Larger TBI on 2.5L

I have a stock '87 MJ. It had a 2.5L with a 1V TBI. I installed a Hi-Perf 2.5L with a Clifford Ram intake(47-4501WH). Clifford say's intake requires 350cfm, but engine draws only 275-300cfm! I would like to utilize the stock computer, but use a 2V TBI from a 2.8L, 4.3L or 5.0L chevy. Clifford's TBI is $1,500!  

The stock 2.5L TBI is a smaller version of the 4.3L TBI. A 4.3L throttle body with 2.8L injectors seems the best combination for mainly high altitude(7000') use. The main issue is the normally alternating injector pulses for a 4.3L TBI, instead of single injector pulses for the stock 2.5L TBI.

Is it ok for both injectors to pulse together? If so, would the stock computer have enough signal strenth to pulse both injectors? If not, can the ROM chip be reprogrammed to handle the new parameters? If needed, would another computer(V-8?) give me the proper signal strenth, or alternating pulses?  

At 5000 rpm a 150ci/2.5L running at .85% efficiency, which is a good guess for a modified motor, would flow 184.5 cfm. Stock motors are about .75% efficient.

Fuel injectors have a rated flow at a given pressure. Either increase the injector size or increase the pressure. Either will give you a little more fuel. Bigger injectors will fix a lean condition and last longer if the duty cycle for your current injectors has been exceeded. With an adjustable MAP, a wideband O2 sensor and some laptop software, you might be able to tune it to run a little better.

The ECM will pulse the injectors longer or shorter in order to meet stoich as determined by the O2 sensors and the ECM's existing fuel maps. So, the ECM will likely be fighting what ever you're trying to do with increased fuel delivery.

A bigger throttle body will not change the airflow requirements for the engine, and will almost always have a negative effect on performance in the lower rpm ranges.

JP Tech Editor, Hazel, has already determined the outcome for a lot of what you're trying accomplish with the 2.5L. He basically thinks he ruined a perfectly good running Jeep by messing too much with the 2.5L, even though he increased it's hp numbers by 14%. His quote was "live and learn".

The write-up was called "YJ Wheezer Squeezing". Here is a link to his endeavors.  

I read the spec's on the stock 2.5L project. Common mistake! With a stock 2.5L, he should have used an unbored, 4.0L TB with the stock 2.5L TPS, IAC and computer. Plug and Play, Simple and Cheap!

I'm just looking to match the maximum flow requirements of THIS engine and intake combination. Goal: 90% Vme.

My engine is built for racing, and is far from stock.  Figuring in the increased bore, as well as the higher RPM range available, the CFM draw is closer to 300cfm(173 x 6000/3456 = 300.35cfm. 90% Vme = 270cfm.

The 4.3L TBI is rated at 330 cfm, and shares the same TPS and IAC(and their corresponding plugs) as the stock 2.5L unit. The (2)2.8L Injectors flow slightly more than a (1)2.5L injector. Plug and Play, Simple and Cheap!

My main concern is the injector pulse(s) and strenth. Does the stock computer have enough power to pulse them together? Should they pulse alternately? Does anyone know about GM type computers used in 1987 MJ/XJ's?

Option 2: Forget this whole TBI idea, and install a 390cfm 4 barrel. The smaller primaries of a 4 barrel, should give me better drivability than a 2 barrel of simular size. I can also benefit from the 4 barrels' lower pressure drop, to reach my 90% Vme goal.  

Have you dyno'd the motor or do have some track testing times that can be used to figure apprx hp?

Do you race the truck? What type of racing?

The ECM has an injector driver that grounds the injector coil and typically each injector has its own injector driver. I doubt using one driver to run two injectors would be a good long term solution.

Have you done any wideband O2 testing? That will let you know what's actually happening and that can be compared to what you're expecting power wise.

If you stick with the TBI, how do you plan to modify your fuel and ignition curves?  

The engine is new, and has never run. I haven't even gotten around to putting oil in it yet. I used marine fogging oil to coat all the internals prior it install.
Sould I use synthetic or conventional oil for break-in?

