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Just wanted to bump this thread, and touch on something that was mentioned earlier. You guys told me that some of the factory Cross-Fire Injection manifolds came with "equalizer" holes cast in between the runners to help equalize flow... for the purpose of emissions I assume. You had said to look for manifolds to modify that doesn't have these as they negatively affect the air flow.
Just wanted to mention that the intake manifold I bought as a spare came from a 1982 Corvette, and it didn't have the holes. After removing the intake from my own 1984 Corvette, I noticed that it also did not have the holes. It may be an 81-only Corvette thing? Just a thought...
yes early model crossfire didn't have holes. I have no idea what the holes are for. Maybe someone knows.
yes early model crossfire didn't have holes. I have no idea what the holes are for. Maybe someone knows.
i found it online. AI, always incorrect. It says holes are for balancing air flow between tb's. I think that's what super l98 was saying. Over my head. Someone with better understanding could explain it. I know the runners with holes flow less.
another thing I noticed when testing mixing blades. blades will bias flow. add to some runners and take away from others.
I have no answer for why this happens.
Last edited by mike1111; Apr 29, 2026 at 12:02 AM.
1982 and 1984 were the only years with CrossFire on the Corvette. 1983 and 1984 Camaro Z28 and Pontiac Trans Am with the 305.
I think you mean 82-83 F-body. In 84, GM removed all fuel injection from the V8 and went back to a carburetor. Their high-performance motor was a 9.5:1 compression 305 V8 with a 4-barrel computer controlled carburetor with ESC. It also came with crazy-high gearing too... 3.73:1. In 1985, GM went with TPI in their V8 performance cars, including the Corvette and Camaro / Firebird. TPI/MPFI was basically introduced in essentially every single GM car model on that same year.
But yeah, for some reason I thought the 81 Corvette had Cross Fire Injection also.
Here's what I'm confused though. My 84 Corvette did not have the holes... and my intake from eBay said it came from an 81 (but I guess it was an 82). It also did not have the holes. I know it didn't come from an 84 because it had a bunch of things attached to it (minus air cleaner) and it was all C3 Corvette stuff. So I'm curious WHICH cars actually got the CFI intake with the holes?
I think you mean 82-83 F-body. In 84, GM removed all fuel injection from the V8 and went back to a carburetor. Their high-performance motor was a 9.5:1 compression 305 V8 with a 4-barrel computer controlled carburetor with ESC. It also came with crazy-high gearing too... 3.73:1. In 1985, GM went with TPI in their V8 performance cars, including the Corvette and Camaro / Firebird. TPI/MPFI was basically introduced in essentially every single GM car model on that same year.
But yeah, for some reason I thought the 81 Corvette had Cross Fire Injection also.
Here's what I'm confused though. My 84 Corvette did not have the holes... and my intake from eBay said it came from an 81 (but I guess it was an 82). It also did not have the holes. I know it didn't come from an 84 because it had a bunch of things attached to it (minus air cleaner) and it was all C3 Corvette stuff. So I'm curious WHICH cars actually got the CFI intake with the holes?
I really don't know. My 84 had holes. maybe not all 84's got holes.
Last edited by mike1111; Apr 29, 2026 at 12:55 PM.
My 84 Corvette's intake had no holes, and the engine was also painted blue.... which I absolutely know is not normal... but was a previous-year thing as you elude to. It was hard to tell because it was covered in oil, but when I degreased it... there were blue splotches everywhere. It has all the 84 Corvette equipment on it, and the VIN also matches too... so I know it came with it. But my 84's intake had no holes... no idea what this means... I just find it really weird.
