Acceleration Off-Idle

[asdfghjkllkjhgfdsa]

(1986 Ford F-150, 300 I6, Rebuilt Engine, Heavy Cam, HEI Distributor, Offenhauser Intake, Headers, Motocraft 2150 2 barrel Carburetor. No electronics/emissions control, c4 automatic transmission)

Restoring a previously owned Ford F150 that was being turned into a race truck.

When I go to accelerate from a stop I get very little power/almost none until I hit 1700-2000 rpm and then the thing takes off. This means I can never ease into acceleration. Its always all or nothing. It accelerates great but I dont want everyone to think Im on some starting line at every stoplight.

What is the primary cause of this? Is it timing and the module in the HEI distributor? Or is it entirely the heavy cam with a large degree and heavy overlap? I also believe the torque converter was replaced with a different one and a shift kit was put into the automatic transmission, but am unsure how that might effect drivability. I've messed with all the carburetor settings and dont think any of those effect this issue.

[ArdWrknTrk]

You already mentioned the timing in another thread.
I would have to say that the combination of cam (and you don't know what the cam timing is) and perhaps too much carb are your big issues now that you have unlocked the distributor.

The torque converter is just set up so that the truck has to be really wound up and into the cam before it starts loading the drive line.

Don't be faint of heart in un-butchering this truck if you actually want to use it for it's intended purpose.

[1986F150Six]

My gut feeling is that the low RPM performance has to do with that specific distributor. I feel like it may be defective.

[asdfghjkllkjhgfdsa]

When you say "The torque converter is just set up so that the truck has to be really wound up and into the cam before it starts loading the drive line." Isn't this exactly what I'm experiencing with a lack of power until high rpm?

Is it I have to get the RPM up to a specific amount before the TC cuts in and delivers power to the drive line? Im not very familiar with torque converters, but if this is an issue, would no amount of engine demodification I do make a huge impact on the ability to make a slow take-off speed until I also change back to stoke the TC?

[ArdWrknTrk]

Torque converters have what's called 'stall speed'
A drag vehicle should be pushing redline from when it leaves the line all the way to the traps.

You can't seem to differentiate between "The engine is gutless below X", or "It's not putting any power to the wheels below X".

If your truck has a 2,800 rpm converter then it's not going to be friendly on the street, and you can't do anything but change it.

[Gary Lewis]

1986F150Six wrote

My gut feeling is that the low RPM performance has to do with that specific distributor. I feel like it may be defective.

David has a point.  Has it been proven that the mechanical advance is working properly and starts pretty quickly off idle?  I've not been following this very closely with all else going on at the moment.

[ArdWrknTrk]

Have either of you read the OTHER thread where it was discovered that the dizzy was locked out, but it was put right?

I mean, I doubt that this guy has a Sun machine, or anything, but if it's advancing and the static timing is okay what more can you do?

[Gary Lewis]

No, I've not.  As said, things have been rather busy for me at the moment.

But I'm glad that bit has been fixed.  Carry on!

[ArdWrknTrk]

This is what happens when the same problem gets spread across multiple threads.

[asdfghjkllkjhgfdsa]

My original problem was an off-idle stumble. After unlocking the distributor and another fuel issue tweek, that has disappeared. What hasn't disappeared or what I'm trying to figure out now is why it's so under powered at a low rpm vs high. Hence the sperate thread because, being very new to this, I thought they were two separate issues.

Sorry if starting a new thread messes things up. I'm just trying to figure stuff out best I can. I'm not going to stop asking questions either just because one person says "this is all that can be done". I've learned to many times there's more than one way to skin a cat, and I love hearing different people's ideas and learning how everything works. Please and  honestly, give me a little bit of slack, I'm trying to learn something I've never done before.

[viven44]

Jim has given me trouble for starting a new thread .... my memory isn't as good and I lose track on long threads... I would rather have smaller threads that focused on smaller problems  

[viven44]

Whenever HEI is brought up... I always ask the question... how stable is the alternator voltage at idle and low RPM ?

If you put a multimeter/voltmeter on the battery terminals while the truck is idling, are you seeing over 14V? If so, what happen when the blinkers are on? or when the headlight is on? Do you have at least 13.5V?

[ArdWrknTrk]

I don't mean to come off as contentious.
Sorry!  I never want anyone to feel unwelcome.
I'm telling Gary he should get the background....

Otherwise we all chase our tails, with people suggesting stuff that's already done... two or three times!

So please explain, is it just that the truck isn't putting power down (very loose converter) or is it that the cam timing is way off and the engine is unable to pull at low RPM?
Or both???

[mat in tn]

not that it makes a great amount of difference but in the sig it says c6 yet in the thread lead in it says c4. one bit I will say is that the c4 has been used a lot in racing as it robs far less power from the vehicle than the c6 although the c6 is a MUCH better truck transmission. this "might" lead to the builders' intentions.  the camshaft cannot be dismissed however I think I remember this reaching a pretty good vac signal in another thread. that pushes me to look at ignition first. even if the dist is new i still test as much as possible as new parts are not what they should be. hei conversions are nearly all discount imports and I have had good luck but with at least a 10 percent crap rate.

[ArdWrknTrk]

Perhaps the actual HEI can be identified?
Is it a DUI?
With the intention of a race truck, and evidently the thought and effort put into "waking up" the old 300, I'd be a bit surprised at a $50 distributor.
But, like I said in the other thread it would be wise to look at how much advance it actually starts with, how soon it comes in and where it stops.

[Gary Lewis]

ArdWrknTrk wrote

But, like I said in the other thread it would be wise to look at how much advance it actually starts with, how soon it comes in and where it stops.

Yep.  I've turned mild-mannered engines into jack rabbits off the line by bringing in the advance a lot quicker.  So the opposite is quite possible.  If someone put heavy springs on both sides it'll be slow to accelerate from idle.

[ArdWrknTrk]

If they want a drag racer they're going to have it all in right off idle. (Or locked out, like it was)
Are you unclear on the concept, and what's going on here?

[Gary Lewis]

ArdWrknTrk wrote

Are you unclear on the concept, and what's going on here?

If that's to me, I am quite clear on the concept of centrifugal/mechanical ignition advance.  Really light springs bring the mechanical advance in very early and in a 69 SuperBee with a 383/727 combo it'll render it almost undriveable on snow.  Look at the throttle and it'll spin the tires.

As far as what is going on here, I'm not sure. The OP said "When I go to accelerate from a stop I get very little power/almost none until I hit 1700-2000 rpm and then the thing takes off."  I could read that two ways - either the engine is lethargic at lower RPM but when it hits 1700 it lights up.  Or, the engine revs but the truck doesn't roll much until it hits 1700.

And it appears you and I are on the same page because you said "So please explain, is it just that the truck isn't putting power down (very loose converter) or is it that the cam timing is way off and the engine is unable to pull at low RPM?
Or both???"

So until we get confirmation on what the issue is we are spinning our wheels.

[ArdWrknTrk]

ISWYDT

[Gary Lewis]