I am planning to swap the 305 tpi in my 86' Iroc with an 88' 350 tpi. What parts will I need to do this swap(computer, etc...), and where would be the best place to get the 350 from? Also I,ve been toying with the idea of going with a 383 stroker, seeing as how a 350 block is used would I have to change any components for this swap also? Any and all help is appreciated, thanks.

 

Welcome aboard.

I'm a little confused. You said "88 350 tpi", and then asked where to get the 350. Do you have access to an '88 350 TPI but the engine is bad, or what?

Basically, the TPI systems between '86 and '88 were the same, with the differences being specific to 305 or 350. The 350's had larger injectors, different PROM tuning, different knock sensor. Oh, the '88 has a different bolt angle for the center two base bolts on each side ('86 would be the same angle for all bolts).

A 383 TPI isn't a very good idea. TPI short changes a 305, let alone a 350 or 383. By the time you replaced everything necessary to support a 383 with aftermarket TPI parts, about all you'd have left would be harness and fuel rails (maybe plenum, if ported properly).

 

Thanks,

Sorry about the confusion, I don't currrently have access to the 88 350 tpi ,but it is the year that I'm thinking about going with. I have in fact found a great place to get a tpi or lt1 engine from. The addresss is www.cdpautomachine.com. Anyone thinking of replacing an engine should definitely look there first. Also, fbodymotorsports.com is a great web site with just about anything you could possibly want for an 82-02 camaro/ta/corvette. I definitely agree with you on the fact that a stock tpi intake system is not anywhere near adequate for a 383, but on the up-side I have found a great induction system at www.tpis.com, it's the mini-ram II. Be sure to check it out, you won't be dissapointed. Again thanks, and I hope some of these web links will help someone.
(Mod edit to fix URLs)

 

TPIS is well known around here. The Mini Ram is pretty much a new system controlled by the TPI computer (some would say it's no longer TPI). Great system, very expensive. If you go that route, you should go with the later SD system, rather than the '88 MAF. More tuneability.

 

Sure SD sounds good, but I know nothing about it and even less on how to go about installing it. Exactly what is Speed Density, how does it work, and how do I install it? Also, what advantages does it have in the area of tuning ability?

 

speed density is nothing more than the computer using the MAP sensor and a couple other factors to calculate A/F. It is actually a little more user friendly to tune but if you think about it, the computer is kind of "guessing." MAF sensors tell the computer how much air and how fast it is travelling, thus converting the signal to air density with the help of the air temp sensor. This is the most efficient way of going about it but you can only go so far with the setup. That is why the speed density setup is more commonly used with high horsepower apps.

If you are swapping from a 305 to 350, the only difference is the prom and the injectors (no counting the internal engine components). It is truly as simple as changing the cam to something a little more useable for a 350, burning a new chip, and buying a set of 24# (minimum) injectors.

 

COLOR=red]Here's an article I found posted on a Car Craft site. Happy Readings to all ![/COLOR] EFI: Mass Flow vs. Speed Density
N Alpha, Speed Density, and Mass Flow Metering

By Marlan Davis
Photography: Marlan Davis

Once upon a time an engine needed three things to run: fuel, air, and fire. That’s what carbs, coils, and distributors are for. Modern EFI engines still need these three elements, but they use different hardware to provide them, and a computer to run the whole process.

Today’s electronic engine management systems can process millions of instructions per second to continuously adjust spark and fuel for optimum performance. The computer regulates the electronic fuel-injector pulse width (the time that the fuel injector is open) and ignition lead with input from various sensors. One of the key things the computer needs to know is how much air the engine consumes under a given set of conditions. Three different measurement strategies have evolved to supply the computer with this basic information; in order of sophistication they are: N Alpha, Speed Density, and Mass Flow metering.

N Alpha
A relatively simple design, N Alpha systems use only engine speed and throttle angle to calculate the amount of fuel needed by the engine. This system doesn’t measure airflow directly; instead, engine load is assumed based on throttle-angle versus engine rpm. The various load-rpm points make up the computer’s lookup table, with the amount of fuel needed at each point manually programmed by the tuner. N Alpha systems work well on engines that operate primarily at wide-open throttle—such as race cars—but are much less accurate at part-throttle than more sophisticated systems because of their relatively simple fuel map. They generally do not have a closed-loop mode for air/fuel correction, resulting in part-throttle calibration that is crude at best when compared to other systems. This also makes them incompatible with modern catalytic converters. Any significant engine change requires remapping.

