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ANY info on 2.5L motors in 1991?

4578 Views 26 Replies 11 Participants Last post by  PerformanceWithEconomy
Am looking for info on 2.5L motors that were supposedly installed in the Taurus in 1991. According to the info that i've been able to find, they supposedly switched from MPFI to SPFI in 1991 on the 2.5L motors. This would be a year earlier than all of the other Ford vehicles, as MPFI was not available until 1992 on most of their product line. Don't know how many 2.5L equipped Taurus' were sold in 1991, but Car-Part.com--Used Auto Parts Market does not even list that motor as being available for that year. ANY and ALL help appreciated. Sean
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Thanks to those with pertinent responses :)

To be honest, i'm building a 2.5L HSC motor from scratch to go into a 1994 Tempo. Yes, the Tempo's ARE slow, but like any other cheap, mass produced vehicle / motor, they respond pretty well to basic modifications that correct existing design deficiencies.

I'm taking that a step further and building a bigger, more powerful motor with custom intake, valvetrain, exhaust, heavily modified head, etc... Dyno simulation projections range from an estimated HP of between 175 - 200 HP. The reason for the variation has to do with specifics pertaining to the cylinder head and flow characteristics. I haven't gotten the head(s) onto a flowbench, so i'm having to "guesstimate" figures.

The ONLY places that i can find info pertaining to the change from SPFI to MPFI injection in 1991 on the 2.5 is in Ford literature and on this site. My guess is that the info on this site was taken from that same Ford literature. I can not find ANY info ANYWHERE ELSE to substantiate this info, let alone a 1991 Taurus with a 2.5L in the engine bay. I know that most folks bought these with V6's, but there should be at least a few of these around, let alone more info.

Any & all help appreciated from one Ford enthusiast to another!!! Sean
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I'm one of the moderators of TempoTopaz.com and will soon be taking over the Webmaster position. As such, i'm well familiar with that site. Glad that some of you guys over here know of it though :)

As far as horsepower goes, do the math. The 2.5L HSC motor is 153 cubic inches. A reasonably well thought out normally aspirated street motor can achieve 1.5 hp per cubic inch without a lot of fuss. This would equate to appr 230 hp based on 153 cubic inches. Since i'll be running a heavily modified & decked HSO ( High Specific Output ) head, flat top pistons, appr 10.5:1 compression, a custom ground cam ( .550 lift with a split pattern 224 / 230 duration @ .050 ), full roller rocker arms, a TRUE high pressure ram air system, aftermarket C&L MAF, larger Throttle Body, Ford Racing injectors, high volume fuel system with a variable pressure regulator, a custom designed header, no cat, a high flow straight through muffler, etc... my calculated output of 175 - 200 HP is actually pretty conservative.

As far as running a Vulcan goes, that would be a LOT more work. My car is already set up for the 2.3 HSC motor. As such, the longer stroke 2.5 motor is a drop-in.

Other than that, making 200+ hp out of a Vulcan would be cake. It could pretty much be done using factory Ford parts IF you know what to do. If you've spent $4K and you're just hitting 200 hp, not enough homework or shopping around was done. I've got less than $1K into my motor & that started with a brand new FoMoCo block in the crate with all of the aforementioned custom made parts. Then again, i've got two less cylinders that i need to buy parts for, only one head and a single exhaust system, so that could equate for slightly higher costs. Not $3K worth though.... Sean
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Never said that i would stay under a grand, just that i had acquired the mass majority of parts mentioned above for less than $1K.

Through a LOT of research, careful shopping on the net and a LOT of patience, i was able to locate KILLER deals. On top of that, i'm more concerned with performance & reliability at a fair price than prestige of specific brand names at a high price.

As a few cases in point, i found a brand new 2.5L block in the FoMoCo crate for $175. A new crank set me back $50. Flat topped pistons, pins & moly rings were $50. Rods with SPS racing bolts were $9 apiece. A fully rebuilt 2.3 HSO head cost me NOTHING and a fully rebuilt 2.5 HSC head cost me $50. I'll end up porting & extrude honing both of them and see which one flows better. Aluminum pedestal mount 1.73 ratio roller rockers with a lifetime warranty were $120. Custom cam ground to my spec's was $60. I came up with the design after experimenting with my dyno simulator. NEW Ford racing injectors set me back $50. C&L MAF was $40. Larger throttle body was $28. Grade 8 head bolts were $7. Comp Cam's High Energy hydraulic lifters were $14. You get the idea.

