No one has. There was a claim floating around that it flowed 2000 CFM. What that means, I don't know. I know it doesn't flow 2000 per runner, that's for sure. Maybe it's 2000/8=250?

The stocker, unported flows ~170.

 

Never knew the crossfire intake ports were like that WTF?

 

A necessary step to meet the criteria, at the last minute. Criteria being emissions/economy/drivability with the crossram style intake.

The runners are only that small at the exit. They open up (some) w/in an inch of the flange. Still, they are small over their entire length and need a lot of grinding to work right.

 

What should I use to port the intake? Dremel?

 

Interesting. It reminds me of the restrictor plates nascar was using on the old Hemis. The only benefit I can see is restriction.

 

josh, if you dont have a flowbence, then leave it stock and trust the manufacturer ,you can kill alot of HP if you grind in the wrong place/The best thing you can do is smooth everything up in the intake, that can make a big improvement without taking risks

 

Air die grinder or a rotary tool with the powerhead connected to the grinder via a flexible shaft.

Carbide burrs for quick metal removal (and be careful they can remove a LOT of material quick) and sanding cartridge rolls / flap wheels for finer shaping / smoothing and polishing up.

For an air die grinder use about 35-40 PSI to start as the lower pressure will slow it down and give you a little more control when you're starting - once you get the hang of it you can ramp it up a bit...

For any of them - use safety precautions - minimum of a set of safety goggles/glasses that hug the face, hearing protection and a dust mask.

I don't think you can screw it up too bad - just waste a bunch of time (instead of a lot of cash )

In general - you want to create a gentile taper in the runners from the "inlet" to the port when you're measuring cross-sectional area. You want to make the transition slow and 'gentle' and not make any abrupt changes in flow area - you don't want the port area to increase as it goes towards the intake valve as it will actually slow the flow and can cause dead spots where fuel can fall out of suspension (and there are reversion as well as other issues to consider that's out of scope here)

Also - shortening up the runner length will move the power band "up" in the RPM range, lengthening them will move it "down" in the RPM range (great for matching the intake to a cam and other mods)
I prefer to use a shirt with long sleeves and the blue nitrile "surgical" gloves to prevent small splinters getting on the skin and irritating things...

 

The CFI was a missplaced idea from the start.

Quote from Hib Halverson
"In the mid/late-70s, with the new Corvette's powertrain under development, the state-of-art at the time was throttle body injection, however, Delco-Rochester did not have a throttle body assembly which flowed enough air to use on a Corvette engine. So someone thought, "Why not use two of them?"

Rather than use two on an in-line intake manifold and create a hood clearance problem, deep inside Chevrolet Engineering, some genius remembered that back in the late 1960s, the Camaro's '67-'69 302cuin had a factory dual-four-barrel, low cross-ram that Chevy homologated for the SCCA Trans-Am series. They took that idea and figured since it worked great on a race track, the same type of intake manifold would work great on a Corvette street use if fitted with two Rochester throttle body injectors.

Bad idea.

As the system proceeded from design to development, Chevrolet soon found that while the system made pretty good high rpm power, it had terrible throttle response and awful low-speed driveability...so bad that not only was the engine off-idle and low-speed response very poor but it's exhaust emissions were lousy too.

What these wizards had forgotten is that the long runners, the huge plenum volume and the throttle body injectors so far from the intake valves, had fuel condensing out of the air stream and puddling on the runner floors when the velocity of the charge air dropped as the throttles were opened quickly.

What GM should have done was either stick with the QuadraJet 4ME for another two years or use a time machine to bring TPI from the future. But, most likely, for political, marketing and perhaps cost reasons, Chevrolet continued to try and put lipstick on a pig.

The development of CFI was long and difficult. I interviewed a GM Engineer back in the late 80s who told me he knew personally two powertrain engineers who paid for new homes with the overtime it took to get the CrossFire Injection to run well in the 82 Vette with an automatic trans and tall gearing.

The biggest problem was low port velocity at tip in. The eventual solution was to drastically decrease the port volume so that, when the driver whacked the throttle open at low rpm, port velocities remained high enough such that the air/fuel mix remained a vapor and little or no fuel condensed out of the air flow onto the port floors.

Of course, the end result of the tiny, high-velocity ports was significant restriction and poor performance at high rpm."

 

listen anyway, the runners on a fi back then are only about 0.60 a 16th of an inch, theres no porting to do in the first place, change the intake if you want to make a difference

 

later fi's have alot bigger runners and more cfm's as tom said

 

Similar to Fords Boss engines. The ports were so huge there was no velocity at low rpms, so they would try to compensate with smaller cfm carbs to make them streetable. A band-aid solution.

 

no, we use to run in the bob glidden circles and he was a nut about air flow, we put a set of heads on his old pinto with a 302 boss in it and ran 4 tence under the record at the us nationals in indiana, unforunatly the bearings could not handle 11000 rpms. hehe

 

Tom, Thanks for your reply, very thought provoking. Maintaining the cid to duration raito in order to match the engine to the ECM is a concept that would not have crossed my mind. The truck computer is something that I will look into. A aftermarket ecm would not be out of the question either. As I plan out a path for this car the ECM is the problem I dont see a solution for. I would be happy with 360 - 375hp as long as it tunes well. Crisp throttle response is a must. This engine must run properly at track days without taking up a lot of my time.