Speed Density
Speed Density systems accept input from sensors that measure engine speed (in rpm) and load (manifold vacuum in kPa), then the computer calculates airflow requirements by referring to a much larger (in comparison to an N Alpha system) preprogrammed lookup table, a map of thousands of values that equates to the engine’s volumetric efficiency (VE) under varying conditions of throttle position and engine speed. Engine rpm is provided via a tach signal, while vacuum is transmitted via an intake manifold-mounted Manifold Air Pressure (MAP) sensor. Since air density changes with air temperature, an intake manifold-mounted sensor is also used.


Production-based Speed Density computers also utilize an oxygen (O2) sensor mounted in the exhaust tract. The computer looks at the air/fuel ratio from the O2 sensor and corrects the fuel delivery for any errors. This helps compensate for wear and tear and production variables. Other sensors on a typical Speed Density system usually include an idle-air control motor to help regulate idle speed, a throttle-position sensor that transmits the percentage of throttle opening, a coolant-temperature sensor, and a knock sensor as a final fail-safe that hears detonation so the computer can retard timing as needed.

GM’s Tuned Port Injection (TPI) set-ups used Speed Density metering from ’90-’92, as did ’91-’93 LT1 engines. All ’86-’87 and ’88 non-California Ford 5.0L-HO engines used Speed Density metering. Most Mopar fuel- injection systems have used Speed Density too.

Because a Speed Density system still has no sensors that directly measure engine airflow, all the fuel mapping points must be preprogrammed, so any significant change to the engine that alters its VE requires reprogramming the computer.

Mass Flow
By contrast, Mass Air Flow (MAF) systems use a sensor mounted in front of the throttle body that directly measures the amount of air inducted into the engine. The most common type of mass-flow sensor is the hot wire design: Air flows past a heated wire that’s part of a circuit that measures electrical current. Current flowing through the wire heats it to a temperature that is always held above the inlet air temperature by a fixed amount. Air flowing across the wire draws away some of the heat, so an increase in current flow is required to maintain its fixed temperature. The amount of current needed to heat the wire is proportional to the mass of air flowing across the wire. The mass-air meter also includes a temperature sensor that provides a correction for intake air temperature so the output signal is not affected by it.

The MAF sensor’s circuitry converts the current reading into a voltage signal for the computer, which in turn equates the voltage value to mass flow. Typical MAF systems also use additional sensors similar to those found in Speed Density systems. Once the electronic control module (ECM) knows the amount of air entering the engine, it looks at these other sensors to determine the engine’s current state of operation (idle, acceleration, cruise, deceleration, operating temperature, and so on), then refers to an electronic map to find the appropriate air/fuel ratio and select the fuel-injector pulse width required to match the input signals.

GM used MAF sensors on the turbo Buick V-6 Grand National, ’85-’89 TPI, ’94-’98 LT1, ’96 LT4, and all LS1 engines. Ford has used MAF metering on ’88 California 5.0L engines and all ’89-and-later V-8 engines.

MAF systems are much more flexible in their ability to compensate for engine changes since they actually measure airflow instead of computing it based on preprogrammed assumptions. They are self-compensating for most reasonable upgrades, as well as extremely accurate under low-speed, part-throttle operation. On the other hand, the MAF meter, mounted as it is ahead of the throttle-body, can become an airflow restriction on high-horsepower engines. On nonstock engine retrofits or EFI conversions on engines never produced with fuel injection, it may be hard to package an MAF meter within the confines of the engine bay and available intake manifolding.


Which Is Best?
In a perfect world, virtually all street-performance engines would use Mass Air, due to its superior accuracy and greater tolerance for engine changes. In the past there was a problem on high-horsepower engines because larger-capacity MAF sensors were scarce and prohibitively expensive. Nowadays, oversize MAF sensors are available from Pro-M, Granatelli Racing, and other sources that are compatible with Ford engines and computers. Custom MAF calibration keyed to the specific vehicle, engine, and injector size is also available. With a correctly calibrated oversize meter, reflashing the Ford computer usually isn’t required. (However, before you run out for a larger Ford MAF meter, Fast Track Performance points out that the first limiting factors are the puny Ford 19 lb/hr injectors, which can only support about 320 hp.)

Some oversize MAF meters have also become available for the second-generation (’94-and-later) GM MAF systems, but the selection isn’t as broad as for the Ford guys. The GM MAF engine management computer isn’t as adaptable as Ford’s. Although it will accept larger MAFs, you can’t go up and down more than one injector size with reflashing the computer.

Bigger MAF meters are not readily available for old GM TPI systems, but Granatelli says it is possible to adapt Ford meters to them via a conversion wiring harness. Custom calibration is required, so Granatelli prefers to do the changeover in-house.

