more power from f-head???

Re: more power to f-head???

so,homebrew2 you told to me that the best off all is the MSD6?20% is a lot of power.and i think that for the smoother running,acceleration and more power it's ok for the money.
well,plans changed.no electric fan.MSD first.can i use it with the pertronix ignition for triggering?
if you say that holds at 30 advance i guess that 8-10 is very good.i will give a try.

 

Re: more power to f-head???

Well, I didn't say the MSD was the BEST. But, if I had to pick one BEST, yeh, the MSD is probably the best. As I did my upgrades, I would do the exhaust first. Also, I have a VERY good performing Carter YF 951SA carb, thanks mostly to running about 10 bottles of fuel injector cleaner thru it

Yes, from the MSD literature, the Pertronix output will work as the trigger.

Yes, 8-10° initial advance is much better than 5° ... ~15° is even better, but just work up to whatever you're comfortable with.

 

Re: more power to f-head???

ok,
i will buy the msd first.the exhaust is on plans.i will change the muffler first.because the tube are in very good condition.
i have a solex which i will fit one better cone type filter.
hope the msd will make big difference to me too.it will work to one standar coil without burn it?

 

Re: more power to f-head???

for the advance i will start with 8 and will look how it will goes.i think it will work with 12-15 and with the 92-95 oct gas

 

Re: more power to f-head???

I agree with Homebrew2, These engines will take allot of initial advance ( possibly due to todays fuel formulation as opposed to the lower octane fuels back in the day ) but there is a hidden demon to watch out for........ spark knock from over advance can be inaudible in low compression engines.

I have done some road testing with a stopwatch and digital tachometer after I rigged up some linkage to move the distributor from inside the vehicle, I too wanted to know the limits of advance so I will share the results.

I tested the stock distributor at 5,10,15 and 20 degrees BTDC and logged the following results.
1. At 5 degrees results were predictable, acceleration off the line was acceptable and low to mid range torque was good. Easily revved up to +3600 on high end.
2. At 10 degrees idle speed came up a little and performance was, best I could tell the same as for 5 degrees.
3. At 15 degrees Off the line acceleration seemed to improve but low to mid range torque seemed to level off a little sooner than at 5 or 10 degrees and the engine seemed to take longer to reach its top end.
4. At 20 degrees idle was very good and off the line power was quicker than at 5 or 10 degrees but low and midrange torque was noticeibly hampered and the top end was 200 rpm slower than at 5 or 10 degrees.

I made a temporary stop plate for the Reluctor and restricted the mechanical advance to around 15 degrees and made another run at 20 BTDC, Off the line was good, mid range "seemed " ok and the top end time and rpm came back.

Opinion / Conclusion from limited testing, Any initial advance with a stock distributor beyond 10 to 12 BTDC may cause power robbing inaudible spark knock from to much total advance. Individual engines may respond differently so approach anything over 10 to 12 degrees with caution.

There are two ways to have the best of both worlds if one is so inclined to tinker;

1, Stock distributor with 10 degrees initial, find an old dual advance stock unit or convert to a dual advance distributor ( a lot of work and hard to find a good adjustable vacuum unit ) that will pull on another 10 to 15 degrees at the crankshaft when manifold vacuum is above 8in.

2, Modify the mechanical distributor, with 15 to 20 initial shorten the slots in the reluctor to restrict mechanical advance to around 12 to 16 degrees at the crankshaft. this means that if the distributor allows 12 to 13 degrees ( 24 to 26 at the crankshaft ) you need to shorten the reluctor slot to reduce this to 6 to 8 degrees ( 12 to 16 at the crankshaft )


Any combination of settings that would result in the total advance exceeding much more than 36 degrees could over time cause engine damage, Especially if the engine is worked hard as on the freeway or in the mountains or pulling a trailer.

Use good judgment and keep notes of what works and what does not, Hope this information from my limited road testing helps...........Good luck

 

Re: more power to f-head???

As usual, GREAT input Brian!!! This may actually be the thread that finally addresses REAL F head performance by owners/users of the F head.

I found your initial timing results very interesting.

In thinking back about my adjustments, I realized that PRIOR to the MSD box I had left my timing at ~8°, but, for no particular reason, I just hadn't tried anything greater.

I wholeheartedly agree with your cations! Please straighten me out, if necessary: If one checks the plugs after a trial (or after a certain timeframe using a certain setting) and does not find a pure white condition or any burning appearance/deposits, isn't that a "safe" condition? (This is in response to "Preignition can be inaudible")

I would like to take the time to re-enforce your cautions about damage to the eigine without due diligence. I have, and advise others to, check the plugs on a regular basis for signs of a dangerous condition.

