Too low max RPM?

BroncoDarin · Jun 1, 2009

I have a 69 351W that is maxing out at 4800 RPM. It has the D0OE Heads, a 6000 RPM ISKY cam, and a duraspark ignition. Numbers wise, MAX HP holds steady from 3700 - 4400 and Torque Spikes at 2500 and then holds steady from 2700-3300.

I am wanting to know if this is something I should be concerned with? The motor only has about 500 miles on it. I do know the distributor is advancing a little too far. I am thinking there is a chance I might have an original duraspark distributor and a Duraspark II module? Could this be my problem? Is that even possible?

Like I said, I am not sure if this should be a concern, I just don't want to be leaving power out there that I can easily get back.

DirtDonk · Jun 1, 2009

The way I see it Darin, it's one of those "all-of-the-above" things.
The relatively new motor (though that in itself should not limit rpm), too much advance, old worn out distributor and stock module.
The Ford Duraspark module's weren't known for limiting rpm THAT low, but stock stuff is sometimes a limiting factor, rpm-wise, and maybe yours is just one of those that can't quite keep up it's spark in the higher ranges. Ditto an old worn out dizzy with wobbly shaft and old weak reluctor and pickup.
How much is too much advance? How much spark plug gap are you running? Higher compression, non-stock cams and a not-quite-perfect air/fuel mixture can require a slightly smaller gap at the higher rpms. You might run fine at .060" up to 3500 rpm, but choke off the spark event at 6000 with just .048" gaps.
Try fine tuning the advance, reduce the plug gap to .040", update the ignition components to something more modern (you can still stay with the Duraspark theme, just newer hi-po stuff), double check your carb metering and wait for another 500 miles.
Then see what you get.

Paul

broncnaz · Jun 1, 2009

Without knowing the specs on your cam I would say its probably fine. A cam may have a 6000 RPM limit due to profile and springs used whick is really the point of valve float but that doesnt mean it will make the most power at 6000 rpm most cams are like that. It actually sounds like you have a well build low RPM torque curve it should be good for a bronco.

The duraspark I and II dist and modules work fine together theres really no differance. I dont think the dist ever changed a bit when duraspark II came out all it does is signal the box. Now the duraspark II box is supposed to be a little different maybe better than the duraspark I. You might be leaving a little power out there with the timing a bit to far advanced but as long as you dont have any detonation you should be fine.

Viperwolf1 · Jun 1, 2009

Get it dyno-tuned. They'll be able to measure and adjust air/fuel ratio and timing across the entire rpm range.

DirtDonk · Jun 1, 2009

That reminded me of a question I had. Did you match the cam with the proper springs? You're not running older stock-ish springs are you?
And by "maxes out at 4800", I took it too mean that it just won't rev any higher. Is that correct? Or did you mean it just dynos out there and falls off after that?

Paul

BroncoDarin · Jun 1, 2009

DirtDonk said:
That reminded me of a question I had. Did you match the cam with the proper springs? You're not running older stock-ish springs are you?
And by "maxes out at 4800", I took it too mean that it just won't rev any higher. Is that correct? Or did you mean it just dynos out there and falls off after that?

Paul

The cam was purchased from the same shop I Had build the motor. They are a good shop and am pretty sure they did it right.

I have a new 650 Proform carb that was tuned on a dyno and gave a huge hp and torque boost after re-jetting. Yeah, it pretty much maxes out at 4800. Sounds like it might explode if I go any further.

BroncoDarin · Jun 1, 2009

Viperwolf1 said:
Get it dyno-tuned. They'll be able to measure and adjust air/fuel ratio and timing across the entire rpm range.

Did it and was an awesome learning experience.

BroncoDarin · Jun 1, 2009

broncnaz said:
Without knowing the specs on your cam I would say its probably fine. A cam may have a 6000 RPM limit due to profile and springs used whick is really the point of valve float but that doesnt mean it will make the most power at 6000 rpm most cams are like that. It actually sounds like you have a well build low RPM torque curve it should be good for a bronco.

The duraspark I and II dist and modules work fine together theres really no differance. I dont think the dist ever changed a bit when duraspark II came out all it does is signal the box. Now the duraspark II box is supposed to be a little different maybe better than the duraspark I. You might be leaving a little power out there with the timing a bit to far advanced but as long as you dont have any detonation you should be fine.

