Whats the difference between EFI, TPI, DFI, and others... Are there any really good sites for Fuel Injection information (or corvette related FI)?

 

There are several different styles of fuel injection. TPI is Tuned Port Injection. This is basicly the current fuel injection on corvettes from '85 to now, give or take a few changes.
It has 8 fuel injectors pointing at each cylinder & it also has 8 seperate ports that feed air into the cylinders that are suppose to be all the same length, hence the name 'Tuned Port'. This is also the most expensive type of fuel injection. (not counting the early Midyear fuelies)
Accel makes an aftermarket setup $$$

The next step down would be Multi-point. (MPI) This has the 8 seperate injectors
similar to TPI, but it uses a common throttle body to control air intake. The intake runners are not the same length as the TPI, so some cylinders will have a power imballance. (even though it has an imballance, it is an excelent system) The throttle body looks similar to a carb - positioned in the center of the intake manifold, but it only meters & controls airflow. The intake with this style is called a dry intake since no fuel flows into it.
This type is much less expensive than the tunned port. Edelbrock makes a Multi-point system

Lastly, there is a Throttle Body Injection (TBI)
This is a system that is basicly like a carb, but it uses 2 or 4 fuel injectors located in the throttle body unit (similar to the throttle body for the MPI setup) and it uses the intake manifold style designed for a carb (wet intake) This is the least expensive type & also the least effeceint system. Holley's Pro-Jection uses this setup.
Holley recently released a Pro-Jection and they are calling the computer or brain "digital".

Another difference that seperates all of the above systems is how they meter or measure airflow.
The less expensive models measure a pressure drop in the manifold and are considered manifold density FI systems.

The high end systems use an air flow meter - by a vane that moves or a heated wire that is cooled by incoming air.
The amount of sensors for a given setup also determins cost as well.




[Modified by 71coupe, 11:56 PM 9/13/2001]

 

Did they ever check if the airflow in each port of a TPI is equal? I've looked at both TPI and MPI and serisouly I'm going for a MPI with ram air cause I don't think TPI is worth the hassle (and it looks ugly IMO)

 

Thanks very much for the info, that clears it up.

 

Lohkay
I think all of the runners are equal. The problem is that they are all connected at the inlet by a central "box" if you will.
GM's main competitor, F@rd, tried to make that same "box" more equal.
That's why it looks so wierd.

I think a Multi Point system is the only way to go for a conversion.
IMO



[Modified by 71coupe, 11:40 AM 9/13/2001]

 

TPI was used from the mid 80's to early 90's. It's not the best FI, IMO. Tuned port refers to tuning intake runners and in the case of GM TPI it is tuned for a low rpm range. Stock TPI's run out of umph at less than 5000 rpm. TPI has been made in both SD (Speed Density) and MAF (Mass air flow) versions.

GM TPI is also MPFI. All MPFI means is multi point FI. Since TPI has 8 injectors it is MPFI.

The LT-1 and LS-1 engines used from 92-up didn't get a special name like TPI did. They're usually just called MPFI or SEFI (Sequential Electronic FI) on the later models. They use short runners with a common plenum and the throttle body is front mounted with either one large (LS-1) or 2 smaller (LT-1) butterflies. These are much more suitable for high rpm and make power well over 6000rpm. They are also noted for extremely flat torque curves, albeit with less low end torque than TPI.

Now for the aftermarket... Accell DFI refers to Accells controller. This is just the computer. In addition Accell offers complete systems in several configurations, such as the Stealth which is a low-profile system similar to the LT-1, and the Superram with longer runners.

Accell, as well as Holley and Edelbrock offer top-fed systems for retrofits. These look like single plane manifolds with a 4bbl throttle body on top. They are all speed density.

There are a multitude of controllers on the market, all the way from stock GM controllers that can be used, to mid range aftermarket controllers such as Accell DFI, Holley Commander 950, and Edelbrock Pro-Flo, to high end such as Motec, F.A.S.T and Electromotive. The high end controllers often offer such things as sequential fire injectors and wideband O2 sensors. Some even offer staged injectors where a small injector is used at idle and low rpm and a larger one kicks in at WOT (total of 16 injectors on a V8). Most of them (Except stock GM) can handle super/turbo charging as well as control a nitrous system.

