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Steps to scratch build a VW

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Pops

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I'm running a 52" prop (52/42) on my 1835 dual port. I see about 3,150rpm on takeoff. And, a little more than 3,300 WOT straight and level at SL. I can typically see 750fpm on climb out at 90kts.

I don't baby that engine. Tooling around the local area, I tend to keep it up around 3,200 RPM. And, I regularly do aerobatics. It has over 400hrs on it. And, it still purrs along. The builder swears it'll go to 1,000 and then some. I believe him.

This biggest concern I have is the heads. Those 8mm studs seem to have grown just the tiniest bit every time I check. I retorque the heads and change the oil every 25hrs. I'm sure if I wasn't doing this, the 3-4 head would have already failed by now. But, compression is still very good, the CHTs stay below 400, and it doesn't burn any oil. So, I must be living right.

I just recently flew it 400 miles round trip to Van's to pick up a small part for my RV-8 build. It purred like a kitten all the way. At 3100rpm and leaned out cruising at 4,500'msl, it burned slightly less than 3gph.
I think you are doing everything right and have a sweet running engine. What carb are you using ? What prop hub ?

At the rpm's you are cruising at, it's really a toss-up between single or dual port heads. I would lean towards the single port at that rpm just because the lack of cracking problems in the single port heads compared to the dual port heads. But most of the cracking problems of the dual port heads are the result of running the heads to hot.
Have fun.
 
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karmarepair

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Pops, 88mm bore on 76mm stroke give higher torque at lower rpms than 92x69 and could use more effective 63-65" prop - recomended by Sauer. Then You surely climb better, than with 92x69mm and 60" prop.
Pops, who has far more experience than I, has made some points about why you might NOT want to go that way, I'll add that the clearancing on the cam, rods, and case adds hours/money, and weakens those parts. It's a harder to build a good stroker than a big-bore, stock stroke. My view is if you're going to build a stroker, GO BIG - the biggest barrels you feel comfortable with, the biggest stroke, and forged, stroker rods, not cut down stock rods.
 

N804RV

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Are you using the 4130 SCAT 8mm studs?

Matt
I'm not sure. This engine was bought from a guy who built it, put about 100 hours on it, then decided he needed more horsepower. He put a lot a detail in this engine, he's quite the craftsman. everything is balance and blueprinted and the heads were custom built. So, I'm pretty sure he would've used the premium studs, especially with all the bad press the cheaper studs have gotten when used in performance builds.

I think you are doing everything right and have a sweet running engine. What carb are you using ? What prop hub ?

At the rpm's you are cruising at, it's really a toss-up between single or dual port heads. I would lean towards the single port at that rpm just because the lack of cracking problems in the single port heads compared to the dual port heads. But most of the cracking problems of the dual port heads are the result of running the heads to hot.
Have fun.
Thanks Pops!

I'm using a Zenith 1819 updraft carb. The prop hub is the shrink-fit style. I think about 85% of this engine is right off the shelf from Great Plains. But, the paint job looks like the old RevMaster. The guy that built it really went the extra mile on this engine. He scolds me occasionally for not running the balance tube between the intake manifolds. But, I just haven't figured out a way to get it under the Sonerai cowling.

The one change I need to make is have longer exhaust stacks welded up. It came with short straight cut stacks that, because of the aerodynamics of the wing root, causes my CO detector to go off periodically. I've verified with a handheld meter that CO only spikes up momentarily under certain conditions. But, its irritating. And, I'm getting a lot of soot on the cowling.
 

fly2kads

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One of the cool things about the VW engine, as a platform, is that the robust parts support it enjoys makes all kinds of combinations possible. For example, I was just reading recently about a "budget, small stroker" motor based on a 74 mm crank and 88 mm cylinders, for 1800cc (close to what simflyer suggested). The only machining required for that build was to bore the heads. More than one way to skin a cat! That said, the Force One hub on the GP 82 mm crank, and their shrink-fit hub on a good 69 mm crank offer good, proven starting points for an aircraft build, and that's worth something all by themselves.
 

Pops

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One of the cool things about the VW engine, as a platform, is that the robust parts support it enjoys makes all kinds of combinations possible. For example, I was just reading recently about a "budget, small stroker" motor based on a 74 mm crank and 88 mm cylinders, for 1800cc (close to what simflyer suggested). The only machining required for that build was to bore the heads. More than one way to skin a cat! That said, the Force One hub on the GP 82 mm crank, and their shrink-fit hub on a good 69 mm crank offer good, proven starting points for an aircraft build, and that's worth something all by themselves.

