Cars by name
Trucks and Jeeps
Engines / Trans
Repairs / Fixes
Tests and Reviews
by Daniel Stern, 1999
[My 2.5 TBI powered 1992] car is much more driveable now than I can ever recall it being. When it was in for some upgrades and repairs (headlamp conversion, repeater installation, preventive head gasket) I had them use my Mopar Performance multi-key cam sprocket to advance the cam 4 degrees, and supplied a new Bosch O2 sensor. The old one wasn't dead, but at 90,000+ miles, was getting "lazy." A new, revised intake manifold found its way off my garage shelf and onto the car, as well (this was the one released in 1994 or so with the cleaned-up and reworked airflow and more even distribution between cylinders). The car starts faster than any FWD Chrysler I've ever heard ("che-VROOM") and has noticeably better around-town driveability.
Advancing the cam works increases low-end power at the expense of high-rpm power; it may have a greater effect at high altitudes, where it would compensate for the lack of air pressure. Designers must make many compromises to make the engine meet everyone's needs, but few people spend much time at very high rpm with the 2.5 engine.
The engine responded well to the cam advance. It doesn't seem to have affected the high-RPM operation of the engine at all (using my standard test of manually shifting with my foot on the floor as I go up a long uphill highway on-ramp). We're 1.6km above sea level, though; this amount of advance at sea level would probably require mid-grade gasoline.
Edward J. Kelly wrote: As you face the belt end of the engine, the cam sprocket turns clockwise. So to "advance" the cam (lobes hit the valves earlier in an engine cycle), you need to move it 2 degrees clockwise of the sprocket (or move the sprocket 2 degrees counter-clockwise of the cam...). So the offset key should be placed into the cam such that the sprocket portion was offset towards the fire wall (assuming that you the cam key slot is up)... I got a better result at 2 degrees retarded rather than 2 degrees advanced.
We went for a "MagnaFlow" muffler from CarSound products. It's a knockoff of the Walker Dynomax UltraFlo, and it's too loud and growly on this non-turbo 2.5.
Timing spec in 1992 is 12 degrees advanced. I run ours at about 14. We get over 30 mpg (highway). The 2.5 cam is factory advanced 8 degrees from the position used on the 2.2.
At higher altitude, octane requirements are less and available octane is less. We get 85-87-91 (some stations sell 89 instead of 87, and 87 instead of 85, but we don't get anything above 91, while I've seen 93, 94 and 95 at other elevations.
Don’t get a "Magnaflow" or "UltraFlo" straight-through muffler. Too loud! I'd pick a stock 3-litre muffler. A Goerlich or Walker muffler for a 3.0-litre V6 Acclaim, for instance. Pick a quality brand (Oldburg, Arvin, Goerlich, Walker). This [an upgrade to a V6 muffler] also will involve a pipe size upgrade, which any good custom exhaust shop can handle.
Always gap the plugs before installing them; never believe what's printed on the box. Production tolerances are such that the gap will seldom be what it should be, will almost never be what I want it to be, and will never be consistent from plug to plug. That is why we gap spark plugs before installation. The best tool to measure the gap is a round-wire gap gauge, not a flat gauge. Spend $1.89 and buy one of the disc-shaped spark plug gap tools that includes about six different wire sizes (make sure it includes 0.035" and 0.040") and a little hook shaped tool that grabs the side electrode and bends it open or closed. These tools tend to come in "ranges", such as 0.020" to 0.045" and 0.040" to 0.070".
Don't use flat feeler gauges to gap spark plugs; it is nearly impossible to get an accurate or precise setting with them. The same goes for the "tapered ramp" or stepped-flat type gauges; stick with round wire. Note that round wire is the only acceptable gauge if the plug has been used, because the round wire gauges will still give accurate measurements with a slightly pitted electrode whereas the flat type will not.
Once you have a spec you want to attain (0.035 or--be adventurous!--0.040") in mind, first you measure the gap. You do this by inserting the wire loop of the specified diameter, perpendicular to the axis of the plug, between the centre and side electrodes. If it doesn't fit, the gap is too small. If it is loose and sloppy and slides between with no resistance, it's too big. You want a snap-fit, i.e., the gap is exactly as big as the wire is. If the gap is too large, hold the plug loosely between your thumb and index finger and tap it against a hard (i.e. concrete) floor, landing it squarely on the end of the side electrode.
If the gap is too small, use the appropriate "hook" tool to grasp the side electrode at the corner, and gently bend it open.
This "hook" tool also is useful for aligning the side electrode so it is centered over the centre electrode to help avoid the problem that was recently mentioned where Bosch Platinum spark plugs burnt the edge of the side electrode to a crunchy crisp. The goal is all plugs with a uniform gap and the side electrode aligned correctly. You cannot depend on the rather loose production tolerances on the plug production line if you'd have optimal plug life and performance; you must do it yourself.
Once you master the exceedingly simple art of plug gapping, you can use your plug gapping tool for other purposes. For instance, you can use it to J-gap the plugs. This involves opening the gap very wide by bending the side electrode away from the centre electrode, using a cutoff wheel in
a dremel tool to cut a slice off the end of the side electrode, and regapping the plug to your spec. This should be done such that the side electrode comes halfway across the centre electrode, and the cut should be taken from the INSIDE to the OUTSIDE of the side electrode to avoid a
"ridge" on the inside that would stymie (sp?) correct regapping.
J-gapping spark plugs unshrouds the spark (as the Splitfire people used to claim their plugs did, before FTC told them to siddown and shaddup) while still allowing you to control the brand and heat range of plug you're using. Plug life is slightly reduced, but with some combustion chamber
designs, the unshrouded spark really is noticeable. An unshrouding effect is what the NGK V-power, the Nippondenso U-groove, and Bosch's tapered side electrode are all trying for. You can do the same thing in your own garage to any plug.
