420A 420A Engine rebuild

[Dumplings]

Hello, I am thinking of rebuilding my 420A engine to make it faster. I’ve seen people build them up to 700 horsepower, and while that seems awesome, I am just looking for something that is not what I have now. Is anywhere around 400 a good number to running?
I am also not sure what I need to achieve that number, should I just throw a turbo and call it a day? or should I rebuild the whole entire thing with new forged parts?
I am thinking of getting all my parts for “CI Motorsports”. does anyone know if that’s a good brand and a trustworthy one too?
Any information helps a lot, thanks

 

[jesse12345]

I hate to be that guy because your probably excited to start this big journey, but this topic has been absolutely beaten to death. You'll save money by doing the work yourself but making 400hp isn't going to be cheap. You'll need pistons, rods, head studs, turbo kit, clutch, fuel pump, injectors, and something to tune with like megasquirt. There's alot of other things to You'll need to like gaskets and gauges. If you just throw a turbo on it you will for sure just blow it up and then hate the car. If you want to make a little more power BLACK'98DSM knows alot more about what needs to be done. Good luck on whatever you do decide and just know we've all been there.

 

[Dumplings]

I hate to be that guy because you’re probably excited to start this big journey, but this topic has been absolutely beaten to death. You'll save money by doing the work yourself but making 400hp isn't going to be cheap. You'll need pistons, rods, head studs, turbo kit, clutch, fuel pump, injectors, and something to tune with like megasquirt. There's alot of other things to You'll need to like gaskets and gauges. If you just throw a turbo on it you will for sure just blow it up and then hate the car. If you want to make a little more power BLACK'98DSM knows alot more about what needs to be done. Good luck on whatever you do decide and just know we've all been there.

i figured i would need to rebuild the whole engine, which is fine with me . thank you for the feedback. i look forward to hearing what BLACK’98DSM has to say, if they respond to the thread .

 

[VelocitàPaola]

Here's some information about turbocharging the 420A. The first is a guide written twenty years ago (wow!), about how to do it cheap. A lot of the original vendors aren't around anymore, but the basic information is still good. The second is an updated parts list I wrote back in 2021, given what was available back then. I just looked through it, and I don't think it's too out of date in 2025.

420A - How to build a 420a stage 2 turbo kit for under $1000

Well, I have been getting a lot of e-mails and PM's asking me for this so here it is.Basically, I've been dying to turbo my car since the day i got it. But I've always been way to poor to afford a $3000 stage 2 turbo kit. I also realized that the price you pay for the kit is a lot more then...

www.dsmtuners.com

420A - Turbo my 420A

I have a 97 eclipse gs and I’m wanting to turbo it. Does anyone know exactly how much work would need to go into doing this? Any modifications that need to be made to make it work? I’ll be doing it myself along with my boyfriend You must be registered to see element.

www.dsmtuners.com

This is Corbin's guide to overhauling the 420A. I followed it back when I built my engine. I believe most of the parts are still available. I just glanced at a few websites and JE and Wiseco still make pistons, albeit for $800/set, and Eagle still makes rods.

2GNT.com - A_Proper_Rebuild

www.2gnt.com

From there, like Jesse said, you'll have to think about upgrading the clutch and working on a more robust fuel system.

 

[Dumplings]

Here's some information about turbocharging the 420A. The first is a guide written twenty years ago (wow!), about how to do it cheap. A lot of the original vendors aren't around anymore, but the basic information is still good. The second is an updated parts list I wrote back in 2021, given what was available back then. I just looked through it, and I don't think it's too out of date in 2025.

420A - How to build a 420a stage 2 turbo kit for under $1000

Well, I have been getting a lot of e-mails and PM's asking me for this so here it is.Basically, I've been dying to turbo my car since the day i got it. But I've always been way to poor to afford a $3000 stage 2 turbo kit. I also realized that the price you pay for the kit is a lot more then...

www.dsmtuners.com

420A - Turbo my 420A

I have a 97 eclipse gs and I’m wanting to turbo it. Does anyone know exactly how much work would need to go into doing this? Any modifications that need to be made to make it work? I’ll be doing it myself along with my boyfriend You must be registered to see element.

www.dsmtuners.com

This is Corbin's guide to overhauling the 420A. I followed it back when I built my engine. I believe most of the parts are still available. I just glanced at a few websites and JE and Wiseco still make pistons, albeit for $800/set, and Eagle still makes rods.

