No FM Turbo for a 1.8-swapped '91 Miata--now what?

Keith Tanner said:

Rods are probably unnecessary. IIRC aftermarket rods aren't usually any lighter, it's the pistons where you save weight. A lightweight flywheel helps as well. To help spool, you'll want high compression, a good flowing head and not a lot of exhaust backpressure. High compression doesn't mean you can't drive it at sea level, it just means you can't run as much boost.

The Carrillo A beams that I bought from you guys 20 years ago (OK, that makes me feel old) are claimed 20% lighter than stock, although I can't say the weight made any noticeable difference behind the wheel.  The extra boost allowed by the strength obviously did, but that's not the topic at hand.  The H-beam ebay/manley/etc rods that most people buy for turbo builds are about the same weight as stock, I think.

Do they still make 2554s?  That sounds like it might be the right turbo if responsiveness is the goal.

So maybe it's the rods that are lighter and no so much the pistons. Or maybe this dates back to the pre-A era. I forget. In theory, taking reciprocating mass out of the engine should be more effective than taking rotating mass out, but the quantities are smaller.

2554s still exist, but we don't sell them anymore. They were discontined due to low sales, but they are very fun on a 230 hp 1.8. That's what I have. 

Definitely starting to wonder about the sanity of an ECU swap as I try to think through it.  The 1.8l ECU is behind the passenger seat and is a bit chunkier shaped than the 1.6l one that goes beneath the passenger's feet.  I'm assuming I can figure out how to mount it in the 1.6l location, otherwise I'd need to extend the harness.  Definitely wondering about how much legroom I'd have to give up if I do sort it. The AFM in the 1.6 has 7 pins (2 grounds) vs 5 (1 ground) in the MAF, so that part seems more doable.  I know the A/C wiring is different, as well as the fan control and the temp sensor stuff.  And that's just what I've thought about in a few minutes.

In reply to Keith Tanner re: piston/rod weight:

The FM website description for the Wiseco pistons says, "Perfect for extreme use, such as high boost operation. Use with our Carrillo rods for a bulletproof bottom end. This combination weighs 1/4 lb per cylinder less than stock."  That's what got me thinking about wanting it just for the light weight.

Definitely sad that the 2554 isn't an option anymore (I looked for it today)--it's what I would have opted for.

I'll try to put together a swap wiring diagram for you if we don't have it already.  Feel free to remind me. 

Keith Tanner said:

I'll try to put together a swap wiring diagram for you if we don't have it already.  Feel free to remind me. 

That'd be awesome.  No huge hurry--I'm probably not going to get started on this immediately.  I do have both a '91 and a '94 factory manual with the wiring diagrams which I'm sure will come in handy.

For now, any tools that would make swapping pins easier, or just a tiny screwdriver?  What's the best way to achieve a durable splice in wiring like this?  Even if I'm not splicing on the ECU end, I'll need to splice things like the MAF sensor connection.  Solder and heat-shrink?  Crimp splice and heat shrink?  Something else?

You need a small pokey tool to depin a connector. A sharpened bike spoke or a dental pick. Amazon sells tools for it but I just use a pokey tool. 

My go-to for crimps are the ones with a built-in heat shrink, crimped with a ratcheting tool. I'll put up some suggestions later. My concern with solder is that it doesn't allow flex and is more prone to cracking. There are no solder joints in the factory wiring harness, but there are crimps. 

Crimp-splice with the built-in heat shrink has been my go-to as well.  I've got what seems like a nice ratcheting crimping tool, but I'd guess I have about a 50% success rate using it.  I used it a bunch on the rally car and got to where I crimped with the ratcheting tool then went back over the crimps with a crappy wire tool before the heat gun because that actually seemed to work better.  I'm using the correct connectors on the correct size wire with the correct size crimp, but totally unhappy with the results.  I'm not sure if the problem is my crimping tool or the connectors I'm using, or just that it's hard to get it right.

EDIT: researched crimping tools a bit, and ordered one of the fancy ones with separate dies for heatshrink/insulated/bare, as mine has a single die and it's probably the wrong one for whatever I'm using.

A related note: you might want to update FM's 1.6 to 1.8 swap hint document to help manage customer expectations.  It suggests adding a turbo kit while doing the 1.8 swap in about a dozen places, which is one of the many reasons I was sure you'd be happy to sell the appropriate kit, with lines like, "Aside from one of our turbo kits (just think of all the horsepower!), the 94 - 97 crossover pipe is the best option."

De-pinning depends a lot on the type of connector.  Some come apart pretty easily with a dental tool, others really need the correct de-pinning tool.  The good news is you can get the tools pretty cheaply on Amazon.

I'm not a huge fan of soldered connections for high vibration environments.  Crimped connectors usually work well using a quality crimping tool, but I have had them fail randomly in the past.  Look up "telegraph splice" for what's considered to be the strongest wire splice method (also called 'NASA splice' or 'Western Union' splice).  These can be done with/without solder.

The thing with spool, that is very noticable to the driver, isn't necessarily boost onset at full jam, but turbo response at part throttle.  Boost onset is just the RPM range where  the turbo and engine start to be happy together but higher compression engines are much more responsive at part throttle both as engines and as a turbo spooling device.

One of the most ridiculously responsive turbo engines I ever drove was an 87mm turbo (!!!) on a 4.5l Buick.  The key was besides having very good intake and heads (basically the Champion catalog was thrown at the build) but it also had 10:1 compression.  I'd driven plenty of turbo Buicks and none were as responsive no matter what the turbo was or the engine airflow package.  The turbo would wake up and start making serious boost at part throttle while the engine was cruising under vacuum!

