400 carbon/soot

[PolaraFury]

Hello,

I would like some advice concerning a carbon/soot problem. I’m going to give you the information I have off the build sheet that was provided by the previous owner.

Motor is in a 67 Satellite:

I have a 76-78 Mopar 400 and the current build sheet says it has a Comp cam 274/286 488/491 hydraulic and I believe, that is an Extreme Energy series. The heads have Proform 1.5 roller rockers, it’s got a 727, with shift kit and 3K stall. Heads appear to be stock and are definitely cast iron. Also has a set of Headman Headers with flow masters.

With this cam and the 3:90 Suregrip, the car will definitely get up and go until I hit about 90mph and then I’m out of top end. My concern is carbon/soot.

I am getting a LOT of carbon out of my exhaust. I have adjusted the timing back and forth, the carb is very responsive all around (Holley 850 with Holley electrical fuel pump) so I don’t suspect it’s my carb or timing.

I also run 91/93 octane in it. It runs really crappy on 87 no matter what I do with the timing. I (personally) think my soot problem is the camshaft (I could absolutely be wrong and that’s why I’m asking for guidance).

I have been doing lots of reading on camshaft theory and I’ll be honest with you, I have a massive headache from all of it but, I do have a better understanding of lift, duration, and lobe centerline angle.

My plan when I tear into it this winter is to do some mild port/polish work, check all my clearances, replace gaskets/seals and re assemble. I am also going to get off that 3:90 and get a 3:23 or 3:55 depending on the advice I receive.

(Next year it will get a 500 stroker kit but that’s an entirely different subject.)

Thank you for your time

 

[493 Mike]

Your cam is not a "idle friendly" grind but, I think you should look at the carb jet sizes and check the advance curve. 90 is not enough speed for your combination either.
Mike

 

[Curiousyellow71]

I don't know what you have for pistons for compression but it sounds like your rich. 850 is pretty big for a 400. Checking with a Afr gauge would be a good idea.

 

[PolaraFury]

I am going to assume it has stock bore and pistons.

I don’t mind the right idle but I won’t go out of my way to get a cam just because it sounds cool. Performance is where it’s at

It never occurred to me about the jetting or the carb being too much because (other than the carbon out the tailpipe) it runs great.

 

[PolaraFury]

Your cam is not a "idle friendly" grind but, I think you should look at the carb jet sizes and check the advance curve. 90 is not enough speed for your combination either.
Mike

I’m a little over 6k at 90 mph and it quits pulling. Do you believe a jet adjustment will fix that?

 

[Don Frelier]

There is no way a 3.90 gear gives you 6,000 rpm at 90.
Either the tach is wrong or the speedometer.

 

[440Coronet500]

I agree with the previous post regarding the carb jetting. It does sound like you're running rich. How do your plugs look? 440'

 

[PolaraFury]

I agree with the previous post regarding the carb jetting. It does sound like you're running rich. How do your plugs look? 440'

The plugs are fine and I haven’t had any fouling issues. I don’t baby it when I’m on the road.

 

[PolaraFury]

There is no way a 3.90 gear gives you 6,000 rpm at 90.
Either the tach is wrong or the speedometer.

I will look into both and verify.

I ran it along side my buddy on the highway right after I got it and I had 55 mph when he did. He was in a car with an honest speedo.

I have never ran a gear that high so I am not familiar with what speed/RPM I should be cranking

 

[Photon440]

If you have black exhaust, you have too much fuel. Jet it down, you might get even more power. I had 4.56 gears in a car, it showed 5200 rpm at 90 mph.

 

[PolaraFury]

If you have black exhaust, you have too much fuel. Jet it down, you might get even more power. I had 4.56 gears in a car, it showed 5200 rpm at 90 mph.

Will do. Thanks

 

[PolaraFury]

Than

Your cam is not a "idle friendly" grind but, I think you should look at the carb jet sizes and check the advance curve. 90 is not enough speed for your combination either.
Mike

Thank you. I’ll look at jetting it down

 

[Don Frelier]

I will look into both and verify.

I ran it along side my buddy on the highway right after I got it and I had 55 mph when he did. He was in a car with an honest speedo.