Yeah, I don't have any detonation. Here are the cam specs http://iskycams.com/timingchart.php?product_number=388270

BroncoDarin · Jun 1, 2009

DirtDonk said:
The way I see it Darin, it's one of those "all-of-the-above" things.
The relatively new motor (though that in itself should not limit rpm), too much advance, old worn out distributor and stock module.
The Ford Duraspark module's weren't known for limiting rpm THAT low, but stock stuff is sometimes a limiting factor, rpm-wise, and maybe yours is just one of those that can't quite keep up it's spark in the higher ranges. Ditto an old worn out dizzy with wobbly shaft and old weak reluctor and pickup.
How much is too much advance? How much spark plug gap are you running? Higher compression, non-stock cams and a not-quite-perfect air/fuel mixture can require a slightly smaller gap at the higher rpms. You might run fine at .060" up to 3500 rpm, but choke off the spark event at 6000 with just .048" gaps.
Try fine tuning the advance, reduce the plug gap to .040", update the ignition components to something more modern (you can still stay with the Duraspark theme, just newer hi-po stuff), double check your carb metering and wait for another 500 miles.
Then see what you get.

Paul

Thanks paul. The dyno guy didn't seem too concerned, just made the comment that I may want to consider a distributor upgrade and that it was advancing a little too far. the whole day was a complete system overload for me and if there wasn't so much going on I probably would have inquired more.

I will pull the plugs and check the gaps. I am running motorcraft plugs. Should I maybe look for an upgrade there?

I really would like to stick with the duraspark set-up. Which upgraded components would you recommend that are still based on the duraspark?

BroncoDarin · Jun 1, 2009

By the way, here is a link to a thread I started last week describing my dyno day..... http://classicbroncos.com/forums/showthread.php?t=141038&highlight=dyno

broncnaz · Jun 1, 2009

I'm no cam expert but the specs look about normal for a RV type cam. They are not desinged for the high RPMs. in the specs where its says RPM ranges just means it really starts making power at 2000 rpm and falls off at 6000 rpm. There are many factors which can move the torque range up and down a few hundred RPM or more ie intake, exhuast, heads, ect.

I would expect that cam to do exactly what your describing by falling off at 4800.

Might want to google duraspark recurving it will give you a lot of info. More there are 2 timing advance settings in the duraspark that you can change to remove some of your total, The only upgrades so to speak for the duraspark are some advance springs which I would recommend if you get all your advance in by 3000 rpm you should be good to go.The only downside of the duraspark is the work it takes to change the advance when compared to other dizzys but all in all for the price its still better than most out there. Stay with the motorcraft plugs you really dont get any performance out of different plugs. The only other upgrade I would suggest if you dont already have them is some good aftermarket plug wires I would suggest Ford motorsports wires but any good ones will do.

BroncoDarin · Jun 1, 2009

broncnaz said:
I'm no cam expert but the specs look about normal for a RV type cam. They are not desinged for the high RPMs. in the specs where its says RPM ranges just means it really starts making power at 2000 rpm and falls off at 6000 rpm. There are many factors which can move the torque range up and down a few hundred RPM or more ie intake, exhuast, heads, ect.

I would expect that cam to do exactly what your describing by falling off at 4800.

Might want to google duraspark recurving it will give you a lot of info. More there are 2 timing advance settings in the duraspark that you can change to remove some of your total, The only upgrades so to speak for the duraspark are some advance springs which I would recommend if you get all your advance in by 3000 rpm you should be good to go.The only downside of the duraspark is the work it takes to change the advance when compared to other dizzys but all in all for the price its still better than most out there. Stay with the motorcraft plugs you really dont get any performance out of different plugs. The only other upgrade I would suggest if you dont already have them is some good aftermarket plug wires I would suggest Ford motorsports wires but any good ones will do.

