gollum

iTrader: (1)

Has anyone ever given this idea much thought when building a 402. The lighter rotating weight would rev quicker. Any good ideas?

Scat makes a light weight LS1 stroker crank.

I Beam rods are lighter than H Beam rods (6.125 length).

OEM LS7 Titanium rods (6.064 length) sound cool but will they work in a LS1 402 engine? I know downsized (smaller 4.00" bore) LS7 style custom pistons would be needed.

SStrokerAce

iTrader: (2)

You can always spend lots of timing lightening it.... you don't need to do Ti rods to do this either, and you don't have to go nuts on spending $$$$$.

gollum

iTrader: (1)

An aluminum flywheel would also help .

SStrokerAce

iTrader: (2)

yeah but that's not in the motor... you could put that on anything

DavidNJ

The flywheel clutch will have more impact than anything in the engine. It is simply on a bigger radius and weights more to start with.

After that, first place your wallet on the scale. Lots of piston blanks come in LS1 sizes. A custom 1" compression height 4.03" piston would weigh under 370gms. You could use a 2.25" pin. Even a 2" pin. You could also use a .866" pin. Reducing pin weight to maybe 80-90gms. You could use thinner rings....043/.043/3mm. A few more gms.

Rods are a different issue. GM Ti rods are probably less expensive than aftermarket. However, the 1" compression height piston will need a 6.2 rod. Custom Ti rods are something like $3-4k. They would probably weigh around 400gms. Custom steel rods, using 1.88 or 1.771 journals, maybe the smaller pin, in a design like the Crower Maxilight that takes advantage of the smaller sizes, would probably be in the 550-600gm weight range for a 500-600hp power range.

Of course the small journals will require a custom crank...maybe $2500-3000.

Unless you are going to spin the heck out of it, why would you do this?

RednGold86Z

A flywheel will not affect steady state power. It is simply a storage of kinetic energy (turns it to potential). You can argue that it will have more effect in 1st gear than 6th, which it does due to delta RPM. Reciprocating mass (up down, or side to side), like pistons and rods, and frictional losses, take up real power (at any speed or gear). Spend your money on the reciprocating and frictional losses for the most benefit. Rotating mass won't have so much effect (but some of course, when RPMs are going from low to high quickly, but a good gear shift will recover some that loss when the stored energy is put to the wheels - assuming power-shift or auto tranny).

Adrenaline_Z

I'll agree with that ^

It doesn't take much power to maintain a vehicle at a steady speed.

I wonder what a dyno graph would look like if we held the motor at
3000 RPM? Hmmmm... I'd say a flat power line with a fairly low power value!

SStrokerAce

iTrader: (2)

You would be suprised what lightweight parts actually do in terms of performance....

Ric

Does anyone make aluminum rods for Gen III engines???

SStrokerAce

iTrader: (2)

Most aluminum rods are custom anyways. BME would be a good place to start.

Bret

DavidNJ

Steady engine speed? Are you using a CVT or competing in tractor pulls?

Generally, the total energy in the piston/rods is pretty constant at a fixed speed. As one piston accelerates another is going in the opposite direction.

Bret, have you seen more than 5lbf-ft difference between light and heavy components? Say 350gm pistons and 550gm rods vs. 500gm pistons and 700gm rods?

SStrokerAce

iTrader: (2)

The steady state comment is just that... low acceleration rates on a dyno say 300rpm a sec or step testing where you get a TQ reading at a RPM and then move to the next stabilize the dyno at that RPM and continue. You really can't see most of the benefits of the lightweight stuff at that RPM.

Lighter rods and pistons mean you stress the crankshaft less, at the same piston g's, so you can run the bottom end to a higher RPM. At the same time that lower bobweight can also help you take more material off the crankshaft counterweights and you can lower the inertia of the setup as well. That's where you get the performance advantage, in the lower inertia and increased acceleration rate of the motor.

If you look at a stock LS1 bottom end, 610g rods, 450g pistons, 160g pins etc... your around 1800g bobweights, racing applications can get that down a huge amount, 30% or more.

