Don Terrill’s Speed-Talk

I have a 400 SBC with AFR 235 heads. About 13.2 to 1 compression. 4150 4bbl 950 CFM I'm told. The engine has a season of racing on it and it is in my shop to find out why it's not fast.

One thing I found is there is piston to head contact. This seemed to have shined up the bottom of the piston skirts. They measure correctly at the gauge point but Diamond could not tell me what the size should be at the very bottom.

Based on the pictures I'm thinking I don't like the intake roof swirl lump. It seems to be directing the fuel to one side of the head.

Thoughts?

How about some piston pix, tops and skirts?

Pig fat and fuel wash. How do you start to determine there is something wrong with the heads or pistons until that is fixed. I have no doubt its a slug.

Seems way too rich.

Check the compression ring land, probably the piston to head contact distorted it and the ring is stuck ,leaking cylinder pressure to the crank case.

The clean area of the chamber is the absence of fuel.

lorax wrote:Pig fat and fuel wash. How do you start to determine there is something wrong with the heads or pistons until that is fixed. I have no doubt its a slug.

X2 Fix the carb. Blown power vlv., leak, too big jetting.

I bet he was READING his plugs


JOE SHERMAN RACING

Fuel wash not a very good burn pattern, I would say that the engine is over fueled.

bigjoe1 wrote:I bet he was READING his plugs


JOE SHERMAN RACING

If he was, he did it in the dark with his eyes closed. I can read the one plug in the head on an I phone and know its stupid fat.
What was he reading? The name & numbers on the plug?

lorax wrote:

bigjoe1 wrote:I bet he was READING his plugs


JOE SHERMAN RACING

If he was, he did it in the dark with his eyes closed. I can read the one plug in the head on an I phone and know its stupid fat.
What was he reading? The name & numbers on the plug?

The spark plug in the picture is not from the head. That is my flowbench spark plug. I didn't take any piston pictures but they look a lot like the head. Wet carbon on the dome and clean around the edges. Too cold to get pictures tonight but I will add some after work when I have to be there.

No matter how fat the engine is/was, your still going to get that goofy burn pattern look.

However the intake port is nice and clean.

Is that all fuel or is there oil contamination as well?

BrazilianZ28Camaro wrote:
The clean area of the chamber is the absence of fuel.

have to be careful with that statement... fuel does wash carbon away

dieselgeek wrote:Is that all fuel or is there oil contamination as well?

There may be some oil mixed in. Several pistons hit the head good enough to shine the top and leave dark carbon edges where the chamber pad ends. My thoughts are the piston was knocked out of square at TDC and probably the ring seal was compromised. The quench of the head didn't show contact but the small pad under the spark plug left marks on the piston crowns. The head has dark carbon but the piston was clean AL in the same spot under the plugs.

Could also be a weak ignition/electrical system. How was the motor running overall. Missing? Popping? Surging?

JoePorting wrote:Could also be a weak ignition/electrical system. How was the motor running overall. Missing? Popping? Surging?

I was thinking the same thing. Very weak ignition, or very late timing, possibly due to wrong timing tab.
Or all of the above.