Carb Recommendations for 5.7L Vortec?

[76SeaRay]

Mostly a test run. Until I finish the hull restoration, I will be periodically run it on the test stand to keep it in good running condition. That said, I need to mount the reset button and relay in their final position (behind the carb) so I can remake the wire harness with everything going in the right place.

 

[Lou C]

The only Mercs that had Holleys I am aware of date back to the 70s when they were using Ford V8s. I know that in OMC/Volvo applications there was a bolt on bracket for the throttle assembly on the carb that makes the connection to the throttle cable. Then there is a bracket that is at the rear of the intake manifold that bolts to the last 2 manifold bolts that stands up vertically. Next there is a 2 piece clamp that bolts to the bracket and holds the throttle cable. Might have to search some pix of OMC/Volvo installations to see what I’m referring to.

 

[76SeaRay]

Here is what I mean by the reset button and relay. This is not my engine. Looks like I need to custom make a bracket or modify the one I have. Michigan Motors doesn't have a bracket to do this.

 

[Rick Stephens]

Don't mount it to the carb bracket. Make your own, or modify the one you have and stick it on the starboard riser.

 

[Scott Danforth]

When I put vortec heads on the 350 in the Rogue

I had to relocate all these bits because they didnt fit. ended up zip-tying most to the harness itself. made a relay bracket for the transom just aft of the motor

coil was held with a generic P-clamp to the back of the cylinder head



I used a generic throttle bracket



I carried over the same thing on the BBC build - you can see the relays on the new harness I built that are now mounted on the transom just above the motor.

the coil is still held to the back of the cylinder head with a P-clamp

 

[LAWRENCE Owen]

guessing your boat is about #4000 dry, about #5000 wet

the cam you have will require more CFM from mid-RPM up

I would definately go bigger. you have more cam than I had with my vortec headed Small Block and I was feeding it with the 715CFM holley running larger jets pushing my 3600# dry, 4400# wet hull (now I am running a big block with an 850)

I would suggest 650 CFM at a minimum

You all know the carb size formula for a basic engine: CID x RPM, divided by 3456. In my case; 350 x 5000 / 3456 = 506. My engine is a refirb Gen 1 with vortec heads and roller cam, rated by Summit to be 373 HP. So adding 50 or so volumn points for the mild added grunt, I figured 506+50=556. I tend to over-size carbs and this time I wanted to be more sensible. Therefore, I just ordered a 600 cfm Holley with elec. choke and vacuum secondaries. I will be operating around 4000 rpms cruise and no more than 4800 full in my '77 22' Aquasport CC, weight no more than I figure 3300# loaded (tower in photo has been removed). Did I make a good choice re carb?

 

[Scott Danforth]

You all know the carb size formula for a basic engine: CID x RPM, divided by 3456. In my case; 350 x 5000 / 3456 = 506. My engine is a refirb Gen 1 with vortec heads and roller cam, rated by Summit to be 373 HP. So adding 50 or so volumn points for the mild added grunt, I figured 506+50=556. I tend to over-size carbs and this time I wanted to be more sensible. Therefore, I just ordered a 600 cfm Holley with elec. choke and vacuum secondaries. I will be operating around 4000 rpms cruise and no more than 4800 full in my '77 22' Aquasport CC, weight no more than I figure 3300# loaded (tower in photo has been removed). Did I make a good choice re carb?

your missing things like BMEP, cam profile, plenum size, heads, etc.

depending on how your motor was built, you may be a bit lean on the top end.

 

[76SeaRay]

I think I have the mounting of the reset and relay resolved. I have another bracket for it that mounts above the fuel filter and in front of the starboard exhaust manifold. That will just leave needing a bracket on the carb for the throttle cable only.

 

[LAWRENCE Owen]

You all know the carb size formula for a basic engine: CID x RPM, divided by 3456. In my case; 350 x 5000 / 3456 = 506. My engine is a refirb Gen 1 with vortec heads and roller cam, rated by Summit to be 373 HP. So adding 50 or so volumn points for the mild added grunt, I figured 506+50=556. I tend to over-size carbs and this time I wanted to be more sensible. Therefore, I just ordered a 600 cfm Holley with elec. choke and vacuum secondaries. I will be operating around 4000 rpms cruise and no more than 4800 full in my '77 22' Aquasport CC, weight no more than I figure 3300# loaded (tower in photo has been removed). Did I make a good choice re carb?

Thanks, Scott. I agree, and will try to up the size to 650 if I can catch the order before shipped.

 

[76SeaRay]

After moving the reset and relay to the front of the engine, I ordered a Holley Carb bracket from Hardin. So, now I have brackets to fit Rochester, Edelbrock, and Holley and the Reset and Relay won't interfere with any of them.

So, an additional question on the carb recommendations is about a carb spacer. I have always thought that a carb spacer was intended to reduce heat in the carb but I just watched Engine Masters as they tested single plane and dual plane manifolds (mine is dual plane) with both 4 hole and open 1 inch spacers for differences in performance. The results showed driver performance (which I would relate to boat cruising) as the single plane should use a 4 hole spacer and the dual plane should use the open spacer. Anybody have experience with different carb spacers or comments/thoughts?

 

[Scott Danforth]

Yes, a carb spacer adds plenum volume which aids in midrange

 

[76SeaRay]

So, I picked up a carb spacer today. Actually it is an adapter for square bore to spread bore. Doesn't look like it will work. The square portion doesn't match up to the Holley body. It leaves passages unsealed by the gasket and mount. Looks like I need a 4 hole spacer instead. That will block off the two sides of the intake plenum instead of sharing across the two sides with an open spacer. Pictures of the spacer sitting on the Holley carb base and the top of the dual plane intake manifold. Any suggestions on the correct spacer?

 

[Scott Danforth]

I normally make my own transition spacers.

I start with a 4-hole spacer and a die grinder.

 

[76SeaRay]

Hey, that's a good idea. Do you grind the center of the spacer to allow clearance over the center wall in the manifold to provide cross over?

Also, a new problem. If I put a carb spacer on, the fuel line connection on the fuel feed rail runs right into the hose from the TStat housing to the starboard exhaust manifold. Is there a flexible hose option for the fuel feed lines?

 

[Scott Danforth]

my dual plane manifold has a reduced height divider

I did basically turn a 4-hole to a 2-slot.

currently have a 1.25" thick spacer

 

[76SeaRay]

Here is the fuel feed line interference. Fuel feed rail with longer side tubes available? Flexible fuel feed rails on Holley that are longer to the side to bend them below the hose a possibility?

With Spacer



No Spacer

 

[Scott Danforth]

90 degree fitting

 

[76SeaRay]

90 degree won't work with my new fuel line. It is hose with just the metal end that you see. It is too stiff and to short to bend to a 90 degree fitting.
Maybe I can find a short extension for the fuel rail fittings at the carb to move the rail out and down at the angle of the rail.

 

[Scott Danforth]

or use a tubing bender and bend the two legs of the fuel log.

 

[76SeaRay]

Well, at this point I am about ready to give up on the whole carb thing and go back to a stock GM Vortec QJet manifold and buy a new QJet Carb. If you look at the intake manifold in my picture above (that is sold everywhere as universal), I can't find a gasket anywhere to mount a carb or spacer(s) to the intake manifold ports correctly. Closest thing I could find is the QJet base gasket and even it doesn't line up correctly and doesn't have mounting holes for a Holley or Edelbrock. So, even if I use a 4 hole Holley spacer, I can't get it adapted correctly to this manifold without disrupting airflow. Looks like if you use this intake manifold you have to make your own gaskets as well as the problems with spacers and openings.