WOGI

I have a nice running 84 L83 cross fire. That's face it in its stock form to say that it lacks power is a understatement, I am fishing for info on just how tolerant this system is on camshaft profile changes, increased cubic inches, better flowing intake, heads and exhaust.
I like the cross fire sytem, I know many out there have deep sixed theirs for carb and vac advance dist. I don't want to go that way and would like input on mods to this systems ecm to work with such changes

Tom400CFI

If you can keep the tq curve the same SHAPE as stock then you've got it made. A tq curve w/the same SHAPE -only, higher is easy to accommodate with more fuel.

Once you start radically changing the SHAPE of your tq curve, then there is no reasonable way to accommodate that "mechanically" and you're going to have a compromised tune, and an engine with drivability issues.

I ran a SBC 400 (stock long block), with a heavily ported intake, 224/234 cam, roller rockers, 53mm TB's (I bored them myself), removed swirl plates, radiuses lid, headers and exhaust. I made it work by feeding it what it wants. I started off w/the Walbro 255lph pump, 90pph injectors and ~14PSI fuel pressure from my home-modified, factory fuel pressure regulator. That worked pretty good, but ran rich at idle, not surprisingly. I fixed that by installing a marine TBI application, vacuum referenced fuel pressure regulator. I set the pressure to 15 PSI and manifold vacuum would pull the pressure down to about 10 lbs at idle and after that it ran fantastic.

There is no standard "package" that will work for anyone, but I've given you some tools above; use a cam that mostly keeps the tq curve the same shape, use your fuel control tools (injectors, pressure etc) to try to "feed it what it wants" and with some focused effort, it can turn out pretty good. If you want to add more cam, then the more radical the cam is, the more you'll need to get into ECM tuning to maintain acceptable drivability (what ever that is, to you).

IDK what your goals and budget are, but these cars are extremely responsive to basic tuning changes; Base timing and fuel pressure adjustments alone, combined with a good exhaust system will make a great difference. As evidence of that, my car whens still mostly stock, went 14.5@95 with "free mods" (fuel pressure and base timing), shorty headers and a cat back exhaust. Keep in mind too; MY car was a F-body, so my CFI was only 305 CID, originally. So I was close to "TPI territory" with a 305, and I hadn't even ported the intake yet.

JoBy

The stock computer has some learning ability based on Lambda sensor but that is mostly for low load/cruising situations. Removing battery cable for a while and the ECM will have to re-learn from factory settings.

Ahnenerbe

I cut my teeth on a 84 vette, I also opted to keep the crossfire setup. I sold the car as I just didn't like the look of the crossfire, the TPI looked much better and makes more power IMO. My advice would be to switch to carb if you are keeping the car. You will get more power, and better tune ability. I hogged out the cross fire intake, added a true dual exhaust, went to a bigger cam, and still didn't get the power that engine is capable of making. I wish now I would have did the carb conversion, as it looks easy, and gives great power. My next Corvette is likely to be a 89, so I am anxious to get back in the game again.

Tom400CFI

What were your results? Should have been faster than about any stock TPI car.

On a properly running CFI car, ported intake + set up ("free mods") = late TPI performance.


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James84vette

Had a set of long tube headers installed last week on my '84. Really woke the car up. A bit of a deeper sound and the performance upgrade is noticeable. Seems to run more smoother as well.


So far I've added a K & N filter, '85 fuel pump(have not adjusted the FPR yet) and headers. Who those mod's I've noticed a good increase in power and a smoother running car.


Next up I'm going to up the fuel pressure and may look at a free flowing cat. Also hoping the Canadian dollar starts to improve so I can get the Renegade intake.

Ahnenerbe

Tom, you hit the nail on the head when you said "Properly" part of the problem was balancing the TB's, never thought I got it right. So I got frustrated and sent the car down the road since it just didn't seem to make the power that TPI vettes had. Got smoked at the strip by a 87. My best time was 14.20 @ 101 if I remember right.

James84vette

My mechanic had an '84 and said he had his ported but it didn't make much a difference. He felt it probably wasn't done right. Not saying your wasn't, but everywhere I've read, an intake that's been opened up will improve the car.

I had an '86 that ran 14.90 95ish mph. With the headers done and k & n filter my '84 would beat it no doubt easily.

ex-x-fire

He probably didn't increase the fuel pressure with the ported intake.

James84vette

Has to be something. Doesn't make sense why it wouldn't perform better. Like I said, I've seen a big difference in mine from the little work I've done. Car needs to breathe which the stock version wouldn't allow.

Tom400CFI

That's too bad. 101 says you were making ~250hp or more. Your ET had at least .4 in it; at this elevation I run 13.7x's -13.8x's....at the same 101 mph or so, with my LT1. Your mph says you were making some hp. ET says the driving needed work.



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WOGI

thanks guys for input, keeping the cross fire because girlfriend drives car and is not equipped to deal with a choke system LOL.

James84vette

lol....just from my own experience, I'd start with the simple mods. Filter, fuel pump and exhaust. Then move on the the big gain item the renegade intake. Like I said before, I got pretty good gains from the headers. Just make sure they are long tube.

corvettenorway

WOGI

Thanks all for input and please keep it coming

James84vette

Lot's to learn. I've had a fun time doing so thus far. I bought my '84 in Feb of 2016. This site has been a great resource, whenever I have a problem or need a question answered I come here first.

billschroeder5842

You will get 250ish of of your system if you do the following>

1. Renegede manifold
2. Timing advance to 12-14 (as much as it will take
3. Headers and a "true" dual exhaust

Others will mention heads and cams, but you are really going to mess with drive-ability issues and how much the computer will "learn" (this is early 80s computers, so not much AI yet).

Dont forget the fuel pump upgrade--- this is a MUST

Simple is better on these engines

James84vette

I agree. 250ish is great for a summer car.

Tom400CFI

and would add one other option;

1. Or porting your own manifold. That will get you to the same point.


Fuel pump is pretty lame but can meet the damand I went 14.5/95 with mine and there was another forum member here who had gone into the 13's w/a stock pump...so replace when it fails to meet the demand...unless you like wasting money.

James84vette

I'm taking mine in next week to get the fuel pressure checked and bumped up. What should it be bump it up to? Also what gain will I see from it? Thanks.