(( Please note: every effort has been made by me to insure the
accuracy of the information on this page, and any other page that I post. However, I
freely admit that mistakes can and do occur, and I encourage anyone with factual,
indisputable, provable, verifiable FACTS to contact me, and I will immediately make modifications to this
and any other page, noting your contribution ! I really would like to put this Diesel 4.11
gear thing to rest, if possible, or PROVE that a Diesel car with a FACTORY
INSTALLED 4.11 gear exists. I would require proof of it's existence, consisting of a
factory RPO for example, or a scan of the factory build sheet, and a scan of the VIN
number. Remember, it's not necessarily proof that the rear end was factory installed just
because it's there. I know LOTS of people who have changed rear ends, including me, and
you couldn't tell that it was not factory installed. ))
The Diesel Chevette 4:11
rear end gear mystery
( myth ? )
It seems that I have been reading and hearing about on various forums, Newsgroups, emails and conversations for years how Diesel Chevette's have 4:11 gear ratio's. I would sure like to dispel this rumor/myth once and for all, or prove that it's true. ( Doubtful since most people will never read this, or ever see this webpage. )
First of all, never let facts get in the way of a good story, myth, or rumor. I know dozens of Chevette racers who were led to believe that the Diesel car has 4:11 gears. Not one person that I have spoken to or been contacted by who has actually pulled the rear end cover from a Diesel Chevette has ever seen anything but 3:36 gears. This is pretty good empirical evidence in my opinion, but not story ending conclusive. After all, we haven't checked ALL Diesel Chevette's yet.
I have two Diesel Chevette's. I know for a fact that the '82 5spd car has 3:36 gears, the cover was pulled, and they were looked at. My 1981 Chevette Diesel automatic car was checked by using the "rolling the car on the ground, and marking the driveshaft and wheel" method*. This car also has the 3:36 gear ratio.
All of the "authoritative" Chevette people that I have spoken to have never seen 4:11 gears in a Diesel Chevette.
Now, lets introduce a little math and logic to the mix:
**********************MATH ZONE
***********************
By using the formulas necessary ( which can be found here, and on my homepage ) to find an engine RPM at a given speed, using a specific tire size and gear ratio we arrive at the following conclusions:
3:36 Automatic transmission @ 60MPH = 3000RPM
4:11 Automatic transmission @ 64MPH = 4000RPM
@ 80MPH = 5000RPM
3:36 Manual transmission @ 68MPH = 3000RPM
@ 80MPH = 3500RPM
@ 91MPH = 4000RPM
4:11 Manual transmission @ 56MPH = 3000RPM
@ 65MPH = 3500RPM
@ 75MPH = 4000RPM
( using a 155-80-13 or 175-70-13 tire which is approximately 22" tall ( generous ), and noting that the 5spd manual transmission vehicle has a .86 5th gear ratio. Since the automatic cars have lock-up torque converter, they may actually be turning somewhere near the RPM's listed above, where all calculations are correct for the given environment. )
As can be determined from the chart above, the little Diesel engine is turning quite a few RPM at highway speed even with the 3:36 gear ratio. It doesn't make a lot of sense knowing that Diesel engines are primarily a low RPM engine, ( even knowing that the 1.8L Isuzu Diesel has a rating of 51 horsepower @ 5100RPM, which is rather unusual ) to spin this engine that hard. It's not logical to assume that the engine would be sacrificed at highway speed in the interest of slightly better acceleration. The 5spd car already has a ridiculously low 3:79 first gear ratio anyway, and the auto car has the advantage of torque converter slippage to get moving. Also, most people fail to realize the incredible importance of tire size concerning final drive ratio. The Chevette usually uses a very small diameter tire, which has a significant effect on final drive ratio affecting acceleration and highway RPM. Most vehicles ( excepting tiny cars, and big 'ol trucks and SUV's of course ) have tire sizes of 24" and above, with 26"or so being somewhat normal. Since the Chevette used a very small tire, the 155-80-13 or 175-70-13 ( normally ) which is barely 22" tall, this will significantly affect final drive ratio. I am using 195-60-14 tires on my automatic car in an effort to slow the engine down at highway speeds ( and for better handling of course ! ), and since these tires are 23¼" tall, they have helped somewhat, not significantly affected acceleration, and are probably the tallest tires that will comfortably fit this vehicle.
