[Adrian Worman]

Hi mates,
When an aftermarket distributor is advertised as having a "performance" curve is it really any different than a stock unit? I know some are advertised as having an adjustable mechanical advance, but does it offer any real advantage over modifying your own unit?
Cheers, Adrian

[dave-r]

They usually have one lighter spring. Making it advance a bit quicker. But not quick enough usually. So you will have to modify it anyway. Also because you will need a lot of initial advance you will have to limit the amount of advance.

Most Mopar electronic distributors come with a "performance curve" as standard.

[Adrian Worman]

I had sort of figured tthat out from reading your old posts Daveman, just needed the official word, so I'll save me coin and do me own mods

[fbernard]

I just had a distributor curved by FBO for my cuda (small-block stroker, mid-12s in the quarter), and the end result is this :
Turning the rotor by hand requires an effort, and travel is limited, whereas the stock dist I have on now ca be turned easily and swings twice as far.
I see one medium spring and one heavy spring (old dist has two light, rusted springs).
the new distributor gives only 12 degrees of mechanical advance, which will translate into 24° of initial (idle) advance.

From my previous trials, I'd say my engine should be quite happy with that much initial advance. I just got the dist, I haven't installed it yet.

The OEM dist I'm comparing too is OEM 1973ish.
I've read several times before that the springs in the MP unit were too soft, too.

By the way, FBO sells a kit to modify your own distributor (with an advance plate to limit the mechanical advance, springs, etc.). That may be a good alternative to welding and grinding the advance plate...
I've ordered that too but haven't received it yet.



Since FBO has a dealer in England (Jon, sales@fbo-uk.com), you may want to contact him.

[dave-r]

Yes Jon (MMA username Turnip) has taken over the UK FBO franchise from Neil (MMA - Wil).

He was selling the FBO advance plate kits at the Mopar Nats for around £20-£25 each I think?

[Adrian Worman]

Ta mates, just sent him an e-mail

[Adrian Worman]

Thanks for the tip Fabien and Dave, I've had a recurve kit turn up in the post this morning and I've just ordered one of the e.c.u kits they do, very helpful people
Bit like you

[fbernard]

I just installed my new distributor this week-end. I was a bit worried about cranking and starting with 24° initial advance, but it's OK when cold. Hot, it did stutter *once*.
It's rather the shutting down that's weird. I have some preignition which tries to keep the engine running when I switch it off. Not all the times, but I don't like that (even though I can stall it in 1st gear, at least I have a manual transmission). I might consider a retard box (which would defeat some of the purpose of having a straight, simple, OEM-compatible ignition system. If I start looking at ways to have a dual-stage rev limiter and start retard, well, the FBO ECU might be replaced by a MSD box).

Driving it is very different from before.
The engine power delivery feels totally linear now, and engine noise sounds much steadier, whereas it used to feel like power was increasing as the revs went up.

The seat of the pants feeling is somewhat disappointing (power-wise). It could well be a false impression. The timeslips will tell (next year).

Drivability-wise, it's better. I can drive at 1400 RPM without the stuttering in the driveline I had below 1600 before. That's better, with the huge spread between 4th and 5th gear at highway speeds, I can stay in 5th and keep at the posted speed limit, when I used to have to switch down to 4th.

I have a racetrack session next saturday, so I'll see a bit beter how it does at higher RPMs.

[dave-r]

The run-on problem was something Chrysler had on their high compression 440 six pack engines. Which is why they used a solenoid to close the throttle further when you switched off.

I use 24 deg. initial but have no starting or run-on problems at all.
In fact when the engine is hot or even just warm i can lean into the car, turn the key, and the engine will instantly idle without any intervention from my right foot.
Cold starting seems easier too. I don't have to hold the rpms up as long for the engine to start to idle by itself.

[Adrian Worman]

I've got a spare distributor, so I'm going to mod that while I wait for Jon at F.B.O to send me a Mopar e.c.u kit. The plate and spring guide looks really easy to follow, but I too was a bit worried about dialling in so much initial advance, I still may end up disconnecting the vac, I think Dave's done that anyway. Thing is, the exhaust is so loud that even in the car I'm not sure if I could hear it pinking anyway. The tech line at F.B.O is very good and they offer a service where you fill in a very detailed tech spec form and they can guide you to the correct settings. I hope

[fbernard]

Which is why they used a solenoid to close the throttle further when you switched off.

I have that setup for the 440-6pak. I could use something similar for the small-block (I do have the idle set somewhat too high now with the initial advance, I should probably aim to get it around 800 RPM (around 1000 now).

[dave-r]

Possibly part of your problem. If you can get it down below 850rpm you might just also fix the running-on too.

