Which rear end (and tires?) for my JW powered 65 Special Wagon?

Discussion in 'Got gears?' started by elagache, Aug 1, 2012.

  1. elagache

    elagache Platinum Level Contributor

    Dear V-8 Buick rear end experts . . .

    Automotive rear ends I mean!! :grin:

    As V-8 Buick regulars know. Jim Weise has completed a rather assertive big-block Buick engine for my trusty wagon. The trouble is . . . maybe a little too assertive!! I had the 200-4R tranny built by CKPerformance so it should be up to the task. The components from then on to the road . . . well - I think they need a little beefing up!!

    I'm starting this new thread to avoid hijacking Jim's thread on the engine too much. Where I last left that thread LarryGS70 had written:

    Unfortunately in the meantime, Paul Muller deeply hurt my price and insisted . . that I get out a measuring tape and actually measure the tire height.

    So I crawled on my hands and knees, reinflated the tire just to be sure, and found the distance between the floor and the center of the tri-shield logo to be 11.5" *GULP*!! :shock:

    Clearly these tires are really getting compressed under the weight of the car. Now I understand the tires will expand a bit under road conditions, but it won't expand 1.5". Now if you assume say a diameter of 23.5" then the RPM at 60 MPH becomes 1767 RPM (with a 3.08 rear end.) If you stick to a 2.78 rear end ratio, what do ya know it arrives in the ball-park that Larry proposes: 1597 RPM. Given that the speed limit in California is 65 and 70 in some spots, more realistically the engine would be ~1800 RPM and that's plenty.

    Now to say this is an unexpected - is an understatement!! :Do No:

    So it seems time to open up the question a little bit and ask: "what wrong with this picture?" more generally.:confused:

    I was resigned to upgrading the tires from the P205/70R-14 that are on the car to at least P215/70R-14. Given my eventual hope to do some serious towing, can I hope to find tires for these 14" rims that will be adequate for the task? It breaks my heart to replace the 14" rally wheels, but it seems insane to cripple the car if that turns out to be a weak-link.

    The plan was to go with some sort of positraction rear end to prevent the torque from destroying the rear end gears.

    So what is the opinion of the experts here? :Smarty: Is is realistic to go with a hardened 2.78 rear end and stick with my 14" rims and the biggest tires I can get for those rims . . or am I asking for trouble? :af:

    Cheers, Edouard :beer

    P.S. The transmission has a stall converter of about 2000 RPM.
     
  2. Jim Weise

    Jim Weise EFI/DIS 482

    Ed,

    I would put it together with what you have there, and see what it's like. Converter stall speed will be no issue here, as that motor would do fine with a 1200 rpm stock unit, and your 200-4r has a lockup clutch in the converter, so under crusing condtions, the fins/stator angles are not a factor.

    You can always change things later.


    JW
     
  3. elagache

    elagache Platinum Level Contributor

    Thanks Jim! (Re: Which rear end for my 65 Special Wagon?)

    Howdy Jim and V-8 Buick fans,

    Thanks for the good advice to avoid changing too many things at once! :TU:

    I think I'm going to have to go where no V-8 buick has gone before when it comes to the rear-end ratio simply because I'm trying to achieve better gas mileage that most fellows.

    Still, at some point I've got to compromise and pick something that operate in a wide range of conditions. If I stick to the 14" rims, then the 2.78 rear-end ratio will keep the RPM down where the car should be able to really "sip" on the gas.

    Once I've gotten the car on the road and run a few tests - then I can start making adjustments!!

    Thanks again!

    Cheers, Edouard :beer
     
  4. urbancowboy0307

    urbancowboy0307 Silver Level contributor

    Edouard,

    I'm not sure if my experience will help much.....

    the rear end on my '66 4-dr is the same as yours (open 2.78 gears) with 14" steel rims and I have 205/75R-14 tires (the brand name escapes me, but I will take a look if your interested in knowing).
    My car is a great highway driver (even with just the two speed ST-300) though I keep my speed to 60 at the most, the last trip I got about 20mpg (this all with a original, non-rebuilt 340-2bbl and trans, and I had my rallies on so the tires were just smidge shorter and wider 235/70R-15s).
    Obviously your putting in a much different engine and trans combo......but I've found with the low end on my 340 i never have to go above 2100 on the tach with my driving style.
     