Instead of boring for the 88's you can install the bolt on 87's. Yes, they are thinner than the 88's and some people have had problems with them. I put about 100K miles on a VW bus camper with using 87's with no problems. My OSH runner for many years.
 

simflyer

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My unvalidated thoughts:
.....
-- Stroker = higher piston speeds = more stress on conrods, the case/bearing saddles, etc. So, depending on RPM, advantage likely goes to the 1835 at SL.
Please, could You explain Your thought? Where people are making strokers, they wanting to get higher torque at lower rpms, to can use bigger diameter props 63" - 65". Compare rpms specs of 1835cc with SAUER strokey engines - SAUER is getting at 300-600rpm lower, so piston speeds should be lower.
 
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simflyer

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One of the cool things about the VW engine, as a platform, is that the robust parts support it enjoys makes all kinds of combinations possible. For example, I was just reading recently about a "budget, small stroker" motor based on a 74 mm crank and 88 mm cylinders, for 1800cc (close to what simflyer suggested). The only machining required for that build was to bore the heads. More than one way to skin a cat! That said, the Force One hub on the GP 82 mm crank, and their shrink-fit hub on a good 69 mm crank offer good, proven starting points for an aircraft build, and that's worth something all by themselves.
Yes, actually are forged cranks offered with 74mm, 76mm and 78mm strokes (if talking strokes over 69mm). Small 74mm "stroker" is nice way to go with using 88mm bore. I like to know more about "Force One hub", if anybody could share study materials. I got JPX crank with 75mm stroke, so hoping to build small stroker. Prepared one of latest VW bus CT blocks, which have on block filter mount and some port for installing support bearing for prop hub.
 

simflyer

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Pops, who has far more experience than I, has made some points about why you might NOT want to go that way, I'll add that the clearancing on the cam, rods, and case adds hours/money, and weakens those parts. It's a harder to build a good stroker than a big-bore, stock stroke. My view is if you're going to build a stroker, GO BIG - the biggest barrels you feel comfortable with, the biggest stroke, and forged, stroker rods, not cut down stock rods.
High stroke - 78-82mm needs to make clearances. Did You exactly found what have to be done with 74-76mm strokes and if it depend on 88mm bore?
 

TFF

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Different strokes at same RPMs do make different torques. If limiting RPMs it does matter. Restricter plate NASCAR motors would not be long stroke if it wasn’t an advantage. If you let the RPM run to max of each it’s a wash. We have restricted RPM due to aerodynamics of the prop.
 

Vigilant1

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Please, could You explain Your thought? Where people are making strokers, they wanting to get higher torque at lower rpms, to can use bigger diameter props 63" - 65". Compare rpms specs of 1835cc with SAUER strokey engines - SAUER is getting at 300-600rpm lower, so piston speeds should be lower.
My reasoning:
As commonly done, making a stroker VW Type 1 aero engine involves a fairly significant step-up in cost and complexity. It's not a big deal, but it's not a small thing, either. This is partly because of the case clearancing issues you've mentioned, but also because the general consensus* is that using a stroke longer that 69mm requires a beefed up bearing (Force One) on the prop end and appropriate crankshafts.
If we are going to the expense to buy the new bearing and the crankshaft, and the trouble/expense to machine the case for the new bearing and do the case clearancing, then (IMO) putting 88mm cylinders on it doesn't make much sense. Why not put 92mm or even 94mm bore cylinders and pistons on? They weigh about the same, good ones cost about the same. Even if you want to turn the prop much slower than 3600 RPM, you'll have more torque (and power) at whatever RPM you choose.

* The consensus on the need for a beefed up bearing if using a stroker crank is not universal. Aerovee uses the stock bearing and a shrink-fit hub on their 2180cc engine. Again, I think it's safe to say that most folks building these engines would prefer to use a Force One bearing and hub with stroker engines--it's what Great Plains does, what Scott Casler does, and comes from hard-won experience.

Do you know the details of the Sauer prop hub bearing? Is it stock VW, or something else?
 
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fly2kads

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I like to know more about "Force One hub", if anybody could share study materials.
Great Plains Force One Hub: Force One Hub Kit
Matching 82mm cranks: 82mm Top Bug Crank
Installation instructions: Force One hub installation

The hub has a 3 degree taper, and the crank is machined to match. A bolt on the snout of the crank draws the hub tight onto the taper of the crank. The crank rides inside an aluminum bearing, with seals. The nose of the case must be align bored to open it up to fit the new bearing.
 
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