Hey Swartlkk,
I've read your explanation, make sense, so I'll leave it as it is!
Thanks again!!


Grz. Hank.

 

So I`m confused, isn't cleaner good? And since the motor sit forward not sideways, whats the front 3. So it still ran good right? and 20,000 is more than I would put on a set of plugs

 

Cleaner is good, but inconsistent plug color indicates an issue. In the case of the throttle body blade mod, the front 3 cylinders were getting more of the EGR gases, making the plugs dirtier than the rear 3. The front 3 cylinders were not burning properly due to the lack of combustion supporting fresh air. In my case, the #2 plug was by far the dirtiest, but with #1 & #3 close to the soot level of #2. #5 was the cleanest; all relative to the distance from the EGR outlet into the manifold. Given that the 96+ 4.3L engines have the throttle body placed at the front/top of the intake plenum, it can cause an inconsistent distribution of EGR gases without the deflector in place such that it can divert a significant portion of the incoming air towards the center of the plenum at throttle levels typically seen while cruising.

As far as the front 3 vs the rear 3, anyone who has had the upper plenum off should understand this reference. There are 3 intake runners towards the front of the lower intake manifold and 3 towards the rear. Specifically, the front three cylinders are cylinders 1,2,3 and the rear three are 4,5,6. The attached picture shows the orientation.

 

So with the deflector in place, effectively slowing down airflow is better I dont understand. You would think with a slower airflow the egr gasses would be apt to be sucked in the front three before making it to the back three. Which are partially blocked by the spider. Do you have pictures of your plugs? would also like to compare them with pictures of non mod plugs

 

Sorry, I do not have pictures of the plugs. It wasn't something I was thinking about back then and I pulled them one at a time just to take a look at their condition. The Bravada has not been in my driveway for a VERY long time.

There isn't much blocking of the back three cylinders by the spider as it is fairly open under and to either side of the main body.

What you think is slowing down air flow is actually completely opposite. The engine will move very roughly the same amount of air for a given RPM regardless of the restriction at the throttle body (within reason). By forcing that air over the top side of the throttle blade, the air flow is actually moving faster through that opening than it would if it could also move through under the throttle blade; again at a specific, fixed rpm. By having higher velocity air moving towards the center of the plenum, a region of higher vacuum is created directly under the throttle body pulling the EGR gases towards the air flow coming off the throttle blade.

I can go on if necessary. Fluid flow is pretty instrumental in my profession.

 

OK with all that aside, what damage could it incur other than premature plug wear . Although I change my plugs about every 10,000

 

The imbalance can eventually lead to burnt exhaust valves on those cylinders not getting the EGR gases. The EGR system serves to reduce exhaust temperatures, limiting the formation of NOx.

Besides that, with an over concentration of EGR gases in two cylinders on bank 1, cylinder 5 would have a tendency to run lean while the opposite would be true for cylinder 2 on bank 2.


All in all, the only positive thing that comes out of the throttle plate modification is a more sensitive throttle reaction. If that is your goal, have at it. The problems that can result from such a modification outweigh the benefits for such a marginal "gain" in my opinion.


If your goal is more performance and not just the butt-dyno or placebo effect type performance you will have to spend some money. As discussed, a tune is a VERY good place to start. I couldn't believe the change in my old Rainier with a tune from PCM4Less.


I will be getting my Denali tuned by Black Bear Performance probably in the spring. It is considerably more expensive with the AutoCal device than it was for my Rainier which was just a new PCM ($250 for the Rainier vs $599 for my Denali), but the benefits of having AutoCal far outweigh the cost. I am very tempted to get EFILive v2 Scan & Tune GM then sell my AutoEnginuity scanner to recoup some of the costs.

 

Run 3 colder plugs? or put in a 350?

 

Your comment about fuel economy at 1/3 throttle is making sense to me now. I recently did the throttle body plate mod and am pleased with the quicker throttle response, but have realized it came at a cost of about 1/2 MPG. I went from 18.6 to 18.1. So better performance, but less MPG. So I guess this would not be what your looking for...

 

how can I convert my 1996 chev blazer 4 wheel drive from the vacunm shift to a mechanical shift. thought I saw a cable conversion kit on line-can't find it again