Installing a 70mm Mustang Throttle Body on a `92 Dodge Daytona

In January of 2003, I began the project of mating a 70mm Mustang throttle body to the plenum of the 3.0L engine in my '92 Daytona. This is the absolute biggest TB that can be installed on the plenum without using some type of a reducer. In order to keep the car drivable in the interim, a second plenum was obtained for the work. Below are pictures of the project taken throughout the process.

My shop setup is currently very poor. All work was performed while kneeling on a concrete floor or sitting on a milk crate and working in my lap. This is not the safest way to drill metal by any means. Also note, that the amount of sanding and grinding makes a HUGE mess. Many thanks to my wife for tolerating the blanket of metal dust that covers that room of our basement (and the endless grinding and sanding racket).

Tools Used: Dremel (cut off wheels, wire brushes), 4" Angle Grinder, Finishing Sander, Multiple Drills (bits, sanding drums, wire brushes), Soldering Iron, JB Weld metal epoxy, Various screwdrivers, Various pliers, C-clamps, Jigsaw, Safety Goggles, Ear Plugs, Dust Mask, Masking Tape, Sandpaper (various grits), Flap Wheels, Pieces of Aluminum flat bar from www.OnlineMetals.com.

Tools that would have been nice to have: Work Bench, Vise, Drill Press,

Car preparation: Installed a digital Air/Fuel gauge from www.GadgetSeller.com and 26# Accel Fuel Injectors from www.atlanticspeed.com. Also purchased new upper plenum gaskets.

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pictures:

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Top and Bottom Portions of the original plenum	Bottom half of plenum, divider removed	Top half of plenum, divider removed	Bottom half of plenum, another look

JB Weld used to build up the bottom of the bottom half of the plenum. Cardboard pieces are taped in place to shape the JB Weld.	After the JB Weld dried	Major port of bottom half of plenum. Notice the JB Weld peaking through.	220 grit sandpaper taped to a 3/4" sanding drum and used for final sanding

Plenum end view without neck. The height of the opening is almost exactly 70mm.	4"x5"x1/2" piece of aluminum from www.onlinemetals.com.	Home made spacer created using a drill, a jigsaw, and some sanding drums. The surface was roughed up with the angle grinder.	Plate is bolted to the top of the plenum using two small machine screws. Prior to bolting, JB Weld is applied to the surface between the two pieces and to the bolts.

Tape is used so that the JB Weld will drip in and form a smooth surface when applied. Also note that the spacing of the small bolt heads used to join the plate and the plenum fit into the groove of the EGR plate perfectly.	Top view of plenum attached to spacer. Two long bolts were inserted at this time. The heads are ground down slightly to fit in the curve between the plenum and the plate. JB weld fills the valley between the two.	90 degree steel brackets are held to the lower plenum with machine screws. JB Weld is used around the screws for additional support and to seal the holes.	Lower half of plenum with the plate up against it.

Tape the top half to once again, make a good surface with JB Weld.	Bottom half of plenum is held to the plate with machine screws and JB Weld is applied. Note, the heads of these screws do not fit in the grooves of the EGR spacer and required countersinking in the aluminum plate.	Another view. Note the way tape was used to shape the JB Weld.	70mm Mustang EGR spacer with two small holes drilled to get vacuum to the vacuum ports. Apparently on the Mustang, the seal isn't made on the inner ring.

Side view of EGR spacer. A piece of metal has been ground off of the side of the original plate (not shown in any pictures).	Penny used to block one hole. Masking tape used to block the other	Both holes filled with JB Weld	This is an `86-92 Mustang AIC. It is like an AIS however rather than a pintle that moves in and out, a solenoid moves a stick with a ball on it back and forth

Gut the AIC. ($10 on eBay)	Bore the top of the AIC housing out a little bigger so that the base of AIS will fit in it	Plug up the end with JB Weld and a large fender washer.	End plugged with JB Weld

A view of the AIS. An AIS from a Jeep was used initially but in later stages of the project, the stock AIS from my Daytona was used. The only difference is the color and the shape of the pintle. Note the way the bolt holes have been widened.	A view of the stock AIS (which was used rather than the Jeep AIS because of the shape of the pintle). Note the 5/16" and 3/8" washers.	The washers fit the stock pintle perfectly. The 3/8" washer rides right up against the lip of the pintle. The 5/16" one fits perfectly on top of the first. These washers will be used to make a hole that the AIS can block or unblock to control the idle.	The washers were placed on the end of the AIS, clamped together with a pair of vise grips, and then ground down with an angle grinder. After grinding, superglue was used to hold the washers together before they were epoxied into the AIC housing.

