4.3 long block replacement carb question

[adam003]

I am replacing my 4.3lx block and with a newer block without the mechanical fuel pump. Wired my oil pressure switch and new carter fuel pump. But what to do with the fail safe tube off the Quadra jet carb? Just let it hang or block it off? It’s the tube that use to run to the mechanical pump in case a diaphragm failed.

 

[Bondo]

Ayuh,..... Just rubber cap it at the carb,.... Like a vacuum cap, from an auto parts store,.....

 

[Lou C]

Is the newer block a Vortec (intake manifold has 8 bolts vs 12 for the pre vortec)? If not you can still use the divorced choke but if it’s a Vortec there is no exhaust crossover in the intake to heat the choke coil spring so you will have to figure out a way to rig up an electric choke...

 

[adam003]

No it’s a 12 bolt intake with the same mounting spot for the choke on the intake

 

[Bondo]

No it’s a 12 bolt intake with the same mounting spot for the choke on the intake

Ayuh,..... That won't bolt onto Vortec heads,......

Michigan Motors used to sell new cast iron Vortec intakes,..... Donno whether they sell do,....

Do you Have Vortec heads,..?? What "Vintage" does this block replace,..??

Are you replacin' the block casting alone,..??
or a short block swap,..??
or a Long block swap,..??

 

[achris]

Is the newer block a Vortec (intake manifold has 8 bolts vs 12 for the pre vortec)? If not you can still use the divorced choke but if it’s a Vortec there is no exhaust crossover in the intake to heat the choke coil spring so you will have to figure out a way to rig up an electric choke...

Blocks are not 'Vortec'/'non-Vortec'... Heads are what makes the engine Vortec or not. You can bolt either heads to the same block. The manifold bolts to the heads, again, not the block. "Is the new block Vortec?" will always be answered, "It doesn't matter."

Chris.......

 

[adam003]

I am replacing with a jasper long block. I do not believe they are vortec heads on either motor cause they were both 12 bolt intakes. Only real difference is there is no hole for fuel pump and new motor has a balance shaft. But both has the plastic “vortec” valve covers on it. Everything bolted right up but the fuel system.

 

[achris]

I am replacing with a jasper long block. I do not believe they are vortec heads on either motor cause they were both 12 bolt intakes. Only real difference is there is no hole for fuel pump and new motor has a balance shaft. But both has the plastic “vortec” valve covers on it. Everything bolted right up but the fuel system.

There are many 'iterations' of the 4.3 block.

First generation was mechanical fuel pump, no balance shaft. Gen II was a balance shaft and no mechanical pump mounting pad.

The covers with 'Vortec' on are just a marketing tool. Proper Vortec are 8 bolt manifolds/heads. 12 bolt and it's still pre-Vortec, despite what's on the valve covers.

Chris......

 

[adam003]

What is the purpose of the balance shaft. Is it better than my old block?

 

[adam003]

Also with the balance shaft motor will it have more hp or be about the same as my old motor? Not really to worried about it just wanna get the boat back on the water...haha

 

[Bondo]

Also with the balance shaft motor will it have more hp or be about the same as my old motor? Not really to worried about it just wanna get the boat back on the water...haha

Ayuh,..... Same power,.... just means ya don't need the fluid motor mounts, the standard Merc rubber mounts are used with the later 4.3s,....

 

[Lou C]

The GM V6 was built from the existing 90* 5.7 V8 and as such the power pulses were not evenly spaced causing a lot of vibration. GM tried to even this out by using a crankshaft with offset connecting rod bearings and this helped but not 100%, so they added the balance shaft and that took care of the rest of it.
I have a pre Vortec with no balance shaft. OMC used soft engine mounts so you don’t really feel the vibrations which seem to peak at about 1700-1800 rpm. Not annoying though. If I eventually repoweeed I’d like the smoother balanced shaft engine with 20 more hp (Vortec)...

 

[Rick Stephens]

Also with the balance shaft motor will it have more hp or be about the same as my old motor? Not really to worried about it just wanna get the boat back on the water...haha

My understanding, the balance shaft costs 15 HP to spin.

I run a converted pre-balance shaft block with Vortec heads. It sits on squishy mounts and I have never noticed vibrations.

 

[achris]

The GM V6 was built from the existing 90* 5.7 V8 and as such the power pulses were not evenly spaced causing a lot of vibration. ...

Oh, really? Then why does the engine fire at EXACTLY 60° intervals? Maybe it's because it IS an even firing block.

The reason for the balance shaft is to do with the fact that a 90° V6 is inherently unbalanced, and will set up a harmonic resonance at around 1700rpm. And the more load on the engine, the more noticeable that harmonic is. The balance shaft spins counter to the cam, and with the offset weights count-balancing the harmonics it reduces them to the point where normal rubber mounts can be used.. Without a balance shaft, the harmonics are dealt with by using fluid mounts.

Chris....

 

[Lou C]

Oh, really? Then why does the engine fire at EXACTLY 60° intervals? Maybe it's because it IS an even firing block.

The reason for the balance shaft is to do with the fact that a 90° V6 is inherently unbalanced, and will set up a harmonic resonance at around 1700rpm. And the more load on the engine, the more noticeable that harmonic is. The balance shaft spins counter to the cam, and with the offset weights count-balancing the harmonics it reduces them to the point where normal rubber mounts can be used.. Without a balance shaft, the harmonics are dealt with by using fluid mounts.

Chris....

I explained that Chris, a 90 degree V6 is inherently imbalanced UNLESS it has the split connecting rod journal crankshaft. Even then there is still a harmonic at 1700-1800 rpm. If that totally removed the harmonics (split journal crank) why do you think GM spent the money to add the balance shaft? And did you ever drive a vehicle with GMs first 90* V6? Know what it was? What vehicles it was used in? It was the Buick 231 cu in V6....early versions did not have the split journal crank..Buick used it in the mid sized Skylark from the early 60s to the mid 60s then sold the tooling to Kaiser Jeep where it was used in the CJ series due to the compact size but those really had a bad harmonic. Later after the 1st gas shortage (1975-76) GM bought it back from then owner of Jeep (AMC) and it was re-engineered with the split journal crank for use in mid size Buicks Oldsmobiles and Pontiacs. As we had a 78 Pontiac LeMans with that engine for years I can tell you it had the same harmonic at 1700 rpm! Better by far than the original 231 but despite the even fire crank the balance shaft was still needed!

 

[adam003]

I looked up the fluid motor mounts and I think someone changed them cause it had hard rubber mounts. Could that cause damage to anything with it running a non balanced shaft motor with hard rubber mounts?

 

[Rick Stephens]

I have never run my 4.3L without the fluid mounts, so I can't opine on running that way. Never really thought about it until Scott Danforth said in another post that he would leave them out. I was always under the impression if you didn't have a balance shaft you ran fluid mounts.

 

[Scott Danforth]

I have never run my 4.3L without the fluid mounts, so I can't opine on running that way. Never really thought about it until Scott Danforth said in another post that he would leave them out. I was always under the impression if you didn't have a balance shaft you ran fluid mounts.

the factory installed the fluid mounts (liquid filled goo mounts or squishy mounts) on the non-balance shaft motors to remove some vibration within the hull because the non-balance shaft V6 has some vibration like the 3.0

on a balance shaft motor, no need to run squishy mounts.

 

[Lou C]

I don’t think there is anything special about the mounts under my non balance shaft 4.3. Same ones used by Volvo on many V engines, maybe they are softer rubber than V8 mounts; you’d have to compare parts •#s to know for sure...