AHH I remembered my password to my old username!!
Z28Man = Z28dan

Anyway..After reading Bruce's spark plug reading article, which cylinders tend to run more lean the the others? Or is it different or every motor? I was wondering if the TPI (fuel delivery) would cause the same cylinders on every motor to run lean.

Sorry if this is not a PROM related question.

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1988 L98
Vette Heads/no EGR
SLP Headers/Y-Pipe
ARAP bin

 

From my last plug readings, I found #1, 2, 7 and 8 ran a tad leaner than the inner cylinders # 3, 4, 5, and 6.

You also have to consider other factors such as the condition of your heads, valves, wires and fuel injectors. But over the years and the various plug readings I have done with each tune up, I have found my TPI to be basically "balanced" with no one cylinder overly richer/leaner than others.

 

Dang!!! That number 8 plug is a pain to get out

 

Understanding where your going, and where you have been calibration wise is what prom burning is all about, we need questions, and answers on issues like this, IMO.
We also need folks to use the search tools, and just read thru some of the old postings to stir their imaginations, about what is going on.

Now to answer your question, there are a number of variables.

Changes in Pre Trottle Body ducting can make for fueling differences, as well as operating temp, water pump flow, and even coolant type.
With higher operating temps., the combustion chambers have less variance in operating temp., when you run say a 140d Thermostat the rear cylinders will always look a touch leaner, add a maifold like the miniram, and the situation gets ugly fast.
If you were to look at the calibration for a 95 LT1 you can see the cylinder corrections for a stock manifold are very slight.
while folks harp about the runner lengths on the TPI for torque, I'm beginning to think they are for isolating each cylinder from each other to have each cylinder working in unison with the rest.
I also think the deal with roller cams is about how accurately cams can actually be ground repeatably. I know folks talk about accleration rates, less friction etc., but let the truth be know a 7/8 flat tappet can generate a faster valve accleration rate then any roller lifter that you could fit in the same room.

 

I may not know what I am saying..but to get a faster valve accelaration you need a steeper pitch cam lobe, right?? I always thought that due to the nature of the flat tappet you can't run the real steep lobe becuase of binding that occurs when the edge of the tappet digs into the lobe. Is the true?

 

It's easy to kick a valve open so fast that it won't follow the actual cam profile, and exceed the ground in lift spec of the cam..

Using larger OD lifters is "a good thing".
It hard to picture correctly, but a flat tappet cam is a very good design, the roller lifters also add a ton of weight to the valvetrain, and really increases the springs work load. At low rpm they can generate a slight HP gain, from reduced friction. Which is good for MPg, the CAFE numbers are
what forced their use.

 

I think that's what gives them the right to call it "Tuned Port"... Wasn't that the reasoning behind the setup?

 

There are numerous rumors to way they did what they did.
I've heard several, from rather good sources, that cosmetics was the tie breaker. Considering it was released in late 84 there was a high Wow factor at the time.

 

Have you ever run a set of "mushroom" lifters? I saw a set down @ Crower & thought they were the totaly trick setup, but it seems like they did not really get very far considering the mass exodus to Rollers.

BW