Hey guys, long time no see. I've been trying to somewhat restore my 84 and have been too busy to keep up with the forum.

I'm looking to get more power out of my CFI L83. I love the look of the CFI intake, and it is starting to grow on me. I cannot be arsed to switch to TPI, and I kind of don't want to, so please dont suggest it.

I've been considering the normal things - cams, exhaust, heads, ecu tune, porting the intake, injectors, 85+ fuel pump.

Now, I am a rookie and I'm not sure what the CFI can and can't/won't work with. I've been told and read on here that a lot of upgrades are 'ignored' by the CFI system. Can that be rectified by getting a tuned ECU?

I'd love to upgrade the heads, cams, and injectors but I don't know how they'll affect the system.

The exhaust, ported stock intake and 85+ fuel pump are already guaranteed upgrades, because I know they'll benefit the car.

any help on what I /can/ do with the L83 would be great. To give a bit more info which I'm not certain is necessary, this will be a circuit racer when I'm done.

Thanks in advance!

 

I don't know who can dyno tune the thing so you would have to struggle with balancing the extra air and jiggling the fuel going in. I wouldn't bother but that is me.

 

Oh, I should have been clearer. I wouldn't be getting it dyno-tuned, although that is possible, there's a guy in AU who enjoys working with chevs.

I was moreso thinking of the Hypertech pre-tuned ECU that is available for the 84 vette/L83 motor.

 

I'd think the money you're thinking of for the Hypertech could be much better spent in something that would actually improve performance.

 

HyperJUNK might turn the fans on earlier but won't do much for performance.

 

You're on the right track! Stock cam is very conservative, so lots to be gained there. Same for exhaust. Heads & intake definitely must be addressed for better airflow...the biggest shortcoming for a factory Crossfire. Obviously with more airflow, you need more fuel, so yes to injectors & pump--but also, you'll need to parallel plumb the throttle bodies.


The stock injectors are stagger sized; 24#/hr for the passenger's side, and 26#/hr for the driver's. The first injector needs to flow less, thanks to the pressure drop quirk of series plumbing (less reaches the second). There are no appropriately staggered injectors in a higher flow range, so you need to run the same size & equalize the fuel pressure acting on them.


Remove the regulator & accumulator in the TBs, add a Y-block to the feed line to supply them with equal volume, and plumb them both to an external regulator on the return side for equal pressure. Like many, I am using the Aeromotive 13301 unit, which has a boost reference port which you can join to one of the vacuum ports at the rear of the TBs. Don't use the center port; it's used for balancing the TBs, and the vacuum signal is much weaker. The resulting variable pressure helps avoid an excessively rich idle, and starvation at WOT.


Here's the setup I referenced while putting together my parallel plumbing (thanks CorvetteNorway!): http://www.technovelocity.com/chevyh..._delivery.html He uses overbored TBs, which may help, but not necessary IMO unless they're flowing less than your heads. Haven't been able to find explicit flow numbers for these 1bbl TBs, but by extrapolating from other flow data, I'd estimate a combined 670 CFM, which should be plenty to support SBC street heads. I'll know more when I finish the build & see what the wideband O2 tells me about the air/fuel mixture, and how much fuel I can push before the airflow can't keep up.


I would add (I'm in the process of doing so myself) a programmable ECU like EBL or Megasquirt, so you can better match fuel & spark maps to the new parts, but others who have modded only the hard parts architecture have tuned with base timing & fuel pressure, and have been satisfied with the results. If you or someone you know can learn to make changes with it, I'd call it a good idea, but optional. I strongly agree with skipping the Hypertech.

 

I would also think he could control it with the TBI 1227747. There's a learning curve to tuning and the sad reality for the 84 is it has never been hacked that I know of. There might be one guy in the US and good luck getting ahold of him.

 

Your best bet is to port the heck out of the intake, make your fuel pressure regulator adjustable, bump the timing up, & do the exhaust. If you want to get into tuning you might look into those ham boards. Its not worth the effort to swap out chips with the stock ecm. You'd be surprised how well it will run with the stock tune when you do the porting & increase the fuel pressure a lbs or two.
If you do decide to swap cams & heads, use parts that are going to help the strong points of cfi (strong low-mid range torque). Really you have to plan everything around that intake.

 

BINGO! We have a winner. Do those things and you should be above 250hp, no ECM tuning required. It's amazing teh difference in answers between those who HAVE experience w/CFI's...and those who have not.

You don't need to "parallel plumb" the TBI's, either.

 

Don't need to do that. Waste of time, IME.


None of this is necessary. Stock injectors are actually 64# and 66# -or something like that. Definitely not 24/26. That would only support up to about 90hp. The stock injectors were staggered to meet emissions requirements that we don't have to meet and don't care about. Matched injectors and factory plumbing works just fine.


The center port is what's called a "ported vacuum" port. It provides far less vacuum at idle (when the throttle plates are adjusted properly) and MORE vacuum, at part throttle/cruising. Used for vacuum timing advance and sometimes EGR. 84Z51 is right that you don't want to use that port for a VRFPR. You can buy a ~$50 VRFPR for GM TBI from a marine application, GM VRFPR.


