How can I tell if I have a 3.1L swap? (Page 2/2)
Blacktree MAR 19, 12:14 PM
Here are some quick checks you can do:

-- 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.
olejoedad MAR 19, 12:31 PM

[This message has been edited by olejoedad (edited 03-19-2019).]

Will MAR 19, 02:22 PM
'90-'92 F-bodies and minivans had factory iron head 3.1 engines with distributors. One of those would pretty much be a drop-in swap into a Fiero.
fierofool MAR 19, 04:32 PM
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.
Raydar MAR 22, 05:09 PM

Originally posted by fierofool:

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.

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).]

fierofool MAR 22, 07:46 PM
Hey, Raydar. GTRS was asking about that plug/sensor on the top of the block. What is it? Cam sensor? Knock sensor?
Raydar MAR 23, 07:27 PM
The one in the top, behind the timing cover, was for a cam sensor. Edited my post.

[This message has been edited by Raydar (edited 03-23-2019).]