 

Re: more power to f-head???

this may or not be helpful and was discovered completely by accident:
an L4 camshaft installed into an F4.
the intake lift is higher on the L4 camshaft and will eventually break F4 intake rocker arms, one at a time. (It will drive you nuts trying to figure out why).BTDT.
If one was to compare notes between the two cams, one might be able to overcome this problem.
In 2 identical flatfender Jeeps with the same engines (F4), trans, diff gears, tires etc, the L4 cammed F4 blew away the stock F4 in drag races. (In F4 terms)
There was a noticable difference in power and performance in my opinion.
That's all I can tell you as once we discovered our error, we put the correct F4 cam back into the engine.
Need a motorhead to study this more.
(Unitl proven, this may not be tech section worthy)

 

Re: more power to f-head???

The cam is a good point. Clifford still sells a cam, eventhough it can only be found via email (for me anyway). As with their header, there is no data supporting their claims. The only thing I got out of them was "260° duration" and that their cam "changes everything". It was $200. I'm not taking my motor apart. Maybe someone else can try it and post.

As we all say, this thread is worthless w/o pix. Attached is a crappy pic of my motor showing the MSD and wires. Please ignore the illegal siren near lower left. And, I have no idea if the K&N filter made any diff because it was on it when I got it.

 

Re: more power to f-head???

With regard to reading the plugs for inaudible preignition. From what little testing I did there did not seem to be any obvious clues to this condition by looking at the plugs, I dont think the kind of plug damage we are used to seeing in the newer higher compression engines will manifest itself quickly under the conditions I am trying to discribe ( I do agree that it is a valuable tool and could help ). The reason the engine seems to run better with more initial advance is because under little to moderate load the fuel mixture is leaner and it takes more spark lead to light up a lean mixture ( takes longer for the flame front to cross the combustion chamber ).

As soon as we start working the engine hard the fuel metering system in the carb richens the fuel mixture, This richer fuel mixture lights up faster than a lean one. If the initial advance is to far BTDC ( set for a lean mixture ) the piston will have to slightly compress a burning fuel mixture before it can begin its downward power stroke, This will cause an engine to loose torque at low and midrange under heavy throttle and not allow it to develop its full WOT potential.

In a low compression engine a slight loss of torque under heavy throttle due to slight over advance may not be dramatic and hence could go undetected for quite some time. From my experience while doing the test runs the loss of torque throughout the powerband under heavy throttle at 20 BTDC ( no reluctor stop plate ) as compared to 10 BTDC felt similar to having tires one size to big, A little slower but easy enough to get used to.

The mechanical advance systems in our distributors are curved to provide the proper spark lead throughout the rpm range for the richest fuel mixture the engine can handle, Thus producing maximum torque............not maximum economy, This is what the dual advance distributor does. It essentially provides spark lead for both rich and lean mixtures by having two separate spark advance systems operating independently from one another.

It is very tempting to run allot of advance on the little F-Head ( L-Head should be similar ) because they do " seem " to run better, Unfortunatly many of us my be unknowingly hampering the engines ability to produce maximum torque under heavy throttle.

In my opinion based on limited testing there is not much to gain performance wise trying to custom tune/curve the F-Head distributors, I tried it.....various springs, reluctor stop plates, flyweight modifications etc and I am back to running a stock distributor with the retrofit dual advance.

I feel the best ignition modification for most of us jeepers is a good electronic ignition system and accept that maximum torque under heavy throttle was what the original design was after..........not maximum economy, There is no easy way to get both out of a straight mechanical advance distributor.

 

Re: more power to f-head???

in simple words you say that don't touch the distributor and the timing and use one good electronic ignition.i think that this is wise!!anyone else tried the msd ignition?
in my opinion everything else except one solex and one electronic ignition are waste of money and time without some significant power increcement.

 

Re: more power to f-head???

I really like the dual advance idea Brian. How much trouble is it to retrofit?

As to power and economy and our measure of it: Unfortunately, I, and probably most others, don't have cheap access to a dyno so, it's mostly "butt dyno" for us.
My goals have been to see IF I could get the F head to mostly feel like I was driving a real car, be able to pull onto the state highway (3-5% grade) and get up to 55 in a decent time while having the reserve power to get up to speed quickly if necessary, and to be able to pull 15-20% county roads in second gear, and do it all with 31" tires.

I have been able to achieve all of this so far.

So, my first measurement was accomplishing those tasks. My next measurement was, if normal driving could be done at a reasonable level of manifold vacuum (economy) ... 3-10"hg. (I don't have any flat roads in my area so, everything is work.)
I have been successful with the vacuum gauge too. I can get up to speed on the highway grade in a time that is reasonable to me and maintain 5"hg in the process as well as tool around the majority of roads at 5-15"hg. The steepest grades still require 2nd gear and lots of juice.

 

Re: more power to f-head???

Sorry I didn't respond to this earlier. The following are just my opinions. I'm just tagging along like most others and am not an engineer or expert.

