78mm crank?

is your heart set on a 78?

I hear good things about DPR welded cranks...

john has the bugpack(4340 chromoly) for 300.... CBPerformance has their super race crank(4340 chromoly) for 290 CB has their 4140 chromoly in 76 and 74 for 180...

we carry 3 different 78mm cranks. The Flanged one is like $1400 (totally overpriced IMO), but we have a 4340 crank for $300, and a precision welded crank for $450 (it specs out nuts on, that's why they cost more).

I strongly suggest you stay away from the 4140 cranks.

John Aircooled.Net Inc.

to add to my own response, i've read(I.E. no personal experience) that the

4340 cranks sold by Darren at DRD are really good cranks and a heck of a deal.... 230 bucks

John...good to hear from you... never heard too much about the 4140's longevity or performance... can you give us some insight? there were folks on other forums that bought them and promised reports back about quality of machinework, performance, etc... never heard back...

good information from someone with the knowledge of parts and your experience would be great for all of us... [/asskissing]

78 mm is as far as I can go without too much bottom end work or I would go 80mm. I'll have to check again but the forged cranks I saw on John's site were all around $600. I would like to explore all my options before spending that much...

Tony

Thanks John, I must have missed the welded crank when I was looking over your site last night. So far this sounds like my best option. I'm building a low RPM high torque engine and I should be able to get away with stock con-rods.

I was also looking at that torquer Web cams you carry, do they produce more torque than a stock cam?

BTW, it's good to see you posting again. Take care.

Tony

bugpack 4340:

my recommendation is a 82mm 4340 crank with 5.4" H-beam rods. It's easier to build than a 78 IMO.

John Aircooled.Net Inc.

How so? Wouldn't the case have to be releived more for the extra 4mm of stroke?

BTW, when you posted the link to the welded type one crank on your site I was able to see it but I can't seem to browse to it from your home page. Any idea what am I doing wrong?

T> my recommendation is a 82mm 4340 crank with 5.4" H-beam rods. It's

yes you have a touch more clearancing, BUT pistons are setup for 82mm strokes, so while you have less clearancing, with 78mm strokes you have another problem which is excessive deck height. That solution is to shorten the cylinders. I find it much easier to get the case clearanced by a place like RIMCO and you simply deburr and clean, then you do not have the headache with the piston being in the wrong place. The 82mm is an easier build than a 76 or 78 IMO. When guys are building 76 or 78 it's almost always because they are afraid of the clearancing work, and it's not a big deal, really.

John Aircooled.Net Inc.

Are you referring to the 85.5mm stroker piston and cylinder set or the stock cylinder set? I was thinking about using stock cylinders with spacers with the 78mm crank. One advantage of more stroke would be that I could possibly have more low end torque and that would be good.

Would the Webcam torquer cam give more low end power than a stock cam?

Ton

I think building a stroker 85.5 is a complete waste of time and money, and have stated this for years. You should increase the bore size, and if you have $ leftover in your budgeting get an 82mm crank and 5.4" H- beam rods.

John Aircooled.Net Inc.

I built a 78x90.5 with B pistons, and 5.5" rods. Everything came somewhat close to where I wanted it with minimal shimming, I can't remember if I used any shims. I may have shortened the cylinders, and around the same time I shaved some material off of piston tops too but it could have been a different engine... LOL. The longer than stock rods should help it run stronger at higher rpms. Redline is around 8000.

I'm building a low RPM torquer and I neither need nor want the engine to rev over 4k RPM. OK, I'll fess up, this is for an airboat and it will be running it flat out most of the time. Peak HP is of little use to me, I'm looking for maintainable low RPM power to drive a prop.

The 82mm crank sounds interesting if I can use it with stock cylinders...

Tony

that engine would be somewhat similar to what folks need in the aviation field... We just happen to have a very experienced VW guy that knows vw engines and aviation... Ping Bob Hoover...

I already did, now I'm looking for the parts.

The 82mm crank sounds cool if I can get it to work with 85.5mm cylinders. There's no problem making more power than I can use, the problem is making that power at a low RPM.

Tony

gotcha.... smart move!