All Four Corner Cylinders Rich on SBF

[BlackKnight]

I recently pulled the intake and heads off my engine and noticed that all of the corner cylinders were a lot richer than the four center cylinders. The center piston tops are grayish where the outer piston tops are blackish. The engine is a SBF with Yates C3 heads and a 2863 intake. The intake was ported to match the MCSA/CSA of the heads. However, something wasn't in harmony. Any idea what was going on there? I always thought SBFs had lean issues on the corners but, mine is the opposite.

[BlackKnight]

It's harder and harder to get any feedback on this forum. Thanks.

[Ron E]

Could you post a pic of the plenum?

[BlackKnight]

This is the best I have:

Could you post a pic of the plenum?

[Tuner]

Spivy

It isn’t necessary to use such a large tie-wrap as in these pictures. Those just happened to be what was available close at hand in that dyno session. The smallest tie wraps work good on 4150 carbs. The AFB booster is from a ’67 440 carb.

A spivy can move the EGT as much as 200°F, move a cold cylinder up 200° and at the same time move a hot cylinder down 200°. It diverts fuel from one place to another. Sort of a Robin Hood deal, take from the rich, give to the lean.

Point it toward where you want the fuel to go. If you have a rich cylinder, aim the spivy toward the runner entrance of the other (lean) cylinder fed by the same venturi. If is a lean cylinder, aim the spivy toward it and it will take fuel from the other (rich) cylinder on that venturi and put it in the lean one, so be prepared to jet up as required for the amount of fuel diverted if necessary.

The low pressure in the flow downstream of the spivy pulls the liquid fuel in that direction. It is a lot like putting your finger in the side of a stream from a garden hose, it pulls the liquid toward the direction of your finger.

http://racingfuelsystems.myfunforum.org ... ut230.html

[BlackKnight]

That's interesting. I believe the intake needs more work in the corners but, I won't be using it with the new heads. I'm going with the new CID Intake for the Yates D3 head. I have taken a few intakes and heads off my engines over the years but, that was the first time I had seen the corner pistons/chambers so rich/dark and the four in the center just right. Wasn't sure what was the cause but a little research elsewhere points to the intake needing more work in the corner runners.

Prior to taking the heads and intake off I did a leak down and all was well there. So, obviously porting intake manifolds is an improtant science.

Thanks,

[statsystems]

So, if you had the time and the choice, would you just use a spivey or would you correct the intake by using a dam in the rich runners?

[BlackKnight]

I would have the intake fixed. I talked to Jim Kuntz today and he said he could fix it without too much trouble but, the guy that I essentially gave it to will have it fixed. My mind is set on the CID piece that Kuntz will do for me.

So, if you had the time and the choice, would you just use a spivey or would you correct the intake by using a dam in the rich runners?