Pentastar-Powered 79 Fiat Spider

Hello, all! I've been researching and preparing for a Chrysler 3.6-Pentastar swap for a long time, and I've finally reached the point where it's worth starting a build thread. I'll do a quick rundown of the project here, answer some quick FAQs, and we'll be off to the races!

The plan is to install a Chrysler 3.6L Pentastar V6 and 845RE 8-speed automatic into my 79 Spider. All told, the engine should make approximately 330hp/280ft-lbs after some mild modification and tuning. With the addition of boost down the road, it should hit 425-450hp.

Why this engine? - Frankly, I'm a Mopar nut, so I didn't want an LS or small block Ford or K-series. I considered an SRT4 engine as well as a Mercedes M112K from a Crossfire SRT6 (which would have had a NAG1 trans). I decided against the SRT4 because I'm not a turbo guy, and against the M112K because of availability and complexity (rare, 12 spark plugs, complex, would've used the NAG1/W5A580).

Why an automatic? - The 3.6 Pentastar is available in Jeeps with manuals, but a little research led me to realize that they aren't particularly suited for performance driving. On top of this, the ZF-based 845RE 8-speed is an amazing, tunable transmission that will give me wicked acceleration down low and high-mpg, low-rev performance on the highway. I want this car to be a Grand Tourer first, then a track machine second. Also, paddle shifters.

What's your plan? - It evolves daily. As it stands, the car will be receiving an NA or NB Miata front and rear suspension (inspired by the Isabella Pininfarina Azzura project, which is amazing, that project can be found on BringATrailer by searching "Miata-Swapped Pininfarina Azzura" or on Mirafiori.com under the name "Isabella the Spider". I have the entire wiring harness and all relevant computers and modules from the same 2014 Chrysler 300S as the engine and trans: I've already got it running on a pallet. I also have the radio, gauge cluster, shifter, and more to integrate into the car to make everything happy.

I'll do my best to keep this thread open. The folks on the Pentastar V6 Performance facebook page have been incredibly helpful as I got this far: a massive, massive thank you to all of them.

Sounds awesome. Watching. 

Very cool. I'm gonna learn some stuff in this thread.

That 124 is spooky clean body-wise. And there is another one right next to it. That must be another story.

I know nothing about the proposed drivetrain. Assume it is still going to be RWD?

Ooh, I am here for this. Love the run stand!

Unreal! Will be following closely. The pentastar 3.6 is one of those engines I can't stop considering, and I'm a sucker for miata suspension swaps.

Odd to consider the Miata was re-skinned and sold as a Fiat Spider!? Now you are re-engining a ancient Spider. It's hard to determine who is showing who what here but I'm watching!! BTW, I've been looking for my motor, please return it to my Jeep ASAP. (JK) I had liked the new Spider/Miata mash up, they kept much of the Spider personality in the new unit. Someone transported from 1982 would recognize it as a Fiat Spider. Yours would blow their minds while mussing their hair!

In reply to NOHOME :

The red one is a stock 78 I picked up. It's no beauty queen but it's bone stock and runs well. A great play toy that can get dirty and dinged and I don't have to sweat it. The white car will still be RWD, yes. 

This is gonna be great!

*Grabs popcorn, plops down on couch*

Recon1342 said:

This is gonna be great!

 

*Grabs popcorn, plops down on couch*

Move over and grab some more popcorn.

At first glance I was going to post the Blazing Saddles 'Kinky' pic, but this is a wonderfully conceived vision.

Interesting!

Is the Chrysler 3.6L Pentastar V6 you mention the same engine used in the Grand Caravan/Town and Country?

Because in 5 to 10 years it would be absolutely hilarious to have people going into junkyards and yanking engines from minivans as a viable option for a performance upgrade.

Yes, I have a 2018 Grand Caravan. Unfortunately not with the paddle shifted 8 speed RWD transmission.

... please return it to my Jeep ASAP. (JK)

I'm sure that if he has your engine you don't need to tell him what kind of Jeep you have.

In reply to RandolphCarter :

Yup. All 3.6 Pentastars* are the same. They just swap around intakes, oil pans, and accessories to make them fit. As it stands I'll be using a Cherokee/200 PF oil pan, and I measured a Pacifica intake (I think that's the shortest one). Hopefully those will facilitate some extra room

*there is an upgraded version that came out in certain vehicles called the PUG that got cooled EGR, VVL, and some other tweaks

RandolphCarter said:

Because in 5 to 10 years it would be absolutely hilarious to have people going into junkyards and yanking engines from minivans as a viable option for a performance upgrade.

