how much does fuel does TPI save? What is the average mpg difference?

 

My 83 K20 truck went from 14 mpg with the stock 350 to almost 18 mpg with a bone-stock L98 Vette engine. I think it might have been a touch higher if I had TPId the original 350 in the truck. It has a 700R4 trans and 3.42 gears.

I had an 89 305 IROC that got about 18 mpg city with 3.55 gears/5-speed.

My Vette gets 17-18 city with 3.7 gears and 700R4. I think it would be 18-19 with 3.36 gears.

I would use 3 mpg increase for a "safe" number on a relatively stock-engine retrofit. I don't think 4 is unreasonable.

 

TTT-I am interested in others experience.

 

only bad thing about TPI is that you choke the motor above 4700rpm or so. We are porting the heck outta the intake, runners and plenem on our 88 so it can feed the 383 thats getting tossed into it. Should be good for about 5800rpm. If you want more rpm, you need to go with a superram or slp big mouth intake and runners.

 

I looked at TPI systems and came to the conclusion that they wouldn't
be worth a swap for the mpg savings...

The number 4 appears to bear that out...

However EFI has a bigger mpg savings and looks like a better route
to take. Unfortunately, its about a $2k step...

Good luck - take care of the car, or it will take care of you!

 

well im getting 18-22 mpg with 3.70 gears 700r4 trans 510 roller cam,ported intake and runners gets 5300 rpm out of it.

 

When I bought my '72 L48 4 speed car, it was mostly stock 336 rear geared drivetrain, engine rebuilt with mild cam.....it went from 12-13 around town to 18+, and 24 on highway, even crusing 4 grand at 80.....

now, with the newer engine, a roller 355, ZZ9 cammed either aluminum or iron heads....headers, H pipe, etc....and 700r4, same 336 rear....it's doing about 16 or so around town, and 19 on the highway...got nearly 7+ years on it now, and about 80k miles....lost lotsa compression, I suspect maybe that K/N air filter on the intake snout is not filtering quite as well as suggested.....

GENE

 

Good luck seeing anything over 5,500rpms w/ that L98. I owned a '91 L98 Vette for 10yrs and did it all, ported plunum, intake, simeased runners etc. We installed this on my roomates 383 and SEVERLY choked this engine, the car would run great in the 1/8 )L98 are torque monsters) but after the 1/8 it would fall on it's face. I sold him my LPE SUpper Ram, base intake and 588mm TB and 6,000rpms+ is not a problem.

TPI are great for street light grudges and MPG, but as far as Serious performace, I'd look elsewhere IMO.

 

TPI is EFI, it is multi-port electronic fuel injection (Tuned Port Induction). You might being thinking of sequential port injection that fires each injector individually while TPI is bank fired (fires driver side bank or passenger side bank 1 side at a time).

 

> TPI is EFI...

Yes, you are right...

I was thinking of the sequential fire stuff. It seems the systems like Zwede has
gets better mileage than the TPI systems.

 

Assuming $2.50/gal fuel it costs $178.58 to go 1000 miles at 14mpg. It costs $138.88 at 18 mpg. Using that it takes roughly 25k miles to pay back $1000. Depending on what you can do yourself, that may or may not be fast enough. You can do TPI pretty cheap, say $300 unit, $100 fuel pump, $100 f-body harness and computer, and $100 for a PROM. At that rate it pays off in about 15k miles.

You also have to take into account what that does for you. I can take a bone stock low HP long block and make 300 hp for less than $1000 upgrade with TPI. Granted, the next chunk of power is a lot of money. Or I can change cam, intake, carb, and maybe heads and get 300 hp. It could also cost me around $1000 to get there. The next step up in power is not as expensive, so to me you have to answer 2 questions:
1) How much power do I want? If 300 hp is enough, then TPI is good.
2) Many people consider this swap when they have something break anyway. If you already have to spend $200 on a carburetor, then to step up to fuel injection pays back even faster. ($400~10k miles)

The low end torque of a TPI is an added bonus. Also your exhaust is cleaner for whatever that is worth to you. You have a system that is optimized many times per second instead of a system (carb) that is optimized the day you tuned it for the temperature and altitude you were at that day. My .02

 

Don't have the 4 grand for an accel superram kit right at the moment. And it really isn't worth it in a daily driver. :P

 

Taken from www.megasquirt.info :

There are two common sorts of injection:

Throttle body injection - usually one or two injecotrs for the whole engine
Port injection (aka. Multi-Port) - one injector per cylinder
Then there are three common modes of injection timing:
batch - all injectors fire at once, but not timed to any specific cylinder,
bank - ½ the injectors fire at once, but not timed to any specific cylinder,
sequential - each injector fires at a specific point in the 4-stroke cyle for each cylinder (i.e., 8 independent timing events)
Throttle body injected cars are usually batch or bank fire, simply because of the geometry. Most port injection set-ups before the mid-1990s were bank fire as well (including GM Tuned Port Injection for the 305/350).
Sequential injection requires:

as many injectors as you have cylinder, with one dedicated to each cylinder (i.e., not a 4 injector TBI on a 4 cylinder).
as many injector drivers as you have cylinders,
and also requires a camshaft position sensor (a crank sensor is not adequate for a 4-stroke cycle engine).

