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420A Increasing 420A Output- Detailed Information & Specifications

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It seems to me that every ambitious 420A owner wants their engine to have a higher output. I did too, which is why this article exists. And that's an understandable desire, as the 420A was designed to be a fuel efficient daily use engine. And not a high performance engine, despite what Wikipedia says.

Now there are many ways to get more ouput from an engine. But due to the ONLY fuel efficient designing of the 420A cylinder head (undersized ports), it takes quite a bit of time & money for larger gains, and spending little money brings little or no gains. For a random example: if you were to put cheap long tube headers on a 5.0 Ford you could possibly gain 15hp just from the bolt on. But with a 420A I wouldn't expect more than a 4hp gain, if that. This is because, aside from having half as many cylinders, the cylinder head is a most restrictive factor. You could potentially gain more if the engine is properly tuned, but tuning a 420A with a cast iron manifold and tuning a 420A with an exhaust header doesn't look very different.

To kick things off I'm only going to name a few modifications that help with output (categorized as "cheap" or "best"). As I build more of these engines and come up with new ideas, I will update this article with more modifications and the specifications about them.

Mandatory:
- Obviously, start with maintenance and verifying engine health. Do not start modifying if you are due for engine repairs or maintenance. Focus on that first. Your engine will have zero output once it self destructs.

Cheap, output on a budget:
- As mentioned already, the exhaust header. $48 is the cheapest 4-1 that I've seen, but 4-2-1 can go upwards of $500. A 4-1 is your classic, cookie cutter, short exhaust header. The 4-2-1 is the closest thing to a long tube design you can get, are usually higher quality, and in theory would be a greater help to the mid RPM power range.
- Also to increase airflow, a cold air intake; or at least an intake that flows better than the stock airbox. $33 is the cheapest "CAI" that I've seen, but I do not recommend using an Ebay filter. I recommend assembling your own custom air intake. Get yourself a name brand filter, some quality aluminum piping, couplers and clamps. Route the filter as far away from the header/manifold as possible, but not low enough that it will inhale road puddles. If you car is not fog light equipped, placing the filter behind the fog light vent is optimal. You can also fiberglass wrap the pipes to prevent heatsoak from engine components.
- 60mm Jeep throttle body from the 4.0L models. $35 from my junkyard, or you can search for a used one online. This will require slight modification to the throttle body and the intake plenum. There is a 2gnt.com guide for this if the site hasn't died.
- Coils, ignition wires, spark plugs... See my posts below for more information on these. A stronger ignition system is key once you start adding fuel and adjusting ignition timing.
- One of the most popular starter upgrades: Cat-back exhaust system. The cheapest that I've seen is $115. Be careful with basic Ebay systems as they are low quality materials and may not last long. Quality systems can be pricy. 2024 update, options have dried up. The Yonaka is still a nice system that I use, but slightly undersized for very high boost applications.
- This will improve power to weight ratio, but not necessarily engine output!: Weight reductions. Remove emissions & accesories, EVAP system, vacuum lines, EGR, cruise control, A/C. If strictly a race car you may consider the power steering. This is  free, you may even be able to sell parts for $.

BEST modifications, no more penny pinching:
- Let's get it tuned up - electronically. MegaSquirt MS3. $775 is the total bill for the components I installed, but a used MS2 can be sourced for cheap sometimes. This is required to tune the 420A, and is a bit time consuming to install & set up. If you want to fully delete the stock ECU you will basically need to make an engine wiring harness from scratch.
- Performance camshafts. Price depends largely on the grind and brand of the camshafts, but the cheapest that I've seen were $285 for the OBX camshafts, which are HORRIBLE quality and I do not recommend! They are produced from a soft scrap metal essentially and the lobes will round off as the journals become scored. High zinc engine oil may prolonged their failure but I would never install those in one of my engines. You want Brian Crower, Crane, or Crower which were quality brands for the 420A at one point but they have all stopped producing 420A grinds in 2024. You can still custom order any grind you want from Crower but expect a multiple week turnaround. I use the Crower Stage 2 camshafts and they perform exceptionally well. The Brian Crower Stage 2 camshafts have more duration though, and may be preferred for full race applications.
- Now of course, you could just BOOST the 420A. The dollar per horsepower really makes sense. You'll spend thousands on a naturally aspirated 420A just chasing the power of a low boost application. BUT, that's the easy way out and probably not why you're reading this article. :D
- You may also consider spraying it - and I don't mean with those rattle cans you sprayed your shitty calipers with LOL. I'm talking about NITROUS! Now I believe this is also cheating... But indeed an easy way to increase output. Keep the shot small unless you want to pace around in search of your connecting rod remains. Forged pistons & rods are really preferred, which is why this modification conjoinment is not placed in the cheap category.
- This is the key to greatly increasing 420A output! Do some port work on your miserable cylinder head! Advice from experience: Be careful polishing the intake ports. You still want some texture for optimal fuel atomization. I found a 120 grit finish to work nicely. And also be careful how much material you remove from the intake ports. Adding volume can decrease air speed. You can go crazy with the exhaust ports though. Much is to be desired with those. Get them as smooth as you'd like to. I've actually noticed casting defects within the exhaust ports on multiple 420A cylinder heads.


