TBI 350 engine

Silverstanger · August 1, 2003

Could someone tell me if its the Throttle body, the heads or what exactly is the big problem with TBI 350s.

It supposed to have Torque with a TBI 350 engine.. It is a slug!!

What exhaust can I put on here to give me the best torque. I have a heavy boat and need more low end torque.. shoot the thing don't start decently pulling till like 3000 RPM!! -- Right now I have headers then two small (2.25) running into one 3"pipe going back to a dual outlet flowmaster and No cats.

I need exhaust advice and a few more horses.. would underdrive pulleys help?? or an electric fan or something. Anything!!

** What mods would be worth the $$ to change.. How about that bored out TBI unit that they are selling.. or a TBI spacer?? is it worth anything?? Will gas mileage improve with Any mod?? **

I can't believe how slow this thing is off the line.. good lord!!

Guys I let my friends 5.4L F-150 Supercrew cab (heavy also) get like 5 cars behind me, we left, and before I could get to 2nd gear he passed me!! Do 285/75-16 tires slow you down that much??

I changed the plugs, they looked like they were burning fine. They had a brownish tint to them with some carbon build up.. but not where it was firing. It runs a whole lot smoother now.. but no additional power!!

SteveCZ · August 1, 2003

Sounds like a gearing issue... what rear end gears are you running?

you may want to consider changing out the gears, yes you will lose some gas mileage, but bang for the buck, versus engine mods, you will get more out of gears.

Just my $.02

Tree_Hugger · August 1, 2003

Did you increase the tire size to 285/75/16? from what?

If you did, the ratio of the diameters of the tires will tell you the ratio by which you need to increase your final drive ratio.

e.g. if you had 30" tires and you now have 33" then you increased your tire size by 10%. So if you had a final drive ratio of 3.73 (probable), you would need 4.10's to get the same performance (or close to it, your larger tires are also a lot heavier and that will slow you down some too).

99-2door · August 1, 2003

It supposed to have Torque with a TBI 350 engine.. It is a slug!!

shoot the thing don't start decently pulling till like 3000 RPM!! -- Right now I have headers then two small (2.25) running into one 3"pipe going back to a dual outlet flowmaster and No cats.

Well, you have headers on your truck, That's where some of your torque went right there. Checkyour MAP sensor and the EVAP system, especially the vapor canister. If you want to mod, start with a high flow air intake system, pulleys will help a little, eradicate your fan & clutch and go with electric fans (this is a big one), get a performance PROM

Tahoe933 · August 1, 2003

I have the same issue and can tell you definitively, don't bother with a TB spacer.

I added that to my 95 TBI 350 and it made zero difference. Not in power of mileage. Mike

Tucson_02Silverado · August 1, 2003

The Throttle Body itself has been known to start becoming sloppy resulting in vacuum leaks. Jet Performance and a few others do performance TBI rebuilds. It's usually not needed until going to 383 stroke, but you could also look into using a Throttle Body from a 7.4L application.

robsawatsky · August 1, 2003

The big difference between the TBI 350 and Vortec 350 is breathing, primarily the ports in the heads but also a better tuned system from intake/heads/exhaust. I believe the Vortec may be a bit higher compression as well. The fuel injection system itself is better but probably not a big factor for HP and Torque.

96 Vortec · August 1, 2003

Do you have an O2 sensor after the factory cat location? If so, your computer is getting false readings from the lack of the cat.

Wingnut · August 1, 2003

You have already opened up the exhaust side, so my would be have the heads done (open the intake side) and some kind of aftermarket tuner.

Make sure that the tuner will allow you to change your tire size.

That TBI 350 can produce some pretty good torque if it's breathing well.

The tire size is a huge factor if the computer thinks you have 235s on there, and you have 285s. Most even notice a pretty big loss in low end when they step up to the 285s from the factory 265s that come on most of the 1/2 tons. This also messes up your odometer readings which makes your gas mileage calculations a little off as well.

Like I said....Just my

KonradSayek · August 2, 2003

You can swap out your existing cylinder heads for Vortec heads. To do this and still be smog legal you would have to buy a kit with the heads that redirects the EGR valve. Pace Performance appears to have a nice setup here.

99-2door · August 3, 2003

The tire size is a huge factor if the computer thinks you have 235s on there, and you have 285s. Most even notice a pretty big loss in low end when they step up to the 285s from the factory 265s that come on most of the 1/2 tons. This also messes up your odometer readings which makes your gas mileage calculations a little off as well.

The appearent loss of low end power with the bigger diameter tires is not caused by a loss of power in the engine. It is because of the change in final gear ratio by the larger tires. The engnie is still producing the same amount of power it is just having to go through a higher gear ratio to get the truck moving.

Silverstanger · August 3, 2003

What about my exhaust that I meantioned.. How can I get more low end torque back. Should I get 2" true duals or 2.25" true duals or what??

Thanks for all of the replies !!

Silverstanger · August 6, 2003

It supposed to have Torque with a TBI 350 engine.. It is a slug!!

shoot the thing don't start decently pulling till like 3000 RPM!! -- Right now I have headers then two small (2.25) running into one 3"pipe going back to a dual outlet flowmaster and No cats.

Well, you have headers on your truck, That's where some of your torque went right there. Checkyour MAP sensor and the EVAP system, especially the vapor canister. If you want to mod, start with a high flow air intake system, pulleys will help a little, eradicate your fan & clutch and go with electric fans (this is a big one), get a performance PROM

How do you check the MAP and EVAP system??

Silverstanger · August 6, 2003

One other problem is..

in the morning until after driving it a while..

it doesn't take all of the gas pedal. Shoot it don't even take 1/4 the gas!!

If I try to get across an intersection without nursing it (gradually) then it will stumble and if enough throttle is given it will sputter through the intake.

99-2door · August 6, 2003

One other problem is..

in the morning until after driving it a while..

it doesn't take all of the gas pedal. Shoot it don't even take 1/4 the gas!!

If I try to get across an intersection without nursing it (gradually) then it will stumble and if enough throttle is given it will sputter through the intake.

Hmmm....this is starting to sound like a timing problem to me. Either check that out, or have somebody that knows how do it. the computer can compensate for slightly off, but majorly off is another thing altogether. As someone said earlier, if you don't have the O2 sensor installed your truck will run poorly. Also you may want to consider having cats installed back into the system. Use the newer monolithic style instead of the older pellet design.