HELP! I lost 1200 rpm!
 

Yesterday I got the chance to run my boat hard for the first time this season, and it was not pretty. The boat felt like it didn't want to get on plane and I could barely hit 4000 rpm. Last season it snapped on plane and I could touch 5200 rpm. I had the engine out over the winter. Here are the specs and what I did to it:
Specs:
Small Block Chevy 406
Vortec Heads
Installed new last season approx 30 hours on it
Alpha outdrive
21p Rapture prop

Mods:
Pulled Outdrive
Pulled Engine
Removed Heads
Removed Oil Pan
Installed new oil pan (with dipstick welded in)and pickup
Re - Installed heads With no mods
Re-installed engine
Added Eddie Marine oil cooler and perma cool stat
Replaced stock coil with MSD blaster coil
Installed new bosch platinum plugs
Had Alpha professionally rebuilt including new seals, and lower gear set.
Reinstalled drive

Before starting I primed with an oil pump primer
Initially I had the timing out and could not get it to fire, so i did crank on her quite a bit before she took.

Engine starts easy and sounds normal (except I think one or two rocker arms may be out of adjustment), but it just doesn't have any grunt.

What could cause this massive power loss? I suspect that my valve train could be a little loose. Could that cause a 25-30% drop in power. How do I go about finding the problem?

Regards
Mike Olson

If it is loose it could yes. You would not be opening your valves properly. Timing?

Verified timing yesterday. 12 degrees initial advance, 34 total. Just like last year.

ttt

What kind of carb? How's the oil pressure? Could the crank be submerged with the new pan?

Carb is an edelbrock performer 750 cfm model # 1410. Oil pressure looks perfect, roughly 70 psi at wot, and 40 psi at idle. Same as last year. The pan is a milodon 7 qt pan for early sbc's. It's pretty similar to the old pan just kicked out at the bottom a little. I added the universal dipstick because my exhaust interfered with the block mount dipstick. I don't think that the crank is submerged, but I can probably do a rough check based on the dipstick. Could that cause such a major power loss?

Thanks!
Mike

Well, it doesn't happen often, but submerging a crank could cause something like you are describing. All things being equal, and the pan being the only variable, that would be the first place I would look- especially on a stroked SBC.

As for the carb, that would be the second place I would look. Sounds like the secondaries aren't opening...

Who adjusted your rocker arms? If some are off, some may be too tight, bad news. Your power loss seems to be accross the board. Are your wires (spark) hooked up right?

RPM Loss
 

Olysan.
Check all the small stuff, timing, are the plugs gapped properly and wires set up with the correct firing order.
Did you possibly hook up the throttle linkage in a different position not allowing you to get full throttle?
Valve adjustment would effect the motor pull the covers and have someone reset them.
Could you be lacking fuel, is there something crimping the fuel line?
Is is possible you may have a loose connecton on the inlet fuel line causing some lack of fuel.
Is your water seperator new? I have seen filters with three inches of water in them and one inch of fuel due to a bad batch of fuel from some marina with a water problem.
Post your findings so we all know what happened.
Tank U

Thanks for the feedback guys that gives me a few things to look at.

BBToys: The fuel lines are good, and the water seperator is new, I will pull it and check for water. I did make some minor adjustments to my throttle linkage, so I will verify that It's opening fully, but wouldn't a carb problem be more of a top end only issue? I feel like power is down across the board.

John B: I did the rocker arms on the stand. I was really paranoid about getting them to tight, so if anything I think that they're loose. I guess we'll know tomorrow when I pull the valve covers.

Havasu: You're scaring me. Pulling the pan means pulling the engine, and I really don't want to do that. I'll bite the bullet and check it tomorrow. Wouldn't submerging the crank create frothy oil, and if so what symptoms would that produce. In other words are there any other indications that the crank is submerged?

Here's my plan:

Replace Bosch plugs with a new set of Champion RS12YC plugs, because that is what I ran last year.

Verify all wires are correct, pull distributor cap, verify condition.

Pull valve covers and adjust rockers while engine is running.

Check oil level vs. crank

Verify throttle linkage adjustment

Verify water seperator is full of fuel

Post results!

Thanks again.

Mike