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Thread: Reduced mileage when using 52mm TB

  1. #41
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    Re: Reduced mileage when using 52mm TB

    They weren't going to go to a 52 as that would of meant re-doing all the intakes to match. That's a lot of production money spent in re-tooling, design and recasting.

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    Re: Reduced mileage when using 52mm TB

    Quote Originally Posted by GLHNSLHT2 View Post
    They weren't going to go to a 52 as that would of meant re-doing all the intakes to match. That's a lot of production money spent in re-tooling, design and recasting.
    How much money was spent going from 2-piece intake to 1-piece?

    FYI they could have gone to a 52 mm right then and there when the 1-piece went into service in 1988


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    Re: Reduced mileage when using 52mm TB

    Quote Originally Posted by thedon809 View Post
    I think anything that helps make more power will hurt fuel economy at WOT. That's kind of the idea. Get more fuel and air in the engine.
    Not necessarily. If the mods make more power, and increase the efficiency of the motor, then you can see an increase in mpg's. I did on my Scamp. When I rebuilt the engine on my Scamp, I ported the head, installed a bigger cam, bumped the compression, and installed headers and a free-flow exhaust, and I instantly gain 4-6 mpg, depending on how I drove it. Best previous mpg was 27, afterwards, I regularly hit 33... This wasn't a worn out engine either. It only had 75K on it when I tore it down.

    Of course, all this is highly dependent on your performance goals. Taking a stock TII, and modding it to make 400 hp, sure, you will hurt fuel economy. But for folks interested in making just a little more to make a fun street car, you can have both.

    There is one absolute law for fuel mileage: Your mileage is always inversely proportional to the pressure applied by your right foot.

  4. #44
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    Re: Reduced mileage when using 52mm TB

    That is also the beauty of turbo engines, you can make them stupid powerful but sip gas when not going all out.
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  5. #45
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    Re: Reduced mileage when using 52mm TB

    Quote Originally Posted by turbovanmanČ View Post
    That is also the beauty of turbo engines, you can make them stupid powerful but sip gas when not going all out.
    Absolutely!! Especially if you get a flashable module. You can really tweak the cruise settings, and lean them out for top mpgs. Oh the beauty of EFI!!!

  6. #46
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    Re: Reduced mileage when using 52mm TB

    Quote Originally Posted by mopar-tech View Post
    How much money was spent going from 2-piece intake to 1-piece?

    FYI they could have gone to a 52 mm right then and there when the 1-piece went into service in 1988
    they probably didn't spend so much as not to save it back again in the first year or so of only produceing one casting

    and one look at the one piece says they were not concerned with haveing an intake that makes more than 175 hp so there's no need tor the 46/52 mm swap

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    Re: Reduced mileage when using 52mm TB

    Quote Originally Posted by 83scamp View Post
    Not necessarily. If the mods make more power, and increase the efficiency of the motor, then you can see an increase in mpg's. I did on my Scamp. When I rebuilt the engine on my Scamp, I ported the head, installed a bigger cam, bumped the compression, and installed headers and a free-flow exhaust, and I instantly gain 4-6 mpg, depending on how I drove it. Best previous mpg was 27, afterwards, I regularly hit 33... This wasn't a worn out engine either. It only had 75K on it when I tore it down.

    Of course, all this is highly dependent on your performance goals. Taking a stock TII, and modding it to make 400 hp, sure, you will hurt fuel economy. But for folks interested in making just a little more to make a fun street car, you can have both.
    Blame low-tech emissions controls for that. Many of the steps taken through the 1980's to meet emissions standards were at the cost of fuel economy and power.
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  8. #48
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    Re: Reduced mileage when using 52mm TB

    Quote Originally Posted by Dr. Johny Dodge View Post
    they probably didn't spend so much as not to save it back again in the first year or so of only produceing one casting

    and one look at the one piece says they were not concerned with haveing an intake that makes more than 175 hp so there's no need tor the 46/52 mm swap
    1) It would have cost nothing to introduce the 52 mm TB on the 1-piece in 1988 as the intake was a new piece already, it would have been a simple matter of designing the intake for the 52 mm TB right out of the box which was already in production on the 87 3.0 minivans.

    2) They were very concerned about the design of the 1-piece intake, have you read the SAE paper on the 2.5 Turbo I engine package? It is discussed in some detail.

    The one piece was introduced to further reduce the number of parts in the package (cost savings!) which buttresses my position that there was another reason for retaining the smaller throttle body. Chrysler accountants despised redundant parts and went out of their way to pare back parts complexity and packages to save money. Hell the 2.2 engines ended up with small block mopar spark plugs in an effort to reduce part numbers! RN12YC wasn't the first choice.

    If they could have pitched the 46mm and reduced parts in the parts bin they would have. Either there was a drivabilty issue or an emissions issue at play.


