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75mm throttle body for 4.0L SOHC?

Discussion in 'Modified 1995-2001 Explorers' started by 2000StreetRod, July 17, 2009.

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    1. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      I've heard that the 75mm throttle body for a Mustang 4.6L V8 might work on my Sport SOHC. My stock throttle body arm is a rotating round molded throttle cable guide. STOP.JPG
      There is small rod attached to the end of the throttle cable (perpendicular to the cable) that slides into a mating slot on the arm. (ignore the red arrows which point to the gap at the stop)

      All the photos of 4.6L 75mm throttle bodies I've seen on the internet appear to have a different way of connecting to the throttle cable. I don't want to change my throttle cable or the way it connects to the throttle body. I want to be able to switch between the stock and 75mm throttle bodies.

      Does anyone know of a 75mm throttle body (new or used) that is physically compatible with my stock setup? If so and new, who makes/sells it? If used original equipment, what make, model and year(s) of vehicle uses it?
       
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    3. RickOTR

      RickOTR Active Member

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      The TB on the 4.6 is not a 75mm, it's a 70mm. It will fit your X, just turn it upside down. Get the one from Ford Racing, it's a perfect fit.
       
    4. CDW6212R

      CDW6212R Elite Explorer

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      Ditto, the stock 4.6 TB bolts on, I have one that came from eBay and is ported/polished. The stock SOHC is almost the same, one is 65mm or so and the other is 68mm. Most people have gone to the 70mm, either FMS or another aftermarket TB.

      The opening in the intake is about 70mm, that's why most people haven't even thought of the 75mm size. But there is a huge following of the belief in smaller is better, so 99% of all posts are going to wrongly tell you that 75mm is too big.

      I mentioned the 75mm size because it is a common 4.6 TB to find, and I'm sure that it will bolt on. It wouldn't hurt to clean up the opening of the plastic intake just a bit to make it match the TB. There is an aftermarket TB on eBay now that's about $90.

      FYI, the TB we have, like the 4.6, is very simple with no EGR or IAC holes. Just take care of the old gasket of yours and swap the TPS to the new TB. Adjust out any slack in the cable with a zip tie on the foot pedal cable end. It's a bolt on, I would go with the 75mm if I did it again. Regards,
       
      Last edited: July 3, 2013
    5. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      Thanks Rick and Don for the info! I'll start searching the internet for a "bargain" throttle body. When I get one I'll do before and after dyno testing. If there is a definite improvement then I'll try my hand at tapering the intake plenum opening to match the throttle body output opening. I seem to recall that the intake plenum has an opening of 65mm. My plan is for the intake airflow velocity to increase as it makes it's way to the plenum. That would be achieved with a 4 inch dia air filter output, a 90mm MAF sensor and a 75 or 70mm throttle body.

      By the way, since I have my own throttle cable mod (http://www.explorerforum.com/forums/showthread.php?t=248731) under the hood, I won't need to crawl under the dash to zip tie the foot pedal cable.
       
    6. Carguy3J

      Carguy3J Well-Known Member

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      Not a good plan


      First off, I would stick to the 70mm. The 75mm, for a SOHC, is too big. Why, well for one thing as the throttle body gets bigger, you will lose throttle response. There are numerous reasons and aspects to this factor, which I could spend all day typing explainations for. I don't have time for that right now. I would recommend an excellent series of books by David Vizard. Do a google search, or try amazon. I'm reffering to the " How to Build Horsepower"
      and "Carburators and Intake Manifolds" books. While they are geared towards carb'd small-block chevy's they have a lot of engine tech and theory that applies to almost all engines.
      2nd, while a 75mm TB might make more top-end power IF the intake inlet and all the upstream piping (from air filter/MAF/etc..) were a matched size, in the case of our SOHC motors, the PLASTIC intake manifold can't be ported big enough to match a 75mm TB. This will create a "lip" at the transition. This will in turn create a very turbulent airflow that will reduce overall flow.

