when i began the project of modding my stock TBI car it was suggested by my buddy that i was making a major mistake by not "just throwing on a carb". he suggested that performance wise i would be better off. maybe so. day one after mods car ran poorly giving support to his opinion that i made an error going the route of modding and leaving TBI in place. no tuning done as of that date 4/2003. now keep in mind this is a individual that has many years experience drag racing and is a competent engine builder but little experience with EFI tuning. first 18 months i had struggled to get tune in line without WB help. late last summer the WB comes into play and i am more confident and more experienced. seems light at end of tunnel. also late fall my friend and i add the bigger cam and this further reinforces his belief i am nuts adding a larger cam as car day one after 2nd cam swap car runs poorly. further reinforces his opinion. this is on prior tune/prior cam and not yet logged WB nor winaldl. that process starts anew 11/2004 and i have first aldl log and about 10 WB logs on new setip(phase 2). AE was the issue with new cam and it is somewhat clear as to what i need to do.

the Q is with my level of mods how is it that a person that knows carbs can just "throw on a carb" make the necessary changes to fuel pump and distributor and drive away with a car that runs nicely. is a carb so much easier/ faster to tune? it has been said the "tune" is so much better with a computer controlled car vs carb. emmishions and the like. is that true only for a engine combo with a intake/cam/head stock configeration that produces significant intake velocity and low VE and mild performance where the EFI/TBI can shine? add a decent intake/larger cam/heads does it appear the carb is a better choice with overall better drivability? disregard fuel mileage benefits in this compare. in therory it seems the TBI design seems similar to carb(manifold) just has an TPS/MAP/02 feedback via ecu. think carb needs to be complimented in some way?

 

Tbis operation is fundamentally different then a carb. With tbi, the fuel needed is inferred from the manifold pressure and teh values entered for the BPWc and the VE tables. Its entirely dependant on teh tables and there is no way for a speed density system to know how much air its really taking in. Anything that changes the efficency of the motor will throw the entire cal. to pot. After my head swap, my motor wouldnt even run on my old SD calibration that was set up for the faux 883's that my crate came with.

With a carb, the pressure differential in the venturies is what controls the fueling. This means that, unlike a tbi, the carb can see how much air its taking in and so long as its calibrated properly, it will still work ok for the most part even after mods have been done. Any system that can see airflow will immediatly have an advantage after mods since its metering of the fueling will be less, or even not at all dependant on whats happening in the motor underneath or behind it.

 

good point. more clear now. OK. then are you suggesting carb vs TBI on a modified engine possibly carb may have some advantages to consider?

next Q. so take one step further. then a MAF car has the ability to see the air entering engine. correct? if so why do i read the SD TPI is better than the MAF? am i misinterpreting? what is the advantage of SD vs MAF when it comes to a TPI system/ECU?

 

You need to compare apples to apples.

If you want to talk Holley vs oem efi then the Holley is easy to get going. If you had a simple enough efi then they would reguire about the same level of effort to tune correctly.

Take a set of Webers, and a Min-ram, and try to taylor the Webers to work as well as the EFI, and you'll see what work it takes to get a carb to be as good as an EFI. Start making you own emulsion tubes, and custom idle jets, and the carbs get EXTREMELY labor intensive.

Doing anything CORRECTLY takes effort. Effort can mean having a huge learning curve.

Given time, you won't even see carbs on lawn tractors.

Try a blow thur carb setup to equal what a 87 Buick Turbo Regal does, and get back to me about how good carbs are.

 

my knowledge is strictly based upon the SD TBI 7747. i know little of others.

were the aftermarket initially developed more simplistic in approach? what sensors did they utilize or better yet which did they not utilize? i think i read the IAC may have been ommitted in earlier versions. i had the opportunity to see an early issue edelbrock multi point EFI system installed on a chev small block at a local small town auto show. i believe the driver adjusted the A/F from seat on a "module" of sorts. seemed quite simplistic. did not have the time to ask many questions. seems it was VE tables, AE, and possibly PE. not sure if spark was part of system? werre the early aftermarket systems designed for simplicity so beginners would not get frustrated or were they just under engineeered as compared to GM being state of art? i wish i had some car mags from back then that highlighted the coming of age in aftermarket EFI.

 

The SpeedPro, Fast, Holley, were all based on John Meaney's work. Needless to say he, as well as other engineer's have had a steep learning curve. The Accel Gen VI, was the first mass produced aftermarket that really caught on. If you look at the tuning software, you can see it's shortcomings, at a glance.

The early Holley was an analog system with trim pots for tuning. Simple yes, and a sudden serious weather change would take a retune to get it back to being close.

If you look at the newest offerings, they've figured out it takes a serious bit of sophistication to get EFI right. They're almost to being at an oem level now with the BigStuff system. By the time they get the aftermarkets Correct they'll be just as complex as the oems.

BTW, John Meaney holds some of the original MSD Patents, if that tells you how long he's been at things.

 

Stick with it Ron, you can tune it to run better than it will with a carb.
Last week i swapped a bigger cam into mine (224/224 @0.050", 0.560 lift, 110 LSA) and after a bit of work, it is running like a dream! It does still need a bit more fuel up top, but its not gonna be a problem. Idle is 60-62kPa MAP.

