I modeled two opposite runners with two balance holes located approximately like the CFI runners.

The runners are a little larger Fel-Pro 1205 size to give some extra elbow room.

Have two equal Shop-Vac's pulling on each runner, so I can't easily control all the smoke and had to move everything out to the garage.

Made it very hard and frustrating to get decent videos, but here are some

First I made some GIF's to help you see better what is going on.

The first part of the video is just one Shop-Vac pulling vacuum from the left side.

You can see the two paths the smoke takes, down the runner and through the first balance hole.

Not much seams to come through the second hole?

A substantial amount is flowing through the first one!




At the very end of the video I turn both Shop-Vac's on and you can see how the second balance hole starts drawing air and cuts off the normal flow through the left runner.




If you visualize each runner flowing 25 times a second out of sequence with the other, than they never should be cutting each other off.

But if you visualize the two runners flow over lapping at some point, than they would choke each other off and most of the flow would be going through the balance holes and not the runners?



I wondered why the flow was necking down at the runner entrance and thought it might be because of the turn into the runner.

I removed the wall so that the flow could go straight into the runner, but it still necks down in the entrance.

This is caused by the square blunt end of the runner wall at the entrance and probably why a nice generous radius helps the flow so much.



I will dig through and process some of the other videos

 

great videos.
makes me wonder if the square edge of the hole is lowering the flow. taped up holes flows the best. wonder if a radius hole would help flow more

 

I don't even care about "flow", in this case. I mean, who cares if the holes help or hurt flow? It's terrible either way, and the holes kill runner tuning benefits.

To elaborate, what I like about the CFI intake, (besides that it's different/cool/underdog) is that it has a nice, medium length runner that should hit a resonant frequency at about 5000 RPM (including the head port, portion of the runner system). It is MY opinion that this is responsible for the '84 L83 CFI engine having a higher peak HP RPM rating than the '85 TPI b/c they're otherwise about identical (short block, heads, cam, compression, exhaust,) other than intake. Also, hot rodding techniques seem to work better on CFI engines -especially at higher RPM- than on TPI engines. In MY mind, if you can get the CFI runner to flow, then you got a pretty OK intake that doesn't limit RPM like TPI intake does, b/c of runner length/tuning.

Now....you chop a couple holes, in some of the runners and what does that do to runner tuning? Well it depends on the size of the holes, but with those sized holes, I have to think it eliminates it or it makes the runner behave like one with a length = to where the first hole is. That would be close to the runner length of an LT1 intake which is basically un tuned in any reasonable street engine RPM range. And that's O.K.; it works in the LT1, but here is the thing: IF the holes eliminate tuned frequency (w/in the normal operating range), then why even have the rest of the runner?? At that point, it's just a poorly cast, restrictive tube that's longer and harder to port than necessary.

If what you're really after is FLOW, and you've (GM) sacrificed tuning with the holes already, then chop the whole runner(s) back to put the mouths at the length where the first hole would be, then port the bejeezus out of what's left (an easy task, at that point), and you'll end up with a runner that'll annihilate the flow of the ported/hole'd runner..... about a LT1 performing, CFI looking intake.


That is an experiment that I would enjoy playing with.

 

I can't imagine that any engineer started off with a runner design that flowed half it's air through a rough cast hole.

This stinks of an "oh crap" quick fix either for emissions, Egr distribution, or low rpm mixture quality.

I would imagine the "Turbulator" is in the same boat.

Maybe the ram and resonance tuning waves travel too fast to be bothered by the side holes?

But all these "tricks" make things way more complicated than they need to be ... I agree

Just wish there was an easy way to cap those holes

 

Those holes, and the swirl plates.

Cap'em with PC7 Mouldable epoxy.

 

I'm going to cap the hole on my intake manifold this week. I'll take pictures and post them. going to drill from top. create a slot for a piece of aluminum and weld the top. done deal.

 

Thats how I intended to do it originally.

 

have you guys tested the diy ported CF intake that had the welded "fat lips" on the mouths?

AWESOME THREAD.

I have two questions for the air/fuel flow guys on here: If the PLENUM space was all dimpled top bottom and sides (like a golfball) would that add any benefit? For a golf ball analogy i think you would have to dimple the runners but tough to do.

and another question, i've seen one thread where the poster was supercharging a CF. He cut is runners back to 2.5". But I see that there are some runners that exit the plenum on the ends. Those would have to remain long. Or maybe he did it another way. I will post a picture. What do you think of this?

I have an extremely cheap 4+3 early 84 with the cool door handles available local to me and im barely able to resist buying it. Love the thread and sweeeet numbers so far. I dont' think i have seen the DIY ported CF intake tested on the dyno yet....any chance it will happen over the winter?




i cannot recall where i even found this image.

 

That image is on third Gen I believe.

I do plan to dyno my intake at some point. I would like to get it reflowed first then go from there but weather and road salt permitted I will get it on the dyno by spring.

And I love the T pull handles on my 84.

The third gen link

 

easier to port short runners

 

im taking it that we have not seen anyone do this with a NA crossfire though.

 

I mean... I could butcher one of my 5 intakes in the name of science.

The only issue i see is that 1 and 8 are full length but I suppose you could wall them out... the runner still ends up being shrouded by the plenum but maybe it'd work... I think they'd go very lean.

 

i was thinking the same thing, just cut the inside walls out. you can make them allthe same length. above and on the outside walls of the 1&8 ports you would want to remove as much material as possible to push the shrouding back.

so if these cylinders go lean would there be a tendency to pop a headgasket there even if studs were used? they could be flowed to find out first though right?

 

Not sure it would pop a head gasket so much as detonate the crap out of the piston/rod... Being I have a very thin head gasket in place to begin with that I am afraid of leaking... I might lean towards it being a possibility but I'd more just not want to hurt the short block...

 

I plugged 2 of the holes and did a quick test on one of the runners. It flows more than when holes are taped. made pattern with a piece of cardboard. cut pattern out of aluminum. welded top, didn't worry about completely sealing it. still could, but I don't think there would be much to gain

 

that's how I'll do it then.

 

I keep looking at at the intake sitting on the bar downstairs and I can't help thinking about the LQ4 intake... it is very similar just curved up to have better packing on an LS... observations is all.

 

Now that has an interesting observation.

 

new to CFI and sorry to have missed the Renegade. did you ever consider using the bottom of the manifold with a revised top to accommodate a 2 x 4 X-Ram setup like the Edelbrock STR-10, the Z-28 clone? don'tf know if the flow characteristics would have matched at all, but it might have been a good seller for anyone who wanted a good looking setup for their sbc

 

Been done with the Offy, SY-1 and likely some others.

There is ONE FOR SALE on your local SLC classifieds that keeps taunting me...