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1966 Plymouth Belvedere II twin turbo project

Discussion in 'MOPAR Turbo Tech Forum' started by Punk.Kaos, Sep 25, 2023.

  1. Punk.Kaos

    Sep 22, 2023
    Hello! I've been having fun reading through the Mopar section here on The Turbo Forums as I work on my own build, a 1966 Plymouth Belvedere II.

    Seems like its been a little dead here lately, so I figured I'd share my own progress.


    I've owned the car for about 15 years, and its gone through various iterations of engine and configuration.

    Currently its got a 426 Wedge that I've decided to overhaul. Its been sitting about 3 years now because I was busy building other things, so I decided to either play with it or move it on... Long story short I sold my motorcycle and use those funds to go engine building!

    The 426 got port-injection via Megasquirt along with crank fired ignition and a pair of twin eBay turbos.

    I went with T04E's because I want a street car thats fun light to light. They're probably a little on the small side but they start to spool around 1800RPM which isn't too far from right off idle, which is fun.

    I used a set of flipped shorty headers and went up and over for my exhaust to the turbos which after some hammer-surgery seems to have worked out ok.


    Don't mind the wire nest, its not fully wired yet. I'll clean that up honest :p

    I've got the Megasquirt tuned-ish. It runs and drives, but I've got to iron out some kinks before its really road worthy...

    The biggest is that its got an old school Mopar 'purple-shaft' 509 cam in it which is really a poor cam for turbo, EFI, and in general. It doesn't really make power until 4500RPM, it pulls basically NO vacuum which is causing pains in tuning, the huge 74 degree overlap is making my wideband nearly useless, and its not a good turbo grind anyway. So its going to get swapped out here in the near future.

    I've so far been keeping mostly out of boost while I tune it, the most I've pushed so far is 5PSI just to be sure things on the turbo side were functioning.

    Anyway, thats my ride!
  2. Russell

    Jan 13, 2019
    I have always liked those cars!
    Punk.Kaos likes this.
  3. Punk.Kaos

    Sep 22, 2023
    Me too! The 66/67 seems to be the least favored of the Mopar B-Bodies. But its always been my favorite.
  4. MrBelvedere

    Dec 2, 2008
    What is the power output potential of those turbos? How much do you plan on pushing it? What did you do to the engine to prep for boost?
  5. Punk.Kaos

    Sep 22, 2023
    They're supposedly good to 450HP each for a total of 900HP if I want to push it that far.

    The engine has a forged crank, rods, and pistons. Its got cometic head gaskets as well. The heads are early casting 516 closed chamber heads which have been worked over but are not the highest flowing stock heads out there so its not an RPM monster. It makes its power by 5500RPM which is fine for my goals. Those heads on that block does give me a static compression of 10:1 which is a bit high, but the Mopar Performance 509 cam has a LOT of overlap (76 degrees) which brings my dynamic compression down to 7.5:1.

    I don't plan on pushing it wildly far, 8psi or so is what I'm aiming for right now because my transmission and rear end are currently totally stock so I don't want to break other bits while I sort out the engine bits. Eventually the goal is to beef up the trans and rear but I spent my budget on rebuilding the engine so I have to recover funds a bit first. I also don't currently have an intercooler so that limits how much boost I can run as well.
  6. MrBelvedere

    Dec 2, 2008
    I'm really interested in this build as I have a BB Mopar sitting on a pallet and am contemplating BB vs SB routes.

    Regarding max power capabilities of the stock block you get so many mixed answers it's hard to really know. I have seen pretty consistent reports about cap walk on the BBs so that might be something to consider.

    With those heads and cam you're probably 400hp NA right? That would put you up around 800hp at 15psi. That'd be a wild ride
  7. Punk.Kaos

    Sep 22, 2023
    While I never dyno'd it NA Desktop Dyno sits it at 525HP with open headers. Other cars I've built and HAVE dyno'd says Desktop Dyno tends to be reasonably accurate but even if I conservatively say its only 500HP thats 1010HP at 15PSI. Which.... Holy hell!

    Cap walk can be an issue, and like you said there's a LOT of mixed answers on what the stock block can do. I've built a couple of 650ish HP NA 440's before without any issues and I know turbos are supposed to be easier on the engine than building NA power so we'll see! Cap walk tends to be a byproduct of detonation, so as long as I can keep that from happening I suspect I'll be fine. My 426W has a bit more meat in the block than the 440's do as well which is what most people base their big block info on.

    Honestly I've yet to take it over 3700RPM (Its only been out a few times since the break-in of the engine) and even at low RPMs it SCOOTS. I actually just got back from a test runa few minutes ago where I discovered I need to work on my wastegates... They're supposed to be set at 8PSI from the factory(Which is about where I'd like to run it) but I stomped it and saw my boost gauge hit 12. I was busy enjoying the tires breaking lose making nice rubber lines on the road so its hard to say how it'd actually pull if it'd hooked....

