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

[OldNBold51]

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

Guys, todays current gasoline formulation makes spark plug color readings very difficult. Black is about the only thing you can assume means too rich.

A wideband exhaust monitor is a much more accurate than trying to read a plug.

 

[whitney]

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

A wideband exhaust monitor is a much more accurate than trying to read a plug.

Is that even possible on a water mixed marine exhaust? I'm new to marine engines (but been wrenching on wheeled motor vehicles a long time), and it looks like the water gets plumbed in too "early" to be able to put a bung anywhere...

 

[whitney]

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,

Well I finally took a minute to lay down and look into the plug holes (why didn't I do this before?) and it's obvious that there are a LOT of threads in these heads that my short plugs aren't touching. I'm picking up the BPR6EFS plugs from Advance Auto tomorrow, and hope to do a lake test on Fri. I bought 10 plugs so I have a few spares to do WOT runs. I also bought the FULL kit of Holley jets (it was like $50, about 2x buying 2 pair) and I may want to try swapping a few jets on the water.

I've lost count of how many idiot prior mechanic problems I have corrected on this boat (8?), but that's part of the fun of buying a fixer-upper to me

Thanks for all the advice so far, I appreciate everyone taking the time to post.

 

[MBAKER]

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

I would also prob check timing and set it to the 96 vortec specs. If its like the v8 vortecs they take less timing than the older ones, and its better to be safe than sorry.

Let us know how it turns out.

 

[whitney]

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

I would also prob check timing and set it to the 96 vortec specs. If its like the v8 vortecs they take less timing than the older ones, and its better to be safe than sorry.

Let us know how it turns out.

Interesting you mention that, I was just poring over the OMC 1989-1998 manual last night. It has specs for all years/models in one place so it's really easy to compare. Here's what I found:

I effectively have a 1997 4.3GL engine with 1992 ignition system on it. Which makes things a bit ... complicated

Timing: All years 92-97 (except 96) spec 6 BTDC with higher octane. So I'm good there since it spans both head styles

Plugs: For thje 4.3 went from the "LT" to "LTS" in 96->97 which makes sense with the head style change

Gap: Here's where it gets interesting. Gap (035 or 045) follows the ignition type, not the head style, across all engines.

- Points and Presolite BID (electronic breaker in dist) = 0.035
- Spitfire/EST solid state ignition = 0.045

Turns out points or BID was never used on a Vortec 4.3 OMC/Volvo. However, look at 1997 5.7 GL/GS. BID on Vortec = 0.035 plug gap on long plugs. So I'm going to run 0.035 gap on mine too.

Am I over-analyzing? I won't stop until this boat runs perfectly!

 

[MBAKER]

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

As far as timing, even though both state 6 BTDC they could have different advance curves and you end up at different amounts of total timing. If the older dist sets initial at 6 and you have 30* advance you end up at 36, the new one (electronic controlled) might set at 6 and only have 24* advance and end up at 30, which is quite different. If you tried running 36 total in the vortec heads you would be asking for trouble. Ideally you could find out what kind of advance curve the 97 ignitions used and try to match that or at least match that total timing using your 92 setup. If your distributor now simply has advance weights and no electronic control, I would shoot for 32* total timing (have to rev engine to check it) then let the initial fall where ever it does at idle.

 

[whitney]

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

As far as timing, even though both state 6 BTDC they could have different advance curves and you end up at different amounts of total timing. If the older dist sets initial at 6 and you have 30* advance you end up at 36, the new one (electronic controlled) might set at 6 and only have 24* advance and end up at 30, which is quite different. If you tried running 36 total in the vortec heads you would be asking for trouble. Ideally you could find out what kind of advance curve the 97 ignitions used and try to match that or at least match that total timing using your 92 setup. If your distributor now simply has advance weights and no electronic control, I would shoot for 32* total timing (have to rev engine to check it) then let the initial fall where ever it does at idle.

Very good point, thanks for that ... so I spent some time looking into info in at least 5 different manuals and I'm confused as ever, but I have a plan.

Bear with me here:

Total timing at 600, 2000, 3000, and 4600 listed

1989 OMC 4.3 Points non-vortec
6 15 17 18

1992 OMC 4.3 BID non-vortec
6 ? ? ? (not listed in OMC manual)

1997 OMC 4.3 EST vortec
6 ? ? ? (not listed in OMC manual)

1997 Volvo (LK) 4.3GL EST vortec
23 29 30 30

1999 Volvo (WT) 4.3GL EST vortec
11 19 21 23

2001+ Volvo 4.3GL EST vortec
18 24 25 25

Quoting is mine, I found these numbers in various manuals online. So what can we see here?

