I have had my Fiero for nearly a year now and in that time I have noticed a number of strange things and modifications that have been made by previous owners. I have the lower geared Grand Prix getrag 5 speed for example. I am 99% sure my car was converted from an automatic as I have a third "shift cable" going toward the front of the car among other little hints like no rev limiter.
My question: Is there an easy way to tell the difference between the 3.1L and 2.8L bottom end? Anything I can look at in the bay to tell? Only thing I have come to so far is to look and see if the heads are aluminum.
------------------ 87 GT in Blue ~ Drive what you love and love what you drive ~
If you still have the RPO code sticker on the front left wheel well, you can confirm what transmission your car was equipped with from the factory.
If you have a stock-looking engine, you most likely have the iron heads. GM gave the iron-head 2.8 engines flat-top pistons from the factory. 3.1s got dished pistons. So, you could poke a borescope through one of the spark plug holes to see what you have.
The method is fallible, as if someone's already messed with the engine, all bets are off.
In general, the only way to reliably know the displacement of an engine is to strip off the heads, and measure its bore and stroke.
I don't know why you would need to know the displacement of your Fiero's engine.
Didn't the 3.1's have a crankshaft sensor like the 3.4? If so there will be a sensor or at least a place for one on the trunk side of the block near the middle freeze plug.
I checked the heads and they gave the same surface rust as my logs so they are cast for sure. So it's the 2.8
That just tells you the heads are cast iron. They fit on the 2.8, 3.1, and the 3.4. There are posts in the forum that tell you how to ID a 3.4 block from the outside but I don't know about the 3.1 on the outside.
dyno it, a 2.8 will only make about 165-170 ft*lbs of torque, a 3.1 about 185 and a 3.4 about 200.
Haha I was hoping there would be a stamp on the engine somewhere telling me. I guess I'll have to. My butt Dyno says 2.8 and the 0-60 is not very good. On the other hand it runs side by side with my buddies BMW 328i so it's difficult to say.
I guess I will just have to Dyno it
------------------ 87 GT in Blue ~ Drive what you love and love what you drive ~
Originally posted by xzeion: Haha I was hoping there would be a stamp on the engine somewhere telling me. I guess I'll have to. My butt Dyno says 2.8 and the 0-60 is not very good. On the other hand it runs side by side with my buddies BMW 328i so it's difficult to say.
I guess I will just have to Dyno it
The 2.8 block could be rebuilt and stroked to 3.1 and then bored to 3.4L (after being stroked) so a dyno really is the only way to know what you are actually running... Usually when going to 3.4L I rebuild the 3400 block with 3.4 DOHC pistons from something like a 94 Grand Prix with the 24v 3.4L DOHC motor. The higher compression using those pistons should get out over 200 ft*flbs. Some of us have even made as much as 250 ft*lbs but that would also require headers and a free-flowing exhaust.
-- Remove the flywheel inspection plate, and see if the flywheel has any weights on it. If the flywheel has weights, it's a 2.8. If not, it could be a 3.1 or '88+ 2.8. -- Look at the oil pan, where it meets the timing cover. If the oil pan angles down, it's a 2.8. If the oil pan is straight across, it's either a later model 2.8 or a 3.1. -- Is the oil pan sheet metal (steel) or cast aluminum? If it's aluminum, it's a 3.1. If it's sheet metal, it could be a 2.8 or an older 3.1. -- Like mentioned above, look for a crankshaft position sensor on the side of the block (trunk side). It'll be close to the middle. The 3.1 uses a crank sensor, but the 2.8 doesn't. The 2.8 doesn't even have a hole in the block for the sensor.
There are some other things you can check, but they require partial disassembly of the engine. For example, you can remove the oil pan and see if the crankshaft has a crank trigger wheel. You can remove a cylinder head and measure the piston stroke. And you can remove the lower intake to see if it has a roller camshaft.
One final note: I don't think a dyno test is going to be very conclusive. First of all, dynamometers read differently based on weather conditions, and how they're calibrated. The difference in performance between a 2.8 and a 3.1 is small enough that weather or calibration can easily skew the numbers one way or the other. Second of all, a 2.8 with minor mods can put down numbers similar to a stock 3.1. So you're still playing a guessing game.
And those 90-92 3.1's can safely be bored to .060 over and stroked to get you up to the 3.5 range. I'm not sure about the car engines but the van engines had thicker cylinder walls than the other 3.1's according to Dave Belville who built one of the first Formula Fastbacks with a bored FWD van 3.1.
Didn't the 3.1's have a crankshaft sensor like the 3.4? If so there will be a sensor or at least a place for one on the trunk side of the block near the middle freeze plug.
This. If it has the boss in the trunk side of the block, it's at least an 88 2.8. If it has a metal plug in the center of it, it's at least a 3.1. Maybe a 3.4. If it has a large "F" cast in the side of the block, it's a 3.4. Also check the top of the block, above the timing cover. If it's got a metal plug, or an unused sensor, it's probably a 3.4. (This location was for a cam sensor.)
[This message has been edited by Raydar (edited 03-23-2019).]