Don't know how many other common parts from other motors can be swapped onto a Vulcan. Given the VERY limited use of the 2.3 / 2.5 HSC within the Tempo & Taurus, i would have to assume that the far more widely used and differently sized Vulcan would be more versatile in that regards.

Several of the prices that you quoted, such as rocker arms, seem VERY high to me. Especially since you've only got a 6 cylinder, not an 8. For instance, careful shopping with a bit of creative research on your part could have netted you pedestal mount 1.73 ratio full roller aluminum rockers for less than $225 total. This price would have also included 4 extra's rockers that you could have sold or kept as spares.

As to the ram air system, there are MANY different ideas as to what this constitutes. My idea of "ram air" is when you have measurable positive pressure in the air intake tract at reasonable cruising speeds. Just because one person's installation wasn't what they expected doesn't mean that it isn't possible.

With the proper tools and enough research, it's not that hard to design a system that actually achieves the aforementioned goal of producing VERY MEASURABLE levels of positive pressure within the air intake system. I would suggest picking up an inexpensive Magnehelic gauge and doing your own research on the matter. Combining positive air pressure with a well tuned intake & exhaust system and properly timed valvetrain, volumetric efficiency can be drastically increased. Sean
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Something else to think about. MOST intake systems are operating under negative pressure. That is, the air intake system is drawing air in from a spot that is under negative pressure. Minimizing this problem increases air into the system, even though it might STILL be operating under negative pressure. Kind of like having twenty holes in your boat and plugging 18 of them. You're still operating with losses that require more work & attention, but not nearly as bad as it was. Relocating the air intake to a point where you actually have positive pressure, no matter how small, can typically result in VERY positive gains in terms of throttle response and bottom end torque. Sean
If you're creating positive pressure in the intake tract, that would be "ramming" the air in. By "positive pressure", i'm talking about a system that has pressure within the intake tract WITH THE THROTTLE CLOSED i.e. there is no suction drawing air into the intake tract. The intake tract is literally being "force fed" or "rammed" air regardless of the vacuum of the motor. Granted, it might not be the same thing as running a turbo / super charger under boost, but it is "ram air" none the less. As previously mentioned, a Magnehelic gauge can be used to measure changes ( good OR bad ) in air pressure within the intake tract.

The key here is to not only produce positive pressure under the above conditions i.e. with the throttle closed, but also be able to maintain that pressure under Wide Open Throttle ( W.O.T. ) conditions. This dictates that you have a FAR greater volume of air being forced into the intake tract than anything that the motor can ingest on its' own. When you can pressurize the intake with a HIGH volume of cooler air during normal operating conditions, you ARE going to show performance gains in both 0-60 and 1/4 mile times. That is, so long as your fuel system can keep up with the higher levels of air flow.

Anybody with their air inlet mounted under their hood, or especially in the fender well, can stand to gain LOTS from doing some research on the subject. Sean
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I would suggest doing some snooping around Autospeed.com and looking at some of the testing that they've done. In several different cases, simply REDUCING "negative pressure" within the air intake tract has been worth .2 in 0-60 times. This would translate to even further gains in 1/4 mile times. This was not even achieving POSITIVE pressure, simply minimizing negative pressure.

Outside of that, your comments about "ram air" improving CAFE is absolutely 110% backwards. Cold air is denser than warm air and requires more fuel. More fuel means higher emissions AND lower mpg's. Most manufacturers are specifically working with warm air intakes for this reason. I've seen multiple Mopar's that draw air in from directly behind the radiator for this very reason. Then again, they were working with Smokey Yunick, the "inventor" of the hot air engine. I do something like this every winter with my daily driver. The difference in MPG's is VERY measurable.

If you want to go the opposite route i.e. making more power at the expense of economy and emissions, the highest pressure point on a vehicle is directly in the front middle of the bumper i.e. right where the license plate mounts in some States. If your bumper is plastic and is of a hollow core design, this can make for one helluva transfer tube to other large diameter ductwork that feeds up to your airbox. Obviously, you have to do some surgery to seal it up and achieve high flow routing. Adding a small radiused flare at the inlet further increases the ability to capture air.

Like i said, do some research FOR YOURSELF and see what YOU find. A magnehelic gauge won't set you back more than $30 including shipping on Ebay. Believe me, i've got a couple with different ranges. You don't have to be under "boost" conditions to improve volumetric efficiency. The greater the cylinder fill, the more potential for power and atomization of the fuel.

Outside of the increased net cylinder pressure due to greater cylinder fill, for every 10*F reduction in intake temperature, a 1% increase in power will be realized. If drawing in hot air from under the hood behind the radiator in a low pressure zone, moving your intake to an outside high pressure zone will help you to realize some of the potential that you have for power gains in this area. Sean
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They do not contradict each other, they reinforce each other.

