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Mercruiser detonation chevy 350 with 4bbl carb

The boat is a 27 foot cabin cr

The boat is a 27 foot cabin cruiser which is 23 years old so it's kinda hard to justify spending 10 to 15k to convert to a big block and bravo drive setup. Even with the engine running at 2 deg btdc i can hit 4200 rpms with a max speed of 34 mph it currently cruises at 23 mph at 3300 rpm's. If u look at today's cabin cruisers in that size range the base engine is still a chevy small block. I know it's never going to be a speed demon
 
John i understand what you are

John i understand what you are saying whole heartedly but keep in mind that the pinging/laborknock is something you are gonna have to get use to i may be wrong. you sound pretty confident that you are gonna solve the problem. good luck and definatly keep us posted
 
It might be worth trying a pro

It might be worth trying a prop with a little less pitch to see if that helps...Continuos detonation is not only annoying but can eventually cause serious piston damage. Can you hear the detonation at cruising speed or just at WOT???
 
detonation starts as the secon

detonation starts as the secondaries start to open up. I'll get it to work one way or the other..lol
I'm lucky cause i can do the work myself plus i have access to a back hoe so i can have the motor out in 15 minutes. living with the detonation isn't an option. I pull this boat with a 1997 chevy k2500 suburban with a 350 vortec engine.When going up a steep hill the tow vechile never pings. I know it's different setup. Hmmm maybe i need to drop a vortec engine in it...I'm going to back off the rockers a 1/4 turn and c what that does. Thinking i might have a couple of tight valves. If that doesn't change anything then i'm swapping out cams. One of the perks of working for a chevy dealer for the last 20 years alot of spare parts and easy access to parts that i don't readily have..
 
"The valve adjustment should b

"The valve adjustment should be done while running.

I like to set at, clacking, then 1/4 turn let it settle and the 1/4 turn and let it settle.

So 1/2 to 3/4 turn in all, engine dependent

Yes your EFI 2500 will not ping due to the electronic controlls.........

Remember that when you sprayed water in and the detonation did NOT go away that tells me that there is a real missmatch of cam/heads. the cam profile is most likely wrong for the combuction chamber size. Or the cam is out of time or both.

If you do put in a different cam make sure you at least buy a new timing chain set up $30 buck is short innsurance!! and try to stop using ""used motor parts". If the other engne was worn out from trying to move that heavy boat it woulb be expected that all the internal parts had seen better days!!!"
 
"compression readings seem a b

"compression readings seem a bit high ,could the cam be off a bit causing "dynamic compression"
issues"
 
is a marine head gasket the sa

is a marine head gasket the same thickness as an 'auto" gasket?? I'm getting ready to pull the engine to replace the camshaft.I thought i read somewhere that marine head gaskets are thinner then regular head gaskets
 
Different material.......... s

Different material.......... stainless steel or composite specifically for marine (salt water) enviroment.

Thats the only differsnce!
 
Well i spent the afternoon tak

Well i spent the afternoon taking the engine out of the boat. Replaced the camshaft with a stock truck/rv grind. Just got back from the lake and guess what the sucker still pings!!!!!!!!!!
So now it's a stock 350 1987 engine. I'm at a lose here. The only thing that struck me as odd was the fact that when i started it up it was showing atleast 20 deg retard and the engine was idling smoothly..and was running nicely at 2000 rpms as we moved out into the center of the lake. Then i adjusted timing. I think tomorrow i'm moving it back to 20 deg retard and actually c how it responds....I'm real tempted to install the efi setup i have from a truck into this marine engine...lol
 
"Any possibility that the harm

"Any possibility that the harmonic balancer has slipped and as a result, the timing marks are no longer accurate???"
 
"Impossible,

You could not

"Impossible,

You could not run at 20 degree retard.

Sometihing is not right.

You would not be able to idle at 20 atdc if you could get that far!!!

You have something else out of wack here. recheck your sp plug wire routing and are you on number 1 plug when checking timing?"
 
i agree. I think my timing lit

i agree. I think my timing lite might be messed up. Cause the mark was atleast an inch to the left of the 0 deg mark when looking from the back of the engine.
 
"What type of light do you hav

"What type of light do you have ? does it have a knob on it so you can adjust it? is it electronic ??