Bret

DavidNJ

Reducing the mass absolutely reduces the load on the crank, rod bolts, rods, and pins allowing higher revs.

However, it only has a token effect on inertia...unless you have empirical evidence that it does. Maybe 2 to 5 lbf-ft of torque.

SStrokerAce

iTrader: (2)

You'll see it in the performance, not the power output.

DavidNJ

If the benefit is 3 lbf-ft at 600rpm/sec acceleration, why would you ever see more? Admittendly, first gear acceleration can be faster. And under deceleration the or blimping the throttle on a downshift the acceleration rate is much higher. However, 600rpm/sec is pretty representative of 2-3rd gear acceleration.

Ari G

iTrader: (25)

Woulden´t the engine loose TQ with a lighter flyweel due to less rotating mass but gain hp?

J-Rod

No you won't see a loss of torque. Mostly what you see is the need to increase launch rpm since the flywheel can't store as much potential energy, as its mass is less. So in turn you spin it higher to make up the difference.

Now, as for a super light crank. They are out there. you can take one of the forgings that is out, and have the throws re-done to take weight out, or you can go with something like a HTC or Callies. Both can do very light cranks.

I have a friend with a 45 lb Ls1 crank. But the issue is he went with a heavy steel rod to handle the power levels he makes. That in turns means a TON of mallory metal to get the balance right. So, you have to balance the reciprocating mass agaist what you are doing with the crank.

As for an AL rod. You might look at a Jager transformed AL rod. Same strength as steel (or better), not the replacement factor of regular AL (same life as a steel rod), same basic price (probably $1400 set), and about a 400gr rod that'll take 2000HP.

Less weight always equals good. Look at a forged 346 vs a stock cast 346. The stock 346 will usually make about 5-10 HP more just based on the increased weight of the components.

steve2001sh

Recipricating mass (up and down, such as pistons, pins, rods (sort of)) effects power and fuel efficiency (if you care).

Rotating mass (spinning things like flywheel and crank) effects accelleration. You won't see it on a dyno, but you'll see it on the track.

Here's some math, just for fun. It's been a while since my last physics class, so someone correct me if I missed something.

An engine with a 9cm stroke (3.54 inches), 14.4kg recipricating mass (1.8kg per cylinder for pistion, rod, pin * 8 cylinders), and rotating at 6,000 rmp or 100 rotations per second is using 12.4hp just to make the pistons move, not counting friction. If you manage to reduce the recipricating mass by 30%, that would return 3.7hp to you.

3.7hp isn't much for the price you pay for low weight engine parts, but the real value comes from being able to rev your engine faster if ALL your parts are low weight / strength.

Below is my math; again, I may have missed something.

Basic equations:
P = E / T
E = F * D
F = M * A
A = 2 * D / T^2

Putting it all together:
P = F * D / T
P = M * A * D / T
P = M * 2 * D / T^2 * D / T
P = 2 * M * D^2 / T^3
P = 2 * M * D^2
D = stroke * rotations * 2

Final equation:
P = 8 * M * stroke^2 * rotations^2
P = 8 * 14.4kg * 0.09m^2 * 100^2
P = 9.3kw = 12.4hp
0.3 * 12.4hp = 3.7hp

Edit: Dang, multiply all that by 2, so 25hp used to move the pistons, and 7hp potential savings. You have to move the pistons up AND down, hello.

SStrokerAce

iTrader: (2)

Well if making the angular inertia of the crank less isin't worth much these two days on the lathe cutting the coutnerweights down is just a big waste of time then....

Great article about this by David Vizard in the Feb O6 Pop Hot Rodding. pg 86.

One of the best ways to comprehend the difference is look at a chassis dyno pull from a dynojet in 1st and 4th gears. The more you lighten the crank, flywheel etc... the closer those two curves come within each other.

Bret

chuntington101

i allways thought (and its true for all the racing stuff over here in the uk) lighter components ment potencialy higher rpm (due to less force to hold things to other things) and thus the potencial for more power and a wider opperating range!!!

now as far as i can see this is aplicable for all engines!

and a very good point H8 LUZN!

thanks Chris.