      Next, the 90mm MAF. Also WAY to big. You MIGHT be able to get away with an 80mm. ( I'm planning a trying one down the road) In any case, both the 70MM TB and the larger MAF (80mm or 90mm) WILL require a flash tuner and custom tuning, to work properly. Call James at Henson Performance. He'll set you straight on all this, and sell you an SCT Xcal3, w/ some really great custom tuning.
      In any case, I would improve your exhaust before you worry about your MAF, or the TB for that matter. Doesn't matter how much air you can get in, if you can't get it back out.

      Oh, as for the TB, I would highly recommend Professional Products. As you can see from my sig, that I haven't updated; I originally ordered a MAC. I was very disappointed. Build quilty was horrible. I sent it back w/o even thinking about installing. I was also not happy with their response to issues with it. I ended up with a polished 70mm Professional Products TB, for less than the un-polished MAC, and fit and finish are 1000% better
       
    7. CDW6212R

      CDW6212R Elite Explorer

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      Well done with that adjustable throttle cable project.

      I would stay with matching inlet pipe sizing to the MAF and TB. There isn't much to gain with making the pipe bigger than the MAF and TB, maybe for all out racing. There are many other things worth doing before that. The 70mm TB fits the intake opening well enough that no porting is really needed. Fitting the 75mm is not a huge change, it wouldn't take much to match that better.

      It's worth making the TB larger than the intake manifold, but not a bunch larger, and the gains drop as you do. But it does help, and the key to getting the most out of it is the PCM tuning, it needs programming to richen the mixture.

      Any airflow increase will increase power, at all rpm's, given the proper A/F ratio and timing. The A/F and timing are entirely controlled by the PCM, and it is not perfect. The PCM does not make perfect adjustments for all changes. It does very well for anything except big changes, like the MAF, injectors, boost, or boring/stroking. But for all the little things, there are gains with new programming, thus wait to do the PCM after the big stuff. Live with the random results of the minor changes, some will improve power at all speeds, some will not(result of leaner mixture).

      I will not debate bigger versus smaller. I know that I'm correct in my power theory's, and I know that the smaller is better is wrong 99% of the time.

      I also know that bigger up until some random magic figure you make up as an individual, that is wrong also.

      Bigger is always better for most I/H/E parts except a very few. The headers are very critical, they need to be big enough to support maximum power in the upper rpm where the vehicle is run, and no larger. The collectors also need to be sized for the primaries to gain the most from scavenging. Those parts just like camshafts should not be selected by non professionals. Always get a pro to select those for you.

      Consider the parts you are looking at, what will they cost given a smaller cheaper version, versus the bigger higher end stuff. Pick the parts that are in your budget, don't plan to buy multiple parts. Do not buy two sets of heads, exhaust sizes, TB's, MAF's etc. If your goal is acceleration, go for the biggest that you can afford, and start with budgeting the PCM programming. Programming is not dirt cheap, but compared with buying more than one of any part, it is inexpensive.
       
    8. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      Thanks for your advice! I'm also concerned about a possible loss of throttle sensitivity at low airflow. However, the standard throttle design is very nonlinear for airflow vs rotation angle. I believe that the change of airflow from 5 to 10 degrees is much less than that from 30 to 35 degrees.

      Also, I should point out that I'm more interested in fuel economy than maximum horsepower. I was surprised when Al Aldive concluded that his fuel efficiency improved after changing to a customized Ford racing 70mm throttle body. Apparently the larger cross section reduced air restriction resulting in more efficiency. I'll try to duplicate his results. Your comment about the "lip turbulence" in theory is a valid concern that I've considered. However, there is a Ford designed "turbulence generator" between my stock throttle body and the intake plenum. The speculation is that it's function is to reduce noise.
       
    9. CDW6212R

      CDW6212R Elite Explorer

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      I cut those "comb fingers" out from my TB gasket, but I have a new gasket I may install some day. For maximum fuel efficiency you don't need to go so far at increasing sizes. Just be sure that what you change is no longer a restriction, compared to the adjacent parts.

