Converting a small block 94/95 from MPFI to TBI - in case anyone else wants to go this route

[dsrtjeeper]

IAC should be sitting around 5% at a hot idle with no accessories running including fans.

 

[dsrtjeeper]

Also, butterflies should never be fully closed. This can often cause the butterflies to stick in the bore. If the car idles fine with the butterflies fully closed, there's either a vacuum leak or the IAC is opening to supply air. What is the IAC % at idle?

 

[shovel]

Since I drove a lot of older cars in the 1990s I've had my share of carbureted vehicles but I've never had a carbureted V8 - that's relevant because one of my observations has been a familiar chugging sound from the engine that I know I've heard a thousand times on other peoples' old cars, trucks and boats. After some digging around and reading it makes sense that the chugging sound is just normal expected dual plane intake noise which is great for an actual carburetor because it maximizes vacuum signal but it's not great for a TBI - all that's doing is increasing noise in the sensor signals and hindering flow because every cylinder only gets access to half of the throttle bodies.

I also gotta say as a subjective experience the chugging might sound nostalgic but it's also sort of like having drone again.

The obvious solution is to take the intake manifold back off and machine out the wall but that's not free.. I don't just mean the machining itself - it's a set of intake gaskets, RTV, oil change, coolant change. That's a job for the future.

For now I have a couple spare gaskets so I'm going to glue them together with gasket tack & get myself a roughly 3/16 to 1/4" gap on top of that wall. I'd buy a phenolic spacer if I had clearance between the air cleaner and the hood blanket for something like that but I do not. Since total air flow and manifold air density is low at idle and light throttle I hope the little gap is enough to at least reduce the velocity of air rushing back and forth in the tiny channels Holley uses for their sensors and vac ports & thus reduce the (data) noise, even if it's not enough to reduce the acoustic chugging noise I have to hear.

The relevant take-home here for anyone following along is it probably makes sense to cut down the wall before installing everything or get a single plane. Most single plane intakes are too tall under the stock hood. The Edelbrock Torker II appears to be within range so I'd probably look there first.

 

[dsrtjeeper]

What your experiencing is common. The Sniper 1 has issues when using a dual plane intake. I've read that the Sniper 2 does as well. You can Google it and see the accounts from Sniper users. It's also addressed on the Holley Sniper forum.

Here's one solution:

 

[dsrtjeeper]

I had a Vic Jr. Under the stock hood using a Spectre low profile carb hat. I connected the carb hat to my Anderson power pipe which ran into the passenger fender.

 

[shovel]

A bit more to report; I stacked 6 gaskets with a thin smear of RTV between them and weighted them down between a couple boards to cure so it became effectively a single solid spacer 3/8" thick. Installed that and was not at all happy with the sound. Still all the dual plane chugging but with the added sound of somebody chopping carrots on a butcher block. I guess that 3/8" gap at the top of the wall with sharp edges is enough to just create a lot of turbulence and not much else.. so, later on in the future maybe I'll take off the manifold and cut down the wall for now I'll just live with the chugging. I took the stack back off.

Some good news is I got a progressive linkage made for a carburetor and was able to bend it a little & work on the Sniper 2. It's a shame Holley doesn't just provide a correctly sized progressive link in the box to begin with, their throttle arms already accommodate it and the laptop software accommodates it. Couldn't be that difficult to also throw in a little piece of bent wire and enable the tick box + % input field on the phone app..