My 84 Corvette's intake had no holes, and the engine was also painted blue.... which I absolutely know is not normal... but was a previous-year thing as you elude to. It was hard to tell because it was covered in oil, but when I degreased it... there were blue splotches everywhere. It has all the 84 Corvette equipment on it, and the VIN also matches too... so I know it came with it. But my 84's intake had no holes... no idea what this means... I just find it really weird.
when was it built. Mine was built in 83. Also a california car. California could of had different smog laws
My '84 (federal emissions) was built in March of '83 (first month of production)...Black engine....balance holes in the intake runners. There is no way that any '84 corvette left the factory with a blue engine....they even had Delco change the battery top colors to match the black and silver engine compartment color scheme. I'd double check that engine stamp....Also, I never seen or heard of an '84 without the balance holes in the intake runners...What's the casting # on that intake (not the eBay one)? If it's the old #, it wouldn't make any sense, because the parts manual that GM produced right away for the '84 does not list the '82 part # as an option! The scrutiny and pressure GM was under by early '83 to get the new vette produced, meant... by that time they were needing perfection...A Corporate Blue engine with an intake casted in 1981-'82 on the production line, would have given the Plant Manager a nervous breakdown or heart attack👍
Last edited by '78CorvetteS.A.; Apr 30, 2026 at 03:53 AM.
My '84 (federal emissions) was built in March of '83 (first month of production)...Black engine....balance holes in the intake runners. There is no way that any '84 corvette left the factory with a blue engine....they even had Delco change the battery top colors to match the black and silver engine compartment color scheme. I'd double check that engine stamp....Also, I never seen or heard of an '84 without the balance holes in the intake runners...What's the casting # on that intake (not the eBay one)? If it's the old #, it wouldn't make any sense, because the parts manual that GM produced right away for the '84 does not list the '82 part # as an option! The scrutiny and pressure GM was under by early '83 to get the new vette produced, meant... by that time they were needing perfection...A Corporate Blue engine with an intake casted in 1981-'82 on the production line, would have given the Plant Manager a nervous breakdown or heart attack👍
I've seen some pretty bad things from GM manufacturing, so I'm not surprised... I special ordered a Pontiac Solstice back in 2005, and was the first one to get one in Fort Lauderdale in December of 2005. It had all kinds of stuff. I got the fog lamp lenses with bulbs and harness, but it was missing a switch and relays. The interior panels had most of the tabs broken off on them, and the factory had used double-sided black foam duct tape to re-attach them. I discovered this when I took it apart... so I don't put it past GM, even with the Corvette. But I am pretty fascinated by it too... I should probably clarify though, the engine was black, but after degreasing it and scraping it with a wire brush, most of the black paint came off, along with the grease, and there were multiple areas where it had blue paint ... you can see some of it here on the side of the cyl head and block:
And I verified that the VIN on the block matches the VIN on my dash:
Hard to see, but they both end in 18324
And here is the casting on the intake that was removed:
Note, this intake doesn't have the holes between the runners.
The car was a ratsnest, but it looked unmolested. Everything was there, and the bolts did not appear as though any of them had been removed. My guess is that possibly they used an assembled long-block they had laying around from a previous year and then just painted it black like the rest to fill demand?
For what it's worth, I ended up painting the engine Corporate Blue because I'm not a fan of black engines. You can't see when there's an oil leak, etc... so this is what it looks like now:
To the best of my knowledge, there are only two "Cross Fire" intake castings.
#14031372
and
#14057017
Common sense says the 31372 came before the 57017 intake.
The earlier #14031372 is the one without the "balance" holes and was probably found in C3 corvettes only.
The later #14057017 was found in the 1984 C4 and has the "balance" holes.
These holes have all the earmarks of a last minute design fix.
My guess is the C4 had to pass stricter emissions standards than the C3 and the holes help balance the airflow between the throttle bodies at low engine speeds.
82-T/A .... I would be very surprised that your #14057017 intake didn't have the "balance" holes?
They can be a little hard to see ... might want to look again?
To the best of my knowledge, there are only two "Cross Fire" intake castings.
#14031372
and
#14057017
Common sense says the 31372 came before the 57017 intake.
