The_Punisher454

I am about to install an HSR on a 350 in a few weeks and was thinking about trying an experiment with porting the idle air directly into the ports with small tubes drilled into the bottom sides of the ports right close to the heads. having the air stream aimed right into the port, and blowing across the injectors spray pattern towards the valve.

I've read someplace before that this technique helps with the idle quality on LT-1's and it makes sense to me. So I am thinking about trying it. Cant hurt, and worst case scenario is that I disconnect this system and go back to the typical way back at the throttlebody.

My question is:
What is the diameter of the holes in the LT-1 ports?

I figure that will be a good starting place, but I dont have an LT-1 intake here to measure. and I cant find any good pics either.
I guessing that something between 1/8 and 3/16 inch would be good.

This more of an science experiment than anything else, I intend to test this with the idle air done both ways in back to back comparisons. If it proves to be a positive thing I have another bigger and more importnat project later that may benefit from this technique if it makes any positive difference.

Anyhow, if you know the hole diameter or have some good pics let me know please.

Marvin

RBob

iTrader: (1)

There is something to the LT1 IAC passages. It has been quite a while since I handled and looked at one. IIRC, the holes at the ports where more like an orifice.

That is everything leading up to them was a larger diameter. Then a small diameter (maybe 3/32"??). Of the one LT1 manifold (limited observation), one of the front holes was smaller then the others. Can't recall if it was #1 or #2, and have no idea why it was.

RBob.

Thirdgen89GTA

iTrader: (5)

I don't have a LT1 manifold to check, but I do have one at my Dads house in storage. The next time I'm up there I'll have to pull the intake off the shelf and measure them.

I do know that one of the big cam tricks on LT1s is to use a step drill on the IAC valve intake at the Throttle Body to solve split BLM issues. I think I remember someone asking about increasing the diameter of the individual intake runner holes as well.

The_Punisher454

OK thanks.
My thought is that at idle the manifold is at very low pressure throughout and the velocity is very low. The air in the orifices at the ports will be much higher reletive pressure. The nozzles will be blowing across the injector spray stream towards the valves, and thats the air the engine will be breathing at idle.
I intend to keep the throttle blades closed and any extra air needed thats normaly provided by drilling holes in the butterflies and cracking the blades slightly open with the idle screw, will be regulated by a small needle valve and ran through the idle air passages only, not just dumped into the plenum.
Its just something I've always wanted to try, and I just picked up another project car (C4 Vette) and I plan to make it a test bed for a whole bunch of ideas I've been having for a while.

Six_Shooter

iTrader: (2)

Interesting idea using this on a single TB intake. This same idea has been used on ITB intakes, though just because it's a necessity to do it that way when using an idle air valve.

ULTM8Z

lol... I did exactly what you're describing to my Miniram a few years ago.

https://www.thirdgen.org/forums/diy-...ram-split.html

Since the time I did this, I've changed the intake air tube. Rather than the muffler contraption you see behind the A/C delete pulley, I ran a really 3/8 hose to a small air filter located under where the battery sits. The long tube quiets down the air intake hissing quite a bit (which is what the earlier muffler contraption was meant to do).

Any rate, the idle smoothed out quite a bit and the BLM's became consistent from side to side at idle speeds.

The_Punisher454

so a couple of questions.

1. what size tubes are you using to feed the ports.
2. cant see anywhere in the pictures, but do you have any sort of angled nozzles in the ports, or just a hole?

Your setup is very similar to what I have in mind, and it sounds like it confirms my idea that this may be helpful on some engine.

I plan to remote mount the IAC, but feed it through the IAC feed hole in the throttlebody and just put a pipe nipple where the IAC used to mount.

I have access to plenty of small precision flow control valves, but I was starting to think that screw-in Holley carb jets might work fine for the fixed minimum idle air metering. And I think I'll run the PCV into the idle air manifold as well, but I'm going to run the PCV hose through an air compressor style oil separator first.

Thanks for the link to the old thread, this is a big help.

ULTM8Z

I believe it was simply 1/8 tubing. And yes, just a small hole in the bottom of the intake rubber.