      Consider different headers, and a higher flowing exhaust(cats/mufflers). I have not seen anything comparing the OEM headers to the few expensive others. If I knew that there was an improvement, those would be higher on my list. The stock headers look very very good, so I doubted that much would be gained there. The cheapest brand I ran across was OBX, at near $250 a set.
       
    10. Carguy3J

      Carguy3J Well-Known Member

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      1.) with regard to your goals; if maximum HP is not the purpose, then all the more reason to stay on the smaller side. Yes, a 70mm TB will reduce restiction and improve fuel economy. Going bigger on N/A 4.0L-SOHC motor is getting into diminishing returns and trade offs. As CDW... said, bigger (heads, intake,exhaust,etc..) will make more HP. However, I still firmly disagree with his bigger is always better theory. If we were talking about 2,000lb drag strip vehicles w/ a stick or high stall converter,and gears; or a top speed Silver-State car, then HP at any cost might be the winning solution. ...but we're not talking about that kind of car. We have daily driven 4,000lb+ trucks. Here the bigger is better theory fails. Why? Well, as you go bigger (intake, heads, exhaust) you kill low to mid range flow velocity. This will reduce cylinder filling, as well as exhaust scavenging. All this will, in turn, sacrifice very valuable low to mid range torque ( and alot of it in some cases) for a relatively small gain in top end HP. Our vehicles NEED torque. In this application, a "peaky" top-end motor will reduce overall performance and economy. Since someone mentioned Aldive, ask yourself: is he using a 90mm MAF? No.

      Obviously, you are getting some conflicting opinions. Again, I would highly recommend that you talk to James @ Henson Performance, before going any further. I think he has a "Ask James" thread on here somewhere. I would also, again, highly recommend those two books, or something similar.

      2.) With regard to the "comb" thingy; I asked several Ford techs. Most had no idea what it was there for. A couple gave me what I think is a very plausible explaination. Have you noticed that the egr is introduced right there at the TB-intake interface? They told me that the comb does indeed create a turbulent airflow, on purpose. Supposedly, it's to prevent carbon buildup, due to the egr gas. Makes sense to me???? They also agreed that the "fins" could be safely ground off the gasket, as long as you remember to clean the TB and intake once in a while.
       
    11. CDW6212R

      CDW6212R Elite Explorer

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      These are facts, not debatable, and that is where most people fail to comprehend airflow and power in any normal gasoline engine.

      There are absolutely countless examples of larger components being used, and low end power being lost. Absolutely every one of those examples shows a fool who did not properly tune the engine after the modification. Of course power is lost all over the place when the A/F ratio is moved from ideal, which is what most changes do.

      The PCM must be reprogrammed, even after little changes, if you want all of the potential.

      I don't deal in fashionable schemes(current go fast fads), I go for the best always. Don't skimp ever, do it right always. Night,
       
    12. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      "Pig in a poke!"

      Last week I purchased another ford stock throttle body (Pig in a poke) on eBay for $25 plus shipping. I thought it was a 75mm for a Mustang V8 but it turned out to be off a 97 Expedition. It has a side port below the TPS that bypasses the throttle plate to a base port. There's also a female hex head adjuster that controls the bypass flow. The port probably connects to the PCV. The throttle plate diameter is about 70mm but the inlet and outlet diameters are smaller (about 68mm). The inlet has an abrupt bore change just prior to the throttle plate.

      Today I purchased another throttle body that hopefully will be more suitable for testing. It is a 75mm limited production (or no production) Ford racing unit that has been ported and polished. It comes with no TPS so I'll use the one on the Expedition throttle body. From the photos the inlet and the outlet port both look to be 75mm in diameter.

      75mm_racing.jpg

      Rather than try to port the intake plenum to match I'll probably fabricate my own tapered adapter. That way I can switch back and forth between my stock and racing throttle bodies. I'll mount my unmodified stock gasket at the intake plenum and buy or make another gasket to fit between the throttle body outlet and the adapter.

