RE: Issues with Mercruiser 5.0 LX 4 Barrel Carb

[Scott Danforth]

Guys:
I'm now looking into a Repower for this boat.
I've found a Vortec 5.7L which looks promising from local rebuilder.
I'm waiting for answers based on my question to him but thought I'd post here also..

I'm assuming with this Engine I'd need to
- Get Replacement Intake Manifold to suit?
- Perhaps get Replacement Carb? (or would that be changeable?)
- Can Thunderbolt IV be used with Vortec Engines... or should I look at alternative Control?

Otherwise I believe I'd just need to move Fuel Pump and Ancillaries across from Original Engine etc..

Yes on the intake, you will need one for vortec heads

If you have a good 4-barrel now you may need to retune it

You can migrate the exhaust, front accessories and ignition over. Do you know what advance curve your T-bolt has. 20 deg, 22 deg, or 24 deg?

 

[Scott06]

Later vortec blocks do not have provision for mechanical fuel pump. So you would need an electric fuel pump and associated oil pressure switch.

on a good note this would be a significant upgrade in power 230=>295 hp.. you may find you will need more prop pitch when you get it up and running

 

[BusinessConnected]

I'm currently at 22 Degree on the Thunderbolt IV... But actually have a 24 Degree Module as well if that's more suitable.

 

[Scott06]

I'm currently at 22 Degree on the Thunderbolt IV... But actually have a 24 Degree Module as well if that's more suitable.

I would think those modules plus the 10 deg initial timing on a vortec 5.7 would work well. Might have to do some trials with different total advance but they would land you 32 & 34 total respectively. Should be ok

 

[Scott Danforth]

with stock exhaust, I would use the 24 degree module and no more than 10 degrees base timing.

with elevated risers, or aftermarket exhaust such as Stainless Marine, etc. I would use the 22 degree module and 12-14 degrees of base timing.

this is to control reversion at idle.

 

[BusinessConnected]

Guys:
Just a bit of a further update... Determined my Alternator was caput.. so thought I'd try taking it on the water again today... Was happily plodding along at around 2000-2500rpm up to around 15-18kmh.

Anything further than that and the Engine sounded like it something was rattling around inside... otherwise it was quiet.

Water Vapour/Steam was pretty prevalent at more revs and Milky Residue on the Breather's so I'm guessing I have some sort of Water Incursion etc..

 

[BusinessConnected]

Further to other messages... If I was to look at getting a 5.7L Vortec Block Swapped over...

What else would I need to complete the task?

I'm guessing
- Alloy Intake Manifold to Suit 8 Bolt Vortec Engine
- Some Sort of Carb Adaptor to Suit Intake on this Engine?
- Electric Fuel Pump & Oil Pressure Sender/Cut-Off Valve etc.

is everything else a changeover?

 

[BusinessConnected]

Guys:
Just another update for this thread...

I've gone ahead and purchased a New Crate Vortec Block (5.7L).
Dropped at a New Local Recommended Marine Guy around 50km away... Will be getting installed next week.

I've purchased the
Electrical Fuel Pump Conversion Kit
New Intake Manifold
New Alternator (Just because it's about the only thing I haven't replaced yet).

Looking forward to having some reliable boating going forward