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Thread: 2.7 heads on 3.0
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05-04-2011, 10:47 AM #16
[QUOTE=baja200merk;2157449
Im sure Al is doing a face palm while shaking his head after reading this but we had fun [/QUOTE]
LMAO.
You can also have 3.0 heads milled to raise compression. Be sure the machinist is experienced with this before you have him hack away though. My motor had between 95-100 lbs of compression stock. After having the heads done by MJ performance (works with Monty) the compression went up to 125-130lbs. I can easily plane off with 4 people, a full tank and cooler with a 30 pitch MACH chopper. My boat is also quite heavy for an Action also. Bottom end is significantly improved. Only drawback is, you HAVE to run 93 octane and you need a fully charged battery to spin the flywheel fast enough on cold starts. I have used 90 octane rec fuel when I was about to run out on the water but I kept the RPM's in a respectable range while running it.
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05-04-2011, 10:50 AM #177000 RPM
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So whats the procedure to plug the relief holes. How would you drill and tap them for a plug. Do you have to disassemble the motor to get at them??
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05-04-2011, 11:03 AM #18
Dave if i remember correctly the 2.7 chambers will make about 7 hp and 8ftlbs more at the same compression as 3.0 heads.
You have to pull the heads to do idle reliefs and you wont notice much of anything on the butt dyno if your gonna pull the heads swap some 2.7s on and bring compression up to around 135-140 run 93 it will have more punch just dont forget to rejet
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05-04-2011, 11:15 AM #197000 RPM
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Already had them off once to check the cylinders. Once I get the fuel pump installed I'll look for some heads. Or is it better to have Monty or someone cut the ones I have? Plan on putting new reed valves in it too. If you plug the holes from the inside, you must have to make sure its flush right, or the piston will hit it??
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05-04-2011, 03:21 PM #20
i just clean and fill them with epoxy like metal marine tex never had any problems. yes its gotta be recessed a bit.
Your ocean pro style heads make less power then the 2.7s. The 2.7 chamber will make more power even if the compression is the same as cut "ocean pro" (94ish and up).
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05-04-2011, 03:37 PM #21
I am so cheap I just cant bring myself to put the 2.7 heads on with the price of gas, plus we have a 750 gallon tank of 87 octane at the shop and it is free, some day I will cave and put the big bores and heads on, Matt
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05-04-2011, 05:42 PM #22
Since this topic is being touched on again can someone explain why Chris at CCM recommends NOT using the 2.7 heads? He told me they were too much for pump gas and I should mill the ones that came with my 99 looper 200. Is it because it can be difficult to find 92 or 93 octane on the water?
JohnI was going so slow I almost crashed. - JamesGang
1978 24 Superboat - 250 EFI
Sold: 1991 Starliner - 250 EFI Merc 3.0
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05-04-2011, 06:49 PM #23
When going from the stock 3.0 heads to the 2.7 heads...WITHOUT plugging the idle reliefs, is it always necessary to rejet? I've got 2.7 heads on my 89' 3.0 Looper, and I'm 99% it's got the stock jetting. I've been running it that way since I've had the boat, and the plugs always look good, and I've never had a single problem with the motor. If I remember right, the compressions is around 120psi on all the cylinders, and I always run 91 fuel or better (93 when I can find it), and 40:1 oil mix.
Ian
...boatless for now.
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05-05-2011, 12:22 AM #24Junior Member
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Have an '89 GT200 also and wondering what the relief ports do and what differencewould be if plugged. I used to have an '88 120 looper which is basically the same motor with 2 less cyl & it had 125 psi stock as opposed to 85 psi. Why is that? I used to run 87 octane in that motor & it was fine. Would like to bring up compression in my 200 but want to run 87 octane
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05-05-2011, 01:12 AM #25Scream And Fly VIP
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Any time you add compression to keep an engine safe it needs more fuel unless it was overly rich to start. The V4 can run more compression because the exhaust tuning is totally different, if you want to run 87 stay with stock compression. With proper mods to the heads and correct jetting/timing you can run .700 depth 2.7 heads on a 99 model engine if you run 91 octane, run correct rpm on a some what light rig. I however would get a set of 225 carbs.
