'98 Intrepid Upgrades

[Dale Walsh]

I have a '98 Intrepid ES with the 3.2L V-6. Does anyone have any suggestions about what can be done to increase performance? The only thing I've done so far is install a K&N filter and PIAA head/fog lamps. Hopefully when the Intrepid begins racing in NASCAR more people will offer performance parts for it.
Thanks, Dale

[Fluid]

I have done a few things to my 00 ES with the 3.2. I removed most of the stock intake and replaced it with an ABS tubing and a K&N cone filter ( I can provide instructions for those interested ). With this mod I could feel a slight increase in throttle response from 3000 rpm up. There was very little noise increase, but I have left the first inlet resonator in place.

I replaced the wheels with silver TSW 'Imola' 16x7.5s. These are 15-spoke wheels which are not like the "tuner" wheels often seen on imports; instead they are classy and have really improved the looks of the red ES. They vaguely look like wheels seen on current Chrysler concept cars like the 300M vairents. With the stock tyres, the additional 0.5" of rim width isn't really noticeable from a performance standpoint.

I also replaced the front swaybar bushings with a set of 1" Energy Suspension bushings. This did stiffen up the cornering, without an objectionable increase in noise or ride harshness. There aren't too many things to do to the current LH motors - no cams, larger TBs, etc. It may be possible to substitute the TB off the 3.5 from the 300M, but I don't know if that one is any different than the stock 3.2; it may also cause problems with the PCM, and may hurt low rpm torque too much.

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fluid
00 IR ES
00 IB CC R/T

[brun064]

The 3.5L has dual throttle bodies. Does your 3.2L? I haven't seen any of the new 3.2L engines. If anyone here gets HOT ROD magazine, in the May 2000 issue they have an article on something called a "Hot Rocker" Its a variable ratio rocker arm. They are initially offering the system only for puchrod engines but I e-mailed the inventor and he said they are working on a OHC system to be released by late 2000. If anyone doesn't know what this would do, it opens the valves at different lengths throughout the RPM range to give a broader torque curve.

[Fluid]

I cannot confirm that the 300's 3.5 does NOT have two TBs as I don't have one to look at, but the evidence points to a single TB for both of the new engines. According to my shop manual for the 3.2/3.5 engines, the 3.5 has a single TB just as the 3.2 does. Drawings for both engines show the TB and where the TPS and IAC are connected. There is a section on removal and installation of the TB for both engines, so I assume that if the 3.5 had dual TBs there would be a detail showing the difference.

I have no idea what the "old" 3.5 had for TBs - I haven't seen one up close in years. The new all-aluminum 'big-block' ( 3.2/3.5 ) engines are different from the old ones in many regards. The 'new' intake for both engines has variable-length runners and two resonators between the air filter and the TB.

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fluid
00 IR ES
00 IB CC R/T

[brun064]

I have an old 3.5L (iron block) and they do have dual throttle bodies. I wasn't sure if the new ones have two or not. By the way, you wouldn't know if the new air intake plenum would fit on the old engine?

[Fluid]

Brun064 - I don't know if the new runners will fit on the old 3.5 or not, but I would suspect that even if they did they may not work that well. Since they are tuned for the new engine with its power curve and interior flow dynamics, the tuning may not match the old engine...or it may.

I've toyed with the idea of porting the TB on my 3.2, but it would have to be done conservatively. Some DC computer-controlled engines will actually lean out the fuel mixture with a larger TB, since the computer sees a lower pressure in the TB, even though the flow through the TB is greater. Result - lower power, not higher. Gotta do a little more research on the LH engine controller first.

[brun064]

If your worried about the computer gettin' in the way of more power, why not replace it. Superchips makes something for that. And I think Hypertech makes a fully customizable controller for it, but I'm not sure. Do you know if DC changed the intake manifold with the engine change? You said you a shop manual...are the part numbers the same?

[Fluid]

If only it were that simple! First, no major company currently makes a "chip" or a "controller" for my 3.2 so that isn't a route I can take. Second, those "chips" only make minor changes in timing and fuel mixture, and these are still based on inputs to the computer from the stock sensors - they gotta stay emissions-legal, so the tuning changes are quite minor. Even the performance PCMs from Mopar Performance can't solve all the problems of fuel delivery with most modifed or aftermarket parts. This is one reason why factory-based computer controlled engines seldom match the power output of carbureted engines. The computer engines 'could' deliver equal power, but without custom software to match the exact engine tuning envelope it won't happen. Check out the recent 'Mopar Now' magazine for the Dodge Ram with the 425HP 360 running low 12s in the quarter in a "stock" class. Lots of other DC street truck owners have tried to get there all-motor, with lots of money, but can't even get close. The biggest "secret" of the fast Ram? Custom software which can be tuned by the driver.

My service manual is for the '98 and later engines, so I can't tell if the manifolds are the same or not. The new plenums are plastic and quite large, covering the entire engine, if this helps.

[brun064]

How does your 3.2 tell the pressure of your TB. Mine runs through a vacume hose at the top. If yours runs like this and your worried about the TB sensor getting a too low pressure reading then all you have to do is "pinch" the vacume hose slightly. If not then you might want to try to fool the sensor by gluing it or something.

[Fluid]

At WOT( wide open throttle ) the 3.2/3.5 PMC computer goes into Open Loop mode. It doesn't read from any of the sensors, but relys on pre-set programming. Under some other conditions like part throttle acceleration it is in Closed Loop mode, where it does rely on the sensor input. But the two sensors on the TB are the IAT and MAP - both are electronic with no vacuum hoses, just wires.

So there seems to be no easy way to "fool" the OBD II computer at WOT. Placing resistors, etc. in-line from the TB sensors might work for part throttle, but the trial and error method would be tedious with no guarantee it would work, or that it wouldn't damage the PMC.

That's why it is so difficult to even develop a "chip" for the modern PCMs, especially the OBD IIs. The custom programmers have to "back engineer" a sample PCM to find out how it even works - this all can take months or longer. Then they have to modify it, testing to see if it damages anything or if it even helps performance. That's why it is so expensive to buy a decent "chip" - there is a lot of development time involved, with limited sales potential.

[Fluid]

Another tidbit - the PCM uses the input from the MAP ( Manifold Absolute Pressure ) sensor to adjust the fuel ratio. If a large TB is installed, the PCM will "see" lower velocity through the TB and assume that there is less air passing through it. To accomodate the lower volume of air, the PCM will lean out the AF ratio - just the opposite of what we want it to do with a TB that actually flows MORE air. This is why a larger TB may reduce performance, particularly at part throttle. Plugging off the MAP sensor could have the same effect, reducing the fuel delivered and losing power.

Dang computers!