[fbernard]

Back from the track day. Weather was exceptional (3 days in a row with no cloud in sight).
Engine behaviour was really good. Including on the way to and from the track, much smoother than before.

I do have a slight problem starting the car cold, when it's cold outside (it takes a while).

Other than that, it's perfect. Apart from that tiny tingling metallic sound I have been experimenting for the last two weeks, which has grown from something I heard when cornering, to something I heard sometimes even in straight, to something louder that started when I cranked the engine...

Oh, and I don't have engine run-on. What I mistook for engine run-on was that funny noise too.

Let's call that "POS vibration damper run-on"...

I drove back home with the outer ring in the trunk.

I ordered a SFI approved damper yesterday...

[dave-r]

Lucky that didn't fly loose and put a hole through the side of the car.

[fbernard]

Lucky that didn't fly loose and put a hole through the side of the car.

Well, it was held in place by the pulley, but I don't want to think about what would have happened if the ring had grenaded at 6K RPM...

[Jon]

Lucky that didn't fly loose and put a hole through the side of the car.

Well, it was held in place by the pulley, but I don't want to think about what would have happened if the ring had grenaded at 6K RPM...

Do you guys think it is a good idea to replace the original damper just in case? How would a replacement be balanced to my motor? (340 forged crank)

[dave-r]

Most SFI approved dampers are internal balanced. Some have an optional bolt on weight for external balance.

[fbernard]

Do you guys think it is a good idea to replace the original damper just in case? How would a replacement be balanced to my motor? (340 forged crank)

If you regularly rev up to redline at full load, I'd say yes.
f you jsut drive around and give it the occasional blast, I'd say that's not necessary.

But I've been known to do unnecessary things just for peace of mind.

Just like I sometimes write long, almost off-topic posts in the middle of the night for no apparent reason (although this time, I have a reason. I've been holding my club's booth at an old car convention all day, and I've been asked if that car -an orange 70 challenger- was the car from "Starsky & Hutch". Twice today. I have to go back tomorrow).


The engine on my cuda was built 3 years ago, and has been used for rally and road racing, and drag racing. Not that we get that many drag racing events in France anyway. It also got around 7000 miles on the road.
Engine redlines around 6200, never been above 6500.
I did 4 full races this year, so probably around 40 runs.

The $80 damper installed by the engine builder just wasn't meant for this.

You can check from time to time that yours doesn't wobble. Mine gave clear audible warnings, at first during turns, then all the time, then it became obnoxious. On a small-block, the damper hitting the cast aluminum timing chain cover is a very cristalline metallic sound.
Had I known what to look for, I would have known, two weeks ago, why I had a hard time setting ignition timing.

Here's what I know about dampers (and it has expanded a great deal in the last 10 days).

OEM dampers are all elastomeric. That is, they're made of a center ring (which also serves as the hub), an outer ring, and a rubber bond injected/molded in between.
OEM dampers have no insulation, the rubber portion is exposed to elements, oil leaks, and any chemical that may happen to be around the front of the engine. Temperature cycles don't help either.

OEM dampers have no safety feature whatsover to prevent the outer ring from getting loose, once the rubber is too damaged to keep it seated.
OEM dampers are most often cast iron, which can crack, and may easily fragment under stress (you get the idea).

The main purpose of the vibration damper is to limit the torsion angle on the crank snout (the crank twisting on its axis), which is induced by the rods pushing on the crank throws during operation.
The damper also absorbs harmonic vibrations.

Balancing a cast crank is another function altogether, although it is also performed by the vibration damper (and converter weights) on cast-crank engines.

There are several types of aftermarket dampers.
Elastomeric (like OEM, and slightly different ones), fluid-based, and the TCI Rattler.

Let's start with the latter. One of the more recent marketing fads, the Rattler uses a harmonic damping principle which, though perfectly valid (and extensively used in jet engines), can only control vibrations in one axis. I don't know if it's an issue or not in a V8, which, by definition, is not balanced. That principle was patented by TCI for use in cars, hence the Rattler is currently the only model using this principle.
The Rattler is dimensionnaly identical to an OEM damper (which is better for pulley alignment).

Next, the FluiDampr family, which has been around for a decade or so, and was probably introduced as a (then) new marketing ploy to sell something new.
Principle : compared to the elastomeric damper, the fluid damper's hub and first ring is integral to the housing, and the second ring is enclosed inside it. Free to turn. Bathed in a silicon fluid.
Pros : the engine sees only a fraction of the damper's weight when accelerating, since the second ring is free-wheeling. It's very durable, being totally sealed. They're very durable, have degree markings up to 50° and every 90°, and I have one that's 10 years old at least on a big block.
Cons : The clearance for the secondary ring is really tight, and even a slight dent on the housing may pin the second ring in place and render the damper useless. There's no way to check for yourself that the ring is free to turn.

