103mm -vs- 105mm P/C

Jack · Post by **Jack** » Wed Jan 24, 2001 9:11 pm

Does anyone have any experience running 103mm or 105mm piston/cylinders with a stock 71mm crank?

Pros and cons?

Suggested source for these larger p/c?

Average price for each size I should expect to pay?

TIA,
Jack

John Massengale · Post by **John Massengale** » Wed Jan 24, 2001 11:22 pm

look on page 120 in the new Hot VWs magazine, It has an add in there for 104s and 103s for the 71mm crank both at reasonable prices I will say. I ran 103s and the thing seems fine, good luck in your project

steve stromberg · Post by **steve stromberg** » Thu Jan 25, 2001 8:24 am

See our site www.914underground.com scroll down to links hit Riechert tuning they have 103mm p/c's. Steve

74Super · Post by **74Super** » Thu Jan 25, 2001 1:39 pm

John,
What effect will this "oversquare"* configuration have on the powerband vs. stroking the engine for displacement?

*[I believe some v-8 guys used to call an engine with a radical increase in bore over a stock stroke--or even under-stroked -- an engine with "over-square" displacement]

Which is the most reliable way alone to increase displacement: Stroking or Boring the engine?

TIA,
Doug

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Jack · Post by **Jack** » Thu Jan 25, 2001 3:16 pm

To the responders:

The Type 4 engine I am trying to build will power a homebuilt aircraft. That said...I have been told by a reputed AeroConversion Kit producer to stick with the stock 71mm crank, increase jugs to 103mm or 105mm, change the cam, and I will have a more reliable engine than a Type 1 stroked (92mm jugs x 82mm crank) 2180cc engine. I am looking for RELIABILITY, DURABILITY, and TORQUE. Take-off RPMs would be close to 3600RPM with cruise at 3000RPMs average.

All comments or suggestions are welcomed.

TIA,
Jack Lockamy
Camarillo, CA.

Dave_Darling · Post by **Dave_Darling** » Thu Jan 25, 2001 6:37 pm

What kind of RPM are you looking for? Are you going to be running a reduction box between the crank and the prop? If you're running without the redux box, you'll have to work pretty hard to get good torque at 2000 RPM.

--DD

steve stromberg · Post by **steve stromberg** » Thu Jan 25, 2001 7:08 pm

Try Jakes dual plug heads. With the low rpms you will be turning and the fact of the lower air density at cruising alltiude of 7,500 or there about.You might think about running a fairly high comp. ratio to get max takeoff power. Are you going with belts or gears in your GRB ? Steve

[This message has been edited by steve stromberg (edited 01-25-2001).]

Alberto · Post by **Alberto** » Thu Jan 25, 2001 7:52 pm

See if you can find a copy of Sport Aviation
Feb.99. There's an article in it of a KR-2
with a type4. The builder states that "he installed bigger pistons to boost the displacemet to 2400cc." Some nice shots of the insallation.
Al

turbo6bar · Post by **turbo6bar** » Thu Jan 25, 2001 8:02 pm

<BLOCKQUOTE>quote:<HR>Originally posted by Jack:
To the responders:

I am looking for RELIABILITY, DURABILITY, and TORQUE. Take-off RPMs would be close to 3600RPM with cruise at 3000RPMs average.

<HR></BLOCKQUOTE>

Hello, Jack. If you are looking for torque down low, then perhaps a stroker crankshaft would be desireable. It would be similar in cost to the 103 and 105 mm cylinder sets. I have always associated stokers with more torque, but at lower rpm. The bigger bore will give you power, but at higher rpm. I am sure others can weigh in on this issue. At the rpms you are turning, you certainly don't need to be worried about fancy cylinder heads and high rpm valvetrain.

I feel you should keep it simple and not go with any radical engine modifications. In the end, it's your rear on the line.

My cousin had a gyro with a Mcculough 90HP two stroke engine. That thing scared me. I prefer keeping four wheels on the ground or flying in something bigger.

Good luck.

JohnConnolly · Post by **JohnConnolly** » Thu Jan 25, 2001 10:57 pm

just make it as big as you can afford. There's no point in worrying about whether to bore or stroke it unless you have a displacement limitation in a racing class, THEN it matters. Use 96s or 103s (depending on application), and a big crank (78 or 80).

JohnConnolly · Post by **JohnConnolly** » Thu Jan 25, 2001 11:47 pm

Plan on $600/set for 103s. I don't recommend 105s. We have them at aircooled.net

<BLOCKQUOTE>quote:<HR>Originally posted by Jack:
Does anyone have any experience running 103mm or 105mm piston/cylinders with a stock 71mm crank?

Pros and cons?

Suggested source for these larger p/c?

Average price for each size I should expect to pay?

TIA,
Jack<HR></BLOCKQUOTE>

Jack · Post by **Jack** » Fri Jan 26, 2001 7:12 am

To the group:

The plan is to mount the prop (direct drive) to the pulley end of the crank. This is how many sucessful Type 4 aeroconversion are done. I had a Type 1 1835cc in a different aircraft setup this way with NO problems.

As far as the crank is concerned. The SCAT single-piece billeted 78mm crank is out of the question....$1375.00 Does anyone have any thoughts on the DeMello C/W cranks? Any known problems? At about $370 that may be the way to go. If I go with the DeMello 78....will the stock 2.0L rods be okay or do they get replaced? If they need to be replaced, what size/type is recommended?

The aircraft I intend to install this T4 can be seen at www.sonex-ltd.com.

TIA,
Jack Lockamy

Jack · Post by **Jack** » Fri Jan 26, 2001 7:16 am

<BLOCKQUOTE>quote:<HR>Originally posted by Alberto:
See if you can find a copy of Sport Aviation
Feb.99. There's an article in it of a KR-2
with a type4. The builder states that "he installed bigger pistons to boost the displacemet to 2400cc." Some nice shots of the insallation.
Al<HR></BLOCKQUOTE>

Yeah I have the magazine article. Have spoken on the phone several times with the builder (Tom Crawford, Alachua, FL). Tom recommended going with single ignition (save weight and $$$) and going with larger valves over the stock size. He is having problems with the 100LL AVGAS pitting his exhaust valves. He is running the engine at 9.0:1 CR and recommends lowering to around 8.0:1 so 92OCT MOGAS could be used.

Thanks,
Jack

GDRBO · Post by **GDRBO** » Fri Jan 26, 2001 7:52 am

DeMello makes a quality crank. We used a 75mm with 103s in a class 1 offroad racecar. No problems and good power.

vw@micron.net · Post by **vw@micron.net** » Fri Jan 26, 2001 9:48 am

http://www.aircooled.net/cgi-bin/s1.cgi ... .979241147

Steve