DOHC turbo ?

Discussion in 'Front-Engine Rear Drive Fiats' started by Dr.Jeff, Mar 23, 2019.

  1. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    First I must quality this. I have not been involved with anything "DOHC" is ages, and even then it was stock. And I spend all my Xweb time on the X1/9 section so I'm not current on what has already been discussed here. So apologies if this question is non relevant or redundant. :oops:

    I know Fiat once did a boosted version of the Spider, but I'm not referring to that. And I'm sure others have at some point built a turbo'ed 124 or other DOHC engines, but I'm not familiar with them. So I'm wondering about the practicalities of doing a mild turbo DOHC? I'm not talking high boost (maybe less than 10 PSI), nor a race/track performance application. But more along the lines of what a factory might do. Conservative, low boost, with lots of safety built in. That would require electronic fuel injection with a aftermarket ECU that controls fuel, spark, boost, etc., as well as cooling system upgrades, etc., etc.. The basic concept is not to build a monster, but to make a more "livable" and "enjoyable" power plant (ie. a bit more power yet still very streetable).

    And yes, the twin cam can be built to all sorts of levels without going to boost. But that is not what I'm interested in here. Thank you for not going down that road. :)

    Is this something that has been pursued? And if so, how did it go? Could this be considered with a stock engine (without custom pistons, rods, crank, valves, etc)? And I ask that last question specific to the DOHC components, not to boosted engines in general. In other words, I'm familiar with the limitations/pitfalls of going turbo, but not with these engines specifically.

    I've been developing the same idea for the SOHC engine and appreciate any input on this concept potentially applied to the twin cam engine. ;)
     
  2. Kevin Channer

    Kevin Channer True Classic

    I am definitely not the expert, but I believe the DOHC 124 engine was as we know it, not so suitable for turbocharging. The commercial Turbo version was only producing about 130hp at a fairly low boost. Not a lot of gain, Torque increase was a plus. Lancia of course did race a motor derived from this at high boost but it was a very expensive racing built motor. My question about the 1.4 T jet engine was because this motor is still produced and should be fairly easy to import it maybe the best Fiat option. The numbers are good, stock 150hp plus, ECU tuned and chipped up to 230hp. There are also 6spd trans options, straight cut gears, LSD, available.
     
    Dr.Jeff likes this.
  3. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    It might be a little difficult to compare the turbo attempts from 35(?) years ago (I think it's been about that since the commercial turbo 124 projects were tried) to today's potential. Because the technology for electronic controls (fuel, spark, boost, temps, etc) have developed so significantly since then. Plus the turbo's themselves and the design of the rest of the system (intercoolers, control valves, solenoids, sensors, etc) have also improved significantly. However the engines in question (Fiat DOHC from the 70's-80's) have not changed, so there is some validity to the point. After all there is only so much that can be done to improve an old inefficient engine design.

    I'm not at all familiar with the newer "T-jet" engine, so can't comment on that.
     
  4. ghostdancing

    ghostdancing True Classic

    Location:
    italy
    lancia marketed a volumetric supercharged beta (1995cc) in the early '80s the lancia beta "volumex" was rated for 136hp
     
  5. kmead

    kmead Old enough to know better

    Location:
    Michigan
    I would think that with a modern computer controlled injection, ignition and cooling pump that a stock North American Fiat DOHC engine could be converted to a low pressure turbo with success.

    One thing that would likely want to be changed is the exhaust cam or at least it’s timing to reduce overlap.

    A modern injection system which also controls ignition and uses a knock sensor to manage that side and the blow off valve should be able to deal with the relatively low compression the Fiat engine has. The water pump could be converted to an electric unit (Mark Allision sells a set up for this) to better manage cooling the engine and ensure a more consistent cooling environment.

    I would want to keep the pressure down, ten psi would likely be the limit, though I would be thinking in the 8-9 lb range. I would also look to limit high rpm pressure. Like the original 124 Turbo this would be a torque motor, not a high top end solution.
     
