Rotrex onto a built N/A 1.8
 

I'm looking at putting a Rotrex on my track car but I don't have a lot of experience with F/I so I figured I'd start a post here to ask a few questions.

First off, my current setup:My target is to nearly double HP to around 300-320HP. I was thinking of using the C30-94 Rotrex and installing it low on the engine where the A/C usually sits. I have a half width radiator so I was thinking I could put the IC next to it and keep the plumping short. This would give nice cool airflow to all radiators.

My questions are:

1) Compression: Can 11:1 work safely on pump gas (98 octane) or do you have to pull timing too much? I've heard it can work but would be risky with temp changes etc. I'm planning on rebuilding the engine so compression can be changed... What would be the ideal compression? I'd prefer not to use race gas or ethanol but I suppose I could if my existing compression would then work.

2) Cams: My cams are very aggressive. Does that still work the Rotrex? My understanding is that anything that works on a N/A engine will work well with a Rotrex. So high flow heads, big cams, free flowing exhausts (all of which I have)

3) Temps: Adding a SC I'm adding a lot of extra bang and thus heat. How much extra is there over a N/A engine? 10-20% can probably work for me but any more and I doubt my current cooling will be enough.

4) WG / BOV: I figured I'd use a electronically controlled wastegate to control boost. I can run a larger blower and get more PSI earlier, vent the excess high in the rev range. Can the wastegate also act as a BOV via the map sensor on the ECU? ie can it respond quickly enough to release pressure or do I really need a BOV/recirc valve as well as a WG?

That's pretty much it for now, any feedback / suggestions would be helpful.

1. Since you quote 98 octane as pump gas I am assuming you are somewhere outside of North America? 98 RON octane is around 93 octane AKI (how we measure in North America) and I would not run high compression with boost on pump gas.

2. Good NA setup should be fine with Rotrex.

3. Beats me. Half width radiator may not cut it unless you are in a cold climate.

4. In this type of setup with a large supercharger using a wastegate to control boost at high revs, the wastegate would be on the intake manifold (after the throttle) and you would have a BOV on the pipe between the intercooler and the throttle body.

Sounds like a cool setup,

Keith

1. Yes, you are correct, I'm in Australia. I could step my compression down a bit by running a thicker (ie 2mm) gasket. I'd have to do the calcs but it would probably drop it closer to 10:1. What would be considered the upper limit on 'safe' compression for 98 octane? I read something once about cams affecting dynamic compression but it was a bit over my head. I'll have to do some more research.

3. Temperature wise I can run in a pretty hot climate, so a few events around the 37deg C (100F) mark. So far I've had no issues and maybe adding venting on the bonnet will give me that extra cooling I'd need. I suppose I won't know until I try. In terms of IC sizing, I think I can fit around the same volume IC next to my radiator as the ones that sit across the front. It will have better airflow and can be thicker. I found one that had good thickness and with a top port that would basically pipe straight into the inlet manifold.

4. I was thinking of making a custom IM based on a Magnus Honda IM, cut the flange off and weld on a new one. It means I can run a bigger TB and could even add a port for the WG like you suggest. How much impact does a better flowing IM have on a supercharger setup and what is the benefit for having the WG after the TB?

cheers

I think Father_Leadfoot and CodingParadox, (both on this board) had this type of setup, but they were purpose-build for a specific type of racing. Try reaching out to them to pick their brains. Intercooling isn't too different between Turbos and SC, so don't limit yourself to this section. What everyone would agree on is ducting the crap out of whatever setup you use to ensure it's efficient.

CodingParadox's setup

Father Leadfoot's setup

TNTUBA also has that intercooler/rad setup.

both TN and CP have roots type twin screws, not a brotrex.

might want to ask Emilio and I think Bellwilliam who both have 300-400whp rotrex track cars.

FTFM

If you're going to waste gate it, at what psi are you planning to dump boost? You're likely gonna need to drop down to 8.5-9.0:1 static. Do you know how much overlap is in your cams? Do you have adjustable cam gears?

I'm not sure on the actual overlap in degrees though it would be a lot. I have adjustable cam gears and I'm about 2-3 degrees off contact with the piston on both intake and exhaust cams though I suppose that's more driven by lift than overlap.

I tried a few calculators to get overlap. If I use the 0.05" durations I get around 62 degrees separation. Advertised duration is 120 degrees.
Not sure if that helps!

psi wise, I would think somewhere in the 12-14psi range... this will all depend on efficiency of the air intake, exhaust etc to reach the power goals.

In terms of radiator / IC setup I have no issues changing it, building custom ducting etc. I'll see if I can find some more info on those other builds.

I think you'll overheat unless you do something else- cut the hood, bigger rad etc.

My car never overheated in the California desert (running NA, but way less power than you though) and as soon as I installed the Rotrex it would overheat in a few laps.

After sorting some belt issues and the cooling problems I've been extremely happy with my Rotrex.

Your duration isn't far off from mine. However, you must also have a lot of lift if you're only 2-3* from piston to valve interference. I'm about 12* from interference.

My opinion would be you either need to put new pistons in it or run race gas/e85. With no range to play around with cam positioning, I think you'll end up de-tuning and it isn't gonna run hard.

FIFY

Saw that one coming :giggle:

right right I conf00z those two lol

Sent you a PM regarding my big pile of Rotrex parts.

Sorry, can't send pms to you yet because my post count is too low. Can you send me your email via a pm and then I can contact you?

Strange you cant even reply to a pm that's been sent to you.

I think the lift is around 10.5mm though I'd have to check.

Problem with E85 is one bad batch and your in strife with too much compression. So if I'm buying E85 from a can, may as well stick to unleaded and run 110 or higher race fuel.

I think the only option for me is to put in lower compression pistons. No point battling compression expecially when I don't know enough of the tuning side. Maybe I could run a larger bore whilst I'm at it for a few more ccs.

The "deviate" 949 rotrex car was running 10.5 to 1 pistons. 11 to 1 should be doable with your much better fuel access. Dyno'ed right at 300hp with a c30-74.

On 93 octane?

Crap. No, that's e85.