View Full Version : 262 Vortec V6 timing issues, need some smart folks to help. sorry a bit long and technical.

Cameron Rector
10-20-2010, 05:47 PM
I have a 262 Vortec V6 that isn't making much power after the original heads were rebuilt. This is not the original engine for the boat and I am not even sure if it is a marine engine or a car engine or wether it even matters. BTW it has a Berkley Jet on it.

So here's what I know. The engine runs smooth however takes awhile to get on plane. It feels like it's only getting part throttle. I checked the throttle and the primarys are opening all of the way. I checked the vaccuum secondaries and they only open about half way on accelleration. You can force them open with your finger but you don't get any additional power. This pointed me to ignition timing.

On the lake without a timing light I gave the distributor about 1/8" turn in the advance direction and the engine came alive. It sounded crisper and really accellerated well. I only did a couple of hole shots and put the boat back on the trailer.

Now that I am home with a timing light here is what I find.
My initial timing is sitting at 20 BTDC and with the Thunderbolt IV advance it adds 14 deg. making a total of 34 deg advance. The engine runs pretty dang good here, although steep for initial timing.

The Thunderbolt IV timing for a 262 shows is should have the initial set at 8 deg and the Thunderbolt IV will add 14 deg for a total of 22 deg.

I am not an expert boat mechanic (that the reason for my post) but, on most stock Chevy V8's they like 32 to 34 deg total timing. Why would a boat engine differ so much from a car engine for total timing?

I verified the TDC mark on the ballancer is correct using the positive stop method. I have also verified that 8 deg initial + Thunderbolt IV gives me another 14 deg as per the book. The problem is this leaves a bunch of power on the table.

So, could I have a car engine that has a magical difference from a marine engine?
Should I a after market distributor and curve it my self?
I see that the Thunderbolt V has a Acceleration Advance Envelope that pushes up to 34 deg total timing. Should I change to a Thunderbolt V distributor?

I have spent a bit of time working on magnitos and disturbutor in my life so I don't understand why you wouldn't want more than 22 deg total timing. But before I go burning up an engine out of ignorance to the marine industry; I am asking for some expert opinion and advice.

Thank you all in advance,

10-22-2010, 01:17 PM
Waited a couple days for some more seasoned response - that said, here goes:

First - the load a marine engine sees is almost constant when compared to an auto engine. One "equivalence" is to think of a station wagon, bagged out, towing a 25' camper, going uphill, at 80 mph, the whole way to yellowstone, etc.

Bottom line is a boat engine won't tolerate blind tuning adjustments. When it detonates, it is usually junk. That said, you have to appreciate that the engine builder can NOT control what hull the boat builder puts the engine in. This means that the default tuning is usually very conservative (modest timing curves and liberal [rich] A/F ratio).

Very limited first hand v-6 experience here, mostly all BBCs. Agree with your SBC timing advance values but can't relate them to the V-6. 20 deg is a bit much for initial but if it starts okay when hot, may not be too much. May wanna check on the mercruiser board for some first hand v-6 data on what is 'too much'.

The t-bolt V setups are usually used with the ECU and a knock sensor. Lets the computer 'back off' the timing if the engine starts knocking. I'd be more inclined to go with a mallory setup where you can dial in your own advance curve.

A jet drive with a V-6 infers a light boat. That means less load on the engine (but still more than a car) so it may be a bit more tolerant.

Most vacuum secondaries don't move when rev'ed at idle as there isn't enough pressure drop to overcome their damping mechanisms. Depending upon the carb, the secondaries may not open fully with the smaller displacement engines. Some have limit devices on them to match them to smaller engines, too.

As far as the boat vs car engine - the biggest item to be careful of is the camshaft. For the boat, you want modest lift and duration. What normally gets labeled the RV/Towing cams usually do well in both catagories. The marine engines usually don't rev much past 4500 (5200 for the newer ones) so having a cam for any more RPM is a waste.

