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Thread: 2.7 heads on 3.0
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05-06-2011, 02:30 PM #467000 RPM
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Did it run 87.8 with a stock lower? Or was the power head bone stock?
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05-06-2011, 03:14 PM #47
I had a bobs cone and a tab plus i couldnt drive worth a chit cause it was my first vbottom and only had 30hrs or so behind the seat (same amount of time driving as the fresh rebuild pushing it ). I have been 86 on a stock lower with no cone or tab but it blew out BAD at 86 made a hard left and put the passenger face down in my lap that was on my vegas xt tunnel V.
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05-06-2011, 03:24 PM #48New Member
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hi if the 2.7 heads were second hand check to make sure they have not been milled, for best results mill them 50'' as the squelch band is fine com should be 130 135 cheers
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05-06-2011, 05:23 PM #49
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05-06-2011, 10:01 PM #50
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05-07-2011, 10:36 AM #51
Have anybody tried to raise the exhaust port height to 250 specs while going to 2.7 heads? I read somewhere that 250 v6 looper exhaust port height is 1.791" from top of liner. That figure was from someone that actually measured during a rebuild, not from a spec sheet. I would think it would be possible to grind the top of the exhaust ports without a full tear down of the engine.... maybe... hmm. Any opinions?
Hal
"Ton o' metalflake" 1982 Concord Mach II with 1997 Johnson 225 Venom
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05-07-2011, 11:26 AM #52
Yea we did it on a open deck motor my brother had about $30 in, it had a billion hours on it came out of a commercial mullet boat. We got the idea from gary on here, shop vac up the exhaust and a double cut carbide burr cut a bit higher then 250 spec (i dont know how much it helped we never ran it stock). Then we cut 2.7 heads to bring the wore out motor's compression up from 70psi to around 110-120 and re-jetted. We had no money in it and were just screwing around but it ran for a long time with out issues, even did about 90 miles at river ranch with it cruising around 5k almost all day . Of coarse it will not make as much power as a real professional port job but we had the heads off and were just playing around with the junker, they are a lot of fun when you dont have anything to loose. We beat that thing like a circus animal (then again we do that to the real ported motors also)
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05-07-2011, 11:42 AM #53
Sounds like a fun project
Of course raising the exhaust port will also lower the compression a bit, so I'm thinking that this would work great together with the small chambers and plugged relief holes. Only 87 & 89 octane fuel is available on the water here on our lake so I have to be careful not to go to high on the comp. I know this is not to be compared to real porting, but OMC did it on those 1999 250 v6 motors so it should work OK. If I can get a few more hp this way without killing the bottom end torque it would be worth it.Hal
"Ton o' metalflake" 1982 Concord Mach II with 1997 Johnson 225 Venom
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05-07-2011, 11:54 AM #54
oh no, it had 70 with the stock heads and stock ports before we even took the heads off
When we went to pick it up and the guy flipped it out of the center of the mullet boat it fell on the deck, then he flipped it over the gunwale and it fell about 3ft into my truck bed then we left Got home and it had a bad hole (found out it was a 3.0 on a 2.7 mid) so we put a used piston, used rings in it, ground on it and began abusing it.
Heres a quick video of its life from there on till we sold it running (upgraded to a real ported motor). This was only about half of the pass i herd him hit it on the other side of the lake (couldnt see him) so i jumped in the boat grabbed the camera and filmed the last part of hte pass.
http://www.youtube.com/watch?v=jdvDPmAC9Tk
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05-07-2011, 12:00 PM #557000 RPM
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Thats AWESOME!!!!!!!!!
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05-07-2011, 12:07 PM #56
That's the fastest $30 I have ever seen! Way cool!
Hal
"Ton o' metalflake" 1982 Concord Mach II with 1997 Johnson 225 Venom
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05-07-2011, 12:58 PM #57
I have thought about the shade tree port job alot, just widen to ho specs on exhaust, plug reliefs and 2.7 heads, Garys was a screamer like this, Matt
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05-07-2011, 01:53 PM #58
I have been searching for info on the 250 / H.O. exhaust ports, but the little I can find is rather confusing. Anybody knows the specs?
Hal
"Ton o' metalflake" 1982 Concord Mach II with 1997 Johnson 225 Venom
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05-07-2011, 02:07 PM #59
PM Gary instigator on here I am sure he can tell you what works, Matt
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05-07-2011, 02:52 PM #60
I searched some more and I think I found it: 250/H.O. exhaust ports height from deck = 1.730" versus 200/225 = 1.8" and width = 2.340"
Hal
"Ton o' metalflake" 1982 Concord Mach II with 1997 Johnson 225 Venom