TBI vs MAF

[paint.roper]

What's everyones opinion on the two, which is the better conversion? I've talked to a few offroad shops and they recommended TBI.

 

[lonicus]

your going to get a lot of opinions on this - do a search, loads of info on this site about both.


If your engine is in good shape mechanicaly, and you want as simple as possible swap, the TBI might be the way for you to go.

If your engine is in need of rebuild, you may want to think about just going for a full SEFI system from a 89-93 mustang. This is what i did, replaced the engine with a '97 Explorer and '93 computer. obivously this is more involved and costly, but I would venture to say the SEFI is a better system then the TBI.

Do a search, and check out fordfuelinjection.com that will help you out in the decision making process considerably.

 

[Broncobowsher]

Shops will sell the TBI, that is something they buy, bolt on and charge money for. They are after profit.

MAF isn't a fuel injection, it is a part of fuel injection. EEC-IV more specificly. MAF is the better of the two way of controlling the EEC.

 

[paint.roper]

I am looking for more reliabilty and performance. I have been doing a lot of research and it seems like it's all personal preferrence. Each side says their application out performs the other.

 

[Broncobowsher]

I never seen a TBI out perform an EEC-IV SEFI injection.

TBI is generally a GM throttle body EFI off a late 80's or early 90's truck. GMs bargin aproach to making EFI, make something that will drop on top of a conventional carbed intake. Properly tuned they run like a properly tuned carb. There are a handful of companys that make kits based on this sytem with a semi-custom chip to try and match your engine. For the most part they start, idle and drive around very well. Seen a few on the dyno, under load both were so far out of tune it pegged the dynos wide band oxygen sensor. Biggest design flaw is they are guessing at airflow. Look at RPM, manifold pressure, spit out some fuel. Closed loop driving it will tend to compensate for having the volumetric effiency of the engine not programmed right. Under load it goes open loop and all bets are off on how well it will run.

The mustang based EEC-IV computer ('89 to '93 has the MAF) is more able to adapt to an engine. It looks at the airflow, knows how much air is entering the engine, figures how much fuel it needs, knows how big the injector is and squirts the right amount of fuel. You can play around with volumetric effiencys of an engine (cam and heads) and it will change the airflow through the engne. But the MAF will give readings and for the most part the computer will still get it right or at least very close. Much better choice to put on a non-matched engine.

If it doesn't have a MAF, it is speed density based. Which is a perfectly good way to manage fuel injection. Trouble is the computer must be matched to the engine just right for it to stay tuned and working right.

Shops are in business to make money. TBI systems are a better business deal for them. More profit for less work. Buy a kit, bolt it on, cash your check. The mustang based EFI is a better system, but not as fast or easy to install. No quick mail order "kit" with everything in it. They actually have to think and work. Often using used parts which are not as pretty and profitable as shiney new parts.

 

[Nightstick]

I never seen a TBI out perform an EEC-IV SEFI injection.

TBI is generally a GM throttle body EFI off a late 80's or early 90's truck. GMs bargin aproach to making EFI, make something that will drop on top of a conventional carbed intake. Properly tuned they run like a properly tuned carb. There are a handful of companys that make kits based on this sytem with a semi-custom chip to try and match your engine. For the most part they start, idle and drive around very well. Seen a few on the dyno, under load both were so far out of tune it pegged the dynos wide band oxygen sensor. Biggest design flaw is they are guessing at airflow. Look at RPM, manifold pressure, spit out some fuel. Closed loop driving it will tend to compensate for having the volumetric effiency of the engine not programmed right. Under load it goes open loop and all bets are off on how well it will run.

The mustang based EEC-IV computer ('89 to '93 has the MAF) is more able to adapt to an engine. It looks at the airflow, knows how much air is entering the engine, figures how much fuel it needs, knows how big the injector is and squirts the right amount of fuel. You can play around with volumetric effiencys of an engine (cam and heads) and it will change the airflow through the engne. But the MAF will give readings and for the most part the computer will still get it right or at least very close. Much better choice to put on a non-matched engine.

