The Stovebolt Site Forums The Shop Area Engine Shop 292 inline with TBI

Hey all! I have a hot street built 292 inline 6. Im looking into adding TBI in place of the 4 bbl carb.
My 292 (bored to a 298) has over 300 HP and over 400 ftlbs of torque. Im running a 600 CFM edelbrock. I have a painless harness and a complete TBI from a 1993 Suburban with a 350 v8 with computer. My question is what CFM does the 350 TBI have? and what CFM does the 454 TBI have? and will any of these provide enough fuel to power the HP im putting out?
Motor is in a 1954 Chevy 5 window pickup.

THANKS AND MERRY CHRISTMAS !
PS my motor mods
Chevrolet High Torque 292
300+ HP 400+ Torque
Block: 1974 Chevy 292
Crank- Polished
Cam- Clifford 264 Hot Street
Bored .040 (298 CI)
High Compression Forged Racing Pistons
Zero Decked
65K HEI Distributor
Chrome Moly Push Rods
Head: 1966 Chevy 250
Machined .030
Oversized Stainless Steel Valves 1.94/1.60
Bolt Bosses Removed
Premium Hi-Flo Lump Port Kit
Big Block Roller Rockers
Port and Polished
Offenhouser 4bbl Intake
Edelbrock 600 CFM Carb
Pace Setter Full Length Tube Headers
12" Heavy Duty Clutch

TBI was/is a poor substitute for real port injection that the manufacturers used as a stopgap measure while they developed SEFI systems. Your carburetor probably does a better job than any TBI system would. If you're going to go to the effort of installing fuel injection, why not adapt a sequential port injection system off a newer engine like the Atlas DOHC six?
Jerry

Jerry, where would the best place to put the injectors be, a big one in each Siamese intake port to take care of two cylinders or?

Ed

TBI for what it did was dependable. And a lot easier then trying to convert a straight 6
to a port injection engine.

CFM has nothing to do with the carburetor being used or TBI system.

CFM is the maximum amount of air that an engine can take in and pump out.
It is based on the total displacement of the engine. A 350 SB would have about
a 600 - 650 CFM. Though engines do not move the full amount of air that they
can. Average volumetric efficiency, the real amount of air that an engine can flow
through it is about 80% of what the mathematical determined amount is.

So that 600 CFM becomes 480 CFM.

So would go with the 350 TBI system because it's CFM will be much closer
to your 292 then using the TBI system from the 454 engine.

The 454 system would be calibrated to flow more fuel then the 292 would need.
Wasting fuel does not yield more power.

Also you are going to use a TBI system don't forget you will have to change the
engine pipe because you will need a oxygen sensor.
Jeffrey

A single injector in each port would work, just program the computer to fire it twice in each 4 stroke cycle. Since the inline six firing order alternates between front and rear cylinders, each injector shot would need to supply enough mixture for only one cylinder. That's also why 3 carburetors work better than two. Each carb of a 3-carb setup only needs to have the volumetric capacity to supply one cylinder. If the 292 has already had the lump port modification, aiming one injector dead center of each port would be an ideal situation.
Jerry

port injection with siamese intake is hard to get to work right
usually end up with one rich and one lean cylinder one steals part of the other's charge

O2 sensor isn't hard to add just weld a threaded bung and drill a hole

Beast;

Do you have dyno runs to verify your HP and torque numbers? If so, what modifications did you do to the engine to get there?

Look at the firing order on an inline six. It's hard to steal a charge when one of the intake valves sharing the port is closed for 360 degrees of crankshaft rotation.
Jerry

Im just looking to do a simple fuel injection. i dont want to get too crazy. I have all the stuff for a 350 TBI. Here is what I did to my 292:
Chevrolet High Torque 292
300+ HP 400+ Torque
Block: 1974 Chevy 292
Crank- Polished
Cam- Clifford 264 Hot Street
Bored .040 (298 CI)
High Compression Forged Racing Pistons
Zero Decked
65K HEI Distributor
Chrome Moly Push Rods
Head: 1966 Chevy 250
Machined .030
Oversized Stainless Steel Valves 1.94/1.60
Bolt Bosses Removed
Premium Hi-Flo Lump Port Kit
Big Block Roller Rockers
Port and Polished
Offenhouser 4bbl Intake
Edelbrock 600 CFM Carb
Pace Setter Full Length Tube Headers

I got my numbers from what the stock 292 put out and added the HP of each upgrade. I got all my performance parts and HP/Torque numbers from the famous inline 6 builder Tom Lowe.

Jeffery, would the 350 TBI handle 300+ HP?

How about sharing some dyno run numbers with us? It would be helpful to know where the torque curve is now, and whether or not there are any RPM ranges where the torque needs to improve. A 264 duration cam probably doesn't need much over 9.5:1 compression. What's your static compression ratio?
Jerry

i dont actually have any dyno numbers. my compression is 9.5

Without dyno info everything is just a guess. Rear wheel info is way more usable than flywheel readings as everything parasitic is in place during the pull. Crude injection, while reliable, will never give the power readings of a good carb set up. Corvettes with the Rochester injection always got their butts whipped by the carbed ones. We have built a few hot I6's but NEVER one without a 12 port head. Before the Atlas we put a 240/300 Ford and even one Slant 6 Chrysler in Chevy trucks. After just 70 years GM finally gave performance inline guys something to work with. Now if Jerry would just his idea engine purring on the dyno we have a couple of candidates waiting. Old age, weak muscles, and bad eyes must now wait on the young(er), strong, and smart.

