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Upgraded Throttle BodyI replaced the throttle body on my engine with a throttle body off of an engine equipped with an automatic transmission. Why? I'll explain below.
The throttle body for a stock 2.7L engine with the manual transmission has a 64 mm bore. There is a venturi-style restriction before the throttle plate. The plate itself has a plastic wedge on it, which aids in part-throttle control, that sticks out 8 mm from the surface of the throttle plate. The wedge itself is not aerodynamically shaped, so it presents a flow restriction. The effective WOT open area for this throttle body is about 2207 mm^2.
The throttle body for a stock 2.7L engine with the automatic transmission has a 62 mm bore. There are no restrictions in the bore. The throttle plate is just a plate, with no plastic additions. The effective WOT open area for this throttle body is about 2430 mm^2. This represents about a 10% increase over a stock manual throttle body.
This means that the effective WOT open area for the manual version of the throttle body is 9% smaller than the effective WOT open are for the automatic version.
Now, for the results. Part-throttle response has become much more responsive. Fuel economy has risen by as little as 2 MPG and as much as 7 MPG. Top-end power effects remain to be seen, but the power curve has shifted up at low-end and mid-range.
I have also tested a bored out throttle body that was purchased by Matt (LB3711 of 2GSS.org fame). The body itself is bored out to 65 mm. The throttle plate is just a plate, with no plastic additions. The shaft has been partially removed, which results in a larger opening at WOT. The effective WOT open area for this throttle body is about 2977 mm^2. This represents a 22% increase in opening area over a stock automatic throttle body, and a whopping 34% increase in opening area over a stock manual throttle body. The bored throttle body also shows improvements, although not as dramatic as was noticed with the stock automatic throttle body. Dynamometer results of all three throttle bodies can be found here. In the meantime, I have included pictures of each throttle body. You can view a gallery of the different throttle bodies here. Manifold Tuning Valve Installation with 68HC11-based ControllerThe 2001 JR body cars with the 2.7L engine also came with something called a manifold tuning valve (MTV). Basically, what this valve does is change the resonant frequency inside the the intake manifold, depending on whether the valve is shut or not. When the valve is open, the power peak shifts upward. When the valve shuts, the resonance frequency of the intake manifold changes, resulting in a downward shift of the power peak. My engine does not have this valve installed.
My educated guess, along with data optained from DodgeIntrepid.net, indicates that the MTV ought to be active at greater than 35% throttle opening. Further, as the MTV is activated, the MTV ought to be shut between 3000 RPM and 4300 RPM, and then open up between 4300 RPM and 5800 RPM. Once past 5800 RPM, the MTV ought to be shut again. At 3800 RPM with the MTV open (or with no MTV), the 2.7L engine develops about 180 ft-lbf of torque. With the MTV shut, the engine develops about 195 ft-lbf of torque. To date, the results of retrofitting the MTV to my engine have been noticably good. I've controlled this valve with a Motorola M68HC11 microcontroller, that gets input from the throttle position sensor and the crankshaft position sensor. I have dynomometer results of the MTV as being open all the time, and as being shut all the time. I have optimized the HC11 program, and at the next available opportunity, I will run the improved HC11 program on the dynomometer.
Deyeme Racing Firm Engine MountsI replaced the stock rubber front and rear engine mounts with Deyeme Racing firm engine mounts. This was intended to reduce some of the wheel hop I have experienced when starting out from 1st gear. The normal engine mounts allow some back-and-forth movement of the engine and transmission, so as to reduce noise and vibration that the average Sebring Convertible owner would find unpleasant. However, they also allow the engine and transmission to move about whenever the car is under any decent acceleration. This changes the geometry of the driveaxles, which causes some of the torque transmitted from the transaxle to act against the suspension instead of against the wheels. This causes the suspension to move about, and in so doing will also cause the wheel to move along with the suspension. The wheel will then exert less pressure against the road surface, and will then be more susceptible to wheel hop. Why is this bad? Well, under normal driving conditions, the driveaxles may be under a little torque stress from when the wheels resist being turned as a result of the car's weight and aerodynamic drag. However, when wheel hop occurs, the driveaxles undergo much greater transient torque stresses. When the wheels actually free-spin due to wheel hop, there's next to no torque stress at all. However, when the wheels regain traction, the driveaxles almost instantaneously undergo a large amount of torque stress due to having to work against a suddenly stopped wheel and having to push the car forward. In 1st gear, due to gear multiplication of the torque from the engine to the driveaxles, the driveaxles themselves could experience momentary torque of up to 2600 ft-lbf due to wheel hop. Under this amount of torque, the driveaxles could very well shear. Now, the firm engine mounts will cause the engine and transmission to resist moving forward when the car accelerates. The end result is that the driveaxle geometry between the transaxle and the suspension changes less, and allows more torque to be transmitted to the wheels, than to the suspension. This results in less wheel hop, and more torque to the wheels to move the car forward. A welcome side benefit of these mounts is improved gas mileage. I gained about 2 MPG from these mounts under highway driving, and about 1 MPG during city driving. I reason this is because I improved the torque transfer from the transaxle to the wheels, as discussed above. Noise and vibration have increased a little, but not much. Under acceleration, it's barely noticeable as a somewhat high-pitched noise from the valvetrain. At idle, engine vibration can be felt. This vibration is more noticeable when the engine is being shut off, as its speed drops to zero RPMs. Other than that, I have not noticed any problem related to noise or vibration. However, another 2GSS.org member who also tried firm mounts, reported that he had a lot of undesirable noise. Since he had an automatic transmission, I think his increased noise was due to fluid dynamics that occur inside an automatic transmission. Since I have a manual, I would not see that problem. Polyurethane Shifter Cable "Booger" BushingsI replaced the stock shifter cable rubber bushings with these "Booger" bushings from a Dodge SRT-4. They remove a lot of the slop associated with rubber bushings, and make shifting more responsive. I've noticed that it does not take as much effort to shift as it used to do, even considering the change I noted previously when I installed my engine mounts. This is especially true for shifting into 2nd gear. The transmission comes with a dual cone 1/2 synchronizer that enables the transmission to better handle the torque output at 1st and 2nd gear. However, it also makes it harder to shift into those gears. The booger bushings do help in making it easier to shift. MSD Stacker-8 IgnitionThe MSD Stacker-8 is an aftermarket capacitive-discharge ignition system that provides more spark power to each spark plug. This will provide a more powerful spark, ensuring reliable ignition under boost conditions. Since the 2.7L engine uses a coil-on-plug ignition system, the traditional MSD 6AL (or similar) ignition cannot be used.
Installation of the wiring harness to the individual coils is the hardest part of actually getting the Stacker-8 to work, and took me about an hour to complete. Actually locating a mounting spot is proving to be one hell of a job. I cannot use the same spot for the Stacker-8 as I did for the MSD 6AL on my 2000 Limited, since that area is taken up by a vacuum reservoir. I cannot mount the Stacker-8 in the area that the TCM normally takes up, because it's too large to fit properly. I have rested the module in that area for now, but I will have to fabricate a mounting plate for the module.
I have noticed a slight improvement in tip-in and part-throttle response. Dynamometer results will be forthcoming. I did not get a chance to test this unit on the dynamometer during the last dyno run because the unit itself proved to be defective and had to be shipped back to Summit Racing for a replacement.
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