Unsprung weight reductions/benefits

rhjames · rhjames's Garage

For Mule's benefit:

I went back to my posts about nineteen inch wheels/tires and their weight reductions from the stock 16 inchers our 928's came with. This post was last added to on April 9, 2007. I had to go back that far.....

I DID NOT, however, find the discussion where the formula was originally presented to me (in another discussion), as it was too old. Unfortunately, I CANNOT credit where this formula came from, I can only say it was presented to me by another Pelican......

There is Algebra involved in these calculations, so Mule and Sniper may be a little challenged in their understanding of the results that I present......Please be patient with them-----Mule will no doubt try his best to debunk this theory, but it's his shot.....I have no problem with my presentation, as he did with his...... Please read the whole post, not just the parts you like or dislike.

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What was in the discussion about the nineteens was this:

When calculating performance gains with regard to unsprung weight reduction, the following formula is used:

For every 20 lbs of weight reduction, you may apply a "theoretical" gain of 17 horsepower.

In other words, it is a .85:1 ratio, horsepower gain to pounds lost.

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By using this formula, I have calculated that my 44 lbs unsprung weight reduction resulted in a "theoretical" increase of 37.4 horsepower.

My Euro is rated at 229hp, so by applying the above theory you could say I now have a horsepower of 266. (You can apply this to any 928 using the parameters I have laid out in this discussion.)

I could also invoke the theory of static weight reduction (as presented by Sniper--he is dead on correct about the benefits of this), which says there is an (1.4 mile drag racing) ET reduction of 1/10 second for every 100 lbs weight reduction. (I have proven this theory correct in my many drag racing days with cars that I campaigned).

However, when you use unsprung weight reduction, the ET reduction is more significant. I do not have that formula at this time, but I seem to remember an ET cut of nearly 1.5 seconds off the factory listing. Again, this is just off the top of my head and one should not take this as fact at this time....

NOW------ SO EVERYBODY INCLUDING MULE, SNIPER AND OTHERS UNDERSTAND, A DYNO TEST WILL NOT/MAY NOT SHOW THIS GAIN. I CANNOT VERIFY THAT IT WILL, OR NOT.

ADDITIONALLY:

I WAS INCORRECT ABOUT A 33% GAIN IN MY EARLIER POSTS REGARDING WEIGHT REDUCTION AND UNSPRUNG WEIGHT REDUCTION. (Yes, I do admit my mistakes, unlike others on this forum......)

USING THE ABOVE FORMULA, IT IS ACTUALLY CLOSER TO (THEORETICAL) 16% HP GAIN.

I am being very specific about this, that I have not verified this theory at this time of posting, and I make no claims to it's validity.

If there is someone out there that is familiar with this theory, and can provide further information as to it's validity, please speak up.

You are free to dismiss this as junk or what ever you like.

Again, I make NO claims to it's validity as factual, proven theory.

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WHAT EVERY 928 SHOULD HAVE ON ITS REAR--------

Danglerb · 06-03-2007, 11:27 PM

Mule · 04:26 AM

You can copy & paste the encyclopedia Britanica & you will still look like a fool for your 33% performance increase statement. Did you check into Formula 1 & Indy car tire aspect ratios yet. Once they find out your performance secret lap times should plummet. So now it's 16% but it doesn't show up anywhere. This is great. Did you call Ferrari yet?

I'm waiting for the next post "Tires filled with helium nets 5% hp gain but it doesn't show up anywhere."

Dangler, If they put some lightweight SKINNY tires et's should drop right?

Red Baron · 06-04-2007, 04:23 AM

Quit hitting these guys with the frisbee, Mule.

Mule · 06-04-2007, 05:36 AM

I can't wait for the next post.

Bicycle tires & helium yields ultimate performance advantage.

That and the "police interceptor" badge.

I'm not worried about hamster abuse but buffoon abuse is starting to concern me.

Red Baron · 06-04-2007, 06:04 AM

Quote:

Originally posted by rhjames

WHAT EVERY 928 SHOULD HAVE ON ITS REAR--------

[/B]

I have some 5.0 emblems I can mail you to match....

Now I understand where your coming from, rh.

Danglerb · 06-04-2007, 11:45 AM

Quote:

Originally posted by Mule
You can copy & paste the encyclopedia Britanica & you will still look like a fool for your 33% performance increase statement. Did you check into Formula 1 & Indy car tire aspect ratios yet. Once they find out your performance secret lap times should plummet. So now it's 16% but it doesn't show up anywhere. This is great. Did you call Ferrari yet?

I'm waiting for the next post "Tires filled with helium nets 5% hp gain but it doesn't show up anywhere."

Dangler, If they put some lightweight SKINNY tires et's should drop right?

My next post should be Mule filled with #### should go play with his dog, but once more into the breach ...

Its the MASS not the WEIGHT that makes a difference, so He in tires won't do much. If saying weight is confusing you I can stop, but it works fine in reasonable examples to just say weight.

Lighter weight skinnys did show a gain at the track in the second link, which was full of wt savings you might try.