Cameron Rector
10-22-2010, 02:00 PM
Thanks for the reply.
The factory ignition module only provide 14 deg advance above the initial. However the engine runs really crisp at a total of 32 deg without any signs of detonation on a cool dry day. I am now wondering why I couldn't swap out the V6-14 module for a V8-24 module. That would give me the 8 deg initial timing and then a total of 32. I don't know the history of the engine close enough to know what was changed and when. I only know that my friend said it made more power before the heads were rebuild. I am guessing that the timing must have been cranked up before and the lastest mechanic timed it by the book. The plugs look good, engine runs smooth, it just sounds like it is lumbering along at 22 deg total and cleans up a pulls at 34 deg total timing. I don't think it has a high compression ratio and it has all stock parts so, I don't see that 32 to 34 should cause any problems. I have seen some high compression, popup piston drag engines that like a lot more timing than that. Although not the same by any means, I still think low thirties isn't out of line.
Yes it is a light flat bottom aluminum fishing boat. According to the charts on the Berkley Pump web site. 200hp should be around 4200 rpm.

10-23-2010, 09:54 PM
I'm pretty sure the V-8 module will not work correctly in the V-6 application. I'm sure it will fire but the timing function will be off as there's only 75% of the "sparks" for a given RPM. I'm thinking the Mallory is gonna be the most flexible solution.

As far as the Berkley pump chart, that shows how the pump loads the engine so you can match the pump/engine/impeller to work properly. You should need the impeller number to select the correct 'chart'. That is the 'what should be supplied' - from the engine - in order to get full thrust out of the jet.

10-24-2010, 07:43 AM
Cameron, you will want to educate yourself on Gasoline Marine Engine Ignition Timing, and what and how timing affects performance, and the risks of too much TA (total advance)!
As Mark said, "the marine engine won't tolerate blind tuning adjustments"..... and I'll add "Particularly incorrect ignition timing adjustments"..... and even more particularly, excessive TA.
You mentioned "Detonation"! Good for you, because that 4.3L uses the full dished piston. Not a great combo for marine use.... and especially if you are considering TA numbers in the range of 32/34 degrees!
If gone un-checked, detonation is one the worst enemies of a gasoline marine engine!:mad:
Also, it is not always audible enough for us to detect by ear alone!
Again....."the marine engine won't tolerate blind tuning adjustments".

I would agree that the Thunderbolt IV module is a bit on the conservative side with regard to TA.
A mechanical system may be a better choice, but ONLY if you can find an ignition curve chart for this exact engine in this exact jet pump scenario. Then you could plot a new curve, and not worry.

Question: is the Thunderbolt IV ignition one that must be put into BASE mode in order to set BASE advance?
I'm not a M/C guy, so don't know the answer to this (see the appropriate M/C OEM manual for this procedure).

Cameron, you mention 22* total, and then you mention 32* and 34* total, but make no mention of RPM.
When we start playing with ignition advance numbers, there must always be an RPM associated with spark lead in degrees BTDC......... IOW, at which crankshaft degrees BTDC this advance comes on.
It is critical to know the RPM at which the TA will occur!
Furthermore, the greater TA #'s that we can toss at a car SBC engine, will not work with a Marine engine. You'll burn some nice holes in the piston tops if you do.
So I'd suggest NOT using any ignition advance curves, or any ignition TA numbers, etc, that pertain to automotive..... they simply will NOT work!

If this were mine, I'd try to get my hands on an ignition curve chart/timing specs that work well for this engine/jet pump application. It may be considerably different for this engine being used with the jet pump -vs- an I/O application.

Cameron Rector
10-24-2010, 09:57 AM
I agreee totally about blind tuning, that's a good way to smoke your engine. I didn't log the RPM exactly when we were on the water but it was running 3700 +/- 100 when the total was set at 22* and was running around 4200 with the timing at 34* total. The timing advance is all in at around 2500. I worked on supercharged aircraft engines for years and I agree about not hearing detonation. The first indication you get is a head temp rise, followed by loss of power, followed by smoke out the exhaust. And of course it was running great right up to that point. Now on a drag car; to determine the maximum total advance you can watch you MPH at the top end as you add advance 2* at a time. The MPH will increase as you find the sweet spot and decrease when you pass it.
I am not sure why I couldn't apply that method here. Although; I would need to back it down like 5* from where it makes best power as a margin of safety. I don't know where I would look to find a timing curve that has been developed for this engine, jet and hull combination. The company that manufactured the aluminum hull is out of business.
I understand fully; that is is dangerous ground. That is exactly why I am here on the forum and not out cranking the distributor around. However; I do believe there is several hundred RPM left on the table that could safety be brought into the game.
Every engine configuration will have a different total timing that is runs the best. This is best done in a controlled environment and documented carefully (now like I did ie. +/- 100 rpm). That was my mistake not logging exactly what was happening.
I do know that at 22* factory setting; the engine sounds good but is lumbering along. At 34* it also sounds good but it is crisp and responsive. So, even if 34* was best power (which I don't know) backing it off 12* down to 22* would be a crazy safety margin.

