Atlas 4.2 / Vortech 4200 engine build.

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I am beginning the build of a GM Vortec 4200, also known as the ATLAS 4.2 straight six.  it is all aluminum, DOHC, VVT on exhaust cam, makes 291 hp and 270 tq stock.  Peak torque at 1800 RPM and hold it to 5000 RPM.  A lot of these are being built on YouTube, etc., and I decided to build one. I will also be using the Aisan GM AR5 5 speed transmission which came in the 4 cyl ATLAS 2WD Chevy Colorado pickups.  bolts right up and I will get a custom flywheel to work.

 

[jeffer949]

I have been. And for those searching its nivlac57 on YouTube. I have a 84 maxima wagon and I measurd once when I had my engine out and it was to close to try. I am interested in yhe 5 cylinder though as it would fit under my hood. 

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Yep.  the 5 cylinder hasn't caught up yet to the six.  the six cylinder 4200 is REALLY taking off now.  I have one I am putting together, and possibly put into another Z at some point.  It will be turbocharged, etc.  you start with 291 horsepower and 270+ torque, and then go up from there.  weight is 350 lbs.  They are a beast.

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So I went ahead and bought one off of eBay and it showed up the other day.  It is a 2006, which is the 2nd of 3 variants.  It has larger ports and larger valves than the 2002-2005 models.  I have ordered a few of the high dollar pieces needed so far, my T shaped oil pan made by Forever Fabrication has arrived and I have it in silver engine enamel, within a few days my turbo header from the same shop will be here and I am awaiting the intake flange, runners from DMZ and plenum from eBay I will use to put together and have welded, then have the welds sanded smooth and either polished or powder coated.  I picked up another S30 engine crossmember which I will use, strapped tot eh bottom of the engine and measured from my Z car to fashion the motor mounts.   An Aisin AR5 5 speed is also on the way, and my Turbo is here, I ordered a T76 with T4 flange off of eBay, along with a Tial knockoff external wastegate. A chromoly 17.1 lbs flywheel from Atlas Industries is on order.   Cool stuff!

 

 

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oil pan:

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09-27-2025 More 4200 stuff. I stripped off all the unnecessary junk and was able to get one side of the engine cleaned up. I didn't worry about the oil pan as it is going to junk pile soon. Progress....sometime slow but moving forward. Pics show the cleaning in stages on that side. I got the springs into the external wastegate, and it shows a crack pressure of 8 psi and wide open at 12 psi. Not too bad.

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My turbo header from Forever Fabrication for my 4200 build came in today. Top notch craftsmanship as expected:

[jeffer949]

Very nice. will be cool to see how tight it is in the engine bay!

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on Youtube, you can see the 280Z a guy is building right now.  actually fits very well!

 

(3) Red Hot Channel - YouTube

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More work on the 4200 today. cleaned up the rest of the block and head, and then pulled the oil pan and cam cover. NO SLUDGE. very clean inside. I got the outside of the cam cover clean enough to at least get started on the modifications I will do to it (add an alloy oil fill to the back, add a breather port, shave off 2 original ports, cut off unnecessary brackets, weld up the original oil fill hole and probably lower it a bit as it is very tall . To fit under a Z car hood it has to be chopped about an inch......although a small rectangular hole in the hood with the polished cover sticking up can be made to look really cool. Yeah I had an adaptor snap on me, the crank bolt is SO tight, I will probably need heat and PB blaster and smack it a few times to shock the treads to get it off. I need to clean behind it and it needs to be cleaned up and painted.......I wonder if the heat will ruin it? Before I called it a day, my AR5 transmission arrived.....in need of a rebuild, the pilot shaft has wiggle room. pics follow:

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10-04-2025. I got some more 4200 work done today. I installed the modified pickup that came with my T oil pan from Forever Fabrication, and then installed the oil pan. It came with new bolts, and I used Permatex Grey to seal it. After that I jumped on the valve cover. It is a common thing on 4200's to cut down the valve cover on if you want to use it in certain cars, as the height of the engine causes issues. You either cut a hole for it to poke through or cut it down. the 2006-2009 4200's have a cast aluminum valve cover, so pretty straight forward. Using my die grinder, I cut the top out and then ground most of the other stuff off I didn't want on the cover, and drilled the hole in the back for my oil fill. I picked up this sweet cap and threads on Amazon for under 10 bucks. So, after the initial cut I then used a marker and drew some lines for further cutting and then drilled small holes so when I took it off I could draw a pattern. as the pics show it took off a bit too much where the intake cam is.....but no worries, I kept some of the cut off aluminum, and can cut strips to put there it will all be welded in Next, I will use a cereal box to make forms for how I need to cut the plate aluminum, and get it all welded up, sanded down and off to polishing. Block is about 90% ready for paint, just more corner cleaning. Going to go ahead and paint the block silver....I don't want to be tied down to a color, a neutral color is best, and the silver makes it easy to just use a thin coat. I will also probably use clear engine paint over it to give it a little more pop. Pics follow.

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I worked on making the forms for the valve cover today. I can now use them as templates to cut them out of some 1/8" thick aluminum plate I got off of Amazon, and it should be here tomorrow. Also stuck the dip stick in a little bit to get an idea. It also comes with the oil pan and pickup. Lastly, I am getting ideas on alternator fitment.....pics.