The benefits of sequential injection are that:

you may get slightly better mileage and lower emissions at low engine speeds,
you can tune each cylinder's fuel amount independently (if you know how).
The effect on maximum horsepower is general negligible.

Al Grippo has an EFI332 controller on his vehicle that can do sequential injection. As a real-world test, he programmed his EFI332 ECU to start the injection when the exhaust valve closed (intake already open), but if the pulse width was such that injection could not finish by the time the intake closed, then the ECU advanced the injection timing so the injection would end when the intake closed. From this theoretical optimum, he varied the timing through the whole cycle and confirmed that what he picked as default was optimum based on the highest rpm, lowest map reading. This was all done at idle. There was a small but measurable difference if the timing was such that injection took place coincident with the exhaust being open.

However, sequential injection does not necessarily mean you are injecting into an open intake valve all the time. The intake valve is only open less than 30% of the time in a typical 4 stroke engine. Once you are trying to produce more than about 25% of maximum HP your injectors are firing for longer than the intake valves are open. If your maximum HP is correctly calibrated to a safe 80% duty cycle, your injectors are injecting well over 50% of the time on closed valves.

At higher rpms, it becomes increasingly difficult to inject while the valve is open. For example, if your Req_Fuel = 15.0 ms, and your maximum duty cycle is 85% then the interval between injections cannot be closer than 17.6 ms. The time available to inject during the entire 4 stroke cycle is:


timecycle = 120/RPM
the intake is typically open for less than 240° of 720° in an engine cycle in a hot street engine, about 1/3 of the time for a complete cycle. So:


timeinject = 40/RPM
and


RPMmax = 40/timeinject
Using the numbers above,


RPMmax = 40/0.0176 = ~2300 rpm
Above this RPM, it is not possible to inject the entire amount fuel through the open valve at 100% VE and 100kPa. At idle, however, VE may be 30%, and kPa might be 35 kPa, yielding a pulse width of ~1.8 milliseconds, which certainly could be injected during the intake valve opening. So sequential injection is primarily effective at idle, and not much different from batch injection as pulse widths get larger at higher engine speeds and loads.

In any case, when fuel is injected while the valve is closed, it will simply stay in the port until the valve opens. In some cases, this period of time may allow enough heating of the mixture to better vaporize the liquid fuel, improving efficiency and emissions.

So the effect of sequential timing is relatively minor, and applies mostly at low rpms. The OEM manufacturers use it mostly for emissions reasons (most of the OEM fuel injection systems up to the mid-90s were bank fire). However there is a real benefit in sequential systems in that you can do individual cylinder tuning (if you have the time, skill, and equipment).

-------------------------------------------------

Let me know if you have any questions about injector calcs...btw, it's all on the above site.

 

To address the original question:
GM TPI was sold in two configurations - Speed Density and Mass Air Flow.
Speed Density depends on a chip to map air fuel mix and spark timing. Mass Air Flow uses a chip but has the ability to adjust AF and spark within limits. In both cases the chip was designed by GM for the OE components: trans, differential, air filter, exhaust, cat converters, fuel injector size, fixed fuel pressure, etc.

If you install one of these systems in a vehicle with different components - larger displacement, cold air, dual exhaust, hi flo cats, Muncie, different differential ratio - the chip will not be right for your vehicle and your performance -HP, TRQ and MPG will suffer. To use hot rodders terminology, your carbureter and distributor advance are not tuned.

Tuning tpi is not as simple as inviting Lars over for a beer or two. You can take your chances with a mail order chip burner who will map AF ratios and spark curve based on his experience and the engine and trans specs that you supply. Or you can invest in a dyno session at a shop that has the necessary computer hookups and software to record the curve of your existing chip and then burn one to correct the AF ratio and spark curve for best performance. This session should also include fuel pressure adjustment and perhaps a change in injector size.

This is a very long way of saying that to compare gas mileage of tpi retrofits, you need to know a few other things about the vehicle components and about the tpi system components.

As you can see from my sig, I have a Speed Density tpi and, while I haven't gotten it perfectly dialed in, I'm very happy with it.