Best Rear Gears For a 502

[PAYUP$UCKER]

I'm gonna be putting in a 502 Big Block straight from GM into my 71 Nova. My question was I just ordered a new ford 9 inch rear. My buddy is telling my to put in 3.73 spider gears because 4.11 will make the car to wound up. I wanted to get a few more opinions before I go ahead and do this. So 3.73 or 4.11?

[twistedtech]

I think your getting some , ahhhh , mixed terms here.3:73 ring and pinion maybe but spiders, uhh not so much.There's a whole lot more to your question that YOU need to answer before anyone can offer you anything.Alot more.What are you doing with the car,how far will you be drining it,what do you want out of the car, I could go on for about a page and a half.

[PAYUP$UCKER]

Originally Posted by twistedtech

I think your getting some , ahhhh , mixed terms here.3:73 ring and pinion maybe but spiders, uhh not so much.There's a whole lot more to your question that YOU need to answer before anyone can offer you anything.Alot more.What are you doing with the car,how far will you be drining it,what do you want out of the car, I could go on for about a page and a half.

Mainly what I'm going to be doing with the car is taking it every once in a while on weekends and having fun with it and drag race it a little. I would say I will be driving it about once a week maybe. I've already done all the other prep work which was front coil springs, 4 link subframe and now the last part the rear end.

[twistedtech]

For myself,I would be doing the tire size mathe with both gear ratios and then go from there. At 55 mph and 4:11's you going to be revin out around the 38-3900 mark.I don't think the big block needs that much gear but it would feel good down low for sure.A " nice " gear would be the 3:73.If you dont mind taking a bit of a hit try the 3:73 and if you don't like it i bet it would take long to sell that ratio,alot of guy's looking for them.Then you can kick in the 4:11.

[Blue Bowtie]

You'll need some taller gears to make up for the 5-6% driveline loss caused by the inefficiency of the Ford 9-bolt - Yes, it's been proven on the dyno. I know they are cheap and pleniful, but even Ford stopped using them years ago. There's nothing that can be done to solve it either, since it is due to the intersection point/angle of the pinion into the ring. They went too low and lost some power transmission efficiency as a result.

If you need real strength, find a 10½" GM corporate 14-bolt from a truck, and twist to your heart's content, or go with a Dana. If you don't have more than 600 ft/lb out the transmission, you probably could get by with a 12-bolt with no longevity issues. Granted, the Ford's are easy to set up, but you pay for that ease every time the car moves.

Personally, with a daily/recreational driver with occasional track use, and particularly with no OD transmisison, I'd consider 3.42 or 3.73 at a maximum. To double-check the results, look at the torque cirve (not HPO) of the engine and see where peak torque is produced. Being a Mk IV crate engine, I'll bet you don't want to be much over 5,800 when rolling through the traps. It's not like the 502 is going to struggle to make launch torque. You're going to have enough trouble getting that power to the ground as it is. SFCs are going to be a must unless the car is already caged.

[PAYUP$UCKER]

This is what I had in mind http://cgi.ebay.com/ebaymotors/9-Nin...63966157QQrdZ1

but I think I'm gonna go ahead and cancel my order if there's 5-6% driveline loss. That is definatley not something I want.

[Blue Bowtie]

O.K. - I may have exaggerated a bit. To be completely fair, it seems that the concensus is that the losses are only 2-4 percent. On one dyno test, a 400RWHP car lost 15 HP due to the Ford 9-inch compared to a Saginaw 12-bolt. That calculates to about 3.9%. CHP dyno results showed a varying 3% loss, which would only be about 12 HP. Even Ford dumped them in the early 1990s because they were costing them too much in their CAFE averages.

I suppose you could install some 15 HP decals in the windows to make up for it.

Personally, unless you need the extra few ft/lb (and I really mean FEW) of strength that the 9-inch can take over the 12-bolt, or you don't know how to set up an axle, there's no need to use the less efficient setup. Moreover, if you really need the strength, you should bypass the weaker 9-inch and go directly to the superior 10½" Saginaw 14-bolt housing or big Dana/Eaton axles - Unless, again, you have no skills at setting up a rear end.

[PAYUP$UCKER]

Originally Posted by Blue Bowtie

O.K. - I may have exaggerated a bit. To be completely fair, it seems that the concensus is that the losses are only 2-4 percent. On one dyno test, a 400RWHP car lost 15 HP due to the Ford 9-inch compared to a Saginaw 12-bolt. That calculates to about 3.9%. CHP dyno results showed a varying 3% loss, which would only be about 12 HP. Even Ford dumped them in the early 1990s because they were costing them too much in their CAFE averages.

I suppose you could install some 15 HP decals in the windows to make up for it.

Personally, unless you need the extra few ft/lb (and I really mean FEW) of strength that the 9-inch can take over the 12-bolt, or you don't know how to set up an axle, there's no need to use the less efficient setup. Moreover, if you really need the strength, you should bypass the weaker 9-inch and go directly to the superior 10½" Saginaw 14-bolt housing or big Dana/Eaton axles - Unless, again, you have no skills at setting up a rear end.

Are you sure this is accurate, because if this was the case I wouldn't see why 90% of hot rods today would use them.

[Blue Bowtie]

Almost everyone who sets up or sells axles (like Moser, Currie, and almost everyone else) will grudgingly admit that they are less efficient. Only a few will actually dyno test them and reveal the results. Ford did, and you see their response. They went to their own 10-¼" 12-bolt and Dana axles in new diesel trucks with serious torque output. And even by Ford's example, they never ended up under anything bigger than the F-150 half-tonner. Anything bigger, heavier, and needing more torque throughput didn't use the 9-inch.

The 9-inch is reasonably strong, but the lower angle of the pinion which helps give it good engagement and strength also costs some power. You will see a lot of 9-inch housings at the track, unless there is a lot of money involved. You'll see a lot more straight bevel gear axles where there is serious money invested in getting every last ounce of power to the ground and efficiency is important. Big sponsorship dollar circle track cars don't use them. Big money road racers don't use them. They are very common and successfully used under a lot of street rods and weekend warrior rides at the track, however. They'll usually take the abuse of a pro-stocker for 1700' trips, plus a few tire warming episodes. The AA boys and girls are all using the 12" straights, but that's another world entirely.

A 9-inch is also very easy to set up, since it can be done with only the center section on the bench. They are very easy to change out, and parts are readily available from numerous sources. The one "dirty little secret" that almost no one wants to let out or admit is their higher parasitic loss. It's not so bad that it will bind up your driveshaft and lock your wheels like a split ring gear, but there is more loss inherent in the design. They also generate more heat as a result, and internal gear oil pumps are available to counteract that in constant-use or longer duration applications.

Don't take my word for it:

http://www.chevyhiperformance.com/te...nd_comparison/

http://www.halibrand.com/rear_choice.htm

The really heavy-duty axles are usually ignored, probably since they weren't mass-produced for 30 years like the Ford 9-inch. The Saginaw 14-bolt 10½" units and Dana 70s (and even some 60s) outperform the 9-inch, but are more expensive due to the overwhelming popularity of the 9-inch.

[crazycal]

In another point of view, my '65 Nova with a 383 crate motor has a 9" Ford rear axle built by Currie with 3.89 gears. I added synthetic gear oil, an axle brace and a pressure vent. It runs top notch, not any problems.