Stopping here for now. Updates and additional information in the posts below. We still have much to discuss.
 
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Something I did not mention above: Underdrive pulley. The name derives from the belt rotation speed being decreased, and your accesories are "underdriven", but usually not to an inoperable degree. This will reduce the stress/resistance placed on the engine's rotating assembly at any given RPM. The other gaining factor with these pulleys is the difference in weight. Having less weight on the rotating assembly should free up some existing horsepower (better crank to wheel delivery), even if minimal. There will only be a single digit difference on the dyno, and while sounding meek this is a great bolt on modification for the 420A. I personally use the Modern Performance Neon (MPx) style pulley. Since it is intended for Neons, you will now need to use a 4 rib power steering belt. The Eclipse/Talon used a 5 rib belt.
Another 2024 update, the 4 rib belt is plenty strong enough, and this pulley seems to be the only one available now.

https://www.modernperformance.com/p...-00-05-neon/00-05-neon-engine-accessory-drive


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Here's 2 more subjects that I haven't written about yet, and are great ways to increase output. Raising the compression ratio and valve size! This compression ratio increase can be achieved by multiple methods. The easiest and most common method is to install high compression pistons. Shelf-stocked are 10.5:1 and 11.2:1 pistons. And a good note, all of these high compression pistons are also FORGED, meaning no more concern of breaking your brittle ring lands! Another method is by valve upgrades. You can purchase semi-flat valves with much less dish than stock. This will decrease combustion chamber volume, which of course raises the compression ratio. Precise measurements will need to be taken to calculate the exact compression ratio with these valves, but even a slight increase is good. I highly recommend going +1mm oversize with your new valves! I was surprised at the difference they made on the ass dyno. Now, the final method for this CR increase will be by removing material, either from the cylinder head or block. It's best to keep block material removal at a minimum. I usually do a simple resurface in preparation for an MLS gasket, and though it's minimal you should still take it into account! You can remove quite a bit of material from the 420A cylinder head. With stock valves I was able to safely remove 0.030" from a head. Pair this with valves & pistons, you'll be needing knock control (que the MS3 ad). Please keep in mind the very slight change in valve timing as you remove material and the camshafts sit closer to the crankshaft. That is of no concern if your 420A is equipped with adjustable cam gears. The valve timing is only waiting for those 10mm nuts to be cracked loose :D.

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Another way to get more air flow is by extrude honing the lower intake manifold runners. Many people, including myself, have tried to smooth and polish the lower runners themselves using air tools and electric rotary tools. But what I have learned is that you will only waste many hours or even days only to burn up all of your bits just for weak results.

So, the best option is to just extrude hone it. This paired with the 60mm throttle body and port matching should bring great throttle response and a few more hp.

Now, the issue with this process is that not many places in the U.S do it. Below I have posted a few links where you can learn more about the extrude honing process (otherwise known as abrasive air flow machining), and see where it can be done.

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https://www.extrudehoneafm.com/
https://www.businessinsider.com/extrude-honing-putty-increase-car-horsepower-automotive-2019-1
 
This has been a great bit of information. I appreciate it as its been hard for me to find parts without knowing anything about these cars. I'm use to calling up Jegs or Summit Racing and telling them I'mb building a 350 and need this this and this!
 
Now I will be discussing spark plugs.

I do not recommend using the dual or quad electrode plugs. The inconsistent spark will cause a variation in idle speed and, even if not noticeable besides by logging, inconsistent acceleration rate. Who cares what's being used in the 2000hp drag needle. Those plugs probably get replaced after every pass.

I recommend using a set of NGK spark plugs. I use NGK in all of my engines... You can buy 420A compatible NGK's on a wide variety of websites. Pretty much any parts website should have them, even your local auto parts joint should have them.

For the plug gap, run a .048" if you're N/A with the stock ignition system. With a much stronger ignition system such as my COP setup, a 0.052" gap performs very well. Please do check and adjust your plug gaps! They will almost always be too small out of box. And of course for boosted applications you'll want a smaller gap due to the higher cylinder pressures, but discussing boosted applications is not the full intention of this article...

