NO. Not in a meaningful way. Did no one read Matthew Miller's posts?


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..... But we're not just spinning alternators , crankshafts , and flywheels ... we are moving a large lump of mass from a standing start with some added forces like wind resistance , etc . ... Will a lightened engine actually have an advantage in getting to the finish line if the power output is the same and car weight is the same ? .....

 

..... Give this man a beer ! ... I read ALL of the posts including some spin-my-head science lessons ... the engine's ability to produce work is measured by horsepower and torque ... NONE of the calculators like Wallace Racing ask if you have aluminum or iron heads or if you have a light flywheel and clutch ... its strictly based on weight vs horsepower ... My rig is set up for bracket racing where it doesn't matter who has the fastest car or the slowest car but who can take an advantage at both ends of the track to turn on the win light ... predictability and consistency are key for the car but its the driver that will win races .....

 

Energy balance around the car. Still requires the same amount of force (or energy depending on how you want to define it) to push it with the same mass. Alright now the only difference in the energy balance is the rotational (reciprocating) losses, momentum changes for direction changes for the mass of the rotating parts. I'm not gonna do the math because I don't feel like it but car weight > rotational (or reciprocating) losses I'd guess. If you could accurately launch each exactly the same each time then maybe just maybe you could measure an infinitely small difference. Real world. Probably never. That's also not accounting for the fact that as you are accelerating the car the force fighting it is increasing it making the differences even less significant. Just a guess though.

By the way, it's cool you're doing something different. If you have it at your disposal why not.

 

..... Here is a way to measure ... both cars leave at the same time ... shift at the same time ... and both cars break the driveshaft at the same time , @ 5000rpm for this experiment's sake ... then we measure the amount of time it takes for each engine to reach its rev limiter @ 7500rpm ... I'm guessing the lightened engine gets there 1st by nano seconds .....

 

Lightening what parts of the engine? And measuring power how?

For rotating mass: it requires extra power to accelerate the extra mass. But we're talking her about accelerating the engine's rpm, not necessarily the car. If you measure two engines, one with a lot more rotating mass than the other but otherwise equal, on a brake dyno (where the engine is held to a constant rpm at WOT using a variable load), they will have exactly the same power. If you measure them on an inertial dyno (where a fixed inertial mass is accelerated and the power is calculated from the rate of acceleration), then the engine with lighter rotating mass will show more power. The difference in power with the inertial dyno will depend on the load: the greater the load the engine has to accelerate, the less difference in power there will be, because the rotating is a smaller proportion of the total load. As previously stated, though, the mass can actually be saved in a crankshaft or the big end of rods will be so minor that it can't realistically have a measurable effect on an engine's ability to accelerate a real-world mass. Flywheels are a different story, however, and that's why it's important to standardize inertial chassis dyno runs to 4th gear - lower gears would show less power.

For reciprocating mass: theoretically the greater the reciprocating mass (heavier rods in this case), the more power that is soaked up at all rpms, whether the engine is at a static rpm or increasing speed. This is because the engine has to accelerate the reciprocating mass twice for each crankshaft revolution (or once, if we're talking about valvetrain mass). The power that reciprocating mass absorbs should increase as the square of the speed (rpm). However, since we're talking about saving grams of reciprocating mass, and each cylinder is making hundreds of pounds of pressure for every firing cycle, I am sure there is no measurable difference in power output. That's not the point of using lightweight reciprocating parts.

In short, reducing crankshaft mass or rod mass isn't going to make any measurable difference in your trap speeds or any other measure of vehicle performance.

 

The lighter parts are simply to help keep the bearings from getting beaten to death right?

As for free reving after a driveshaft breaks, now the only forces countering the engines ability to increase rpms is it's own internal forces. At that point, the one with the lighter flywheel and other parts gets there first since now the difference between the two becomes significant.

 

I just copied a small clip from Reher Morrison racing engines, lighter rods and cranks will show a small power increase in real world racing situations but it is not huge. That being said if the someone wants to use a lighter rotating assembly I see nothing wrong with that.

The article is referencing alum but the point is less mass has the potential to make some additional power.

 

Right. The bearings, piston pins, etc. all sustain much lower forces with lighter weight rods, and/or the engine can be safely revved higher which potentially allows more power to be produced.

