DIY Rotrex stage 2 on stock internals?
 

While I wait for CCR Racing to get approval for road legal installations of Rotrex SC's on '99 - '00 1.8's here in Denmark, I'm already thinking about what to do with the setup when I can buy one.

I expect it to be very similar to CCR's kit for the '01+ in terms of pulley size and restrictor. The '01+ kit, which is a modified version of the KW kit with water/meth injection, puts out around 191 hp and 236 Nm (both crank) at 5 psi with an aftermarket muffler. Here's a dyno plot: http://www.five-speed.dk/Forum3/view...=asc&start=285

I plan on sticking with stock internals and add an intercooler as odds are that the '99 - '00 kit will not come with water/meth injections. If need be, I'm also prepared to add injectors and a fuel pump. The question is what I should do to make moar powah and stay relatively safe for DD and an odd track day here and there:
- Spin the Rotrex faster
- Pull the restrictor

I understand that keeping the restrictor in place and spinning the Rotrex faster will produce a more desirable power band but wouldn't it be possible to reach higher top-end power with the same load on engine components by pulling the restrictor and not spin it as fast?

Cheers,
- Tom

There should be plenty of info on this forum regarding the durability of stock components. The "weak points" as it were are the rods and the 5 speed. It's torque that kills BP rods and Miata transmissions and the rotrex is not exactly famous for its low end torque output. Meth/water injection can fail or run out of liquid, my vote would be for an intercooler simply for reliability. Its passive and pretty hard to screw up, virtually no parts to fail.

I believe there are a couple of guys that have pulled the restrictor AND run a smaller pulley on stock engines. IIRC someone on miata.net was running a C30-74 on a 1.8 matching blower redline and engine redline, unrestricted, and was making something like 225-ish hp? Not sure if it was backed up with a dyno plot, but its out there somewhere.

I believe Falcon had a post on here about matching blower & engine RPM, should be somewhere here in the supercharger section. Unless you have a mechanical engineering or fluid dynamics background, I'm not sure where you would get information about the restrictors and there effects on top end output. There are a few guys that have screwed with them (look for the rotrex on a spec miata video on youtube) including KraftWerks/Jackson Racing, but they are keeping these cards pretty close to the chest at this point. If anyone else has done it, with a dyno, they have not shared either (as far as I've seen.) If you DO move ahead with this, please document your findings ;)

The rotrex makes like negative 100 torque...your internals are fine :)

I have bought his rotrex setup (C30-74 rotrex, 75mm pulley, intercooler, no restrictor) and add a MS and Rx8 injectors. We will see what that will give. ;)

Well, I kind of assumed that both uncorking the C30-74 and spinning it to 120,000 rpm would put the engine internals in the danger zone. If that is not the case, that's what I'll be aiming for.

Arny, I'll be very interested in hearing about your experiences.

- Tom

once you get close to 200rwtq at 7250RPM (engine speed) you can start to worry.

Rotrex impeller speed for 75 mm Rotrex pulley would be 7000 (engine) * 135/75 * 9.49 => 119,574 rpm
Previous owner recorded 224 whp at 10 psi with this rotrex but with larger injectors and forged pistons and rods.

We will see what will be the pressure on my stock engine and when it will be properly tuned, I will go back to the dyno to see the changes.

I would post the dyno graph [if I wasn't in Ohio and wasn't so computer illiterate]

Thanks guys.

Arny, I found your project thread over at m.net - I see we are having pretty much the same thoughts on upgrades and durability. I also see that you have a face-lifted NB, which means .5 higher compression ratio than me and 1 higher than mx594m. Out of curiosity - what are your plans for controlling VVT? I think that you could perhaps see more than 224 whp.

Something else I came across: The '99 - '00 fuel pump may be close to it's limit at max rpm under stock conditions. Does anyone know if this holds up - and if so, what should I be looking for, aiming at no more than 220 whp with perhaps 550 cc EV14's?

Walbro 190hp should do the trick.

I don't know if I have a higher compression ratio than mx594m because he had a 99 head on a MSN block bored to 84 mm with 9.0:1 pistons and M-tuned H-rods whereas I have stock internals. And if I have a higher compression ratio, I don't know if it will change the power a lot.

As you write, he has 9:1 pistons. The stock '01+ 1.8 NB has 10:1 and the '99 - '00 9.5:1.

I think what one-niner is trying to say is that from the factory, your 01-05 should have a .5 additional compression in the stock engine. My owners manual for my 2000 claims 9.5:1, so based on one-niner's numbers, I would assume the 01-05 is 10:1 and the 93-97 1.8's were 9:1? It's been a while since I looked this stuff up.

Someone will correct me if I'm wrong, I'm sure :loser:

Also: Arny is in France, I have no idea if the EUDM spec 1.8 followed the same compression numbers as the USDM spec cars.

When naturally aspirated, higher compression ration = more powah. Under forced induction, higher compression engines tend to be more prone to pinging than low compression engines. Yes it will make more power but IAT's and timing will be critical at higher boost/load levels.