  5. elagache

    elagache Platinum Level Contributor

    Very interesting!! . . . . (Re: Which rear end for my 65 Special Wagon?)

    Hi Bill and V-8 Buick rear-end tuners . . . .

    Well, it is very interesting in unexpected ways because your setup is very similar to what the car originally had . . . . except for the rear-end.

    Actually the car basically hasn't had the 2.78 rear end for any length of time. It was swapped in about 2 years ago and 2 months later - the car was smacked by an Audi and basically still hasn't fully recovered. Until then she had the standard wagon 3.08 rear-end and the gas mileage was abysmal. Right now the car has the same rims and tire sizes as you have right now.

    So your experience shows the virtue of keeping the RPM down as much as possible.

    Since my super-deluxe JW engine produces so much torque, I should be able to bring the RPM down much more when in overdrive. Basically going on the freeway should occur at about the same RPM as traveling a city street at 25-35 mph. The engine should still be able to gently accelerate the car for mundane freeway maneuvers and if something drastic needs to occur - the car can jump out of overdrive in a hurry.

    So that's why I'm wondering how "tall" a rear-end ratio I could go with. Certainly 2.78 is a safe choice. However, with the small tires I have now, even that may not be "tall" enough. However, I think I do need beefier tires, so 2.78 looks like a good starting position before further tinkering.

    So thanks for sharing!! :TU: Definitely food for thought! :idea2:

    Cheers, Edouard :beer
     
  6. pmuller9

    pmuller9 Well-Known Member

    What I would like to know is if the Tempest rear end is going to hold up to 500hp/535 torque?
    If not, what rear end should be used that will fit the 65 Buick Special Wagon and handle the power?

    Paul
     
  7. Doo Wop

    Doo Wop Where were you in '62?

    Clearly these tires are really getting compressed under the weight of the car.


    Please educate me on this and how that happens. Can't see how a tire diameter can reduce some 2" or so??
     
  8. elagache

    elagache Platinum Level Contributor

    Flavors of GM A-body rear-ends? (Re: Which rear end for my 65 Special Wagon?)

    Dear Paul and V-8 Buick gear experts . . . :Smarty:

    Oops! This was one of my homework assignments that is still sitting on my to-do list. :Dou:

    I just never thought about the differences between the rear ends for 65 A-Bodies. I assumed that if you replaced the differential with a heavy-duty positraction differential, the remaining components were the same. So a low-end Special sedan had the same rear-end as an El Camino or Sportwagon.

    Does anybody know? :confused:

    Thanks in advance for someone who might "do my homework" . . . . :)

    Cheers, Edouard :beer

    ---------- Post added at 05:00 PM ---------- Previous post was at 04:44 PM ----------

    Dear Korrie and V-8 Buick scientific skeptics . . . .

    Hey, I'm the newbie around here . . . don't expect me to explain it!! :confused:

    However, I'll be the first to admit how disturbing I find this. So just in case . . . . something is amiss in this picture . . . . I decided to - take some pictures!!

    Picture #1 is of the tire and a 12" ruler. Clearly the radius is less than 12" when according to the formula for tire height it should be something like 12.6"

    [​IMG]

    Sorry if the photo is a bit dark, didn't open up the garage just to get a good photo . . . kinda warm around here!! Still, looks like a normal radial bulge to me.

    Just to leave no doubt, these tires are P205/70R14 as described:

    [​IMG]

    So can somebody explain what I'm doing wrong here?

    Curious minds want to know!! :)

    Cheers, Edouard :beer
     
  9. Doo Wop

    Doo Wop Where were you in '62?