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  9. #49
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    Re: Reduced mileage when using 52mm TB

    I don't think the first 3.0L engines came with a 52 mm throttle body. My last trip to the junk yard found a smaller one installed on a very stock looking 87-90 engine.

    On topic, I never was looking for MPG's with my shadow, but I can see how your point (mopar-tech) because I haven't looked into the SMEC side of the program.as well as seeing it as a moot point on my mega squirt experience as Manifold pressure was the primary input for fueling calculations and TPS used more as a "fuel enrichment" calculation. Either way, if that's what you found, cool.

  10. #50
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    Re: Reduced mileage when using 52mm TB

    I haven't noticed any changes in MPG when I put the 58mm TB on my R/T, still 24 in town 30-32 hwy. The only noticeable difference it made is that at lower engine speeds the throttle can feel soggy depending on how far the loud pedal is pressed down. I remember 5didgits explaining the how&why of that. It boils down that the engine is ingesting all the air it physically can at the lower RPM at a given throttle opening, so opening the throttle up more doesn't make any difference since the engine can't take in any more air.

    I can see how that effect could cause a slightly lower MPG depending on driving habits. Engine doesn't feel responsive to throttle input, so you give it more and more throttle until you're in boost and then you sharply back off the throttle. I've caught myself doing that countless times. Even though the engine is making essentially the same amount of power out of boost, the smaller TB gives the feeling of more responsiveness so you're less likely to be as heavy footed. The second thing that would have an effect, albeit very minor, is the additional fuel used to mimic the accelerator pump shot when opening the throttle more due to the unresponsive feeling.
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  11. #51
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    Re: Reduced mileage when using 52mm TB

    Quote Originally Posted by shadow88 View Post
    I don't think the first 3.0L engines came with a 52 mm throttle body. My last trip to the junk yard found a smaller one installed on a very stock looking 87-90 engine.
    87-88 had the 52 mm throttle body and then they reduced it to the smaller unit.


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  12. #52
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    Re: Reduced mileage when using 52mm TB

    True dat, same issue with diesels right now, they are plugged up with emissions at the expense of MPG.

    If the 52mm t/b was already around, wonder why they made a 46mm version? That surely added costs.
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    Re: Reduced mileage when using 52mm TB

    Quote Originally Posted by mopar-tech View Post
    1) It would have cost nothing to introduce the 52 mm TB on the 1-piece in 1988 as the intake was a new piece already, it would have been a simple matter of designing the intake for the 52 mm TB right out of the box which was already in production on the 87 3.0 minivans.

    2) They were very concerned about the design of the 1-piece intake, have you read the SAE paper on the 2.5 Turbo I engine package? It is discussed in some detail.

    The one piece was introduced to further reduce the number of parts in the package (cost savings!) which buttresses my position that there was another reason for retaining the smaller throttle body. Chrysler accountants despised redundant parts and went out of their way to pare back parts complexity and packages to save money. Hell the 2.2 engines ended up with small block mopar spark plugs in an effort to reduce part numbers! RN12YC wasn't the first choice.

    If they could have pitched the 46mm and reduced parts in the parts bin they would have. Either there was a drivabilty issue or an emissions issue at play.
    I've been told that the one piece design was more or less botched due to a leave of absence in the engineering dept.

  14. #54
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    Re: Reduced mileage when using 52mm TB

    Quote Originally Posted by 83scamp View Post
    Not necessarily. If the mods make more power, and increase the efficiency of the motor, then you can see an increase in mpg's. I did on my Scamp. When I rebuilt the engine on my Scamp, I ported the head, installed a bigger cam, bumped the compression, and installed headers and a free-flow exhaust, and I instantly gain 4-6 mpg, depending on how I drove it. Best previous mpg was 27, afterwards, I regularly hit 33... This wasn't a worn out engine either. It only had 75K on it when I tore it down.

    Of course, all this is highly dependent on your performance goals. Taking a stock TII, and modding it to make 400 hp, sure, you will hurt fuel economy. But for folks interested in making just a little more to make a fun street car, you can have both.

    There is one absolute law for fuel mileage: Your mileage is always inversely proportional to the pressure applied by your right foot.
    Key word in my sentence was WOT (wide open throttle). At wide open throttle, if you modify an engine to get more air in and out, it's going to use more fuel as well. I'm talking strictly wide open throttle.

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    Re: Reduced mileage when using 52mm TB

    Quote Originally Posted by cordes View Post
    I've been told that the one piece design was more or less botched due to a leave of absence in the engineering dept.
    So botched it required two paragraphs of detailed information in the 2.5 Turbocharged SAE paper #900852

    It notes in the paper "throttle response was excellent" so clearly this was a concern for Mopar.

