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    1. #1
      Join Date
      Jun 2002
      Location
      Long Island, NY
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      Gearing and drivetrain experts inside, please.

      Matt and I need your help to settle a slight disagreement.

      Here's the deal. Matt and I are trying to select the best rear gear for Fantom, in order to meet the project goals.



      Project Fantom should make 600rwhp(Blown LS1 @ 12psi), hopefully more.

      The goals for the car are as follows:
      Mid-High 10 second 1/4 on either slicks or ET Streets.
      185mph top speed

      Here's the data
      Power: 600rwhp
      Max RPM: 6600 (est.)
      Tire diameter for 1/4 duty: 28"
      Street tires (top speed): 26.1"

      Here is the gear ratios for the T56. I think these are the correct ratios for the LS1 T56.

      1st: 2.98
      2nd:1.99
      3rd: 1.35
      4th: 1.00
      5th: .79
      6th: .62

      Basically what we need here is the lowest gear possible that will net the 185mph top speed.

      You may find this link helpful: http://www.csgnetwork.com/rearendgearcalc.html

      I, personally want to run a 3.55 or 3.73 gear. Matt recommends 4.33.

      From a pure math perspective using that calculator, 6500rpms, 3.73s, .62 final gear ratio, and 26" tire equals a possible top speed of 217mph.

      4.33s = 187mph.

      My arguement is that, the Coefficient of drag is going to drastically reduce the possible top speed. I personally don't see the car running 185 with anything in excess of a 3.55 or 3.73, Matt obviously sees it differently. Matt knows much more than I do, so I am probably wrong, but we'd both like a second opinion..

      Any opinions on what ratio to run /comments/expertise is welcome.

      I asked Tony (nineball) his thoughts, and his recommendation was for a 4.10 gear for a 10 second car, with the T56.
      Last edited by Ralph LoGrasso; 09-22-2004 at 09:01 PM.


    2. #2
      Join Date
      Nov 2003
      Location
      Paradise, Ca
      Posts
      1,411
      I’ve been hearing that some people will go to the trouble of installing a six speed, but only use 4 gears. What the hell is that??? They say that the car “tops out” in fourth gear. Well, it wouldn’t do that if they had the correct rear end gears!!

      For Ralph’s car, 4.33’s look to be perfect for obtaining 185mph @6500rpm with the tires he’s going to run. (Will the motor pull 185? I doubt it…but we’re talking about gears, not horsepower)

      3.73’s would bog the hell out of the motor in sixth, and to some extent in fifth too….might as well put a 4 speed in the car and call it good if he runs those 3.73’s.

      Ralph mentioned “from a pure math perspective”. My point is that math is the only thing involved when picking gearing. If the motor will only pull the car to 150mph, then even shorter gears could be used.

      This never came up in our conversation, but another area of concern is cruising rpm…don’t wanna be spinning that motor 4500rpm going down the highway!! 4.33’s in sixth gear would have him motoring down the highway at 80mph @ 2800rpm.

      Bottom line is that 4.33’s are perfect for Fantom, and I just need help getting that through Ralph’s thick head!
      -Matt

      Welders: The only people that think a co-worker catching on fire is funny.

    3. #3
      dennis68 Guest
      All you are doing by running 4.33 in a 6 speed is eliminating the need for 1st and 2nd instead of 5th and 6th.

      Ralph, you are not going have enough HP to pull top sped in 6th gear with 3.73. The car will actually go faster in 5th gear beacuase the engine will be able to pull the gear to a higher RPM.

      Matt, we (Chrysler) tried doing the same thing on the new Jeep, re-gear the diffs so top gear (6th) would be able to actually be a usable gear, now 1st is worthless, only good till about 2 MPH.

      6th gear is designed to be a freeway cruising gear only. It was never intended to be used for top end passes, that is why both 5th and 6th are overdriven, in 5th the engine can operated in or near its peak HP while approaching top speed. In 6th the engine is not near that powerband yet and the "wind wall" affect is already in place-the engine just can't pull the car into that "sweet spot".