The earlier #14031372 is the one without the "balance" holes and was probably found in C3 corvettes only.
The later #14057017 was found in the 1984 C4 and has the "balance" holes.
These holes have all the earmarks of a last minute design fix.
My guess is the C4 had to pass stricter emissions standards than the C3 and the holes help balance the airflow between the throttle bodies at low engine speeds.
82-T/A .... I would be very surprised that your #14057017 intake didn't have the "balance" holes?
They can be a little hard to see ... might want to look again?
I just went outside and fingered that intake like no one's business. Like a teenager after prom, I found the holes. I was totally wrong. I expected them to be between the individual runners, but it was only between the opposing runners, not the ones that run in parallel.
I did confirm the one I used (ended up installing after the fact) was one that did NOT have holes...
... irrelevant for this discussion, but wanted to verify myself based on the numbers you posted. Sorry for taking this discussion off track.
I am still curious why my engine was originally blue though under the factory black paint (and all the grease from the last 40 years).
Question: I remember on Vice Grip Garage, the guy mentioned that the intakes made by the "Snowflake" company were really good. That the snowflake symbol on the intake used to represent something significant. I couldn't really find anything about that. Was that some special branch of GM that did this, or did GM contract this work out? I know GM would occasionally incorporate OEM parts from performance companies... e.g., the throttle bodies on all V6 Fieros were made by Holley (stamped on there)... so curious if this is something similar? EDIT: Found something that says it's from "Winters Foundry" from Canton, Ohio. Looks like they made a lot of specialty low-production work for General Motors, and anyone else who paid for their services.
Managed to machine the other runners to accept the "Big Mouth" insert.
Got lucky ...
Turns out the runner casting design is symmetrical.
Just rotating my insert, all the walls lined up nicely.
I did decide to machine away the bolt boss that was flipped to the inside and replace it on the insert.
Put a bolt flange on the end runner insert top to secure it to the outside wall.
I could use this new insert on both sides, or just add a bolt flange to the other insert.
Going to refine this design a little more and maybe print them out in high temp carbon fiber plastic.
I will eventually port these four runners to match the others.
Because they are identical, I expect they would flow the same.
This should easily be a 230 average cfm intake, without breaking through
Simply AMAZING work. I'm diving into preparing to port my "extra" manifold for my 1982 crossfire Vette. I'm sure you may have been asked about this, but I couldn't find the discussion. Any advice about the duffusers (or swirl plates). Do you delete them, modify them? Any pictures of what you've done with them would be greatly appreciated. Thank you. Mike
Simply AMAZING work. I'm diving into preparing to port my "extra" manifold for my 1982 crossfire Vette. I'm sure you may have been asked about this, but I couldn't find the discussion. Any advice about the duffusers (or swirl plates). Do you delete them, modify them? Any pictures of what you've done with them would be greatly appreciated. Thank you. Mike
Just my opinion....
There is nothing in the "diffusers" design that would induce a swirl in the airflow.
I think it's just three angled blades that create turbulence to shear the fuel droplets into smaller size.
They restrict the airflow but would probably help with low rpm, low throttle, driving.
Comes down to which is more important to you?
Originally Posted by SuperL98
The "diffusers and balance holes" are long debated features of the CFI intake ... as you know
If you go way back to earlier tests I did in this long - long flow bench thread, the balance holes hurt the ultimate flow numbers.
I am an engineer, so I've been known to side with them "just doing their jobs".
That being said, these "diffusers and balance holes" scream of someone trying to fix something after the design was done.
The earlier intakes don't have the balance holes.
Could be cold start and running, emission problems, EGR mixing.
Maybe things that OEM's care about but we typically don't?
Just finished some smoke tests of just this issue, but haven't had much time to mull over them.
I'll post them now anyway.
I don't think I see any swirl from the diffusers.
They just look like "shear plates" to me to possibly help atomize the fuel spray.
This is the four end runners ... video at half speed.