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05-05-2011, 05:56 AM #26
With the 2.7 heads getting harder to come by, I've been experimenting w/the late model deep chamber heads. I deck them then add a lead in taper similar to the 2.7's while leaving the compression low enough to run crap gas. I've done probably a half dozen sets so far and they seem to run well.
I have a set cut to 58cc on my 3.3 hot rod motor @ about 140 psi (on 93 octane) and 55cc on my Sonic motors. W/the relief's plugged I'm getting about 115psi (which was my target) on them but that will likely change when the rings seat. They were only about 100 - 105 w/the reliefs open which was my initial plan on how to run them but chickened out and closed them to raise compression.
As to plugging the idle relief's, I've cleaned them w/acetone on a Q tip and filled them w/Marinetex and never had an issue.
Here's a couple pix's.
#1. is of a 2.7 head @ .690" depth and 50cc's of volume.
<a href="http://s290.photobucket.com/albums/ll255/Instigatorspixs/?action=view&current=27literopendeck50cc.jpg" target="_blank"><img src="http://i290.photobucket.com/albums/ll255/Instigatorspixs/27literopendeck50cc.jpg" border="0" alt="Photobucket"></a>
#2. is what I have been experimenting with. The late model 3.0's have a smaller diameter but deeper chamber which I like/feel helps direct the fuel charge more to the center of the chamber as opposed to being more spread out w/the 2.7's.
<a href="http://s290.photobucket.com/albums/ll255/Instigatorspixs/?action=view&current=cut30heads.jpg" target="_blank"><img src="http://i290.photobucket.com/albums/ll255/Instigatorspixs/cut30heads.jpg" border="0" alt="Photobucket"></a>I'd rather be competitive w/junk I built in my garage than win w/stuff I bought.
I refuse to allow common sense to interfere w/my boat buying decisions.
Checkmate 16' 140 Johnson
Hydrostream 17' Vector FrankenRude I
Laser 480 (?) 21' w/GT 200
Glastron Carlson Conquest w/XP 2.6
Glastron Carlson CVX 20 w/XP 2.6
24' Sonic w/twin 250 Johnsons
24' Sonic w/twin 250 HO Johnsons
19' STV River Rocket w/FrankenRude II
Allison XR 2002 w/Frankenrude II
Hydrostream 18' V-King w/Frankenrude II
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05-05-2011, 10:00 AM #27
gary, what are the late model heads? thanks
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05-05-2011, 10:29 AM #285000 RPM
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If your timing is right and you have an adequate amount of 93 octane fuel, you can run 140-150 lbs compression on a looper. I ran a v-8 with that compression for 17 years with no problems. Tom Booth at Riverside Marine jetted the motor and it lived a very long life. Since you live in Arkansas, I would call Tom at his business in N Little Rock. 501-372-0985. He is the best OMC/BRP man in the Mid-South and is extemely honest and fair.
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05-05-2011, 10:52 AM #29I'd rather be competitive w/junk I built in my garage than win w/stuff I bought.
I refuse to allow common sense to interfere w/my boat buying decisions.
Checkmate 16' 140 Johnson
Hydrostream 17' Vector FrankenRude I
Laser 480 (?) 21' w/GT 200
Glastron Carlson Conquest w/XP 2.6
Glastron Carlson CVX 20 w/XP 2.6
24' Sonic w/twin 250 Johnsons
24' Sonic w/twin 250 HO Johnsons
19' STV River Rocket w/FrankenRude II
Allison XR 2002 w/Frankenrude II
Hydrostream 18' V-King w/Frankenrude II
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05-05-2011, 10:59 AM #30
ar300johnson: Thanks for telling me about Tom Booth. I live in Heber Springs so he's not far away from me. It helps a lot to have a experienced local guy to go to and I haven't been able to find any before.
See U on the lake!Hal
"Ton o' metalflake" 1982 Concord Mach II with 1997 Johnson 225 Venom