Black residue in intake ports

[Guest]

In taking a motor apart today I found a good number of the intake ports to be very black with combustion residue. Some are worse than others, with the blackness extending up into the manifold runners. The motor didn't seem to have a problem with oil control on any cylinders as the plugs were all dry and it leaked down normal. The leakdown test tells me the intake valves are all sealing well, so I'm guessing this is due to reversion? Do you all think this is normal for a motor with a big drag race cam?

[maxracesoftware]

Black residue is from reversion caused by combinations of not enough Exhaust Flow or high enough Exh/Int Flow Ratio, and/or not enough Exhaust Lobe duration, and/or the wrong Collector Length or wrong total length of Exhaust System, or restricted Muffler.

the Intake bowl area, and all the way up the Intake Port, Manifold Runners, and Plenum Area, should look like the day the Head was ported
There should be a Day and Night difference in the Color between the Exhaust and Intake Bowl areas...if your Intake Bowls/Valves look like Exhausts, you're loosing HP and TQ from reversion.


i've seen Heads even though they had high E/I Ratio, have reversion in the Bowl and up the Int port , from having the wrong Collector length for the operating RPM range.

also if the Car is Street driven with Mufflers mostly below the Tuned Exhaust System Length RPM range

[Guest]

The cam has a lot of exhaust duration (292 @.050), so I'm guessing that's not the problem, but you really have me thinking about the collectors. The guy runs a merge collector that necks down to 2.75" and then back out to 3.50" at the exit. He bought these collectors after consulting with one of the merge collector fabricators, but he never tested them against a regular 4 into 1. The rest of the header is 1-7/8" to 2" with 27" primaries. This is a 825 horsepower comp eliminator motor. Do you think the 2-3/4" merge may be causing the reversion?

[maxracesoftware]

One method to checkout is when you're doing Dyno testing...
use the Air Turbine on a few of the Dyno tests to see effects of
wrong Collector Lengths .

When things are wrong there will be a large rate loss in Ve % and SFCM shown by the Air Turbine as the Exhaust Wave disrupts or changes Flow amount going thru the Engine..also at those same RPM points you will be loosing TQ/HP

you can't really Test this with a completely sealed Dyno exhaust system attached to your Collectors..it has to be tested like the Headers are run
in the RaceCar, and that's with nothing attached to them.

my Shop is out in the country and i Dyno test with the Customer's Headers
without any Dyno exhaust hookups
i have a Blow-Thru System 48" inch 3-phase 3 HP 22,000 CFM fan above the Engine

the pressure in the Dyno Room is 0.1" tenth inch of water above atmospheric pressure when the fan is turned on..it delivers a great volume but with little room pressure .

[Guest]

Interesting. Do you seal off the carburetors or do you feed them air from within the same room? Do you just rely on open windows or doors for exiting exhaust gas?

[Darin Morgan]

Black residue is from reversion caused by combinations of not enough Exhaust Flow or high enough Exh/Int Flow Ratio, and/or not enough Exhaust Lobe duration, and/or the wrong Collector Length or wrong total length of Exhaust System, or restricted Muffler.

the Intake bowl area, and all the way up the Intake Port, Manifold Runners, and Plenum Area, should look like the day the Head was ported
There should be a Day and Night difference in the Color between the Exhaust and Intake Bowl areas...if your Intake Bowls/Valves look like Exhausts, you're loosing HP and TQ from reversion.


i've seen Heads even though they had high E/I Ratio, have reversion in the Bowl and up the Int port , from having the wrong Collector length for the operating RPM range.

also if the Car is Street driven with Mufflers mostly below the Tuned Exhaust System Length RPM range

As usual, maxracesoftware is correct. I have seen the reversion residue in bracket cars that idle or putt around the pits a lot as well. If you make a lot of rounds and putt around at part throttle a lot you can get that tell tale black sooty crap all over the intake tract. It take a LOT of putting around to do it though. A lot of our Super Series engines that have over 400 runs on them come in looking like that. If you make clean runs and it is black after only 20 or 30 runs, you have problems for sure.

[Guest]

low spring pressures will also allow this

[SuprStk400]

Quite common in super stock engines with Q-Jet carb, occurs from driving around pits. Q-jet (toilet equivelent) is very rich at low rpm and can make a mess out of an engine. It is best to drive to lanes and back at end of run with an extremely lean hanger on and put proper hanger on only for the run. This helps to minimize the soot in the low rpm blowback in the port. Is the car driven to the lanes? Probably not if it is comp.

[maxracesoftware]

Interesting. Do you seal off the carburetors or do you feed them air from within the same room? Do you just rely on open windows or doors for exiting exhaust gas?

there are [2] 3 Ft x 7 Ft steel doors= 6 ft x 7 ft in the rear for Exhaust to exit out.... the Blow Thru Sytem seems to work very well as i can even successfully Dyno Test an engine like a A/ND SBC with zoomie type headers like in this Pic Link

http://www.maxracesoftware.com/AND_Dyno4.jpg

and a few more Pics here
http://www.maxracesoftware.com/bbc.jpg

http://www.maxracesoftware.com/Del_Camcorder.jpg

i played around with using various additional Fans in different locations in the Dyno Room and watching the Flow pattern, but the 1 large single fan above seems to be good enough . also hard to see in Pic is that the Carb centerline is centered on the center of the Fan blades , not in the center of the box.