Just received my new Crower 4340 BB crank and was little surprised to not see any profiling of the leading edges of the throws. I will be using a crankscraper, and vacuum pump….but how important is some radiusing to the leading edges in an engine with these systems.

572” 7500 rpm. Good scraper with 13-14” vacuum.

Thanks.

That seems odd, for the price I'd expect their cranks to be fully machined. I haven't used a Crower crank in a long time but they used to be good stuff. I can't tell you how much power you'll be losing but I do know that the serious engines all use fully machined cranks and most of them are fully polished or REM treated. I've seen some Winberg cranks that look like jewelry.

Reason #1: cost$$$, not everyone understands why or wants to spend the money.
"Leading edge" means you know which way the crank turns. Not as common as you would think. I've seen some with both edges end as sharp blades...
The leading edge should be close to a full radius (using all the web thickness) not just smoothed, the trailing edge as close to a knife as you can.
This will ruin the balance.
It has almost no effect until high RPM, then it reduces CC pressure cycling, reduces oil temperature, and entrains less air.

David Vizard did some videos about this. You will need to work with the shop doing the balancing, and I doubt they'll be willing to do it for you, but that depends on how much manpower they have to spare. Not much would be my guess, based on local conditions here. S/F....Ken M

https://www.youtube.com/watch?v=14q5xp1epCY

Thanks all for the replies. I was also surprised that the leading edges were not profiled/radiused after how much this crank cost. However, other than that it is a very, very nice piece. I think I will give a call and ask why. I have seen mixed photos from Crower of radiused vs non-radiused throws.

Here are 2 pics:

Extensive work on VW Type 1 (beetle) engines produced a crank where each cheek/CW is a full cylinder.
Even changes in the OD of the CW create turbulence.
Every cross-sectional area or shape change should be profiled as well - no sharp edges.

Appearance is nice, but the people who do the polishing are not engineers or machinists.

Reasons not to offer this as an option:
Huge extra cost
Slows down the production line
They sell faster than they make already

Interesting thread.
Some coatings are available to reject oil; I have Cerakote in my Geo Metro which regularly sees 6k rpm.

What heads ar you using to get the power range up to 7500?
Doug

I have 572-13 prepped by Dwayne Porter.

in my machinist career, cerakoat [coated] carbide cutting inserts were frequently used. they cut very well using little or no lubrication liquid, and would cut at almost twice the rpm and feed rate as a bare carbide insert would.

Ooooh, I never knew that
I wonder if mill bits would be helped

I've bought and use many different brands of stroker cranks from CAT (Call Auto Transport (China company) to) to KB, Bryant, Oho Crankshaft CO, and Molnar. Most of them had the front edge of the counterweights rounded off like the front edge of airplane wings and the back sides tapered down to nothing like the back edges of airplane wings are

Yes…that’s what I thought of throughout this whole topic. I thought exactly of airplane wings. Rounded raidius front and tapered edge on rear. If calling gets me nowhere, I might do this myself. I have the equipment and ambition.

Interesting
with a 4" typical radius, surface speed
>>> ((5000 * 60) * (12 /4.)) / 5280
170.45 mph

Reynolds # is probably 150k to 200k for hot air with some oil droplets
the more you can shape it like a NACA strut foil the better - ie between round and "knife" front edge

we had a few ceracoated carbide end mills in 3/4" size used to cut T6061 aluminum. those were used with a cutting fluid so the aluminum didn't stick. 3000-3200rpm, but i forget the ipm. it was up there though.
man, the chips flew with those babies !

Ideally, the trailing edge should taper down from full thickness at a 15° angle. Needless to say, there's no room for that.

This is also a favored shape for the back of LSR vehicles. The "Kamm" principle dictates that if this isn't possible, the next best shape is to reduce both length & width of the tail at 15° until the cross-sectional area is 50% of the car's full dimensions, and cut it off flush at this point (no radius). Is the closed end vertical, or 90° to the air flow? IDK.

Not sure what it cost you? No-doubt that's a 'good' CCW crank! I'll look at my old Crower BBM crank and compare but, I doubt you'd notice any power difference. So don't risk anyone messing things up to fix what isn't broken IMO. Keep us updated on your build, so far it sounds promising.

It has little value at lower RPM, but is especially helpful with big strokers where the crankcase air volume is nearly OEM but the pressure cycling is higher.

Yeah, and maybe a better overall option is to just coat it to sling oil off and add a crankcase vacuum pump that switches on at high-rpm/throttle or low vacuum to lower the air density it sees.

Getting the oil off the crank is a different question, even a sharp tail will do that.
The blunt CW leading edges create a lot of drag trying to plow through the hurricane of hot air, oil vapor, blah. Reducing the air density with a pump is a great idea: do both.
It's why modern boats have a "bulb" in front of the bow, but a rounded nose was used on the Nile 6,000 years ago.