# Steps to scratch build a VW

Discussion in 'Hangar Flying' started by Little Scrapper, Aug 13, 2019.

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1. Aug 17, 2019

### pictsidhe

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It's amazing how few people can grasp the concept that tuning an engine for 5000rpm doesn't work so well when you only spin it at 2500rpm. Few believe how long and skinny the optimum 2500rpm intake runners are.

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2. Aug 17, 2019

### Little Scrapper

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I was looking at engine cases online. They list 10mm vs 8 mm studs. Whatvis most common in Aircraft conversions?

3. Aug 17, 2019

### dmar836

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I’m foggy but I think the 8mm with the thread inserts. I think most all cases now come with all the mods (deep stud #3, cyl stud thread inserts, dual oil relief, universal mounts, etc.) Others might know as I haven’t played with my parts for a year. VW made cases like mine in the 70s that weren’t serialed to a specific production vehicle - just as replacement blocks for repairs.
Remember the stock style magnesium cases are still sold new for more  but are 15lbs lighter. That’s yuge! An extra $200 to lose 15lbs on almost any small plane would be a bargain! That’s also weight you cannot remove later even if you wished to. The Megacases or whatever they are called have all the goodie mods and reinforcements but have that unnecessary hump back for big strokers. Nice mods but not worth the weight penalty for a sub-5000rpm motor. They are for high rpm racers IMO. For a mild stroker(<2000cc) I would want a stock-type “universal” replacement case meaning it has the bus motor mounts on the front for any application. In magnesium! Those mounts allow more mounting options for motor mounts, mag brackets, whatever. Some poopoo an old VE block. Yes they will be pounded out but there are online guides that show what to look for. If not cracked or too worn on the thrust surface they are a reasonable option. If they already have the thread inserts the machine for line honing and thrust facing is around$150 if you have a VW shop near you. Many say just go with a new block but there is a lot to be learned by redoing a core. And some hardware parts you can use. It’s a pig in a poke though so don’t pay much and don’t buy a story. Couple hundred max. Even if complete with exhaust and carb(s), without lots of receipts, seeing it run(and taking some readings), etc. a core is a core is a core - pretty or not.
I know you likely aren’t ready to buy but just stuff to consider.
JMO,
Dave

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4. Aug 17, 2019

### Little Scrapper

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Dave, can't I just buy a new magnesium case I'm a 1600 and just build it? The machining should already be done. I'm near Milwaukee so there's lots of VW shops, two in particular specialize in VWs only.

I'm fine with a standard 1600. I want to build the engine from scratch just like I did in my teens and twenties. I still have my 67 Chevelle and have built multiple motors, I miss that process and when done I had an intimate relationship with the ins and outs of it.

The money part is irrelevant, I want to learn. I'm in love with the process.

5. Aug 17, 2019

### Little Scrapper

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6. Aug 17, 2019

### TFF

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I think you should do a 1600. If you see an upgrade needed , do the 1835. It starts with 1600 anyway. Just bigger pistons and cylinders and some machine work. Now days most don’t start with an engine they have; they just buy everything. No difference when pulling it all out of a catalog. I doubt you want to try and fly the race prop. I bet they spun it to 4000 rpm. My pick for the bigger engine is mostly sane prop to get like performance. I need to look at prop pictures to see what is on the plane now. Wittman was still flying his up to his death, he may have been flying with a normal prop.

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7. Aug 17, 2019

### Little Scrapper

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Pretty excited about building this, the more I read the more I like a basic factory motor set up. Keep it simple and have fun.

8. Aug 17, 2019

### Vigilant1

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At the risk of being a pest:
Is it possible to find out how Wittman had his 1600 set up, and maybe estimate its HP?
The V-Witt has a short wing (17.5' span), which does impose a penalty in climb rate. Steve Wittman was not a large man--from the photos, maybe 180 lbs in the early 1970s. So, climb performance might have been okay for a light pilot and a racing 1600cc engine running 9:1 CR and maybe 4000 RPM. Climb wasn't important anyway for a racer, his design had been optimized for speed.
Now, if we go with a mild/stock 1600 engine (50 HP continuous), maybe we've lost 10-15 HP? And if we increase the pilot weight on top of that--well . . .
A "mild" 1835cc engine gives about 10 more continuous HP than a "mild" 1600. It weighs virtually the same and looks virtually the same from 10 feet away. The cost is the same. Obviously, this isn't my project, but I wouldn't leave 10 HP on the table if it could be had for free and for zero weight.
Sorry--I will not intrude again on this.

9. Aug 17, 2019

### Little Scrapper

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Good questions. You're not intruding, you can post any opinion or question you'd like as long as it's relevant.

You could very well be correct. I'm still reading. Still learning.

10. Aug 17, 2019

### Hot Wings

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Consider nothing but the 8mm.
VW copied the Porsche studs for a reason. It may seem counter intuitive but if the studs are too strong/stiff it causes problems. There may be and advantage for drag race engines, that never warm up, to use the 10mm but for everything else - use the 8mm. Rolled threads as well, not the 9mm junk with cut 8mm threads.

"Many say just go with a new block but there is a lot to be learned by redoing a core."

There is a lot to be learned - before - rebuilding the case. If you have the experience and knowledge (and a source) there is nothing wrong with using a case with some miles on it.
Much like the debate over 'Lycosaur or automotive engine it depends on your skill set and time. I'd start with a good used case, but for the average guy new is going to be far easier and probably cheaper.