2GNT.com - A_Proper_Rebuild

www.2gnt.com

From there, like Jesse said, you'll have to think about upgrading the clutch and working on a more robust fuel system.

This is really helpful, thank you so much. I will look into it.
Is there a difference in which brand I go to for pistons or are they all the same?
Also my car is an automatic, is the automatic transmissions able to handle that much HP or should I just manual swap it and get a new clutch?

 

[VelocitàPaola]

Both JE and Wiseco are owned by the same company now, for what it's worth. They both cost about the same too. They're essentially equivalent, as far as I'm concerned, but maybe someone more familiar with the nuanced differences will chime in. The main thing to consider is compression ratio. Traditionally you chose low CR (e.g. 8.8:1) pistons for turbocharged applications, and higher CR (e.g. 10.5:1 or 12.0:1) pistons for N/A applications--but I know some guys were experimenting with 10.5:1 pistons in turbo 420A's back in the day.

I've never owned a 420A A/T so I'm not too familiar with their limitations. I think most folks would upgrade the torque converter and that's about it, but I'm no expert.

 

[Dumplings]

Both JE and Wiseco are owned by the same company now, for what it's worth. They both cost about the same too. They're essentially equivalent, as far as I'm concerned, but maybe someone more familiar with the nuanced differences will chime in. The main thing to consider is compression ratio. Traditionally you chose low CR (e.g. 8.8:1) pistons for turbocharged applications, and higher CR (e.g. 10.5:1 or 12.0:1) pistons for N/A applications--but I know some guys were experimenting with 10.5:1 pistons in turbo 420A's back in the day.

I've never owned a 420A A/T so I'm not too familiar with their limitations. I think most folks would upgrade the torque converter and that's about it, but I'm no expert.

ok thanks for the feedback, I will look into the pistons I want to get. Hopefully someone can answer our questions

 

[BLACK'98DSM]

CI Motorpsorts is more of a distributor than a brand. They were a good place to source 420A performance parts back in the day though. You can order built shortblocks and ported cylinder heads from them as well, but their prices are hefty for stuff like that. You can build a damn stout 420A at home with the right tools and knowledge. If you're new to this engine, keep reading on and soak up as much knowledge and advice as possible before diving in. As tempting as it is to dive right in, there are some quirks and the build will be much more rewarding if you get it right the first time. As someone that had to build multiple cylinder heads and transmissions before getting a reliable street rocket, I can say that you'd definitely be better off building things properly from the start. You won't learn as much without breaking shit though.

As already suggested, it isn't smart to just bolt on a turbo and go. Tear the engine down and get forged internals so you don't have to worry about cracking the ring lands early on, and get some studs to clamp everything together. Make sure all seals and gaskets are new and can hold high heat and pressure.

The guy making 750whp definitely has more labor and funds than you'd want to spend on a practical street car. If you've never driven one of these cars with 300whp, then don't aim for something so high. These cars will haul ass at less than 250whp if properly tuned and driven.

If you're piecing the build together, make Megasquirt one of the first puzzle pieces. This will unlock the capabilities for maximum reliability and efficiency. There's a large learning curve with this as well but it's greatly rewarding in the long term.

There are already some good write ups on building the 420A, but if you have any deep technical questions feel free to reach out. Fortunately I know most of the specs and processes off the top of my head.

 

[Dumplings]

CI Motorpsorts is more of a distributor than a brand. They were a good place to source 420A performance parts back in the day though. You can order built shortblocks and ported cylinder heads from them as well, but their prices are hefty for stuff like that. You can build a damn stout 420A at home with the right tools and knowledge. If you're new to this engine, keep reading on and soak up as much knowledge and advice as possible before diving in. As tempting as it is to dive right in, there are some quirks and the build will be much more rewarding if you get it right the first time. As someone that had to build multiple cylinder heads and transmissions before getting a reliable street rocket, I can say that you'd definitely be better off building things properly from the start. You won't learn as much without breaking shit though.

As already suggested, it isn't smart to just bolt on a turbo and go. Tear the engine down and get forged internals so you don't have to worry about cracking the ring lands early on, and get some studs to clamp everything together. Make sure all seals and gaskets are new and can hold high heat and pressure.

