SBC TBI kit pros and cons

[tree MDS]

I was not familiar with the term spread bore till now either. It sounds like someone put a 350 intake on it somewheres along the line. The old 283 4 barrel intakes had four small holes all the same size, just like the two primaries on you rochester, and ran a very small carter afb. My point was maybe yer getting too much gas for the smaller heads that a 283 is equiped with. My old man was real old school chevy back in the day, used to make his own headers out of copper tubing and a flange you could buy from Hot Rod Magazine - ya know before you could buy headers. I've got four 283's hanging around the shop at present.

 

[DTW902]

But, on a properly set up system, they ain't likely to mess up. The most common failure (guessing) is the fuel pump, and that'd kill either system.


TBI systems can go hundreds of thousands of miles without any troubles. They're easier to start, run at any angle, and change their "jetting" to match atmospheric conditions.

Nothing wrong with a carb for sure, but there's nothing wrong with TBI either.

That’s true Carl, but there is a big difference, off road verses on road miles. With a carb if you lost your pump you could set a can of gas on the top of the vehicle and drive out. Try that with TBI, especially in an older vehicle the simpler the better. Things break and quit out in the field in the middle of B.F.E that you never have break just driving on the road. This is just my opinion of course, but I have been there....

 

[Frans]

I was not familiar with the term spread bore till now either. It sounds like someone put a 350 intake on it somewheres along the line. The old 283 4 barrel intakes had four small holes all the same size, just like the two primaries on you rochester, and ran a very small carter afb.

Prob. is a 350 manifold. Edelbrock performer. Maybe I should look into getting the original parts.

Just talked with this mechanic today who said he could prob. hook me up with an old school tbi factory system for around 500 bucks not installed.

But I think the system he is talking about came off of a 305

 

[lumberjack]

Dave, you've driven out with the can on the roof/hood? I've often heard that, but never seen it done. I know it'd work, assuming you had a large enough piece of tubing.

Snarf drove this thing to the GTG, so I'm thinking he still goes down the road a goodly bit.

If you frequently wheel, especially in the boonies alone, I'd suggest a back up fuel pump. My theory is to already have it plumbed, just flip a switch and keep going. I don't disagree that carbs are simpler.



Too big of a carb doesn't change the fuel mixture very much (assuming it's properly jetted), however you'll loose bottom end and throttle response.

Vacuum secondaries make the carb act like a 2 barrel until the throttle is open and the vacuum drops. If they are opening sooner or later than you care for, change the power valve (or metering rod). More economy would dictate a lower pv, so the engine is under more load before they open, at the expense performance.

Assuming you'll wind it up to 6k rpm (if it's built for low end) a 500cfm carb would be nearly ideal. 5krpm would be around 400cfm. Quadrajets come in several flavors, do you know which one you have (what rating)?

 

[DTW902]

Sure I've done it, tubing copper or plastic. If you have a siphon hose you can make it work. You get real creative when you are stuck in the middle of no were. Then again I had to walk 8 miles to the nearest phone one nite, no cell service and stuck bad but thats another story. Remember I live way out in the sticks.

Frans the performer manifold is a good dual plane manifold (better for lower rpms and low end power). And a lot lighter than a stock manifold 2 or 4 barrel. Good luck with your project....

 

[GASoline71]

All Rochester 4 barrels are spreadbores, and when tuned right are decent carbs. But they have some issues like air leaks at the throttle blade shaft and other stuff.

I have a lot of experience with Rochesters, but on a 4X4 with off camber situations they suck.

If you really want a TBI setup for your SBC on the cheap... hit the wrecking yarrds for a 1992 to 1995 Chevy or GMC truck/SUV. All of them came with the TBI setup. Small blocks, and big blocks. The big block units will bolt on small blcok manifolds, but will be to much cfm and fuel for a small block. You could prolly land the entire SBC system including the intake manifold (which is aluminum from the factory), TBI unit, The computer and all the harnesses that go with, and the electronic Distributor for it for around $400 bucks. You will have to convert the exhaust to run O2 sensors as well. You will also need to run an electric fuel pump to provide constant pressure, as the stock fuel pump only puts out about 5 psi.

The early model TBI's 1991 and earlier, had injector problems... and the Injectors for those TBI units are not cheap.

The next step up would be the Vortec FI that came on the 1996 and later model trucks/SUV's. The cylinder heads are superior on these model trucks/SUV's as well.

TBI's are great units for 4X4 situations and very popular, and an easy upgrade. You just gotta make sure you get all the necessary parts from the donor vehicle.

BTW... as far as fuel mileage from a TBI... not gonna happen. You prolly won't see very many gains from a TBI in that department.

Gary