5.7L 350 Vortec Carb replacement

lutzinmn

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Sep 30, 2009
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I bought a 5.7L 350 Vortec engine for my 1992 Sea Ray Sundancer. I currently have a Rochester Quadrajet. I am not getting the power that I should from the engine. The company that I bought engine from says to get the power that I want out of it I can't use the Quadrajet and that i should use a Holley carb. is this true and if so, what carb should I get for my engine?
 
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I just bought a first mate marine crate engine, 5.7 vortec to replace my '94 5.0 merc after she pout a leg out of bed... Have bought a #7116 edelbrock inlet manifold (vortec) and a #1409 edelbrock marine carb from summit.. just waiting for them to arrive now. My marine guy reckons they get around 300 horse and 500NM from the 5.7 vortec with these bits....

Just my 2 cents
 

Bondo

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I bought a 5.7L 350 Vortec engine for my 1992 Sea Ray Sundancer. I currently have a Rochester Quadrajet. I am not getting the power that I should from the engine. The company that I bought engine from says to get the power that I want out of it I can't use the Quadrajet and that i should use a Holley carb. is this true and if so, what carb should I get for my engine?

Ayuh,..... I've never known horsepower to be carb manufacturer specific,...

A Holley will be a problem to hook up, as Merc hasn't/ don't use Holley carbs,...
 

midcarolina

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Millions of 350's are feed with quad's...............Did the quad work fine on the replaced engine? I would be double checking the timing, If not advancing correctly or set to retarded that will play a huge role in the power........
 

lutzinmn

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I don't know if quad worked fine with replaced engine. I bought boat with the 260hp merc torn apart due to a cracked head. Owners never covered the cylinders and they had rust in them. For a few hundred more I bought a new engine instead of rebuilding the original. I bought a 350 5.7L vortec 330hp from Center State Engine. I added an electric fuel pump and carb. I rebuilt the carb myself. I had a marine mechanic install the engine. He told me I did a good job on the rebuild of carb. Anyways, Sea Ray said the 260 merc top speed was between 37mph and 41mph. The new motor has a WOT of 5000 rpms. With a 15 pitch prop I could only get WOT of 4200 rpms and top speed of 28 mph. I put a 11 pitch prop to bring the WOT to 4900 rpms. My top speed is 29 to 30 mph. This engine should out perform the 260 merc. Per Center State Engine I can't get the power I want from the quad and I should get a Holley carb. He did not tell me what model to get but that I should call Holley to find out what maodel I should get. So to answer where I think the performance is lacking would be power. I do not think with this motor I should be at a 11 pitch prop to get to 5000 rpm and top speed should be over 40mph. Sorry for the long story but wanted you to know where I was coming from.
 

achris

More fish than mountain goat
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LOOOOONG time before you replace the carb you have a lot of checking to do. Start from the very beginning.

1. Compression and leakdown test. Yes, I know it's a 'new' engine, but stranger things have happened.
2. Timing, advance and spark quality check. And check, double check and triple check you have the firing order correct... :facepalm:
3. Fuel pressure check.
4. Put a vacuum gauge on the engine and see what that's saying.

ok... Quadrajets were used on 370 and 400hp big blocks, so saying the quad can't feed a 300hp small block is just a load of horse hockey... (Col. Potter. 4077 MASH)....

Chris.....
BTW, I wouldn't use a holley on a bicycle!
 
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NHGuy

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Holleys are for cars. Either get the qjet right or get an edelbrock 1409, which is a true marine carb.
 

NHGuy

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And speaking of cars and Holley carb fans. I wouldn't be surprised if your shop built you a car engine instead of a boat type. If you post a build sheet we can help you get it sorted out. Get the cam info, piston dish or dome size, head type and chamber size. With that info we can see what your engine should do in a boat.
If it turns out to be a high rev, high compression. hot cam car motor you might be wanting a cam change to get it to act better in a boat.
And if they went way high on compression it just won't work unless you like a lot of noise.
Hope I'm wrong.
 

midcarolina

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Nothing necessarilly wrong with Holley carbs just imo they are simple easy to modify race carbs.......... and in most marine applications is not the best option

BTW......... checked out Center state engine......They are sellers, remanufacturers of Marine engines........
 

Fastatv

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Sep 28, 2013
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I bought a 5.7L 350 Vortec engine for my 1992 Sea Ray Sundancer. I currently have a Rochester Quadrajet. I am not getting the power that I should from the engine. The company that I bought engine from says to get the power that I want out of it I can't use the Quadrajet and that i should use a Holley carb. is this true and if so, what carb should I get for my engine?
I read this entire thread. Q-jets are great carbs IMHO, however, going from a 260 horse engine, to a 330 horse engine and expecting to use the same carb...well, that's a 70 horse difference and I would imagine that tuning your current Q-jet would be required. If you choose that route, here's a link that you may want to investigate prior to purchasing a new carb and if you want to give the tuning a shot. Good luck. http://www.thecarburetorshop.com/
 

JaCrispy

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Holley makes marine carbs, they're listed on their website.

I have a 260hp I'm looking to maybe upgrade over the winter with vortec heads and carb swap. I rebuilt my Qjet but I get a bog going to full throttle. Even cruising above 3/4 throttle and hammering down it's bogs hearing those gaping secondaries open. LOL Runs decent everywhere else.