I doubt an indy car has tires and wheels that weigh more than a few ounces above the absolute minimum possible. Rim discussion here is completely different since we are starting with in many cases fairly heavy wheels designed to look nice on a street car, not minimum weight wheels for racing. RH found some street wheels in 19" that weighed less than his previous smaller diameter wheels, which has nothing to do with what might be the optimal wheel weighing even less in a smaller diameter, improvement is improvement.

This isn't real difficult math, you shouldn't be that afraid of it, just look at the energy it takes to spin a wheel up to the trap speed in the 1/4 and subtract that from the RWHP to see the differences. You only see half the effect on a dyno since its just two wheels, seems to be easy to measure at the track.

rhjames · rhjames's Garage

Regardless of where "anyone" is coming from, Mules are ASSes and he just takes pleasure in making statements that he won't admit were wrong, and then admits he was wrong, and then backs up and says I didn't know an damn thing about what he was talking about.

No wonder he uses the name "Mule".

There's an ASS in every assumption------he has proved himself to be the ASS in everyone of his childish rants.

Reminds me of a politician that flips and flops every time he opens his mouth....

He's busting on me for the 33% figure, but if he had read this post, which it is obvious he has not, I admitted my mistake and corrected it. He has not admitted his, but did admit I was correct in my rebuttal. And like a politician, he has now gone down the route of "Well, everyone knew I was talking about peak horsepower. And everyone knew I was talking about 'at idle'."

To answer my last question to him:

"Who wrote the theory of atmospheres versus horsepower gains?" to which Mule answered, "God".

Close, but no cigar. It was either Pascal or Boyle, I personally can't remember which, but at least I can name one of two possibilities......

At this point:

Who cares?

No wonder he got banned from Rennlist------again.

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Mule · 06-04-2007, 12:48 PM

This is great.
Dangler says"Lighter weight skinnys did show a gain at the track in the second link"

True. The underpowered Mazda (I think) went faster when it didn't have more tire than it could pull. Stunner.

Then comes Buster:
"He's busting on me for the 33% figure, but if he had read this post, which it is obvious he has not, I admitted my mistake and corrected it."

Yeah, you changed your claim from saying that your tire & wheel change would only result in 11.70 ets in stead of your original claim of 9.20s. Great.

Then:
""Who wrote the theory of atmospheres versus horsepower gains?" to which Mule answered, "God".

Close, but no cigar. It was either Pascal or Boyle"

Yeah, I think it was "Big Tony Boyle," the mob guy.

I hate to break it to you but it's not a theory but general knowledge among "knowledgeable" people in this field, and the dog, and the hamster, but apparently not you!
Dog & hamster 1 Buster 0

Danglerb · 06-04-2007, 01:36 PM

Does kind of make me wonder what a set of really light wheels with drag slicks might be good for in the 1/4, compared to factory slots and street tires.

rhjames · rhjames's Garage

Danglerb-----

first thing is the 928 suspension probably won't hook up on a drag strip (it's the wrong design). I base this on my own 928, with a broke motor and the 315X19's I have on the rear.

Try to launch it at 5500 (or more) and you get nothing but wheelspin.......at 4500 you tire hop......less than that and it just bogs off the line. With a good set of slicks, properly heated and on a good track, the results would be poor at best.

There are plenty of videos of 928s doing burnouts on the web, but are any of them using slicks? (I do not know?) Even Mark Robinson was using street tires on his turbo-selling videos.

for drag racing, you would want a soft/thin sidewall and a tire height that will maximize the fenderwell volume (put the tallest tire you can in the fenderwell). For example, on a Camaro with unmodified fenderwells, that might mean a 26 inch tire height, with tubs it might mean a 32 inch height----you can see where this goes. I know of one 928, that's tubbed and runs a narrowed 9 inch Ford rear, and he runs a set of 14x32x16 W's for an overall width of 16 inches each---the outside fenders are uncut.

Wheel offsets, suspension pieces, body parts, etc., all limit tire width and height.

Wheel diameter is not that critical, as most drag racing wheels are 15's, however the serious ET cars and Pro cars are running 16's. Tire sidewall is critical, as you want the sidewall to wrinkle, allowing the tire to "plant" itself under acceleration.

Mickey Thompson and BFG make DOT legal drag tires, as well as other manufacturers.

for 928's with stock suspension, unmodified body work, and street tires, you can go with the same 19x11 w/315x25x19 set up I have on mine. This is the max for the non-wide body 928, without body modifications.

you don't find a set of street slicks in these sizes (19"), so you will need to drop back to a 16 inch wheel, probably 10 to 11 inches wide with et 65mm offset, and then run a 26 inch tall by 10 inch wide tire. This will probably require modular wheels costing ?$$$?. That's probably the max you can go with out a sledge hammer and a flaming hacksaw.

A cheaper route to go may be a 16X9 off of a 928 GT (or GTS maybe?) and then select a tire that fits your fenderwells. A 10.5X26X16 tire comes to mind if that size is available.