If it doesn't have a MAF, it is speed density based. Which is a perfectly good way to manage fuel injection. Trouble is the computer must be matched to the engine just right for it to stay tuned and working right.

Shops are in business to make money. TBI systems are a better business deal for them. More profit for less work. Buy a kit, bolt it on, cash your check. The mustang based EFI is a better system, but not as fast or easy to install. No quick mail order "kit" with everything in it. They actually have to think and work. Often using used parts which are not as pretty and profitable as shiney new parts.

I couldn't agree more, well stated sir

 

[Dave]

I agree with everything mentioned above. A MAF sensor could be used to measure the mass of the air on a TBI system. I think you are looking for recomendations between TBI and multi point(port) fuel injection. (one injector at each cylinder) SEFI or sequential electronic fuel injection is an implementation of that. MAF or Mass Air Flow is one of several different ways for the computer (EEC) to calculate the amount of air that is entering the engine. Other methods were pointed out above.

For all practical purposes in our typical applications none of these systems are usually optimized or tuned to anywhere near perfection. A properly setup carb will kick ass over a poorly configured TBI. Or a properly designed TBI will kick ass over a poorly configured SEFI. As far a bolt stuff goes I think the SEFI systems come the closest to optimum based on the adaptability of the ECC to tune itself. This is one reason I'm a big fan of doing entire system (engine and EEC) swaps from the donor vehicle.

Then there's the whole dry runner vs wet runner argument. Carbs and TBI are wet runner systems in that the fuel air mixture travels through the intake manifold. Port injection systems are dry runner systems in that the air is mixed with fuel at the intake valve. There are entire books written on the design and dynamics of both. The main disadvantage of wet runner systems is that it is nearly impossible to get a uniform fuel air distribution between cylinders. SEFI systems do a very good job of that. That makes for a much cleaner running engine. Lots of arguements as to which system will actually get more fuel/air mixture into the engine. I think the main reason that everything migrated to SEFI is more based on emissions and economy than performance.

So pay your money and take your choice. I do SEFI systems with the entire engine and control system as the engineers designed it.

 

[paint.roper]

thanks for all the information guys. as you can tell, i am quite new with the EFI thing. so SEFI sounds like it functions better in the fact that it is distributing fuel to each cylinder as required, vs just opening the flood gate and letting it pour through. Once the system is installed, how stable is it being matched up to an early model engine that was not originally built for electronic? would i be better off just dropping on a Q-jet carb and getting a new model engine? if so, what year and model should i look for from the donor? i woud like to stay with the 351w.

 

[Ourobos]

Now MAF vs. Speed Density, that would be a good debate.

 

[DirtDonk]

I am looking for more reliabilty...

Well, GM used it on cars and all the trucks from the late-eighties to '95, and had a very good track record of reliability. So there's no argument against their reliability. Neither is there an argument that the MPFI setups are unreliable either though.

...and performance.

Here's where that personal preference comes in I guess. Because that's about all it would have going for it any more. It's where personal preference has nothing to do with reality.
Sure, someone's uber-tweaked and freaked TBI setup could probably out-perform someone else's under-achiever milk-toast MPFI system, but add equal tweaks, and I don't see how a TBI could possibly keep up with a semi-comparable MPFI setup.

There are plenty of high performance TBI setups running around, so there's no real issue and nobody's saying they're dogs. It's just what level of performance you're shooting for. Or if you're comparing between the two types.
From the O.E. standpoint, if the TBI were the better performer though, don't you think they'd still be making them? They don't, and literally everything using gas a it's motivator is using MPFI setups now. Most GM divisions went that way, while only the trucks carried the TBI banner into the nineties I think. Ford virtually skipped right over it (with a little hiccup in the middle) and Buick was using SMPFI in the early eighties!
Is it cheaper for them? Heck no. Bottom line is that MPFI is capable of delivering better power and fuel economy, while reducing emissions and increasing reliability well beyond the required 100k mile warranty on smog-related items that I think was put into effect a few years ago.
And now they're even tweaking that design, with most factories experimenting, or heading full steam, into direct injection.

