I did a search (as usual) and didn't find anything on this.
3000 RPM at 70MPH on a V8? The redline is 5,250. That's over halfway to redline! Would this still get me low 20s gas mileage? What about top speed? I calculated it to a gearing-limited 122.5.

(5250/3000) * 70 = 122.5

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4.9... Top speed?

Why do you care? you get there before you finish a 1/4 mile!

The stock ECM will stop you before you get to 122 MPH. Why would you even consider the TH125 if you are concerned about fuel mileage? Just use a 4T60E and forget about it. You'll be happier.

I would consider it because
a) It's already in my car and I know it works.
b) It's lighter.
b) I don't have to buy it.

I am on a rather tight budget ($1,500) and time constraint (really need to get it done.. this is my top priority).

1-2-3-4-5 done. Now exit the intersection.

Are you nuts? The motor doesn't rev high enough to be anything short of annoying with a 4/5 speed.

Unless you are in the rowing club, of course

quote Originally posted by rockcrawl: The stock ECM will stop you before you get to 122 MPH. Why would you even consider the TH125 if you are concerned about fuel mileage? Just use a 4T60E and forget about it. You'll be happier.

Wouldn't the 4T60 be easier? No electronics to mess around with...?

...however, he's said he wishes to stick with the TH125.

WipeOut, what's the speed limit where you are? I had a '75 Impala (5,000 lbs, aerodynamics of a brick) with a 305 and it got about 20 mpg at 55 mph--that's with the engine turning at about 3000 rpm. I have to believe that a lighter, more aerodynamic car like the Fiero would get at least 20 mpg at 3000 rpm, even if you are going 20 mph faster.

Ed

What is the top speed of a 4.9 with the od trans. I am now stuck between a 4.9 and 3800sc as a christmas present to myself and would like a top speed of around 155.

quote Originally posted by freedog81: What is the top speed of a 4.9 with the od trans. I am now stuck between a 4.9 and 3800sc as a christmas present to myself and would like a top speed of around 155.

Now where can you drive a Fiero at 155 safely?

I had my 3.4L dynoed in Daytona in 3rd gear and it was running at 142 at 5500 rpm with a t440 transmission. How fast can it go, I don't know. The fastest I've had it was 120 in 3rd gear and I was running maybe 4500 rpm. In OD it runs 100 mph at 2500 rpm. So I guess at 5000 rpm I can do 200 mph.

At 120 mph, I got thinking what if I have to stop, I have touring tires on the car and I'm an old guy..What am I nuts?

So you don't need a 4.9 to go fast.

In normal driving I can obtain 30 mpg on old 87 octane gas.

quote a) It's already in my car and I know it works. b) It's lighter. b) I don't have to buy it.

OK, I can go along with that.

I don't think the Caddy ECM will let you do more than 115 MPH unless you trick it. Same with most other GM stuff I think.

quote Wouldn't the 4T60 be easier? No electronics to mess around with...?

Not exactly how I see it. The 4.9 ECM is designed for a 4T60E. Use anything else and you'll need to make it think the 4T60E is still there.

I rarely drive over 70 MPH, and I don't really drive any of my Fieros very often, so I don't put much consideration into fuel economy and gearing. I use whatever I have to make a quick car. Notice I said quick, not fast. I don't really care how fast they are.

Can someone answer the mans question without harassing him about how fast he wants to go.

In every 4.9 thread I've seen with someone asking the top speed question people tip-toe all around it.

Is a 4.9 limited by drag or RPM? At what speed does this happen?

I've heard California Kid say he's been up to about 165, hanging with a viper. Thats Fast. He also has 400hp in a chev small block... so how fast is a 4.9 with half the horsepower?

So, who wants to answer the man's question?

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86 GT 4 speed 135,000Km

Maybe everyone who builds the 4.9 understands that it is NOT a revving motor. Try a ~4500rpm power peak... You ain't gonna go much higher than that.

What's a Duke top out at? I'd think it'd be similar, since they have similar RPM restraints. The 220-odd HP of the 4.9 (and brutal torque) should be more than adequate to peg the tach to 4500rpm...

What's that work out to in MPH?

Sooo what your saying is the top speed is limited by RPM.

Thank you Mach10

Now with his final drive ratio he can figure out his top speed.

I'm going to have a 4 speed standard on my Cadero once i get it

I understand that i'll be changing gears before i'm out of the intersection, however, its the same case even with my 2.5L. I don't think that the shifing will be much more frequent with a 4 speed cadero then a 4 speed Fiero.