I have never ran a gear that high so I am not familiar with what speed/RPM I should be cranking

See if the tachometer is set for 6 cylinders. You would need a 20" tall tire to break 6,000 at 90mph.

 

[Cranky]

There are calculators on the net that will give you a close speed range vs rpm for your gear ration and tire size. Got to take into account your slippage of your torque converter too....and your speed doesn't sound anywhere close to what it should be for 3.90 gears at 6k. Heck, ran a 72 Demon with 4.88's, 29 inch tall tire, stock converter and it was doing 102 @ 6200 according to the drag strip.

 

[PolaraFury]

See if the tachometer is set for 6 cylinders. You would need a 20" tall tire to break 6,000 at 90mph.

The tires on the rear are 22” or 24” tall. I don’t recall off the top of my head

Now we are getting into math

 

[beanhead]

Is the "lot of carbon" something that's been witnessed as blowing out of the exhaust, or are the insides of the tips just black? Black inside is gonna happen on a performance engine but it should never be blowing soot.
BUT! I would not just go changing jets if you don't know where/which carb circuit is too rich. How do you know the transition or idle isn't the rich issue, and jets are okay? I know you said 'plugs are fine' but pull a couple and post up a picture, with and without the threaded portion.

In other words if your jetting is not the problem and you go dropping jets sizes and then hammering on it you can do some damage at high RPM...which goes back to my first question. If someone's reporting, or you can see it in the rear-view, blowing smoke at WOT high RPM then okay yes it's probably jets. You didn't give that information though...

As far as everyone questioning the gears and RPM.....I don't think he said it was in 3rd gear? He sure as sheeat could do 90 at 6K in second...just sayin...my car w/3.73s hits 90 in 2nd at about 5800...

 

[1 Wild R/T]

There is no way a 3.90 gear gives you 6,000 rpm at 90.
Either the tach is wrong or the speedometer.

Well, that's no exactly true... A 19.5" tall tire would do it...

But a 26.5" tall tire will hit 90 mph at about 4500 rpm...

Black smoke = to much fuel...

 

[PolaraFury]

Is the "lot of carbon" something that's been witnessed as blowing out of the exhaust, or are the insides of the tips just black? Black inside is gonna happen on a performance engine but it should never be blowing soot.
BUT! I would not just go changing jets if you don't know where/which carb circuit is too rich. How do you know the transition or idle isn't the rich issue, and jets are okay? I know you said 'plugs are fine' but pull a couple and post up a picture, with and without the threaded portion.

In other words if your jetting is not the problem and you go dropping jets sizes and then hammering on it you can do some damage at high RPM...which goes back to my first question. If someone's reporting, or you can see it in the rear-view, blowing smoke at WOT high RPM then okay yes it's probably jets. You didn't give that information though...

As far as everyone questioning the gears and RPM.....I don't think he said it was in 3rd gear? He sure as sheeat could do 90 at 6K in second...just sayin...my car w/3.73s hits 90 in 2nd at about 5800...

It leaves carbon on the garage floor when I fire it up and it leaves carbon on the garage floor when I bring it home. I have a 3/4 mile trip through the subdivision before I get home.

I have never had anyone follow along to see if it’s all the time but I do get a light residue on the back of the car.

I am definitely in third gear at top end

 

[PolaraFury]

I’m beginning to think the gearing is not what I was told.

I have a lot of homework to do when I get home from work in a few weeks.

Thanks for the input

I will keep you posted and I am certain I will have more questions

 

[beanhead]

It leaves carbon on the garage floor when I fire it up and it leaves carbon on the garage floor when I bring it home. I have a 3/4 mile trip through the subdivision before I get home.

I have never had anyone follow along to see if it’s all the time but I do get a light residue on the back of the car.

I am definitely in third gear at top end

Ok now we're getting somewhere.

So you are in 3rd when looking at the tach that answered my devil's advocate 'what if' on the RPM/speed stuff but forget that for now. One thing at a time....

Now unless you're on the mains pulling in and out of the garage (you're not) it's not a jetting issue...not that they aren't overly rich too, but it sounds like the carb needs to be tuned. Start with the idle circuit first.
Realize too---a little soot at start-up can be normal. But, if you're getting it after a drive then it needs tuning.