V6 Chevy 90 degree engines

by: Cobalt327, Mmerlinn
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Overview

A look at the Chevy V6 90º engines used from 1978-on.

Blocks

The Chevy 90º V6 is formed by the removal of the #3 and #6 cylinders of a SBC. All three V6 engines share the same 4.4" bore spacing and 9.025" deck height of the SBC engine.

Displacements

There were three displacements of the Chevy V6:

• 200 cid (3.4L) cid, basically 3/4 of the lowly 267 cid V8. Made 1978–'79.
• 229 cid (3.8L, not to be confused with the Buick-derived 3.8L 231 cid V6 used through the years), is 3/4 of the not-quite-as-bad 305 SBC V8. Made 1980-'84.
• 4.3L (262 cid), the best of the bunch by far. This is 3/4 of the SBC 350 and as such, shares some of the parts and dimensions with the 350. Made 1985-present.

Bore and stroke

200 cid: 3.50” bore x 3.48" stroke. 229 cid: 3.736” bore x 3.48" stroke. 262 ci/4.3L: 4.00” bore x 3.48" stroke.

Crankshafts

All the Chevy V6 cranks are 3.48" stroke. There are major differences between the 200/229 engines and the 4.3L engine, though.

Scat makes a cast crank for the 4.3L engine, p/n 9-4.3L-3480-5700. It's for the 1-piece rear main seal engines.

Firing orders

All the engines share the same firing order of 1-6-5-4-3-2. The two smaller engines, the 200 and 229, have what is called a "semi-even fire" sequence which alternates between 132º and 108º. This comes about due to the "slipped disc" crank pins; each pair of rods are offset by 18º. This required the connecting rods to have 0.050" narrower ends to fit onto the available rod journal space.

The cam and distributors are specific to these two engines and they cannot be interchanged with the 4.3L V6 engine.

The 4.3L V6 engine has an even-fire sequence. This is accomplished by having a larger 30º offset on the rod journal pairs. To gain back the strength that the wider offset takes away from the crank, the rod journal diameter is larger than the other V6 engines and also larger than the SBC, at 2.25", which makes them unique among the Chevy V6 and V8 engines.

Intake manifolds

There is only one Q-jet intake available and it was only made for two years, 1985-'86. It's a heavy cast iron dual plane piece, has EGR and a heat crossover. It works OK for mild builds.

OEM 4.3 L V6 Q-jet intake 1986-back

Marine intakes

There are several marine intakes, both for the Rochester 2G-type 2-barrel and the Q-jet spreadbore and Carter squarebore (uses an adaptor) 4-barrel carbs, all cast iron. In fact the only aluminum intake for the V6 Chevy 90º is a 2-barrel single plane(!) piece that was used for several years on the 200 and 229 cid engines. Not a performance-oriented part, it has a bolt pattern for the Dualjet (basically the front half of a Q-jet), which means no other carbs will fit it and there are no adaptors, either.

1995-back non Vortec intake

4.3L marine Q-jet cast iron single plane intake for the '96-up Vortec heads

1996-up 4.3 L V6 MerCruiser Vortec dual plane intake for 2 barrel carb, c/n GM 12552422

1995-back Mercruiser 4.3 V6 squarebore P/N 14095286, Carter carb 339196005

Rear main oil seal

In 1985 the 4.3 L V6 rear main seal was a 2-piece design, identical to the SBC. Beginning in 1986, the 4.3 L started using a 1-piece rear main seal, just like the SBC engines.

Oiling system

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