I don't see what the problem is. I think the 4 or 5 speed would be great for a Cadero.

*except for the fact that changing gears is not very smooth at all*

I will try my 4 speed fiero. I might even buy a Getrag 5 speed to change just in case...but i'm sure its not THAT bad. I'll just have to suck it up and have better 1/4 mile times the the Autos

Do you think that a Cadero could be somewhat of a everyday car? if driven gently?

>if anyone has any opionions on that
question PM them to me<

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Steven Rossi
2M4 to GT conversion underway

I've tried the Fiero sticks... Can't say I'm impressed.

The 2.5 4spd I played with... God, I HATE having to row through gears that quick, even under LIGHT driving.

Just feels wrong.

Then again, get me a nice sequential 5/6 speed

So basically you're saying that even with the extra weight and effort, the 4T60-E is still the best choice?

I've driven my friend's '88 Ranger and the gears come very quickly in that. 20mph in first, 30 in second, 40 in third, 50 in fourth, etc.

quote Can someone answer the mans question without harassing him about how fast he wants to go. In every 4.9 thread I've seen with someone asking the top speed question people tip-toe all around it. Is a 4.9 limited by drag or RPM? At what speed does this happen? So, who wants to answer the man's question?

Are you serious?

I have a 3800SC with a 5 speed Getrag. I don't understand all the fuss about having to shift. If its a real sports car in my book then it will have a manual trans. (No flames it is just my opinion) So what if you shift quickly even before you are through an intersection. The sweetest part of driving my car is the fun from first to third. I would love the 4.9 with a 5 speed too.

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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Red 88 GT T-Top 3800 Supercharged
White 88 GT T-Top Stock
White 88 GT Stock

Alright I can answer part of this question. Fuel economy with a 125, in the city we get just over 220 kms on a tank, which we never got with the V6, it was just under 200 kms on a tank. On the high way it is worse because of the reving. We have had as bad as 120 kms on one tank on the Fiero cruise, which is mainly highway with a/c on and alot of showing off in the city. But we did not put in a V8 for the fuel economy side. And the top speed, we could not answer this because we do not drive fast. The fastest it has gone is 120 kms/h, thats about 75 mph or so. The top speed would be rev limited on ours at 5500rpm.....so whatever an auto fiero with 3.33 gear ration's speed at 5500 rpm is would be our top speed. But we have not yet lost when the light goes green.

Pete

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For everyday driving, I would believe that the 460t trans and 4.9 in the Fiero would be AWESOME. It's basic hot rodding concept applied a modern car and motor; motor from big car shoved into little car. The four speed electronic auto is smooth and gas milage freindly, the V8 is - well, it's a V8 no matter how you slice it (!) in a stylish mid engined car...done (relatively) cheap. Gotta look at the total package though: is the handling up to par? And how doggy does your machine look?

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John DuRette
85 SE

Just my .02 here since i am currently doin this swap....

I went through a lot of thinking and planning and ideas before i decided on what i am doing now. It all depends on how you plan to drive your car. For me, i have a 40 mile commute to and from work. thats about 80+miles a day. I was gonna use the 125 trans in the beginning due to, as you said, its already in the car and working and you dont have to buy it. But after driving it and at 70mph having it go about 3k on the tach, and the noise that just the 4cyl makes at that speed, a v8 would be hard to take on a day to day basis! Granted it would be a rocket around town, but most of my driving is on the expressways. Also taking into account the fieros small gas tank, and a v8 goin 3k every day for 40 miles, i would be filling up all day long lol.

All that made me decide the extra $$$ for the 4t60e trans and the effort to make it work was well spent. Keep in mind youll also be replacing axles to get the o/d trans to work. Figure about 150ish for a good set of re-maned axles plus the cost of a tranny. Also figure about $25 for a trans bracket from a 440t4 car.

If your just goin for a quick car for fun, the 125 trans should be fine, though personaly i am not convinced its up to a v8's torque daily in stock form.