Hard to find much data on those. I've seen ~275 CFM thrown around. What ever it is, it's better than good enough; bored TB's on a heavily ported, cat back exhaust CFI did nothing, for CFI-EFI. I'd bet that the swirl plates are the limiting factor and not the TB bore itself.

 

My bad on the numbers. I regurgitated them without applying any noggin
The only way to know for sure what is "necessary" would be to test...either by comparison of very similar builds, or better, both fuel setups on the same car, same conditions, one after the other. I suppose in that regard, I misspoke when I said the OP will "need" to parallel plumb. I didn't mean to imply you "couldn't" run without it. Call it a good idea, like having fuel and spark maps you can match to new parts.


My opinion is the one with parallel plumbing would feed a more consistently even mixture between banks throughout the RPM range, and thus produce more area under the HP/TQ curves. Power for the cost of rerouted fuel lines, not a bad trade IMO. Take your easy gains where you can get them & they add up. If you tested though, I'll defer to your results!

Learned something else today, muchas gracias

 

If you modify an EFI system that bases its data on a vacuum signal then it is always wise to tune the system. To assume if I only do x and it will still operate within the ECM's given parameters is a fools game because you're leaving power unused as the ECM switches its mapping to make up for changes. Adding to your base timing will provide the same ignorant result. Sometimes you go to far in your hillbilly advice to the point of it being completely ridiculous.

 

I knew many that were what I'd consider "Cross-Fire Enthusiasts" and a couple very well. Neither of them modified the base system on the car. They kept that as a "fall back on" solution and had another entire system they "tinkered with". One guy had I think 2+ units.

The OP's location I think might behoove him to maintain a "fall back on" configuration when it comes to fuel. "Tinker" with nothing OR very little.

Most/many Cross-Fire enthusiasts pre-date the Internet and even earlier message boards. Often the "shared" information was intentionally mis-represented to keep the competition handicapped.

There's many, many, many reads and it's very difficult to sort the fellows that "really knew" and the well ......

The re-sellers will/would tell you anything that would "sell you" on the what-ever it was they had. The Internet spread the "gospel according to..."

This has been a very interesting read thus far - interesting

 

Thanks all!

I think I'll stick with the heads, intake porting*, exhaust and cams for the moment until I learn more.

With the heads and cams, any recommendations? I've already chosen an exhaust system that I'd like to aim for, but with heads/cams I'm not sure what's compatible or what gives the best power for value.

Great responses guys!

 

crossfire was also used on F bodies, right? I think I might be mistaken on that as I'm no expert.

Do you think they'd have any useful info for working a CFI motor? Since they used the same intake on what I assume would be the same or extremely similar SBC.

Just trying to get a bit more perspective and as many opinions as possible.

 

Crossfire was used in 82 thru 84 F-Body and 82 and 84 Corvette. It is speed density and very sensitive to change. While mild mods are okay they may just not improve performance.

 

I'm a tad confused by that, what do you mean?

 

There's 2 ways of EFI. Mass air flow meter measures incoming air and it is easier to accept changes. Speed density measures the engines vacuum and defaults to a volumetric efficiency map to decide how much fuel to use. Since 1994 GM uses both together, although I'm not that great at those systems. So if you make the engine flow better but it is still using the stock VE map it may not provide enough fuel. I hope this makes sense. In 85 thru 89 they used MAF (mass air flow) and in 82 thru 84 and 90 through 93 the used MAP (manifold air pressure).
Therefore, with the stock ECM that can't be tuned you're better off staying as close to stock as possible or changing to a system that can be tuned. That is why I mentioned the 1227747 from the TBI trucks. It could be made to use with the stock intake and mod all you want because you can tune it.

 

So basically what you're saying here is that the mods I want to do will need to be supplemented with more fuel delivery, if the system might starve it? Hypothetically speaking, how would such an issue be rectified? My first thought was bigger injectors and a higher pressure pump/fuel system (likely the 85+ version) but even so, that would need the ECU to utilize it which is the problem I think you're talking about.


Is it really that easy? just swap out the engine control and hey presto its tuneable? surely there is something else I'm missing, it's never that simple.

But just to reiterate, If I did the following mods:
-ported intake
-cams
-heads
-injectors + 85 pump

All I would need to get all that running with the CFI is a tuneable ECU? Seems straightforward enough. If that's all there is to it I'm more keen to get some more 'go' out of this thing.

 

You can do any of the things mentioned in this thread but I am of the opinion that all speed density systems should be tuned when changes are made. Read this

http://scotthansen.net/data.html

Added pressure will help but it is a band aid to a growing problem. I don't even know if the 1227747 would work because my head starts swimming about 2 TB vs 1. My thought if the base pulse width could be cut in half. I've only dabbled in this ecm because it uses an outdated 1732a chip that needs ultraviolet light erasure. That can be overcome by sending it here www.moates.net to have an updated 28 pin socket put in. There's also aftermarket systems like megasquirt to be looked at.