RT2SJB

I have several questions regarding fuel injection for my 1974 L48. Has anyone done a conversion from a carb to a fuel injection system, if so what was the cost and did it improve the performance of the car, any details would be appreciated.

Rotonda

I have a heavily modified TPI unit on my 77. You can expect easier starting, better response and improved economy (especially with an overdrive trans). FI will also usually reduce tailpipe emissions.

There are several different varieties of FI:
1) Throttle body injection as used on older Chev trucks (and 82 C3 crossfires) This is a low pressure system (15 lbs) that sprays fuel into the manifold.
2) Wet flow systems that use higher pressure (approx. 45 lbs) and again spray fuel into a carburetor like manifold. These systems are usually more performance oriented and usually have more sophisticated electronics, sensor inputs and air metering.
3) Dry flow systems. These are high pressure systems that have individual injectors situated in the intake manifold near each intake valve. The manifold carries only air. There are LOTS of variations on this, and this system is what most manufactures are using.
4) Direct injection. A very high pressure system that injects fuel directly into the cylinder just prior to ignition. Many manufactures are going to this. It produces higher horsepower, better economy and lower emissions, but I have not seen such a system on the aftermarket.

Richard454

Couldn't have said it better-

Just forgot to mention modifying/replacing tank and depending on the type of system- a return fuel line to the tank.

Costs? Will vary greatly.


Richard

Mike Ward

You might get a few more HP out of it but given that you've got a low HP smog motor (195HP) it's the probably most expensive way of getting there. Much easier and cheaper ways.

Carl in LA

I went with the MSD system as it is smog legal here in Cali...


https://www.corvetteforum.com/forums...tall-76-a.html

The questions... the grand total cost was $3k for full ignition control in conjunction with throttle body injection. The performance improved primarily in cold start performance including cold drive-away - just like a modern car. Secondary performance gain in is the total real-time tuning for air/fuel ratio, ignition timing, idle speed, etc... on the road performance did not change much for me because I had a well tuned Rochester which worked normal and perfect.

7T1vette

Generally speaking, the top performance of an engine can be achieved with either a carb or F.I., assuming both are properly tuned for best WOT performance. F.I. almost always will be an improvement for good starting, idle quality, and, certainly, lowest emissions when compared to a carburetor. But, performance will probably not be improved, as long as both are properly tuned.

If you are looking for performance improvements, this is your list...in priority of 'amount of improvement per dollar spent':

1) recurve distributor and set timing for performance [reference Lars Grimsrud's papers];

2) tune/rebuild carb, as needed; also verify that throttle cable/linkage is allowing carb to fully open at WOT pedal position;

3) free flowing exhaust system (headers/CATs/mufflers/pipes);

4) cam & lifters;

5) cylinder heads (cam AND heads are what allows the engine to breathe properly); this upgrade MAY require an improved induction system [carb & manifold];

6) upgraded crank and balanced engine internals to increase CR and achieve higher RPM's.

RT2SJB

Thank you all for the information it will help me decide the direction I want to go. I am not looking for performance, just drivabilty and cold start/drive off. Has anyone used the Elelbrock injection conversion set-up? Since this car is just used for clear day outings I am not worried about keeping the car original and my 2011 GS will satisfy my need for speed.

7T1vette

Properly setting up your carb and choke system is a LOT less expensive than throwing money at a F.I. system. Invest a few bucks in the 1974 Chevrolet Chassis Service Manual; then go to the "Engine-Fuel" section to read/digest the info on proper carb and choke setup.

It's not really that hard, and you can get your carb to behave close to what it did when new.

Mike Ward

The car when new fired off immediately and idled perfectly cold and hot. If yours is not doing that today, fix what's wrong.

EASYGEAR

If your decision is towards the sequential injection, which is today`s standard and has it`s advantage, next to decide was if you go MAF or SD.
Aftermarket systems all are Speed Density based, only one offering a Hot Rod unit that is MAF-controlled.
I have it but cannot provide own driving experience yet.
There is also a version with a 4bbl setup available.

It is also the only available system that is OEM quality, as it is produced at OEM facilities at same standards.
The OEM`s all go MAF.
If you decide for Speed Density don`t forget in your calculation the dyno tuning-days add to the bill and you need a good tuner to be safe.
The MAF system is plug and play, it arrives pre-programmed according to engine-/car-data the customer provides when ordering.
Still could be tuned by anyone who wants to play, less difficult than the table-tuning on the SD-systems.
It is not a "self-learning-system" like the lesser 4-bbl systems, more self-correcting, just like OEM late model MAF systems.

SD all relies to the tuners job. MAF always perfect when street-driveability is your goal.

For power - i was always believing you cannot get more HP from the EFI system.
I would have said the horses are in the specific motor or not, the injection system cannot add power, but definitely can help to reveal the engine`s potential.
If the carb set-up was not perfect before, you get higher power output from the EFI, but than that is because it was not ok before.
Power did never drive me to use EFI, but aside the power aspect i see lots of advantage.
Wouldn`t want to go back to carbs.

mrvette

20 years ago, I put a L98 speed density system on my '72 vette, the mpg went up to 24 at 80 mph on a Florida trip a year later, the system cost me 350 at Carlisle parts meet, computers were 10 bux at a junkyard, chips burnt for anything between 75 to 150 bux....

The engine was an L48 with Muncie, and 336 gear set.......

obviously the engine was busy at 80 with no overdrive...

the car used to get about 16-18 at best with the QJ on it... ~12 around town....

Since the Florida move in '97 I have put in auto/overdrive same 336 gearset, and the L98 induction parts went away in favor of a much modified LT1 manifold/rails/HEI ignition retained....still batch fire speed density....

Rotonda

The debates about MAF vs Speed Density and batch fire vs. sequential fire injectors are a chimera for aftermarket/add-on units. Manufactures have gone to Mass Air Flow and sequential fire injectors primarily to meet increasingly stringent emissions targets. With fairly complex ecu's, software and additional sensors they will also produce somewhat more power and fuel economy (though this may not be observable under real world conditions and driving habits).

Any of the currently available high pressure systems (45 lobs or more fuel pressure) will give you better starting, response and fuel economy than a comparable engine using a carb. This includes MAF, Speed Density, batch fire or sequential fire injectors. The real world differences from the drivers seat are minimal and fall into the same category as arguments about which brand of spark plug gives the most performance.