**GEAR-HELP-PICK-ONE**

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I hope this is the correct place for this post. Although technical it is off the wall! I am installing a gear in my 1970 GTO Convertible next week, WHICH-ONE?
It will be my Daily driver for the Summer, the motor is a 455 C.I.D. puting out 512 H.P. on Pump gas w/ THD400, 255/60/15's on 8" Rims, motor is built to run up to 6,500 RPM. As it is a Convertible I will never install a cage.(Wife will need to ride in this ) I believe this forum has a group of tech heads, that can bring some Real Wisdom to the table. Also Because of the tremendous torque involved,(approx 600 ftlbs,will Dyno-Tune after gear install) I will not require as much gear as most believe!(Throw away your calculators) What do you think? Next week it goes in,WHICH-GEAR? P.S. If this seems like a test it is! LOL MRDAN7

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That is a good question to ask. However, answerable. If your wife likes to do burnouts and drag races, go with some 4.5 and greater. If she likes daily driving, get her some < 4.5 or less gears. That's just my opinion. I see that alot of people put 3.73s or less likk 3.5s, and so on. Then you see some mustang people going with 4.56s.


[Modified by snsmarkviii, 9:16 AM 3/2/2002]<BR><BR>
[Modified by snsmarkviii, 9:17 AM 3/2/2002]

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It would be more helpful to know what you have now for a gear, how your car performs with it, and what your opinion is of it. But being a convertible and a daily driver, you probably want to keep the rev's down when cruising. Something in the 3.08-3.73 range will let you cruise at 60 in the 2300-2800rpm range and give you a 170-140mph top speed whenever the bug bites you. However, I've had a 3.73, non-O.D. car before and I kept waiting for it to shift while I have few complaints of the acceleration with 3.08's in my Mark and it has half the RWHP as your Pontiac. The Dodge Viper even uses a 3.07 gear. But having never driven a car with 600lb/ft of torque, I'm wondering if it would continuously light up the tires if you went with a higher ratio gear. Maybe something in the 3.23-3.42 range would be a happy medium. As far as burnouts go, I doubt any gear will prevent you from smoking the tires at will. Good luck.

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Matt, Good answer, I'm uncertain what gear is in it now, I believe it is a stinky 2:76 or equivilent, im just now putting it on the road. The current gear when traveling at 25-MPH and I hit the gas, lights them up!,& PULLS VERY HARD! You are right I believe to stay in the Power RPM range longer, by using a lower than normal gear choice with this torque, I'm thinking I will never need more than a 3:55-3:42, (MAYBE LESS?) and am leaning in that direction now. This should keep the RPM Sane, and the miles per hour still good when needed. I have not had a Street Car with this much torque before, so as a daily driver it is, quite a different choice than just going for 1/4 mile times! Thanks for your input, Sometimes a second or third opinion helps us to see more clearly. I Have To decide this week! MRDAN7

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Steve, Thanks for the reply, I am still uncertain exactly which gear to go with,in the beginning I thought more like 3:73, but after giving it some time, I believe because it is a Daily Driver, I wont need as much gear. because of the torque factor, & I'm leaning toward the lighter side, 3:42-3:55. Well it goes in this next week, I will post later with results, and gear I choose, if I can figure out how to get an MPEG up that would be nice, to post. Also Ive got some good sound clips of my Mark-VIII exhaust, I don't know if it is just me or not, but most of the Mark-VIII duals I hear are delicate, with too much back-pressure, I would like to post the sound to let other Mark-VIII owners decide.

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Alright! Your contributions are always welcome at the MTC. <IMG NAME="icon" SRC="http://images.zeroforum.com/smile/emthup.gif" BORDER="0"> Iwill be willing to give you my opinion on the exhaust. Whatever gear you put in that car, make sure you have some fun. I rode in a couple of modified pickups that were running 5.13s. It was great off the jumps and as soon as they landed they were spraying dirt. yeeeeehah! Just some good ol' boys having some fun!