  6. MikeHynes

    MikeHynes True Classic

    Location:
    Goodfield, IL.
    When Legend did the turbo conversions for Fiat back in the day, they pretty much just bolted a turbo onto an otherwise stock, US spec FI engine. It worked out okay. The boost levels/power increase was limited of course, but for what you've asked about - it's very doable - Fiat/Legend has BTDT.
    I think the biggest challenge anyone attempting a modern turbo conversion will have is finding a suitable exhaust manifold. There are options out there. You might find an original Legend manifold (easiest install?). You could also build your own header, or possibly build an adapter for the stock exhaust manifold (it's got a 6 bolt flange). Or, you might consider simply mounting the turbo downstream in the exhaust system like some Corvette conversions that place the turbos back in front of the rear bumper.
     
  7. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    Karl, your description is exactly what I was thinking. With the current aftermarket ECU technology, the only "stock" component that might be utilized is the factory fuel injection intake manifold. While you could go even a step further with independent throttle bodies, I really don't see that as necessary for a conservative 'mild boost' system like this (and actually it could cause issues without a plenum). The rest of the Bosch fuel injection components would no longer be utilized; no 'flapper' AFM, no Bosch ECU, different injectors / sensors / fuel pressure regulator, etc.. Likewise all of the original ignition system would go away, replaced with individual 'smart coils' that are controlled by the new ECU and a crank trigger wheel; no distributor, module, Bosch coil, etc.. All in all it makes things much more modern, better managed, cleaner, and reliable.

    With an appropriate intercooler and the ECU programmed correctly, knock or other thermal issues should not be a problem - especially with the low compression of these engines. But an improved cooling system in general would certainly be beneficial. As would typical heat management in the engine bay with heat shields, insulation materials, and good air flow.

    As for the exhaust manifold, turns out that is actually not an issue. Since my initial post for this thread I've already found a couple companies that make different styles of turbo exhaust manifolds for the TC engine. Who knew - I did not realize these engines were that popular for turbo use, but apparently there is enough demand for the aftermarket to produce the manifolds. And they are available in more than one design, so hopefully at least one of them should locate the turbo conveniently for whatever vehicle it is to be utilized in.

    Also since I started thinking about this concept, I've come across a few articles discussing turbo'ed TC engines. Guy Croft made the statement that the North American spec engine (low compression) in stock form should handle a low boost (under 10 PSI) system without any problems. If you want to go to higher boost levels then he recommends replacing the pistons with ones specifically designed for boosted applications. Otherwise the head bolts could be replaced with studs and a MLS head gasket used (both are readily available in multiple options). And that's about all that would be necessary (unless you start talking about really high boost levels, which I do not think the TC's old design would be appropriate for). I do like Karl's idea about retiming the exhaust cam. With this engine having individual cams, and the use of adjustable cam sprockets, it should not be necessary to replace the cams...just retime them. For low boost systems a stock cam is usually quite adequate.

    The concept for this came about from the same idea I had for the X's SOHC engine. When I was considering options for making my X a bit more drivable (i.e. some more "oomph") I decided to go turbo rather than build a stressed-out NA screamer or do a complete drivetrain swap. It isn't that much less expensive than the more traditional NA performance build, but in my opinion a boosted engine is much more 'drivable' (or 'practical') in normal street applications. And the system I've been developing (SOHC) could be offered as pretty much a bolt on kit for a stock engine. So why not do the same for the DOHC? It's head design is even better suited for boost than the SOHC.
     
    Last edited: Mar 25, 2019
    kmead likes this.
  8. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    Then I saw this, for the TC engine:

    s-l1600.jpg

    Add something like this onto it:

    images - Copy.jpg

    And "boost" is your daddy.
     
  9. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    Although those "Weber" style independent throttle bodies are neat, they would require a lot more work to function with a turbo. In addition to fabricating a inlet plenum for the turbo to feed into (as shown in the prior post, yellow circle), they also need a second smaller plenum to balance reference air from all four runners at the head end. Plus a throttle position sensor needs to be added somehow. This level of intake design really isn't necessary for a low-boost stock-engine set up; the stock factory FI manifold would be fine. But I was surprised the one shown (in my last post) is only $400 delivered. Seems not long ago each Weber-style injector body was much more than that, as was that style of manifold without carbs/bodies.
     
  10. kmead

    kmead Old enough to know better

    Location:
    Michigan
    I suspect that a single throttle plate would be best for a turbo motor versus the multiple ITBs.

    I have always thought that a turbo on the far side feeding forward into an intercooler across the front leading across the left side of the car to a throttle plate and plenum on top of the OE 124 fuel injected manifold with modern injectors would be the preferable approach.
     
