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Hey peeps i used to own a 2005 civic ex sedan. I just sold a lot of my toys including my 2008 tundra crewmax and bought me a 2007 civic si sedan. I keep looking up videos to choose a exhaust. People keep saying you can run the car in VTEC all day. is this a button that i need to push or are they saying just running in in the 6-8k rpm range? I noticed that when i hit high rpm the car kinda takes the hell off again going with a SRI and a skunk2 i think. I really just want a deeper sound since i had 40 series flowmasters on my truck

 
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I just read through the forums and people say they are putting premium fuel in the SI. I just filled the tank with 87 did i mess it up or will it just run a little slower with the low grade?

 
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No putting 87 wont do anything serious. but if ur owners manual says to put premium i would sugest to follow wat it says but putting regular in one time wont hurt it. there is no button for vtec either im not sure how vtec works but i know there is not a button lol

 
Rep Power: 218

SIs need premium because of its higher compression ratio. Newer cars have knock sensors to adjust for lower octane fuel usage. I don't think you did any harm though. I just wouldn't make a habit of it. Stick with what the manual tells you to use.

 
Rep Power: 368

i believe in the fule door should be a recommendation of which fuel to use.
V-TEC is coded on the car, under cetain conditions it will engage. Not sure, but guess the 8th gen have different conditions than the 7th gen to engage.

 
Rep Power: 813

yeah your ecu will correct the timing to compensate for lower grade gas, but you will also lose power. i would use premium if the owners manual recommends it for best performance. regular will not kill the engine but i wouldnt use it all the time.

 
Rep Power: 218

It's probably the same for the most part except for RPM range for engagement.

 
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Vtec for 07 SI engages at around 6000 RPM. You should hear it open up and really pull you at that point.