I need advice for a good street performance/economy slant 6

2 Darts said
Both block and head can be milled to get you close to this. While upping the compression ratio will improve efficiency, it may be necessary to use higher octane fuel which is sufficiently more expensive to wipe out the savings created by the higher compression ratio.

Good luck

i agree that running to high of compression that you will need better octane but i dont think anything lower than 9.5 will have any trouble on our crap regular... especially with the stock lazy curve... have to remember that with such a small bore and flat tops the plug is really the only thing left to cause detonation...(generally speaking)

ran 9.4 on reg with no issues... and its 110 outside with the engine @ 210... 32* locked out timing