I have clearance issues so I'm looking into the Qjet spreadbore replacement or maybe just bag that and get a squarebore manifold and a 650cfm.
 

midcarolina

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Holley makes marine carbs, they're listed on their website.

I have a 260hp I'm looking to maybe upgrade over the winter with vortec heads and carb swap. I rebuilt my Qjet but I get a bog going to full throttle. Even cruising above 3/4 throttle and hammering down it's bogs hearing those gaping secondaries open. LOL Runs decent everywhere else.

I have clearance issues so I'm looking into the Qjet spreadbore replacement or maybe just bag that and get a squarebore manifold and a 650cfm.

There's a reason for back in my day we called em Quadrabogs............
 

Scott Danforth

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:popcorn:....... Holley vs Q-jet is like Volvo vs Mercruiser or oil and fuel threads. They both are basically glorified toilets that get fuel from the tank to the combustion chambers.

first off, in 1992, the 260hp GM 350 mad 260hp at the flywheel. so add about 15% (parasitic loss) to that and you get a small block with 300hp at the crank. a 330hp reman is only 10% more

the same carb that fed the old motor should feed the motor just fine, however based on post #6, Chris hit the nail on the head with his answers in post #7

NHGuy also hit on a point in post #9. What motor was built. just saying a reman 350 is like saying I made soup. What ingredients, prep, and proceedures is what determines the kind of soup. in this case, what kind of motor was built? an auto parts store reman is NOT a marine motor. wrong head gaskets, wrong cam, wrong core plugs. A marine motor is closer to a dump truck motor built to haul a load up a 10% grade while driving in sand.

to expand on a few of the posts, my suggestion is as follows:
first - get the build sheet of the motor. specifically the cam specs, piston specs, static compression ratio and rocker arm ratios
second - post the information here
third - perform a compression test and leak down test
fourth - verify base timing and perform the ignition tests
fifth - post results here.
 

midcarolina

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:popcorn:....... Holley vs Q-jet is like Volvo vs Mercruiser or oil and fuel threads. They both are basically glorified toilets that get fuel from the tank to the combustion chambers.

first off, in 1992, the 260hp GM 350 mad 260hp at the flywheel. so add about 15% (parasitic loss) to that and you get a small block with 300hp at the crank. a 330hp reman is only 10% more

the same carb that fed the old motor should feed the motor just fine, however based on post #6, Chris hit the nail on the head with his answers in post #7

NHGuy also hit on a point in post #9. What motor was built. just saying a reman 350 is like saying I made soup. What ingredients, prep, and proceedures is what determines the kind of soup. in this case, what kind of motor was built? an auto parts store reman is NOT a marine motor. wrong head gaskets, wrong cam, wrong core plugs. A marine motor is closer to a dump truck motor built to haul a load up a 10% grade while driving in sand.

to expand on a few of the posts, my suggestion is as follows:
first - get the build sheet of the motor. specifically the cam specs, piston specs, static compression ratio and rocker arm ratios
second - post the information here
third - perform a compression test and leak down test
fourth - verify base timing and perform the ignition tests
fifth - post results here.


Perhaps you overlooked the last sentence in post #10
 

lutzinmn

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Sep 30, 2009
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Thanks for the suggestions. I will see what I can get done this weekend. I already put in a request for the build sheet. To be clear I purchased a new engine and not a reman. The company sells both. Paperwork says it came from ATP Engines & Machine Inc. Also known as Marine Engine 4 Less. I will post what I find out over the weekend. I appreciate everyone's help. It will be nice to figure this out before I have to store boat.
 

NHGuy

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May 21, 2009
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Well, now we at least expect that it's a boat engine.
A properly built Quadrajet will run that motor fine. My quadrajet ran the engine stock, and again this year with a cam upgrade. If yours actually is correct you could have something else going on. What is it timed to? Does it advance to about 32 at upper rpms?
 

lutzinmn

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Success!! I did a compression test on all cylinders. All cylinders were at 160psi. As did the compression test, I noticed that the ground electrode from plugs #2 and #4 were shining silver as if they have never fired. I checked the plug wires and they were ok. I traced all plug wires to the distributor. It turned out that #2 and #4 crossed in the firing order. I switched the two plug wires and took boat out. I put the 15 pitch prop that came with the boat on and test drove it. I was able to go 41 mph and my wot was 5200 rpms. 5000rpms should be the max. I will need to drop to a 16 or 17 pitch prop. I never suspected the firing order because the engine did idle smooth and when I accelerated, that was smooth also. There was no sign of any missing on the cylinders. Achris was right to check, double check and triple check the firing order. The quad worked great. My question now is: When the mechanic that put my engine in, I had to have timed the engine with the 2 cylinders not firing. Now that I have it fixed, would it be correct to say that I need toi have it timed again? Again thanks for everyone's help.
 

achris

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Timing will be correct. No need to redo. Only #1 is used to set the timing, and the problem was 2 & 4, so no harm, no foul. Glad you found it... Now go out and have fun....

V8s are notorious for running 'well' when things are not well. Most people can't even hear the difference on a V8 that's only running on 7. When a V8 sounds poorly, it's usually terminal...
 
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