There is a curved (taco shaped) surface in the middle of the AIC housing. Grind it flat so that reducing washers can be inserted to narrow the opening. JB Weld was used to glue the washers into place, and it was a real pain to get the washers to sit level (not shown).	AIS bolted onto AIC housing. In order to do this, the holes both the AIC housing and the AIS were drilled bigger. This picture was taken before the reducing washers were added to the AIC housing. Otherwise, they would be just barely visable in the right hand opening.	AIC installed using cross threaded 1/4 machine screws.	`86-92 70mm Mustang throttle body disassembled (MAC version) ($150-$170 w/ EGR spacer on eBay)

Bore the opening for the TPS sensor slightly to accept the Chrysler TPS. Also, shave 1/16" off of each side of the end of butterfly shaft so that it will fit inside the Chrysler TPS (not shown).	Bolt 2 1/2" pieces of aluminum together and us a jigsaw, angle grinder, and dremel to make a cable holder like the one on the Chrysler throttle bodies. This just bolts to the flat panel on the Mustang TB.	Another view of cable holder. The dips that the cables sit in were created using an angle grinder while holding the aluminum with a C-clamp.	This is a 4"x4" corner support from Home Depot (~$1) Once side is cut to the height of the TB. The other side will be bolted to the bracket that holds the cable sleves. Additional holes were drilled that are not shown in the picture.

1/4" piece of copper tubing soldered into the Mustang vacuum port (~$1 at Home Depot). Vacuum port has also been twisted upward using a pair of pliers. It is just rotated but still very firmly attached.	The TPS is held on with machine screws that are cross threaded. It is also supported but some small washers between it and the throttle body. Not using the washers puts pressure on teflon ring around the shaft and prevents the valve from closing.	Note the difference in angle between the blade on Chrysler and Ford throttle bodies. Failure to address this will result in a code "24" from the computer.	In order to get around the angle difference, I used a dremel to notch the head of a machine screw so that it can fit inside the TPS. I then cut a slot in the shaft of the screw to fit around the blade of the TB. This involves some trial and error but I got it to fit on the second try.
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The Ford spring is VERY weak compared to the typical Chrysler spring. To make the pedal a little firmer, I added a supplemental spring.	The beast assembled minus the TPS. This is huge, but the hood shuts and it doesn't hit anything else under the hood.	Picture of the TB installed on the car	End view of TB installed on the car. Note that the vacuum tubes connect but require some bending.
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TB comparison. 70mm Mustang on the left. 46mm in the middle. 52mm on the right.

Latest Updates

5-4-03

Well, this project appears to be a bust. I do not intend to continue pursuing it because of the idle problem. Perhaps at some point I'll get industrious enough to swap on a Jeep Throttle Body or something <70mm with a tighter butterfly, but for now I'm tired of playing with it. That said, the following are my final discoveries, notes, etc.

Idle Problem:
Last weekend, I started working on the throttle body and figured out that the butterfly fits just loosely enough that it can actually be put in different positions when screwed to the shaft. The position difference is subtle, but it's the difference between seeing almost no light through the TB and seeing a bright line around part of the butterfly. Needless to say, even when seated perfectly, light still gets through. The result is that there is just too much air blowing by the butterfly to make this work on a 3.0L application and keep the idle down. After refitting the butterfly, I put it back on my car and took it for another spin. The idle came down to 750 at first but climbed back to 1000-1200 shortly into the drive. The gist is that a 5.0L engine is going to be more tolerant of a little more air slipping through at idle than a 3.0L. Knowing this, the manufacturers of the Mustang TB apparently didn't waste any engineering effort on making the butterfly fit tightly. I would say it's really cheaply built, but then again, I am trying to use it in a way other than it's intended purpose.

Throttle Response Update:
In my final test drive, I also cut wider holes in the L bracket I used to connect the throttle cable holder to the throttle body. Prior to this, the cables were not pulled very tight. The wider holes allowed me to bolt everything together with a tighter pull on the throttle cables, which is more like the stock fit. HOLY COW! Apparently I had just enough slack in the cables on my initial drive that moving my food to the normal "back out of the driveway" position just barely opened the throttle. As a result, the throttle response didn't seem that high. After tightening things up, the throttle response was amazing. We're talking 0 to 3000 rpms at the tap of your toe. I drove the car around like this for a little while, but it wasn't very practical. Significant effort was required not to gun the engine when pulling away from a stop light or shifting gears. I suppose keeping a little play in the cables wouldn't hurt anything, but it's not really the right way of doing things.

