Lightened crank

[Thornhill45]

Is it actually worth doing?

I know that a lightened flywheel helps and everything but what will it do at the crank end?

Ive removed aircon and may take out power steering. So if these are gone will it make much difference?

[NAspirated]

if your not racing at a highly competitive level, dont bother.


many people will have opinions on this, but the basis is that a lightened and knife-edged crank will create less windage due to oil being removed from it quicker, allowing the engine to spin quicker.


Ive seen a strobe picture of a Crank under acceleration, it "grew" 1.5 times due to the oil film sticking to it. that was at 7000rpm.

generally, you dont want to remove more than 15% of the original weight of the crank. Its more about making the Cranks leading and trailing edges Areodynamic to shed the oil film.


if you lighten the crank, make sure you have it dynamically balanced. static balancing is next to worthless.

but again, unless your making a lot of power and racing every weekend, theres a lot more important things you can do.

[monsterbishi]

or get it knife edged, to help the crank pass through the oil

[Andrew]

But wont that reduce inertia thus loosing torque for the sake of revability? Which in the case of our Hondas, making less torque means we then make 3/8ths of fuck all?

[NAspirated]

Originally Posted by Macro

But wont that reduce inertia thus loosing torque for the sake of revability? Which in the case of our Hondas, making less torque means we then make 3/8ths of fuck all?

simply put, No.

Torque (relating to Automotive use) is a measure of the twisting force of an engine, Inertia has absolutely nothing to do with this. Inertia is the continued motion of an object without any outside forces acting on it. I.E, you rev an engine to 6000rpm in neutral, Engine Torque is what spins the flywheel, Inertia will keep it spinning until it returns to idle.

removing weight from the crank (or flywheel for that matter) will do nothing to the torque output of the engine as they will not move the curve in anyway. they only affect revability. obviously removing weight from the rotating assembly makes it easier and quicker to turn.

a low mass flywheel has its own set of problems, but as i said above these are modifications that are mainly used for circuit racing (drag racing has slightly different needs). Basically, with a honda on a circuit, rev matching and rotating mass becomes important.


HTH.

[Naturally Aspirated]

I heard that on race motors that aernt running ac ps etcetc... the amount of power lost from crank/flywheel to power at the wheels only depreciates by 7%.

[xsiv]

well im looking into getting a aftermarkit crank from the states they are 29lbs what is the waight of a std one>??

[Macros]

Originally Posted by xsiv

well im looking into getting a aftermarkit crank from the states they are 29lbs what is the waight of a std one>??

hang on I'll just weigh one.

[Moclov]

A whopping 3lb saving... Barely seems worth it

[NAspirated]

5lb....


the only advantage of Aftermarket cranks is most are Forged Billet, but factory cranks and factory rods, from 99% of manufacturers, are forged anyway :wink:

Originally Posted by Naturally Aspirated

I heard that on race motors that aernt running ac ps etcetc... the amount of power lost from crank/flywheel to power at the wheels only depreciates by 7%.

Id love to know who you heard that from.

there are many variables related to power loss other than A/C or PS. i.e.,

Manual or Auto (if auto then Stall point of convertor will give differences as well),
2wd or 4wd,
Constant or Variable 4wd,
Weight of crank/flywheel,
even style of Main/Rod Bearings can make a difference.

Typically (this a generalistaion for the use of this thread),FWD manuals will lose 15%, FWD Autos will lose 25-30%, RWD Manuals will lose 20%, RWD Autos will lose 30-35%, 4WD's will lose 25-35%.

then theres the loss from Heat that you have to factor in :wink:

[xsiv]

Lightweight 4340 chromoly crankshafts
Approximate weight: 29 lbs b16a stroker



std demintion eagle crank std weight

[NAspirated]

personally i wouldnt use an Eagle Crank, there are better companies for the US$650-750 odd youll pay...