Any suggestions of a marine distributor that is electronic and provides adjustable advance curves?
Any idea how to contact a mercury marine engineer? It would be interesting to here the original design logic.

Thank you very much for the input,

10-24-2010, 11:23 AM
Cameron, BASE is BASE all day long. We idle and fire up on BASE, but we don't place any load on BASE advance.
Granted, it must be within limits!

Your rate of ignition advance (aka advance curve), and the point of being Full In (aka TA @ a given RPM) is your critical goal here.
The boat manufacturer will not provide this.
You may want to look towards the pump manufacturer for this info.
These pumps are designed with certain engines in mind, and they no doubt have this type of info to offer you!

10-25-2010, 03:22 PM
Rick: The t-bolt IV systems are all RPM driven; as the RPM increases, the trigger delay (timing advance) increases according to the predetermined curve. of course, like all electronic devices, there are component tolerances to deal with.

I'd say Cameron has a good grasp of the potential that a bad adjustment can bring. The boat maker's don't warrant the engine (most of the time) so they won't provide anything 'new'. Berkley doesn't warrant engines so I doubt you'd get that info there. I suspect, like most other technical areas, there's a board or two covering jet boats, and I'd start looking there.

Cameron Rector
10-25-2010, 04:05 PM
I contacted Berkley and told them I had a 262 V6 and a Berkley model 12JC-B and asked them for initial timing, what rpm should the advance be all-in and what the total advance should be. Here is there answer:

"I would use 8 to 10 degrees on the initial timing you can go to 12 if needed and have the curve done by 2500 rpm and if possible a total timing of 34 to 36 degrees would be great."

That sounds about right to me too, I think I am going to buy a mallory marine distributor and make this V6 sing.
This may take a few weeks to get the results back but, I will post the results.

Thank you very much for the input and discussion,

10-25-2010, 08:17 PM
Rick: The t-bolt IV systems are all RPM driven; as the RPM increases, the trigger delay (timing advance) increases according to the predetermined curve. of course, like all electronic devices, there are component tolerances to deal with.
Mark, thanks for that, and I do understand!
The mechanical advancing ignitions are also RPM driven!
This is why TA (total advance) numbers must always be associated with an RPM! They are meaningless without!

What Cameron needs is an accurate curve graph that he can use to check and see what his system is doing.

I contacted Berkley and told them I had a 262 V6 and a Berkley model 12JC-B and asked them for initial timing, what rpm should the advance be all-in and what the total advance should be.
Here is there answer:

"I would use 8 to 10 degrees on the initial timing you can go to 12 if needed and have the curve done by 2500 rpm and if possible a total timing of 34 to 36 degrees would be great."
Cameron, the 8 to 10 initial (aka BASE) sounds reasonable.
The full in TA of 32* or 34* @ 2,500 rpm does not sound reasonable for marine use!

I work mainly with the SBC marine engines.
We can throw as much as 32 degrees at a well built SBC using a Quench style piston/chamber configuration, if we hold this until approxiamtely 3,200 RPM, or so.
(keep in mind that we can allow TA to continue increasing a few more degrees above the 3,200 rpm. But 3,200 rpm is a greater concern since this is very often at/near cruising RPM.......... and where detonation has more destructive potential.)

Your 4.3L is very likely using the full dished pistons, of which means absolutely ZERO quench area, of which means a greater potential for detonation, of which means the need to hold back on TA...... at least in my book!

If I were to throw 32* at a SBC marine (using full dished pistons) as early as 2,500 rpm, with a marine load on it......., I'd have some cooked pistons!

What I cannot suggest, would be what the 4.3L can handle since I am not as familiar with this engine!
My initial thoughts are that 32*/34* @ 2,500 rpm is a recipe for burned pistons.