The guy making 750whp definitely has more labor and funds than you'd want to spend on a practical street car. If you've never driven one of these cars with 300whp, then don't aim for something so high. These cars will haul ass at less than 250whp if properly tuned and driven.

If you're piecing the build together, make Megasquirt one of the first puzzle pieces. This will unlock the capabilities for maximum reliability and efficiency. There's a large learning curve with this as well but it's greatly rewarding in the long term.

There are already some good write ups on building the 420A, but if you have any deep technical questions feel free to reach out. Fortunately I know most of the specs and processes off the top of my head.

dude you are so awesome. thank you so much for the information.

this is my first time ever building an engine from top to bottom with wanting more horsepower so i’m definitely getting as much info as possible.

i suggested 400 HP from the start because i have a eco boost mustang that pushes around 330 HP. but if 300 HP is alot for this car then i can definitely shoot for 300.

i’m not familiar with megasquirt and how it works. is it just another plug and play ECU, that’s what i’ve been seeing, or is it something totally different?

do you know any other websites that have parts i can buy from that aren’t such a hefty price?

also do you have any advice on the transmission i should run with the upgraded engine? can i keep the automatic or should i switch to manual?

thank you

 

[BLACK'98DSM]

I would totally swap to a manual transmission. Please do understand that this will add quite a hit of work to your build. But I've driven the autos with bolt ons only and was far from impressed. Even with a good convertor, I wouldn't run the auto at anything near 300whp. IMO that's one area that Mopar completely failed. Go ahead and source a good NV-T350 and the necessary hydraulics to actuate it.

For your other question, Megasquirt isn't plug and play. The amount of labor needed depends on which unit you get. None of them plug right in though. You'll need to heavily modify or remake your engine wiring harness.

And I wasn't trying to knock your power goal, just stating that is an outrageous number for someone which such little knowledge about the platform. We currently live in a world where nothing but 1000whp is impressive, but I promise being behind the wheel of a 2GNT with even 200whp gives many smiles per gallon. And comparing a Mustang to a 2g DSM is just not a fair comparison. You have two totally different platforms that deliver power in very different ways.

 

[Dumplings]

I would totally swap to a manual transmission. Please do understand that this will add quite a hit of work to your build. But I've driven the autos with bolt ons only and was far from impressed. Even with a good convertor, I wouldn't run the auto at anything near 300whp. IMO that's one area that Mopar completely failed. Go ahead and source a good NV-T350 and the necessary hydraulics to actuate it.

For your other question, Megasquirt isn't plug and play. The amount of labor needed depends on which unit you get. None of them plug right in though. You'll need to heavily modify or remake your engine wiring harness.

And I wasn't trying to knock your power goal, just stating that is an outrageous number for someone which such little knowledge about the platform. We currently live in a world where nothing but 1000whp is impressive, but I promise being behind the wheel of a 2GNT with even 200whp gives many smiles per gallon. And comparing a Mustang to a 2g DSM is just not a fair comparison. You have two totally different platforms that deliver power in very different ways.

I was already thinking of manual swapping it so now that gives me an extra incentive to .

which megasquirt would be best for something that I am trying to achieve, i can look more into it but i figured i can just use whichever people use since they have built the 420A.

yeah you’re right my two cars now not the same . and ik you weren’t knocking on the power goal but you are right. I forget how small and light that car is compared to others . 400 is outrageous for that car.

thank you for the feedback

 

[Breach7Performance]

Hello, I am thinking of rebuilding my 420A engine to make it faster. I’ve seen people build them up to 700 horsepower, and while that seems awesome, I am just looking for something that is not what I have now. Is anywhere around 400 a good number to running?
I am also not sure what I need to achieve that number, should I just throw a turbo and call it a day? or should I rebuild the whole entire thing with new forged parts?
I am thinking of getting all my parts for “CI Motorsports”. does anyone know if that’s a good brand and a trustworthy one too?
Any information helps a lot, thanks

The stock 420A crankshaft is generally reliable up to around 500 horsepower, and even that is pushing its limits. Around 400 horsepower is a safer range for long-term reliability. If a forged crank were available for the 420A—which I haven’t seen yet—the potential would be significantly higher. I’ve been seriously considering having a billet crankshaft designed for the 420A, assuming the pricing makes sense.

Supposedly ARH Automotive made 804hp on the stock crank. Though I don't have any information on how it held up long term and wouldn't suggest it.