I am going to rebuild my 2.8 into a 3.1, ( i want to keep the car looking stock so a motor swap is out ) meaning that the bore is going to be 3.5 (also bored 0.030 over) and the stroke is going to be 3.31. I am going to use 3.1 pistons and a 3.1 crank. My question is do any of you foresee any problems in the future? Will the crank fit? I have heard that the 2.8 and 3.1 were the same block. Will the computer for the 2.8 work on the 3.1? Any advice or suggestions? What is going to happen if i use the same computer and any advantages to getting a 3.1 computer because i know the 3.1 had a knock sensor and they are speed density and not Mass air flow ( from what I have read ) Also the compression of a 2.8 is 8.9:1 and a 3.1 is 8.5:1. What would the compression be for this motor using the same heads? Thanks

-William

 

Here is some info, think I got it from thirdgen.org
Chevy Production 60 degree - V6 Engine

In 1980 Chevy introduced a new V6 engine design with 60 degrees (deg.) between the two cylinder banks. This design had two advantages; it produced a true even fire engine using a standard common journal crankshaft and it produced a slightly narrower engine. The 1980 design was also the first Chevy all metric engine design. The new engine has a deck height (centerline of crankshaft to cylinder deck measured along the centerline of the bore) of 224.0 mm (8.819") and a height (centerline of crankshaft to top of engine along the center of the 60 deg. V) of 236.0 mm (9.291"). Cylinders are spaced on 111.8 mm (4.40") centers on each bank and the centers of cylinders on the two banks are offset to accommodate the two connecting rods on each crank journal. The 60 deg. V6 is unique among all Chevy motors since the right hand cylinder bank is offset ahead of the left hand cylinder bank when viewed from the rear of the engine. Cylinders are numbered 1-3-5 and 2-4-6 from the front on the right and left banks respectively.
The 2.8L (173 cid) engine was produced from 1980 to 1989. In 1990 the 3.1L (191 cid) engine was introduced and in 1991 displacement was increased to 3.4L (207 cid). The 60 deg. V6 is used in both transverse (front wheel drive) and longitudinal (rear wheel drive) configurations. The 2.8 liter engine was fires introduced in the 1980 Citation and the rear wheel drive version was optional on the 1982 S10 pickup and Blazer.
Below is a table of the main dimensions for all production 60 deg. - V6 Chev engines from 1978 to present :
L/CID Years Bore Stroke Block MaterialActual CID Main Bearing
2.8/173 80-89 3.50 2.99 Cast Iron 172.6 2.83L 2 bolt
3.1/191 90-94 3.50 3.31 Cast Iron 191.1 3.13L 2 bolt
3.4/207 91-94 3.62 3.31 Cast Iron 204.4 3.35L 2 bolt

80-84 engines have 63.35 mm (2.494") main bearings
85-94 engines have 67.25 mm (2.648") main bearings
In 1982 no.3 main bearing was changed to 63.13 mm and enlarged to 67.25 mm in 1985
Rod journals are 1.998 to 1.999"
DOHC introduced in 1991 for 3.4 L; OHV introduced in 1993
All 60 deg. V6 engines have rod length of 5.70" (same as small block V8’s).
Firing order on all 60 deg. - V6 engines is 1-2-3-4-5-6

The heads and block are the same in all 2.8(85 and up), 3.1 and 3.4.
The stock springs are good for about .440'' lift.
Just make sure you get the right year crank for youe block.
KEEP THE MAF SYSTEM. air speed sucks with mods unless you have a way to reprogram the compuper, You would have to pull the compter and flash the chips before you reprogram them.
MAF 85-89 air speed 90-92
Reuse the 2.8 fuel injectors.
Fork over some extra money and get a bigger cam too.
The stock cam is some thing like 196*/198* .396''/.420'' if you get a cam stay away from those numbers.

 

So can i make my 2.8 into a 3.4 with no problems? can you go from a bore of 3.5 to 3.62 with no problems and what size cam should i get? i do not want to reprogram my PCM.

 

YOu can't bore the 2.8 that much. I have herd 3.58 at the most.