Replacement engine has Vortec heads -- need to rejet Holley for increased airflow?

[whitney]

I've been searching for info on this but haven't found anything... I have a 92 Sunbird, OMC 4.3 non-HO with stock 2bbl 500CFM Holley carb. Previous owner had the motor replaced with a 96 rebuilt longblock with Vortec heads.

What if anything needs to be done to rejet the carb (and/or powervalve) for the higher airflow?

I'm still working on getting the boat running well but I have noticed the plugs are pretty white. Carb has been rebuilt to the exact '92 specs -- #70 jets and 2.5 power valve.

(I'm not a carb expert but my initial reaction is, no, it doesn't need to be rejetted. More air flow should just pull more fuel. Right?)

Thanks!

Edit - it's a 500CFM carb, not 600CFM... 80312

 

[chaparall villain 2]

Re: Replacement engine has Vortec heads -- need to rejet Holley for increased airflow

first is it the original carb from the boat.... most marine carbs are jetted richer than car carbs because of the load but if the plugs are white i would say shes runnin a little lean i would go up about 4 to 74s on the jets and try it ... go out and run it for a day and see what the plugs look like .. they shouldnt be wet or black but more tan color ... if you run it too lean it will do damage to motor better a little rich than a little lean ... i am running vortec heads on mine but its a 383 with a 750 holley so a little different but i had to play with the jets for a while to get it right ... most jets are cheap enough

 

[John_S]

Re: Replacement engine has Vortec heads -- need to rejet Holley for increased airflow

See if volvo used the same carb on their 4.3L vortec, and see if their tuning was different. You also have to carefully check all critical part numbers with in carb. I am not familiar with Holleys anymore, but would assume some tuning would be needed.

 

[chaparall villain 2]

Re: Replacement engine has Vortec heads -- need to rejet Holley for increased airflow

one other note vortec heads typically have smaller combustion chambers which will raise compression also needing a little richer mixture to keep it from detonating

 

[jtmarten]

Re: Replacement engine has Vortec heads -- need to rejet Holley for increased airflow

If the plugs are white, you need to increase the jet size. Yes more airflow will pull more fuel, but only as much as the mains will supply.

 

[whitney]

Re: Replacement engine has Vortec heads -- need to rejet Holley for increased airflow

Great advice, thanks.

So does anyone out there know if Volvo made a 4.3 96+ vortec with a Holley 2bbl carb? And where I might be able to look up the stock jet and powervalve for that motor?

I have the manual for my OMC but nothiing newer than 92...

Thanks -

 

[whitney]

Re: Replacement engine has Vortec heads -- need to rejet Holley for increased airflow

What do you guys think? Not melted but definitely not "tan" either... Actually after looking at the pics again maybe it does look a bit tan? Man I'd kill for a wideband O2 sensor on this thing...

 

[John_S]

Re: Replacement engine has Vortec heads -- need to rejet Holley for increased airflow

It looks too clean to me, but it is harder to read plugs today with the alcohol which helps clean them. And then there is what rpm you wee running at before shutting down. If you idled for awhile, just evaluating idle condition.

 

[jerryjerry05]

Re: Replacement engine has Vortec heads -- need to rejet Holley for increased airflow

Be carefull how much you run it.I had a friend who rebuilt a 283 for a Jersey Skiff.It burned a hole in a piston in about an hour.J

 

[bigdan1]

Re: Replacement engine has Vortec heads -- need to rejet Holley for increased airflow

definitely ,this spark plug is on the lean side ,,,,,,no chance to take

get those jets bigger by 2 ,,,,and recheck

 

[MBAKER]

Re: Replacement engine has Vortec heads -- need to rejet Holley for increased airflow

That plug doesn?t look that bad, it might be a tick on the lean side or have slightly too much timing but like somebody said it can depend on how it was run before pulling it too. Best way to check would be put a couple new plugs in and go do a couple of runs under hard acceleration then pull them and check. I wouldn?t worry about it being a dull white color but if it starts to get shiny or the ground strap starts to get the white chalky color all the way back to the base id be more concerned.

Just because a motor is bigger doesn?t automatically mean it needs a bigger main jet. The engine creates a vacuum draw on the carb which is what pulls the fuel through the metering circuits. A bigger motor can at times draw harder on the carb increasing the vacuum and pull more fuel through the same size jet. There can be times when a bigger motor will sometimes need less main jet depending on the overall setup. Overall airflow has less affect on it compared to what kind of vacuum signal the carb is seeing at different loads.

 

[whitney]

Re: Replacement engine has Vortec heads -- need to rejet Holley for increased airflow

Good stuff. I definitely plan to do a WOT read on a plug next time out (WOT, shutdown, pull plug), assuming I fix my ignition issues.

That picture above was after pulling a tube at about 1/2 throttle for 15 minutes and maybe 2 min of no-wake and pulling on the trailer. I expected to see it more rich...

 

[whitney]

Re: Replacement engine has Vortec heads -- need to rejet Holley for increased airflow

Great advice, thanks.

So does anyone out there know if Volvo made a 4.3 96+ vortec with a Holley 2bbl carb? And where I might be able to look up the stock jet and powervalve for that motor?

I have the manual for my OMC but nothiing newer than 92...

Thanks -

Found it I believe. From the Volvo LK (1997) manual, which should be a 4.3 with Vortec heads:

Interestingly, these are the EXACT same specs as for the 92 and earlier non-Vortec OMC motors. It is also exactly how I have my carb set up.

