Inliners International Forums General Discussion Drive Train rear gear

what would be a good rear gear ratio to run in a 4 speed stick car with a 2.2o first gear and 275-75 15 tires .has 4bbl ,cam ,headers,supercharger will be driven on highways 50% of the time.willing to drive a little slower for a bit more ummphhave 3.08 in now and a real dog on take off

a 2.20 first huh thats either a M21 or a M22 being my guess If you can find a M20 it has the lower first gear 63-65 has a 2.56 where as the 66-74 had a 2.52 first gear a 3.32 to a 4.11 will work well But the 4.11s will run you at the limit for the hyw. not to say anything about gas mpg,s as a daily driver I would say the 3.32 would do fine. hope this helps }[oooooo]



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NovaMan/Twisted6/Larry

Huffed6,

My '98 Cherokee has the same rear gears and tires as your car and no doubt your car will have more power. My first gear is 3.83 and second is 2.33. First is unnecessarily low and second IS doggy to take off with, so I would recommend something just about in the middle. Given that, half way makes your first gear about 3.10-1 or a .77 (3.10-2.33)or so difference.

So, IMO your best choice would calculate to about a 3.73 rear gear ratio.

Alternatively 3.55 would give you slightly lesser acceleration in return for a higher cruise speed. I am going guess that your blown engine will provide enough power that should you choose the 3.55's, your 1st gear takeoff will be all you hope it will be.

Good Luck,
Steve

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'98 Jeep Cherokee, 4.0
'56 Willys P/U, 226L

thanx guys wit those big tires on back i was thinkin 4.10 or 4.56 or 4.88 about 30 1/2 inches tall on tires

hello..good choice..I believe anything above 4 is best for street performance....why build a fun engine and slow it down with a slow gear to just to save a few $$$ on gas.....seems more fun to get to 70 very quick-more fun than getting to anything over 70 in a few more minutes.....and bigger tires change gear to smaller gear as you mentioned....

Lee

Huffed6,

I have a little gear ratio calculator in a spreadsheet and I ran some numbers so that you can make a better informed decision.

Know that what you gain in first gear you will lose in fourth gear (given that you do not change transmissions)

So given your tire radius as 15.25" and highway cruising speed of 65mph, and a first gear shift point of 30mph, fourth gear ratio of 1-1 and first ratio of 2.20. I will provide the engine speed for a range of final drive ratios.

Ratio 30mph1st 65mph4th
3.08 2239 2205
3.26 2370 2334
3.55 2581 2542
3.73 2712 2671
3.90 2836 2793
4.10 2988 2936
4.56 3315 3265
4.88 3548 3494

Now obviously you will just shift into 2nd gear at a lower speed, but are you willing to spin that new engine that high to be able to go 65mph? If you race it or just drive around town the lower gears (higher numerically) will give you all the adrenalin boost you can stand, but if you were tinking about cruising to a rod run across the state (or country) a gear set closer to the stock ratio will be more pleasant.

Two other things that you may want to include in your decision process. The faster you spin it, the more heat it makes especially with the blower. Are you willing to dramatically increase the cooling capacity of your car?
Also the lower the gear ratio, the "farther" (more rpm) the engine travels for each mile the car travels. As an example, VW busses typically last about 80% as long as a beetle engine if you count the miles on the odometer. In actuality the engines probably complete a similar number of revolutions during their lifetime. How much are you willing to shorten the life of your engine for more first gear acceleration?
One other consideration, I have the impression that the new engine is not actually in the car and running right now. You may find that the new engine makes so much more power that you don't need to change your gearing because your "doggy" takeoff problem has fixed itself. You might wait and see if you need to change gears.
You now have enough information to make the right choice for you.
Good luck.
Steve


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'98 Jeep Cherokee, 4.0
'56 Willys P/U, 226L

hello...nice comment and math....how many vehicles have you had and played with different rear gear ratios to actually see what you gain by changing? ......Arthur Anderson does great math too, look what they have now!!!.....LOL....it really makes me wonder why one would build a performance engine and NOT change rear gear to maximize accleration- i guess it all depends on goal.... have engine use power band performance cam offers.....its the combination of where engine is built to operate and what gear you use.....after you change and use different gears, its understandable why a gear change is needed for performance engine...good luck

Lee

Lee,

It is obvious we have a different perspectives on this and probably on life in general.

Huffed6 stated in his original post that approximately 50% of his driving in this car was on the freeway. Higher gears make "around town" driving and racing more fun, but make freeway driving a chore.

I currently own and drive vehicles that have gear ratios of; 2.73, 3.08, 3.55, 3.88, 4.12, 4.37, 4.56, 4.88, and 5.38. Every one of them have overdrive, which I do not believe Huffed6 has in his transmission.

Those above 3.55 (except the Willys P/U at 4.88) are VWs which are designed to run most efficiently at 3400 rpm.

The Willys has a 25% Warn OD which gives me about 3.66 when it is in use. That gives me about 2600 rpm at 65 mph. Since I typically shift at about 2300 it feels like I need to shift all the time I am driving on the freeway. Since this P/U is a toy and not my daily driver, I drive it when I am in no hurry or when I do not need to go on the freeway. In this case the 4.88's are a requirement because the vehicle is underpowered. It is an 85HP engine that makes it's max torque of 115 lbs ft at 1400. with more power I would not need nearly so low gears.

If Huffed6's car is a toy and not a daily driver, he can use lower gears and just deal with the noise, if it is a daily driver, then a more moderate gear ratio will probably be more useful.

