Thread: Want to increase performance/efficiency Newly rebuilt 91 chevy 350 TBI

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This is what I have, fresh from the machine shop a 200K mile engine, bored 30K over, new pistons, rings, polished crank, RV cam, lifters, aftermarket heavy duty heads, H/O oil pump, headers. I kept the computer and the TBI carb and basically everything else is stock. The motor is assembled and runs good but would like to tune it. I'm finding it very difficult to find anyone that can re-program the computer chip in this year model, ANY HELP?? Also was wondering if a polished intake would help??

Define: aftermarket heavy duty head, RV cam
That is basically non information.

Welcome to CHR! We're glad you stopped by and hope you decide to stay. Lots of good ol' hot rode folks here. Need a bit more information on your build:

Do you have some numbers for the heads and the cam? Heavy duty can mean a lot of things from valve springs to screw-in studs to hardened seats, etc. The term "RV cam" is all over the place and while it typically means the cam is ground to produce torque low in the RPM range that's not always true.

Do you know the compression ratio?

TBI stands for Throttle Body Injection so I'm thinking that you kept the TBI intake manifold and do not have a carburetor?

What vehicle is this going into?

What transmission? If automatic, stock or aftermarket stall converter?

What rear end ratio?

What is your goal with the engine - i.e., street cruiser, daily driver or?

Fill in the blanks and we can help you out.
Glenn

By trade I'm an aircraft Mech. and can take anything apart and put back together. With that said, I don't know that much about rebuilding automotive engines. I bought a 91 GMC Sierra with + 200K miles on it and took the engine 350, 700R4 xmission, complete wire harness inside and out along with the factory computer, steering column and overhauled everything and put in my Jeep Wrangler. The heads are the factory specs just a thicker cast. The Cam is a MTC-1, Duration 278/288, Lift .420/.443,...The motor is in the Jeep and runs great, just want to make it more gas friendly...I believe all the problems are in the computer. With bigger pistons, a different cam, headers, it is not as crisp as it could be. Should'nt smell raw fuel from exhaust!!! Is their a programmable computer that could be installed??

Do you know the compression ratio? Don't know, how do I figure out?

TBI stands for Throttle Body Injection so I'm thinking that you kept the TBI intake manifold and do not have a carburetor? Yes, factory TBI carb.

What vehicle is this going into? 87 JEEP wrangler

What transmission? If automatic, stock or aftermarket stall converter? Stock 700R4

What rear end ratio? 3.55

What is your goal with the engine - i.e., street cruiser, daily driver or? Fun Toy only driven 5K a year or less

Sounds like a great project - couple things come to mind.

The Melling cam would be fine if you had converted from EFI to a carbureted engine; however, it may be a problem as it will give the ECM fits. A stock GM cam would have been a better choice. You already know the Engine Control Module (ECM) is responsible for making a lot of decisions based on engine temperature and ambient conditions. As a minimum, typical signals it needs to perform are:

1. CTS (Coolant Temperature Sensor) It's typically in the thermostat housing and it needs to be plugged in.

2. Oxygen Sensor - for headers the sensor should be in the collector, just behind the header flange. You may need to get a three wire (heated) sensor to keep the sensor warm. The sensor itself is a one wire plug to the stock harness.

4. Manifold Absolute Pressure sensor (MAP) - typically mounted on a plate somewhere on the intake manifold.

5. Manifold Air Temperature (MAT) sensor in intake manifold

6. Some ECMs have an input for an Incoming Air Temperature sensor (IAT) in the air cleaner or near the MAT that needs to be hooked up. This is often overlooked in conversions and discarded with the air intake plumbing. If your ECM is looking for this signal and not finding it, there will be timing and fuel delivery issues.

7. ESC = Electronic Spark Control - This sends the signal from the knock sensor(s) to the ECM to reduce the timing if it hears a knock

8. Fuel pump – the stock one in the Jeep probably is not sufficient for your TBI engine. Carter 5000 is an inline designed for this type of swap. it flows 45GPH at 75 PSI.

As to reprogramming the ECM - probably not cost effective. There are many aftermarket chip available for less than $100 - check this site:

CHEVROLET SILVERADO 1500 GF Peformance Chip

I'm sure many more will chime in with additional suggestions.

Again, Welcome to CHR
Glenn

Thx Glenn for the warm welcome!! The engine runs great, plenty of HP and great excel. but I know it can be better!! Like I said, this engine is complete, with all sensors connected with original wiring harness, now you did make me think of an idea!! It has the jack to connect a diagnostic computer to, so maybe I should check it and see if there are any codes and make sure of no failures. I'll check that tomorrow....