What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Gm 350 TBI to Carb conversion

D

dixiechevy01

1/2 ton status
Joined
May 30, 2013
Posts
101
Reaction score
0
Location
Southern PA
Im thinking about swapping out my tbi and getting rid of fuel injection for carbureted. Its an 87 k5 with a jasper 350 engine and th400 trans, the engine and trans are stock to my knowledge. Obviously neither are the original drivetrain for this truck.

The engine does have headers a 2 3/4" exhaust with 10 series flowmasters. All of the pollution equipment was removed smog pump, catalytic convertor, and o2 sensors. This is the main reason I want to swap out the tbi, and I think I can get more power out of the engine this way.

I've seen a few other posts before for this swap but not exactly what is needed to do it correctly. I know I may need a different intake manifold or modified one. I'm not sure how much pressure the stock fuel pump puts out but i'll probably need a regulator and gauge. I know the throttle cable may be different also. And I don't know what to do with the vacuum control for the trans modulator valve.

Is there anything else I will need to worry about for the swap? If anyone has done this swap before I would greatly appreciate the advice, thanks.
 
Yeah, the grass is always greener. I'm expecting another post from you in 6 months titled "How do I get this carb to run right".

Here's the easiest path:
1) Install O2 sensor.
2) Do the common TBI fuel pressure mod.
3) Contact tbichips.com, give them the engine specs.
4) Enjoy better MPG and driveability than a carb.
5) Look back later with much happiness that you never put a Holley or (non Q-Jet) Edelbrock on your truck.
 
Blue85 said:
Yeah, the grass is always greener.
Click to expand...

No doubt. You won't get any more power. A 350 is a 350, changing your fuel supply won't make a difference, in fact you'll be worse off, for all the reasons Blue85 said to keep the TBI.

For the price of all those things you want to change, fix the TBI setup you have now, and be all the better off. People WITH carbs, spend all that money to GET TBI (or whatever form of injection).

And for the small exception Blue said about the Q-jet, no carburetor will compare to a TBI, and the exception was that Q-jet is the best you can get that will compare close to a TBI, but not be better.

Not trying to put you off (well, we are, but only about carbs), but do some reading, read all and everything you can about carbs vs. tbi. Here, other forums, other articles online. There's a reason they're not put on new vehicles :) Don't want you wasting your time or money thinking it's better when it's not.
 
A carb alone isn't going to get you more power. An engine's maximum power is basically determined by how much air it can pump. This is why there is minimal difference in the amount of maximum power produced by the same engine at WOT with either a carb or FI setup (assuming properly sized components), because at that point, each system is injesting and compressing the maximum amount of air allowed by the intake, heads, cylinders, etc.

Where FI helps is in driveability, and power across the powerband. A carb has a limited number of tuning points for calibration across its curve, while FI can adjust almost infinitely based on A/F ratio and other factors. I do like carbs for their simplicity and reliability, but they're outdated tech. Nothing beats a properly running FI system. If ultimate power is your goal, it will come from another source than the type of fuel delivery, namely heads, compression increase, etc. While some would note that TBI is not mod-friendly, there are many options these days for hot-rodding your TBI if you want to go that route.

If you just want to ditch the FI for simplicity's sake, it's pretty simple. The intake or carb will provide a vacuum source, and linkage should be easy to find if you need it. You will also need a new intake manifold and distributor.
 
Ok thanks for your advice guys. I'm still gonna think about it but Im gonna find out more about swapping first. The main reason I wanna swap it out for carb is because the way it runs now. It's like it goes through spark plugs every 5,000 miles or so. When there new it runs fine. After awhile it will start loosing power or hesitating and eventually start back firing. Then if I replace the plug it's back to normal again. I think it's because I don't have o2 sensor. Back when I put the headers and exhaust on I never put the sensor back in. I don't know much about adjusting the carbs or TBI. Yea I would definitely rather have more simplicity but I'd also like to have decent fuel mileage and more reliable. I'm on a pretty tight budget and don't really wanna spent to much and get into the internals yet
 
That O2 sensor is definitely most if not all of your issue. Without it, the computer can't optimize the air fuel ratio, so it's fouling your plugs, probably running pig rich, which kills performance. Pop that thing right back in and see where you're at. It will be cheaper and easier than converting to carb. Best of luck!
 
I'll race any of you with a TBI to your carb, even same truck at 1/4 mile times and guess who would win?

Guess which one will always start beter, drive better and get better fuel milage?

Before you guys send any more people to TBIChips.com to get screwed start looking around the net for all the warnings! Here's one to start you off with
http://www.fullsizechevy.com/forum/...obd-i-ecm-pcm/511559-beware-tbichips-com.html

I fix his tunes all the time!

You don't need an O2 sensor for EFI to work... but the tune would have to be spot on. Stock tunes need an O2 sensor for feedback and fueling adjustments. You also set a code without it and no it won't run right!