  10. TheSilverBuick

    TheSilverBuick In the Middle of No Where

    3.08's will be just fine for hauling the car around easily and nicely. I ran 2.73 gears on a 26" (based on tire size calculators) tire with a 700r4 (.70 OD) in my light weight '69 Firebird with a weak and wore out Pontiac 400. It ran happily and got an easy 18mpg around town and stop and go traffic and mid to upper 20's mpg on the highway. It would get a little cranky in overdrive at 60mph, but was definitely good by 65mph, and this was making far less torque I'm sure (though in a lighter car with a better aero profile).

    My concern with the 3.08's is when towing. You may find yourself leaving it in 3rd gear just to keep the transmission from hunting between 3rd and 4th. Or maybe not, but it's a thought.
     
  11. pmuller9

    pmuller9 Well-Known Member

    With a lot of torque available from 1600 rpm and not having to hardly depress the gas pedal, would that keep the tranny from huntiing between gears?
     
  12. TheSilverBuick

    TheSilverBuick In the Middle of No Where

    Maybe. Does anyone actually know how much torque is available at part throttle at 1600rpm? As I figure, driving the car around normally will likely be zero issue, but with a trailer? You can't make extra torque with out extra air and fuel, are we talking from going from 8% throttle openning on normal driving to 12% throttle? And properly setup overdrives, particularly built for high HP/TQ applications tend kick out of OD pretty easily to save the OD gear which is the weakest part of the trans. I'm all for trying it with the 3.08's, especially since cruising in 3rd with 3.08's isn't really that high of rpm considering when 455's were built there were no common overdrives.

    I'm only thinking this from my experience with a lower HP engine in a smaller car that weighs ~3,800lbs that I ran 3.08's in and towed a small camp trailer. Not quite an apples and apples comparison, but with my manual transmission I have driven at sub-2,000 rpm (with the TA118 cam) in OD (.64 ratio) towing my trailer at 70+mph and it doesn't take much of a grade to need quite a bit extra throttle. Flat grades required about 5% nominal increase in air into my engine (10%-12% TPS increase with progressive linkage), and climbing hills went up from there quickly. His engine is more efficient than mine for sure, but his trailer I believe is bigger and his car weighs more. So it becomes how the transmission is set up and the tolerance for load in overdrive. Just because you can run that power while loaded up through the overdrive doesn't necessarily mean you should. I'd be talking to the transmission builder about that for sure, my guess is the builder will play it safe and the transmission will hunt while towing.
     
  13. pmuller9

    pmuller9 Well-Known Member

    Great info!

    The tires measure about a 11.5 inch radius from the floor giving an actual diameter of 23 inches.
    If they grow to 24 inches at 70 mph that still a smaller tire than expected.
    So the plan is to run the 2.78 ratio and see what the running rpms are and go from there.

    The tranny has a billet overdrive section and the tranny itself is rated at 750 hp.
    However it is a better deal for the tranny if overdrive was not engaged during heavy loads
    and if it stayed in 3rd instead of a lot of hunting between 3rd and overdrive.
    That being said it would be better for a numerically lower rear ratio so the rpm was relatively low
    when towing in 3rd gear and leave the overdrive for long stretches of flat or when the wagon is not towing.

    Ed will figure this out once the wagon is on the road.

    The real question is the Tempest rear that is in it now.
    Is it strong enough? and if not what rear will fit the 65 wagon that is?

    paul
     
  14. Doo Wop

    Doo Wop Where were you in '62?

    12 bolt '65 Chevelle rear should work.
     
  15. urbancowboy0307

    urbancowboy0307 Silver Level contributor

    I think the thread on his engine build has the dyno chart (obviously will differ a little once installed, and accounting for drivetrain loss).
     
  16. Jim Weise

    Jim Weise EFI/DIS 482

    Paul,

    Unless he is out abusing it, I doubt rear end strength will be a factor. He won't have enough traction to break anything.

    JW
     
  17. TheSilverBuick

    TheSilverBuick In the Middle of No Where


    The dyno chart starts at 3,000rpm or 3,500rpm, and at WOT. Nothing to correlate to 1,600rpm, especially at part throttle.