      I've read in other posts that converting to a larger throttle body usually results in more cable play. I had 3/8 inch cable play with my stock so I should be able to accomodate a 1/2 inch (or more) thick adapter. I won't know until I receive the racing throttle body if the stock air hose will fit it.
       
      Last edited: July 22, 2009
    13. CDW6212R

      CDW6212R Elite Explorer

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      Part of why these are inexpensive is because the IAC (bypass air) is mounted away from the TB. That one you just got likely has that air bleed for additional air like the IAC.

      You should get the old one off and see the intake entry before making plans. I doubt that much can be removed there, as plastic it isn't going to be very thick in any direction. I would just smooth the entry a little bit, and match the gasket to the TB. For the 2-3mm of difference in the perimeter, just making the mismatch subtle should be enough.
       
    14. Carguy3J

      Carguy3J Well-Known Member

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      The idea of a tapered spacer is nice, to make a smooth blend between the RB and intake, but be careful to keep it as small as possible. By going with such a large TB, you're already going to be dampening the intake vacum signal. Too large a spacer will have the effect of increasing plenum volume; only making an even weaker intake vacum, and further threatening to reduce low RPM cylinder filling and torque. ...not huge, but it all adds up.....

      You really need to match that stock gasket to the TB, and smoothly grind out the "combs". If not, then that new TB is mostly a waste, as the gasket diameter is much smaller than the the new TB. You can easily get a new stock style "thick" gasket if you want one to play with. I think the auto parts store even have them.

      As for the increase in cable play w/ aftermarket TB's, I'm pretty sure it's more a case of the thin paper gaskets that come with most new TB's, as opposed to the stock "thick" plastic one. Although, I'm sure a small bit of it could be due to differences in casting thickness of the base of the TB.

      Well that's my $.02 for the evening..... Now back to work (outside,in the dark)........:rant:
       
    15. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      Don,
      You have apparently misunderstood my last post. I have no intention of modifying (porting) the intake plenum. My plan is to insert an adapter (spacer) between the plenum and the 75mm throttle body. The bore of the adapter will taper from 75mm (outlet diameter of throttle body) to 70mm (inlet diameter of plenum). I may have to purchase longer throttle body mounting bolts to accommodate the spacer. You make a good point about matching the gaskets to the ports.
       
    16. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      I hadn't thought about the spacer effectively increasing the plenum volume and decreasing the vacuum. That's an interesting observation.

      I agree that the stock gasket port should match the plenum port. I have reservations about grinding out the "combs". I'll probably purchase two new gaskets so I can make comparisons with the stock gasket.

      Excellent observations about the throttle cable play! I may need thin gaskets with the spacer to achieve a fully closed throttle position.
       
      Last edited: May 29, 2013
    17. celly

      celly disturber of the peace Elite Explorer

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      I used both the Ford Motor Sports and BBK offerings on my old SOHC equipped Sport. Yes, I did get rid of the comb. I noticed no difference except that my cruise control was screwy afterwards. I never did adjust the cruise at the end of the day because I eventually put the OEM TB back on before selling both TBs and eventually the truck itself. I expected more from this mod and was disappointed in the results especially when I considered how much the TBs cost.

      I think there are better mods for the money. If you want to mod just for the sake of modding, then go for it, but the net gains from an upgraded TB on the SOHC are marginal in my opinion.
       
    18. CDW6212R

      CDW6212R Elite Explorer

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      I was hinting that the gains from any changes to blend the entry will be about the same whether you make a spacer or not. That's why I suggested that first you take the old TB off and see the actual size difference. I think if you just spend five minutes on the plastic intake and keep it clean, the results will be the same.