 

Would a RamJet crate engine be considered "stock gm" and therefore not be suited for super/turbo charging and nitrous?

Also, for drag racing, I'd probably want a TPI system rather than a SD system, right?

 

The RamJet engines use GMs marine EFI controller. I don't know if they have a version of it that would be able to work with supercharging, but I doubt it. They (GM) don't let you inside the controller to play with parameters. It's pretty much a sealed box.

TPI is the last thing you'd want for drag racing. To build a successfull drag engine you need high rpm. Visit the engine mods section on the forum and you will see what the C4 guys (originally TPI 85-91) do for dragracing. They either completely modify the TPI base and runners or scrap it for a more high-rpm setup.

Also TPI has nothing to do with SD. TPI is the type of intake base/runners/plenum. SD (Speed Density) refers to how the controllers measures how much fuel the engine needs:

SD: Rpm and manifold pressure is used for a base of the fuel demands. It is further refined by air temperature (hot air = less oxygen = less fuel needed). The system never truly knows the amount of air (in cubic feet/minute) that is ingested, but extrapolates it. Basically, the controller knows that when intake vacuum is 5" and rpm is 4500 that the engine is using 500 CFM of air, and thus it needs to add x amount of fuel.

With SD, if you change the efficiency curve of the engine by porting the heads, changing the cam etc, you need to re-program the controller. This is since at the same 4500 rpm as in the example above and the same 5" of vacuum, the engine may now use 550 CFM. However, the controller still adds the same amount of fuel so now it is running lean.


MAF (Mass air flow) is more sophisticated. It uses a sensor placed before the throttle body that measures the mass of the incoming air. Priciple of operation is the sensor has a heated wire and measures how much current it needs to send through the wire to maintain a preset temperature.

With MAF you can change cam, port heads etc and the mixture will still be correct. No need to re-program. Drawbacks are increased cost and that the MAF sensor itself is a restriction.

A correctly programmed MAF system runs the same as a correctly programmed SD system.

Depending on model year, TPI equipped cars have been both MAF based and SD.
AFAIK, no aftermarket EFI systems are MAF based.

 

To add a little to Zwede's excellent post. Several of the "second" tier units, such as the Accell and Edlebrock PRO-Flow are sequential units. Another option with the aftermarket units is that most can be reprogrammed, either by hooking them to a laptop computer (Holley and Accel) or via an integrated hand held controller (Edelbrock).

And finally when I was planning my system I found that while MAF is said to be more sensitive it does not respond well to modest modifications to your engine, SD on the other hand is said to be much more addaptive.

-harry

 

I've read that some speed density systems (manifold density) require a minimum vacuum signal to work properly, which is something most drag engines don't have a lot of.
If you want to drag race, it's hard to beat a Victor Jr. with a good carb. Put the extra money in the heads and bottom end.
Keep it simple.

 

wow, you guys sure know your EFI...

So TPI is a no-no for drag racing, what should I be looking at should I insist on FI? MPFI w/ SD? Can you put these units on any engine? (Like a 502HO for instance?) Also, what do you do to ignition with an aftermarket EFI setup? I know the ramjets (which i'm not very gung-ho on anymore) have a turnkey ignition system, do any of the aftermarket FI systems come with ignition systems, or what ignition systems should I look at?

Where do you draw the line between added performance and cost effectiveness? How fancy a FI system is worth the money. It sounds like if you were rich, you could spend as much on FI as the engine itself... unfortunately I don't have that kind of cash. But I'm looking for a quality FI setup for peak performance-per-dollar. Plus eventually I'll want a super/turbo charger or Nitrous or something....

 

Btw, thanks for all this info, sorry if my questions are a little on the beginer side... I'm pretty new to this.

 

This looks like something I should take a look at: http://www.jegs.com/cgi-bin/ncommerc...6&lastcat=2337

With a ZZ502 perhaps...

unfortunately, thats like $9.5k between the 2...

How does that accel one compare to this: http://www.jegs.com/cgi-bin/ncommerc...6&lastcat=2337



[Modified by Bifkin, 6:46 PM 9/13/2001]

 

If it were me, I would either go with the Edelbrock multi-point or that Holley multi-point in your previous link.
Make the Fuel Injection you first purchase, then get everything else (ignition, cam, heads, exhaust) to match the F.I. system.