Final Thoughts:
Although I am very disappointed by the outcome, I did learn a few things in the process. I also don't really feel like the project was a failure on my part, but more so on the part of the quality of one of the components I used. After all, I did successfully port everything out, mate the plenum to the TB, and get the TPS & AIS working without any vacuum leaks. I guess the biggest shame at this point is that I have a beautifully ported plenum with no neck. DOH!

If anyone cares to try a project like this, I'd only recommend it for racing. In that mode, you're pretty much either at full throttle or no throttle so the touchiness wouldn't be a big deal. You would also be running at higher RPMs and benefit more from the increased air flow. While racing, you wouldn't care about the idle either. For a daily driver though, you need something you can loan a friend without fear of them getting themselves killed when they unwittingly hit the gas.

I would be interested in testing a 65mm and 60mm TB to see if they work better, however I don't really want to waste the money on the TBs. After altering them, I also wouldn't be able to resell them, and it is a fair amount of work. I do have a 60mm Jeep TB that I may try to fit on this project at a later time but this would involve more effort than I'm looking for right now. For those looking for a TB upgrade, I'd say stick with the 58mm or try the 60mm from the Neon. Mustang TBs may still have potential, but not the MAC variety. Other manufacturers might use stronger springs and better fitting butterflies but I don't have any information about those. I will say that I did buy the cheapest model out there, so others could be better.

4-6-03

So Close! The idle came down to where it should be and I actually took the car for a spin. This week, I altered my AIS housing so that the AIS could completely block air flow if fully extended (see pictures inserted into the AIS section of the above table). I also added a supplemental spring to the throttle body to make if feel a little more Chrysler like. (The Ford spring is very weak.) In addition to those two changes, I also swapped my 26lb injectors back out and replaced them with some 21lb injectors. The car simply didn't start well with the engine slightly warm or on warm days with the 26lb ones. (We'll see if that solves the problem. ...and yes I know that with an adjustable FPR, I could have just turned down the fuel pressure and kept the 26lb injectors. Unfortunately to do that, I'd have to buy the FPR and an old style fuel rail. That's on the eventual list, but I haven't got there yet. For now I'll stick with cheap injectors from eBay. )

The Good - First let's talk about the good. The car seemed to run smoother with the new throttle body assembly. That is probably due to the fact that my normal plenum is filthy inside and unaltered whereas the new one is ported, polished, and clear coated. During my test drive, I didn't hit the highway because I didn't really want to go too far without first firming up some pieces of the system. Still, I couldn't resist a short spin around town.

Throttle Response: The throttle response was just fine. My prior fear had been that it would be difficult to drive the car due to excessive throttle response. While the car responded well during my short test drive, I didn't find myself consciously altering my driving habits.

Torque: I've been asked by a few people if this setup caused me to lose any low end torque. Many have written that porting the plenum reduces torque. In my 15 minute test drive, I didn't notice any gain or loss of torque. The low end seemed normal to me.

Power: First let me say that I didn't really notice a power increase when upgrading from the 46 to the 52mm throttle body although there must have been one. This could have been because I was still getting used to driving a stick then, but I don't really know. I also didn't notice any gain later when I added the open element filter or when I upgraded to 8.8mm wires and new plugs although the latter did seem to smooth the engine. That doesn't mean that none of those things made a difference, in theory and by the testimony of others, I'm sure they did. It just means I didn't really notice.

That said, with this upgrade, I WAS able to feel an increase in power especially in the upper RPM band. Generally I don't find myself driving around in the 4000+ RPM range but during my test drive, I kept finding that range and the car kept pushing hard. I was very impressed with the initial results and look forward to getting the car on the highway. Assuming I can get this all to come together, this mod will definitely be a keeper.