[Naturally Aspirated]

Originally Posted by NAspirated

5lb....


the only advantage of Aftermarket cranks is most are Forged Billet, but factory cranks and factory rods, from 99% of manufacturers, are forged anyway :wink:

Id love to know who you heard that from.

there are many variables related to power loss other than A/C or PS. i.e.,

Manual or Auto (if auto then Stall point of convertor will give differences as well),
2wd or 4wd,
Constant or Variable 4wd,
Weight of crank/flywheel,
even style of Main/Rod Bearings can make a difference.

Typically (this a generalistaion for the use of this thread),FWD manuals will lose 15%, FWD Autos will lose 25-30%, RWD Manuals will lose 20%, RWD Autos will lose 30-35%, 4WD's will lose 25-35%.

then theres the loss from Heat that you have to factor in :wink:

LOL!! just to generalise... How many race motors do you see around that are automatic? :wink:
Most race motors run a lightened and balanced crank
I am pretty sure most race motors would also run after market Main/Rod bearings to improve performance.

So yeah theres my point, guess i should have mentioned a race setup

My apologies

[NAspirated]

Originally Posted by Naturally Aspirated

LOL!! just to generalise... How many race motors do you see around that are automatic? :wink:

your kidding me right?

ever watch NHRA? Ever seen the doorslammers at meremere?

the fastest Top Fuel and funny cars in the world, cars that run 6 seconds and under, are autos.

any other info there Champ?

[Naturally Aspirated]

u win!!!

i have the link somewhere... will post it up some time

but yes u win!!

[xsiv]

Originally Posted by NAspirated

personally i wouldnt use an Eagle Crank, there are better companies for the US$650-750 odd youll pay...

i can get a aftermarkit eagle std/stroker crank and crower rod for 700 us
or

aftermarkit eagle std/stroker crank and eagle rods for 600us
or

aftermarkit eagle std/stroker crank, eagle rods and je spr pistons for 1000 us,

another 240 us for performance turbo head gaskit, full set of oversized race being and a full balance good to 9500rpm,

sound pritty good to me,

thats a fully forged b16a, stroked to 1775 cc for around 2g

any different companys u know of that make stroker cranks???

[NAspirated]

try these guys, they are probably the best aftermarket cranks around (no prices on the site, youll have to email them)

Their Rods are absolutely stunning, i want their I beams, almost as much as i want a set of IB Rods.

http://www.rpmmaxx.com/

and before you ask, yes they have applications for Imports

[nzcivicracer]

You tried www.scatcrankshafts.com ?

^^^This stuff looks pretty good! Is it quality stuff?

[doo0T!doo0T!]

Here's my lightened, knife edged, and shot peened crank for my next build.(bottom)
I havn't weighed it yet to compare to the original as I dont have suitable scales but it's had a considerable amount taken off.

I wouldn't recommend doing this unless you are seriously committed and prepared to have it all go bang. Game over. This one has gone pop once already. It's been crack tested and checked for alignment and it all checks out. (thank god) There are some dings on the No 1 counter weight from the exploding rod which will have to be ground back and re-shot peened but otherwise it'll be mint. The last engine this crank was in was still running stock rods.

[BTLF3D]

^and thats done by Collier motor engineers, i would reccomend sending them your crank if you need any work done to it :wink:

[nzcivicracer]

Originally Posted by NAspirated

almost as much as i want a set of IB Rods.

Whats the deal with this guy? Does he make his own stuff or use other top brands? He certainly talks the talk

[noslug]

Originally Posted by NAspirated

your kidding me right?

ever watch NHRA? Ever seen the doorslammers at meremere?

the fastest Top Fuel and funny cars in the world, cars that run 6 seconds and under, are autos.

any other info there Champ?

I think youll find top fuel and funny cars are direct drive via a clutch, theres no gearbox in there. Making anything survive with 8000 HP is a bit tricky.

The gearing is all about clutch slippage, and ignition timing.

On the crank thing, A really light reciprocating assembly will suck if you drive it on the road. More likely to bog when launching it, and will be really touchy on the accelerator. Heavy cars and light flywheels and cranks arent a good mix IMO.

[NAspirated]

not all of them :wink:

Originally Posted by dooOT!dooOT!

