Hello all! I've had a 1984 Corvette for a couple years now, and for most of that time I've been under the impression the Crossfire 350 was unable to be modified for performance gains. However, recently through browsing through the forums and other online resources, I've come across some possible ways to upgrade the drive train, but the posts were a few years old so I wanted to know if there were any new developments/options out there. My only real limitation for upgrading the Crossfire is I want to use the stock gauge display because it's one of my favorite parts of the car. Other than that, I'm open to any other modifications.

One of the biggest things I saw was porting the intake manifold runners to match the heads, or replacing the intake manifold with a Renegade system, but I saw they had quality control issues early on. Present day, which option brings the most gains?

Some other recommendations I saw was replacing the injection system with carburetors, updated fuel pumps/injectors, new heads, cams, headers, etc. Which of these are actually valid ways to improve the engine?

I'm open to any recommendations and feedback! Also, links would be appreciated to any items that you recommend.

 

I swapped my crossfire system out for a truck tbi unit and holley tbi intake. With adjustment done to fuel pressure and ignition timing, it runs pretty good. It uses the stock computer and wiring to run it too. The throttle body I used was for 87-89 350 trucks. If I had to do it again, I'd snag a 350 vortec and adapt the tbi to it by using a carb intake and a tbi adapter.

 

Welcome and great question. I had a 82 (same engine) and did the following:

1) Adjust the timing to 11-13. A free bump up in fun
2) install an 85-89 fuel pump.
3) install a high perf cat. HUGE difference in low end and improved sound.

My next steps would have been:

1) Headers
2) ported intake either a Renegade or a DIY

IMHO... skip the cam and the heads. This L83 motor is only going to go so far and if you did all of the above you'd pick up quite a bit.

Think twice about a carb swap. You cars electronics supports a FI system and the addition of a carburetor (although some have had success) will freak your computer out.

 

I'm in a state that doesn't do emissions testing, so would I need to even keep the cat if I do a high performance exhaust system?

Will the stock ECU be able to handle the timing, exhaust, and intake changes on it's own?

 

Dear Dubios Ducky,

IMHO... I think you can go very far.

A full free flowing exhaust would do wonders along with the timing and fuel pump mods.
Full long tube headers and dual exhaust eliminate the catalytic converter completely.
A small high flow heads (AFR or other name brand 180 cfm heads, etc.) and a matching cam (Very Mild) with top notch drivetrain with roller rockers, I would also invest in full roller lifters and full roller rocker arms.
a low temp thermostat and a Hypertech, thermo-runner Chip. Bigger injectors and modified and ported throttle body and modified fuel pressure regulator.

A good MSD ignition and top quality plugs and wires and and a K&N air filter.

You will have to address the intake manifold this is the choking point. I would port what you have.

If you need to rebuild your short block, put good components in it bore it .030 over and make it a 355 cu in motor. Forged pistons a small 1/2 point jump in compression with the best. good head gaskets as light weigh aluminum heads and iron blocks need the appropriate gaskets. I would upgrade to a light weight assembly that is balanced and have a shop blue print assemble of the engine and of course forged pistons and rods and crank and the ARP fasteners on the connecting rods. if you want real overkill put in a splayed 4 bolt main cap on the crank shaft. You could abuse this setup for decades with no problem and of course horsepower well beyond the capabilities of the Crossfire system. None of this affects the computer or how your car run its just to deal with a rock solid bottom end durability and longevity. Also no worn out rings or loss of compression. You would be running good fuel and maybe even a little octane booster to deal with the compression increase and the timing adjustments.

To improve the over all performance of the car, a 2,400 rpm stall torque converter and 3.54:1 gears in the rear end.
Modern tires or drag radials to help you grip. if a 4+3 just put a nice Spec clutch in it.
With the reduced weight of the heads i would also store the spare tire in the garage and not on the car.

Lastly, a 150hp shot of NOS for fun. todays nitro's with the above bottom end is no problem as you can program a progressive system to come on in certain gears and at certain percentage of your throttle position so not a shock to blow off tire but a gradual ramp up to full power.

30 years ago a guy ran 1.6 roller rockers and a healthy shot of NOS and ran an 84 in the high 11's!

Reduced friction valve train, free flowing exhaust, a bump in compression, free flowing heads, an extra cubic inch, light weight rotating assembly will reach rpms quicker.
While expensive and overkill it would be very very fun to drive and you would be happy with a huge increase in performance.