 

SD tpi is better because you dont have that weenie POS bosch MAF. It cant see much airflow so immediatly youve lost your advantage since youll have to lie to the computer to get what you want AFR wise with a decent motor. The solution would be to run a larger MAF for an LS1 and make some minor but perfectly acceptable changes to the calibration and maybe a few code tweaks. The only drawback is you have to make a converter. Some people hear soldering, reading schematics, and some math and they immediatly clinch up. Do that and the MAF based ecms would be on equal footing with the SD ones. I sound like a broken record by now, but Im saying this because Id really like to see some quality MAF setups that where done right from the get-go. This is especially true of some of those vette guys. Theres alot of talk coming from that crowd, but Ive yet to see any useful R&D put towards solving the problems that come up with an early MAF setup.

There is no clear cut advantage to either system. They each have their pros and cons. SD is more intuative and it makes real world sense, but there are lots of variables involved. MAF drastically cuts the number of variables involved and its not really coupled to the motor but the tuning now is just a bunch of numbers in a calibration table or tables. Theres also the fact that theres additional parts and the intake ducting and such becomes much more critical.

As far as a carb goes, Id never even consider it in this day and age for a car thats driven frequently. Youd probably have to bend over backwards to get the precision, flexibility, and drivability that efi has.

 

Simple = crude. After writing alot of my own stuff Ive found that there really is no simple way to doing efi. Its an engine, its complicated, and you have to do alot of stuff to at least get it to do something resembling running right.

 

MAF vs SD is funny. Everything has it's place and from my experience MAF is a lot easier to get close. It's similar to carb in most cases but there is a lot of MAF code that is really annoying when applied to a unique motor combo. I like SD when the code is useful.
When it comes to TBI vs Carb I tend to have one question for the person; what is your ideal goal and purpose for this vehicle? From their answer I've already determined if they'd have the ability to tune the TBI or not. Some times I tell em to go carb to get the ball moving so to speak.
TBI is very capable but it's got a few problems, one is the fueling. If I could offer only one piece of advice to TBI guys it would be to invest the $125 for tuning equipment and crank up their fuel pressure. It's pathetic how often I find TBI setups TUNED that have the injectors going static and the combo just flat. I've seen it happen in port injection too but since TBI is this weird and obscure EFI it's problems are all too easy to just blame on the 3 letters T B I .
Carbs are just like MAF, they measure the air and deliver fuel according to the direct measurement. This is why you can pretty much bolt on any carb or MAF onto an engine and expect it to get good fueling.
A major preference of mine is having the timing based on manifold pressure and not MAF derived load. It's just easier for me, maybe not others... personal preference.

 

Aftermarket EFI (I work for an aftermarket efi company by the way) is generally crude, and compromised for the sake of simplicity. And once you feel how good it can be with a highly tuned factory setup, and also have a wideband (that evil eye just pointing out all the flaws), you start to get spoiled. Nothing is ever good enough any more. It's like a disease, or an addiction, or something.
But, 1980's code doesn't have THAT much power and sophistication. But, it's not easy to get it to run engines that it wasn't designed for, and the .ecu's are generally incomplete and the algorythms are quirky.
But in all honesty, an 85% calibration will drive quite well (i.e. good enough) under most conditions, and most average schmoes won't know the difference (when they have nothing to compare it to). But when it's a daily driver and such, little problems get annoying. Little problems usually take more sophisticated algorithms which are also more difficult to tune correctly, and much more difficult to understand at first glance.
What's my point, nothing really? But, EFI is not for the faint hearted. It's also not for those unwilling or unable to learn. It's not cheap (usually). It's not foolproof. It won't fix an engine problem and it won't fix itself. It doesn't like to "partially" work. It doesn't "Learn" everything. It's not easy to lie to. You can't adjust much with a screwdriver. AND: It's not perfect.
Same for carbs, but carbs won't strand you in quite the same way. And as long as you choose the right carb (not too big, kind of like injectors and TB), then you'll be OK on mild engines. Go wild, and you'll be spending more time on your carb than you would with an aftermarket EFI, or just live with terrible drivability (I know a guy that wanted is SC'd 540 Methanol engine to idle terribly, even with EFI, almost breaking them (huge street slicks) loose during the idle surging).

 

The LV8 never made much sense. I guess GM was just cheap and didnt want to use a MAP sensor in addition to the MAF. The MAP sensor to pressure is what the MAF is to flow.

As far as the code goes, its surprising what they did manage to squeeze into these computers, and alot of this isnt even covered in the definition files, which can make tuning all that much harder.

 

Not really. IMO, it was just more about evolution to get to where they'd use both. The new stuff is a mix of MAF, and MAP.

I expect to see both being used in the future, for the performance crowd. MAP for the transistional stuff, and MAF for WOT. Again, it's a matter of evolution. The aftermarket is still playing catch up, but, I think at some point they'll finally get things better then oem, as far as simplicity, and sophistication, goes. Thou, at the rate they're going, we might be using fuel cells, before they get there. The latest gen of aftermarket seems to have fallen prey to the eye candy brigade, IMO.

 

I could see that. Where GM was proving to themselves that they could effectively have a way of running MAF or MAP incase one fails... but then came along a thing called processing power and OBD-II to shake their world.