      Brad is right, not much will change except WOT and after a good wideband tuning of the PCM. Not many people have done all of that, and of course the change is so small it can't be really felt. No one compares before and after times either. But logically it should help a little, I know, prove us wrong so we can stop doing it. Regards,
       
      Last edited: July 3, 2013
    19. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      I received my racing 75mm ported and polished throttle body from Jerry Strannigan (plenum1@sbcglobal.net) and I'm very pleased. I pulled my stock throttle body off to make some measurements. The air intake plenum has an inlet diameter of 64.7mm. It is composed of two or more pieces that fit together at the inlet. I am not comfortable with modifying (porting) the intake plenum inlet.
      PLENUM.JPG
      The throttle body gasket port diameter is 65.3mm where there are no combs. The combs appear to be shaped in a way to direct airflow toward the plenum chamber splitter in a way to optimize airflow. It would have been much easier and less expensive for Ford to try different comb arrangements than to try different plenum designs. Since the gasket port diameter is larger than the plenum inlet I don't think it is a restriction and therefore will not modify it at this time.
      stockOut.jpg

      The stock throttle body has an outlet diameter of 65.3mm (same as gasket) and an inlet diameter of 68.7mm.
      TNG.JPG
      TBnGFrt.jpg
      My racing throttle body has an inlet diameter of 77.0mm, an outlet diameter of 76.2mm and a throttle plate diameter of 74.2mm. There is a mismatch of 10.9mm (76.2-65.3) which may be enough to warrant an adapter (spacer with tapered port).

      The large size of the racing throttle body should be enough to determine if there is any real gain in performance or economy by increasing throttle body size. I'm looking forward to some before and after test results.
       
      Last edited: July 25, 2009
    20. CDW6212R

      CDW6212R Elite Explorer

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      Very good Dale, and those are good pictures and measurements. I agree that with a 5mm difference in radius, that's too much to expect to smooth out of a plastic entry.

      The upper intake is the biggest restriction of these engines, and the hardest to improve. The later engines are a little better, but we are still stuck with the restrictive tight turns and small ports.

      The TB bolts are fortunately rather long. You may be able to use them if you can make a thin adapter of about 3/8" or so in size. With the tight bends of the intake entry, there isn't anything to gain by having a really long entry to smooth the change from 65mm to 75mm. That EGR pipe is bigger than I remembered, and the air has to turn hard right there also.

      You are making progress. But on second thought I would like to get a harder look at a later intake. It may or may not be worth it to think about swapping. I wonder if there are any decent pictures of 4.0's from late late Mustangs, besides the truck intakes. Regards,
       
    21. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      Cutting board adapter

      I finally got back to working on my throttle body replacement. I fabricated my throttle body to intake plenum adapter from a portion of my wife's kitchen cutting board. It's firm but easy to work with and just soft enough to provide a good seal. It's also dishwasher safe which means it can withstand temperatures at least as high as 200 degrees. I've used some of it before as a temporary MAF sensor to intake hose adapter and it worked fine. It's a little more than 3/8 inch thick which happens to be the same amount of slack I have in my throttle cable without my adjuster.

      I started by cutting a 2.5 inch diameter hole using a hole saw. Then I used a 2 inch diameter sanding drum to flare the hole to a little more than 3 inches in diameter. The results are shown in the photo below.
      Adapter.jpg
       
    22. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      Initial installation

