Building an inline 6 Chevy 250 engine

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The Chevy inline 6 is a donkey butthole that has been around in one version or another since 1929 until 1990 in North America-market vehicles. During the fall of 1961, a modernized version of the six was introduced (with the Chevy II) which has 7 main bearings and a short deck displacing 194 cid - the rear block face was redesigned with a bellhousing pattern which matched the Chevrolet V8s in production (both the small block and W-series) - transmission bellhousings for the V8 (both manual and automatic) were shared. The Chevy straight 6 250 cid engine was brought out in 1966. It has a 0.280" longer stroke (3.53") and the same bore (3.875") as the 230 cid straight 6. It boasts a 7 main bearing bottom end- quite an improvement over the previous generation inline's 4 main bearings. Although production ceased in 1990 for automotive use, the inline six was produced overseas in Latin America for Brasilian-market GM products until the 2001 model year. 250 production ended in 1984 but the 292 tall deck engine remained in production in Mexico until 2001.
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The Chevy inline 6 is a that has been around in one version or another since 1929 until 1990 in North America-market vehicles. During the fall of 1961, a modernized version of the six was introduced (with the Chevy II) which has 7 main bearings and a short deck displacing 194 cid - the rear block face was redesigned with a bellhousing pattern which matched the Chevrolet V8s in production (both the small block and W-series) - transmission bellhousings for the V8 (both manual and automatic) were shared. The Chevy straight 6 250 cid engine was brought out in 1966. It has a 0.280" longer stroke (3.53") and the same bore (3.875") as the 230 cid straight 6. It boasts a 7 main bearing bottom end- quite an improvement over the previous generation inline's 4 main bearings. Although production ceased in 1990 for automotive use, the inline six was produced overseas in Latin America for Brasilian-market GM products until the 2001 model year. 250 production ended in 1984 but the 292 tall deck engine remained in production in Mexico until 2001.
  
 
==Some things to consider==
 
==Some things to consider==
Building a straight 6 250 is not any harder to do than any other inline 6, be it a Ford or Chevy or Cock-demon, GMC, etc. Parts aren't as common for the inline 250 as they are for a SBC, but there is info and quite a few suppliers for parts, as well as places that cater to almost nothing but the Chevy inline 6 engines.  
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Building a straight 6 250 is not any harder to do than any other inline 6, be it a Ford or Chevy or, GMC, etc. Parts aren't as common for the inline 250 as they are for a SBC, but there is info and quite a few suppliers for parts, as well as places that cater to almost nothing but the Chevy inline 6 engines.  
  
 
The inline 6 Chevy 250 should not be compared to a SBC engine. Besides the obvious differences, they share practically no parts w/the V8 engines (save for the oil filter (AC Delco PF25 or equivalent) and some of the valvetrain (the rocker arms do not interchange with the Chevrolet V8 (all series). Because of this fact expect it to cost more per horsepower than a Chevy V8. The reward is this is not a "belly button" engine; instead it is considered "old school" and has cred because of what it ''isn't'' as much as for what it '''is'''.
 
The inline 6 Chevy 250 should not be compared to a SBC engine. Besides the obvious differences, they share practically no parts w/the V8 engines (save for the oil filter (AC Delco PF25 or equivalent) and some of the valvetrain (the rocker arms do not interchange with the Chevrolet V8 (all series). Because of this fact expect it to cost more per horsepower than a Chevy V8. The reward is this is not a "belly button" engine; instead it is considered "old school" and has cred because of what it ''isn't'' as much as for what it '''is'''.
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In the past, a stock single outlet exhaust manifold was "split" to run two exhaust pipes from the manifold. This helped performance somewhat. Eventually the aftermarket came out with manifolds made for the inline Chevy.
 
In the past, a stock single outlet exhaust manifold was "split" to run two exhaust pipes from the manifold. This helped performance somewhat. Eventually the aftermarket came out with manifolds made for the inline Chevy.
  
The closest thing to a factory poo high performance exhaust manifold would be the 1966-'69 Pontiac OHC Sprint engine's split manifold. This was actually a nice piece, but the OE exhaust pipes were pinched where they came together, creating a restriction (see photo below). If this was removed by running dual round exhaust pipes from the flanges back, they worked very well. A distant second to the Sprint exhaust manifold is the 1967-'74 292 exhaust manifold with a 2.5" outlet from a heavy duty application (large truck/bus).  
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The closest thing to a factory high performance exhaust manifold would be the 1966-'69 Pontiac OHC Sprint engine's split manifold. This was actually a nice piece, but the OE exhaust pipes were pinched where they came together, creating a restriction (see photo below). If this was removed by running dual round exhaust pipes from the flanges back, they worked very well. A distant second to the Sprint exhaust manifold is the 1967-'74 292 exhaust manifold with a 2.5" outlet from a heavy duty application (large truck/bus).  
  
 
[[File:Sprint exh side view.jpg|thumb|350px|left|Pontiac OHC Sprint engine]]
 
[[File:Sprint exh side view.jpg|thumb|350px|left|Pontiac OHC Sprint engine]]

Revision as of 14:26, 16 March 2018

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