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Discussion Starter #1
This is something difficult for me to admit but my malibu with its fairly happening engine(i.e. headers 268 cam 3 angle job msd ign.etc)has one of the worst rears possible!Namely an open 8.2 2.56.Its sad I know.I am going to buy a complete rear from someone,somewhere soon.My question is this.Sometimes when reading CAR CRAFT or SUPERCHEVY they will do a gear swap and do a quater mile comparison between stock and the up grade and there is never much difference.Why? Please tell me I'll feel it in the seat of my pants if I switch to a 3.73 posi.This ia a HEAVY with an auto trans.

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71 malibu 350/350
 

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Because there isn't that much of a difference! It is my belief that rear-end gears should be the last performance upgrade you do when building up a car, because the performance bang for the buck is not as great as other "first round" mods when building a car. The exceptions to this are if there is a problem with the current differential requiring it to be torn apart anyway, and when there is too much power for a non-posi rear end, and the tire just spins.

The other way to look at it is when you get down to that 13-14 second range with your car, you maybe pick up .3 or .4 seconds going from a 3.08 to a 3.73 or 4.10. Look what you have to do with your engine to pick up that kind of acceleration gain. .3 or .4 seconds isn't much when your car is in the 16, 17, or 18 second range, the same money (especially if you pay someone to set up the rear end) will get you much bigger gains if it is spent elsewhere. When your car gets quicker, then it's time to think about gears. Just my opinion.

Don't get me wrong, you definitely WILL feel it in the seat of the pants, going from a 2.56 to a 3.73. It sounds like you have already upgraded a quite a few things on your car so maybe gears should be next for you. It is worth the money, just be ready to spend more on gas also.

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Steve

72 Chevelle SS402/4sp

[This message has been edited by SSteve L (edited 12-18-99).]
 

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I switched from an open carrier 3.31 to a 4.10 possie, and it made a HUGE difference!
 

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Try taking off from a stop in 1st gear in a manual trans car. Then do it the same way in 2nd gear in the same car. von
 

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there are four major considerations "before"setting up a street engine.
rear gear
tire size
weight
pocket depth

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Harley
69 461 El Camino Nitrous Model(water Logged), 69 Chevelle coupe
70 El Camino,71 SS Camaro
79 Corvette
Kerrville,Tx.
A Camel is a Horse designed by a commitee
 

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Sean, My opinion is that you will see a drastic improvement on acceleration. The trade off will be highway driving loss of mpg, increased engine noise at speed. Also your tire diameter will determine the final drive ratio. 3:73 is a nice compromise gear that can be manipulated by changing tire diameter, 28" street tire for cruising, 26" slick for drag racing. Also, you might want to save your oem housing as it is stamp coded to your year vehicle. Glenn
 

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Harley, 10-4 on the pocket depth

Rick
67ss bb
TC #326
But all it needs is a harmonic balancer.....
 

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We have a '72 402 with a 2.73 open and I was really looking to get some real "felt" performance in going to 3.90 gears with a posi unit. Will cost around $800 to get this built into our rear housing. Am I way off or will this not result in real performance gains? We already installed a Edlebrock performer cam and intake with Hooker headers.

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'72 SS 402
Denison, TX
 

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went from 2.56 open 8.2" to 4.56 posi 12 bolt with a fairly beefy motor and there IS a difference but it wasnt the world, like I expected.. 1/4 mile times improved at least .3 or .4 like was just said...

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Mike Reeh
Gold #34
San Diego, CA
 

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If you've already done as much as you want to the motor then go ahead with the gears. However, be prepared to start hitting more gas stations cause when ya changed gears like that the mpg drops drastically compared to the ET.

J.J. Fig

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MCC member #256
http://www.clark.net/pub/chevelle/mcc.htm
 

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It's common for people to forget about the rearend when "beefing up" the performance of their car. Before choosing a street gear, you have to know how you are planning on driving the car. For example, a weekend warrior that will see strip time along with some limited street cruising can live with 3.90/4.11's and bigger. But, if you are planning on using it more as a cruiser with some limited strip time, 4.11's would be way too steep.