So either (1) the carb really doesn't need enrichening from the higher flow and higher (?) compression of the Vortec, or (2) the Volvo engineers were lazy and just ran with what they had.

 

[whitney]

Re: Replacement engine has Vortec heads -- need to rejet Holley for increased airflow

One other complication I'm working out if anyone has some insight.

Plugs in the motor now are BPR6FS

BPR6FS is the short-threaded-body and is correct for a 92 non-vortec
BPR6EFS is the long-threaded-body and appears to be called out for all of the Volvo Penta 4.3GL part lookups I can find.

Now I *assume* the engine is a Vortec since it says "Vortec" right on the valve covers.

This would mean I want to use the longer EF plugs right? What are the chances that this engine really isn't compatible with the long plugs?

Edit for clarification -- I had said "short nose/long nose" and I meant "short threads and long threads"

 

[MBAKER]

Re: Replacement engine has Vortec heads -- need to rejet Holley for increased airflow

If you look you can usually see how much threaded length there is in the head and compare to your plugs. If they are supposed to use the long plug then definetly use it, all the v8 vortec heads use the long plug so i would assume the v6 is the same way, but dont hold me to it. Even though the shorter ones will fit it wont run right, because the tip of the plug is tucked back in the hole.

One thing to keep in mind if you are running the short plugs in a head that is supposed to use the long ones, when you put the right plug in it moves the tip out of the hole into the chamber (where its actually supposed to be) it will act like putting more timing advance in it because its closer to teh center of the chamber. So if you have adjusted the timing because of the way it was running before, you might want to take a close look at that when you change plugs and to be safe reset to manufacturers specs if it differs. At least to start with.

 

[Tail_Gunner]

Re: Replacement engine has Vortec heads -- need to rejet Holley for increased airflow

If you look you can usually see how much threaded length there is in the head and compare to your plugs. If they are supposed to use the long plug then definetly use it, all the v8 vortec heads use the long plug so i would assume the v6 is the same way, but dont hold me to it. Even though the shorter ones will fit it wont run right, because the tip of the plug is tucked back in the hole.

One thing to keep in mind if you are running the short plugs in a head that is supposed to use the long ones, when you put the right plug in it moves the tip out of the hole into the chamber (where its actually supposed to be) it will act like putting more timing advance in it because its closer to teh center of the chamber. So if you have adjusted the timing because of the way it was running before, you might want to take a close look at that when you change plugs and to be safe reset to manufacturers specs if it differs. At least to start with.

Hmm that i have never heard of before but it sounds intriging...Recently i went to a long plug in a 4.3 vortec..Its now runs 5 degrees hotter and i have lost 3 mph on the top end...The motor cannot push the prop to 4950 ...I am going back to the short plug and see if that could be the difference...Longer plugs effect timing.....

 

[John_S]

Re: Replacement engine has Vortec heads -- need to rejet Holley for increased airflow

I am not up on all the little 4.3L V6 stuff, but think I remember reading that there are V6 with vortec name on valve cover, that do not have the fast-burn vortec type heads. On V8s it is easy to ID by the intake bolts. I bet the V6 is similiar. Are they smallish bolts mounted near verticle? or larger canted bolts? If you have an exhaust gas crossover(V6?) it is not vortec heads. I'll look in some V6 manuals this evening to give a better description.

 

[MBAKER]

Re: Replacement engine has Vortec heads -- need to rejet Holley for increased airflow

Tail gunner,
Not sure if you are talking long versus short threaded reach, or long versus short tips?
I don?t mean to say that longer plugs actually affect your timing if you checked it with a light. What I meant was it changes the way the mixture burns in the chamber, similar to advancing at the distributor. If you start the spark towards one side of the chamber you will need to start it earlier (advanced) in order for the flamefront to cross the cylinder at the correct time for best power and torque. If you move the plug more toward the center of the chamber you are giving it a head start and it will cross the cylinder quicker and more evenly without as much actual advance. Like how Vortec heads use less timing than older heads, partly because the spark plug is moved towards the center more.

To the Original Poster, I was talking about the long or short threaded reach of the plug not the extended tip plugs. If you are running a short plug in a long hole the tip of the plug isn?t even into the chamber its completely shrouded by the hole. Now the flame front has to start inside the hole and make its way out across the chamber.




I just helped a guy the last weekend with this plug problem, the PO had put short reach plugs in his vortec headed 305 and it just didn?t act right, lazy off idle etc. I changed plugs and we put the correct long reach extended tip plug in it and immeditaly it idled 200rpm higher, and easily ran 200-300 rpm faster at WOT. It sounded different and noticeably ran different, didn?t feel like it was sluggish anymore.

 

[John_S]

Re: Replacement engine has Vortec heads -- need to rejet Holley for increased airflow

I'll look in some V6 manuals this evening to give a better description.

Per service manual 18, the non-gen+ has 12 intake bolts and gen+ vortec has 8.

 

[whitney]

Re: Replacement engine has Vortec heads -- need to rejet Holley for increased airflow

Per service manual 18, the non-gen+ has 12 intake bolts and gen+ vortec has 8.

Yep, I just got done reading a bunch of S-10 and 4x4 forums and learned a lot about the genesis of the 4.3

I definitely have 8 manifold bolts, and they definitely go into the manifold vertically (thus at an angle into the heads), thus I definitely have "gen+" 96+ "new" vortec heads. Which is cool because I understand these are a decent improvements over the 92 motor which was in there.

So I definitely need the long plugs ... right? I'm nervous, considering what the consequences would be of too-long plugs. I'll give them a try!