4.9 overbored?
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Senior User
Joined: Aug 2000
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From: Baldwin, ND
4.9 overbored?
Has anyone here bored out a 300? I am going to rebuild mine and just wondering how much it helped to bore it. would probably go .030 over when I do it, also changing the cam, port and polish and putting a different intake on it at the same time, but I was just wondering what (if any) power increases I would get by boring it out. Thanks.
Justin
1972 Ranger 360 (Grandpa's Truck)
1975 F100 Custom 4x4 360 (My Fixxer Upper)
1976 F150 390 (Grandma's Truck)
1978 F150 351W (Older Brother's-thinks he's a mechanic so why is it sitting??)
1982 F150 XLT Lariat 4x4 351W (Friend's Truck-but he's in MT and it's at my place)
1983 Bronco XLT 4x4 300 (My Daily Driver)
Justin
1972 Ranger 360 (Grandpa's Truck)
1975 F100 Custom 4x4 360 (My Fixxer Upper)
1976 F150 390 (Grandma's Truck)
1978 F150 351W (Older Brother's-thinks he's a mechanic so why is it sitting??)
1982 F150 XLT Lariat 4x4 351W (Friend's Truck-but he's in MT and it's at my place)
1983 Bronco XLT 4x4 300 (My Daily Driver)
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Joined: Dec 1999
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From: Copley, OH
4.9 overbored?
Boring the engine .030" produces very small power increases. You add about 4.5 cu. in and raise the C.R. by maybe 0.1. All in all, probably less than 5HP, nothing to write home about. But since you have to replace pistons, you can raise compression a bit more if you want with taller pistons, shaving the head, or decking the block. Keep it within reason, and you'll see some real HP gains.
Senior User
Joined: Aug 1999
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4.9 overbored?
Boreing your 300 may be a necessity also, as sometimes the cylinder walls will wear unevenly, and could cause oil to blow past your oil rings when rebuilt. A local machine shop could check for sure whether you should bore your block anyway.
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4.9 overbored?
Hmmm, interesting... I have (its not a 300-6) a 351 (in an 87 Bronco) I just had a re-rebuilt last month with 218K original mileage. Because of a poor quality rebuild (of Olympic proportions) last year, my 2nd rebuilder had to bore the block to .060 over. As far as I know, all other parts are stock. I'm curious, though, was there much HP gain by going .060? It feels peppier but that's probably all in my head. What are your thoughts? Indulge me.
Skippy
Skippy
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Joined: Dec 1999
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From: Copley, OH
4.9 overbored?
At .060 over, you gained about 10 cubes and added about 0.2 to your compression ratio. Your gains would probably be something like 10HP, still not enough to feel. What you're likely feeling is the efffect of a quality rebuild on what had been a POS engine. That could be many HP
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