Two things to keep in mind. First, on any hard-core racing app, and especially the kinds of things Reher and Morrison do (they are known for Pro Stock racing), there is very minimal flywheel/clutch mass. In those extreme cases (which would not be usable on the street at all), rotating and reciprocating mass of internal parts could be bigger proportion of total load...but still really small. Second, they are talking about big-block designs of 500cid or way more, where steel rods really could weigh 900g, vs 600g or less for aluminum or titanium. If one can really save a total of 5.3lb of reciprocating mass (300g x 8 cylinders), and then revving that engine to 10,000rpm like they do, then I imagine there are measurable gains in power to be had. Again, that's a very extreme case. In a more real-world case, where maybe we save a total of 1.5lb of mass by going from good steel rods to Ti, and revving to maybe 7k, on a small-block stroker motor, we're going to have trouble measuring a power difference. But we would see differences in bearing and pin wear.

 

Remember back in the 1990's when Underdrive pulleys were one of the standard mods... If I remember correctly - Hot Rod mag did some testing and found that while the difference was typically very small - a set of underdrive pulleys would in fact make a car run faster in the quarter. If slowing down the water pump, power steering pump and alternator made a measurable difference in the quarter mile - I think reducing the amount of rotating mass that has to be spun up will also make a difference - probably a bigger one. I won't even attempt to argue that it will be major - almost unquestionably less than 0.1 sec - but trap speed is a much more reliable measure of a car's HP, and I expect it would be measurable there.

Remember for a 3,000ish Lb car - making around 300 HP - a 10 HP increase is worth 0.1 sec. Same thing with a 100 Lb weight reduction - roughly 0.1 sec decrease...

But - as they say on TV .. opinions will vary ...

 

I bet the Frisbee makes a bigger diff.

 

..... You are correct ... If you put a 3000# car on a diet and lose 100# it will (should) be faster at 2900# than it was when it just had a nice personality ... the crux is that using lighter engine and drivetrain components will not necessarily produce an increase in power but it definitely reduces the amount of mass that needs to be motivated ... and it reduces the amount of stress on some corresponding pieces and parts ... there is a point though where durability potentially becomes an issue .....

 

Mods are accumulative but need to be complimentary to be effective. There are race team/engine builders that will drill equalizing holes in the crankshaft main saddles/webs just to better equalize the pressure from blow-by below the piston and assist in crankcase evacuation. How much power do you think that makes? I'm guessing it's hardly measurable but if it makes more power some will use it.
Complimentary as larger heavier slicks may need more horsepower but if you need them to hook you will go faster adding that weight. Or you can remove/shorten your intake ducting - less restriction and less weight - but if the air cleaner/engine sucks hot engine compartment air your gonna slow down.

But my question is how much science can you take before it's no longer fun? IMHO if my local machine shop can't do it it ain't gonna be any fun to do it.

Oops. I thought those Crower Ti sbc rods were $750 a set. $6000 would be very hard to justify for millionaires.

 

Chevy put em in there cause they had a 500 hp. car with a warranty they knew would be tracked. Anything you can do to cut down on reciprocating weight will be more forgiving of revs. Rods, pistons, pins, valves and something no one seems to consider lifters. Roller lifters are heavy. I think this is a neat build given the opportunity to utilize these rods.

 

..... The part that blows my mind is that Chevy used Cast Hypereutectic Aluminum pistons in the LS7 on the ends of Titanium connecting rods ?!?!? .....

 

Whats to break em? Pistons break from wrong fuel/air or ign. issues. Hyper pistons are installed with less clearance, they are quiet, strong, durable and not too heavy. With modern computer control, knock sensors ect. Pistons dont break from going up and down. Forged pistons are a crutch for other issues.

 

..... RPM ... LS7 has a 7,000rpm factory redline .....

 

So?

 

..... I will continue to use crutches ... like forged pistons .....

 

My understanding is that they used a hypereutectic piston for the same reason they used the titanium rods. Lower weight reciprocating mass in order to not overcome the film strength of the oil on the preferred mobil 1 5w30. From a reasoning standpoint it seems a bit backwards but that's what I've read.