Charlie:

Back to the rear.  I have heard somewhere that the rear cover type rear ends, without the extra pinion pilot bearing, and with different pinion location in relation to the ring gear, have less parasitic drag.  I always figured Ford went to the 7.5 and 8.8 rear ends because they may be cheaper to manufacture, but just maybe they did it to help the corporate fuel mileage to meet government standards.  If this is true, a little less drag in the rear gears could mean 8 or 10 mph more speed, give or take.  Maybe someone here can guide us to a place that compares the two.

John - "The Hoosier Hurricane"

I think John is going the right way with this - in the last year or so I think I saw a series of chassis dyno tests - run with a variety of different differentials. The Ford nine inch was the highest parasitic drag - and the explanation (according to the article) was that it had the greatest centerline offset of the pinion. I believe they had a GM twelve bolt in there and a big Dana too.

Can't remember which was best but it bears looking into - if there is a mechanical advantage to be had, maybe better use it the first time around.  

As an "add-on" .....the article was in Car Craft and they used a chebbie for the sacrificial power source:

http://www.carcraft.com/techarticles/ccrp_0806_chevy_chevelle_rear_axle_swap/index.html

Worthy of mention - for a top speed car - at the end of the article they discuss the use of a "Mikronite or REM process" that has shown an improvement in parasitic loss (+6 hp) and listed a price for coating the ring and pinion at about $275 - and I'm sure this number is old.

 
 Steve Metzger       Tucson, Arizona

This is the Mikronite site I found - interesting stuff.......

http://mikronite.com/documents/dragsterMag.pdf

http://remsuperfinish.com/rem/rem_benefits.html

Creeping into my head......Do you suppose this would work on automatic transmission parts too?

 
 Steve Metzger       Tucson, Arizona

Ok -So we're not really working hard at our regular engineering jobs today.....so the "boys" are checking up on the articles / tests / tech info, etc. for the rear ends. Here's another one to look at with a Ford 8.8:

http://www.carcraft.com/techfaq/116_0701_mikronite_surface_treatment/results.html

Results of our "study" so far......

(1) Yes   The Ford 9 inch appears to have a slightly lower efficiency - and the difference appears to widen as the rev's increase. The greater hypoid offset is thought to be the culprit (but I didn't locate any textbook engineering reference data that backs that supposition). Doesn't mean there isn't something somewhere - but I haven't stumbled over it. The reduced efficiency is a very small amount - and it could be negated by the micro-polishing processes mentioned in the magazine articles.

(2) Yes    The "micro-polishing" of the ring and pinion has shown an advantage in improving gear efficiency (by a small amount percentage-wise) - several automotive tests have shown similar results. Of the two mentioned processes - Mikronite and REM - neither shows an advantage over the other for performance. One abrades and smooths the surface with contact pressure - one uses ceramic powder and chemical etch - both end up at the same place, a very smooth silky surface - and still true to the engineered geometry (mating curves remain). REM seems to have a clear price advantage over Mikronite - and also is mentioned by more than a few NASCAR users of this technology.

(3) From a racing standpoint - the second benefit of the micro-polishing is a reduction in surface fatigue from contact loading of the "rough" (ground) finish the parts start out with. Rough is a relative term here - the ground finish of most ring and pinion sets is by machine tooling standards, very good. The NASCAR references hit this feature as hard or harder than the friction reduction. In short terms - it provides a surface that is already "broken in" - polished - without losing the proper contact surface shape through wear.

We think....use the 9 inch (its a Ford part and the punkins are handy at the track)......and find a good source of getting your choice of ring and pinion sets polished by REM.   

 
 Steve Metzger       Tucson, Arizona

I was doing a little tounge-in-cheek about the 8-10 mph gain with a different rear, rather I was inferring that with a small engine trying to push a brick through the air, any little help is a plus.  I certainly don't deny that the 9 inch is, pound for pound, the best production rear end I've seen.

John - "The Hoosier Hurricane"

Y-Guys:        While we are on this subject,of trying to utilize every small tidbit

             of help, using a thin(75 wt) synthetic gear lube as well as synthetic

             wheel bearing grease should offer some small friction losses to help

             those small "pony's" in that 258" Y-Block......

                                                     Maybe 1 or 2 mph

                                                             Bill

     

Bill

Pelham,Al

I’ll add to what John and Steve have brought up regarding rear end drag.

 

The lowered pinion offset on the 9” Ford rear gears allows the teeth on the pinion to have more contact or surface area which is where much of the strength for the 9” is derived from.  Unfortunately that increase in surface area is also a detriment as far as drag goes.  If not concerned about the overall life expectancy of the rear, then there are several other rearends out there that will reduce the friction and in turn allow more of the engines horsepower to be delivered to the rear tires.  For the 9” housing, both Mark Williams and Strange Engineering have offered unique ring and pinion sets with a specialized gear housing that raises the pinion back up and frees up some of the hosepower that's lost in using the standard design 9” ring and pinions.  These specialized ring and pinion sets do have have some horsepower limitations but are used in those cases where getting just a bit more power to the rear wheels makes the difference between running like everyone else or being just a tad quicker (or faster).

 

For the 9", there are also some low drag pinion bearing supports that are also of benefit in reducing rear end drag.  I have one of these in my roadster and essentially it does away with the tapered bearings and the crush sleeve or bearing spacer and instead uses a stack of roller bearings without a crush sleeve.  With the pinion nut tightened in excess of 200 ft/lbs, the pinion still rotates freely with this setup.

Lorena, Texas (South of Waco)

I seem to remember some early racers talking about "Chromed" rear ends. Did they chrome the ring and pinion for less drag? Chuck in NH

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

Chuck.  I believe they were referring to the housings being chromed.  I had a chromed housing in the roadster when I originally built it but hard launches warped it to the point it was difficult to get the axles out.  What I have now is a very heavily braced powder coated rear end housing.

Lorena, Texas (South of Waco)

No actually it was in reference to the rear end itself. I've seen plenty of chrome housings. Maybe I'm thinking of some hardening process. CRS! Makes it difficult. Chuck in NH

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire