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Thread: Reduced mileage when using 52mm TB

  1. #1
    Supporting Member Turbo Mopar Contributor
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    Reduced mileage when using 52mm TB

    I noticed in Dovovan's Garage the following statement
    The 52 mm throttle body is the largest T.B. I would install on a 2.2/2.5 engine, even then you will lose gas mileage around town due to loss of port velocity caused by the larger opening.
    The statement "due to loss of port velocity" is unclear to me. I would agree that the TB port velocity of a 52mm is less at the same RPM as a 46mm, for example. Since he was talking about Turbos which have multi port injectors, his statement does not make sense to me.
    All comments are welcome.

  2. #2
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    Re: Reduced mileage when using 52mm TB

    I'd guess when that happens its got to do with the map sensor reading slightly differently before vs after. Should be completely recoverable by a tune.
    MinivanRider

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    Re: Reduced mileage when using 52mm TB

    Thanks Rrider,
    That I can believe, Less pressure drop across the TB for the 52mm , therefore slightly higher Manifold pressure. ECU adds more fuel. I guess the O2 sensor does not have enough influence on the fuel equations to overcome the difference in MAP values. I do plan to change/tune to the 52mm at some point but wanted to understand Donovan's comment.

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    Re: Reduced mileage when using 52mm TB

    I think a 1 piece intake manifold has all the restriction you need :P
    What the term port velocity comes down to is restriction. More restriction = higher velocity of airflow and in theory, better fuel atomization and thus more complete fuel burn that leads to improved fuel economy.
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    Re: Reduced mileage when using 52mm TB

    I think that's an old wives tale. Others have swapped with no change and I swapped around from 46-58mm and never noticed a thing. I did dyno 46mm to 52mm and picked up 5 whp on a mild engine, so really, nothing, that could be dyno error etc.
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  6. #6
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    Re: Reduced mileage when using 52mm TB

    TPS vs. MAP would slightly shift as far as the ECM sees it.. I don't know if that matters.
    MinivanRider

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    Re: Reduced mileage when using 52mm TB

    Thanks Everyone,
    I will go with my gut and continue to plan my TII rebuild around the 52mm.

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    Supporting Member Turbo Mopar Contributor mopar-tech's Avatar
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    Re: Reduced mileage when using 52mm TB

    Consider the following analogy- I use to run a 340 engine with a 625 cfm carburetor with a single plane intake. Running a larger 750 cfm carburetor would have netted more hp at higher rpms but at the expense of low rpm torque (making the throttle feel mushy or soft till wound up). The larger opening causes some loss of velocity of the mass of air passing through the intake manifold. Depending on other mods your car already has it may or may not be noticeable. With the manual transmission in my Daytona I was able to feel the difference. Some people may compensate and utilize a larger throttle opening when driving hence the potential for slightly lower MPG. If you are ham fisted on the gas at all times then strictly a non-issue. Steady state operation on the highway should make no difference.

    Gary D.


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    Re: Reduced mileage when using 52mm TB

    Quote Originally Posted by Ondonti View Post
    I think a 1 piece intake manifold has all the restriction you need :P
    I hear people state this but I have found not much truth in it. The 87 to 88 vehicles did not change hp ratings with the only major change being the intake and when I was racing the Reliant and was deep in the 11's I made the change from a 1-piece intake to a highly modified 2-piece (ceramic coated, heavy internal porting, highflow neck) and the difference in between them was within the margin of error. A tenth or two perhaps and that could have just been due to track conditions.

    For most street cars I'd recommend the 1 piece due to ease of access to injectors and availabilty of injector rails.

    The big easy power is in the turbo and intercooler choices.

    Modified intakes become a different discussion.


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    Re: Reduced mileage when using 52mm TB

    IMO if you're just matching TB to tube size behind it, you're losing all the "velocity" within a couple inches of the TB when you have a small TB on a big tube. If you put bigger tube in there, THEN you might lose velocity at the port, but just maxing TB to tube you've got, nope. Throttle response would be another issue.
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    Re: Reduced mileage when using 52mm TB

    Quote Originally Posted by Mopar-tech
    I hear people state this but I have found not much truth in it. The 87 to 88 vehicles did not change hp ratings with the only major change being the intake and when I was racing the Reliant and was deep in the 11's I made the change from a 1-piece intake to a highly modified 2-piece (ceramic coated, heavy internal porting, highflow neck) and the difference in between them was within the margin of error. A tenth or two perhaps and that could have just been due to track conditions.

    For most street cars I'd recommend the 1 piece due to ease of access to injectors and availabilty of injector rails.

    The big easy power is in the turbo and intercooler choices.

    Modified intakes become a different discussion.
    I thought I remember you or someone bringing your testing, very interesting. What HP do you think you were at when you switched intakes?
    1989 FWD Turbo Caravan-2.5 TIII, GT35R, auto, a/c, cruise, pwr windows/locks, fully loaded with interior and ran with full exhaust. RETIRED FOR A FEW YEARS! 12.57@104 :O)
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    Re: Reduced mileage when using 52mm TB

    Quote Originally Posted by turbovanmanČ View Post
    I thought I remember you or someone bringing your testing, very interesting. What HP do you think you were at when you switched intakes?
    I'd really not like to hazard a guess at the moment as my memory is fuzzy after all this time and no further notes in front of me. Enough power to run 11.6 though and the radical weight loss program had not started. Even then that is deceptive, at its lightest the car was still 2250 with me behind the wheel. I'd love to be done around 1700 lbs.