      We go through the same thing with boats, the vessle has to be able to break the coeffecent barrier, be it wind or water and at the same time turn the propellent, be it a prop, a pump, a drive, or a diferential. The key is to place your top end desired speed to match the engines peak HP then gear accordingly (using 5th gear ratio).

    4. #4
      Join Date
      Jul 2002
      Location
      Mesquite, TX
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      4,901
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      Wow, this is some good info... this would seem to tie in with my post in Open about powerbands and fuel economy and gearing - http://66.70.234.198/forum/showthread.php?t=915

      When you're gearing for performance, (assuming a 6spd since that seems to be the assumption in this post) how do gear ratios, RPM vs. Torque/HP curves, and vehicle speed relate?

    5. #5
      Join Date
      Nov 2003
      Location
      Paradise, Ca
      Posts
      1,411
      All you are doing by running 4.33 in a 6 speed is eliminating the need for 1st and 2nd instead of 5th and 6th.
      Ahhh, but Ralph is trying to build the perfect dual purpose car. From where I stand, with 4.33's, now he's got a useable 1st and 2nd gear at the drag race track, and will still run the mph he wants in road race trim.

      6th gear is designed to be a freeway cruising gear only. It was never intended to be used for top end passes,
      And '68 Camaros were never intended to run 185mph.

      If he runs 4.33's, he'll have a decent chance at an ok launch at the drag strip, it'll go easier on clutch's on the street and be easier to drive on the street too.

      Ralph, you are not going have enough HP to pull top sped in 6th gear with 3.73. The car will actually go faster in 5th gear beacuase the engine will be able to pull the gear to a higher RPM.
      My point exactly.
      -Matt

      Welders: The only people that think a co-worker catching on fire is funny.

    6. #6
      dennis68 Guest
      Matt I still think 1st will be totally useless, how about a compromise? Take Tony's advise and run the 4.10's. Ralph, gearing is not really going to determine top speed, the car isn't going to make enough HP to overcome the drag coeffiecent at over 180 or so, not to mention that without some SERIOUS aero work it's just gonna go airbone anyway. A friend of mine died at 190ish in a Viper, left the ground, and it has mega aero work. Those are airplane speeds and lokking at side view siloette of acar they are somewhat shaped like a wing.

    7. #7
      Join Date
      Nov 2003
      Location
      Paradise, Ca
      Posts
      1,411
      Dennis, he's gonna need all the first gear he can get to get that pig moving and have a sub 3 second 60' time. lol

      You make a very good point about aero. I knew it'd take a lot of motor to pull the car to 185mph, but never thought about the wing factor.

      So maybe we should concentrate on figuring out what a realistic top speed for Fantom will be, then gear it from there.
      -Matt

      Welders: The only people that think a co-worker catching on fire is funny.

    8. #8
      Join Date
      Jun 2002
      Location
      Long Island, NY
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      Good info guys.

      Dennis, I read that 4th gens usually top out in 5th gear as well. As for the 185 top speed, I agree that extensive work needs to be done, but the speed is still possible. I have a fully adjustable rear spoiler, and I would swap to some REALLY stiff springs for high speed runs. That's not an incredible amount of work, but Big red ran 222mph, and although the car was before my time, from looking at the one or two pics that I've seen of it, I don't recall extensive aero work. I'd like to think that 185 is definitely possible in a 68 to some extent.

      About 6 months back, Tom estimated my top speed, with the same setup, only 430rwhp (before blower) at around low-mid 170s, safely. I'd think the car could pull an extra 10mph out of that with another 170rwhp, but I could be wrong. Where's Tom? He's the first gen road race man.

      I'm not saying that you're wrong, I'm just looking at it from a different perspective.

    9. #9
      dennis68 Guest
      I beleive Big Red had some belly pan work if I'm not mistaken. Some rear air management below the bumber will help quite a bit too.

      Ralph, I didn't mean lots of "stuff" to put on, however aero tuning is trial and error and unfortunately difficult to do around town.