Aftermarket? Some real good TBI systems out there. Howell and DFI work sweet. Some setups out there too, that look like a carburetor, but with hidden injectors under the skin. Pretty cool actually.
But here again, I don't know of any reason a TBI setup is going to be capable of better performance, in any category, than a comparable MPFI setup will be.
Cheaper? You bet. But better? Not in my opinion. See? There's that "O" word again. But since I'm no higher-edumacated EFI guru, we have to put anything I say about it into the "my opinion" category.

If you're buying new, then TBI is most likely less expensive. If you're willing and able to buy used and roll-yer-own so to speak, for a Ford it's no contest. You can usually buy a full MPFI setup from a comparable engine for much less than buying a TBI setup new.

So now the opinion quest is in your court! ;D
You do the reading, then you do the math, then you decide what aspects of which type are more important to you (make a list?) and then YOU make the decision.

Can't go wrong either way actually. Just which way is going to make you happier?

Paul

 

[DirtDonk]

Now MAF vs. Speed Density, that would be a good debate.

Definitely!
But only with the O.E. stuff. In the aftermarket, some of the most tweakable high-performance systems are Speed Density based. Those types don't care what type of cam or exhaust or other mods you've made. They either figure it out on their own, or you "tell" it what to do with your laptop.
Cool stuff that...

Paul

 

[Dave]

Now MAF vs. Speed Density, that would be a good debate.

MAF is better.

Speed density computers uses a variety of engine sensors like RPMs (speed), engine temp, barametric pressure, etc to determine how much air is entering the engine. It has to know how much air that specific engine will pump at a given rpm. Displacement, efficiency, cam characteristics, etc must all be known. A MAF sensor just measures the mass of the air that passes through the sensor. It doesn't care what's pumping the air. You could hook the MAF sensor up to a vacuum cleaner and measure the air being sucked in. Quite accuratly in fact. Mass of the air directly translates to how many oxygen molecules per unit time are entering the cylinders. The MAF computer calculates and controls the injector pulse width and timing for each cylinder.

Both systems use Oxygen sensor feedback to tweek, trim, or adjust predetermined fuel schedules or tables in the software. Both systems have to compensate for changing parameters such a wear and fuel quality. Transplanting either system to a engine that differs from the one it was designed for throws these values off. Some OE systems are better at compensating than others but its not really their intended design. Aftermarket systems allow you to tune (program) them to your specific engine.

TBI systems can only compensate for the overall or average mixture of the engine while SEFI can adjust for each individual cylinder. Early multiport systems were not much better that TBI in that they fired the all injectors with the same signal and some were continuous flow like the Bosch (Porsche Audi etc) systems in the 80s. Some were fired in banks. Each head had an O2 sensor and and compensation was made on each bank. SEFI evolved and could compensate cylinders on an individual basis. The newer systems are pretty good at learning and compensating as engine conditions change. If the engine you are transplanting the system on is within the parameters that the computer can compensate for, it can work very well. Eliminating parts of the system like the EGR and air injection put the computer out of the range it can compensate. i.e. Why am I only getting 10 mpg with my EFI...EFI sucks...

The OE 5.0L SEFI Ford systems we have access to seem to do a pretty good job of adapting to 302s. I have not seen a MAF on anything but a SEFI engine. One advantage of the MAF system is idle characteristics. Idle is the biggest challenge for a TBI or Carb to get a uniform charge to each cylinder. Durring acceleration off idle fuel is dumped into the top of the manifold in a crude mannor (accelerator pump) and the fuel swirles, pools, flows on the sides of the runners, etc. Not very optimum. That's why you see individual carbs or barrels on early drag racers. SEFI or multi port eloquently solves that problem. I have seen speed density used on programmable multi port systems that use a lot of boost. MAF systems seem to clip and lag with the rapid pressure changes in some performance engines.