Modern cars are barely over a 1000RPM @ 60MPH today, and some are not even at 2000RPM close to 100MPH !
Other facts of note: 5spd gear ratios Automatic gear ratios
| 1st 3.79 | 1st 2.50 |
| 2nd 2.18 | 2nd 1.5 |
| 3rd 1.42 | 3rd 1.0 |
| 4th 1.0 | |
| 5th .86 | |
Darryl Lowes has this page
on his website, and I feel it is important to note his contradiction to the information on
this page. I do not know where Darryl got this information, and would like to track it
down. Also it is worth noting that the information lists the TH200C as not being available
after 1979. My 1981 Diesel Chevette has the TH200C with lock-up converter. Also, it
has been mentioned by others that the Diesel engine 5spd transmission is different
from the gasoline engine. This is true, as the Diesel Chevette uses an Isuzu 5 spd
transmission.
In conclusion, I solicit facts, one way or the other, to finally figure this 4.11 Diesel gear ratio thing out. If anyone has any knowledge of any Chevette ( U.S. ) Diesel car with a factory installed 4.11 gear, please contact me !
Speaking of contacting me, here is some *cool* email I have received on the subject so far !
* Checking the gear ratio without removing the cover:
One way to do this is to mark the wheel and driveshaft ( pick a couple of spots where you
know you can be pretty precise ! ) and turn the wheel once. The best way to do this is
with the car on the ground. (Jacking the car up will skew the results.**) Count the number
of turns the driveshaft makes after turning the wheel JUST ONCE, and this will be your
gear ratio. Be careful when rolling the car and counting !
Example:
One wheel turn results in a *about* 3 turns of the driveshaft:
3:08 gears ( probably )
One wheel turn results in a little over 3 turns of the driveshaft:
3:36 gears ( probably )
One wheel turn results in about 3¾ turns of the driveshaft:
3:70 or 3.62 gears ( probably
)
One wheel turn results in a little over 4 turns of the driveshaft:
4:11 gears
As you can see, the method is far from exact, but you can come pretty damn close, especially if you know which gear ratios are available for a certain vehicle.
** Sometimes with the wheels off of the ground, you can perform this test, but you must multiply the driveshaft turns X2.
Example: One wheel turn results in 1½ turns of the driveshaft will probably be a 3.08 gear.
The information below comes from Mr. Fields, of Fields Racing !
______________________________________________________
The information below comes directly from General Motors.
Chevette Rear Axle Specifications:
Ring Gear Diameter: 6.5"
Pinion Shaft Offset: 1.125"
Ring And Pinion Ratios Available For The Chevrolet Chevette: (3.36:1) (3.62:1) (3.70:1) (4.11:1)
1976 - 3.70:1 Except 4.11:1 w/1.6 Liter Engine
1977 - 3.70:1 Except 4.11:1 w/1.4 Liter Engine, Or Automatic Tranmission
1978 - 3.70:1
1979 - 3.70:1
1980 - 3.70:1
1981 - 3.70:1 Except 3.36:1 (Scooter)
1982 - 3.36:1
1983 - 3.36:1
1984 - 3.36:1 Or 3.62:1
1985 - 3.36:1 Or 3.62:1
1986 - 3.36:1
1987 - 3.36:1
( The 4.11:1 ratio was an option in 1978, and was dropped in 1979. )
I hope this information will help many of you, I know it has certainly helped me!
FIELDS RACING #92
"THE FASTEST CHEVETTE IN TENNESSEE!"
"TENNESSEE MOTOR SPEEDWAY'S 2002 AUTOZONE CHEVETTE POINTS CHAMPION!"