#### Pops

##### Well-Known Member
Supporting Member
My 1835 cc VW engine is cruising at about 33 HP @ 2650 rpm in the SSSC. Not so hard to cool. The first 32 hours I used a 1200 cc, 40 hp VW engine. Turned 3600 rpm in the WOT climb and cruised at 3200 rpm. Took it out because I didn't want to run it that hard for long life and wanted a better ROC in the short fields that I use.