75mm throttle body for 4.0L SOHC?

[2000StreetRod]

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.
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?

[RickOTR]

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.

[CDW6212R]

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 thougth 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,

[2000StreetRod]

Originally Posted by CDW6212R

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 thougth 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,

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/...d.php?t=248731) under the hood, I won't need to crawl under the dash to zip tie the foot pedal cable.

[Carguy3J]

Originally Posted by 2000StreetRod

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/...d.php?t=248731) under the hood, I won't need to crawl under the dash to zip tie the foot pedal cable.

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

[CDW6212R]

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.

[2000StreetRod]

Originally Posted by Carguy3J

... The 75mm, for a SOHC, is too big. Why, well for one thing as the throttle body gets bigger, you will lose throttle response. ... I'm reffering to the " How to Build Horsepower"
and "Carburators and Intake Manifolds" books... 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.

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.

[CDW6212R]

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.

[Carguy3J]

Originally Posted by 2000StreetRod

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.

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.

[CDW6212R]

Originally Posted by CDW6212R

...

Any airflow increase will increase power, at all rpm's, given the proper A/F ratio and timing.

...

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,

[2000StreetRod]

Originally Posted by CDW6212R

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.

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.



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.

[CDW6212R]

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.

[Carguy3J]

Originally Posted by 2000StreetRod

......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.

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)........

[2000StreetRod]

Originally Posted by CDW6212R

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.

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.

[2000StreetRod]

[QUOTE=Carguy3J;2247832]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.QUOTE]

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.

[celly]

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.

[CDW6212R]

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.

Todd 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,

[2000StreetRod]

Originally Posted by CDW6212R

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.

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.

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.


The stock throttle body has an outlet diameter of 65.3mm (same as gasket) and an inlet diameter of 68.7mm.


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.

[CDW6212R]

Originally Posted by 2000StreetRod

... There is a mismatch of 10.9mm (76.2-65.3) which may be enough to warrant an adapter (spacer with tapered port)....

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,

[2000StreetRod]

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.