The Bad - Unfortunately, my idle problem was only solved momentarily. After only about five minutes of driving, my idle bottomed out between 1500 and 1700 RPMs. Once back in my garage, I did some poking around and found that there was no suction coming from the AIS port indicating that the AIS was completely closed. Putting the palm of my hand over the mouth of the throttle body killed the engine quickly. The problem is that air is seeping by the throttle body butterfly. In a 5.0 Mustang, that extra air is probably no big deal, but it's enough to make a 3.0 idle too fast. So what happened? One hypothesis I have is that after the throttle body heated up, the fit of the butterfly changed just enough to make the difference. The other possibility is that somehow the butterfly got stuck just before closed. From what I could tell though, it was still closing all the way while hot.

One thing that I did notice was that a large amount of air is sucked through on the sides of the butterfly where the shaft connects to the throttle body housing. My next attempt will be to make that fit tighter to reduce the incoming air. That could put the idle back where it is supposed to be. All of this news is being typed right after today's attempt so I haven't really inspected the throttle body much yet.

3-16-03

Holy cow, it's in the 60s this weekend. I got to do a little more work on the car.

I solved the problem with the TPS by inserting a modified machine screw between the TPS and the TB blade. (picture has been inserted above) Essentially this involves cutting V shaped notches in the head of the screw to fit the points on the inside of the TPS. The screw I used fits inside the TPS perfectly. I then used the dremel to cut a deep notch out of shaft of the screw. The TB blade fits in this notch. The result is a perfect fit. When the TPS is installed, it must be rotated a small amount which is consistent with the way it fits the Chrysler TB.

Unfortunately, I tried to power in one of the screws holding the TPS on and it broke off in the hole on the throttle body. Looks like I'll be drilling it out and tapping some new threads. Despite this setback, I was able to verify that the change to the TPS setup makes the code "24" go away.

The car still idles way too high. Putting my hand over the TB opening caused the idle to drop and the engine to start to stall. It would have stalled if I had gotten a better seal with my hand but I'll admit that the suction made me a bit nervous so I took my hand away. It's surprising how much suction the engine creates. Based on that test, I'm about 90% sure the idle problem is related to the AIS.

It will probably be a few weeks before I get back to this project. I'll be out of town next weekend and after that I don't know what the plan will be.

3-10-03

After a little more thought, I figured out where the code "24" was coming from. The blade on the Mustang TB is at a different angle than the one on the Chrysler TB. When installing a TPS on the Chrysler TB, the TPS is actually rotated a small amount after it is placed over the blade. Due to the difference in blade angle, this rotation doesn't happen on the Mustang TB, which means there is also some play in it before the blade begins turning the sensor. Good call on the part of the computer. Looks like I need to find a work around.

3-9-03

This project is still underway however the initial install failed. After installation, the car idled at 2000 RPMs and the computer threw a code "12" "24" "55". According to Allpar, the "12" means that the battery was disconnected recently. The "24" means that the TPS voltage is too high". The "55" means that it is the end of the codes. Unfortunately, the TPS voltage would have been fine (because it works fine on the other throttle body) so there is clearly another problem. The AIS was installed with and without the O-ring. Without it, the pintle actually hits the AIC housing. The problem could be due to a vacuum leak or the Daytona computer disliking the Jeep AIS.

Another "problem" is the weakness of the spring on the Mustang throttle body. That spring makes the gas pedal feel as if it is barely there. I'm estimating that the spring is less than half as strong as the Chrysler TB springs.

I probably won't do much with this until it warms up some more. I've been working in an unheated and poorly insulated garage with the temperature between 25 and 38 degrees.

Half-Assed Things/Things to do Differently

One thing I don't like about the project is the way the lower half of the plenum is attached to the adapter plate. This prevents the plenum from being able to be disassembled again (without grinding out the JB Weld).

The AIC housing and TPS are held on with cross-threaded machine screws because Home Depot and Menards didn't have anything that would fit properly. While the screws do hold very tightly, better screws would be preferable. I found that the screws used on the AIC housing could be forced in with a drill and a big Phillips head bit. The TPS screws on the other hand didn't follow suit. Attempting this resulted in me shearing one of the screws after it was well embedded in the TB.

The piece of copper tubing is a little to small for the vacuum tube that fits over it. Wrapping it in a layer of electrical tape solves the problem and makes it fit tightly, but a wider piece of tubing would have been better.

Using cardboard to make a mold for JB Weld is a bad idea. You have to remove the cardboard with a wire brush essentially grinding it away. The sticky side of masking tape works great though because it just peels off after the JB Weld dries.

The corner bracket is kind of flimsy. Adding a second would be more sturdier.