- the numbers for 1997 look absolutely INSANE. 23 degrees at idle?
- as I mentioned earlier I have 92 ignition (Prestolite BID) and 97 vortec engine
- Prestolite BID is an electronic trigger replacing points but still has mechanical centrifugal advance in the dizzy.
- I do not have a source for ignition advance data for 92... can anyone tell me what the proper advance is for the BID unit on a V6?
- Purely based on 99 and 01+ numbers I think I want to shoot for 23-25 BTDC at 4600. Sounds like by then the manufacturers figured out what the motor wants.
- ASSUMING that my BID does a 12 degree advance (which it should since BID just replaced the condenser and points), and assuming I want 25 BTDC total, I would want to set the idle timing to 25 -12 = 13 BTDC at idle
- This sounds high (currently at 6 BTDC) so I will try to run it on the muffs tomorrow with idle timing at 6, and find out how high the advance goes. I don't want to run too high on the muffs, so I will check it at 3k rpm. If it's about 17 at 3k with a idle setting of 6, then I can confirm that I probably have the 12 degree centrifugal advance. Depending on how it's running I may take it up to about 10 at idle which would take me close to the '99 curve (no way am I going to try for the '97 curve!). Then I will do some lake testing ... if it runs well at 6, I will slowly add timing to my "predicted" 13 idle advance and see if it holds with no bad noises. Plan to do WOT plug reads during all of this to try to verify that I'm not running lean.
- Good plan?

As a side note, interestingly, I looked at the 5.7 applications where there is indeed a BID + vortec combination in 1999 which looks like it never happened on the 4.3's:

1989 OMC 5.7 points non-vortec
8 20 29 29

1999 Volvo 5.7GL BID vortec
8 19 29 31

2001+ Volvo 5.7GL EST vortec
21 29 30 30

So from the non-vortec to vortec transition the manufacturers held to the 29-31 total advance figure. This indicates to me that, possibly, the vortec upgrade really doesn't "in general" require additional or less overall timing at speed, and the changes over time with the 4.3 are probably due to other reasons (or screw-ups of the engineers!). I'm an engineer (not on motors) so I can pick on the engineers, they make mistakes

 

[MBAKER]

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

I dont now how the OMC EST modules work, but lots of times EST will take a base timing number and/or curve and modify the curve as needed based on conditions. So those numbers could be max advance number not actual timing numbers and vice versa, or may be listed differently for different years too. But I dont know for sure on that just pointing it out. 23-25 just doesnt seem like much timing at 4600. the curve for the 5.7 stuff looks more like what i was expecting but maybe the v-6 act a little different.

 

[MBAKER]

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

Even though boats are different?.I know on chevy race motors we do and run on the dyno to make best power with older style heads it usually takes around 36*, vortec/fast burn style heads are around 30-32*. Even though that?s a short dyno run you can load it down and control acceleration completely and hold it from accelerating then let it accelerate at the speed you choose, or hold it wide open at a certain rpm, simulating WOT on a boat. Either way I could see in a long continuous run like a boat you might want to stay under those timing numbers a little for worst case conditions, it just seems like 25 is pretty slow. But carb jetting will affect it too because if you are jetted rich you can get away with a little more timing and vice versa. My guess is to improve fuel usage numbers they prob leaned the carb down as much as possible then adjusted timing as needed to stay safe. You might be able to jet up and run more timing both within reason, but that?s all just a guess on my part.

If you really wanted to feel comfortable and know what you are working with, you could try to find a 97 dist and set everything per it, but I don?t know if it?s a plug and play deal or if there is more that you would have to swap in as well.

 

[John_S]

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

I'd just set your base to the low-octane setting, and then measure your curve and what the advance adder is. Examine that and re-adjust toward the higher octane setting. The V6 4.3L timing has always been less than the V8 SBC, on Mercs anyway. Mercs generally had about 16 degrees of advance, with 6, 8, 10 degree base.

There are procedures to test and figure out the best full advance, base, and ramp, timing curves, but takes allot of time and testing. If you have mechanical weights and springs, you can control and adjust it. If electronic, you are stuck with what you have or replace.