Just to clarify, #1 is on the forward PORT side of the engine ( or auto drivers side ) on a GM.. unlike a FORD that is on the starboard Side.

1,3,5,7 is port side and 2,4,6,8 is starboard."
 
Tried the timing lite on anoth

Tried the timing lite on another vechile and it is showing the correct timing on that vechile
 
Yes it has the knob on it to a

Yes it has the knob on it to adjust it. It was set to 0 . I'm using cylinder #1 for the clamp. I tried it at the cap and right at the plug. Even tried power tuning it. Turning the dist clockwise while under power just to where the pinging stops.Stop boat and check timing about 2 deg retarded.I'm seriously considering installing the throttle body setup from the donor truck just to c if i can acheive full power without it pinging..
on a side note i just got a 1998 vortec 350 engine which will be going in the boat this winter (needs rebuild). I wonder what type of new problems will arise with that setup...lol
 
"You might want to verify the

"You might want to verify the timing marks by removing the spark plug from the number one cylinder and carefully crank that cylinder to TDC. With that done, check the timing marks for a TDC reading. Some SBC engines have the marks on a piece of sheet metal at the 12 o'clock position while others are at approximately 10 o'clock. If the indicators have been switched, the timing could be correct but the indicators would give an incorrect reading."
 
"used new cam,crank and timing

"used new cam,crank and timing chain.When i had the dots lined up i installed the balancer and that mark lined up with 0 deg"
 
OK one more piece of info is n

OK one more piece of info is needed I think???

when at 3000 rpms or so take a timing reading with your timing light(set the dial to 32-34 degrees) you should be at or very near 0 on the marker.

You should be around 32 degrees total advance BTDC

if you are not then you may have a timing module issue.

Also are you useing a thunderbolt IV or V ingition?
The V ign uses a knock sensor and retards timing as needed thus If I remember correctly you need to short out some wires to set initial timing properly.

Almost out of ideas here!!
 
i have thunderbolt IV. I will

i have thunderbolt IV. I will check that timing advance curve next out in the boat.. I think i did check it before and it working
 
"did you verify TDC of #1 usin

"did you verify TDC of #1 using a "stop gauge" ,something bothers me when you said the cam marks lined up AND the timing mark."
 
Well i'm going to solve my

Well i'm going to solve my problem once and for all..lol
Just aquired a 350 vortec engine.it's 1997. Not even going to change the head gaskets.I mainly boat in freshwater. Just going to buy a intake manifold for my quadrajet carb.If it works good.Then this fall i'll pull the engine and replace the gaskets and freeze out plugs and paint the bilge
 
Installed a 350 vortec engine

Installed a 350 vortec engine in the boat.Guess what no pinging even at 10 deg Advance intial timing
 
"<[img]"http://www.marineengin

"
rofl.gif
get thee to the water!"
 
"Great solution - i am sure th

"Great solution - i am sure this is not the answer to the old problem......but wasn't 1987 the cutoff year for use of leaded gasoline??? was going to suggest just trying the lead additive if you can still get it. I remember my old truck use to ping when i used unleaded.

too simple i know, but was a thought."
 
"I have a 74 inline 6, that ye

"I have a 74 inline 6, that year used to use leaded and I think leaded went out in the late 70's early 80's, anyway. My engine runs 160psi on 5 cyls and 150/155 on the other 2 and doesn't ping even before the rebuild it didn't ping with unleaded 87 and was designed for leaded 92.

The lead in the fuel was to keep the exhaust valve seats cool else the would and did sink into the head.

this sure was an interesting post, too bad we wont know the real why."
 
"I'm placing this in anoth

"I'm placing this in another one of life's little mysteries...lol
It was engine related cause i used the carb,exhaust and ignition components from the old engine. So if it was one of those components then it should still be pinging. All i know is this vortec engine has alot more torque then the old engine.If i floor it from a dead stop u can feel the stern of the boat lifting out of the water. Use to take 1 min and 20 secs to get on plane now it's 25 seconds BIG improvement"
 
Check your WOT RPMS.. you migh

Check your WOT RPMS.. you might be able to swing a bigger or more pitched prop !!
 
i'm currently at 4100 rpm&

i'm currently at 4100 rpm's should be around 4600 rpm's. Current prop is SS 15.75X15 pitch Probably going to try an alum 15.75X13 which should get be very close to 4600.
 
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