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Cobra 5.8 won't rev out under load

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Pr0zac

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Last year I purchased a 1992 four winns 205 sundowner with a 5.8l. I got it for real cheap because the block was cracked. I'm ase certified and this wasn't a hard undertaking. I put flat top Pistons in it and a comp Cams xe270hr, an edelbrock performer, a quick time fuel 600cfm marine carb and a d.u.i. marine hei with the appropriate shift module. It won't rev out past 3600 rpms with the stock prop. The prop isn't in the greatest shape but it's not terrible. I've checked the cam timing and pushrod length. Essentially everything is new on the engine. I can see fuel in the bowls while the engine is at the highest rpm. I've played with different timing settings. I've ensured the throttle is opening all the way. I replaced the gimbal bearing and the outdrive turns freely. I have no idea what it could be. It doesn't backfire or stumble. It just won't pull any more rpm. I hate to throw parts at it but I'd have to assume the prop is the last thing it could be. It currently has a 19p X 14.5 which is what the stock specs are. Any opinions?
 
2nd on the wrong cam. I read all the specs on the cam you listed, It is a street performance cam. Will not work in a marine engine.

Chances are that cam has more valve overlap than needed in a marine engine and if you keep running it it will be over shortly from water reversion.
 
Docksidemarineservices said:
2nd on the wrong cam. I read all the specs on the cam you listed, It is a street performance cam. Will not work in a marine engine.

Chances are that cam has more valve overlap than needed in a marine engine and if you keep running it it will be over shortly from water reversion.
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I literally called and emailed comp cams to ask them. This was their recommendation. I drove this boat all season last year. It had no such issue. I've researched marine cams. This one is right in line with other cam manufacturers with performance marine cams.
 
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Pr0zac said:
Last year I purchased a 1992 four winns 205 sundowner with a 5.8l. I got it for real cheap because the block was cracked. I'm ase certified and this wasn't a hard undertaking.
I put flat top Pistons in it
FYI: the 5.8L cylinder head incorporates a wedge shape designed combustion chamber (very similar to the SBC), which means that a Q/E can be achieved with the right deck height and compressed head gasket thickness.

1..... If you attempted to achieve a Q/E, do you know what the quench dimension was?
2..... Do you know what the Static C/R turns out to be?


and a comp Cams xe270hr, an edelbrock performer, a quick time fuel 600cfm marine carb and a d.u.i. marine hei with the appropriate shift module. It won't rev out past 3600 rpms with the stock prop.
Was the previous 5.8L engine able to reach the OEM spec'd "testing ONLY" WOT RPM????

The prop isn't in the greatest shape but it's not terrible.
Try another prop of the exact same diameter and pitch!

I've checked the cam timing and pushrod length. Essentially everything is new on the engine. I can see fuel in the bowls while the engine is at the highest rpm. I've played with different timing settings.
Give us an example of the advance curves that you've tried.... especially the TA!

I've ensured the throttle is opening all the way. I replaced the gimbal bearing and the outdrive turns freely. I have no idea what it could be. It doesn't backfire or stumble. It just won't pull any more rpm.
Be careful.... especially during this very critical break-in period. You DO NOT want to over-burden this fresh engine during run-in.
Find out what is preventing it from reaching the "testing ONLY" WOT RPM.


I hate to throw parts at it but I'd have to assume the prop is the last thing it could be. It currently has a 19p X 14.5 which is what the stock specs are. Any opinions?
As said.... try another "like" prop.
Make sure that the hull bottom is clean.
Perhaps check the prop shaft for tru-ness.
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I wasn't able to dial in the quench with the limited options for marine gaskets. But the old engine had a huge dish in the Pistons. Both the boat engine and the 94 truck engine I used. So I figured why not toss some flat tops in it. It's about 9.3:1. The distributor was set up by dui off the specs they asked of the engine/boat. I've tried setting the timing from 0-16 degrees initial. I don't have the paper in front of me but I believe if you set it at 12 degrees initial. It will be at 36 degrees at 3000. I've tried adjusting it by hand while someone else drives. It's getting fuel. I've tried different jetting. All have netted no increase. I just read something about exhaust flappers which I am going to try and check this afternoon.
 
Make sure that the anti siphon valve on the gas tank is not sticking closed and restricting fuel flow. I had this problem when I first got this boat years ago; it would start and rev fine in neutral but would not plane out the boat.
 
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