I wouldn't recommend doing this unless you are seriously committed and prepared to have it all go bang. Game over. This one has gone pop once already. It's been crack tested and checked for alignment and it all checks out. (thank god) There are some dings on the No 1 counter weight from the exploding rod which will have to be ground back and re-shot peened but otherwise it'll be mint. The last engine this crank was in was still running stock rods.

the crank didnt go pop, the rod did. The crank would not have caused the problem, too much power or in Hondas case, bullshit weak bolts, are the problem. Cranks themselves will rarely play up under any circumstance.

there really isnt a huge amount of disadvantages to lightening or knifedging a crank FOR A RACE APPLICATION. for the street, its a complete waste of money. For turbos, is a complete waste of money. for pretty much any situation where you dont need to extract every last ounce of HP, its a waste of money.

and ive heard colliers are good, never had any work done tho.

[doo0T!doo0T!]

Originally Posted by NAspirated

the crank didnt go pop, the rod did. The crank would not have caused the problem, too much power or in Hondas case, bullshit weak bolts, are the problem. Cranks themselves will rarely play up under any circumstance.

there really isnt a huge amount of disadvantages to lightening or knifedging a crank FOR A RACE APPLICATION. for the street, its a complete waste of money. For turbos, is a complete waste of money. for pretty much any situation where you dont need to extract every last ounce of HP, its a waste of money.

and ive heard colliers are good, never had any work done tho.

You're right, in this case it was the rod that popped not the crank, what i was meaning is it was a worked up engine, money had been invested into it and when it popped, the owners wallet took a hit. If you're modifiying an engine to the extent where you need to shed weight off the crank you have to be prepared to get out the efty when somthing fails, when things are reduced in structure for the sake of weight saving, that envelope of engineered safety gets smaller, and as the limits get pushed it gets more likely your going to experience some sort of failure.

However, I dont entirely agree with you in saying a crank will rarely play up under any circumstance.
There are lots of reasons why a modified crank could give trouble.
Look at the pic again.
For one, the counterweights no longer come anywhere close to offsetting the weight of the journal. (from main bearing to mainbearing) over all the crank would still be balenced because it's a flat design and has two journals either side opposing each other. Along it's centre it's average weight distribution would remain on the centre line but when you divide it up, main bearing to main bearing, you get a different picture all together.
With this thing ticking over at any rpm you have unbalenced stresses being imposed along the length of the crank, as the rpm increases the forces increase, 4 fold for every time the crank rpm doubles, the centrifuegal force is wanting to bend the crank in the direction of the centre of mass, and it will, with ease. (and this is not counting the rod and piston which it is throwing out and pulling back contributing to the force even more) The only things stopping the crank from bending till it snaps are the 5 main bearings being held in line by the block, which in Honda's case is not all that stiff anyway. This design is light for sure but it's going to mean some savage beating of the main bearings at high rpm.

There are also self destructive harmonics to take into account, I'm sure you have seen strobe images of axial warpage due to the frequencies of waves up and down the crank's length, this is one of the reasons why a lots of factory cars are fitted with a harmonic crank balencer, it's not to make up for sloppy balencing in the factory as a lot of people think it is, it's to take out the harmonic frequencies in the crank shaft at certain rpm and load points.
The cranks are designed in the begining to be a certain weight and have material concentrated in specific areas for different reasons and other engine parts are designed to work together with it. When you go and shave a crank to with in an inch of it's life like above you screw with all of this. At high rpm this crank would be all over the place like a mad woman's piss.
Same goes for fly-wheel shaving, you know yourself that when you shave down a stock flywheel you put it outside it's designed specification and run the risk of it coming apart and mincing your testicles.
It's a trade off for the benefits of the lighter flywheel.

I'm fully aware that my crank is a liability and I'm prepared to have to replace beaten bottom end bearings regularly and if it pops then ah well shit happens, back to the drawing board, after all it's a ZC not a K20.

[monsterbishi]

if your in auckland i reccomend Bob Mead at Balancing Specialists.

A++