Some last specifications to consider with the spark plugs: heat range and electrode material. Nothing with these will make a huge difference. The good ole copper or nickel plugs have never failed me. Don't overthink it, fancy over-advertised spark plugs aren't the key to increasing output. Sure, iridium plugs have a much longer life, but I have no issue with replacing the plugs once in a while. You probably aren't putting tons of miles on your old 420A.

Some information on ignition wires is posted below. At some point I will add information about the coil on plug setup through MS3.
 
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Now let's discuss ignition coil options. Aside from coil on plug, which will be written about later.

The most common "performance" ignition coil for the 420A is sold by MSD. "Produces a stronger spark, therefore increasing engine output". Right? This is their theory anyway. So I pulled the specs (or lack thereof) on the MSD vs the stock coil. The stock Mopar ignition coil produces 40,000 volts, while the MSD only produces 36,000. Hmm. Of course the amperage is a key factor in arc strength. But they do not advertise a value for that! Is it just a case of "let's advertise a lower voltage rating so the buyers assume the amperage is higher"? With a total lack of product research/testing? That I can't say for sure. But let me note that the MSD coils are something I'd classify as nothing more than a paper weight. The quality is terrible. This is the same part used on the SRT-4 Neons. Go read the reviews for them. While you're at it, go take a look at the Neon forums. "Never fired when new"... "Died after one year"... I used my ORIGINAL ignition coil from 1997 until 2022.

Don't go "upgrading" your ignition coil thinking that you'll net a ton of power (or that the coil will even be functional). The advertising points are scummy. Aftermarket ignition wires are a valid upgrade and so is a coil on plug setup, both of which will be covered below.
 
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Time to write about fuel. I'll keep it blunt.

YOU DO NOT NEED TO RUN RACING FUELS, E85, OR HIGH OCTANE PUMP GAS IN A STOCK OR BOLT ONS 420A.

There's only three legitimate reasons to run higher octane or energy fuel. Higher compression ratio, advanced ignition timing, or boost. If you're still N/A with stock internals and stock tune, just run the regular pump gas. Which may be 87 octane depending on your location, and that happens to be the fuel which the ECU was programmed to run on. You won't gain anything by using other fuels. You'll just be wasting your money. Once you've made changes to require a better fuel, then it is time. Fair enough?
 
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So far the DC Sports headers have proven to be the best for the N/T's. They are the closest thing you can buy to the well known long tube design. Here's the current links to the cheapest headers available, and to the DC.

as far as i know, there are 3 headers for the 420a. the greddy 4-1 , the DC 4-2-1. and the megan racing 4-2-1.
everything else is a copy of one of these designs

the 4-1 design is good for high end gains. the 4-2-1 for midrange

headers are pretty much worthless if all you have is an intake and catback
If you want to see and noticeable gains, you wanna pair the header with a performance cam.

============================================================

on the spark plugs, like you said, use ngk's
bosch spark plugs = $hit

Indexing the spark plugs is the only way to get any performance gain from spark plugs

As for plug material... it doesn't make that much of a difference. You're supposed to choose based on your driving style. But if you're reading this article then you might be a racer. And in that case you'll want copper or nickel because they're colder and spalr best
your a little bit off on this point.

The difference between regular, platinum and iridium plugs is mainly the center electrode . pretty much all plugs have a copper core and an outer casing made of nickel alloy.

the standard plugs have a center electrode. made of nickel plated copper. The center electrode will erode causing the gap to widen. Recommended change interval is 25k-30k miles.
these plugs are cheap and it only takes 10mins to replace them so i change them after 15k
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the platinum, of course have a platinum center electrode . All i will say about these is don't use them. either run standard plugs or iridium.
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iridium plugs have a small diameter iridium alloy center electrode. The electrode will not erode like on a standard plug.

They come in two flavors of NGK, iridium IX and laser iridium.

iridium IX - iridium center electrode but uses a nickel alloy ground electrode. That means the ground electrode will erode. These plugs are good for about 50k miles,

laser iridium = these use a platinum ground electrode so they last longer but they also cost more. Good for about 90K miles.
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You should never adjust the gap on iridium plugs. If you get a plug without the -11 at the end it will be gapped wrong if using stock gap specs.
so you don't want a BKR6E
What you want is a BKR6E-11
-11 indicates the gap, 1.1mm or .044"
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BKR6E-11
6 is the heat range
the higher the number the colder the plug

===============================================

The problem with the test pipes is that they're the wrong diameter. If they were the same diameter as the rest of the exhaust system, then you'd maintain good exhaust pressure and get the best gains.
.

the megan racing test pipe matches. the problem with the one in the pic, is it has no hanger brackets. Its also from bsck in the day, the new ones have the brackets. There are knock off ones on ebay that are listed as megan racing but they have shitty looking brackets so its best to just get one from a place like CI motorsports or other reputable company.
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the main issue with running a test pipe is it is illegal to modify or remove you cat on a street driven vehicle.
you can't tell if a cat (thats installed) gutted or not just from looking. with a test pipe its obvious that you removed the cat.
 
as far as i know, there are 3 headers for the 420a. the greddy 4-1 , the DC 4-2-1. and the megan racing 4-2-1.
everything else is a copy of one of these designs
The Megan Racing headers are 4-1. Most Ebay headers are a copy of them, or whoever made them originally.