TBI EFI is not a miricle, it has to be properly functioning or it will have issues, same as if a carb had issues! You can't take out one important part and expect it to run.
 
The O2 sensor is not for "emmisions". It is so the ECM knows how to fuel the engine. Put an O2 sensor in, and leave the carburetor under the bench, where it belongs.

Martin
 
dixiechevy01 said:
I think it's because I don't have o2 sensor.
Click to expand...
Duh.

dixiechevy01 said:
I'd also like to have decent fuel mileage and more reliable. I'm on a pretty tight budget and don't really wanna spent to much and get into the internals yet
Click to expand...
Again, duh. FI is the obvious choice and much cheaper than a carb conversion.


I have no personal experience with TBIchips.com. All I'm trying to say is that when you rip stuff off the engine or maybe other changes and you want it to run well, it needs to be tuned. But even without custom tuning, just letting that poor ECM into closed-loop will bring big MPG improvements. :thumb:
 
I bought a heated O2 sensor and performance chip from Brian. My truck wasn't running right with the chip so I sent it back. To make a long story short, he figured out some bone headed mistakes I had made on my end that were causing my problems. He also reprogrammed my chip not to look for EGR when I was getting a code. I offered to pay him extra and he refused. Since he wouldn't let me pay him for the extra work he did, I figured I should at least take up for him now! He responded quickly when I had problems and he went above and beyond to help me get it right.
 
Okay well what did you guys do about fuel pump? keep the in tank fuel pump and run an adjustible fuel pressure regulator with bypass or just disconnect it (electrically) and run a mechanical pump?
 
I bought an 87 that was switched to carb, the po had swapped the tank out for one with just a pick up.

When I pulled the other tank if still had a fuel pump in it, but it was never hooked up
 
Another vote for putting a heated O2 sensor in first. It's cheap, easy, and will make a world of difference.

And you will not get the MPG that a TBI can deliver. I drive my truck very mellow, and get 20 mpg around town. When I stomp it, it flies. And it starts in the dead of winter, heat of summer, no problems.

TBI is very, very simple. Pick up a shop manual and you can fix everything yourself (if there is anything wrong) with just a paperclip to tell you the error codes.

I'll NEVER go back to a carb after working with TBI. :D
 
Ok thanks for all the advice and feedback. I will probably be putting new o2 sensors in. It hasn't had o2 sensors in for sometimes now probably like 4 years I just never messed with it.

Would you guys recommend stock bosch o2 sensors from autozone, or should I look for some performance o2 sensor. Also since the emmissions egr/smog pump was removed will this have any affect on the fuel/intake system or the computer.

And do you guys think I should get a chip for computer also? Pretty sure the engine is stock internally. The only thing on it is the headers, exhaust and k&n air filter. It might already have a chip in it actually, when I first got the k5 it had a box in the center console that said some company on it and it had an old used computer chip in it. I cant remember the name of the company though. The company has ads on ck5 pages sometimes

I'm not very familart with these chips on gas engines though, how do they actually work do you just get it specifically tuned for what you have?
 
Bocsh O2 sensors are fine, AC/delco, deso as well...

Headers move the O2 sensor further down exhaust stream and this needs adjustment to "INT - Delay vs. Air Flow"

If EGR is removed it needs to be turned off in chip and not just the error code!.. If not the ECM thinks it is still there and when on it changes fueling and spark to compensate... leaner and more spark. Not good without EGR...

Air pump also needs to be disabled, when the ECM thinks it is on it runs Open Loop.

There are other improvements that can be made for stock engine. PM me when your ready for a chip. Work out the mechanical details first. Put in O2 sensor, disconnect batt to clear codes and drive a few times to see what codes are being set.
 
Actually it was a JET Performance chip box that I found with an old chip in it. Lol I just seen the ad on the site
 
If you saw what changes were made to Jet chips? You'd be pissed that they took your money! We've had them, read them, compared them for many years...
 
Oh ok thanks for the help. Yea I'm not sure what was done with the chip it must have already had it in when I got it. That chip is probably about 10 years old.

Well the check engine light is disabled right now, my dad took the bulb out awhile back to get it to pass emmisions and never put it back in. So it probably has a bunch of codes on there right now. I have to replace some dash lights in the cluster anyway probably just replace them all while I'm in there. Any suggestions on these dash lights? We put new ones in awhile ago and there out again

Well I'll let you now when I get the mechanical stuff taken care of, I gotta weld new o2 sensor bungs in first
 
Take care where you place those bungs. The further from the heads, the cooler the exhaust temps, which means you need a heated O2 sensor. I don't know exactly how far matters, so you may want to Google that first and get it right the first time.

You probably cannot use a stock O2 sensor if it's more than ... 8" away from the head? Someone check me?
 
You must log in or register to reply here.

Latest Posts

Top Bottom