performance tbi

[clstolten]

OK I AM NOT getting into a pissing match here you win! I guess 90lb injectors are the best bet for this kids stock 350.

I specificaly said that 90lb injectors are not going to work with a "stock" tbi 350 in my last post. Just that they could be useful on a properly built tbi 350. Don't put words into my mouth. Apologies to the original poster for getting off topic.

 

[blackk5350]

now im confused i think im gonna run a 45lb injector and a 90lb to make both of you happy jk

i assume i should just run the stock injectors with bumped up fuel pressure

 

[original balzer]

i assume i should just run the stock injectors with bumped up fuel pressure

That's correct. OF course you can run huge injectors at a low pressure but once you check injector prices you'll see why that would be just SILLY. With an adjustable pressure regulator you can make 55lb injectors run like 70lb injectors if not more.

I honestly think the holly 680CFM replacements are overkill unless you do some other serious mods like an intake, cam, headers, maybe even a bigger bore and higher compression pistons and of course a computer tune to match all that stuff up. However Im sure it will run a lot better, and is a fairly cheap mod. In other words the bang for the buck is pretty high. But dont forget you will need to open up the intake holes to fit the 2" bore throttle body.

The list you sugested seams pretty good to follow. My 90 k2500 I did dual exhaust a throttle body spacer, injector spacer, K&N air filter, and underdrive engine pullys all at the same time. It made a pretty obvious power gain. I later used a over the counter "chip" and I honestly dont think that did a dang thing. But at the time a real reprogram tune was expencive. I have been planing a TBI engine build and done a ton of homework there is a lot more options than I expected to get power out of a TBI unit.

 

[dyeager535]

i assume i should just run the stock injectors with bumped up fuel pressure

Well what are you doing to need the additional fuel anyways? Are there engine mods that are going to require it? Bumping fuel pressure up isn't going to make an ounce of difference other than waste gas and possibly run worse, if the engine can't use it.

 

[Wingnutt]

Let me throw my two cents worth in. TBI engines are severely restricted at three places, the exhaust, the intake and the heads. Like it or not these engines are designed to preform at very low RPMs (< 3800 RPMs). They run out of breath around 3500 RPM or so.

The first thing *I* would do (and have done all of the following) is to open up the exhaust. Start with full length small tube primary tube ceramic coated headers.These will open up the flow, help to keep heat in the exhaust and help enhance low end torque which is what you want given the weight of these beasts. While we are at the headers, go ahead and put 3 wire 02 sensors in 'em. This will help later. Following the headers is the place for a good free-flowing cat (best diameter is about 3" in and out). Next in line would be a 3" in, dual 2" out turbo style muffler chased by full length tail pipes. This setup will flow everything that the 350 can push, sound nice, and not resonate off the fiberglass top.

Next up would be the heads and intake. One word...Vortec. When you use these heads, you have to use a Vortec intake for everything to line up. Here is where an after market intake beats the stocker. Look for one that develops peak torque between 1000 and 5000 RPMs and has 2" diameter bores. During the installation, take some time with the Demal and port match the intake to the heads (little things like that add up).

Now we look at the TBI. You have two choices here. You can run either a 7.4 TBI, or like I did, run a Holley 670 TBI. Both have 2" bores and will require tuning to work at their best. The 7.4 is easier to tune for, but the Holley can flow more fuel...your choice.

Now would be the best time to add a different cam. However, don't get carried away. Look for a cam that has a flat torque curve between 1000 and 5000 PRMs. Ideally, you would want to match the torque peak of the intake. Remember torque is what pushes you back in the seat! Depending on the CR and how you degree the cam in, you can run 1:1.6 or 1:1.7 rockers to gain a little extra lift to help the mild duration. Beware of to much duration though. Also, TBI engines like to stay under 112 degrees lobe center line.

Lastly, the tune! Here's where you bring it all together. This is why you select pieces that complement or work with each other. Also here's where that 3 wire 02 sensor helps a lot ( a broadband 02 is the best, but mega expensive). Like the parts, tune the system with low end torque in mind. Resist the temptation the throw lots of timing and fuel in across the board. Take you time, do lots of data logs and give the engine what it wants. Rarely will all of the curves have an ultra smooth curve to them like after market chip makers like to show. Remember, the data logs will show what the engine needs.