The purpose of this first phase was to get the best results without porting the main long portion of the CFI runners.
Just reworking the inlets, outlets and plenum.
I think I've reached that limit with this post
Worked on the lowest flowing runners first (#1 and #8) the corner "pool table" pockets.
The smoke videos helped in seeing the general airflow through the plenum, but a string really helps with figuring out the highest velocity flow path.
In the video below, the air comes from the two throttle bodies, flows like a wave across the tops of the adjacent runners, and turns into the corner runners (#1 or #8).
The high speed flow hits directly on the center divider between the corner runners (#1 & #3, #6 & #8).
I cut this center divider back 0.10 inches at a time.
The flow in the corner runners (#1 and #8) increased with each cut until I removed around 0.50 inches and then the flow in the adjacent runners (#3 and #6) started to drop.
So I stopped there.
The video shows the cut back center divider (at half speed)
Next, I pushed the outer plenum wall out about 0.10 inches and down into the runner.
The intent being to help the air make that turn.
There is a water jacket in both the outer walls we need to be careful around.
A cheap (Amazon) US thickness meter helps here.
The walls are about 0.25 thick, so I remove no more than 0.10 inches here.
The final ported plenum area.
I also went back and cleaned and straightened up the runner outlets.
Removed any casting posts.
Went in less than two inches in most cases.
The results, an increase to 191 cfm average.
All totaled that's a 33 cfm increase from stock, the little increases all add up.
The Next step....
I'm using the clear Plexi top and string probe to guide adding clay to each runners inlet.
Even though I don't know how someone could reproduce this without welding
I have runner #2 up to 201 cfm, but runner #4 isn't so happy.
Going to take a lot of fussing
Hello. I've been following your posts here recently and you're youtube videos. Great work! I hope you can answer some questions. The graph states "CUT EGR passage" Was that at the time you cut the passage only back to the side of the runner as shown in the picture, or does that mean removed completely? And do you get to 185 with only cutting the EGR passage, or that included porting the inlets and outlets? Do you think it is best to port an intake with the crossover passages or without? Thanks, Mike
Last edited by mpoetzsc; May 10, 2026 at 07:56 PM.
Hello. I've been following your posts here recently and you're youtube videos. Great work! I hope you can answer some questions. The graph states "CUT EGR passage" Was that at the time you cut the passage only back to the side of the runner as shown in the picture, or does that mean removed completely? And do you get to 185 with only cutting the EGR passage, or that included porting the inlets and outlets? Do you think it is best to port an intake with the crossover passages or without? Thanks, Mike
Usually, each one of my posts builds on the results of the last on.
If your serious about porting your CFI intake, you should start at post #1061 and read forward from there.
In post #1073, cutting the end off the EGR didn’t help the flow at all.
I wouldn’t touch the EGR tube at this 190 ish cfm flow rate.
The later CFI intake runners, with the balance holes open, lose from 15 to 30 cfm compared to with the holes closed off.
Worse, it only effects the center runner pairs (2-3 and 6-7).
So the runner balance would actually be worse with the “balance holes” at full flow.
Usually, each one of my posts builds on the results of the last on.
If your serious about porting your CFI intake, you should start at post #1061 and read forward from there.
In post #1073, cutting the end off the EGR didn’t help the flow at all.
I wouldn’t touch the EGR tube at this 190 ish cfm flow rate.
The later CFI intake runners, with the balance holes open, lose from 15 to 30 cfm compared to with the holes closed off.
Worse, it only effects the center runner pairs (2-3 and 6-7).
So the runner balance would actually be worse with the “balance holes” at full flow.
Thank you. yes, I am serious and will follow your posts as you said. Picking up an intake without the holes tomorrow. Much appreciated. And a final question regarding the diffusers. Would you still delete them or modify them as 82-TA had suggested in post #1065? (is there any eveidence of atomizing fuel better with them modified?)
