SCAT pro series lightweight crank

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Rt1976

Rt1976

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Planning a NA big block drag only engine. I'm cubic inch limited so need to make the most of it. It will be injected on alcohol. Looking at a 4.15 stroke, 480(ish) c.i.

Anyone use a SCAT pro series lightweight cranks? Do you like them , is it worth it? How much weight savings is there over a std. (i.e. Molnar)?

Thanks

Cross posting this in FBBO as well
 
Rt1976 said:
Planning a NA big block drag only engine. I'm cubic inch limited so need to make the most of it. It will be injected on alcohol. Looking at a 4.15 stroke, 480(ish) c.i.

Anyone use a SCAT pro series lightweight cranks? Do you like them , is it worth it? How much weight savings is there over a std. (i.e. Molnar)?

Thanks

Cross posting this in FBBO as well
Click to expand...

I used a 440Source 4.15 ultra light crank in my RB with a 525 gram piston and one of their 7.1 inch rods to lighten the reciprocating assembly as much as possible in an attempt to reduce cap walk and main webbing breakage. I also run Hughes's main cap girdle and studs.

So far it seems to have worked. My redline is just under 7K, but the combo was putting out just under 700hp. It is the quickest reving 440 I ever drove.
 
Before I worried about crank weight I’d be looking for a crank with 8 counterweights.

You can get a crank too light. Then it flexes. Look into 8 counterweights.
 
Here's something to think about. Actual Racepak data collected from my personal 2525lb driver/car, with some rough calculations applied. Sbc power, but exact same car/trans/flywheel/clutch/gearing/tires. Exact same heads/intake/carb/cam/compression. Only difference between these two engines was the rotating assy...

Scat cast crank (49lbs), steel rods, 1863g bobweight, WOT no-load rev rate of 8500rev/sec.
In 3rd gear @ 535rev/sec accel rate, 31.47ftlbs absorbed by the rotating assy, 468.53ftlbs twisting the transmission's input shaft.
In 1st gear @ 1975rev/sec accel rate, 116.18ftllbs absorbed by the rotating assy, 383.82ftlbs twisting the transmission's input shaft.

Scat F43 lightweight crank (42.1lbs), aluminum rods, 1492g bobweight, WOT no-load rev rate of 11,515rev/sec.
In 3rd gear @ 541rev/sec accel rate, 23.49ftlbs absorbed by the rotating assy, 476.51ftlbs twisting the transmission's input shaft.
In 1st gear @ 2217rev/sec accel rate, 96.27ftllbs absorbed by the rotating assy, 403.73ftlbs twisting the transmission's input shaft.

Comparing the two...
...both engines put out the same torque when operating steady state @ 5000rpm.
...WOT 4500-5500 at 3rd gear acceleration rate, the lightweight rotating assy hits the transmission's input shaft with about 7.98ftlbs more torque.
...WOT 4500-5500 at 1st gear acceleration rate, the lightweight rotating assy hits the transmission's input shaft with about 19.91ftlbs more torque.

The difference in bobweight was about 3.27lbs, crankshaft weight difference about 6.9lbs. Flywheel/clutch weight is typically centered farther from the axis of rotation than the crankshaft, making it an even more effective place to lose weight.

Grant
 
weedburner said:
Here's something to think about. Actual Racepak data collected from my personal 2525lb driver/car, with some rough calculations applied. Sbc power, but exact same car/trans/flywheel/clutch/gearing/tires. Exact same heads/intake/carb/cam/compression. Only difference between these two engines was the rotating assy...

Scat cast crank (49lbs), steel rods, 1863g bobweight, WOT no-load rev rate of 8500rev/sec.
In 3rd gear @ 535rev/sec accel rate, 31.47ftlbs absorbed by the rotating assy, 468.53ftlbs twisting the transmission's input shaft.
In 1st gear @ 1975rev/sec accel rate, 116.18ftllbs absorbed by the rotating assy, 383.82ftlbs twisting the transmission's input shaft.

Scat F43 lightweight crank (42.1lbs), aluminum rods, 1492g bobweight, WOT no-load rev rate of 11,515rev/sec.
In 3rd gear @ 541rev/sec accel rate, 23.49ftlbs absorbed by the rotating assy, 476.51ftlbs twisting the transmission's input shaft.
In 1st gear @ 2217rev/sec accel rate, 96.27ftllbs absorbed by the rotating assy, 403.73ftlbs twisting the transmission's input shaft.

Comparing the two...
...both engines put out the same torque when operating steady state @ 5000rpm.
...WOT 4500-5500 at 3rd gear acceleration rate, the lightweight rotating assy hits the transmission's input shaft with about 7.98ftlbs more torque.
...WOT 4500-5500 at 1st gear acceleration rate, the lightweight rotating assy hits the transmission's input shaft with about 19.91ftlbs more torque.

The difference in bobweight was about 3.27lbs, crankshaft weight difference about 6.9lbs. Flywheel/clutch weight is typically centered farther from the axis of rotation than the crankshaft, making it an even more effective place to lose weight.

Grant
Click to expand...


Yep, you can easily lose 15 pounds off the flywheel. Inertia is a serious task master, especially in 1st and 2nd gear.
 
weedburner said:
The difference in bobweight was about 3.27lbs, crankshaft weight difference about 6.9lbs. Flywheel/clutch weight is typically centered farther from the axis of rotation than the crankshaft, making it an even more effective place to lose weight.

Grant
Click to expand...

Did you reduce E.T.?
 
Rt1976 said:
Did you reduce E.T.?
Click to expand...

Not much difference for me, but your results will depend a lot on how you launch the car. If you are launching from less than finish line rpm, you will likely be quicker w/ lighter rotating assy as you will be spending more energy with the engine gaining rpm vs losing it. Same if you are using a lot of wheelspeed or knocking the tires loose after the shifts.

Grant
 
weedburner said:
Not much difference for me, but your results will depend a lot on how you launch the car. If you are launching from less than finish line rpm, you will likely be quicker w/ lighter rotating assy as you will be spending more energy with the engine gaining rpm vs losing it. Same if you are using a lot of wheelspeed or knocking the tires loose after the shifts.

Grant
Click to expand...

Good info , Thanks. This will be a four-speed car w/ sintered iron clutch so I should be able to keep it in the sweet spot with a heavier crank and gear ratios.

Similarly, I put a lightened flywheel in a Ducati air cooled twin. It would lug if you didn't bring the rev's up when taking off but the acceleration in the mid gears really picked up when rolling into it.
 
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