One further note on tire sizes:

There are plenty of 10.5 (slick width) cars out there running in the low 8's in the 1/4 mile--some even faster than that......I personally wouldn't drive one of these, even though I have driven super comp door cars/dragsters running the same ET's for years. These 10.5 cars are horribly unstable on the top end, and are subject to violent lane swapping at a 10th of a seconds notice. Several years ago, I had a door car upside down because of a broken front strut. The car carried the front tires (in the air) through the 60 foot timers, finally settled down and took an immediate right hand turn. Rolled 8 times before I hit the 100ft mark......That's something I never want to experience again-

I could also mention that the rear suspension on the 928 probably won't handle a good set of hot slicks, tearing the suspension from the body pan.......then there are axle/trans/torquetube breakage issues as well......just a thought.

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Mule · 06-05-2007, 08:27 AM

Here we go again. So 3000lbs Mustangs have been 6.66 at 216 mph on a 10.5w x 33. Supras have been 7.80 on drag radials. Top fuel dragsters have been 4.42 on tires that are 17 x 36. All three of these facts have about equal relevance to improving the performance of our 928's.

I don't think anybody out here is expecting to go 8's. Admittedly that would require a lot of work. Can a streetable 928 go deep into the elevens without "ripping the suspension from the body pan"? Sure, Mark has gone legitimate 12.20's with no lsd. Lsd and some practice, that car is well into the 11's on drag radials in spite of the decree from on high that:

"Try to launch it at 5500 (or more) and you get nothing but wheelspin.......at 4500 you tire hop......less than that and it just bogs off the line. With a good set of slicks, properly heated and on a good track, the results would be poor at best."

Only a moron (or a crash test dummy) would try to launch a 928 at 5500.

m21sniper · 10:10 AM

My 928S launches like it's fired out of a gun at the drag-strip.

The A/T's are MUCH better at this then the 5speeds, which are known to suffer from fairly severe wheelhop. A/T's are much better 'drag' cars as a result. (though the 2.20 rear end in most of our cars is by no means ideal.)

The 'general rule' of unsprung weight reductions/HP gains is 1hp per 2lbs unsprung of weight reduction.

Danglerb · 06-05-2007, 12:16 PM

Part of one of my friends spring time upgrades is having his torque converter reworked to a 2800 rpm stall with a two stage wet No2 100/250 system.

Another guy just joined the hybrid forum, putting a 383 LT1 motor with 8.5:1 internals and 15 lbs of boost from a procharger into an 89 S4 AT.

Or this one, but no telling whats been done.
http://video.google.com/videoplay?docid=-4290736609266117534&q=928+drag

m21sniper · 06-07-2007, 01:10 PM

Both of those are going to haul ass. Muwahahahaha.

I launch mine at 2400rpm and 22psi at the track with brand new tires on a hot day. I run the rears at about 30psi on the street, and launch at about 2000rpm. The extra 400 Rs and reduced tire pressure is worth about .2 diff on a timeslip it seems.

rhjames · rhjames's Garage

actually, .85 hp to 1 pound unsprung weight removed......

not to put tooo fine a point on it-

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Mule · 06:46 AM

Sniper, get rh to explain how 5500 rpm launches are the quick way home. Let's see, if 400 rpms dropped .2 off the 60 ft, my spreadsheet says 3500 would drop 1.75 seconds. Is that right rh?

And then if I install the bicycle tires & wheels I'll gain 92% performance and then?????

Boy is this thing gonna be fast. I'm predicting 7.50 with the stock motor.

m21sniper · 06-08-2007, 08:51 AM

Heheheheh.

rhjames · rhjames's Garage

Mmmm...

Danglerb knows exactly what I'm talking about, but some continue to just beat up on a minor discussion. Too bad....

it's the energy it take to get some thing rotating, in the case of unsprung weight (removal)---- and it's the energy it takes to get something moving, in the case of sprung weight (removal).

Both weight reductions are beneficial, but act differently on the car.

There are formulas to calculate each, and it's no big deal.

.85 lbs per hp gained (unsprung), 100 lbs per tenth of a second ET lost (total weight reductions).

Easy.

Will Mark throw in an LSD and a set of slicks to get some faster/hooked up numbers? I hope he will. However, with repeated use, the unmodified body structure will eventually try to destroy itself, or a suspension piece may let go, or a driveline may not be able to handle the stress, or, ---well, you get the idea.

The point is that Porsche had a design in mind, that took into account certain stress levels before breakage. When you surpass those limits with add on items, bad things can happen. (maybe not soon, but maybe later)

Any arguments about what the car handle are directly related to the design specifications of any of its parts, or the parts you plan to add on. And there are those who will argue this, just for the sake of arguing.

Let this one die quietly......please.

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m21sniper · 06-10-2007, 09:03 AM

"100lbs= .1 in ET" is just a general rule. The exact figures change as vehicle mass and power levels are adjusted.

2900lb@300hp= 1hp:9.66lbs

3300lb@300hp= 1hp:11lbs

The lighter the car, the smaller the amount of weight that's required to 'add' another HP.