So your saying that the carb will be better than the TBI?

MUCH better! I was in a GM Training Center class in 1963, shortly after they discontinued the mechanical fuel injection system on the 283 and early 327's in the Corvette. Being young and wise, I took it upon myself to chastise the GM engineer who was teaching the class over that decision. He commenced to educate me in front of the whole class:

1. "The Rochester 4 barrel makes more horsepower and torque than the fuel injection engine everywhere EXCEPT wide open throttle."
2. "GM loses money on every injection system we make- - - -customers would refuse to pay a break-even price if we charged that much."
3. "If every gasoline engine in the world was equipped with the best fuel injection system we know how to build, and someone came up with carburetion in its present stage of development, it would be hailed as a MAJOR advance in fuel system technology!"

I kept my big mouth shut for the rest of the class, and actually learned a thing or two. When Volkswagen brought out a rudimentary electronic injection system in 1966, things improved some- - - -until the truckers learned that a CB radio with a power booster could turn the injectors off when a VW was passing them!
Jerry

very interesting! Cool thanks for sharing!

EFI advantages:
1. the FI manifold can includes shapes and volumes that will not suspend fuel droplets and would cause fuel distribution issues with a carburetor. Sometimes this is worth some power, but it depends on the manifold design. Example: Ford 5.0, where the air from the TB reverses direction in the plenum.
2. the FI throttle disc(s) area can be greater than a carburetor because engine vacuum does not actually pull fuel from the bowl, and will work below .25 Hg". This gives a slight improvement in pumping loss - but only if you use a system larger than your carburetor. 4 bbl. carburetors are normally calibrated for engines that can pull 1.5 Hg" at WOT. Carburetors rated by CFM are fictional: "600CFM" means it will flow 600 CFM at 1.5 Hg" on an engine that flows 600 CFM. If the engine is bigger, it will flow more than 600 because it will pull higher than 1.5 vacuum. If the engine is smaller, vacuum will drop and the carb will flow less than 600. For a V8* the usual calculation for CFM, where:
D = displacement in inches
RPM = engine speed at peak power
VE = efficiency, less than 100% in anything but a race engine
CFM = D X RPM X VE / 3,456
Example: 298", 5,500 RPM, 95% (excellent) VE
CFM = 298 X 5,500 X .95 / 3,456 = 451
Conclusion: 600 is already too big

* the intake characteristics of engines with less than 7 cylinders are quite different than a V8. The CFM capacity for a 6 cylinder has been estimated at 10% higher than a V8, 4 or less cylinders even higher.

Interesting. I think i get some of that. I have noticed that my truck does smell of gas fumes alot. Espesially through the tail pipe. I put the 600 CFM carb on the 298 because thats what Tom Lowe (the inline 6 builder) told me to use. Maybe im not burning all the fuel thats going in...

An oversized carburetor runs lean, not rich, because the velocity of air through the too-big venturis doesn't generate enough vacuum to pull the fuel from the float chamber into the airstream. It's possible that low intake manifold vacuum might be causing the power valve to stay open most of the time, causing a too-rich mixture. It might also be prone to bog down on quick acceleration or have a flat spot just off idle because of an improper transition from idle to part throttle.
Jerry

I havent had any bogging or flat spots. just strong gas smell at the tail pipe. You think i should downsize the carb?

What do the spark plugs look like? If it's running rich, they will be black and sooty. Proper mixture and good ignition makes plugs have a tan to chocolate brown color with no noticeable deposits. Long duration cams have a tendency to run rich and/or waste a lot of gas at idle, so unless something other than the exhaust smell indicates you've got problems you could probably get by "as is".

Like Evan has said, doing some dyno runs is going to be the only effective way to make a high performance engine work anywhere near right. Before an assistant principal at the school where I taught discarded a file cabinet full of records by mistake, I had a couple of hundred hours' worth of documentation of dyno runs on small block Chevy round track racing engines my students had built for the 5/8 mile NASCAR short track at Nashville Tennessee. Two local car owners supplied the funding, and my students built and tuned the engines. The kids who were at least 16 years old got to be on the pit crews during the summer racing season.
Jerry

I suggest you invest in an Air Fuel ratio gauge with O2 sensor in the exhaust pipe. You will find out in about 2 miles of driving how the carburetor is functioning. I bought a stand-alone gauge from Speedhut, https://www.speedhut.com/gauge/GL258-AFWB-09/7/Standalone-Air-Fuel-Wideband-O2-gauge-8-5-18 , it was the best money I ever spent on getting an engine to run correctly. Its easy to customize the gauge to match your in dash gauges and hooking it up was super easy.
Joe

cool this is great stuff! I will look into all that! Thanks so so much!