  11. Jefco

    Jefco Daily Driver

    Location:
    Portland OR
    Darn it, now you guys have me thinking about the parts I have lying around while I freshen up a 2-liter motor for my sport coupe-

    I had a Volvo 745 turbo wagon, and still have a turbo, tubing, and intercooler;
    from a Volvo 145, I have a complete K-jet injection system; and
    the 2-liter motor I'm working on is a '79, so I have a single-outlet exhaust manifold and downpipe.

    So, I'd need a throttle body and plenum from a later injected spider, and a small amount of fabrication.
    More short-term, get the motor done and in the car.

    To the problem you've caused me:
    Compression increase or not? I suppose it depends on whether I need to replace the pistons.
    Wouldn't consider getting an 1800 head for the compression bump, either.

    Problems, problems. Thanks guys! :confused:
     
  12. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    As I understand it, either way will work well with a turbo IF it is designed properly. And that is part of the problem with taking a aftermarket induction not designed for boosted applications (like the one I posted) and trying to adapt it accordingly. Difficult for a home hobbiest builder to design things right. And while the factory FI intake wasn't designed for boost, it was properly designed for this engine so it is a better starting point in my opinion.

    I agree with your layout ideas for a front engine / rear drive vehicle with cross flow head.
     
  13. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    If you are seriously considering a turbo in the future, then do not increase the compression. The stock compression is about the limit that you want for a boosted stock engine.

    On the other hand, if you want more performance and will not be going turbo, then higher compression combined with a lot of other mods (cams, manifolds, porting, etc) is the way to go. That is why I am leaning more toward a boosted engine rather than a "built" naturally aspirated (NA) one. The turbo will give you a significant torque increase, while the built NA will lower torque. The turbo will also increase top-end HP, almost as much as with the built NA. So with street driving the turbo will be more flexible (with a properly sized turbo that doesn't lag), while the NA will need to be run near redline most the time. Naturally that would be different for a track only engine.

    By the way, that Volvo turbo stuff you have is popular with the early water-cooled VW crowd for turbo conversions. The Volvo components are about the right size for these older design engines.
     
    Last edited: Mar 25, 2019
  14. BEEK

    BEEK True Classic

    Location:
    Clermont Fl
    My son wants a turbo spider with 200+ hp. I am contemplating the build. Stay tuned! because I also want to make this happen. The idea of a megasquirt ecu and a big turbo and intercooler is what is in store. There is a manifold available and any intercooler that will fit in front of the radiator will be a must. cool the oil and use a water cooled turbo. the basic bottom end with upgraded pistons will handle the hp. look at the lancia delta. 200hp is not that far off!
     
    Dr.Jeff likes this.
  15. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    With better pistons shouldn't it be capable of a little more than 200 HP? As part of a proper turbo-prep rebuild, maybe add oil squirters under the pistons? Especially with your experience, knowledge, and skills, I'm sure you can get an easy 250 HP.
     
  16. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    In addition to the pistons, I'm guessing porting, cams, head studs/MLS gasket, inconel exhaust valves, con rod and main saddle ARP hardware, what else would you want to do for bigger boost?
     
  17. BEEK

    BEEK True Classic

    Location:
    Clermont Fl
    I am looking for reliability. Abarth got 460hp from a 1400cc version of the lampredi twin. The potential is there. I also wonder how things will live over 22lbs of boost. that is were things start becoming unreliable. if Mitsubishi can boost a 3.0v6 to 22 lbs with a factory program why cant fiat do that
     
  18. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    22 pounds is a lot for the old design DOHC!
     
  19. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    This is not based on any real data, just guessing from what I've seen on other applications and extrapolating to the TC. I imagine the stock DOHC with only about 8-9 psi (properly tuned standalone ECU, intercooler, etc) would be around 135-140 HP and lots of torque. With a little engine prep (especially pistons) and up the boost to 12-14 psi, I'd guess maybe 160-170 HP. More internal prep and 18-20 psi should offer a good 200 HP. Get to 25 psi and you must be near the 250 mark (if the engine will hold it). Naturally each increased level of prep would also require corresponding thermal management and all components will need to be properly selected/matched. As I said, just guesstimating.
     
  20. Simon Oaten

    Simon Oaten Daily Driver

    worth looking at what the factory did......20 yrs ago

    search fiat croma turbo
     

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