Ryan's Project (new video on page 8 guessing about 600whp)

BADNEWS

Member
alltrac101":pwm47rxs said:
MWP":pwm47rxs said:
Oh right :(
Thats a bit of a worry if a 5S crank with its original big-end journal size cracks like that.
The 5S cranks machined down to 3S size would be a decent amount weaker.
Not true, I've run both big & small rod journals, no issues to date.
could be a bad crank, rare. how does the bearings & pin look

crower will make a custom crank for some $$$$ but if there are stock 5sfe cranks making+ hp for years in drag cars, not money well spent

The bearing looks normal. I never looked at the wrist pin. Gave my rod and piston still together to the machine shop. I'll ask him to look at it and take photos.

Yeah I've been doing some thinking and going back and forth between the custom crank and stock. Starting to lean back to the stock one. I questioned the MR-2 board and only got one response that someone had crack their crank also.
 

CSAlltrac

New member
Time for something like this made with unobtainium.
lkibh.jpg
 

l0ch0w

New member
to be honest with you, that crank probably didnt crack because of too high of HP, but rather because of either excessive knock events or a poor balancing job performed by your machinist. Violent harsh events cause cracking, not load events. Too much unbalanced load can cause warping, but very rarely cracking. Did they electronically balance it? or did they only hand balance it? 5S cranks will have a higher propensity to crack/warp also due to their larger rotating mass and greater centripetal loads because of the longer stroke. This is why racing motors are usually made to be square or oversquare... I know there is no replacement for displacement, but there physical horsepower limitations on certain geometries. I have heard of heads secured down with l19's lifting before cranks bent... There are 800whp motors out there running the stock 3s crankshaft... Frankly if you build has been done correctly there is no need for unobtanium based crankshafts in the 3s/5s community...
 

l0ch0w

New member
I should probably point out, that the guys I know running 800+ HP MR2's and Alltrac's have the most success with oversquare motors running at higher RPMs. They usually do this by using a 5s block bored out to 88 or 89mm and the stock 86mm stroke with the stock 3s crankshaft. This gives them a bit of extra displacement without significantly increasing rotating mass or vibrational mass. 4 cylinder motors have an inherent issue with balance to begin with. While primary balance is perfect, secondary balance is very poor. Lack of secondary balance primarily comes from the fact that the pistons and connecting rods are unable to move in sinusoidal motion with the counterweights on the crankshaft. This means that as power or displacement increases, vibrational forces become more and more powerful, and those harmonics can become powerful forces that crack crankshafts. If primary balance is off Meaning your crankshaft and piston/conrods arent balanced appropriately, it only exacerbates this problem...
 

vip09

New member
I am going to run an 88mm 5s block with a stock 3s crank this time around. Just need to take all my parts to the machine shop then I will assemble it.
 

sleeper

New member
RedCelicaTRD":2lqhp985 said:
Mind if I ask how many people you know that run a 5s block with a 3s crank?


I am, and it`s still on one piece after 4 years with 35psi, 6262 and e85..

I have seen a few ppl with crack`d cranks, ( both 3s and 5s) but it`s extremely rare.. guess you where just unlucky.
I would just get a new stock 3s or 5s crank and try again.. ( and if not, i did see a guy trying to start a GB on crower cranks over at mr2oc. )
 
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