 

[whitney]

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

Got the ignition system back together and did muff testing tonight. Running good. Real test will hopefully be on the lake tomorrow.

I did have a bit of a surprise. I had changed the coil, put in the correct spark plugs w/ 0.035 gap, replaced the corroded coil center wire, and while I had the prestolite BID dizzy apart, I had found that he gap was a lot bigger than spec (0.4mm vs 0.2mm recommended), tightened that up.

Put the dizzy back in (first 180 deg out, oops! fixed that), had made a mark to put it back at the same orientation (was 6 BTDC at idle), and tried to start. No go, and could see the engine pop backwards when trying to fire. Hmm, looks like possibly massively advanced. Cranked the distributor clockwise a good 10 degrees and she fired up fine.

Then I checked the timing at idle. It was like 20 BTDC! Had to retard the dist probably another 15 degrees to get it back to ~8 at idle. My original mark is WAY far off now, like 20-25 degrees.

So somehow the new coil, new center wire, new plugs, and adjusting the electronic pickup gap added about 30 degrees of timing! That, or something else changed that I'm not seeing. I'm guessing it's mostly from reducing the BID gap.

Anyways I was able to see about 12 degrees of advance like I expected from the centrifugal weights. Now I have timing set at about 8 at idle, and it hits max of 20 at about 2500 RPM. Fairly conservative. Will do a timing test under load tomorrow and observe at 4k RPM, expect to still see 20 BTDC. May try to bump idle advance to 12 for total 24 and see if I can hear any detonation. It's sounding great on the muffs -- throttle response seems improved and idle quality is great. Starts very easily. Idle vacuum is a touch low, about 15 inhg, but jumps to 25+ with a little throttle. I also plan to see what my WOT vacuum is, I have heard that if it's not getting to less than 1.5 inhg that's an indication that the carb is undersized. This boat was originally spec'ed at 175 HP with the old motor, and appears to be 190 in more modern boats with a 2 bbl carb and the vortec heads.

One other thing I'm curious to see ... with the improvements in the ignition system I expect to see a bit higher top speed and RPM. I was hitting 4600 before, I wonder if I'll get up to 4800 now. My pitot was broken so I was never able to check speeds before.

Will report back tomorrow!

 

[whitney]

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

Went out today and I'm happy to say it's running GREAT. I did not have a helper to check timing under load but I'm pretty sure it's hitting right about 20 under load.

Speedo is showing 48 MPH, did see a bit faster when playing with trim. This is the first time I have seen over 43mph or 4500 rpm ... see my other thread here: http://forums.iboats.com/showthread.php?t=430118. I saw 50 MPH on the GPS and almost touched 5k rpm. 1.68 ratio, 14.5x19 prop, 18.5' boat. Difference was new coil, correct plugs, properly gapped BID electronic pickup, and an improved center coil wire.

To stay relevant to this thread, which has turned into "what changes are needed when switching from a pre-vortec to vortec motor?", here's what I can report, to summarize:

- pre-vortec and vortec OMC/Volvo motors show the same specs for the carb. 70 jet and 2.5 power valve
- I did a WOT plug read and saw a bit of tan, so I'm happy with the mixture
- Vortec 4.3's seem to want about 23-25 BTDC at 4k+ RPM per the manuals.
- Pre-vortecs are listed at about 18 BTDC total per the manual
- I'm running about 20 BTDC total and can easily get past rated WOT, it's running fantastic, no pinging, sounds great. I could probably get by with more but no need to push it!
- With a prestolite BID ignition, the stock specs (6 at idle, +12 advance, 18 total past 3k) work FINE. I'm running about 2 deg over that
- From what I have seen, rated WOT RPM for most vortec 4.3's is about 4800 RPM. I'm comfortable running for short periods at 5k on a known healthy motor, but do so at your own risk!

Thanks for helping me though the process of sorting this motor out. I think it's in a good place for a while until I get the jones to put in a 4bbl

 

[MBAKER]

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

Good to hear. Amazing what some of those little things like a plug can affect. Sounds like you've got a good plan of attack. If you dont mind post a pic of a new plug after a run just for comparison.

As far as carb, I doubt its a restriction, even on a 5.0 the 2 barrel carbs dont become a restriction at rpms boats run in. Ive seen where guys swap from 2 to 4 on a 5.0 and see no noticeable different.