So sorry you were led down the wrong path, as all hot rod tricks work on the small block Chevy and the bottom end can be made bullet proof as suggested above.

I would still buy a used Renegade Intake and have any issues corrected. If I remember rightly, the 84' and 85' and 86' heads are the same and the block, the CFI made 205hp, the TPI made 230hp or 25hp more with those crummy heads.
The change to Aluminum heads netted 5 more horsepower at 235hp half way through 1986. The Addition of roller lifters netted another 5 hp and 240hp and those AFR heads would out flow stock 113 heads. a revised cam, a free flow exhaust and roller rockers would net you about 30hp plus. Remember the upgrade in horsepower one year came down to better flowing mufflers on the coupe that was not available on the convertible that added 5hp, The 1991 cars with the better mufflers made 250hp.
Your car would sound great and drive great and you would have a smile on your face and a hell of a little performer. The light weight assembly and the blueprinting can add horsepower just by reducing mass, tight tolerances and reduced friction. A car to keep for decades more and enjoy.

Like I said, overkill and expensive but very rewarding, oh and in this configuration you could take out stock L98s and LT1s. The right combination can give you 300hp easily, and 450hp on the bottle all in a lightweight full frame, aerodynamic package.

Just my humble little 2 and a half cents input, lol... Cheers, Jarrod

 

What do you want out of the car?

 

Not really anything specific in mind right now, just looking to see what others have done and to get the most up to date info since most forums on the topic were 4+ years old. The engine is currently in good shape, only about 56k miles so I was going to do whatever I can without rebuilding. Then when the engine dies decide which route to go.

 

@iceman2003 Thank you for the indepth info. If I rebuild the engine someday I'll keep all those upgrades in mind.

 

Well, I'd personally think long and hard about what I'd want to get out of it then go from there. My build thread is from 2020 and should give an idea of what is possible at this point in time... not much has changed or improved since then. My goals were retain the stock dash and not touch the bottom end. Another consideration is how much money and time you want to spend. As of right now, you probably won't find a renegade intake so your only option is porting a stock one. If you want a lot of power it just won't get you there without some extra work.

If you're just looking for some more pep, port the stock intake, confirm your fuel pressure is 12-15 psi and if you can't maintain that then upgrade the in tank pump. And tweak timing. My car liked 8 degrees of base timing. All that should net you about half a second in ET and won't really need any messing with in the computer. Younstart swapping cams and stuff then you are looking at using a different ECM. Things can escalate from there.

 

Thank you for the advice! I'll probably stick with the ported intake manifold, exhaust upgrades, timing, and fuel pump changes for now and see how it feels.

 

Smart and budget friendly

 

The very small cam, good springs and seals and titanium retainers and roller rocker arms free up horsepower without needing a computer chip change.

I ran my modified 86' 4+3, 3.07:1 with a crane comp-u-cam, matching lifters, pushrods, springs and gold crane roller rocker arms (1.5:1). Ported #113 heads, good ported Bigmouth Intake and 52mm Throttle body and an adjustable Fuel pressure regulator, stock injectors, stock exhaust manifold, TPIS Front Y, Random Technology High-Flow converter and TPIS rear Y and TPIS Flowmasters, MSD 6AL Box. so I have strong spark, Strong Fuel Pressure, opened the intake and exhaust. Full emissions, stock injectors, stock exhaust manifold, and stock computer chip. 380hp and 430lbs is roughly what I calculated. No traction quarter mile times were poor but the mile per hour was there. Launching a stick shift car also creates inconsistencies so a 3,750lbs C4 Corvette runs 13.65 @ 108mph is not bad.

A good torquer cam will make more hp it just has to be mild enough for your application. We also put one of these in a TBI Camaro convertible with the 305cu in, we also kept the stock chip and absolutely no trouble. If I remember right they had three levels of cams all designed to run with the stock computer. They had one just for the 305 cars. I believe TPIS still sells a cam called SuperL98 or Torquer or something like that, I remember you could get a similar clone in the JC Whitney Catalogue.

They use to make cams for RV's and pickup trucks that enhance power below 5,500 rpms and improve midrange power.
Good Luck and Cheers, do the free and cheap stuff first and then you can decide how much more you want to spend, at the end of the day its all about what you want and what you are willing to spend, for a fun little street car. Cheers, Jarrod