Intake "Popping" - Help!

quote:

Originally posted by Dr.Oldsmobile: It has a big cam

intake reversion, can you elaborate on the cam?

is this a fresh build / new start-up or has the combo been running for some time & this just started?

The engine was just rebuilt and the intake and fuel injection system is new.

Reversion is exactly what I thought it was too..... but is that possible with an 8 stack ITB setup. The intake runners don't connect to each other, so how can they steal air from each other?

I'm not home and I don't have the cam numbers fresh in my head. I think its around 242/248 and .604/.618

The intake runners don't connect to each other, so how can they steal air from each other?



The intake runners not being connected to each other may be exactly the problem.

Reversion at a certain speed with your cam may be inevitable.

In manifolds with a common plenum reversion from one cylinder is drawn in by another cylinder and so nothing is noticeable at the top of the carb or injection throttle blades.

Interesting... So you are saying that, in a way, I am looking at this backwards...
If revision is inveitible with this cam, then the solution would be to cover it up with a traditional manifold and allow it to steal air from another cylinder instead of from to top??

If that's the case, would it be best to:
1. Use a single plane manifold to encourage the scavenging.
2. Use a dual plane manifold?
3. Turn up the stereo and ignore it?

Thanks
G

My first Pantera had that kind of pop, more at decelration though, that was unburnt fuel exploding in the hot exhaust. Sometimes it's the simple things, law of parsimony: "Among competing hypotheses, the one with the fewest assumptions should be selected"

How do your plugs look? Excessively rich?

quote:

Originally posted by Dr.Oldsmobile:
Interesting... So you are saying that, in a way, I am looking at this backwards...
If revision is inveitible with this cam, then the solution would be to cover it up with a traditional manifold and allow it to steal air from another cylinder instead of from to top??

If that's the case, would it be best to:
1. Use a single plane manifold to encourage the scavenging.
2. Use a dual plane manifold?
3. Turn up the stereo and ignore it?

Thanks
G

Turning up the stereo might be the best remedy.

Seriously, you have to be sure the popping sound is being caused by reversion. You will have to study and observe the airflow into and above the throttle bodies to confirm it.

In a common plenum manifold one cylinder does not really steal another cylinder's air, the reversion in a runner is caused by the intake valve suddenly closing and the flowing air in that runner suddenly hitting and bouncing off the back of the intake valve. Like water hammer in your house when you suddenly turn off a faucet.

In individual runner intakes this rebound energy is wasted, but in common plenum manifolds that rebounding air flows across the plenum and into a cylinder with a open intake valve (supercharging it a little).

IR intakes do look really cool but probably work best at a specific tuned length for a specific rpm range.

A common plenum intake with multi point injection may be best for a wider rpm range and better driveability.

reversion is a product of valve overlap, when the exhaust valve is closing and the intake valve begins to open there is a pathway from the top of the air inlet to the tail pipe

with a common plenum there is likely another cylinder willing to swallow the reversion before it can get past the throttle blades. you have reversion x 8

check this out, beware the fuel vapor cloud http://www.hotrod.com/articles...anifold-tech-engine/

quote:

Originally posted by 4V & Proud:
reversion is a product of valve overlap, when the exhaust valve is closing and the intake valve begins to open there is a pathway from the top of the air inlet to the tail pipe

That only happens at idle on engines with lots of overlap. It is the cause of the rough idle in those engines.

At anything past idle precisely the opposite occurs. Low header pressure allows the cylinder to exhaust quickly, the momentum of the outflowing gas lowers cylinder pressure to below intake manifold pressure and the inflowing intake charge scavenges residual combustion gases out of the cylinder. Sometimes fresh intake charge can even go out into the header pipes.

Scavenging out residual combustion gases is exactly what overlap is for and is why it makes the engine more powerful.

What that article says on reversion is twaddle. The author doesn't know what he is talking about.

Lean?
Mayby one or cylinder is running lean and the popping sound is the result of that.
I would suggest you to synchronize the throttle bodies. Can you read the afr mixture?
/SF

Lean?
Maybe one cylinder is running lean and the popping sound is the result of that.
I would suggest you to synchronize the throttle bodies. Can you read the afr mixture?
/SF

I can read the AFR from the data screen (oxygen sensor). That doesn't really show my an AFR on an individual cylinder though.

There is absolutely no popping at idle or during acceleration. The popping occurs while driving at constant speeds, more notably from around 20 - 50 mph.

Does the popping occur if you hold the engine at cruising rpm in neutral ?

Or only while actually driving ?

Dr. Olds
That EFI/Ecu that you are running is it in cloosed loop funktion? And maybe set to reach/hold lambda 1 (14.7)?
/SF

I agree with SF. I have seen popping out of the trumpet many times on IR cars. When cruising the throttle plates are open so little and the engine rpms are great enough to accentuate any synchronization issues. Get yourself a synchronizer and double check that it is even or relatively close to on all clylinders. It typically wont show on a wideband because the wideband shows an average of several cylinders. Too little timing at cruise can also cause some popping.

Okay.... This is taking me into uncharted territory for me.

The Google tells me there are 3 or 4 different kinds of carb sync tools. Any reconditions?

This is an example of a tool to use:
http://www.ktm950.info/how/Ora...FI/sync/STE_tool.jpg

We used to have one like this. It worked great as well. http://www.piersideparts.net/BP7033.html

I still have my Uni-Sync like Blaine showed. Now 60 yrs old and still works just fine. It has the advantage of rotating the top section for side-draft carbs; I used it on many motorcycles.