TrackHack

Hi all,

Apologies for the long post (and just my 2nd!) but please bear with me, as I need to explain myself a bit...

I have a NB1 which is used only for circuit racing. No road use. Trailered to each event.

Currently runs fully rebuilt naturally aspirated motor, with manley rods, 11.0:1 forged pistons, std rebuilt head. Small set of mild cams. I/H/E, e420c ECU.
Makes about 145whp and 110 torques (due to current class regs in local race series)

Plans are to run it in the next class up which has a 185whp power limit.
I know I could just throw in some bigger cams, port the head, ITBs, etc and get to the 185whp pretty easy but have several reasons not to.
1) other competitors have NCs & ND2s etc which whilst also making the same (capped) 185whp have 150+ lb fts. I'll never be able to match that torque with a little BP4W naturally aspirated so will always be at a disadvantage.
2) getting a nat asp up there, usually means running higher revs which means shorter life span, which I'd prefer to avoid.
3) headwork is expensive, and whilst as a once off I'm ok with that, if anything nasty goes wrong then its a new motor and have to spend all that money again.

so, my plan is to go forced induction, as an equalizer and specifically a Rotrex. (Yes I know this is miataturbo and I understand a turbo will be much better torque, new ecus can map the torque/power curve to whatever I want, blah, blah) but i don't care. I have absolutely zero interest in a turbo. If someone gave me a fully sorted trackspeed EFR kit for free, I'd still prefer to run the Rotrex. So just to be clear. I do not want a turbo. Full stop.
And also why I posted in the Superchargers section. Cos hopefully my flame suit can survive the burns I'll prob still get in this section..

So a Rotrex. Solves all 3 of my concerns up above.(plenty of torques to keep with with 2.0s, Don't need to rev it to the moon to make power, meaning longer life. It if goes boom, a $200 head from the junkyard and I'm back in business)
Plan is an intercooled C30-84 TDR kit with an 85mm pulley to keep power down. And given it will still most likely make over what I need I'll be pulling timing out up top to reduce the peak number down to the reqd 185.

Note that I also have zero interest in EVER going past the 185 cap. Like never, ever.. The car will only be used for this series, and exceeding the hp limit puts me into a 400hp, carbon fibre, money pit of a class that doesnt interest me, so the 'once you taste it you want more' phenomenon wont apply here. I'm also fully aware that the faster you go the quicker things wear out (tyres, brakes, wheel bearings, etc,etc) so another reason why I wont ever be pushing for more powa...

Now as stated my engine has 11.0:1 pistons. I'd like to avoid e85 if possible (extra hassles I don't really want) so want to run on (oz) 98 which I believe is similar to your 93.
Given a 185whp 11:1 naturally aspirated car can survive fine with a decent tune on 93(98) then am I being realistic that a very mild, detuned, intercooled Rotrex build could also survive on 93?

I imagine I will be pulling a fair bit of timing out on the top end to stay under the limit, and my thinking is that this will be my saviour, allowing me to run on 93.

Obviously the proof will be in the pudding, but I dont want to venture down this costly path if the overwhelming consensus is that I'll be wasting my time, and heading for disaster...

thoughts?

Brad..

cpierr03

Only way you're avoiding E85 is with some sort of AI IMHO, otherwise you're playing it fast and loose for a track car.

That's a lot of air being shoved into a tiny space with that CR.

andym

I wonder if you would have better results running a larger blower like a c30-94 and then running a restrictor on the blower to limit the top end power while benefiting from having a more powerful mid range.
I think 11:1 on 93 is possible but it would be beyond the mean best torque threshold so you would need to retard timing.

TrackHack

Mid range isn't a huge deal for me. The car doesn't see under 4700rpm at even the slowest corner of all the tracks we go to, and is usually 5200 or better at every other one, so not sure the bigger blower gains me anything, especially since I've no need for extra horsies.. I think I'd just end up restricting it earlier before it even got to the point of giving me anything over the -84? Happy to be corrected given the -94 is a no cost option at this point..
Most of the C30-74 & -84 1.8 dyno charts I've looked at seem to have >150ft/lbs and > 150hp (both > 75% of max) by 4700 so don't feel this is that detrimental..


I think I'll be retarding a fair chunk of timing as it is to stay under the power cap (given I'll prob be 20-30hp over it ) so might be dropping 9 degrees up top?? (rough assumption 3 deg ~ 10hp??) anyway which I'm hoping is enough retard to remove the risk.


Your restrictor comment prompts another question. Given inlet restrictors tend to cause it to run out of breath up top (which is what I am trying to do anyway) is a restrictor a better way to hold it back, or do they introduce more heat which I prob don't want?

SpartanSV

If you have to pull 9 degrees I think you'll be mid single digits for timing, and I'm pretty sure that will cause extremely high EGT's.

TrackHack

hmm, ok. Good to know..thanks..

Is an inlet restrictor a better option???

Efini~FC3S

iTrader: (4)

Yea...as mentioned before pulling that much timing on a forced induction high compression engine is going to create extremely high egts which will be bad in all sorts of ways.

