Hello,

I have a 1986 Fiero SE V6 with the Muncie 4 speed manual transmission.

My Tach shows 3200 RPM when I am traveling down the highway at 65 MPH.

Is this normal?

That seems like too high an RPM for cruising down the highway. If this were a
standard RWD car I would be considering changing the ring and pinion gear to
drop the RPM a bit at cruise. Since this is a transaxle I would not know where
to begin to change gear ratios.

Is it possible someone installed a TACH from a 4 cylinder and it is showing an
incorrect RPM? I ran a carfax on this car before I bought it and it does not
indicate it ever had anything in it but a v6.

I searched the threads and could find no one who had given their RPMs at
various speeds.

Any data on what is normal would be appreciated.

dzimmerm

I had an 86 se with the isuzu 4 speed, but don;t remember the rpms.
on my 88 with the 5 speed getrag, 65 mph in 4th gear is 3075 rpm, right from an aldl log I have. you would need to lookup the
ratios for the muncie vs the getrag, and do the math, but given the tachs are not all that accurate to begin with, it sounds about right to me.

sounds like you got the 4.10 gearset. thats how mine is also. 2500rpm for 50mph, 3000rpm for 60mph, 3500rpm for 70mph. not a freeway freindly gearset. but - it gets you up to speed REAL quick.

I have the 4 speed econo gear box in my 1984 Fiero and at 65 MPH my duke is going about 2400 RPM.

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quote Originally posted by tjm4fun: I had an 86 se with the isuzu 4 speed, but don;t remember the rpms.

The Isuzu was only the 5-spd trans used with the 85-88 4-cyl. The 1986 V-6 SE's used a Muncie 4-spd with a 3.65 final drive.

Anyhow, at 70 mph with the original V-6 and 4-spd you should be about 3000 rpm, So at 65mph you should read around 2800 rpm.
Since yours is higher, Someone may have installed the 4.10 final drive gear set or swapped in a 1984 4-spd. The 1984 trans case had less webbing so there is a visual way to check if it is an 84 or an 85/86 V-6 4-spd. If someone just swapped the gear set you would need to remove the trans to check it out.
If it was a typical RWD you could measure the ratio by turning the drive shaft one turn and counting how many times the tires turn, But I am unsure if there is a way to check a transaxle in a similar fashion.
If the tach was a 4-cyl tach it would read WAY off. You could compare the tach against the computer via the ALDL/laptop set up. This would verify the tach is reading correctly.

hello dzimmerm,

I have the same powertrain and also the same readings. I am curious, what does it idle at when it is at normal temp?

aconesa

[This message has been edited by aconesa (edited 09-20-2007).]

Aconesa,

After it has warmed up it idles around 1200 RPM. When it is cold it wanders around 1500 RPM.

I guess I could measure the circumference of one of the tires with a tape measure and then figure
out if the Tach is making sense given the gear ratios I have seen listed for a 4 speed Muncie transmission.

dzimmerm

sounds rite i had a muncie in my car but i found a good getrag... so i am not much help

quote Originally posted by dzimmerm: I guess I could measure the circumference of one of the tires with a tape measure and then figure out if the Tach is making sense given the gear ratios I have seen listed for a 4 speed Muncie transmission.

Yes, expected RPMs are a fairly straightforward function of a car's speed, its tire diameter, and its final drive ratio.

Because of this, the RPMs you should expect your car to run in top gear at any given speed can be approximated by the formula:

RPMs = 339 X FDR X MPH, with that quantity divided by DIA.

“FDR” refers to the car’s final drive ratio in top gear (usually expressed as an integer followed by 2 decimals). “MPH” is, of course, the car’s speed in miles per hour (usually expressed accurate to the nearest integer). And “DIA” is the diameter of your Fiero’s rear tires, in inches (usually expressed accurate to at least the nearest tenth of an inch).

Many aren't aware that this formula, or variants of it, also can be used to estimate the effects on RPMs of a change in your car's tire diameter or gearing before you actually spend the money to make that change. For example, as you probably know, buying a shorter tire for your car has the same directional effect on RPMs as does a numerically higher final drive ratio: It increases them.

Incidentally, if for whatever reason you wanted to input the tire's circumference instead of its diameter (as you suggested in the above post), divide the result you'd get with the above formula by the value of pi (about 3.14).

I have an 86 SE with a F308 rebody and Muncie 4 speed manual transmission. At 70 MPH I see about 3400 rpm on my tach. The car is equipped with 60 series 15 inch tires.

After reading this thread...I thought I would see what my car (88GT 5-speed Getrag) runs at when at 65. I am between 2200 and 2300 rpm's. At 55 I am at a little over 1900 rpm's. Thanks!

i have the 4.10 gear setup in my 84 fiero and im running about 3200 rpm or there abouts and its completly normal persanally i enjoy it cause your cruising at sixty and u punch it you can get going pretty quickly but for that idle question mine idels at about 900 rpm when warmed up, if its cold it can go as high as 2500 usally just 2000 though until it warms up then it drops right back down to 900 rpm.

Checked my 86 GT 4 Speed yesterday and it runs 26-2700 at 65 mph. As previously mentioned some one must have swapped an 84 4.10 gear into yours.

My kitcar with an 87 getrag 5 speed shows 2200 to 2300 RPM at 65 MPH (in 5 th), like WisconsinGT

Checked out my car with the V-8 and the 4-spd.
At 65 mph it is running a needle space under 2800 rpm and at 70 mph it is running a needle space under 3000 rpm.
If I move the needle right on 3000 rpm the speedo shows a needle space above 70 mph.

So this matches what I was getting with the 2.8L.

It's fairly common for Fiero tachometers to fail in this way - they'll start reading high. That's almost certainly what's wrong with your car...

87 GT AT and I am at the same RPM at 60, about 3000

quote Originally posted by Mailmule: 87 GT AT and I am at the same RPM at 60, about 3000

1986 SE here, V6 with the 4speed.

I'm getting about 3.1k on the tach at 60MPH

Either it's "reading high" or someone swapped me for 4.10s as well!

What is more likely??? Cause if it's reading 4-500RPMs high that means I've NEVER even seen redline before, cool!

i made a list for the fierotrannys at various rpms with various tires some time ago
www.format-service.de/trannyspeeds.htm

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1984 Fiero Sport
1987 Fiero <- Ethanol powered Batmobile
1984 Fiero SE
2002 Kia Spectra <-LPG powered family car

*** nuclear winter cures global warming ***

Thanks for all the replies!

I will get an inexpensive service tach and see how far off the installed factory one is. I have to keep reminding myself this vehicle is 21 years old and is likely to have some weird issues you would not see in newer cars.

I also plan on crawling under the engine for other reasons so I will try and get some numbers off of the trans axle to see if anyone did a swap from the original.

dzimmerm