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    Re: Reduced mileage when using 52mm TB

    I swapped to a larger TB on my sohc m/t neon and didn't notice any change at all really. I'm swapping to a 2 piece and ported 52mm tb in my omni right now. My buddy had an integra (b16 maybe?) and I was amazed at how massive the throttle body was compared to my neon.

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    Re: Reduced mileage when using 52mm TB

    I wanna say 67mm off the top of my head, but not sure why.
    DD1: '02 T&C Ltd, 3.8 AWD. DD2: '15 Versa Note SV, replacing.. DDx: '14 Versa Note SV << freshly killded :( ....... Projects: '88 Voyager 3.0, Auto with shift kit, timing advance, walker sound FX muffler on 15" pumpers wrapped in 215/65/R15 H rated Nexens.... and a '95 phord escort wagon PnP head << Both may need to go :( ..... I like 3.0s ... so??? ... stop looking at me like I've got two heads!

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    Re: Reduced mileage when using 52mm TB

    I'm not sure I understand how throttle body size would make a difference in fuel mileage. I understand a difference in air velocity through the TB at WOT, but not at part throttle. You'd just need less throttle angle to meet the air demand at a given part throttle load. In the end it's still going to be throttle position and MAP that determine fueling at a given RPM, and the TPS value would actually be lower with the bigger TB. The final say would still go to the 02 feedback.
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    Re: Reduced mileage when using 52mm TB

    Quote Originally Posted by contraption22 View Post
    I'm not sure I understand how throttle body size would make a difference in fuel mileage. I understand a difference in air velocity through the TB at WOT, but not at part throttle. You'd just need less throttle angle to meet the air demand at a given part throttle load. In the end it's still going to be throttle position and MAP that determine fueling at a given RPM, and the TPS value would actually be lower with the bigger TB. The final say would still go to the 02 feedback.
    The same way that engine wear effects mileage. You have to push the gas pedal harder to get the same speed. Inefficiency. So the idea being tossed around is that a bigger TB hurts atomization and therefore power. So more gas pedal would fix that. And therefore worse mileage. Thats the theory anyway.

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    Super Moderator Turbo Mopar Staff contraption22's Avatar
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    Re: Reduced mileage when using 52mm TB

    Quote Originally Posted by acannell View Post
    The same way that engine wear effects mileage. You have to push the gas pedal harder to get the same speed. Inefficiency. So the idea being tossed around is that a bigger TB hurts atomization and therefore power. So more gas pedal would fix that. And therefore worse mileage. Thats the theory anyway.
    That makes no sense at all.
    You still control the throttle with your foot. With a larger throttle body, you'd simply use less (not more) throttle input to maintain the meet the same air demand.

    As far as fuel atomization.... i'd buy that if we were talking carburetors and the mixture was happening closer to the throttle blade. Not with EFI.
    Last edited by contraption22; 05-05-2015 at 08:43 PM.
    Mike Marra
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    Re: Reduced mileage when using 52mm TB

    Quote Originally Posted by contraption22 View Post
    That makes no sense at all.
    You still control the throttle with your foot. With a larger throttle body, you'd simply use less (not more) throttle input to maintain the meet the same air demand.

    As far as fuel atomization.... i'd buy that if we were talking carburetors and the mixture was happening closer to the throttle blade. Not with EFI.
    Reduced atomization caused by a bigger TB cant be compensated for by opening the throttle more on the bigger TB. Or thats the idea here. I am not saying I agree with it.

    Another way to look at it is: forget about the big TB, just have a stock TB. But now make it so the injector spray pattern is much worse and has less atomization. Fuel economy will go down. Opening the throttle more will not fix it.

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    Re: Reduced mileage when using 52mm TB

    Quote Originally Posted by acannell View Post
    Reduced atomization caused by a bigger TB cant be compensated for by opening the throttle more on the bigger TB. Or thats the idea here. I am not saying I agree with it.

    Another way to look at it is: forget about the big TB, just have a stock TB. But now make it so the injector spray pattern is much worse and has less atomization. Fuel economy will go down. Opening the throttle more will not fix it.
    Yeah, I am not on board with the idea that the throttle body size effects atomization either.
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    Re: Reduced mileage when using 52mm TB

    Throttle body's don't affect atomization unless the fuel is being sprayed on them, which in our case, it isn't.
    1989 FWD Turbo Caravan-2.5 TIII, GT35R, auto, a/c, cruise, pwr windows/locks, fully loaded with interior and ran with full exhaust. RETIRED FOR A FEW YEARS! 12.57@104 :O)
    1984 Chev Getaway van, 6.2 Diesel with a remote mounted turbo setup burning WMO-For sale.
    2003 GSW 2.0L TDI, auto, fully loaded, modified, 360K-wife's.
    2004 GSW TDI, 5 speed, fully loaded, modified.

    Aurora ignition wires for sale. Link to info

    Super60 roller cams or custom/billet cams. Link to info

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