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open air cleaner TBI mods

brans87

brans87

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From Harris Performance http://tbichips.com/?page_id=737. The air cleaner. I recommend a little easier route than I used to. open element filters are fine but you can just put http://www.summitracing.com/parts/knn-ce-1503 and cures nearly all the air flow issues with the air intake. if you have the dual stud lid those studs easily come out of those bolts and you can use http://www.summitracing.com/parts/spe-4215/overview/ as your throttle body has the provision for it.

This true verses the stock with the snorkel going to the front of the radiator support?
 
brans87 said:
From Harris Performance http://tbichips.com/?page_id=737. The air cleaner. I recommend a little easier route than I used to. open element filters are fine but you can just put http://www.summitracing.com/parts/knn-ce-1503 and cures nearly all the air flow issues with the air intake. if you have the dual stud lid those studs easily come out of those bolts and you can use http://www.summitracing.com/parts/spe-4215/overview/ as your throttle body has the provision for it.

This true verses the stock with the snorkel going to the front of the radiator support?
Click to expand...


Are you asking about the effectiveness of changing the air cleaner?

To my knowledge no one has flow tested the stock intake tract, but my educated guess is that due to the cam and max CFM of the TBI unit, there IS no flow restriction.

Even if there was, the results would be minuscule, and IMO not worth the expense. If you really want a bunch of noise that makes it sound like you are making some power, flip the air cleaner lid over, assuming you can still do that with the TBI air cleaner like you could the carbed ones.
 
Ah, that makes more sense, thank you Dorian.

To that point, then, I found that running the motor with hot air under the hood made it idle like crap and diesel when I turned it off. Admittedly this was on carb, not TBI.

I ended up installing a cold air duct to feed the air cleaner from the core support. MUCH better idle, no dieseling, and certainly no loss in performance.

IME, keeping the ducting you have to feed in cold air would be best. (Isn't that K&N's big deal, anyway, "cold air intakes"? Seems odd that they sell that pancake filter thing.)

-- A
 
You can bet that GM didn't start using cold air ducting (or even return fuel lines) for their health. :)

My suspicion is that under many circumstances, the cold vs. hot air is not likely to make much difference. The temp probably became more of an issue under specific climatic conditions, and as trucks were increasingly more used like cars, but also subjected to more load like towing, AC, etc. than they were in the past.

Did many/any of the "open" early air cleaners use THERMAC? Going the other way, in cold climates, the open air cleaner on the early trucks probably worked better than a closed one would have, without the complexity/cost of THERMAC.

I had to check, sure enough, back in the day I did take inlet air temp measurements with "cold air induction" (about 115*) but I never got around to testing with the intake open to the engine bay. I may have to revisit that. It's not easy with my setup to get the air intake as close to the engine as it would be sitting on top of the throttle body.
 
I was thinking about intake air flow for the 454 swap I'm doing running TBI. Admittedly it was due to reading the Harris Perf site recommendations that many seem to find dubious these days. But I was thinking about the size of the snorkel opening where it attaches to the core support versus the size of the thottle body. It does seem like you'd want both openings nearly the same size but the snorkel is a good deal smaller.

My thought was to keep the snorkel but use the taller filter in the standard housing so there would be about a 2" gap between the lid and base all the way around. This way when running down the highway you're still getting fresh outside air pushed into the filter housing but there is also provision to allow more air flow. I hadn't thought about the effect it would have on noise level until Dorian's post above, so I am rethinking this idea little now tho.

I'd like to add a second snorkel but I'm not sure I'll have room. It seems like I remember one of my trucks even have the provision to hook up a second snorkel on the driver side of the radiator, you just have to punch out a little block off plate.
 
I don't think any of the intake ducting GM used was consistent enough to get a very good estimate of CFM capability. The carbed convoluted tubing is going to disrupt airflow, and the TBI setups had a few different setups that would affect flow (silencer, and the weird intake thing at the core support), so at best we can probably guess, unless someone flow tests them. The best we can probably do is take the areas with the most restriction, and figure what that will support.

The CFM of the throttle bodies is a known value...535 vs 670. If the rest of the restrictions allow more flow than that, no gain changing anything.

I found this, which will may help calculate the opening in the air cleaner: http://www.engineeringtoolbox.com/equivalent-diameter-d_443.html Still a lot of variables outside of that one measurement though.

I'd be surprised if GM left much power on the table with the air intake tract. There was certainly some traded to reduce noise, but if there was a massive amount, they would have made changes to address it.

I don't know enough about the SBC and BBC TBI setups to know if the intake tract was different, to indicate a different CFM. If they used the same intake ducting for the 350 and 454, you can get the 350 is getting plenty of air.

All the '81-86 core supports I've seen are setup for air intake on either side, one was for the Inline 6 IIRC. I swapped mine around when I went TPI.
 
I have an 89 GMC 4x4. It has TBI. I flipped the lid and drove it for a year like that. It works fine.

Why did I flip the lid? It is what you do on '70s Q-Jets and I did not give it much thought. It was twelve years ago. I'd keep the cold air intake now. I don't know if it did anything. When I got the truck the valves and a few pistons had holes in them. I put on some pick-um higher compression camaro heads and rebuilt the motor adding an advanced timing chain sprocket ($500 rebuild). It drove good enough to haul everything up the hill to build my house.
 
First time I flipped the air cleaner lid over on a car,was on my dad's '68 Chevelle wagon...even the dinky Rochester 2 bbl carb sounded mean that way!..(and if dad ever caught me doing that,and racing friends in it on a 1/4 mile stretch of a dead end industrial park road,I probably wouldn't be here today ! :eek)..
The car sounded so cool when it wound up to 60+ mph in low--the Powerglide lost every race once it upshifted into drive though...
"waaaaaaaaaaaa-------:D..doooooogggg"..:(
 
Now they have a 1/4 mile app that times you. I haven't tried it yet, but assure you if they had that app (any app) when I was in high school, I would have spent every afternoon doing 1/4 mile passes and tuning. Instead I had to do seat of the pants tuning.
 
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