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| Low compression http://mudmotortalk.com/mmt_v2/viewtopic.php?f=3&t=12360 |
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| Author: | OwenDickeson [ Tue Sep 14, 2010 12:19 pm ] |
| Post subject: | Low compression |
I have iron moutain heads, cleaned up stock intake, mikuni, and bps crossover exhaust on my 36 PD. I can barely get on the 4300 built in rev limiter. Before the mods I was turning 4100 rpms. I figured that I should be getting some more RPMS so I did a compression test and both cylinders are 151-153 PSI. And yes I had the throttle held wide open doing the test. Do these numbers sound low to yall for a stage 1 engine? |
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| Author: | fowl habbit [ Tue Sep 14, 2010 12:23 pm ] |
| Post subject: | Re: Low compression |
I m not sure if thats too low I'm gettin like 176-178 on my Mud Buddy with the same mods and I am bumping the 4570 rev limiter. I ended up putting a 48 tooth gear in the low end to drop my Rpms. Mine was really low and I never bumped the rev limiter till I found out my timing was off. Not sure if thats at all your problem but I did all the mods and that and wasn't even hitting 4100 now i could probally hit 4700 |
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| Author: | MaXXis85 [ Tue Sep 14, 2010 1:27 pm ] |
| Post subject: | Re: Low compression |
Owen, I havent checked the compression on my engine since I had the Stage 1 mods done, But with me and another guy I can spin up to 4250 RPMs. I never ran the boat alone But I dont think Id have a problem spinning 4300 Because the OOW RPMS are at 4350. How much are the heads Decked? Bothe cylinders are within 2 PSI and that is great. I am uncertain on how much Compression you should have But IIRC some stock motors have had up to that. |
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| Author: | OwenDickeson [ Tue Sep 14, 2010 1:57 pm ] |
| Post subject: | Re: Low compression |
I want to say the IM heads are decked .065 Are the only ways to lose compression through the head gaskets (leaking or thicker gaskets), intake and exhaust valves, and through the piston rings? |
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| Author: | dpd [ Tue Sep 14, 2010 2:21 pm ] |
| Post subject: | Re: Low compression |
Owen, I have basically the same mods as you except a Marshmellow exhaust. I am close to bumping 4300, but that's it. I haven't done a compression test, but would be interested to hear what BPS says it should be. I was hoping to be bumping the rev limiter and have to re prop. But it doesn't happen often. There are others here such as Poker 1 run the same set up with the same RPM range as well. I don't know what others have to say about compression readings for their satge 1, but you have me interested as well. What about your valve lash setting? have you looked at that recently? |
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| Author: | OwenDickeson [ Tue Sep 14, 2010 2:27 pm ] |
| Post subject: | Re: Low compression |
valve lash is set at .005 |
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| Author: | MaXXis85 [ Tue Sep 14, 2010 2:33 pm ] |
| Post subject: | Re: Low compression |
Owen you got it right on how the engine reatains its compression. I would be curious to know what was your stock compression to know how much boost you got by putting the decked heads on. I would suggest a leak down test just to see if you are losing compression somewhere. |
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| Author: | coondik [ Tue Sep 14, 2010 3:17 pm ] |
| Post subject: | Re: Low compression |
are you checkin' comp wit de throttle wide open? |
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| Author: | OwenDickeson [ Tue Sep 14, 2010 3:46 pm ] |
| Post subject: | Re: Low compression |
| Author: | deadbird8 [ Tue Sep 14, 2010 8:22 pm ] |
| Post subject: | Re: Low compression |
| Author: | OwenDickeson [ Tue Sep 14, 2010 8:24 pm ] |
| Post subject: | Re: Low compression |
I wonder why keith at SETX told me .065 then. |
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| Author: | bayouboy [ Tue Sep 14, 2010 8:56 pm ] |
| Post subject: | Re: Low compression |
Well from .065 to .030 thats a good drop in compression right there. IMO if your getting the power and preformance out of her, than theres nothing wrong with turning 4300! Its a good thing  If I'm not mistaking DDM has the whole Shit and Sha-Bang done to his motor, minus the decked heads and he's only turning 4300ish. Hell thats stock rpms! |
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| Author: | POKER1 [ Tue Sep 14, 2010 10:16 pm ] |
| Post subject: | Re: Low compression |
Thats all I can get out of mine is about 4300 with those mods. I could also bump that stock. But my motor is stronger than it ever was stock. I got the 4570 chip so running 4300 is good for me. I ran it with a load weekend before last with 3 peeps, 2 ice chest and all day gear for fishing and it stepped that load just fine and ran great. Im happy with this package and I feel it will last being a little milder. |
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| Author: | craig [ Wed Sep 15, 2010 8:15 am ] |
| Post subject: | Re: Low compression |
Owen.....those numbers sound fine. You can tighten your valves to .003.....that'll help give you a lil more on tha top! |
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