I think that one or two more opinions, and seeing a Marine 4.3L curve graph, will be important here.


Cameron Rector
10-27-2010, 07:45 PM
Hello, I discoved that the Vortec V6 takes different spark plugs. I am not sure how many people know this (my local boat shop didn't) but, a Vortec V6 takes a plug with twice the thread length as a standard Chevy plug.

I just went to the boat and pulled a plug and looked into the hole and the threads go way in. I took a small piece of welding rod and bent a hook in the end of it. I put it in the hole and hooked the inside of the chamber and marked the rod at the plug seat area. When I hold it up the the old plug the mark is clear up at the hex section.

I learned on another site that a true Vortec engine has 8 intake manifold bolts and all other Chevy V6's have 12 bolts. This engine has 8 bolts and I suspect that is a good indicator for which plugs it requires.

I was having a real hard time departing from the designed timing spec without a logical reason for doing so. I didn't have an answer other than I knew the engine runs better with more timing. The last mechanic that worked on this boat said the engine was just old and that is all you are going to get out of it. That's a crappy answer; old doesn't mean anything when it come to performance. Worn, cracked, streched, loose, leaking, fatiuged, ect. will give you problems; old will not.

What a crazy problem. I knew the Mercuiser engineers were correct or at least pretty close or Volvo would have sold the same engine claiming more power. When you have a competitor you can't leave too much horse power on the table for reliability because the other company will claim it. With this in the back of my mind; I am still trying to figure out why it runs so much better at 34 deg total timing with no signes of detonation.

Well now I know it you light the fuel charge way up in the spark plug hole it takes about 12 deg more total timing to make good power.

Thank you all for the discussion, glad to have you all for support.


10-27-2010, 11:08 PM
I am still trying to figure out why it runs so much better at 34 deg total timing with no signs of detonation.
Detonation is difficult to hear in the marine environment, so be careful if you intend to give this 34* TA. :)
BTW, what RPM is this 34* TA occuring?

Another member, different forum, was looking for the same 4.3L data, and came upon this. Look at 4B 9 thru 4B 16 (http://www.boatfix.com/merc/Techbk/95/95HGB4.PDF)and look at the different curves and limits.
If we trust the engineers, it's why we can't simply guess at this, or use numbers that are not engine and application specific.
(notice that the MCM 3.0LX with EST graph includes BASE in the graph, whereas the others DO NOT.)

4B 10 is apparently for the 4.3L Mercruiser engine with the I/O...... (however, not a jet drive.)
Notice that it is "Full In" by 2,500 rpm and the TA shown is 22* MAX.
Seems early to me, but like said, all engine advance criteria is different.

The goal is to achieve PCP @ 14* ATDC.

I hope it works for you....... Good luck! :)


Cameron Rector
11-02-2010, 07:47 PM
Well, I just got back from the lake and the long reach spark plugs fixed it. We are now turning the Jet at 4000 RPM almost from a dead stop. It takes about a boat length and it is pulling hard and sounds clean and smooth. The timing is set to the factory 8* initial with a total of 22*. I am sure it could use a slight bit more timing but, it runs good and strong so I am leaving it alone.
Before anyone jumps in and says it should turn 4800 or so. Let me explain that they put larger impeller in this boat to reduce noise. They found by running a several hundred RPM's lower they reduce the amount of noise and only dropped a few MPH.
According to the Berkley Pump chart this engine is producing 175 horsepower. Which seams to be inline with the horsepower search I did on the Vortec V6. My search showed 160 to 185 depending on who you believe. So, 175 by the chart sounds about right to me. The engine sounds and feels right, it pulls pretty hard for a V6. Also according to the Berkley chart we were only making 100 to 125 horsepower with the short plugs in; so, we gained 50 to 75 horsepower just by putting the long reach plugs in. Wow, what a difference!
Thank you all, great thread, great conversation, great forum!

11-03-2010, 03:28 PM
Sounds like you are dialed in fairly well.

Good notes on the end result of the wrong plugs....20/20 hindsight shows the benefits of basic troubleshooting - verify correct parts being installed, especially with a setup that is "new" to you.

don't forget another update after you burnt a few more gallons of fuel.