For radical engines or engines never produced with fuel injection, an aftermarket user-programmable computer system is usually preferred. Unfortunately, the more-or-less affordable aftermarket systems—including ACCEL/ DFI, Speed-Pro, and Holley—are Speed Density–based and don’t support Mass Air metering. Those systems that do—including Electromotive, Motec, and Pectel units—are more costly, sometimes considerably so. However, Westech Performance reports that it is possible to use Pro-M’s adjustable Optimizer MAF meter and a stock Ford Mustang computer with Ford’s EPEC piggyback programmable unit to run Mass Air on any engine.

If it is not practical to use MAF on your engine due to packaging or hardware constraints, the programmable Speed Density systems are the next best choice because production-based Speed Density systems won’t tolerate major engine changes without computer reprogramming, which usually requires the services of an outside specialist; if the reprogrammer isn’t specifically familiar with your combo, the end results may be less than satisfactory.

On radical engines (those with cam duration over 240 degrees at 0.050 or less than 10 inches of idle vacuum), even user-programmable Speed Density systems have difficulty due to an erratic or insufficient manifold vacuum signal. If the application is for a race car operated primarily under full throttle, N Alpha is the solution. If you intend to drive on the street, a system that blends N Alpha with Speed Density—varying which is in control per specific operating point and conditions—may be the answer. The higher-end aftermarket systems, including Electromotive’s, support this option.

As electronic engine-management system usage becomes more widespread in the car crafting community, prices and ease of use should become more user-friendly. Already, the latest Gen VII ACCEL/DFI system has the ability to construct its own baseline fuel curve, and the new user programming interface is a full-fledged, Windows-compatible program. Can voice command be far behind? Beam me up, Scotty.


All electronic engine-management systems use a throttle position sensor to monitor the percentage of throttle opening. Connected to the throttle shaft, it tells the computer whether the car is idling or accelerating.



The MAP sensor measures manifold vacuum. Speed Density systems use this sensor to calculate engine load and airflow. Once airflow is calculated, the appropriate amounts of fuel and spark are supplied.



GM ’94-and-up MAF units aren’t a major restriction through 400 hp, but Morgan Motorsports sees gains even on stockers by going to a larger meter ID. Options include removing the GM unit’s (left) screen and dividing fin, then porting it out (center), or installing a larger aftermarket unit (right).



The MAF sensor mounts in the inlet tract ahead of the throttle-body. Like an air filter, if it isn’t big enough it can create an inlet-tract restriction. Unlike carburetors, you can’t install too big a MAF, provided it’s properly calibrated. Granatelli offers precalibrated 81mm and 85mm late-model GM MAFs, ready to bolt on.



GM ’85-’89 TPI MAFs are a restriction over 350 hp. Removing the screen and cutting out the fins aids airflow but can cause erratic air/fuel ratios and idle instability. Lacking adaptive learning capability, the old computers generate a lean condition without an adjustable fuel-pressure regulator.



Ford MAF meters use a venturi-like flow orifice. The popularity of 5.0L-EFI engines makes for many available oversize choices from Granatelli, Pro-M, Vortec, and others. Ford computers are extremely flexible—with a properly calibrated MAF, reprogramming is rarely required.



Granatelli’s Bullet Converter permits using the much broader selection of oversize Ford MAF units on late-model GM MAF systems. A similar converter is available for the early GM TPI MAF systems as well.



Have a bizarre combo? Pro-M’s Optimizer lets the end user fine-tune MAF-meter calibration to sync with fuel injectors up to five sizes off its baseline configuration, which is supplied by Pro-M based on the end user’s engine/vehicle info. It works with Ford ECMs.


ACCEL DFI/Mr. Gasket Group
216/688-8300
www.mrgasket.com/accel.htm Carputing LLC
www.carputing.com

Duttweiler Engineering
805/659-3648 Electromotive Inc
703/331-0100
www.electromotive-inc.com

Fast Track Performance
661/291-2375
www.fasttrackperf.com Ford Racing Performance Parts
810/468-1356
www.fordracing.com/performanceparts

Granatelli Motorsports Inc.
818/996-2753
www.granatellimotorsports.com Holley Performance Products
270/781-9741
www.holley.com

Morgan Motorsports
818/766-3051
www.morganmotorsports.com Motec Systems USA
714/897-6804
www.motec.com

Pectel Technologies
949/586-3609 Professional Flow Technologies (Pro-M)
248/399-4586
www.pro-flow.com

Speed-Pro Electronics/Federal Mogul Performance
800/560-1400
www.tciauto.com/ecu/index_spe.ht

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