To just say that gear ratios above 4 are better (and they may well be better, depending on application) and don't worry about the gas or any other ramifications does Huffed6 and everyone else who reads this post a dis-service.

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'98 Jeep Cherokee, 4.0
'56 Willys P/U, 226L

[This message has been edited by 4.0Jeeper (edited 04-12-2002).]

This is a useful conversation. i have been thinking for some time about the drivetrain that will go into my '52 Chevy two-door behind a 320-cid GMC now abuilding. The time will soon come when i shall have to acquire the rest of the pieces. i intend this machine as a "hot rod" of the 1950s; it is, clearly, a "toy," but i want to be able to drive it wherever it needs to go. i don't own a trailer and don't want one. i want it to accelerate as quickly as it can, but i also want a good top end. Why build it, if i can't drive it . . . fast?

My plan is a "close-ratio" three-speed (2.2 low) with overdrive and a 4.56 differential. i have 235/70x15 tires on the car now, and will use something about that size. A '52 Chevy with GMC is not a lightweight, which is another factor that encourages lower (high numerical) gearing for the street. The overdrive makes it possible to enjoy the power the engine produces on the street and on the road. Or so i think. i intend to find out.

God's Peace to you.

d

car is definatly a toy 1929nash sedan 3200lbs still no int or glass clutch was new 4000 miles ago and starting to slip. on bigger hills from a stop have to slip clutch to get up .if you want to see pic of car e-mail me at gettinun@aol.com

hello....very interesting.....thanks for sharing Jeep.....if what i say doesnt work for you,ok ...I am trying to share what i have experienced myself and learned FROM MANY others about maximizing performance from a vehicle with a performance oriented engine.....what i find intersting is that when your build an engine-ESPECIALLY with higher power-and larger cam, is that with speed limits that we all enjoy(!!),when you use a gear over 4,you can actually increase performance of car....letting the cam operate in the rpm range it was designed for is very key to performance, ...basically if you have never had fun taking the same vehicle and changing the gear it is hard to understand what happens in a real world application....think of it this way, would you build drag engine turning 8000 rpm+ and use a 2.73 gear?...would you build a land speed vehicle using a 5.14?.....by sharing these concepts I am hoping to shed light on maximizing performnce on a performance vehicle...but this may not be the goal for everyone, but to say this is a dis-service ,is well not allowing those trying to gather the big picture,(learn) understand how you need to remember rear gear ratio is as important as cam, compression ratio,compressiion height on pistons,valve size,cam specs,connecting rods,cranks,etc......if you have never built an performance engine, and changed rear gear ratio for that engine, this may seem unimportant.....only trying to share how it works- i have learned alot and enjoy sharing it for free......

Lee

by the way i was a crew chief on northeast modifieds and sportsmans so i know cars and gearing just not how a 6 will react to what gears

Ok Lee, you have convinced me, you are smarter than I am, you know more about cars and gears than I do, and over 4.00 gear ratios are the way to go for performance engines. I am done contributing to this thread.

hello...its not about you, me or anybody else...it's physics.....

Lee

Well, I'm probably way out of my league here, but here's my 2 cents. I'm not the high tech guy that some of you are and that's fine. I am old school hot rodder. That means you install it, drive it, and if it's not your cup of tea (or Beer)you Changeit.I have always believed that a Hotrod should first be a safe vehicle, look great, sound fantastic, then be accomadating to all of your needs. Just through doing alot of different things in my past 36 years of driving, here's what I found out to work pretty well.
Any Inline six is going to give you enough torque to pull a hole shot on most new cars. Even my stock 216 & tranny with a 3:90 rear was decent. My new car, which is a Master 85 Business Coupe was 2849 lbs in stock form. By removing the stock rear, torque tube, tranny, motor,front seat, and front end, I got rid of approx. 1,300 lbs of bulk(I actaully weighed these components, just curious). I replaced those components with a 1970 292,T-5, alum drive shaft, stock 10 bolt nova rear, Dakota buckets, Mustang ll IFS. I added back approx. 750lbs more in components. That's a true savings of 550lbs!
Guy's, you don't need computers to know that loss of weight and increase of horsepower and torque = huge gains!
Now I have a 1984 Camero Z-28 T-5 with a low first gear and fairly low 2nd. Third you can wind out a bit and forth is 1:1. 5th is 0:76 so I get very nice off the line grunt and a cruising speed of 70 MPH at 2200 rpm's! I've never checked the milage but I didn't do all of this stuff for good gas milage. You want good gas milage, buy a horse!

Let me throw in another opinion. A long-time rule of thumb that has always worked for me, is that to get the best torque multiplication in 1st gear, the 1st gear ratio times the final drive ratio should be about 12. Example: a 2.95 1st gear would perform best with a rear end ratio of 3.90 or 4.11. This was about the mix used on early six-cylinder pickups and passenger cars. There are exceptions of course - Power-to-weight ratio can change this. Musclecars can get away with a 2.20 1st gear because of the brute torque of a big block motor. Much lower and the tires will go up in smoke.

Note that this 'formula' does not consider factors like RPM at cruising speed, fuel mileage etc. It is strictly concerned with gearing for getting a manual-transmission vehicle moving from a standing start, in normal driving.

I have absolutely no documentation for this rule-of-thumb. Where it originated, I have no idea, but I have heard it mentioned by several old-timers and it has always produced good results for me.

No guarantees, but this link has an Excel spreadsheet to calculate speed in gears. Just plug in different combos to get where you want to be...
http://www.opeltuners.com/niklasj/CIH_numbercrunch.XLS