If you have higher volumes of colder, denser air being fed into the motor, you are going to consume more fuel and make more power. This comes at the expense of higher emissions and poorer fuel economy.

If you have lower volumes of warmer, thinner air being fed into the motor, you are going to consume less fuel and make less power. This comes with the benefit of lower emissions and improved fuel economy.

On my daily driver, i run a cold air set-up in the summer to try to offset the higher ambient air temps and reduce the potential for detonation. Due to higher levels of traction on clean, warm pavement, the added power can help the car to run a bit quicker.

In the winter, i run a warm air set-up as i have limited traction and don't need as much power. I also want the car to warm-up faster and run more consistently regardless of how cold it gets outside.

I am not worried about emissions or meeting CAFE standards. On the other hand, automotive manufacturers have to be concerned with both of these, and as such, strive to seek a balance in their product line. As such, they use cold air systems for a few select high performance models and try to balance that out with the rest of their product line, which typically run warm air systems.

Pretty simple really.... Sean
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What does the number of posts that one has on a site have to do with their level of knowledge, experience or ability to be right, wrong, helpful or "controversial"?

I have built everything from a 482" Weber carbureted Olds motor to a turbo-charged small block Chevy to a dual quad cross-rammed Ford 302" motor. There are WAY more in-between those that i won't bother mentioning. I currently have a 2.5L motor that i'm building from scratch and will soon be tearing into my Harley motor.

Twenty+ years ago I worked as the head of mechanical maintenance for a large corporation. I was responsible for 30+ vehicles ( cars, vans, box trucks ) and HORDES of mechanical equipment. This meant everything from automotive engine swaps to rebuilding high pressure pumps, repairing high voltage ozone generators, etc...

I currently work in the electronics field and have run my own business for the last 15 years. Outside of my regular work, I have done design consultation work for over a dozen world class manufacturers. I have also had articles published in magazines and been quoted by manufacturers in their sales distribution literature. I'm NOT trying to "toot my own horn", i'm trying to give you background and help you to understand that i'm not using words / lingo / verbage / ideas that i don't comprehend.

As to my seasonal warm air vs cold air induction system swap, cold motors are less efficient and produce less heat in the winter. Using warm air brings the motor up to operating temp quicker. This not only increases engine efficiency and lowers fuel consumption and oil dilution, it also helps to make my personal commutes more comfortable. I understand that the computer attempts to maintain the same air / fuel ratio, but it can only do so much on its' own. I'm simply helping it along with a simple mod that takes me less than ten minutes to perform once in the Fall and then again in the Spring.

Outside of all of that, fender mounted air intakes typically don't work all that well. The inside of a fender is typically a low pressure zone, and many times, can be at negative pressure. Due to the lack of positive pressure and turbulence in that area, the motor gets no assistance when it comes to drawing air into the intake system. Since the natural vacuum of the motor now has to work harder to draw air into the cylinders with no outside assistance, the air tends to be slower moving. Slower moving air typically results in lower ratios of cylinder fill with the resultant drops in volumetric efficiency. On top of that, the air found in this area is typically warmer than the ambient temp. This is due to heat from the cooling system, engine compartment and tire collecting there.

To sum things up, fender mounted air inlets typically aren't all that great on MOST cars. The lack of turbulence and predictable air flow levels within that area does help make it easier for the "engineers" to program the ECU though. By limiting the variables that it will encounter, the ECU can now operate more consistently. This is one of the reasons why heavy modifications to the motors intake and / or exhaust system may require reprogramming or "chipping" for optimal results. Factory ECU's simply aren't programmed to deal with a wide set of variables. Modifying one's vehicle way beyond the programmed set of variables that the ECU can deal with can easily result in poorer rather than better performance.

This why i suggested picking up your own set of magnehelic gauges and doing your own homework. Fender mounted air inlets are typically NOT "high performance". It is NOT hard to beat the diploma holding "engineers" at their own game, especially when it comes to individualized optimization of your own vehicle with free labor vs mass produced products using costly labor. Most mass produced designs are dumbed-down for profitability and ease of production. Our cars are no different.

I'm NOT trying to be "controversial" by any means. I'm simply stating facts that are easily verified by those that are willing to do some simple research. If I ever post something that you don't understand or use terminology that you're not familiar with, simply ask me for clarification. I'll be glad to not only explain it as best i can, but also provide specific points of reference.

In the meantime, i'm still looking for help / info pertaining to my original post. I don't know it all, hence my research in this area and my asking for help on this forum. Sean
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