      I performed some voltage checks on my stock throttle body before replacing it. The voltage with ignition On, engine Off at closed throttle was 0.97 volts. That's slightly more than desired according to what I've read on this forum. At wide open throttle (WOT) the reading was 4.7 volts. The photo below shows the racing 75mm throttle body installed with a 1997 Expedition throttle position sensor (TPS) installed.
      TPS.JPG
      Visible in the photo are the M5-0.80x30 socket head cap screws (instead of the stock Phillips head) I purchased from Lowe's to mount the TPS to the throttle body. The photo below shows the 75mm throttle body with closed throttle.
      INCLOSED.JPG
      The thickness of the tapered adapter was just right for virtually no cable slack with the throttle control against the closed stop screw. The voltage reading at closed throttle is 1.03 volts (higher than I want). I noticed before using my Dyno-Scan that absolute throttle position was 18.8% for the stock throttle body at closed throttle.
      The photo below shows the 75mm throttle body at WOT after connecting the throttle cable.
      INOPEN.JPG
      I wedged a pole between the accelerator and the seat back to check the throttle plate movement. The throttle control was against the WOT stop. The voltage at WOT is 4.7 volts. As I recall this equated to an absolute throttle position of 92.8%. I disconnected the negative battery terminal and then connected the cruise control cable and attached the main intake hose and associated hoses as shown below.
      Complete.jpg
      It was fairly difficult to force the stock intake tube over the larger than stock outside diameter of the 75mm throttle body. I had thoroughly warmed up my engine before replacing the stock throttle body to insure the engine wouldn't die when started with the 75mm throttle body. I reconnected the negative battery cable after more than 10 minutes and started the engine. The engine started fine and idled about the same (not stable and slow) as it did with the stock throttle body. I let it idle for 15 minutes so the PCM could begin to "learn" the new throttle body. During this time I watched the A/F ratio and detected nothing abnormal. I then spent about 10 minutes switching from Park to R to N to D to N to R to N to D letting the PCM further "learn" the new TPS and throttle body. Then I ran the engine at various speeds under 3,000 rpm. During all of this I watched the A/F ratio and nothing looked abnormal. Then I did a couple of throttle "blips" but still nothing over 3,000 rpm. The throttle response seems improved and the intake air flow noise is definitely increased. The noise increase could be partially due to the elimination of the "comb" gasket. No CEL was ever illuminated.

      Next comes a test drive with my Dyno-Scan to monitor O2 sensors, absolute throttle position, MAF airflow and to watch the A/F ratio. I'll also check the cruise control to see if the cable needs to be adjusted.

      I'm not satisfied with the larger closed throttle TPS voltage but I don't want to drill out the bushings to perform the slot adjustment mentioned on this forum. I think the bushings are an integral part of the physical strength of the TPS. I'll play with my stock TPS to try and find an alternative method.
       
      Last edited: October 23, 2009
    23. CDW6212R

      CDW6212R Elite Explorer

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      That's very good, and I like those TPS screws better than what I bought.

      Don't do anything about the TPS voltage, that 1.03 is perfectly fine. What you have read about adjusting the TPS is all false, a complete myth.

      The OBDII and newer PCM's do not have hard TPS voltage data in them. They all read the idle TPS each time the engine is started, and that is the point during that operation cycle that the PCM uses. It doesn't matter if it's off slightly from 1.0 volt, it is fine within say .3-.5 volts. Any TPS check is very easy now, the idle should be around 1.0v, and the WOT should be near and below 5.0 volts. You are done there, well done.
       
    24. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      worse gas mileage!

      Well I can definitely state that my installation of a 75mm ported and polished racing throttle body adversely affects gas mileage. The reason, the engine is so much more responsive and fun to drive that I can't seem to keep from mashing the throttle! It may not actually be significantly more powerful but it sure seems and sounds like it is. I'm still keeping the maximum rpm at 3,000 until I accumulate 200 miles after adding gasket stop leak to the engine oil in hopes of stopping what appears to be a very slight rear main seal leak. It's going to take me a while to get used to it and return to my normal driving habits. No trip to the local dyno until after an oil change.

      So far I have not detected anything negative resulting from the throttle size increase. The A/F ratio seems unaffected as does the idle. Tomorrow, if the weather is nice, I'm driving from Greenville up the mountain to Hendersonville. That will give me a chance to check out the cruise control. This morning I adjusted the cruise control cable to it's maximum length but there was only about 1/8 inch left to lengthen. I haven't figured out how that affects the cruise control speed range.
       
    25. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      Cruise control

      I tested the cruise control functions (On/Off, Set, Resume, Accelerate and Coast) and various speed settings between 50 mph and 65 mph. Everything functioned properly.
       
    26. CDW6212R

      CDW6212R Elite Explorer

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      Good, I just ordered a new cable(actuator) for mine. They are about $20 I think. Mine has not worked for about two years.
       

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