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What is the fascination with deep gears and compression? Another rant.

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  • What is the fascination with deep gears and compression? Another rant.

    So I am cruising another forum, and a guy is building a 403 in a 80 Trans Am. Edelbrock heads, mild cam, Ed intake, headers, decent build really should run good for a street car. Its like they dont even read what he says, and start telling him to swap to 3.73 gears, throw away the heads, change the stock valve springs, and pull the gas tank. One guy even said touching valve springs with sweaty hands ruins them.

    Why is it everyone thinks you need 3.73 or deeper gears to make a car perform? Is it the small chevy mentality where they dont make enough torque down low to move a 3.08 gear? Are they thinking its a truck? I understand that most people dont know that the 403/425/455 Olds and similar size Pontiacs dont need lots of gear because they are grunt engines, but damn, why is it the first thing they start spouting?

    Then they start with the you need 10:1, or 9:1 so you need to mill the heads or run smaller chambers. Why? If you run to run any octane camel whiz gas, you dont want to run lots of compression. You want to keep it under 9:1 if you want to run 87. Not everyone wants to run premium in their toy, just like not everyone wants to run E85 in it. Sure you get a performance increase, but its a small one compared to what it costs for premium now. If they go a bit too far and tolerances stack up then suddenly they need more octane than 93 can give them. The difference in a healthy engine that runs 8:1 and one that runs 9:1 is barely noticeable on the street, and maybe a few tenths at the track. He has aluminum heads so he can run more compression for the crap 87 gas, but why is it supposed to be mandatory?

    They have never owned an Olds or Pontiac engine, yet they keep posting the same drivel over and over. A couple of them dont even own what we would consider a hotrod. If someone starts talking about Mopar builds, I read it and try to learn something, I dont do them but I still like to know. Since I dont build them I am not going to tell someone how to do it. Why do people with no clue try to tell someone who also has no clue how to do things? Sure everyone can be wrong about something, but just making stuff up?

    I dont profess to know everything, but I do know some things. I do my best not to guess because it could give someone poor advice and cost them. Why does everyone throw that thinking out the window and start telling them to build a 403 like a 305, 350 or 327? The 403 Olds and 2.73 gears is a seriously fun combination with just a few bolt on parts, with the engine he has that thing will tattoo a smile on your face as long as it is tuned right. 3.73 is way too deep for it, the 403 just doesnt have the RPM to make up for it, they are all done by 5500. Why the fascination with RPM and pushing ideas that will make people slower, burn more gas, and have a car they really dont like?

  • #2
    403 is a weak sister ..I would look for older 350 or 455 , but olds is head and bottom end limited for durability in the high hp range
    big compression and gears are for drag racing ...street cruising is secondary ...just another way to burn more fuel to make power
    boost and nos is for the same purpose

    nascar uses a low 12:1 compression , but spins the motors very high to make power - 9500 is normal , 900+ hp

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    • #3
      a 403 with 2.73 in a t top cutlass should be a blistering 17 second car

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      • #4
        Lack of low rpm power. RPM is king for most engines.
        Escaped on a technicality.

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        • #5
          I know what you mean. It's even worse with blower motors....the blower takes away the need for gear....try explaining that
          My fabulous web page

          "If it don't go, chrome it!" --Stroker McGurk

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          • #6
            I agree with op.
            the fascination is old school idiot.

            resonance on bad design was the only reason to drop all torque to screamin 12 liter v8s...or limited in a race league, such as straight gears required or recommended.
            else you can in fact go taller and prouder and let the power hit the earth instead of playing itself to death.

            the trans am and their front ends, 70s and 80s.. I can see the call for dropping the torque to short gears.

            this has bugged me a long time: the steel.

            right now on a much smaller example of the same problems, welding a chassis that contains a 1781cc boxer to very hard allows the engine to take a small four barrel and a full non choking advance curve...all becuase the chassis holds the little monster tight enough.

            people do not admit the pansy ass (or front) chassis and wax it on sunday anyway.
            Previously boxer3main
            the death rate and fairy tales cannot kill the nature left behind.

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            • #7
              RPM is king, you realize this when looking at piston speed in "feet per second". So the higher the" feet per second" speed of the piston is, the faster the engine will spin, combine that with a deep gear and you have a car that will accelerate very quickly.

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              • #8
                Different setups for different applications? Jim's car runs bottom 12s with some like Bonneville gears in it, but last weekend I watched Comp Eliminator cars with 272ci V6 engines run into the 8s with steep as ratios in the rear. What works for one doesn't work for the other. The F-Bomb had 3.08s in it and would flatten your eyeballs when the turbos spooled up.

                At the end of the day it is all about torque, right?
                That which you manifest is before you.

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                • #9
                  I would say it's all about torque too. I've seen a direct drive car with 2.90 gears leave at an idle (2200 rpm) .880 60fts and still run over 270mph in the 1/4. Most will run in the .920-.950 though. A blown alcohol car can have 4.10's in the rear and who knows for a first and second gear, leave at 6500 rpm shift at 10,000. They are pretty close for the first 330 ft or so but its so cool to watch a nitro car run them down, and a nitro car has a smaller engine and weighs more too!
                  Originally posted by TC
                  also boost will make the cam act smaller

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                  • #10
                    Originally posted by Brian Lohnes View Post
                    Different setups for different applications?
                    Yup. For a nice street car you don't need a lot of gear if you have a good sized motor. If you are only going racing, then you want to keep the engine as close as possible to the rpm that it makes max HP, for the whole run. You do that with gear and stall.
                    My fabulous web page

                    "If it don't go, chrome it!" --Stroker McGurk

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                    • #11
                      Think of it as distance over time, the faster you can spin the motor, the more distance you will cover over a given amount of time.........

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                      • #12
                        Originally posted by TheSilverBuick View Post
                        Lack of low rpm power. RPM is king for most engines.
                        but an olds engine typicaly does not have this issue. they are mainly Low RPM tourqe engines. and the 403 in particular can not be spun much past 6,000 safely with out a girdle becuase of the windowed main webs and siamses bore
                        Originally posted by Remy-Z;n1167534
                        Congratulations, man. You've just inherited the "Patron Saint of Automotive Lost Causes" from me. No question.

                        75Grand AM 455:Pissed off GrandMA, 68 Volkswagen Type1 "beetle":it will run some year

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                        • #13
                          Originally posted by TC View Post
                          Think of it as distance over time, the faster you can spin the motor, the more distance you will cover over a given amount of time.........
                          Not if your gears are taking all the rpm out. Spin an engine 1,000 revolutions. Which will go further, 4.11 gears or 3.08 gears? Hopefully the engine with 4.11 gears can spin at least 25% faster, if not it's going to lose.
                          Escaped on a technicality.

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                          • #14
                            my machinist says "gear is a substitute for horsepower ", but what does he know?
                            Reading , Pa
                            Good Guys rodders rep.
                            "putting the seat down is women's work" Archie Bunker.
                            Ban low performance drivers not high performance cars .

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                            • #15
                              Originally posted by TheSilverBuick View Post
                              Not if your gears are taking all the rpm out. Spin an engine 1,000 revolutions. Which will go further, 4.11 gears or 3.08 gears? Hopefully the engine with 4.11 gears can spin at least 25% faster, if not it's going to lose.
                              It's not a question of which will go further, it's a question of which gets you there Faster.........If it takes the 3.08's a 1/3 of a mile to catch the 4.11's then the 4.11 will be faster in the 1/4 mile..........

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