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That exhaust sounded great! Sounds like there some power there! What kind of mufflers are you going to do? <IMG NAME="icon" SRC="http://images.zeroforum.com/smile/emcocktl.gif" BORDER="0"> You did better than a lot of people did with a N/A markviii<BR><BR>
[Modified by snsmarkviii, 8:27 PM 3/2/2002]

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Steve, that was the sound of my 1993 Mark-VIII, it has 2.5 true duals, no cats,Flowmaster 2 stage, and handmade slash cut turn downs to simulate stock set up from a distance, I use a Large Custom H-Pipe, located in the proper spot it cannot be beat,(I would match this against the x-pipe) this car ran 340 Horse,(292H.P. @RW)
No matter what anyone says, more power always means louder exhaust, make it too quiet and it will sacrifice Measurable power. No Gimmicks just real world TRUTH! MRDAN7 <IMG NAME="icon" SRC="http://images.zeroforum.com/smile/emthup.gif" BORDER="0">

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Actually, I could get away with running without cats where I am at. The air police are not here. You did a good job with your exhaust project.

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Steve, I found that with these 32 valve motors, matching the intake and exhaust together is critical. It can be done cheaply, without Power Robbing Gimmicks. MRDAN7 Im trying to attach a doc, hope it works

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I was able to get at it no problem. I think that there are a lot of issues with regard to intake and exhaust to push it through for power. Some custom machining is likely to be the answer.

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The big GM engines, Pontiac, Olds and Buick have very large main bearings and don't like living over 6,000 rpm so the best all around gear for SANE driving, with the occaisional lapse into madness is the 3.90. I ran a 4500 pound Olds with a 3.90 posi and a Holley 780 and consistently turned 13.3s at about 105mph. Great gas mileage too, 18+ highway.

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Thanks Mel,:star<IMG NAME="icon" SRC="http://images.zeroforum.com/smile/emsad.gif" BORDER="0">Great Run with that Behemouth OLds) Im trying to find a happy medium, I agree by the time you get to 6,200 RPM they have done enough. I'll post with the gear I drop in, Im leaning toward a 3:55,as I will be using a 3 speed THD. Its been a while since I had a Older Street Cruiser, however I remember the whine of turning those RPM, trying to get down the Highway! Im pulling off the 850 D.P. and dropping down to a Holley 780 CFM-#3310-1 like you ran, THEY ARE GREAT for all around driving & Racing!(Also for my Break In of this Motor) MRDAN7
<IMG NAME="icon" SRC="http://images.zeroforum.com/smile/emthup.gif" BORDER="0">

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Definitely I would go with the 3.55’s.
2 friends of mine both have 69 ramairIII 400’s, 1 4spd, 1 th400. The 4spd car has 3.73’s and the auto car has 3.55’s and ether way they will both cook the tires at will and at almost any civilized speed.

<B>ALERT! WARNING! WARNING!!! BEWARE!!!</B>
So what are you using for connecting rods?
I’m not exactly sure which engine has what, (little rusty on the details) but some Pontiacs have cast con rods and they do NOT like high revs. If you have these cast rods I’d set the rev limiter at 6200 tops. I’ve seem what’s left of a couple of these engines that came apart at around 7000 and it’s not at all a pretty sight. Both engines the only thing salvageable was the intake, after 3 piece cranks and 3 and 4 piece cams it kinda messes everything up.

