I can't seem to find any concrete answers, so I figured I would get advice from you guys.
I have an oil consumption issue in my Corolla and need to open up the top end, clean it up and re-drill the oil return holes (or buy new pistons, which will have the larger holes already). Another thread got me thinking about increasing the compression ratio by milling the head. I thought if/when I get around to taking the head off, that would be the time to do any modifications. The 1ZZ engine is stock 10:1 CR.
My issue is that I really know nothing about doing this mod. I have a few (lots of) questions:
- How much does increasing from 10 to 11 increase fuel economy? I read on howstuffworks, that an increase from 8 to 9 can increase FE by 5 or 6%. Can anybody confirm this and would it be the same increase for a different CR start and end(10 to 11)?
- How much would need to be milled for a one point increase? What is a "safe" amount to mill the head without having to switch out other parts? Can I shave enough off to have a 1.5 or 2 CR increase in a "safe" manner? What else needs to be swapped out, if anything to make this a "safe" mod? Also, how would I measure the CR after a mod?
- Gas Savers has some mixed emotions (including members here, I think). One guy says a smaller bore engine can generally withstand higher compression better versus bigger bore, is this true? Is 79mm (my engine) a small bore?
- The same guy mentions that reverse cooling (head first) is better, which makes sense, keeps the top end from over-heating. I'm not sure if mine does or doesn't, because I can't find the answer anywhere and my Haynes manual is vague. I attached a pic from my Haynes, which may help determine it.
- From what I have read, I would need a higher octane fuel to reduce knock. But I have Variable Valve Timing, so would I need to increase to an 89 or 91 (versus 87) or will the VVT make up for any pinging issues? Also, CA (like most of the US) has ethanol in the gas. So if the octane rating is 87, is that before or after the ethanol is added? I would imagine that would make a difference with ethanol having a higher octane rating. Thought this was an interesting article: CR and Ethanol Blends
I know this is a long list of questions, but I wanted to consolidate the info into one spot, which may make it easier for me as well as anybody else. Thanks for any insight you can give me/us!
