Rotrex Supercharger & Engine Setup

[redequity]

I'm been having more than a few late nights with my eyes glued to this forum, so I'm aware that there are a lot of you Hayabusa gurus out there . I fabricated a Hayabusa powered off-road car and nearly worked out most of the chassis bugs and am now ready to move on to supercharging the engine... I'm more of a fabricator than a engine guy, but I am almost finished reading the book "Supercharged" and now have a little bit of book knowledge. I really could use some help setting up my system. Can any of you comment (e.g. revise, advise, clarify , etc) about my scenario? lease:Am I missing anything important? I just got a great deal on a Rotrex 38-81. I am going to build a pulley shaft and supercharger assembly off the generator rotor basket/shaft. Like many, I am on somewhat of a budget so unfortunately, price is an object. I spoke with Richard over at TTS performance who was a big help. I did not want to eat up to much of his time, so I am still a little unsure in areas. A major thank you in advance for any amount of information large or small. At this point I'm looking at the below scenario:

Oh yeah, what I'm scratching my head over now the most is drive pulley size or pulley ratio (currently have 100mm on SC).

Current Specifications-Car weight: 1,300 lb
-Fuel Octane: 91 Absolute Max
-Current motor: Stock Hayabusa

Changes-Supercharger, SC: Rotrex 38-81
-Intercooler as large as needed
- Horsepower limits Low/High: 290-340
-9:1 compression ratio
-18 lbs boost

Engine Modifications-JE Turbo Pistons
-Cylinder bore Spacer 80 thousandths
-Austrian Built H-Beam conrods sold on Ebay
-APE cylinder studs and spacers
-Richard advised against Crankcase studs and nuts:
- Cometic head gasket torqued at 65 lbs:
-APE Clutch Springs
-Adjustable Cam sprockets

Fuel and computer-Stock ECU & ECU Editor retard timing 10-20 degree at top end (Richard stated to start at 16 degrees)
-Power commander III USB (which I already have)
-Siemens 650cc injectors
-Ignition Amplifier
-Disable map sensor and utilize throttle position sensor
-Rising Rate Fuel Pressure Regulator with needle valve
-Fuel Pump max pressure 60 lbs or less

Thanks Again! Danny

 

[ogre]

is it really necessary to disable the map sensor?

 

[ogre]

oh, and that's a bad ass lil sand buggy

 

[redequity]

Thanks for the complement and good question! Not sure, so I'll do further research to get more opinions as to whether or not the map sensor should be disabled and post the results..

 

[ogre]

i know the second gen ecu can run boost referenced fueling, i don't know how much of that program could be ported to the first gen.

 

[ROTREXPOWER]

As the boost comes up linearly on the supercharger a Map sensor is not really required. Just run off throttle position and tps. The stock map sensor only gets overloaded and caused intermittent spikes at the top end of the rev range. With Gen 2 you can run the |Ecu ed and a 3 bar map sensor I believe. Its another way to go on Gen 2 but not 1. The power is so smooth on gen 1 without the map sensor and with this off road application your not worried about the MIL light coming on (engine management light). 18lb of boost you will need bigger than 650cc injectors. But as you are not using the boost properly (not making much power from it as you have the ignition backed right out) it may be worth just welding in a pop off valve and setting it to blow off excess boost at the top end. I have a simple device I can sell you. That way the big blower will give you the low and mid boost with out over boosting top end. I will be doing this on my big build, just to try with a stock engine. I will post results in the next few weeks.

 

[redequity]

Thanks for the great information! So yeah, I'm interested in your devise. It makes sense.. Please do keep me posted as to how your build goes. Can you give a suggestion as to what size injectors and drive pulley?

 

[ROTREXPOWER]

750cc plus but it really depends on how hard you push the blower, you don't need 18psi for the power you want, so slow the blower down a bit, say a 1:1 ratio, I can't give pulley size as I don't know what crank pulley you have.

 

[redequity]

I'm actually kind of open to the hp that I go for. I'm thinking 290hp might be low for the 38-81 Rotrex that I alredy have (the only thing I have at this point). My biggest worry is the motor still being reliable for the desert and being able to run 91 oct fuel. From what I understand, the engine should be fully strengthened, including tranny, in order to handle hp as low as 290?? I'm hoping to come up with a complete thought out custom kit so I'm not buying multiple sizes of the same part. E.g. Pulleys, injectors etc. By the way, I have a 100mm pulley on the Rotrex and am trying to figure out what size crank pulley to run... 1:1? If I go for a full engine rebuild, what hp do you think I should go for and still be able to run pump gas and still be reliable in a harsh environment (desert)?? That might be a loaded question? Thanks a million for every bit of information you have given me!!!

 

[Commuta_Busa]

I wouldn't focus so much on the HP level but the actual limits running pump gas. You can build the engine/trans/clutch to handle way more power than pump gas will ever give you. Look at the compressor map for your supercharger to determine how fast to spin it and how much air is going to be pushed and compressed through it. Adjust your compression to keep everything in the sweet spot.

The only downside to a build that is focused on max boost is that off boost performance will be down.

 

[ROTREXPOWER]

I agree. Pump gas is your problem, why must it be 91 oct?

 

[redequity]

I burn a lot of gas in the desert. Running race gas would throw the cars operating expense out of my budget. The convenience of getting high octane gas it is a pain as well.... Cost benefit just isn't good. The expense of the engine modifications will be a hard hit but seems well worth it due to the increased reliability. Maybe I can get a few more points of octane with octane booster if 91 is just too low? So it appears the million dollar question is what set up will allow me to run as much boost as possible on pump gas (91 is the highest commonly sold gas in San Diego) using the Rotrex 38-81. I've been working on the math (using math formulas in the book "Supercharged") to be able to read the compressor map but I think I'm leaving out a few variables in order to determine correct drive pulley. Hopefully over time, I'll get it right .. . Thanks again all of you for the incredibly useful information!!!!

 

[ROTREXPOWER]

The answer is to run E85 which I understand is at quite a few stations in the US?

 

[redequity]

Wow, what a great idea. I'll look into the E85. Thanks!!

 

[ogre]

you'll need an alcohol compatible fuel pump, tank, lines, and injectors. make sure the seals are ok for alcohol, it'll dry out normal seals and cause standard plastics to crack in time.

 

[ROTREXPOWER]

My in tank fuel pump is E85 compatable, alloy tank would need the occassional was through with gas, no problem there, most modern injectors will take E85. It's not a biggy.

 

[ogre]

what about o-rings and seals and such?

 

[Commuta_Busa]

+1, check all o-rings, dowty seals, anything that's of some kind of rubber that may come in contact with the fuel. Anything aluminum should be anodized or cleaned every so often.

what about o-rings and seals and such?

 

[ROTREXPOWER]

Everything should be checked after first use, but injector seals i've seen are generally tolerant.

 

[redequity]

Good points being made.. I'm looking into the feasibility of converting to E85 now. Since I have to buy all new injectors, FMU, fuel lines etc for the new supercharger setup that should not be too bad. I'm worried about using my aluminum fuel tank.. Lots of bad stories throughout internet regarding using them with Ethanol. Cleaning my tank ever so often is a real bummer. Currently looking into possibly fitting a E85 resistant tank (which could end up being a lot of extra work) or some type of epoxy like lining for my existing aluminum tank.