SR20DET in a Miata: Why not?

I've been trying to decide how to add more power to my Miata for quite a while now. I've considered turboing the 1.6, dropping in a 1.8 and turboing that, or swapping to a 5.0 Ford (LSx would be great but a little out of my price range yet). I'm not going to be using a kit (again, out of the price range). I hit on this as a possible solution. This is all early-stage thinking; feel free to shoot my logic full of holes.

The SR20 is factory turbocharged and up 200cc of displacement on the biggest BP (barring writing a really big check to Flyin' Miata). It's good for ~200whp in stock form with a freeflowing intake and exhaust. It's good for an easy 300 whp with a new turbo, higher boost, and a bigger FMIC. This would be enough to be very entertaining in a Miata for a very long time. The SR also would probably not grenade a late-model rear end in a Miata (something I think an LS or even a built 5.0 probably would).

An SR20DET swap seems to go for about $1500. By the time I make mounts, exhaust, mount and route lines for an FMIC, a bigger radiator, and Megasquirt I figure I'd be into it for $3k. It would require significant planning, engineering, and I'd pretty much be on my own for figuring out problems. That doesn't particularly bother me.

Swapping in a 1.8 and turboing it the right way (MS, good components, etc.) would probably cost every bit of 3k, if not more. Making 300whp would take some tuning, and IIRC is up near the limits of the stock bottom end on a BP. It would not require as much engineering, and every possible problem has already been encountered, fixed and documented.

Questions:

Where's a good non-fanboy source of info on the SR? I need dimensions, weights, etc., etc.

I know I can't be the first person to think of this. I found a set of mounts on an old and not very informative website for a company out of Australia, but that was about it. Does anyone know of someone who has done this already?

If I did need to swap the rear end, I can get custom hubs to run the TII RX7 pumpkin and axles, but that limits me on gear ratios. Does anyone know what gear ratios are available for that rear end, and are there any aftermarket ratios available?

And of course, what obvious deal-breaker problem am I missing?

it seems like turboing the bp would be alot easier

G20.net

lots of good non fanboi shiznizzle in there.

FYI though, most SR20DEs in stock form arent making near 200 whp - your lucky to get to a bill eighty without some real fierce bolt on + tuning action happening in there.

Been there, done that. Fits with relatively minor notching of the firewall in the chassis and reworking the subframe. Shifter pops right up in the proper hole.

I hate endless hours of troubleshooting. So I'd take the bp route.

I can't see what advantage it would offer over a turbo BP.

ZOO wrote: I can't see what advantage it would offer over a turbo BP.

That's more or less what we figured. If you are going for a 500hp drag queen then go the SR20, if you are streeting it then go the turbo. Interestingly enough it was cheaper to put the SR20 in than buy a FM turbo kit. I don't know it it was easier, just cheaper

Dump in a junkyard BP and turbo it. You can turbo the BP for exceedingly cheaply, and make great power.

I can think of almost no advantage of an SR20DET swap other than telling people that you DID, in fact, get your engine before Race Wars, and YES, it did pull a premium.

carguy123 wrote:

ZOO wrote: I can't see what advantage it would offer over a turbo BP.

That's more or less what we figured. If you are going for a 500hp drag queen then go the SR20, if you are streeting it then go the turbo. Interestingly enough it was cheaper to put the SR20 in than buy a FM turbo kit. I don't know it it was easier, just cheaper

I can see cheaper - but the equivalent would be a homebrew turbo system, not one from FM. After all, you wouldn't be buying a complete engineering SR20DET swap. So use that as your cost comparison.

Easier? No. The FM turbo is designed to go on that engine in that car and there are guys on the other end of the phone to help you. The SR20DET is, umm, not.

My thoughts are - if you're going to do an engine swap, make it one that brings some real advantages to the table, not just very slight improvements.

despite either choice being superior in almost every measurable way, I still want to put a N/A rotary in a miata real bad..

Getting on this thread to see your results should you decide to go through with it.

Having both a 1.6 Miata and an SR20DE equipped car in the driveway (91 Sentra SE-R), I compare the two engines quite regularly. :)

The SE-R, despite being heavier, will outrun the Miata in a straight line all day, any day. The difference wouldn't be as pronounced in a newer 1.8 Miata with the same gearing, but I think the SE-R would still win. The SR20DE is a 2.0 liter, which gives a good amount of low end grunt for cruising around town. I imagine it would be a bit better on an autocross course as well. That difference isn't usually considered, since everyone's all about the SR20DET for its high HP and 7500rpm redline.

I can understand the appeal of the Nissan motor in the Miata. I think it would be a great combo. But I don't think it would be worth throwing out the Miata motor and going through all the work of custom fitting the SR20 when there's so much support already out there for Miata forced induction.

With proper planning, creativity and a talented tubing bender you can make ANYTHING fit ANYWHERE (within reason)

A SR20 would be a nice engine in a Miata.

If I had the money to build a modified bellhousing I would suggest a 1.8T from VW. I can not believe how rapidly I can go from nothing to 80 in my automatic equipped Jetta. Plus the 1.8T was equipped in a N/S layout in A4s and Passats so cooling and exhaust issues are easily dispatched.

belteshazzar wrote: despite either choice being superior in almost every measurable way, I still want to put a N/A rotary in a miata real bad..

