Power from light internals?

[LumpyVR4]

Hey guys, I have been doing research into light weight bottom end bits and was wondering to myself if money was no object how much power you could gain from fitting the lightest crank, rod, and piston set you could get. I was considering it VS a stock displacement engine that with a stock bottom end would give say 350hp at the wheels. So like something with 272 cams, and a FP-71HTA or FP-76HTA turbo.

Bits I were thinking of are a Winberg crank (11.8kg vs stock 14kg), Carrillo rods (567g) and JE pistons (317g). Any thoughts on power gains?

 

[LumpyVR4]

After doing more reading I realize I have asked the wrong question. Lighter internals won't increase the peak power generated by the engine, but does allow the engine to accellerate faster (same bang pushing on less bottom end weight). It would be interesting though to take a car and run it down the 1/4 with a stock bottom end, then swap that out for a super light bottom end and see the difference (I know I'm over simplifying here). I wonder if it would be a second, or less than 1/10th difference, or something in between?

 

[4piknup]

It is twice as effective to lower rotating weight to non rotating weight. Ie 3kg less weight in rims is similar to removing 6kg of trim.
There is a rule of thumb that I cant quite remember. Its something like 2lb of rotating weight frees up 1hp and 4lb of non rotating frees up 1hp. Not quite sure on the ratio.
So a 1/4 mile calculator will work it out for you

 

[Rockabilly]

Your gear ratio & tyre size is what determines your rolling speed vs revs.
How quick you can reach your shift revs for each gear change is your PB 1/4 times.
A knife edged stroker crank would give you more torque & quicker redlines.
A std throw 6 bolt crank knife edged is 14kg. A std 7 bolt crank is 14kg.
I know a fella that preps cranks for rails etc & I've seen many knife edged cranks
there with 25mm dia molly steel inserted into the counterweights to add back the
counterweight throw force. Definately the lighter the rods & piston weights the better.
Cheers

 

[LumpyVR4]

Using 1/4 mile calculators the weight reduction only drops the time by .03 -.04 secs. I guess it's more that with lightened internals you can rev 10000+ and the forces imposed on the parts are a lot less so they won't self distruct. Plus the best parts are rated to 1000hp+. Shame a 1000hp engine isn't practical for a daily driver .

 

[DOUGMO]

one of my big things was lighter internals and rotating parts on the engine, even lighter rockers

it definitely improves throttle response by a noticeable margin, like a lighter flywheel does

 

[croket]

I've got lightened fly and the improvement in response was huge , not sure id like it to be anymore responsive. It's got eagle rods and wiseco forgies . I even toyed with the idea of putting standard fly back on to get a more torquey feel to it

 

[MDK87]

I'm no expert but armed with my basic physics knowledge :lol: my 2c is, it should increase peak torque (all else being equal) as the heavier internals carry a larger momentum, some of the cylinder pressure in the power stroke is shedded in overcoming the inertia of these heavy items.
Although I agree with your second point, lighter internals will have less inertial force at TDC and the boost pressure will have a more effective impact on the lighter components in acting as a sort of mild cushion/damper as it reaches 0deg.
This should result in faster throttle response and perhaps a shifted power band.

Idk if any of that is true in practice but Aldo will set it straight if it isn't

After doing more reading I realize I have asked the wrong question. Lighter internals won't increase the peak power generated by the engine, but does allow the engine to accellerate faster (same bang pushing on less bottom end weight). It would be interesting though to take a car and run it down the 1/4 with a stock bottom end, then swap that out for a super light bottom end and see the difference (I know I'm over simplifying here). I wonder if it would be a second, or less than 1/10th difference, or something in between?

 

[trq-str]

The more you lighten the rotating assembly the more your engine will start to feel like a sporty motorcycle engine. You will notice the reduction in inertia with increased throttle response and a faster revving engine since the rate of change in velocity has increased. The disadvantage is that you may need to be on the throttle more of the time when cruising.

 

[4piknup]

Gp starts at the lights too

 

[Rockabilly]

I'm no expert but armed with my basic physics knowledge :lol: my 2c is, it should increase peak torque (all else being equal) as the heavier internals carry a larger momentum, some of the cylinder pressure in the power stroke is shedded in overcoming the inertia of these heavy items.
Although I agree with your second point, lighter internals will have less inertial force at TDC and the boost pressure will have a more effective impact on the lighter components in acting as a sort of mild cushion/damper as it reaches 0deg.
This should result in faster throttle response and perhaps a shifted power band.

Idk if any of that is true in practice but Aldo will set it straight if it isn't