JBP

Still looking for a car to test it on...

JBP

Product Released! Details are here: http://www.jbodyperformance.com/new/...catName=JP0710

-md- HHR

I beleive the L61 and LE5 are the same....I have been developing a crank for awhile now. I should have a working prototype soon...month or so.

Good luck with your endeavor.

HPVOHHR

I'm interested to see the impact that a lightened (and not underdriven) pulley has on engine performance.

As JoeR mentioned, the difference in rotational inertia of this pulley vs. the stock one, as compared to the entire drivetrain... is pretty much inconsequential.

So, expecting any increase in power due to the mass savings alone is not a safe bet.

The power increases you see with most performance pulley changes is due largely to the underdrive aspect of the pulley. The smaller crank pulley diameter requires less torque to drive the accesories with the caveat that the accessories also turn at a slower speed. In some cases the reduction in accessory speed can be done a small amount, with no adverse affects, and nets a small increase in the amount of the engine's available power to the wheels. The pulley size is the key...

So, if this new pulley is just lighter... I doubt it's going to have any noticeable performance impact.

Regardless, I'm looking forward to the results.

D

-md- HHR

I only make lighter stock diameter pulleys no under driven here.
Does it require more force to move a 20 or 25 lb wieght? The 25 of coarse, than why wouldn't a lighter pulley require less force to move it.

The pulley cuts down on the rotational mass on the engine, and are not "Inconsequential," you will tell a difference in the revs. The engine will rev faster, easier, and free up HP.
This is my before and after dynos from my LD9 2.4l cav with lightweight stock diameter crank and alternator pulley. The only thing changed was the alternator and crank pulley. This was done for my Bachelors in mechanical engineering degree at Cleveland State. No idea why the pics are poopy.
I made 7-8 more HP across the whole RPM range.

HPVOHHR

I agree, it does require more power to accelerate the additional mass of a heavier pulley as compared to a lighter one. Obviously, the location of the mass reduced from the pulley also matters significantly.

The best candidate components for improving engine performance in this manner are those with large diameters since the rotational inertia increases exponentially with radius. This is why lightweight flywheels are such good candidates for this type of improvement.

The point that both Joe R and myself were making was that the relative difference in rotational inertia of the two pulleys is very small as compared to the total rotational inertia of the entire drivetrain:
- engine reciprocating assembly
- flywheel
- transmission components
- halfshafts
- wheels, tires etc.

Note that most lightweight flywheels don't even result in double-digit increases in power... and their geometry is much better suited to having a sizable impact than a crank pulley.



I have a matlab script that I wrote for a master's course in vehicle dynamics at Purdue... it would be very well-suited to this question. The script computes the theoretical acceleration performance of a given vehicle and, among other things, takes into consideration the rotational inertia of the drivetrain. It would be quite easy to compare the relative performance difference between two theoretical vehicles, making a slight reduction in the drivetrain rotational inertia (equivalent to the savings that would result from this particular crank pulley) and to compare performance results. I'll go dig up the script and see what it churns out.


Regardless of all the discussion presented here, it will be neat to see the actual results of this particular performance modification. There's no doubt it will make some kind of difference... the only question is whether it will be measurable enough to be a realistic improvement.

D

-md- HHR

I have all the stock and after market weights if you like. You being a mechanical engineer should understand how rotational mass effects acceleration. After everything reaches a constant RPM, well that is another story.

HPVOHHR

I just realized something about the CAD model shown on pg1.

The CAD model shown looks like the pulley used on the Solstice/Sky LNF, which has an integrated smaller pulley for the Power Steering Pump. I believe the GM p/n for this particular crank balancer/pulley asm is: 12585233


However, the HHR SS does not have power steering and, therefore, does not need a pulley with the integrated smaller pulley to drive the corresponding pump.

Based on this, the LNF in the HHR SS application should use something more like the stock crank balancer/pulley (LE5, L61), without the integrated smaller pulley for the p/s pump. So, correct GM p/n should be: 90537704


For the JBP guys:
Is the picture you have shown just one you already had for the Solstice/Sky LNF's? If it is just the Solstice/Sky-specific picture, is the HHR SS version that you've created actually different than shown, without the smaller pulley? (like the LE5, L61)

JBP

The pulley is for the LNF in the solstice/sky, but the part number should cross to the delta platform as well in the future. The HHR-SS might have the pwr str pulley there, just w/o a belt if it uses the electronic assist steering.

HPVOHHR

The Solstice/Sky pulley likely also fits but the added mass of the integrated small p/s pump pulley (which woulldn't be used in the HHR's case) is a bit of a waste... especially when the entire point is to reduce the mass as much as possible.

Sorry, I'm not intending to be a pain... just investigating the details

JBP guys, how much does the new JBP pulley weigh?

-md- HHR, how much did your stock pulley weigh?