If you have a good 1 3/4" exhaust piping back to the muffler/tailpipe, in stock configuration, I agree: change the muffler and (1.5") tailpipe.
I was very hesitant to increase from 1 3/4" to 2" but, because I have 2 severe crush-bends, I went with 2".
Furthermore, I do NOT believe the F head, nor any other motor, NEEDS a little back-pressure. The key is maintaining exhaust velocity ... to big of a pipe will kill velocity.

I have no info to contribute on the Solex carb.

I have been running a stock (internal resistor) coil for a monthe or so now. No probs. As with other parts, I carry a spare.
Please note that MSD says in their literature that a big plug gap will be hard on all secondary components ... coil, rotor, cap, wires. I just haven't seen any probs yet. But, I am a trouble-magnet so, if there will be any trouble, I'll find it and will report back.

Again, I have no idea if a gauze filter does anything or not. Caterpillar used oil bath for a LONG time, as did most other tractor mfgs. Now, I believe, most use paper, as is on my tractor. I have more problems keeping trash out of my radiator screen than I do keeping the air filter clean on my Kubota.

 

Re: more power to f-head???

I stated my opinion previously. IMO the oil bath element is not a problem, but the restrictive design of the can and piping could be.

If you search for "oil bath air cleaner" in this forum you'll find lots of opinions. Here's one thread that includes some substantive discussion (and that I contributed to) http://www.earlycj5.com/forums/showthread.php?t=51611&highlight=oil+bath+air+cleaner

There's also been discussion of the K&N - from what I've read, they aren't suitable for a Jeep because they don't block as fine a particles as a paper filter. Better filtering than open stacks, but not as good as a paper filter. If you search here and the web, you'll find evidence of street vehicles with higher silicon content in the oil due to the K&N filter. I would not use a K&N without an additional inner paper filter.

 

Re: more power to f-head???

My F-head is currently equipped with the pertronix ignitor, MSD 6 plus digital box and MSD coil - Huge improvement over stock - which brings me to my question....
The digital 6 plus has an adjustable nitrous retard function - that only activates over 2000 rpm when the signal wire is supplied with 12 volts - Couldn't I advance the mechanical timing to 20 or so, then use the nitrous retard settings to back out the total timing when at higher rpm?

The second question I have is regarding spark plugs - J8C is specified, and I am running the NGK equivalent - B6S - is there another plug that will work better in this engine when running an MSD set up?

Thanks for all your help.
Chris

 

Re: more power to f-head???

This is just my impression from what I've gleened from the MSD site and other online sources:

THAT is the only way the retard feature can work, ie, you physically advance the distrib to max (or to a certain point) then, the box delays the pusle(s).

I haven't found much positive commentary on "special" plugs. The MSD (6+) delivers ~300+volts to the coil ... I read one piece that stated the msd fired plugs that had the ground lug burned off I do not know if it's true or even what might have burned the lug off but, I believe that ANY true capacitive discharge system is superior to mostly anything else, and has been since the '60's.

Question for you:
Did you add the MSD before the Pertronix? If so, could you actually notice a diff between the "points" with the MSD and, the Pertronix with the MSD?

 

Re: more power to f-head???

Its not technically difficult to retrofit a dual advance but it is time consuming, For the most part you will have to make your own breaker plates unless you are lucky enough to find a dual unit off a later Go Devil or F-Head. The breaker plate assemblies out of some of the earlier V6 distributors will drop right in but they rotate the wrong direction, I was able to disassemble one of these V6 units and reassemble it as a mirror image that rotated the right direction. The Napa VC1130 vacuum advance unit is easy to adapt to the distributor body. Its pretty much a custom undertaking in every respect.

Dont alter or try to use your original fixed breaker plate, Keep it intact.

You wont net a major power increase but you should be able to feel an improvement in low speed drivability and get better low speed fuel economy ( depending on ones driving habits )

A vacuum advance unit can really shine off road where very little throttle is needed in low range and for general dirt road cruising, Properly installed and adjusted it will improve low speed throttle response and get a little more out of your fuel on the trail.

Your carb should be equipped with a vacuum port that is just a hair above the throttle plate when its in the closed position ( my 938 SD has a port at this location ). Whats referred to as " Ported Vacuum " is the most desirable for vacuum advance unit operation.

This modification may not be worth pursuing for some but for those inclined who have the time and ability it does help low speed drivability and economy.

Its a shame one of the vendors that offers the new electronic ignition distributors does not offer them in a dual advance configuration with a fully adjustable vacuum advance unit..........like the older ones with the spring and shim washers inside. I would buy one in a heartbeat. It really would be one of the best overall performance modifications for the vast majority of us jeepers that could be made to the L and F head engines.

 

Re: more power to f-head???

No, I swapped in the Pertronix and Flamethrower coil first, then I wanted something with a rev limiter, so I got the MSD....