I know this sounds like a bunch of super mild mods, but believe me, when you tie it all together, you will be surprised how hard that engine will pull when matched to the correct gears for the tires you run.

 

[cabledawg]

I actually bought a kit from JEGS that replaces the TB, intake manifold, pressure regulator and injectors and includes the injector and TB spacers. The TB is 670cfm and the injectors were rated at 80lbs. Now when I bought this, it was for a new but stock "K" coded engine. I forked over the money for short tube headers and had previously replaced the exhaust with dual 2.5" that runs to the back doors of the Burb and dumps out the sides. The intake manifold was a Edelbrock that was matched to the TB and the combo works really well. I still top out around 3500 rpm's but this thing can get moving. The Burb was wicked fast with the 700 trans, but isnt as much with the 465 it has now. But when it comes to towing my 32' travel trailer, it whips the snot outta my other Burb that is stilling running a mostly stock engine.

All in all I agree that the first things to do are the exhaust and headers, as well as cleaning up the TBI with some carb cleaner to help the parts work a little easier.

 

[Joe Henderson]

Anybody looking to do performance TBI upgrade needs to check out turbocity.com they do some really trick stuff just for Chevy TBI and sell all the parts you will ever need no matter how you are building your motor they ever sell chips and will re-program your ECU for special situations. Check em out they are definitly the way to go! Seriously check em out!!

 

[K10 KRAWLER]

Sorry to dig up an old thread But I had A newb question. When you are all talking about adding Vortec heads and intake, are you talking about junkyard heads and intake? or can you buy a nice set of performance intake/heads for those newer vortec engines?

 

[82355]

You can buy junkyard Vortec heads, or you can buy them new. As for the intake, you have to buy an aftermarket one, because GM never sold an engine with Vortec heads and TBI. I have a GMPP Vortrc TBI intake.

Martin

 

[79rustyk10]

go read brians stuff at www.tbichips.com lots of good info.

and you have no real exaust work done. the biggest restictor is the stock manifolds.

you can skip the injectors and get a 18 psi spring and bigger pump but all that is listed on brians site.

stock cam is little more than a lawn mower size cam. get a stock 94-97 lt1 roller cam and other parts for a good roller cam swap and power bump.

heck i can list all of it. go read first.

I really like the idea of a roller cam. will that LT1 roller cam work with the stock ecm?

 

[sweetk30]

no but brian can burn a chip no problems for a lt1 roller cam.

 

[82355]

I really like the idea of a roller cam. will that LT1 roller cam work with the stock ecm?

It will work. Will it be the most optimum setup? Probably not, but it will work. I have an GMPP LT4 Hot Cam in my 350 TBI with the stock PROM. It ran okay with the TH700R4, but when I put an SM465 in, it runs a lot better now. I have a set of mildly ported TBI swirl port heads on the engine right now, but I bought a set of Vortec heads for it, and got a free factory LT1 roller cam I am going to install when I put the heads on it. Just to lower my power band, I like the way the engine runs, I just don't like the low end torque.

Martin

 

[79rustyk10]

Thanks

 

[cuervo]

90lb injectors in a 350 is not silly. Two 90lb injectors at factory pressure are only good for about 300 horse with the right motor. You would need two 150 lb injectors to get 500 horse. These numbers are based on the calculator found here: http://www.megamanual.com/v22manual/minj.htm#size

Ok, good to 300 house, but what is the HP rating on a stock 350? 190 to 210 at best? What in the world will more gas do to something that doesn't completely burn what you're giving it now?

The word is RICH, to RICH.

 

[BGKYK5]

As long as the tune on the chip is correct for the injectors, you won't run any richer. You don't want the injectors open 100% of the time at WOT (injectors too small), and you don't want it so they can't open/close quick enought to control fuel flow at idle (injectors too big). As long as you size the injectors so you don't run into either of those problems, and the chip is burned for the injectors you are running, you should be fine.

 

[cabledawg]

That might explain why I cant get over 3k rpms without sputtering. Injectors too big and I never had a new chip burned.

Well now that I have some time and money, I'll do some data logging and get myself a new chip!