    A summary is here- http://www.thedodgegarage.com/turbo_sae_25.html


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  16. #56
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    Re: Reduced mileage when using 52mm TB

    I'm pretty certain the 1-piece isn't half as bad as it's been commonly believed for years...
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  17. #57
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    Re: Reduced mileage when using 52mm TB

    Quote Originally Posted by Dr. Johny Dodge View Post
    tps , map , o2 yada yada ..

    with an ecu that has "learning" wouldn't this be a moot point - IF you remembered to disconect the battery before starting the throttle body swap , thus causeing the ecu to relearn it's parameters when started again with the new TB installed (?)

    also , I don't see port velosity changeing one iota as the port size or shape remains unchanged and the throttle body is a heck of a long way from the port

    as for a seat of the pants feel , there shouldn't be much beyond a slightly different sence in throttle responce - initally (on an otherwise stock application)
    What I said about airflow vs TPS opening is what changes on a larger TB, and no, I don't see how the adaptive ECU would deal with that since its something that was NEVER intended to change. The only way it would adapt for that might be with knowing what the atmospheric pressure is which would change some responsiveness in the engine. That has nothing to do with the Throttlebody.

    Above, I said I don't seriously consider the velocity of the air through the TB mattering for the velocity of air that flows past the intake valves. The plenum kinda puts a stop to all that.

    While I can't speak to what Gary mentions about T1 setups feeling less responsive with a larger TB, when you remove all the semi sketchy turbo setup and just have a simple n/a engine, yes, it makes a huge difference in throttle response. Its the case in ALL happy engines. It is why manufacturers make progressive throttlebodies or twin blade setups (one small, one large, etc).


    Quote Originally Posted by Dr. Johny Dodge View Post
    they probably didn't spend so much as not to save it back again in the first year or so of only produceing one casting

    and one look at the one piece says they were not concerned with haveing an intake that makes more than 175 hp so there's no need tor the 46/52 mm swap
    Here is where I totally agree with you. The setups were only made for so much HP, and T1's were made for much less than even 175hp. I would never sacrifice for the masses to make a few tuners happy if ability to feed my family was on the line at the company.

    Quote Originally Posted by turbovanmanČ View Post
    True dat, same issue with diesels right now, they are plugged up with emissions at the expense of MPG.

    If the 52mm t/b was already around, wonder why they made a 46mm version? That surely added costs.
    The 3.0 moved to 46mm TB and stayed that way. The TB got smaller the same year the exhaust manifolds got larger. The plenum designs also changed. The HP rating remained about the same for 14 years.........Also, realize that the 3.3L came into being so they had to make sure the 3.0 made significantly less power, unlike the 3.0 12 valve put in some mitsibushi versions that were rated up to 180+hp with variable intake manifolds, big TB's, and different compression ratios.
    The 52mm then became the mainstay for the 3.3L and 3.8, with the 3.8 eventually going 58mm.

    As a manufacturer I wouldn't put a huge TB into an already developed factory turbo setup that I had no plans on matching the rest of the system too.

    - - - Updated - - -

    Quote Originally Posted by contraption22 View Post
    I had wanted to work on a progressive throttle cam for my engine as I will be using a 75mm TB. I shelved the idea for now in the interest of getting the car running first to see if it's needed. I noticed an issue with my old DOHC neon, which I had swapped from the MTX TB to an ATX TB which had a larger ID. The autos also had a "faster" throttle cam for throttle response, which made for some jerkiness when installed on the MTX car.
    If you are not trying to be fancy, its really really easy. Pretty sure I already bugged you about this a year or two ago.
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  18. #58
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    Re: Reduced mileage when using 52mm TB

    Quote Originally Posted by Ondonti View Post
    The 3.0 moved to 46mm TB and stayed that way. The TB got smaller the same year the exhaust manifolds got larger. The plenum designs also changed. The HP rating remained about the same for 14 years.........Also, realize that the 3.3L came into being so they had to make sure the 3.0 made significantly less power, unlike the 3.0 12 valve put in some mitsibushi versions that were rated up to 180+hp with variable intake manifolds, big TB's, and different compression ratios.
    The 52mm then became the mainstay for the 3.3L and 3.8, with the 3.8 eventually going 58mm.
    What's funny is that even though they redesigned the intake and put the 46mm tb on it, the hole is still 52mm TB size. A 52 bolts right on, and the gasket for the 52 matches the intake and everything.

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    Re: Reduced mileage when using 52mm TB

    Quote Originally Posted by mopar-tech View Post
    So botched it required two paragraphs of detailed information in the 2.5 Turbocharged SAE paper #900852

    It notes in the paper "throttle response was excellent" so clearly this was a concern for Mopar.

    A summary is here- http://www.thedodgegarage.com/turbo_sae_25.html
    It was clearly fine for the 2.5TI. I've been told that the alternate one piece intake would have been far superior if not for the strange twist of fate that gave us what went into production.

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