I have no dyno info on this engine. It was a back-up motor for a 2wd XJ SCORE race team. It came with a race clutch and built AX-15 trans. All bolted right in with no modification. This truck will be my summer truck, and will be street driven. When needed, I may need to school a rice-grinder about good old american iron.

I suspected that the computer lacked the power to pulse both injectors, and would need two circuits to alternate them. Can you recommend a computer that would accomplish one, or both of these parameters.
I'm willing to reprogram if needed.

I probably will not start it, until I decide on which fuel delivery system I will use. Since this is a winter project, I still have some time to get all the facts straight. With the right computer, or carb, this should be a awesome performing truck.

I'm starting to lean toward the 4 barrel, but still want to look into the TBI a little further, before bailing out completely. What do you think about the Carb idea, versus the TBI? Which one will have the most performance potential with this engine/intake combination?  

Regarding my 2.5L, I did use a stock (unbored) 4.0L throttle body with the factory 2.5L TPS, IAC, and computer.

Use straight 30W oil with zinc additive (Comp Cams, others have break-in additives for flat tappet camshafts available at www.summitracing.com.) You can switch to synthetic after the break-in procedure is completed and you've seated the rings. FYI, no need for the additive on a roller cam engine.

You want simple? Run a Holley 390cfm 4bbl and distributor with a mechanical and vacuum advance.

As for the injectors, talk to Tom Miller at Turbo City. He's the real expert. www.turbocity.com. He'll be able to tell you with certainty what's doing with your TBI setup and whether or not the 2.8L injectors can be made to work with your 2.5L computer.

Good luck with the project.  

Some say never break-in a motor with synthetic, and some synthetic mfgs even say you shouldn't use their product for break-in. But some motors come from the factory with synthetic and they are not broke-in.

But there's an economic reason to not use synthetic. You're just going to throw it away in 500 miles.

I'm a huge fuel injection guy, but the older TBI and OBDI systems are not that easy to tune.  It's a whole different ball game with OBDII and I'd never come up with any good reasons to get rid of it.

I think the S10 2.8 V6 got TBI in 1986 but I don't think the XJ/MJ switched from a carb in '86. The 2.8 V6 was replaced by the 4.0L RENIX injection in 1987. Your TBI is controlled by the RENIX technology, which is not even OBD and its sensors are probably not compatible with the GM PCM.

But, I think in your case you'd be better served with a carb. You can easily adjust fuel metering and you can have your distributor curved how ever you want.

A carb will build more power than fuel injection. There is no debate on that.  

Sorry about the mix-up! I see that the Steal-J had the bored 4.0L TB. Either way, I always thought the 4.0L unit was much to large for a stock 2.5L. I considered a Jeep Performance manifold with a stock 4.0L TB, but couldn't justify changing wires, computer, sensors, etc., to get it all to work. Just curious, does anybody bore 2.5L units?

In keeping with my moto: "Plug and Play, Simple and Cheap", I wanted to use a 2.8L TBI and computer(free!). I became concerned that the V-6 computer, and therefore the TBI were not going to give me the proper number of pulses per revolution. The V-8 computer gives each injector, two alternating pulses per injecter, per revolution. This seems to be the prefered number of pulses per revolution.

The 4.3L TBI unit shares the same body as the larger 5.0L and 5.7L V-8 units. I estimated that the 4.3L injectors were too large for my application. The 2.8L injectors were chosen for their close match to the new engines actual displacement. Since the stock 2.5L TBI is a smaller version of the 4.3L TBI, I expected to re-use the stock 2.5L TPI and IAC, as well as the stock wiring.

I'll contact Turbo City for further info on the injector compatability, and/or conficts between the 4.3L TBI, and the V-8 computer.        

Thanks for the break-in advice. Everyone I talk to, also says conventional oil is best, but are divided on the proper viscosity. Why is 30W best for this procedure? Should a race built motor be broken-in differently from a stock motor? If so, How? This engine currently has only assembly lube between the wear surfaces. After break-in, Castrol Edge seems to be the logical choice. Is there anything else I should be doing to protect this new engine?

Lastly, The AX-15 is freshly re-built. What oil, or synthetic product will give the best performance and service life? Is there an additive that you recommend?