Start with the heart... teaser
Joined: Nov 2001
Posts: 8,484
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From: Cecil County Raceway!!!
From the list of the top shelf items in the build, aluminum rods, tall deck, badass Mast heads, it sounds like your going to make a TON of power... Honestly, the motor sounds like a 2000hp+ combo. Anything over 1600-1700hp, with a 4.250 stroke, I'd be running a Billet CCW crank.
For a 2000hp setup with a 4.250" crank, you better have a Billet CCW crank. A couple hits with a non-CCW crank will wear out the main bearings from the flexing. #3 will wear quick and #2 and #4 will wear with the inner edges seeing the most abuse. The outter bearings #1 and #5 will appear fine.
Depends on the power you want to achieve. The stroke you chose weakens the crank naturally by the 1/8 inch of material in the cross section, this will cause the crank to deflect more than the 4 inch stroke stuff. Being a high cam build with stock type cam the room is available for the BB chevy rod pin to get .050 of that overlap back and give the crank as much strength as possible. When you look at the bearings out of this type of engine you can see the crank is moving like a wet noodle, this is reduced tremendously with the center counterweights. The downside is cost and time for the part to be made, upside is the part can be speced for added strength where you need it.
Kurt
Kurt
Kurt... Awesome feedback. Thanks man... your rep is achieved through the build of some amazing cars. I appreciate it. You talk about the Stroke.. could you elaborate on that more?
I attached a picture of a drawing it looks like my kid did!! The circle in the center is the rod diameter of the stock engine (2.1), the outer circles are the diameter of the main (2.559). I did 4 different strokes so you can see the cross section left with different strokes. As that cross section is reduced the basic crank can be bent with less effort, and by ci added the power cycle is getting stronger with the larger strokes as the crank gets weaker. The better materials help stop this from becoming catastrophicand and it may help explain why some smaller engines get by without 4340 cranks and center weights. One other thing that makes this engine tougher for crank guys is the basic design being short for use in front wheel drive cars, this shortens the crank and narrows the cheek area where the overlap happens.
Kurt
Kurt
Fraser... chime in here too. Ok, so I get that the further the stroke is from the main.. the more inertia in generates thus putting more stress on the crank and the bearings.
The counterweights offset some of that stress caused do the the inertia.
Ok so for a ~2000HP build... how often am I going to have to tear the engine apart? Sounds like replacing bearings will be somewhat common? What other parts will wear quickly?
The counterweights offset some of that stress caused do the the inertia.
Ok so for a ~2000HP build... how often am I going to have to tear the engine apart? Sounds like replacing bearings will be somewhat common? What other parts will wear quickly?
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Fraser... chime in here too. Ok, so I get that the further the stroke is from the main.. the more inertia in generates thus putting more stress on the crank and the bearings.
The counterweights offset some of that stress caused do the the inertia.
Ok so for a ~2000HP build... how often am I going to have to tear the engine apart? Sounds like replacing bearings will be somewhat common? What other parts will wear quickly?
The counterweights offset some of that stress caused do the the inertia.
Ok so for a ~2000HP build... how often am I going to have to tear the engine apart? Sounds like replacing bearings will be somewhat common? What other parts will wear quickly?
Kurt's post relates to overlap of main and rod journals, more cross section that intersects between main and rod journals, naturally stronger, explains why a stock iron crankshaft is strong, it has .519" of journal overlap. Less overlap has more stress on the crankshaft.
As crankshaft flexes, it will wear the bearings.
The aluminum rods we typically swap out every 60-90 runs, for most people that is 1 racing season.
Based on other builds we do, i'd expect replacing, rings, rods, bearings and gaskets every year.
take a 10 pound weight, hold it to your chest, and spin. take the same weight, hold it at arm length, and spin. what exhibits more inertial force?
thats a simple explanation of what you're doing to the inside of your engine, not that a longer stroke is a bad thing, or it cant work. i'd rather have a 7000 rpm 4.25" stroke motor than a motor with a 3.4" stroke that turns 8500 rpm...
thats a simple explanation of what you're doing to the inside of your engine, not that a longer stroke is a bad thing, or it cant work. i'd rather have a 7000 rpm 4.25" stroke motor than a motor with a 3.4" stroke that turns 8500 rpm...