You might be confused with the header that Megan Racing sells for the 2.4 Spyder's. They are 4-2-1.

You should never adjust the gap on iridium plugs. If you get a plug without the -11 at the end it will be gapped wrong if using stock gap specs.
I've seen iridium plugs with inconsistent gaps out of the box. That's partially why I always run copper or nickel. They can be easily gapped and they have the correct heat range for my build.
 
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yup i was wrong, apparently they came out with a special tool to regap iridium plugs years ago but some how i never heard about it.
 
For spark plug wires, ignition wires, or ignition cables. Whichever terminology tickles your fancy:

Granatelli makes the highest performing ignition wires for the 420A. Rated at less than 1 ohm, they deliver the strongest spark to the electrode.
(Part #: 34-1601MPG)

VMS, ThunderVolt, and NGK are tied for 2nd place, rated at 40 ohms of resistance. The VMS cables seem to get brittle very quickly though, which is not good. My preference was Taylor Cable ThunderVolt, which can be bought in the color red. :)

I recommend to stay away from OBX and other Ebay brands. They don't last very long and have sometimes over 100 ohms of resistance.

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For spark plug wires:

Granatelli makes the highest performing spark plug wires for the 420a. Rated at less than 1 ohm, they deliver the strongest spark to the plug. (Part #: 34-1601MPG)

VMS, ThunderVolt, and NGK are tied for 2nd place, rated at 40 ohms of resistance.

Stay away from OBX and other Ebay brands. They don't last very long and have sometimes over 100 ohms of resistance.

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Used the same brand on my old srt4 neon they had the plug wires and the ignition coil. Very good products IMO.
 
Another way to get more air flow is by extrude honing the lower intake manifold runners. Many people, including myself, have tried to smooth and polish the lower runners themselves using air tools and electric rotary tools. But what I have learned is that you will only waste many hours or even days only to burn up all of your bits just for weak results.

So, the best option is to just extrude hone it. This paired with the 60mm throttle body and port matching should bring great throttle response and a few more hp.

Now, the issue with this process is that not many places in the U.S do it. Below I have posted a few links where you can learn more about the extrude honing process (otherwise known as abrasive air flow machining), and see where it can be done.

You must be logged in to view this image or video.
https://www.extrudehoneafm.com/
https://www.businessinsider.com/extrude-honing-putty-increase-car-horsepower-automotive-2019-1
What would the honing specs be to go along with keep Tb?
 
What would the honing specs be to go along with keep Tb?
Not entirely sure what you're asking here. But the Jeep throttle body is 60mm in diameter. So you would need the plenum mouth to be close to that for optimal airflow. I recommend porting the plenum to 58-59mm. Going a full 60mm will leave the walls very thin and I actually cut through a manifold once. Using a hone would take forever to do so since the stock opening was 52mm and that tool is not intended for mass material removal. I used an aggressive carbide bit on a rotary tool to start the porting process. Once I got up around 58mm I switched over to a less aggressive bit to make sure there was a smooth finish to allow good airflow. I should've made a video? Most people skip this part of the process but it's the only way to get the full gains of a throttle body upgrade.
 
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this thread is great but I have to disagree with the high flow cat myth, exhaust backpressure is not important on a 4 stroke engine, now of course running open headers would cause a loss of torque especially at low rpms but the reason for this is because of the lack of vaccum created by individual exhaust pulses. The ideal exhaust to make power on a 4 stroke engine is equal length headers with a straight pipe that continues about 3ft after the collector. this is the perfect exhaust to take advantage of vaccum and help with expelling exhaust gasses from the combustion chamber.
 
Let's face it. Anyone who is truly going to build and race their 420a is going to be revving it higher than the factory rev limiter. And at that point, having the stock cat in place is not an option. Unless you'd like to melt it. I removed my catalytic convertor mainly for that reason. The test pipe is lighter weight and corrosion resistant anyway.
 
Updates, updates... I almost forgot that I started this article. Long overdue, I thoroughly revised the article, making it as useful and informative as possible. Spelling and grammar fixed. I added photos. And added some notes pertaining to the 2024 product market. Soon I will add more relevant information in deep detail. I'm engineering certain components now. I also removed a post I made about convertors with slight misinformation. I have an entire article about test pipes here:

 
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