And last, the elastomeric damper. I've read that this is the most sound techinical principle (on a manufacturer's website which sells this type pf damper, of course). Which I would be tempted to believe, on a pure technical basis. After all, it is the OEM design of almost every damper on every combustion engine even today. For those of us who try to avoid cheap chinese-made junk (and I mean junk, there are some pretty nice Mopar parts made in Asia, but I have some pictures which say "Professional Products" sells real junk), there's an Australian firm which makes fair-priced dampers, in two street (one SFI-approved, one not) and one race versions. I helped install one on a small-block recently. Not in stock at the moment at Mancini's, though.
Most high-end elastomeric dampers nowadays are sealed, laser-welded, so therubber can't be contaminated. The casing may enclose the outer ring, so it can't fly off. The rings may be serrated, so they can't spin out of control.
BHJ also makes very good dampers (and fairly expensive ones).
Since inner mass has no useful purpose on a damper, their aluminum-center dampers look really good. Prices are awful, though. Non-SFI approved at 200 bucks, all the rest starts above 400.

The variant : ATI makes dampers with 2 or 3 steel rings, removable hubs, and the rings are held to the housing with rubber o-rings.
Several O-ring types are available to tune the damper to the engine (which is only really useful if you have unlimited access to a dyno).

Now, if I don't want to make this -already off-topic- post far too long, let's just say the ATI design seems hands down the best design there is. Some OEMs use ATI dampers on their big crate engines.
They're rebuildable. The removable hub makes installation a breeze, and let's face it, they look cool. They have options for weird things (crank triggers, blower pulleys).
Now the cons, as unbelievable as that may seem. These guys seem to have engineered the best damper on the market, and they boldly state on their catalog that the hub is too long. They know it. They did it on purpose! You can machine it (they even give you the length to machine it to).
You are almost assured to have pulley alignment issues with that, and custom pulleys may be the only way to go if you get a 3-ring damper.

Yeah right. I need a damper on the engine before next saturday or my last track session of the year is cancelled.

I ordered a Pro-Race unit, which was backordered, and settled on a FluiDampr.
I already have one on a big-block, now I'll have one on a small-block too.

Whatever type you chose, I'd say the SFI approval at least give some insight into the intended use of the part.

Price-wise, I'd say good dampers start around 130-150 dollars. Below that mark are dampers like the one I had...

SFI approval does not mean the damper works as stated. Just that it can be spun at 12K RPM for one hour and still be there afterwards. Stop and go conditions, accelerations and decelerations, heat cycles, dirt, oil, none of this is part of the SFI test procedure.

[Jon]

Wow, lots of good information, thanks for taking the time.

The reason for such interest in this subject is my father told a story many years ago of a friend (hot rodder) tuning his engine, revving and such, and the damper came apart killing him instantly. That had always been in the back of my mind (not unlike the metal parts in my dads friend).

Something rotating even at only 6000 RPMs, connected with glue, and 40 years old has me a little concerned. I would rather not deal with replacing or modifying the pulley so which unit would you recommend in the elastomeric series? I am still wondering if a replacement will throw the engine out of balance as the stocker was a matched set last motor build. If so how would a shop go about adding or removing weight from the new one to imitate the stock unit?

[fbernard]

I would rather not deal with replacing or modifying the pulley so which unit would you recommend in the elastomeric series? I am still wondering if a replacement will throw the engine out of balance as the stocker was a matched set last motor build. If so how would a shop go about adding or removing weight from the new one to imitate the stock unit?

You can probably find out what you need by looking for the casting number on your current damper.

If yor engine is internally balanced (any engine with a forged crank except the 440 6-pack), you have a lot of choice.

Looking for good, SFI, entry-level SFI-approved internal balance dampers on Summit will return nothing. They start at $365 with the Rattler.

Small-blocks :
I'd go with one of the Pro-Race dampers (http://www.pro-race.com/index.htm ). Australian stuff.
http://www.pro-race.com/index.htm
You can find them at Mancini (and Hughes too).
http://chucker54.stores.yahoo.net/prorace.html
PRO/SPORT #34277. Around $150.
PRO/RACE #64277. Around $300.

The best choice for a race engine might be the ATI 918282E. The hub needs to be shortened .450". an all-out race engine might use the aluminum shell damper, even lighter, #917392E (shorten the hub .450).

Alternatively, some BHJ dampers do have an interesting feature, some have an aluminum hub and first ring (only the outer ring weight is usefull, weight at the center is useless). Extremely pricey though.

