92_rugby_subie Posted July 4, 2011 Share Posted July 4, 2011 I know a SPFI motor can be put under a carburetor manifold with higher compression/more power (how much does this change the reliability?) Can this go the other way? If it was being rebuilt, could it be "altered" in such a way that it would be the same as an SPFI motor? Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted July 4, 2011 Share Posted July 4, 2011 (edited) The difference in compression is 9.0:1 for carb, 9.5:1 for SPFI. Different pistons. You can swap them back and forth all you want - the SPFI blocks are rated at 90 HP and the carb blocks at 84 HP. The difference is too small to really be an issue. You might see half a MPG less with the SPFI if you give it a lower compression short block. 6 HP is really pretty meaningless either way - you aren't going to feel a tremendous difference unless other mods increase the spread between the two. The biggest problem with running high-compression and a carb is that you have no knock control. Not that the SPFI does either but it DOES have the ability to be factory tuned to insure it doesn't ever get into detonation and break something. Someone that knows how to tune carbs can make the high comp. block work but you do need to know what you are doing. GD Edited July 4, 2011 by GeneralDisorder Quote Link to comment Share on other sites More sharing options...
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