I have been having issues with idle air distribution with my HSR. At least that is what I think is causing the front 4 plugs to read normal while the rear 4 show rich

After consideration and input from members here I have tried a new scheme with my HSR idle air. I first changed PCV valves to one which has greater air flow. It is attached to the rear of the plenum so it should make more air available at idle. Next, I added a air bleed valve tee'd into the vacuum line, also at the rear of the plenum. After these changes I was able to close my TB base setting a lot, maybe 4 turns of the screw. Now the TB blades are almost shut. The IAC position at idle went up from ~5 to around 40. This should be allowing much more air to enter from the rear of the intake at idle and low load cruise which in turn will hopefully balance the air flow better.

What I immediately noticed is the idle is smoother and I was able to lower it ~50 rpm to 825.

My question is does anyone know of a reason why this is a bad idea? It seems to me that it wouldn't really matter to the engine where the air is coming in as long as it is sufficient. My engine runs on speed density so the air "bypassing" the TB shouldn't be an issue. Right now it is a temporary setup so it is drawing unfiltered air but if I keep it this way I will plumb the rear idle air to have filtered air.

 

I understand your frustration with the plug issue and the HSR.

I installed a AS&M mono blade TB and ported the plenum to match the opening. It completely fixed my fuel distribution issue. My plugs now all read identical. I believe the larger openings to the TB slow the air down allowing to feed all cylinders properly.

Just wanted to post my satisfying results.

 

There is a thread about split BLMs at idle on an LT5 motor by member DominicSorresso. It makes for very good reading, but IIR, he designed an external IAC that fed both the front and rear (or maybe left and right in his case). He was able to get his BLMs very close at idle and never seemed to have any repercussions. Search "split BLMs" to see if you can find that thread. You may want to PM him but I haven't seen him around in a while. Anyway, I think you may be on to something. GL and HTH!

 

Old thread, but what was the conclusion to this?

 

https://www.thirdgen.org/forums/diy-...plit+blm+beast

This is what I did on my Miniram...

 

The plug issue is somewhat better. Still running a tad rich in the rears but fouling has been greatly reduced. Running a hotter plug for daily driving also. The main benefit is a much better idle and smooth running. Note; the "filter" on the air bleed has to be cleaned regularly or the benefit is reduced. Probably blow it out every 6 months or ~7000 miles.