As far as gaps go, the wider the gap, the larger and higher voltage will be the arc. (It takes higher voltage to jump a larger gap). This brings a more thorough ignition "hit"...like using a larger-than-standard baseball bat to hit a baseball. This is beneficial up to the point where the increased system voltage exceeds the capabilities of the rest of your ignition (wires, cap/rotor, coil) and misfiring sets in. Increasing the gap by small amounts does not generally cause problems, but don't try to run at 0.055" or 0.060" with a stock ignition setup. Though Chrysler continues to stick to the archaic and unjustifiedly small 0.035" gap spec, there are improvements in starting, running and driveability to be gained by going to an 0.040" gap.
1) get a hot coil (Accell Super Stock Can Type Coil)
There's nothing the matter with the stock coil if it's not broken. You can't "push" more voltage through the spark plugs than they call for to fire.
Try a split-fire (or similar)
I'm trying to be polite here, but surely you jest.
Buy Mopar Cap and rotor -- aftermarket jobbers are just not accurate.
This is flatly wrong. There are plenty of aftermarket caps and rotors that are substandard, but I can also name several for you that are much better than the MoPar stuff. Standard-BlueStreak and Echlin Premium come to mind. And what is more, I can put either of these side by side with the OE MoPar units and demonstrate what makes the S-B or Echlin caps and rotors better; it's a matter of materials and manufacturing fact, not just opinion.
On aftermarket, the gap between the rotor tip and the wire terminal is pretty wide.... lots of voltage loss. Mopar Cap and Rotor kit is much more precose and you don't lose nearly as much voltage....
This is untrue both from a blanket-statement point of view (see above) and from an engineering theory point of view. A wider gap means more voltage reaching the plug. There is no "voltage loss" from a gap like this. The opposite is true. By creating a wider gap, more voltage is required for arcover, so voltage will build to the level required to arc. This is why series-gap spark plugs are prescribed for engines that foul plugs quickly--the extra voltage built-up by the extra gap allows the spark to arc the dirty electrodes inside the combustion chamber. It's also why wider spark plug gaps give better starting and running. Of course, all of this only works up to the point where your coil and wires will not supply or contain the extra voltage, and then everything goes to hell.
Where you do want narrower rotor-to-contact clearance inside the distributor cap is when you'll be running at sufficiently high RPMs that spark scattering inside the cap will become a concern. This RPM level is not reached on a TBI street driven 2.5.
The computer in K-cars anyway is just a 1980s version of the 1970s Lean Burn system
Not true beyond about 1984.
Any computer which uses engine vacuum to control engine timing is not doing anything for your performance.
The earlier computers used engine vacuum as an input to tell the computer the load under which the engine was being operated, on which basis the computer adjusts fuel and spark. The use of engine vacuum as an indicator of this type is reasonably well proven over about 70 years of carburetors and vacuum advances.
The smog pump is NOT your engine's friend. It creates HP robbing parasitic drag and also pumps air into the exhaust manifold - creating backpressure which isn't all that great either. The stock Ex manifold is pretty poor to begin with.
Neither of these is true to any meaningful degree. The air pump takes a fraction of a fraction of a horsepower to run and only introduces air into the exhaust manifold under certain conditions (the rest of the time the air is diverted by the air switching system to the catalyst, which dramatically improves the function of the cat and helps prevent cat meltdown. On a street engine, there really is nothing of any significance to be gained by removing the air pump.
Remove all vacuum hoses which do not enhance driveability to the engine. This applies to canister purge lines and all other unfriendly things.
The evaporative emission control system has *ZERO* negative effect on driveability or power, but often has positive effect on fuel economy and engine starting and running. Randomly ripping out emissions system components like this in hopes of magically improving the engine's power is futile and often counterproductive.
The misunderstandings and assumptions that surround computerized engine controls are responsible for a great deal of lost efficiency and funny after-hours stories at service centers.
Stalling often seems to stem from a bad idle air control system. On the throttle body should be a little device that opens and closes a passage that bypasses the throttle plate. This allows the computer to control the idle speed and avoid stalls. (Thanks, Ed Kelly).
Gus, of super-minivan fame, suggested using manderal bent exhaust piping instead of Chrysler's ribbed air hoses to increase air flow and cut resistance. He pieced together preformed pieces from a big truck (semis and dump truck) shop to form his intake. Ed Kelly wrote that "I suspect that for a normally aspirated (TBI) 2.2/2.5 you could get by with having a car muffler shop bend you up a section! When you think about the layout, remember long sweeping turns will flow better!"
The Holley 5200 series are a cheap knock off of the Weber 32/36. My point is why collect parts for something that have these failings when you get something a little nicer for about the same price? Not to say the Webers don't have their own problems but at least they are easy to find and buy
parts for... and are as easy to adjust as the stock 5220. Granted when everything works properly the feedback carbs do work very well, but for that much hassle, convert the car to EFI (factory or something like MegaSquirt)
Most of the rebuilders I've spoken to admit that the Holley 5200 series carbs are pretty difficult to rebuild. From looking at the carbs I've got, I don't know if there is enough room to put new bushings in the carb. Why pay $300 for a rebuilt unit, when a brand new Weber is $300?
There seemed to be a general consensus that the Jacobs ignition system was overhyped, and that replacing aging parts helped. Discussion on coil location and the advantages of performance ignition systems was mixed. The MSD seemed to be well regarded. There was general agreement on the lack of value of Splitfire spark plugs. Good spiral wound wires were thought to be more effective than the stock wires - they certainly have less resistance. Magnecor wires seem to be well regarded.
Chrysler 1904-2018 •
Spread the word via Tweet or Facebook!
More Mopar Car and Truck News