Of course, the engine lived on a diet of C16.  It then proceeded to make 100 more wheel horsepower when switched to E85, although that was also due to adding fueling.

The other key thing is the engine made significantly more power at less boost with 10:1 compression.  We actually had to drop peak boost from ~28psi to ~23psi because the (gasoline) injectors were now maxing out, whereas they had plenty of headroom before.  The car's owner was fixated on the boost numbers and was upset that he had to run a lower number, but we reminded him that we were now maxing out 1000hp worth of fuel injectors   Making the power with less boost means you need to work the turbo less hard, which is also perceptible as responsiveness.  It also works the cooling systems less and is overall a healthier way to go.

Well now you've got me wondering...  can the stock ECU / Voodoo box handle 10:1 pistons? Does this just mean I'd need to turn down the boost a bit to make sure the stock injectors can handle it?

You may have to retard the timing a bit further as well, or run higher octane. You're going to be feeding this 91 anyhow.

In reply to Berck :

Your fuel requirements will still be airflow related and your airflow will still be dictated by your turbocharger and cylinder head and manifolding.  The compression ratio just dictates octane sensitivity as far as engine management concerns are... um.. concerned.

The engine controls and injectors can handle it, but you may need to up your fuel octane game and/or look into water injection.  Or just run lower boost, but that's no fun.

Timing retard to handle higher boost can run you into a "coffin corner" tuning wise where a couple degrees more advance will detonate but a couple degrees less advance will melt the exhaust valves from high EGT.  This is where you need lower compression or more detonation resistant fuel.

The thing with C16 fuel is that it basically never detonates, you can run the engine to where you pour the pistons out of the oil pan or a head lifts off the engine block still attached to the deck but it won't detonate.  Last time I bought any was $110 for a five gallon pail and that was a long time ago!

In reply to Pete. (l33t FS) :

I think you're talking about greater extremes here. Running an engine that was originally 9:1 at 10:1 and at relatively low boost levels (6-8 psi) is not going to require exotic fuel or threaten to melt the valves. Don't scare Berck :)

In reply to Keith Tanner :

Sorry, my brain reverts to engines with horribly shaped 2v/cylinder heads and my idea of low boost is 4psi 

The pre VVT 1.8 engines had compression that high?  Somehow I thought they were a lot lower, like 8:1.

In reply to Pete. (l33t FS) :

IIRC, NA 1.8 is 9.0:1, VVT 1.8 is 10.0:1, not sure about 99-00 1.8.

1994-95 is 8.8, 1996-97 is 9.0, 1999-00 is 9.5, 2001-05 (non-MSM) is 10.0, MSM is 9.0.

IIRC. The old 323 GTX was in the low 8 range, which is why a Miata bottom end (9.4 for the 1.6) is a nice upgrade for those.

Don't scare Berck.  Definitely going to be limited to 91 octane.  I'm not interested in crazy power, this never going to be driven on the track (I have racecars for that), and I'm hoping that I'm totally content with 6-8PSI.  In the world where I get addicted, switch to a standalone and need more, I can't see going beyond the ~225hp level.  And happy to give up peak power for better responsiveness.

Is 10:1 as far as I should consider going?  The fancy FM Miata-specific Wisecos are only available in 9:1.  The only options I'm finding in forged pistons are Supertech in either 9.5:1 or 11:1 or Wiseco 10.5:1.  I know there were NB's with a 10:1 compression ratio, so it seems like there ought to be something available in there in 84mm, but I'm not finding it.

I wouldn't stress over it.  Either is going to be a big jump from engines like the WRXs mentioned early in the thread which were far far lower than that.  Plus you aren't sticking the turbo on a long pipe, which also helps a lot.

Berck said:

Is 10:1 as far as I should consider going?  The fancy FM Miata-specific Wisecos are only available in 9:1.  The only options I'm finding in forged pistons are Supertech in either 9.5:1 or 11:1 or Wiseco 10.5:1.  I know there were NB's with a 10:1 compression ratio, so it seems like there ought to be something available in there in 84mm, but I'm not finding it.

I have 9.0 SuperTechs and they make (or at least, used to make) 8.5 as well.

Leaning toward the 10.5:1 Wisecos. Not at all a fair comparison given its fancy modern engine management, but somehow my GR Corolla is doing 25PSI on 10.5:1 compression ratio...  Is there a point at which retarded timing makes the off-boost response sluggish enough that the extra compression ratio ends up being a net negative?

With dual VVT, you can effectively change the compression ratio on the fly. That's why we can turbocharge 13:1 ND Miatas, because they're not always really 13:1.

I'm going into a management meeting right now, I'm hoping we can talk about the 1.8 swap turbo kits in there.

Berck said:

Leaning toward the 10.5:1 Wisecos. Not at all a fair comparison given its fancy modern engine management, but somehow my GR Corolla is doing 25PSI on 10.5:1 compression ratio...  Is there a point at which retarded timing makes the off-boost response sluggish enough that the extra compression ratio ends up being a net negative?

You cant really compare the GR engine because it has direct injection.  There are differences between a DI engine and a port injected engine that dramatically change the detonation threshold.  With DI, it's normal to have 13:1 engines that run on 87 octane and 11:1 turbo engines, but that doesn't make that possible for port injection.

You won't necessarily lose off boost response (you will gain it) but you won't be able to use standard tuning advice for on-boost tuning, so to a degree you'll be on your own.