Which inconel vavles for my Mercruiser Vortec heads?

[c1steve]

I posted a few weeks ago about probably needing valve work on my heads. I believe I was overpropped, and overheated the exhaust valves. I never did a max rpm test with the boat loaded, only with one person and in smooth water. Typically we will be out fishing in 4 foot seas with four persons, which would be a much heavier load than on the smooth test runs I did.

After doing a compression test today, it became obvious that there is a problem. It was recommended here to use Inconel, and I am ready to do that. Manley has thier:

Manley Inconel Extreme Duty Valve, Chevrolet SB, 11/32", 1.600" Exhaust, +.050" Length, Each Extreme Duty XH-432 Stainless Exhaust Material Chrome Stems Hard Tips

Will these fit the Vortec engine, and what about the .050" longer?

Also for the intake valves, what do iboaters recommend,? The engine is a stock 350 Mag MPI Horizon. Can I order the valves before pulling the heads, based on the specs? Thanks for everyone's help.

-Steve

 

[Scott Danforth]

You dont need inconel. Stainless is more than enough. Ferrea or manley is fine.

Running lean is number one cause of tulipped valves

 

[c1steve]

I did find that there was some water in some of the fuel filters on the boat. The main engine filters may have restricted flow, causing it to run lean. I have to pump water from the bottom of the tank and retest the fuel pressure when the boat is back in the slip. It is on the trailer for the next two months.

 

[alldodge]

Water isn't going to cause the motor to run lean, it will just reduce the performance. Assuming you have a carb I would suspect it first.

Using Inconel on the exhaust side is not a bad idea, but agree stainless is good enough. I used Inconel in all valves for repower.

The steam being longer so long as it matches everything else your doing for the rebuild. This means push rods, rockers, cam, seats, spring height. If your building the motor, need to understand what the plan is

 

[Scott Danforth]

Keep in mind that AD's motor is pushing nearly 80% more power than it came from the factory with.

stock rebuild, stainless is good enough.

 

[alldodge]

Yep, but I installed them when it was only a carb 502 and had some tulip valves due to lean, so didn't need to get them with the last build

 

[c1steve]

The engine is stock, 300 hp, with multi port fuel injection. A few times I ran the motor around 4,000 rpm on the way back from a fishing trip for about 15-20 minutes. When I throttle down near the dock, the engine ran rough as though some exhaust valves were not sealing well. On the next trip, it idled relatively smoothly. However over time power and fuel efficiency went down.

I used to get 1.5 mph, now it is down to 1.0 mpg. Also engine became hard to start when warm, but starts well cold. It is a 24' boat, 24 degree deadrise, and probably weighs 6,500 lbs. when out fishing.

 

[alldodge]

Being an MPI and if the valves are being tuliped then there is a fuel pressure or injector problem.

I'm assuming tuliped valves because of mentioning Inconel valves. Going from 1.5 to 1 mpg is saying its running rich, but could also be rich on some and lean on others. If compression and leak down test have not been done then were just spit balling

 

[c1steve]

I suspect that poor compression is the cause of the efficiency loss. Here are the readings I did yesterday, with the engine cold.
1 180
3 145
5 145
7 near zero.
2 175
4 170
6 160
8 195

This is a center rise exhaust manifold with a 4.5" riser extension. Distance from the waterline to the spill over point is about 14", but probably 3" less if several persons are sitting near the stern.

I sent the injectors out for cleaning and testing 400 hours ago, they should be working well. The valves are mostly original, but a couple were replaced about 500 hours ago. I do not know what Mercury uses for exhaust valves, but most likely they are not Inconel.

I pulled the spark plugs for inspection after a regular run in December. They looked white, like they were running lean.

 

[alldodge]

Merc uses what ever GM puts in the truck motor, and sure its common auto stuff.

Cylinder 7 does run lean on the MPI at higher rpms, and this is why during a rebuild the intake area is opened up some for that cylinder.

If your still running and take it for another run, check the fuel pressure at the rail from idle thru the rpm band and see if it changes much. Could use a scanner to check the MAP and see what the readings are, might have a MAP issue or vacuum leak

 

[c1steve]

The boat is on the trailer, will be for another two months. I ran the scanner in December, and it showed nothing unusual or out of spec. I did not test the fuel pressure though. Looking online I learned that "One version (Vortec) had an Inconel exhaust seat with single angle valve grind and was available on 1 ton trucks."

This is the Horizon model, which is usually used in saltwater, I would expect that Mercury might use upgraded valves from a truck engine.

For stock size valves, the Manly Race Series Stainless are looking good. Most severe duty valves have oversize heads.

 

[Scott Danforth]

I suspect that poor compression is the cause of the efficiency loss. Here are the readings I did yesterday, with the engine cold.
1 180
3 145
5 145
7 near zero.
2 175
4 170
6 160
8 195

This is a center rise exhaust manifold with a 4.5" riser extension. Distance from the waterline to the spill over point is about 14", but probably 3" less if several persons are sitting near the stern.

I sent the injectors out for cleaning and testing 400 hours ago, they should be working well. The valves are mostly original, but a couple were replaced about 500 hours ago. I do not know what Mercury uses for exhaust valves, but most likely they are not Inconel.

I pulled the spark plugs for inspection after a regular run in December. They looked white, like they were running lean.

change compression test gauge and re-test.

Merc lists the cranking pressure at 150 psi - so any significantly above 150 PSI are suspect and would most likely have fuel or water in them. I suspect water in 1, 7 and 8, however 7 sounds like a dead cylinder.

do you boat in salt water? if so, how old are the manifolds and risers?

 

[c1steve]

Yes, the high compression seemed unusual. This is a vortec engine, I believe they have higher compression than earlier small blocks.

The boat is 100% run in saltwater. The manifolds and riser extensions are fresh water cooled, the elbows have about 600 hours on them. These Mercruiser manifolds are the new style, the "Dry joint" gasket system. There is no salt water at the manifold to elbow connection, the passage is somewhat separate.

 

[alldodge]

This is a vortec engine, I believe they have higher compression than earlier small blocks.

Not really, the vortec motor makes more hp from a better and more efficient burning of fuel. The compression differences between pre and current vortec motors is small

Scott is correct, finding pressers much above 150 is either a bad gauge or liquid in the cylinder.

 

[c1steve]

Thanks for all the help. I pulled the heads and found no water or water damage in the cylinders.No lipping either. #7 exhaust valve is obviously warped, but I have not yet removed the valves from the head.

I bought standard Manly stainless racing valves, intake and exhaust. For the head gasket set, can I use Fel-Pro automotive? This is a FWC engine, but runs in saltwater. This would be Fel-Pro HS7733 PT-16. My only concern would be the metal used in the head gasket itself, if in a saltwater environment would there be any problem?

 

[alldodge]

FelPro is good, automotive is not, even more so due to salt. Use FelPro marine gasket, has stainless core

 

[scoflaw]

Auto gasket is fine. Closed cooled there is no salt involved. Yes the vortec heads do have a higher cranking compression , typically in the 180# range