Thanks again. I do have the ford racing wires. I have read a little on recurving and I might go ahead and take little closer look at that. Like I said before, I really am pretty happy with how it is running. Will probably start saving for those gears before anything else ;D

DirtDonk · Jun 2, 2009

Well, since you've done all this cool stuff to the engine already, and even though I'm in favor of sticking with Duraspark too, I'd love to see you experiment (hey, it's not MY money!) with one of Mallory's new E-Fire or Max-Fire distributors.
They both have 7 different electronic advance curves that can be chosen any time. Or, if you prefer to roll your own, you can use the included Windows software to creat your own advance curve. For vacuum advance they use an internal MAP sensor
I think they're both stand-alone units (other than a coil), but the Max-Fire uses an integrated multi-strike digital CD ignition system so no outside module is needed. Add a modern e-core coile and this thing probably puts out one hell of a spark and you'll never worry about lighting off the mixture again!
Even though it's not a "Duraspark" setup, I'm pretty sure that like so many other aftermarket units, the internal trigger mechanism is a Duraspark clone.

Paul

DirtDonk · Jun 2, 2009

BroncoDarin said:
I really would like to stick with the duraspark set-up. Which upgraded components would you recommend that are still based on the duraspark?

Now that I've got all the Mallory stuff off my chest (but you gotta' admit, it's pretty cool stuff!), MSD makes some direct-fit replacement modules that have some higher design quality internals than a stock or cheap replacement. I have used both their Adjustable Timing Control version and the hi-po module made by MSD but sold through Ford Motorsport (now Ford Racing). Both are direct replacements for stock.
I personally use an Accel 300+ ignition box and coil that are triggered by my Duraspark distributor on my 400. BEEEG difference from my original stuff.

And as for the dist. itself, too bad Accel dropped it's "Blueprint" series. Pretty much a high-end "budget" stock replacement. You could probably get away with just any old stock replacement though, as long as it's got new or rebuilt components, you're way ahead of an old worn out one.

Paul

DirtDonk · Jun 2, 2009

As if to prove that I really don't have all that cool new Mallory stuff out of my system...
Here's a link to the MaxFire: http://www.malloryperformance.com/P...jID=530&minID=5302&selection=&minselection=-1

E-Fire: http://www.malloryperformance.com/P...ajID=530&minID=5303&selection=&minselection=2

I can't remember all the differences, but I think the E-fire lacks the multi-strike CD. Still internally controlled though.

Paul

BroncoDarin · Jun 2, 2009

DirtDonk said:
As if to prove that I really don't have all that cool new Mallory stuff out of my system...
Here's a link to the MaxFire: http://www.malloryperformance.com/P...jID=530&minID=5302&selection=&minselection=-1

E-Fire: http://www.malloryperformance.com/P...ajID=530&minID=5303&selection=&minselection=2

I can't remember all the differences, but I think the E-fire lacks the multi-strike CD. Still internally controlled though.

Paul

Wow Paul, that quite possibly could be a great place to spend $400. I am beginning to think that a mallory unit in addition to a wide band O2 censor would really be fun!

DirtDonk · Jun 2, 2009

Absolutely!
Ya know, you might find an Accel "EMIC" (engine management installation center) and price out both. You can find the nearest one through their website and I'd bet the EMIC's, which are usually small shops, are hurting right now and would love the sale. And you might be able to score a wideband unit and a distributor "on the cheap".
As if any of this stuff is going to be cheap!

Then comes the Tech-Article for the rest of us to see how the install and fine-tuning goes. Of course.

Paul

BroncoDarin · Jun 2, 2009

DirtDonk said:
Absolutely!
Ya know, you might find an Accel "EMIC" (engine management installation center) and price out both. You can find the nearest one through their website and I'd bet the EMIC's, which are usually small shops, are hurting right now and would love the sale. And you might be able to score a wideband unit and a distributor "on the cheap".
As if any of this stuff is going to be cheap!

Then comes the Tech-Article for the rest of us to see how the install and fine-tuning goes. Of course.

Paul

Uhh, It might just be cheaper to fly you up for a weekend to put it all together

Will keep my eye out for sure. I could see this being a good winter project!

DirtDonk · Jun 2, 2009

Like Dumbo, I do work for peanuts. The three-P's... Pasta, Pizza and Peanuts.
Throw in some good weather (preferrably no rain or big skeeters) and a well-lit garage or driveway, and I'm good to go.

Paul

Too low max RPM?

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