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3.55 gears can cause problems, especially with a hi hp/torque engine, once the tires break loose they tend to be very difficult to get to hook up again. 4.10s will break loose but with only a little throttle adjustment, lifting slightly, you are back in control again. Not a bad gear for an auto trans if you use a decent converter. <IMG NAME="icon" SRC="http://images.zeroforum.com/smile/emsmile.gif" BORDER="0">

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Dave, thanks for the Heads-Up! My motor has Forged everything, Crank, Pistons, Rods, studded everything,ect. I will be fine, till around 650 H.P. then strange things can begin to happen. (hope not) I spec'ed this motor to run 1000 H.P., YES I will be Spraying The Dreaded GAS!! Later after proper break-in. LOL

I was getting ready to settle on the 3:55's till Kwik-Mel stepped up. He has run the Twilight-Zone Torque Monsters before, and makes a very valid point.
It's hard to Imagine what 600 Ftlbs of Torque OR MORE!! is like, I have run these before, they are Unique Animals, and Unforgiving. But Can Scare a Grown Man, & I like That! lol MRDAN7

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KWIK-MEL, I agree, stepping in and out of the traction Zone can be more difficult, with the 3:55 gear choice.<B> I don't believe anyone would have brought up this point, without 1st hand experience. Thanks for the Tip!</B>

I Really like 3:73's but have not run them or 3:90's with this much Torque before, for daily use! Looks like Wednesday is Gear Change Day! Still time to learn more, Thanks Guy's

Sometimes even a Calculator falls way short!!! in Torque-Land MRDAN7

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I think you will really like the 4.10s and if you don't, they are a lot easier to sell if you decide later that you don't really want them. Have you ever tried to sell a set of 3.55s? you'll probably have to give them away or look at them forever, if you're like me that is.<IMG NAME="icon" SRC="http://images.zeroforum.com/smile/emsmile.gif" BORDER="0"> If you buy your gears from Jegs or Summitt you won't feel the pain if you decide to change later on. I would't sell them until I tried an altenarive gear set first though. I have a T/L and 3.55s for my mark VIII, but I'll put the 4.11s in first as too many people have them and like them. Also, remember to get a Rev Limiter on it and set it at about 6000/6250 rpm and your engine will last a very long time. Those Big Thumpers sound good and feel good at high rpm but they just won't live long in the higher rpm ranges. Keep us posted on your results. Mel

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KwikMel, you are gonna get me into that FAT-Gear yet, also I agree 6000-6250RPM on these motors is a safe stopping point, and I will have the Limiter.

Will post with an MPEG, when done, if someone can tell me how to put one up!
<IMG NAME="icon" SRC="http://images.zeroforum.com/smile/emsmile.gif" BORDER="0"> Thanks Guys, Dan

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Suit yourself but just a thought. Take a long hard look at how and where you intend to drive the beast once you done the round of tweaking. What kind of RPM’s are you going to be spinning at highway speed and how much highway driving do you expect it to get? For me the 4.10 launch would be delightful but half an hour of listening to 3400rpm @ 60mph with a lot of regularity would start to get tiring. I know that’s also how my buddy with the 4spd car felt after a season with 4.30.s after which he went with the 3.73’s.

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If you're going to travel on long straight highways for 30 to 50 miles each day the rpm will get to be aggravating and I was always looking for a 5th gear in my Olds. At that time I was living in Chicago and travelling every other weekend to Cinncinnatti to answer the Booty Call, a very important trip. At cruising speeds of 85 to 100 mph I got an actual 18+ mpg.<IMG NAME="icon" SRC="http://images.zeroforum.com/smile/emsmile.gif" BORDER="0"> I had a stock exhaust on the car also. I had 5.14s in my 427 powerd Ford and that was a pain to drive for the 30 miles or so to the drag strip. I will not talk about the gas mileage on the Ford. <IMG NAME="icon" SRC="http://images.zeroforum.com/smile/emsad.gif" BORDER="0">

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KwikMel is right. A good booty call ride will make you one with your machine. It is definitely a situation that will determine cost/benefit performance. My hats off to you kwikMel. You are so correct!

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KwikMel is right. A good booty call ride will make you one with your machine. It is definitely a situation that will determine cost/benefit performance based on time. My hats off to you kwikMel. You are so correct!

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Well is Official, I Dropped in the 3:55's w/Pro Auburn. It should be Fun and functional at the same Time.

Now on to the Trans...

MRDAN7