As soon as I can find A. a clean shell, and B. Replace the NA of my wife's I wrecked for her. I am going this route.

I'd vote either turbo'ing the BP or LSx. The SR20 is an incremental improvement over turbo BP for the amount of pain you're going to endure (think gauges, wiring, smog, motor mounts, custom exhaust, sketchy 2ndhand motor, trans mounts, plumbing cooling, a/c, turbo, rear upgrade (might as well go to caddy rear if you're going that direction anyway) etc), and then what is the weight difference between that and the LSx? I'd either go with some homebrew miata turbo or LSx just because it's so much easier. I've done the ship in the bottle bit with my 4age Midget, and I'll tell you that there are easier routes. Keith can probably confirm with his BGT LSx conversion.

I'm aware that it won't be a drop-in conversion. But, considering what I would have to do with a homebrew $3k turbo kit (exhaust, intercooler routing, EMS, etc.) , I'm really not that much different between the BP and the SR. I would have to make the gauges work (something I'm still figuring out), but motor mounts and trans mounts are easy enough, as are custom A/C hoses and cooling.

I know that the conversion here is comparable to a homebrew kit. I know that with patience, I could get this in here for cheaper than just going to the FM catalog and buying everything I need. That's not a bad route, but I can't afford it. As for cheaper than a homebrew, I think it might be a wash, but for the same money and a little more time, I think I could be putting quite a bit more power down than a 1.8 BP. If I decide to go crazy later on, the extra 10% displacement will be nice compared to the 1.8. And performance parts for the SR20 are everywhere.

What are the realistic limits for a streetable stock bottom end on a 1.8 BP? Assuming I get the best possible one (MBSP, etc.). Again, I'm thinking that the SR is going to have a stronger bottom end than the BP.

I've owned a N/A SR20 car ('91 SE-R), and it was possibly the most fun-to-drive vehicle I've ever owned. It was just always willing, and it felt like a bigger motor than it was. I've never driven a turbo SR20, but I can imagine how it would up the ante.

Oh, I know it can be done with a little determination- the question is, what incremental gain are you going to get? Doing something different for the sake of being different is fine- if you admit to yourself that is what you are after- but with a 1.8 or well-modified 1.6 you are going to get 90+% of the SR20's stock turbo performance. I think the other problem sort of mentioned was the rear. Your 1.6 will only likely last with very mild treatment, which if you're looking to increase power will best be converted to the 94+ or the caddy diff.

I have a 1.8 diff and Torsen ready to be swapped in. That's both easy and cheap, and will take the abuse of either the BP or the SR.

Doing it to be different is at least a small part of my motivation here, I'm not gonna lie. I do honestly think I can get more out of an SR for cheaper, though, and I think the benefits may outweigh the hassle of getting it in there.

In reply to carguy123:

You say you've BTDT...did you take pictures? Have anything to add other than the fact it fits with minor work?

There's no homebrew turbo, the T in DET stands for Turbo.

I'll look and see if I have pics. They were all film whereas all I do now is digital so the pics are packed and I've moved twice.

200 WHP out of a stock SR20DET (T denotes the factory turbo) should be easy. As White_and_Nerdy mentioned, despite the reputation the SR20 has as a high-RPM screamer (which it is), it has great torque all around. However, I'm with the majority here, I'd do what's been done over and over, and that's turbo the factory Miata motor.

If you want to be different, the SR20 would definitely give you that, and it's one of my all-time favorite motors. The car would be a blast when you're done.

If you're going SR20DET, go for the factory turbo'd motor, and don't just slap a turbo on an SR20DE like some do. The SR20DET factory motor has some nice features (oil squirters come to mind) that you won't get on a SR20DE.

one of my best local friends has run 12.5@113 on drag radials on a homebrew turbo setup on a 250k mile stock bottom end 1.8 using a $125 ebay turbo in his miata, and its been running for years now...

I think the turbo'd miata motor can easily get you what you want for way less than a swap OR a kit. homebrew the turbo setup on a 1.6 or 1.8 and be done.

psteav wrote: What are the realistic limits for a streetable stock bottom end on a 1.8 BP? Assuming I get the best possible one (MBSP, etc.). Again, I'm thinking that the SR is going to have a stronger bottom end than the BP.

The 04-05 Mazdaspeed miatas came with 170 HP turbo'd BP engines. Keeping the turbo & cleaning up the piping (via FM Kits or DIY) can get you 220 HP without too much trouble.

kj

I've heard of 400whp stock bottom end BP's....though I don't think I'd go there, myself. Well tuned, 280-300whp is doable, I believe, but I'd suggest it would be doable for a fun/street car. I'm not sure where the "reliable lapping day car" limit is.

I think I'd be happy with 300whp in a Miata.

If you start with a healthy motor and get a good tune on the car, 300whp is pretty attainable with a turbo BP.

If you want higher, just grab some forged pistons and some Familiar GTR rods from Corksport and have a built motor on a budget.

And really... it's INSANELY cheap to turbo a BP. $3k for a homebrew setup is massive overkill. Granted, if you don't have the skills to do that, then the FM kits are the way to go.