      My buddy Tracy Castro at work is pretty good at the 1st gen high speed thing, he has been 167MPH at ther Silver State a few times. His LT1 RWHP was right about 400 I think. That is with a Tremec and .83 5th gear, 255/5016's and a 3.73. I'll go talk to him tomorrow about the combo to make sure I got it right. He says it feels good at 160, much more than that it starts getting air under it.

      BTW, comparing Big Red to any of the other cars on this site is like comparing my bucket to Earnharts old Malibu-the one that one the Daytona 500. wait or maybe Yunicks Chevelle-

    10. #10
      Join Date
      Jun 2002
      Location
      Long Island, NY
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      Dennis,

      Please ask him. Find out if you could get me an email address or a phone number that I could talk to him at, if possible. I'd like to discuss a few things with him, specifically belly pan work, and other aero work that you mentioned.

    11. #11
      Join Date
      Oct 2002
      Location
      Houston,TX
      Posts
      630
      Here are two examples that may or may not help you. On our 65 Corvette I can run about 180 with a 3:55 rear end, 600hp big block 2,800 pounds. On the 63 small block 430hp I can get up to 165 also with a 3:55 rear end before I have to break. We run 225/60/15 which comes out to something like 26 ½ This is at CMS just passed start & finish. Not brave enough to keep it pined going into the turn.
      Blue car http://www.hotrodhoodlumstexas.com/I...ace%20(22).JPG
      White car http://www.hotrodhoodlumstexas.com/I...ace%20(10).JPG
      Both cars have stock trans in them
      James J.

    12. #12
      Join Date
      Aug 2004
      Location
      north central Iowa
      Posts
      503
      Country Flag: United States
      "Dennis, I read that 4th gens usually top out in 5th gear as well"


      I can vouch for that, My brother has a 2001 SS and to get to the speed limiter you have to use 5th gear, it just won't pull 6th at that speed(that could have something to do with the 3.42 rear gear and the 275/45/17's)

      Another thing to think about is, is the gear itself for 6th going to be strong enough to hold the horsepower its going to take to get to 180+? that is going to be alot of strain on the gearset itself.

      "6th gear is designed to be a freeway cruising gear only"

      6th works great for cruising. personally I would gear for top speed in 5th. with a 600hp ls1 it will still launch hard

      good info though, keep it coming
      72 Nova SS, on the back burner for now.


      current cruiser: "The green machine"

      '70 Impala 4drht, 26K original miles, 2" drop springs and large swaybars, drives pretty good for a land yahct in the middle of an ls1 swap, but thinking about changing directions to a duramax diesel swap.

    13. #13
      Join Date
      Jun 2002
      Location
      Long Island, NY
      Posts
      11,320
      Country Flag: United States
      James,

      Those vettes look awesome!! My Dad would love to have one of those, he had a '64 that he sold many years back. He wants to own a 67 again one day.

      Justanova,

      The T56 will be a G-force built version. I think it's rated at 800 or 900hp. The standard version comes with upgraded 1-4th gearsets, but I'll be using the upgraded overdrive 5th and 6th gear sets as well. I agree, I think it will still launch hard with the 3.55s.

      edit: Dennis, I'm working on getting some pics of the underside of big red to see the belly pan work.

    14. #14
      Join Date
      Sep 2001
      Location
      Rochester, Minnesota
      Posts
      1,410
      Ralph, if you're going to have a T56 built by G-Force, why would you use the stock 5th and 6th gearsets? You'll definitely want to tighten them up.

