Editing V6 Chevy 90 degree engines

==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.

Production 1992 4.3L engines with RPO L35 had modified cylinder blocks where a balance shaft are used. The balance shaft are gear-driven off the front camshaft gear; camshafts for use with balance shaft motors have a longer dowel pin, which cannot be interchanged with non-balance shaft engines. The current engine block in production since 1995 eliminated the front and rear freeze plugs with extra strengthening ribs. The oil pan used was changed from stamped steel to an aluminum alloy casting. The engine block has 10 oil pan bolts, making the early and late oil pans incompatible.

==Cylinder Heads==
The cylinder heads used on the 200 and 229 had 58cc combustion chambers using perimeter-bolt valve covers. 1985-'95 4.3L cylinder heads came standard with 64cc combustion chambers, swirl port intake ports and centerbolt valve covers. The 1996-present 4.3L engines use the Vortec head, similar in design to the L31 5.7L V8 head. 

==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. The 1992 model year saw the use of balance shafts; all 1995-present 4.3s are balance shaft equipped.

==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.

==Rods==
There are four different 4.3L rods in two different weights that come from two different engine plants (Tonawanda, NY and Romulus, MI), so be sure of what is being used if the parts come from different engines or the source is unknown.

The 4.3L V6 engine has an even-fire sequence, occurring 120 degrees apart. 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. That means the 4.3L rods are not interchangeable with the traditional small block. The smaller 200/229 cid V6 rods aren't interchangeable either due to their narrower big ends.

==Firing orders==
All the Chevy V6 90 degree engines share the same firing order of 1-6-5-4-3-2. The two smaller engines, the 200 cid and 229 cid, 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. The design of the crank required the connecting rods to have 0.050" narrower ends to fit onto the available rod journal space due to the material added to the cranks for strength. 

The cam and distributors are specific to the 200/229 cid engines and they cannot be interchanged with the 4.3L V6 engine. Distributor bodies used on the V6-90 are identical to the one used for the Chevrolet small-block V8 except for the pickup coil and pole piece assembly. The main difference between the semi-even fire series (200/229) and 4.3L distributors is the 4.3L distributor pickup coil and reluctor wheel has six equal points every 30 degrees. Also, a majority of the distributors used on the 4.3L has a small distributor cap (commonly used with the TBI and CPI motors) with an external coil - the 1985-'86 model year 4.3L used in Chevrolet trucks, vans (including the Astro/Safari) used the traditional large-cap HEI on the RPO LB1 motor. Marine applications used a unique small-capped distributor not interchangeable with those used in automobiles.   

==Intake manifolds==
There is only one Q-jet intake available and it was only made for two years, 1985-'86. It is found in light duty pickups/vans (the 1985 Astro van had this intake; passenger cars came standard with TBI fuel injection). It's a heavy cast iron dual plane piece, has EGR and a heat crossover. It works OK for mild builds.
[[File:OEM 4.3 L V6 Q-jet intake 1986-back.jpg|thumb|left|OEM 4.3 L V6 Q-jet intake 1986-back]]
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Passenger cars (B and G-platform) and trucks/vans manufactured after the 1986 model year (including 1988-94 S-series trucks) came with TBI intakes. 

===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. 

Marine intakes have either the traditional 12-bolt pattern (200/229 and pre-1996 4.3L) or the 8-bolt Vortec pattern for 1996-present. The angle of the center intake mounting holes changed during 1987 to 72 degrees, same as the SBC.

[[File:Marine 4.3 L V6 1995-back non Vortec intake.jpg|thumb|left|1995-back non Vortec intake]]

[[File:'96-up 4.3L MARINE VORTEC INTAKE OPEN PLENUM, CAST IRON.jpg|thumb|300px|right|4.3L marine Q-jet cast iron single plane intake for the '96-up Vortec heads]]

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[[File:4.3 L V6 MerCruiser Alpha One Generation Two Vortec Intake w- 2 barrel carb c-n GM 12552422.jpg|thumb|left|350px|1996-up 4.3 L V6 MerCruiser Vortec dual plane intake for 2 barrel carb, c/n GM 12552422]]

[[File:1993 Mercruiser 4.3 LX V6 SQUAREBORE INTAKE P-N 14095286, CARTER CARB -339196005.jpg|thumb|center|300px|1995-back Mercruiser 4.3 V6 squarebore P/N 14095286, Carter carb 339196005]]

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==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==

[[File:4.3L V6 OILING 1.jpg]]
[[File:4.3L V6 OILING 2.jpg]]

==Front accessory set up==
The early engines and 4.3L (without balance shafts) shared the accessory drive used with the SBC including the pulleys, harmonic balancers, and water pumps. Marine applications used a short water pump and a 6.75" harmonic balancer. Like the SBC, two-piece rear seals were used until the end of the 1985 model year; 1986-present are one-piece. 1987 saw the use of roller lifters. 


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[[Category:undeveloped articles]]
[[Category:Engine]]
[[Category:GM]]