    But evidence suggests that it's totally fine up to 12PSI for at least 3 seconds :p

    There's lots of pros and cons BB vs SB. I think a lot of it depends on what it's going into. I've gotta B-Body so a relatively large engine bay even though its an early B so not as much as post 68. I'm betting by your name you're running something similar to mine.

    The Big Blocks make GOBS of torque which is a lot of fun, and its trivial to get them over 500HP even using fairly basic stock parts, which means they don't need a ton of boost to make wild numbers.

    Small blocks are fun to rev high which makes for some fun as well, but I feel like they tend to not be as nice out of boost as a big block is (Though with the cam I have, low RPM power isn't stellar). Small blocks are easier to turbo though. Things like turbo headers exist for the small blocks, where I had to build my own for the big block.
    nxcoupe and MrBelvedere like this.
  8. MrBelvedere

    Dec 2, 2008
    I have a couple cars. One is a project 67 belvedere. It's a small block car so converting it would be a thing. Not a huge deal but plenty of work nonetheless.

    My other car is a 67 valiant, ex drag car. Tubbed etc. Currently that's the work in progress car, the belvedere is on hiatus.

    I'm very curious what you end up achieving with your combo. Not enough documented boosted Mopars out there.
  9. MrBelvedere

    Dec 2, 2008
    Just curious how come no intercooler? Just the complexity and piping?
  10. Punk.Kaos

    Sep 22, 2023
    Mostly space and cost. At 8PSI I shouldn't really need one. I do expect at some point I'll add one but I was already over budget on the build from some other bits that I didn't expect to need to replace that turned out to need replacing along with having to partially redesign my headers as I measured wrong by about 2 inches and couldn't get the hood to close after putting everything back in the car so I had to modify some things so it all fit.

    Once my checking account recovers from this it'll be getting a few more changes. Intercooler, manual valve body and some power upgrades on the trans, fixing some rust, paint and interior...
  11. MrBelvedere

    Dec 2, 2008
    If I do ultimately go turbo I'll just run manifolds. Also planning to do away with the inner fenders, and move the rad core support forward. Which will help with heat and also make piping much easier.

    What megasquirt system are you using?

    Tell us more about the fuel and ignition management...
  12. Punk.Kaos

    Sep 22, 2023
    It wasn't really manifolds vs headers in my case. I chose to go up and over, and just welded up my elbow for that a little too high. I just had to bend a new 90 degree elbow with a smaller radius so it cleared a bit better. No big deal, but a bump in the road.

    I contemplated cutting out the fenders but ultimately left them mostly in place. I cut a window on each side for the downpipes to exit into the wheel wells but other than that its still full fender.

    Moving the rad support would have opened up a LOT of extra room, but I don't think it actually needs to be done in my case. Everything fits. I've got enough room to run a long intercooler down low, or two vertically mounted intercoolers on the sides without them interfering with anything when the time comes. Optionally I could easily mount one in front of the rad on the other side of the core support without any problems. There's quite a bit of room between the grille and the core support.
    nxcoupe likes this.
  13. Punk.Kaos

    Sep 22, 2023
    So I was doing some testing on my wideband this afternoon, and discovered a fairly big ground differential! When I told the wideband to output 2.5v for all AFR readings what the ECU was reading 2.75v! Moving the ground off the block and to the ECU directly corrected the wideband readings!

    It still won't read below about 1500RPM due to cam overlap, but above 1500RPM its reading fine now which is awesome, as I can tune it effectively now. Previously I had been tuning my EFI via old school plug chops and by ear... Surprisingly now that my wideband is working properly it looks like I nearly nailed it. Its a little on the rich side in some spots but all in all well within safe parameters which was nice to see. I've never tried to old-school tune an EFI system before!

    Now that I know things are where they should be I can dial it in and start playing with it harder.

  14. Punk.Kaos

    Sep 22, 2023
    I'm running an MS2 right now, mounted up under the dash.

    I'm running sequenced batch fire injection with two banks of 4 injectors wired left/right bank.
    I thought briefly about going sequential injection but that would have required me going to an MS3 at quite a bit more cost, and sequential only really matters at idle and low RPM. Even with fairly huge injectors(1000cc) and a cam with large overlap its idling fine without sequential.

    For ignition I built a 16-1 trigger wheel inside of an MSD pro-billet distributor which gives me both crank and cam sync. A crank mounted wheel would be better but I wasn't able to find a good mount for the sensor without having to fabricate something from scratch so this works out cleaner. I cut the posts of the distributor cap and fiberglassed the top to create a blanking cap for the distro for a clean install.

    I'm using GM D585 truck coil-near-plug packs firing wasted spark. They're mounted on the fender skirts in front of and below the turbos, 4 to a side.
    MrBelvedere likes this.
  15. Punk.Kaos

    Sep 22, 2023
    The Belvedere has been running well over the last week, however its still boosting higher than I'd like it to. I finally checked in with the place I ordered my turbos from and discovered that instead of the 8PSI wastegate actuator I THOUGHT they'd sent me, they sent me a 14PSI actuator. So that explains why I'm going over 8PSI!

