I have an '89 S10 Blazer 4.3. I was looking at the 670 cfm Holley TBI. It claims to improve horsepower by 25%. I would like to buy one but I thought I would get a second opinion from everyone. Also, if it negatively effects gas mileage too much, I probably won't do it because it is a daily driver. Someone on ebay claimed that it actually improves mileage, but I don't believe them.

I would give holley a call and talk to their technical support.