Honestly, I think your best bet is to swap the pistons to 9:1 and go from there

TrackHack

Yeah, I get this is the logical solution, but I won’t be pulling the motor apart again anytime soon (well unless something really bad happens)

if the high comp isn’t doable on 93 then I’ll just suck it up and run e85 full time. I was just hoping to not have to.

thanks all for the responses. Looks like I’ll just have to try it and see, and have some fallback strategies in the toolbox. (Tune, restrictors, e85, block of wood under pedal to limit full throttle...)

andyfloyd

Honestly I dont think the rotrex is the best tool for what you want. As you know its a centrifugal supercharger so it makes boost limearly with rpm. Problem is is really doesnt come on until the mid range and top end only. If you want more tq you could just throw in a m45 and it will also easily stay under 185whp with maybe 6 psi and the boost will be there immediately.

TrackHack

Actually its exactly what I want, given its a track only car that spends 98% of its life between 5500rpm & 7500rpm so only ever in very upper mid range - top end.
So a m45 or MP62 etc wouldn't be of any benefit for me as I couldn't care less about sub 4000rpm grunt,where these typically have it all over a centrifugal.

Also it's kinder to the transmission as doesn't make massive (any!) torque down low.
And finally I hate the incessant whine from those kind of superchargers as imho, they sound like you are a gilmer belt drive tragic from the 80s, so a rotrex ticks all the boxes for me..

sixshooter

iTrader: (12)

I disagree. The Rotrex is much better for a track only car. It's far more efficient than a Roots blower and makes its power (and torque) in the higher RPM range where he intends to operate it. And it doesn't create as much waste heat due to its greater efficiency.

andyfloyd

But efficiency is thrown out the window when you try to keep it at 185whp. Retarding the ignition timing a bunch to keep power down is going to drive up egt like crazy.

Ken Brock

Talk to the guys at TDR - William and Gary can put together a kit for your specifications. I just installed their kit on my 1.6. I got 198 hp but used a Megasquirt. With the Fuel card, it might be right at your goal

concealer404

iTrader: (3)

I don't think you can make that little power with any modicum of safety with your existing motor.


However, everyone who has said any valid reasons why it's not a great idea has been met with "But i want a Rotrex and nothing else."

So, good luck. Have fun. Next time preface your thread with "tell me i'm pretty" or "positive feedback only" or "I'd like to hear my own idea parroted back at me."

TrackHack

Huh?

Actually, my thread title was (reworded) "can I get only 185whp on A ROTREX using 11.0:1". It wasnt 'whats the best F/I for my car to get 185" so forgive me for clarifying that to the fellow who suggested a M45 as a valid option.

So, someone said maybe but will need to pull timing, I replied I was planning to, and others chimed in to say thats not a good idea since EGTs will skyrocket, so I took that on board, and asked about a restrictor instead.

Then another suggested new pistons, but with $$$ just spent building the motor, I'd rather not throw that out the window.
And then I thanked those that replied and said it gave me some directions to try.
Didn't see any parrots floating around there?

I have spoken to Gary at TDR and will be getting their kit, to be fitted once this years racing season is over, In early December. (Just doing my research ahead of time..) I did ask Gary a heap of questions, and he gave me some solutions which I was just attempting to confirm here since there is a lot of guys running rotrexes on this site, and real world customer experience is usually better to follow than a vendor pushing their wares..

Anyway I'll report back once its fitted, and tuned, and what I had to do/issues I ran into keeping it under the cap. (or whether I had no choice but to run it at 5000hp)

I'll no doubt throw up some more questions between now and then, but I'll make sure I put my lipstick on and get my hair done first

concealer404

iTrader: (3)

The real takeaway is that no, you probably can't get only 185whp from your motor safely.

I say this as someone who thinks that Rotrex is the best option for force-feeding a BP on the market today.

TrackHack

Yeah, its looking like its not going to be as easy as I'd hoped..
Previously I just pulled some timing& fuel up top to successfully drop 10hp on my nat asp motor to fit into the current class. And gave me a nice flat curve from 5800 to 7000.

But dropping up to 40 hp (most dynos seems to be ~225hp) using this approach doesn't seem to be as doable. bummer.

I'm kind of committed to this course of action, (well, I don't really have a plan B) so I'll probably have to use a multitude of options to bleed off the power.
A small bit of tuning, maybe an inlet restrictor, a lower redline, maybe even running the C30-74 instead of the C30-84...

Anyway, thanks everyone for the input, it is appreciated..

Ted75zcar

iTrader: (2)

Why not run an EWG valve across the SC and regulate the manifold pressure using EBC. This is obviously throwing power away, but so are the other methods you are considering and is significantly better for your exhaust valves. You could presumably tune this to provide your 185hp across the entire usable rpm range (dynamically controlled torque, constant hp).

I use one to bypass the roots in my compound setup and it works very well.

TrackHack

I had wondered about this option.

Most I can read says that this option is overheating the rotrex unnecessarily, as its compressing(heating) a heap of air that you then bleed off anyway, and an inlet restrictor is a better option to achieve the same thing, as the rotrex is only compressing the air its using. But then others say that restricting the intake will heat up the air anyway which isn't ideal either, so cant seem to find a definitive answer either way.

Also an inlet restrictor apparently will drop the psi across the entire rev range (unless its designed properly to only limit air at max velocity?) so EWG style sounds a better approach...

???? I

TrackHack

yes, throwing power away is unfortunately what I need to do...

Could you expand on the "is significantly better for your exhaust valves" comment please. (Another chance for me to learn something..)