 

A couple of point to add to the topic.
*They are making after market wiring harnesses to convert Rams over to Closed loop. The current ECM is open only.
*MAP's are good as long as you live by the rules. Cam duration under 220 at .50 and at least 15 psi of vacuum. And Steady.
*As far as racing. Check out Beach bum's site on the C-4 forum. He's running 11's with a 383 TPI system. Cool videos of him trashing vipers on his site. So racing a TPI system is not a handicap.
Good Luck

 

Electromotive makes a very trick system that uses a crank-fire ignition system. Not only does it not use a distributor, but the system knows exactly where each piston is in it's stroke. The Electromotive system uses a custom designed manifold and includes the whole ignition system. Unfortunately the system (for a big block) costs about $3,500. The Electromotive uses a MAP system. It is a VERY nice system.

I talked to a guy from www.force-efi.com yesterday who was very helpful. We discussed my application (street driven fast C3 with a 454) and he actually suggested the Holley system. He says for the money it really can't be beat. The other option is the Accel DFI, but you have to setup your own manifold.

 

Take a look at my webpage in the sig below. I recently installed the Holley MPFI on my '71 454.

Be aware that a carb will make the same power as EFI. The difference is driveability, cold starts, no vapor lock, etc. Basically, it makes an engine much more liveable and driveable. If all you're doing is racing, go with a carb. If you also want to drive it on the street everyday, EFI is probably worth the expense. Just don't expect any power gain with the EFI over a good carb.

The Holley system is hard to beat. You get everything for $2400. It includes the manifold, your choice of injectors, sensors, controller, fuel pump, throttle body, wiring harness etc. The only thing it doesn't come with is a distributor. You can use any HEI or points and make it run, but if you want to control the timing curve you will need some form of computer ready distributor. I got a 82-up HEI from accell and it plugged right into the harness and gives me full control over the timing.

The holley system can also be used with boost (super/turbo charger), as well as nitrous and it will work with a regular GM knock sensor if you want knock retard (very nice especially with boost or nitrous).

 

I added TBI to my 73. It's not a race setup for sure. What it does provide is a inexpensive replacement for a carb. No more floats or chokes, and it operates at a reasonable pressure. I have a setup from a 87 van including the harness & ECM (mounted under drivers seat). I drive it almost daily. It's reliable, gets 18mpg w/4.56 gear & 700r4, and fits under the stock ram air.

 

I have a bored and stroked ZZ502 (532 cid) in a 1980 Vette.
I kept the 850 vac secondary Holley for about two months and finally got one of the first Holley Commander 950's for BBC with oval port heads. The system works well - great driveability, and after appropriate time spent programming, it handled (very well) a totally GOOFY mechanical roller cam! After almost two years I found out that you MUST do the following:

:smash: Ensure that hot lead from the alternator to the battery is at LEAST 8 gauge wire with soldered and heat shrinked ring lugs. The ECU likes 12VDC with no noise caused by corroded connections. Ensure NO automotive crimp connectors are used anywhere in the EFI wiring harness. They are NOT weathertight. They corrode - and eventually cause power degradation to the ECU. MAke sure you main ground leads in the motor mounts are good and clean.

:smash: Make sure the fuel line and return lines are BIG ENOUGH. Do NOT use any of your original fuel lines. Use the AeroQuip stuff - be safe!

:smash: Take the time to properly program "steady state" (constant MAT, MAP, TP an RPM) fuel delivery cells. No accelleration here. This will take 40 hours of "wimpy" steady state driving. Put in the time and enjoy the future benefits.

 

As for the distributor qustion, one of the requirements I had was to be able to continue using my tach drive distributor. The issue comes in that sequential injection systems need to know exactly where the engine is in strock and firing order, batch on the other hand just needs to know where the engine is in it's stroke.

The Edelbrock system has a triggering mechanisim that fits into a stock distributor, well on the older distributors it requires about an hour with a Dremel tool, but it fits quite well after that :D . Below is a picture of my distributor during the conversion process, the yellow arrows show where I had to work the Dremel tool.



-harry


[Modified by Harry74, 8:39 AM 9/15/2001]