The Honda J35 from the Odyssey is already a sought after performance upgrade. It was only a matter of time before the other vans gained the same popularity.

This is super cool

Lucked out and stumbled upon this guy, a super clean NB shell with everything I need and nothing I don't. Straight axle be damned!

I'm a fan of the concept.  If 4700 lb Chargers and Challengers can manage to be fun to drive with a 3.6, no doubt that powertrain lugging half the weight will be a hoot.

Having driven both, I would lobby for the 2.0 turbo used in many Jeep and Alfa products.  We own a 2021 Wrangler Unlimited that I ordered with the 4, and it is nothing short of amazing.  

That being said, since I'm not contributing even one cent of my money towards this mashup...carry on!  Haha.

In reply to Stealthtercel :

(JK) as in Just Kidding.

  Your comment lost me because I don't actually own a Jeep. I had to look up Jeep definition of JK. Funny coincidence.

  I still like his attack, good motor and trans choice for that chassis. Now I hear that motor is in many cars and vans and I have not been hearing many complaints about them, a early head problem but that cleared up and there are many eating up the miles complaint free.

In reply to Loweguy5 :

The 2.0T was on my list, but at the time I was staunchly anti-turbo (that sentiment is going away, given that my only other option may be to cut the hood. I'll keep everyone updated on that). I also couldn't find evidence of the 2.0T making equivalent power to a boosted 3.6, plus the 3.6 makes 300hp (and I'm not particularly worried about torque). Plus, the 3.6 is significantly more common right now: except for a few different oil pans, intakes, and accessories drives, "all" of them are identical

I was checking this out a little while ago and about to say something about the motor being a bit to stout for the stock transmission and rear end. Then I saw the rest of what you said with that being a good reasonable solution to that issue. 

Not really to sure if a live rear axle or the independent are much different time wise on a race track. Now on a road course or off road racing yes the independent is a bit better at soaking up the uneven surface.

Are you going to try to keep the stock axle width or work around the extra width of the miata? Group 4 Flairs might work good with the added width. 

What is the difference weight wise of the motors if you know? 

I've had a couple warmed over 1.8 fiat motors that were at 125-130hp. Dual carbs are great until they get out of sync then it's a little work and you're off having fun again. Only thing I would do is to cage it the best you can. That thing will flex a bit with that kind of power.

Torque is still good to have especially on the street. That's what gets you from point A to the speed you want to go. HP keeps you at that speed. 

The easy button for this build is going to be a chassis swap. Peel a few  layers off the NB and slide it under the 124. There is a lot of good engineering already done for you in the nugget shown below.

In reply to brad131a4 (Forum Supporter) :

As far as the engines go, from what I could find, the 3.6 and fiat 2L are within pounds of each other. The transmissions...no clue. As it stands, I'm pretty sure this thing is going to end up front heavy, so there's going to be special attention paid to keeping the rest of the weight back. As far as the rear end, I'm switching to the miata IRS primarily for ride comfort purposes: yes, on track with an experienced driver it probably doesn't matter, but I'm not that and this car will see gross Ohio roads 99% of the time. It's a tradeoff I can live with

In reply to NOHOME :

I'm holding on to the NB chassis for now. When I started this, I really wanted to stay as Fiat as possible. But seeing the bare NB chassis and 30 years of engineering advancement has turned me around to the point of using framerails as well. Ideally, I'll mimic what Isabella's builder did: front and back half it, tie it together in the middle. I will never suggest the Fiat chassis is superior, but keeping as much Fiat character is important to me (two ashtrays, as I say, one for the parents and one for the kids!)

Made some solid headway yesterday, dropping out the Miata suspension. Still need to break out the torches/Sawzall to get everything else. But we're getting there.

When I was doing the Molvo I actually took the Miata chassis apart spot-weld by spot-weld in order to preserve the sheetmetal parts. I just knew that if I cut something I was going to need it later to fill in a gap or some other unforseen reason. It paid off a few times. 

The wheelbases on your project are quite close, The other critical dimensions to compare if doing a full chassis swap are the distance from front axle to middle of the seats and the distance center to center of the seats. 

One of the big benefits to a full Miata chassis swap is that servicing the car into the future becomes very easy. Should you sell, it will be easier to explain the car to a buyer and allay any maintenance fears they might have. These may or may not be concerns for you. Do carry on.

Pete