Q&A / Tech

Monday Mailbag: Upgrading Your Rear Axle for More Horsepower

 

You’ve got questions. We’ve got answers — Mondays, when the Summit Racing tech department tackles your automotive-related conundrums. This week in our Monday Mailbag, we’re outfitting an ’89 Camaro with a beefier rear axle.

Q: I am in the process of building a 383 stroker engine for my 1989 Camaro. It should produce about 450 horsepower (the current engine’s a V6). Will the stock rear axle be able to handle that much power? If the axle is no good, which one would you recommend using? Will I need to install subframe connectors?

A: The 7.5-inch ring geared 10-bolt that came with the Camaro is a marginal piece. If you set it up properly and don’t abuse it, it may live behind 450 horsepower. We’d suggest swapping it out for a Moser custom made 12-bolt or Ford 9-inch. It will take a lot more than 450 horsepower to break one of those.

We’d definitely install subframe connectors on this car. Any V8 engine with moderate power can easily twist the unibody. BMR Suspension, UMI Performance, and Competition Engineering all offer good choices.

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8 Comments

  1. Michael Jensen says:

    Axle-Ratio availability for custom rear-ends seems to be about 3.5 and numerically higher. If running a 1:1 top gear (no overdrive), this means a lot of cruising rpm.

  2. Robert Wise says:

    I swapped out for a 340 locker, made a huge difference.

  3. AnalogDan Wilson says:

    The On All Cylinders Staff offered some excellent advice to the reader about upgrading the ’89 Camaro’s 7.5″ differential and complete axle housing assembly to what most people in the performance aftermarket industry consider to be the standard for strength and simplicity, the Ford 9″ differential carrier and axle housing assembly. The 9″ designation refers to the diameter of the ring gear in the differential which can be ordered in dozens of different ratios to suit the users specific needs, ranging from a fuel efficient highway cruising 2.50:1 up to a Drag Racing specific 6.50:1 drive ratio.

    To those not familiar with the process of swapping out the low performance standard GM rear axle assembly to the vastly superior Ford 9″ unit, it might seem overly difficult and expensive but that isn’t the case thanks in part to the manufacturers who offer complete kits that in many applications are direct bolt-in replacements. Companies like the previously mentioned Moser and also Currie Enterprises offer vehicle specific axle housing assemblies built to the exact dimensions of the existing mounting locations
    for a true bolt-in installation. They even offer options like complete drum or disc brake packages and differentials featuring a choice of gear or clutch type traction systems and best of all, these and other name brand axle/differential conversion packages are available from Summit Racing !

  4. Good article, on rear axle upgrade 4 89’camaro

  5. As a novice, I enjoy reading these tech articles. I have often wondered how to determine which rear end to install in my daily cruiser. I don’t race it nor do I abuse it. It is a ’62 Impala which has a 350 built to a 420. I installed a 700R automatic with a stall speed of 2200 rpm. which allows me to cruise on the hwy in 3rd gear at 2000/2100 rpm. I do know my rear end it nearing its life span because I can hear it humming (low hum). How do I determine what rear end to purchase and install to keep everything in check. As I said, I do not race or abuse I want to keep things in proper order. I do “punch it” occasionally just to get away from traffic but nothing dramatic. Should I install a Moser or Curie limited slip or ???
    thank you for your response.

    • OnAllCylinders says:

      Moser or Currie are both quality brands. Call the Summit guys at 1-800-230-3030 and they’ll be able to provide some insight on the ins and outs of both…and maybe some other options.

    • AnalogDan Wilson says:

      Tom, your question contains some detailed information and is well thought out so you deserve a little more than a generic answer. I’m certainty not an expert but I will try to help.

      You’re in luck as far as parts availability is concerned because in addition to the two companies previously mentioned, there’s another excellent source. Strange Engineering offers crate rear end assemblies for stock applications like yours and everything else on up to professional competition full blown Drag Racing differential assemblies.

      All three companies have very good websites with detailed downloadable catalogs and you can order their printed catalogs too.

      If you want a GM type rear end, they have a small selection of parts and complete assemblies that are typically known as GM “12 bolt” differentials. But brand loyalty doesn’t really matter when strength, durability and simplicity of assembly and service is desired. Look under most street cruisers and especially Drag Racers to see a strong 9″ Ford differential and housing assembly. Even the diehard GM guys that unfairly bad mouth Ford engines will usually show some respect for the Ford 9″. Thats why the companies that specialize in all differentials will usually offer a much bigger selection of Ford 9″ items at a lower cost than similar GM or Chrysler products.

      For product technical information, recommendations and price, Summit Racing can help. I’ve always preferred dealing directly with the manufacturers on items like differentials and transmissions. Their customer support staff are usually gear heads with hands on experience and knowledge of the product.

      I don’t know your level of mechanical experience or knowledge of the various options available, but before you grab your gold card and start dialing toll free order numbers, you need to do some online research first. Knowledge of the product can save you from the expense and frustration brought on by an overly aggressive sales creep.

      Some do’s and don’ts would be….you don’t need a spool. Spools are great for Drag Racing only. A spool mechanically locks both axle shafts together which is great for traction when going in a straight line but it won’t allow for the different rotational speeds encountered between the left and right wheel and axle shafts as they go around corners. The result is a poor handling street car when needed most going around curves and excessive twisting loads on the axles causing wear and parts breakage.

      For your driving style and the power available from your engine combination, a “posi-Track” or “limited slip” differential is highly recommended. The most common for the Ford 9″ are the Traction Lock which uses friction material in clutch packs that allow the differential to apply power to both drive axles while going straight but allows enough slippage for each axle to rotate as required without binding when turning corners. The Traction Lock is reliable without costing a fortune and can be rebuilt if and when the time comes.

      The Detroit True Track uses a series of helical-cut gears for positive engagement of both axles during hard acceleration but
      still allows disengagement for trouble free cornering. It’s great for higher powered street/strip vehicles. The design doesn’t use friction materials that would wear out over time but the cost is a little higher than the Traction Lock.

      A rock solid design thats been a favorite for decades is the Detroit Locker differential. It works great for radical street and strip applications. It will provide full power to both axles similar to a spool but the superior gear design can sense a cornering load and provide a wracheting action which allows for different axle rotational speeds during cornering. The only area of concern for some users of the Detroit Locker is the mechanical thumping sound the locking mechanism normally makes while cornering. But that’s a small price to pay for the rock solid dependability that the Detroit Locker brings to the game.

      There’s more but I’m sure you can get it right with all of the technical information available online. I hope this helps in some way. Besides, nobody reads this junk anyway.

  6. patrick mockus says:

    flip a coin if price is close to same

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