 

I hear you on your critera. I would want the same things. I feel that I was well on my way to meeting the criteria that you listed (crisp response, clean running, and ~375hp with my 400...but gave up too soon. I sold it before I put on some AFR heads that I had, ported the intake more, and installed a roller cam that I also had. Why did I do that (sell before finishing)?? Because of a girl. So I'll never know for sure. But that I got to where I did on stock 400 heads/valves, an only partially ported intake, 7.8:1 compression, and a $89 flat tappet cam is an indicator to me, that more was available. Oh, and those Edelbrock "headers". lol.

Definitely an aftermarket ECM/controller would solve a ton of problems and allow a huge increase in build flexibility. The stock ECM is mostly a dead end -tunning wise. That is, if you decide that you want to tune it. I say "mostly" because there is one person that I know of who has been able to change the tune in the stock ECM, but I believe that he is still in the learning stages with that project.




I'm not sure what "fi" you're talking about but the runners on the stock CFI intake have quite a lot of material for porting. I have seen first hand, a .7 reduction in ET from a ported CFI intake ONLY. I've also seen a ported CFI intake that measured 2.08"sq in the runner. To say
"theres no porting to do in the first place, change the intake if you want to make a difference"
...is ridiculous, and not true at all. At least not w/in the confines of the topic at hand which is the '84 CFI intake system.

 

Josh, The ported intake is a proven DIY upgrade. The first major mod you should do.
There is a thread on here some where that had some good pics on porting the intake. I searched around but could not find it. You might have better luck. Consider picking up a used intake and port it, 2 reasons, no down time while grinding and if you screw it up, no big. Dr J's performance used to sell abrasive roll kits.


Look what I found!

http://www.technovelocity.com/chevyh...rt_polish.html

This is a great thread, just wade through a little childish bs. You will reconise a name or two;

http://forums.corvetteforum.com/c4-t...-critique.html

 

Question time
As many have achieved good results with a ported CFI intake ;
Why have they not had the low speed drivibilty problems that GM had during CFI testing ( refer Hib's comments above ) that resulted in filling the port in the first place to maintain port velocity?
If a backyard guy with angle grinder can get it work , why couldn't GM with millions of test $$$$?

 

Seems to me that if fuel was going to fall out of suspension it would be in the dead areas of the plenum, during cold weather start/warm up. The way the last part of the intake necks down then dumps into the cyl head int port looks like velocity, pressure and fuel suspension all would take a giant dump in the length of the head port. Who wants to build a plexiglass manifold top?

 

I firmly believe the answer to that is in these two elements;
1. GM's critera are not the same as a "backyard guy"'s. The emissions tests that we have to pass at the local IM station aren't anywhere near as stringent as corporate requirements. Likewise, the drivability conditions that we put the car under, aren't generally as severe as what GM needs to accomodate....

2. The "Backyard guy" can control the variables better. GM has to produce a car that can run in virtually ANY conditions...with any idiot behind the wheel. The guy that ports his intake for more power, probably doesn't live in the MOST extreme conditions, probably does understand about warming the car up (some) before flogging it, and so on. To wit, when I ran my CFI car with the under plenum coolant channel removed, swirl plates removed, 160 T-stat, heat stove eliminated, exhaust crossover eliminated, and Cowl induction open all the time...it had a slight hesitation when stone cold, started in 20*F or colder temps. Of course it did. I know WHY it did, and I was "OK" with that hesitation, that was gone w/in 2 minutes of a stone-cold start. But GM can't sell a car that exhibits that symptom. Know what I mean?

The "problems" that may crop up from porting/moding etc aren't problems that one would ever experience in "normal driving". They would only occur in the extreme conditions that and OEM has to account for. Anyway, I don't think velocity and suspension are issues w/in the runner for our criteria. The issues are bigger in the plenum. GM shrunk the runners, IMO, to get velocity and atomization in the runner, to meet emission requirements that we don't have to.

I feel this way for two reasons;
1. every ported CFI car I've seen runs SO GOOD: good power, wide power band, and wicked crisp throttle response. Evidence that for a practical application, it works.
2. GM isn't stupid and they don't leave power on the table for no reason. If the car runs fantastic with ported runners, then there must have been criteria that they had to meet...that I don't. Ie. emissions, extreme (cold) temps, and lowest common denominator owners.

 

HA! I was thinking the same thing. Also.. Remember that 1983 Corvette with 250 HP CFI? What was wrong with that? I'd venture to guess nothing. Afterall, how good would TPI look at 230HP when it's TBI predecessor was more powerful. Thank you GM =) I think I will port my intake though. One could use an air die grinder anyway, so I'll go buy one.

 

Tom is right GM had to cover bases and be conservative, they know they are going to be modded by some anyway but they have to meet their own criteria to be reliable.