RAGEman

iTrader: (4)

How much do you guys think my 9" rear with 4.56 gears is affecting my dyno numbers when compared with the old 10-bolt and 3.42's?

I know this topic has been done to death, but I've heard so many different things over the years, I thought I'd post and see if I can get sort of a synopsis of opinions/guesstimations/insights here. I am curious because my trap speeds at the track don't seem to have suffered much, if any.

Another question I have that's kinda related: what difference, if any, would a 12-bolt (let's say a Moser for reference) make over a 9" (also Moser) of the same gear ratio? Some people are certain that gear ratios don't affect dyno numbers either way, but others swear that the taller gear ratios rob horsepower (at least as it is measured on the dyno).

THANKS FOR ANYTHING YOU CAN ADD TO THE DISCUSSION!

Cheers! <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

Fly By

If my memory serves me correctly, Shane, extracajunss(?) Lost some 20+ HP on his 9" swap with his 409 solid roller. I want to say his new dyno #s were high 400s, or 500 even.

Id have to say that the 9" saps more power, due to the size. <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

Fenris Ulf

Hey Alan, another thing to keep in mind is the average torque applied (which translates to acceleration and trap speed) with 4.56s is higher and will offset the drivetrain losses.

bigSS

Why do ya ask? <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

I'd say that a 9" with 4.56s is showing a 20+ rwhp loss over a 10bolt with 3.42s on the dyno. Maybe even 25 or more.

<small>[ March 01, 2003, 10:58 AM: Message edited by: bigSS ]</small>

bigSS

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Fenris Ulf:
<strong> Hey Alan, another thing to keep in mind is the average torque applied (which translates to acceleration and trap speed) with 4.56s is higher and will offset the drivetrain losses. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Fenris - Although what your saying seems to makes sense when I think about it, i've heard the opposite is true.

AMS

I have dynoed back to back with a 9inch....10-bolt with 3.73's vs 9 inch with 3.89.....3 rwhp differance! Also had another local guy dyno from 10bolt/3.73 -> 9 inch/3.89...and he also saw a 3 hp differance SAE. Hope this helps

Chris

35th SS

iTrader: (2)

curious about this too.had the 10bolt with 3.42 before and now have the 9inch now.will dyno soon.will post result here. <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />

The Juggernaut

iTrader: (7)

I would guess 15rwhp loss.

9" is a little harder to turn.
It will not be a 1:1 RATIO,so it will be more
like dynoing in 3rd gear.(for example)

Just dyno before(at least 3 pulls)
then dyno after (at least 3 pulls)
then do the averages to see true gain.

Don't care about the #'s,care about the gain. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

WMSuperSport

iTrader: (23)

Every experienced tech has told me that there is virtually no loss of HP on the dyno, like Chris said.

Fly By

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by AMS:
<strong> I have dynoed back to back with a 9inch....10-bolt with 3.73's vs 9 inch with 3.89.....3 rwhp differance! Also had another local guy dyno from 10bolt/3.73 -> 9 inch/3.89...and he also saw a 3 hp differance SAE. Hope this helps

Chris </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Right, and in the LG thread, you mentioned how bad *** your 452 RWHP seemed, cause it had a 9", and it would have made the same as the LG car IF It had a 10 bolt. Whats up with that? <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />

2MCHPWR

iTrader: (10)

see my B1 thread, but i made 387.5 hp/370 TQ with 10 bolt and 4.10's. no other changes except switching to a moser 12 bolt with 4.10's.
384 hp and 365 TQ. so i lost 3.5 hp and 5 TQ.

LG Motorsports

Now for some facts.

A 10 bolt and a 12 bolt have, as their only difference, the diameter of the ring gear. ie; a 7.5" vs an 8.5". The entry of the pinion and it's relationship to the ring gear is the same. The tooth camber and curvature are very similar, and will only differ in their contact pattern and friction equal to the ratio of the size of the gears. That means that the increase in friction surface is 12%. Keep in mind that that doesn't mean that the hp loss is 12%, it means that the friction is increased by 12%. and that plus the energy needed to spin a 12% larger ring gear computes to 1% less rwhp, (4 rwhp on a 400rwhp car) give or take.

Now take a 9" rearend. It has the the ring gear increased from 7.5" to 9" which increases the friction surface to 17%. that alone would account for a 5.6 rwhp loss over a 10 bolt rear on a 400rwhp car.

BUT the Ford 9" ring and pinion is a "Hypoid" gear. The pinion on a Hypoid differential contacts the Ring gear at the bottom of the ring gear, and the gears/teeth of the pinion are extremely long, and curved. The pinion on a 9 " rear stays in contact with the ring gear over 2 times as long. That increases the friction by a factor of more than 2.5 times. So if all things were equal, and the rear ends were equally set up, the 9" should be 14rwhp less on a 400rwhp car, than a 10 bolt.

All the above assume that the gear ratios on all 3 are the same. If you increase the tooth count, by going to a shorter gear ( higher numerical ie 3.42 to a 4.11) the losses will be greater due to increased friction.

These numbers are all aproximate but they are very close to what really happens.


Later,

Lou Gigliotti LG Motorsports

John B

iTrader: (10)

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">A 10 bolt and a 12 bolt have, as their only difference, the diameter of the ring gear. ie; a 7.5" vs an 8.5". </font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Just because I know you're picky Lou I wanted to correct your typo.....a 12 bolt has an 8.875" ring gear <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

Pro Stock John

iTrader: (34)

Cool info, I have heard 10rwhp or a bit more so it's similar to what LGM is saying... I did 472rwhp thru my 9" and on slicks, so that sounds about right.

Fireball

iTrader: (21)

this makes me wonder too...

I've pulled 444 RWHP thru my 9"/4.71 gear combo with my lil h/c setup...

almost tempted to put 10bolt/3.42 combo in to see what it'll do <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />


NOT <img border="0" alt="[evil]" title="" src="graemlins/gr_devil.gif" />

Fenris Ulf

The topic is misleading without giving the spline number and posi/spool specification...

Those two factors will greatly affect the reciprocating mass and thus the dyno numbers.

RAGEman

iTrader: (4)

That's true, and really the only way to know for sure would be to actually do several back-to-back pulls. Even with 31-spline axles and a spool, the 9" is still far heavier than the 10-bolt, not to mention the position of the pinion relative to the ring, and the taller gears.

LS1LT1

iTrader: (16)

And what about the actual weight of each?
We generally know that the 10 bolt weighs the least but is the 12 bolt 'always' lighter than the 9 inch or are there ways to outfit a 9 (aluminum casing etc.) to actually be lighter than the 12 bolt (or even lighter than the stock 10 bolt for that matter)?

Paul F

iTrader: (2)

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by 01-Z:
<strong>It will not be a 1:1 RATIO,so it will be more
like dynoing in 3rd gear.(for example) </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I'm confused by that statement. <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" /> How does the rearend effect your engine to transmission to rear ratio?

We found on back to back dynos with Shane's car a loss of about 20rwhp going from a 10-bolt with 3.42s to a 9" with 4.56s. The Moser 9" was set-up with a locker, 35-spline axles that were gun drilled and star flanged, and 4.56 gears.

RAGEman

iTrader: (4)

Thanks, Paul. Good info. Quite a bit different from the 3 RWHP AMS claims they saw.