Big-blocks :
Same advice about the Pro-Race models, same prices.
ATI's catalog does not even state how to make their big-block dampers OEM-compatible for pulley alignment...
If you have an externally balanced engine, there are still some good dampers you can find, but they're scarce. Pro-Race does have dampers for external balance, I wouldn't look further.

Watch out : in some older engines (but I don't know the changeover date), one of the 6 crankshaft pulley bolt holes is offset.
Most dampers are made for the even-spaced late pulleys. Redrill the 6th hole in the pulley in that case.
Another thing to watch out for is the timing pointer location on small-blocks, which apparently was passenger-side before 1970, driver side afterwards. BHJ offers both styles.

[Adrian Worman]

I've finally installed my F.B.O ignition e.c.u and related stuff (made an instant improvement to starting,idle quality and off idle response, even made timing easier) but when I checked timing ready to start modifying the dist for the F.B.O advance plate and springs, I was surprised with tthe timing results I got. I acheived 35deg but at only 2200-2400rpm, initial timing was rechecked and equates to 15deg. If I reconnect timed vac I get 52deg total, but still as early as 2400rpm. Have'nt pulled the dist yet to look inside, was just a bit surprised to see it all in that quick. The kit of springs will be able to slow down the advance ok, I'm aiming for about 3000-3200 are'nt I? Got no issues with a high initial advance, the starter seems to crank it over no matter what I dial in.
Had a really nice drive about on Saturday, left rubber all over Milton Keynes

[dave-r]

Right. OK.

So you have 15 initial with 35 total.

That means your distributor has 20 degrees available in it. With me so far?

Now. With the engine fully warmed up and at idle, slowly turn the distributor either way to see which way the engine is getting faster.

You should be able to find a sweet spot where the rpm increase starts to level off. Find that spot and then back the dizzy off just slightly so the rpms only JUST drop a fraction.

Now lock off the dizzy at that point, re-set the idle speed down to normal (800-900rpm) and then shut the engine down.

Then try to restart the engine.

If it struggles to start or kicks back on the starter back the dizzy off slightly more and try again.

When you are happy it starts fine let the engine idle again, check the idle speed is not too high, and then see what the initial timing figure is.

Now you need to remove timing from the distributor so that from your new initial it does not exceed 34-36 degrees total.

For example if your new initial is 20 degrees you will have to remove 5 degrees from your distributor using that plate thing. Not sure how that works but you should figure it out. I just weld the slots in the weights but i don't have fancy plates etc...

Once you have the amount of advance correct you can play around with the springs to get the rate of advance right. Aim for half the advance in by around 2000rpm and the rest all in at 3000rpm.

Forget about the vacuum advance. If you have done this right you won't need it.

[Adrian Worman]

How much difference does it make being a manual trans? That plate is a godsend, saves a load of work
Sounds easy enough so far Daveman

[dave-r]

How much difference does it make being a manual trans? That plate is a godsend, saves a load of work
Sounds easy enough so far Daveman

You can let it idle at a lower rpm. Down to 600 if it will. But the alternator might not be charging at that speed.

[Adrian Worman]

Pulled the spare dist apart and cleaned it up nice ready for mod. Think I understand why the advance is so rapid, one of the springs, the bigger one of the 2, has an elongated slot on it which appears to put no tension on the weight all the time.
F.B.O plate and springs look ever so easy to install and they provide a reference chart to help plot the adv curve at precise rpm's.
My cam is a Comp Cams Xtreme Energy copy of the Mopar 509 cam, but just slightly more aggresive, the rear gears are not brilliant either, 3.55's I think, from what I've read on here (other MOpar sites are available) I should be looking to delay total timing to maybe as much as 3200rpm's.
Gonna try it at the weekend and see

[dave-r]

I would have it in at 3000. Particulaly with a cam as big as that. They like a lot of advance. But another 200rpm is not going to make a heap of difference. Just don't go beyond that.

[dave-r]

Think I understand why the advance is so rapid, one of the springs, the bigger one of the 2, has an elongated slot on it which appears to put no tension on the weight all the time.

That probably takes up the slack at idle and is a way to take a few degrees out of the dizzy.

[Adrian Worman]

Ta Daveman

[fbernard]

That plate is a godsend, saves a load of work

Take pics while you do it, I haven't started mine yet!

[Adrian Worman]

Umm, yeah, I took some pics last night cos I could'nt wait to get started on it. Had a look at them on my phone this morning and they are crap
and i installed one of the wrong springs so its coming apart again!
However its such a simple task now I've done it that its gonna be no issue, it honestly took me only half an hour to do and that was mainly spent trying to get the little circlip back onto the rotor shaft
Anyway I'll attack it Friday evening and post nice piccies