3.73's is about as big as you will want to go for a street car that will get regular street time. Anything larger, and you'll be revving the snot out of the motor on the Highway. While you will feel a difference, it won't be a major difference with that motor. You'll really feel a difference with the larger motor.

I personally have 2 cars. One is a cruiser and the other is a bruiser. My 69 Chevelle SS is the cruiser and is a mild 396, TH400, 3.73 posi rear car. I persinally think that this car is running too much gear and would love to go down to 3.31's.

My 68 LeMans is the racer and can live on the street with the steep gear. I just can't take it out on Sunday for a drive in the country.

Just remember this. Build the Motor, Trans and Rearend so they correspond with each other. I also recommend building the Rearend first, then the trans then build the motor last. The car is no fun sitting in the driveway waiting for a rearend tthat can handle the new found power. Build around the motor.

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Ted Stojkovski
Syracuse NY
Team Chevelle #172



[This message has been edited by Tedster (edited 12-20-1999).]
 

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Discussion Starter #12
Tedster I have been thinking the same thing about the gear situation.Maybe 3.31 or 3.55 would be a better gear selection.This chevelle is my sole transportation.The thing is (and this is really immature)but MUSTANGS seem to follow me around,lurking everywhere!Im not a wild constant street racer at all its just that when I hear those 4.6 and 5.0's at 3500 r.p.m. sitting there next to me at every light,It makes me wanna get them and get them good.I dont think the car would have much trouble now.I just wanna make it a little more impressive.The car is already obviously intimadating them.ThanksAll
 

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Another thing to remember, is that an automatic equipped car will run higher RPM's with the same rearend gears at the same speed. I've noticed this difference to be as much as 10%. I just mention it so if you are basing a desicion on other peoples RPM's with certain gears at cruise speeds, make sure you take the transmission into account.

Just another reason torun a 4 spd


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Steve

72 Chevelle SS402/4sp
 

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Sean,

Back when my '71 was my only car. It had an 8.2 with 2.73's(one-legger). The car would barely spin the tires. It ran a best of [email protected] at Houston Raceway Park. I swapped in a set of Richmond 3.55's. The car would then spin about halfway through 2nd gear. I took it back to the track and ran a traction limited [email protected] with no other changes. Check out my web page if you want more details.

Jason Gore
AKA DragRacer
[email protected] http://members.aol.com/jgchevelle/index.html
 

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Hi, everyone. I have a '68SS w/ a 402, th400, and 4.10:1's (posi). Its fun to make a few short runs, but any sustained speed is horrible. If you mainly drive it on the street or if you ever take it on the highway, don't do it! [email protected] isn't real bad unless you go more than 50 miles, but [email protected] about 75mph on the highway? 10 miles is horrible! Personally, I don't like getting passed by everyone, so I run about 4500. If you've never ridden in a car with 4.10's on the highway, don't get them. I wish I had 3.55 or so. Even higher (lower numerically) would be better, but I'm afraid it would be to slow to take off. (I still want to be able to spin tires off rim in first and into second) I've had the car for 7 months now, and sometimes still can't tell if it's in 2nd or 3rd (speedometer broke). If you're going to get low gears, get an overdrive! That's what I want.

If you are thinking about it, put your car in first, accelerate to about 4000-4500 rpm and stay there for as long as it takes to convince you not to do it.

Oh, and another problem I have is horrible gas mileage on the highway. (Were talking much less than my normal 10-11mpg) At highway speeds it makes just enough vaccuum to open the secondarys with 1/8" more throttle. Then I'm doing 20 mph faster at zero miles a gallon!

If you drive it much or rely on it for transportation, <3.55 or overdrive. I'm sure its much better on the engine to run at lower rpm's too. Sorry to take up so much space, but this is a annoying problem.
 

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Had a 68 Nova with 2.7x rear, that made decent power. Swapped the rear for a 3.73 posi unit, and it made a huge differnce in the standing acceleration. But as others have commented the RPMs will go up on the freeway, although the 3.73's weren't too bad at 60MPH. I wouldn't go higher than 3.73's though.
 
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