If you are going to use big bore cylinders the welded #3 is a good idea - not mandatory, but good insurance.

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11. Aug 17, 2019

### dmar836

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Lol. Not bad advice but to many it’s a slippery slope that’s hard to resist. Certainly not intrusive IMO. Setup wise,
Wittman ran with a carb on top. It’s interesting to look at his plane as it appears he ran copper oil cooling lines around the extension cone. The carb above the engine thing was against the final rules(IIRC but maybe that is just SV) but he was at the first FV race so I’d bet the developing rules worked around him. After all he was Steve Wittman and proposed the whole FV thing. I think it’s safe to say weight savings was more important to him than any additional hp. His philosophy was to get off the ground and flying to the first turn before the others.
Ed has a lot to contribute here as he was there building, racing, and managing teams in FV but I don’t think he built engines.
And what’s wrong with 4000 rpms?! I’d bet they all turned at least that. Ed told me most all ran 48” prop.
That mg case is the one to get and you could certainly build it up. It’s just that every little thrust spacer and fitting gives you something to start with. Not necessary but nice to learn from for a simpleton like me. Same with,say, a vintage car bought disassembled and in boxes. Might all be there but it’s sure nice to know how it all came apart.
Dave

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12. Aug 18, 2019

### Pops

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I have to agree on this 100%. You will not be turning 4000 RPM in racing conditions with the 1600 cc engine. Go to the almost stock 1835cc engine and run it at the lower rpm and get the same performance and enjoy the cool running and reliable engine. Actually the weigh is the same, at 116 lbs for the long block for each. Looks the same, just the little extra cost to have the case milled for the larger 92 mm cylinders and pistons over the stock 1600, 85.5 mm cylinders and pistons. When you buy a new case, they will mill it for the 92's if you want.
Another thing, if going to the 92's you can have the case milled for 94's (1915cc engine) and buy the thick wall 92's for the 1835 cc engine . Some people likes the slightly thicker cylinder walls but I have never had any problems with the stock 92's so that is what I use. Going to the 94's makes the case paper thin behind #3 cylinder and should be welded up. Some people has had problems with the case warping when the weld was done. Another reason the stay with the 92's over the thick wall 92's.
Like I always say, the 1835 cc is the best bang for the buck and still have the reliability of the smaller engines.

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13. Aug 18, 2019

### Hot Wings

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And next to the stud inserts as well.

I've got a few 10mm stud cases left and have been saving them to put the 12mm inserts into, but moved out a couple of mm. I've got an Assenmacher jig for the standard VW stud dimensions. Wonderful tool for converting cases to 8mm studs. Need to build something similar someday for the offset inserts..........

I don't know if there ever was, or are, 92mm piston sets that use the 94 head cut but the 92 case cut. I'm one of the ones that likes the thicker wall and prefer 90.5 to the 92.
One could get the thick wall 92s and turn the cylinder skirt down to the standard 92 dimension?

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14. Aug 18, 2019

### Little Scrapper

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There's a video.on Hoover mods.

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15. Aug 18, 2019

### Pops

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Yep.

16. Aug 18, 2019

### Pops

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That is the way I do it except in marking the long drill bit, I use masking tape or a large model airplane wheel collar that has a set screw. In drilling down with the small drill you can feel when the drill drops into the passage. In using the stock rockers the hardest part of the mods in grinding the grove inside of the rocker arm. I buy a 3" or 4" dia x 1/32" thick grinding wheel at the hardware store and drill a 1/16" dia hole in the wheel material and use a compass and draw a very small circle ( 1/2") dia and cut out with aviation snips. I use a Dremel tool with a long flex shaft with a 1/8" chuck and put the rocker arm in a vice and very carefully make the grove inside of the rocker arm bushing. Before using , lightly touch the wheel on a scrap piece of steel to round out the outer edges of the wheel before using.

If not using a flywheel drive , On the #4 bearing there is a soft plug that needs to be drilled out and tapped for a 1/8" pipe plug. The soft plug has a .040 restriction built into it. Need to get rid of this restriction for more oil flow to the #4 bearing. The restriction is OK for just the car pulley load but not for the load on the bearing when using a prop hub and prop.
I drill all the soft plugs out on the case and tap and use a 22 rifle gun cleaning kit with the rods and brushes to clean ALL the oil galleries out. New cases can have metal shaving in oil galleries. Cleanness is very important.
The engine I'm building now is the second engine with the Bob Hoover mods. I will also have the mods on the engine for the VW pipe buggy that I have been building.

Last edited: Aug 18, 2019
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17. Aug 18, 2019

### Pops

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18. Aug 18, 2019

### 12notes

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Thanks for posting this, reading the mods without a case to reference made it seem to me that the process was a lot more complicated than the video shows it really is.

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19. Aug 18, 2019

### Little Scrapper

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The 1776 gets mentioned online periodically.

Trying to wrap my head around these combinations get a little confusing.

20. Aug 18, 2019

### Vigilant1

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Here's a cheat-sheet from a dune buggy site I think:

The common displacements used on airplanes and sold by Great Plains are:
1600 (69stroke x 88.5bore), 1700 (69s x 88 b), 1835 (69s x 92 b), 1915 (69s x 94 b), 2180 (82 s x 92 b), 2276 (82 s x 94 b).

Scott Casler sells a 86 stroke x 94 bore engine (he calls it a 2400)
Revmaster makes a "2300" which has an 84mm stroke and a 94mm bore

Last edited: Aug 18, 2019
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