    Towing in 3rd with 3.08's is really nice though! Put's the engine in a real sweet spot, rpm wise, climbing hills. When I would kick down to the 1:1 gear it rev up to around 3,000rpm and pull up a hill like the trailer wasn't even there, and 3,000rpm isn't even working the engine. 3.23's would wind up a bit more that I like highway cruising to be at. My Skylark came stock with 3.23 gears and I run 3.42's now, which puts me at ~2300rpm in 5th gear and that pulls the trailer up hills with minimal notice where as the 3.08's it was quite noticable.

    ---------- Post added at 10:07 AM ---------- Previous post was at 10:03 AM ----------


    x2. It's seems easier to spin the tires with a trailer hooked up, something about all that extra inertia and only an extra ~120lbs of tongue weight.
     
  18. urbancowboy0307

    urbancowboy0307 Silver Level contributor

    :Dou: didn't even notice that.
     
  19. elagache

    elagache Platinum Level Contributor

    Rear-ends and . . . other matters (Re: Rear end for 65 Special Wagon?)

    Howdy Korrie, SilverBuick, Bill, Jim, and V-8 Buick "rear end admirers" . . . . .

    :grin: What's the matta' with you guys!! I take a few hours to bike over to Trader Joe's and pick up Langostino Tails . . . and I come back to all this discussion!! :confused:

    I've got news for you . . . if you want to enjoy looking at rear ends, you'll find much more appealing scenery observing the lady joggers on the trail!!
    :Brow:

    Ahem!

    Okay, I'm back in the computer driver's seat and let see if I can catch up.

    Unfortunately Korrie your table simply gives me back the same numbers my formulas do. I don't understand this, but these numbers I think refer to the diameter of a tire that isn't carrying the load of the car. :confused: Is there any way to compute the radius of a tire under load? Obviously the good old measuring tape works, but if I decided to go with beefier tires then I won't know what the actual (not to be confused with the theoretical :rolleyes: ) radius turns out to be.

    :grin: Actually right now the trailer doesn't weigh anything . . . . I haven't bought one yet!! :bla:

    Uh seriously, I still haven't decided which trailer I'll buy. However, I was trying to give myself the option to tow something as heavy as the car ~4000 lbs. I did tell CKPerformance what I was trying to do, and they did what they could to beef up the tranny. However, I think indeed the only way to resolve the matter is to get the car on the road and find out. Given that I may end up with a smaller trailer than the Airstream I had initially used for specifications, the problem may never arise.

    Certainly practically speaking, it isn't reasonable to push the tranny too hard. If the car seems to strain when towing in overdrive, I'll have to follow your experience and put the tranny back into 3rd and pay the gas penalty.

    This is basically what Paul pointed out of course (thanks Paul for pinch hitting for me! :) )

    Which leads conveniently to Paul's question . . . and my resulting puzzlements . . . . .

    Okay, I did my homework and still believe that there was only one model of rear-end that were used on all GM A-body cars of the period.

    Pulling out my 1965 Buick Chassis manual I see that my wagon was fitted with GM FAB9 rear end. Doing some quick checking on the web, it appears that all GM 64-67 A-body cars had the FAB9 rear end - including the 64 Tempest. I did find one fellow who beefs up the FAB9 rear ends: Chris Alston's Chassisworks. However, I haven't found any indications of another rear-end that was actually used on the 64-67 A-body cars. Is this relatively fast bit of research correct?

    I think Jim is correct on this one, but it does remind me of what Greg at Orinda Motors was telling me when I complained that I probably had to replace the tires:

    "No worries, because by the time we are finished testing the car . . . there won't be any rubber left on those tires!!" :shock:

    GULP!!!! :eek2:

    I now return you to your usual rear-end observation and admiring . . . . . . :laugh:

    Cheers, Edouard :beer
     
  20. urbancowboy0307

    urbancowboy0307 Silver Level contributor

    Re: Rear-ends and . . . other matters (Re: Rear end for 65 Special Wagon?)

    We're just passing the time till you get this set-up together and we can all :shock::eek2: at it :grin:

    I've found the best way I can increase MPG on any car is to find the right engine speed and stay just below that.

    On all the v-8s i've driven (my Skylark and my '97 Ram 318, 3.55 rear, .69 OD, 2wd) it was just around 2K.
     

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