    That isn't a huge deal for the time being as boost is very easy to control with the gas pedal, as long as I'm paying attention while I wait for my replacement actuators to show up. Running it up to 14PSI without an intercooler makes me twitchy so I don't want to leave those actuators in place.

    I decided since the weather was nice I was gonna take it out to a local car show. We had a blast, and I got a LOT of interest in what in the world was going on under the hood of my car. Most of the old guys had never seen a turbo V8, and the tuner guys were excited to see someone apply modern tech to an old school motor and had tons of questions about the setup.

    Unfortunately on the way home a new problem cropped up.

    The driver's side turbo had a failure of the front nut. The nut and part of the front of the shaft sheared off, leaving the compressor wheel mostly unattached to the shaft. Obviously that's not ideal for creating boost!

    I pulled off the road and pulled the intake tube off that side so any further failure wouldn't end up inside my engine and drove the rest of the way home NA.

    After talking with the turbo company, they believe it was a manufacturing defect and are sending me a new turbo cartridge under warranty, so ultimately its not a huge deal. Just annoying.

    I've ALSO got parts coming to add water/meth injection to my setup.... Because accidentally having hit 12PSI means now I'd like to keep that much boost, and I'm not going to do so without meth or an intercooler. And since I've got most of a meth setup left over from a previous vehicle I might as well use it!
    Russell and 91turboterror like this.
  16. 74chlngrTT5.9

    Dec 16, 2009
    Cool on your build.
    Working on duals with my E-body. Currently a 360la. But 5.9 Magnum will enter soon. Just getting off off effectively a 6 year hiatus.
    Running MS for mine as well. MS3X.
    Currently wasted spark because I hit a roadblock with cam signal issue.
    Look forward to watching yours progress.

    I post my shenanigans on the build page.
  17. Punk.Kaos

    Sep 22, 2023
    Very nice! I thought about going MS3X but ultimately I decided that I didn't gain a ton from going full sequential for the ECU costing 3X the amount and I could put that money to use better in other parts of the build, though I *DO* have full crank/cam sync if I ever choose to go that way.

    I'll have to find your thread and checkout your build. I'm curious what you're gaining from swapping the 360 to the magnum.
    74chlngrTT5.9 likes this.
  18. Punk.Kaos

    Sep 22, 2023
    Got my replacement turbo cartridge over the weekend, and finally had some time to install it... I think there's a good chance it had been showing an issue from start as the new cartridge is spooling quicker and I'm building boost faster on my one test run. I think the other turbo was masking the defective turbo a bit... Either way, I'm back to boost.

    Now I've just got to get the rest of the bits together for meth injection... Tested out my pump, solenoid, and nozzle today and everything seems good to go. Just have to decide where in the piping I'm going to put it.
    Hopefully I can get that in and going soon as we're just creeping into the rainy season here in Portland so it'll be a bit harder to tune in the wet!
    74chlngrTT5.9 likes this.
  19. Punk.Kaos

    Sep 22, 2023
    Over the weekend I built myself a water/meth injection setup so I can keep my boost up a little higher.
    Took it out for a test run and was quite happy with my intake air temps on water only.

    I let it get up to a new boost record of 15.2PSI, and my intake temp only went up to 119F which is far less than it was doing at 13PSI(That was hitting 163F). So even on just water I think thats a win!

    Now to get my tune. done. At 15.2PSI I was pulling a LOT of timing just because I wasn't sure what it was gonna do, I was pulling 21 degrees taking my down to 15 degrees. Now that I know my injection is working I can start working on that.

    I'm also getting a bit of what I'm pretty sure is rich popping when I'm at WOT, so I'll have to work that part out too as I'm running pretty rich across the board.

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    Last edited: Oct 22, 2023
    TurboSnake281 and MrBelvedere like this.
  20. Punk.Kaos

    Sep 22, 2023
    I got out today, found a large parking lot, fired up my datalogger and took my first real good hard pull.
    Then using a fantastic bit of software called Virtual Dyno I can spit out a reasonably accurate dyno graph of the run using a buncha really fancy maths involving vehicle frontal area and drag coefficient and nonsense like that.
    The bump in the middle there was me letting off the gas for a moment as my wastegates opened and the sound of it startled me, thats the first time I hit them and a big block running open downpipes gets a LOT louder when the wastegates open!
    I also didn't have enough room to do a pull to high RPMs so I stopped at 3438RPM. Which is really low.

    So if this thing is half way accurate (And it has been on other builds I've done) at 3438RPM the software calculates that I was putting down 676WHP and a MONSTEROUS 1033FtLbs torque.

    I also sucked down almost 1/2 of my water injection tank in one long pull. So I might need to go a bit bigger on that thing...

    And holy crap. I'm gonna start breaking stuff at those power levels.

    TurboSnake281 likes this.
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