      Using my spreadsheet, plugging in 26" tire, 6500rpm, and 4.33 gears, I get:

      Axle ratio-> 4.33
      Tire radius-> 13 (from Tire Radius sheet)
      RPM-> 6500

      GEAR GEAR RATIO Speed @ 6500 RPM
      1 2.66 43.6 mph
      2 1.78 65.2 mph
      3 1.30 89.3 mph
      4 1.00 116.1 mph
      5 0.74 156.9 mph
      6 0.50 232.2 mph



      I say drop in .86 5th and a .76 6th gear with a 3.70 rear:

      Axle ratio-> 3.73
      Tire radius-> 13 (from Tire Radius sheet)
      RPM-> 6500

      GEAR GEAR RATIO Speed @ 6500 RPM
      1 2.66 50.6 mph
      2 1.78 75.7 mph
      3 1.30 103.6 mph
      4 1.00 134.7 mph
      5 0.86 156.7 mph
      6 0.76 177.3 mph
      Scott
      Twin Turbo 434 SBC, T56, Baer brakes, HRE wheels, etc...
      My 69 Camaro
      Lateral-g.net

    15. #15
      Join Date
      Sep 2001
      Location
      Rochester, Minnesota
      Posts
      1,410
      Ralph, I forgot to include this for comparison. Here are the numbers for 3.73's, stock T56 gearset, and 6500rpm:

      Axle ratio-> 3.73
      Tire radius-> 13 (from Tire Radius sheet)
      RPM-> 6500

      GEAR GEAR RATIO Speed @ 6500 RPM
      1 2.66 50.6 mph
      2 1.78 75.7 mph
      3 1.30 103.6 mph
      4 1.00 134.7 mph
      5 0.74 182.1 mph
      6 0.50 269.5 mph
      Scott
      Twin Turbo 434 SBC, T56, Baer brakes, HRE wheels, etc...
      My 69 Camaro
      Lateral-g.net

    16. #16
      Join Date
      Jun 2002
      Location
      Long Island, NY
      Posts
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      Scott,

      Thanks for the spreadsheet data. That's really helpful, I couldn't find anything like that online, just final speed calculators with the overdrive, and the rear end ratio.

      I'm going with the upgraded overdrives, but I think I messed up in my post and included the stock overdrive ratios, instead of the upgraded ones. Sorry 'bout the mixup. Thanks again for the data.

    17. #17
      Join Date
      Nov 2003
      Location
      Paradise, Ca
      Posts
      1,411
      Scott, thank you. I'm seeing that this conversation is pretty useless until Ralph nails down exactly what transmission gearing he'll be using.
      -Matt

      Welders: The only people that think a co-worker catching on fire is funny.

    18. #18
      dennis68 Guest
      Raplh, I talked to mt buddy at work, I'll post a new thread to discuss the specifics-this is not the correct forum for it. Check in open discussion.

    19. #19
      Join Date
      Aug 2004
      Location
      Alta Loma,SoCal
      Posts
      396
      I think one problem is the tire choices for each goal. If you pick the gear for top speed, you will really kill 1/4 mile performace with the switch to the taller tire. And vice versa. I would suggest using a 26" tall tire for both events, and running a 4.10 rear gear.
      The 4.10's will at least allow you to pull the overdrives better than 3 series gears, plus give good 1/4 mile performance also.
      Trying to calculate the 1/4 miles stuff is a bit hard without knowing the weight. i was guessing 3600lbs. With 600hp 3600lbs you should be able to get into the mid 10's at around 128mph. Calculating that back for gearing would get you to a 3.90 gear with a 26" tall tire. So a 4.10 would help you off the line a bit more, and help pull the overdrives.
      1965 Buick Skylark

    20. #20
      Join Date
      Jul 2002
      Location
      Muskegon, MI
      Posts
      4,494
      Dont forget about "The Twister" it also ran over 210MPH. Ralph will have a lot more HP than the Twister if memory serves me correct. The Twister had 460Hp and 450TQ So Ralph you should have way more than enough HP to push your car to over 180. The Twister had 3.89 gears.
      Adam_______Offical Car Name "ILLUSION"
      383 Stroker, Stock cast heads, T-56 tranny, 4.11 gears, 2002 T/A dash, 4th gen interior including seatbelts, power lumbar seats, 18" Budnik Wheels, Hydraboost, QA1 shocks, DC Controller, Power steering conversion, fuel cell, unique exhaust set up........
      ILLUSION Website-----------Old Website--------------My Car on Lateral-g.net----------- Need something designed?-AdFabDesign

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