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'88 Red SE (4.9 PFI in progress, currently in wiring stage)
'99 Black Dodge Intrepid (daily driver)

Sorry it took so long. Most of my driving is done on the highway and I would perfer the transmission that came with the caddy but as for where can I go 155 I live in a SECLUDED area in SC and there are so many places to do that within 10 miles of my house that it is a shame. That is not to say that I would go that fast because I only have H rated tires with 16 in rims but I was planning on upgrading to z rated tires. I just wanted to know how fast it would be going with its trans in 4th when it gets to 4500 rpms. The takeoff of my car with the 3.1 is brutal now and the top end is where it runs out of steam. I already planned on a od trans swap but figured if I were going to go trugh all that trouble just do both at the same time.

quote Originally posted by LoKey88: Just my .02 here since i am currently doin this swap....But after driving it and at 70mph having it go about 3k on the tach, and the noise that just the 4cyl makes at that speed, a v8 would be hard to take on a day to day basis

don't EVER let me catch you comparing a well-balanced aluminum v8 with a cast-iron boat-anchor I-4 again...
EVER

This motor is so stupid-quiet, until you hit the 'loud pedal'

It's VERY nice and quiet at cruise... And I have it SOLID mounted to my cradle. AND I have a split muffler...

I have gone beyond the peg on a 120 mph speedo, was told that I was doing over 130 when I was blowing black smoke - I had a bit of a fuel delivery problem (It actually accelerated some when I lifted). I was being followed by another Fiero member on our way to Ed's swap meet. That's with a 305 SBC ECM and a custom chip by Greg Duncan, and a 3.35:1 Isuzu 5 speed. And carrying a passenger.

My rev limiter is set at 6000, have never got even close. But my shift light is at 5100, and I light it up daily . According to the tach I float the valves around 5400.

To reach 155mph, you would have to have either a gawd awful low FDR (in the 2.25 range) or rev to over 8,000 RPM. Oh, and have about 600hp or more to push the car through the drag. Few cars can achieve that, and those that do have more money in it than a new Viper/Porsche would cost. (Personally, I would rather have the new exotic, as much as I love the Fiero).

(The Fiero 4.9 decklid stickers are in,
Team Cadero windshield banners to follow - See CaderoOwnersForum@yahoogroups.com )

G

Cadero2max do you have the 125 or the 4t60 trans in your car. thanks?

FOR TOP SPEED and MPG and quiet

just use a duke's version th-125
some years are 3.0 F/D

my fake formula [88 coupe v6 swap]
has a duke's trans and is only a little
slower but a lot quieter.

other th-125 gears are in the 2s

DID CADDY EVER USED A th-125 with a 4.1-5???

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Question wonder and be wierd

Our Cadillac with a 4.1 and 4T60E has the acceleration of a dead horse and averages about 17.5mpg city and 20mpg highway, but it would be better in a fiero because less weight and bit better aerodynamics.

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--Adam--
1987 Blue GT 5-speed
IM AOL: GTFiero

My 86 2M4 W/ A 125TH in top gear runs 22mph per 1000 rpm. Sooo
4000 = 88.0 mph
4100 = 90.2
4200 = 92.4
4300 = 94.6
4400 = 96.8
4500 = 99.0
4600 =101.2
4700 =103.4
4800 =105.6
4900 =107.8
5000 =110.0
5100 =112.2
5200 =114.4
5300 =116.6
5400 =118.8
5500 =121.0
5600 =123.2
5700 =125.4
5800 =127.6
5900 =129.8
6000 =132.0
To get to 165 one would need 7500 rpm. It's just a question of playing chicken with your motor. "How high can I rev this sucker before it goes BANG!!!?"
A bigger engine only gets you up to speed faster. Unless one changes gearing, the top speed is not going to be any higher than before you pulled the orginal engine.

http://www.quiknet.com/~ke6vut/rpmcalc.html

You can kinda use this to figure out top speed. All you need is the tire diameter, rearend gear ratio, and transmission final drive gear ratio. Just play around with the speed until the RPMs get close to the rev limit. I used this to figure out the top speed of my Cutlass w/ 383, TH350, 4.10 posi rearend, and it was about 103. But, it sure gets there fast!

By the way, you can figure out tire diameter at: http://www.fieroshop.com.au/tyrecalc

quote Originally posted by freedog81: Cadero2max do you have the 125 or the 4t60 trans in your car. thanks?

I have a 3.35:1 ratio Isuzu (stock 4 cylinder trans).

But whether stick or auto, the top speed is dependent on the final drive ratio. I have a TH125 I had built up for the now defunct Grassroots Motorsports Challenge Fiero. It had a 2.84:1 ratio, and I put kevlar clutches and a shift kit in it for racing. I anticipated about 140mph from that with a basic stock 4.9 at 5000RPM.

G

[This message has been edited by cadero2dmax (edited 08-24-2002).]