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Look at all that power you are losing running a restrictor instead of a wastegate. Shame.
Don't think the horses are any bigger, we just obviously use a different measuring method here is Oz..
Yes, there is a fair chunk of hp/torque I'm giving away, but given I cant weld to save my life, and plumbing in a wastegate & controlling it opened up a few extra problems to solve, the biggest of which was lack of time to get it running for my next event, the super easy option of a simple (virtually no cost) drop in restrictor ring was too juicy to resist.
I've still to get it tuned properly which will pull back some of that under the curve shortfall, but for now I can live with the knowledge its not as optimal as it could be..
As an engineer, I rely heavily on standards, the BS that gets fiddled with by dyno operators blows my mind. It is either a unit of measure or it isn't. You think the difference between US/AU/EU is bad, local operators use a "correction" factor of 21-25% to pay their bills.
Understandable on the opting for the easier route, and now you have a pretty big easy-button when the need-more-power-monster arrives, which he always does. That TQ loss looks like it is right in the money spot for a track oriented application.
Edit: don't worry too much about controlling it when (snicker) you decide to go with a wastegate. It will be easy, probably won't even need to go closed loop. It will be way easier than a turbo.
Stuck the car on a proper dyno this week. It was a hot day, temp was 32oC (90F) which wasn't ideal, but not a show stopper.. It made 239/181 (unrestricted) at 8psi on e85 which I'm very happy with given the soft timing/fat fuel tune. Run was done in 5th (1:1 in 6speed), which is 25kmh/1000rpm. peaked at 177kmh = soft cut at 7100rpm.
Below is the dyno readout. Note Australian chassis dynos read on average about 12% lower than US ones, so I've factored that into above figure. (239whp -12% = 213whp/159kw)
What have you done to your NB2 and what power does it make at that 13psi?
and more importantly what pulley ratio do you have?
03 VVT Engine, MS3 PNP Pro, 640cc injectors, skunk 2 intake manifold and throttle body, racing beat header, 2.25 magnaflow cat, yonaka 2.5 catback, rotrex c30-84 75mm pulley. I think my HP was logged somewhere around 250ish to 260ish. I don't remember specific numbers.
Your specs are similar to me other than mine is non VVT NB1 but slightly bigger cams than std, 11.0:1 and e85.
I am running on a custom pulley which works out about 83mm which would mean lower psi than yours. though not 50% lower....
Last edited by rascal; 02-19-2021 at 09:59 PM.
Reason: corrected mm
Your specs are similar to me other than mine is non VVT NB1 but slightly bigger cams than std, 11.0:1 and e85.
I am running on a custom pulley which works out about 83mm which would mean lower psi than yours. though not 50% lower....
If you are sticking to a stock revlimit or around 7200 rpm limit, why not run the blower with a 75mm pulley to get the charger to just under rev limit when engine is at rev limit?
If you are sticking to a stock revlimit or around 7200 rpm limit, why not run the blower with a 75mm pulley to get the charger to just under rev limit when engine is at rev limit?
Cos I'm not interested in chasing power. I run in a power limited class (185whp) so even the 240 it makes now is way more than I need..
I'll be running an inlet restrictor for 95% of the time, so gearing it up to make more power only to choke it down with a restrictor isn't much point...
The reason I chose a rotrex in the first place is because it is the easy button for extra power/torque.
I only needed 40-50hp more than my nat asp motor was making, but that meant bigger cams, port work and running a higher rev limit to get there, all which shortens the lifespan of the motor.
This way I get to the power cap I needed, get way more torque than the n/a was going to give me, and it will (hopefully) last a long time, cos its not getting revved to the moon all day long...
And on the one event a year I do that isnt limited, I can still just pull the restrictor and run it unleashed, and 240whp is plenty in a 1000kg car..
I am not 100% sure what your particular use case is and if your power cap is an average over rev points or a peak cap. But, i'd be curious to know if you can try using a much smaller intake tract pre rotrex to limit the air coming in at the top end. Use a smaller pulley and reduce some timing on the top end. This would give you a fatter mid range since it will have more boost and you can play with timing and restriction for top end to get top end limited to 185hp.
The inlet restrictor I am using does exactly that, in that it starts limiting the air above 4k, and essentially flat lines the power curve from about 5500. So I just sized it to make the figure I needed. Job done.
No doubt I could get a bigger & better mid range by spinning the blower faster, and capping it from a lower point. Using a wastegate on the inlet manifold and an ebc to bleed off the extra air would work perfectly to mould the curve to whatever I wanted.(185whp over a 4000rpm rev range)
Though I am only doing club racing, not state or national level stuff, so the sheep stations aren't at risk, therefore the easy option of just fitting an inlet restrictor works fine for me.
Also on the odd occasion when I run unleashed, the 180ft lbs I get from the 83mm pulley isn't going to be troubling the driveline at all, whereas spinning it faster would put me closer to the driveline limits, potentially reducing its working life.
I'd rather be driving (at a few tenths slower each lap) rather than replacing stuff I've worn out....
It made 239/181 (unrestricted) at 8psi on e85 which I'm very happy with given the soft timing/fat fuel tune.
Due to having the engine out atm, and the rotrex loose I decided to measure a few things, I've just realised why mine only makes 8psi at 7k with a 145/90 setup (roughly equiv to stock crank pulley with a 80mm rotrex pulley).
I ordered a 90mm rotrex pulley to go with the 145 crank overlay the vendor provides, and it seems that they provided a 105mm pulley instead.
So 145/105 is roughly equiv to stock pulley of 130 with a 95mm pulley...
Pah, strike 3 for this particular vendor. I've now ordered a TDR mounting bracket and pulley.. (which I should have done all along!)
Cos I'm not interested in chasing power. I run in a power limited class (185whp) so even the 240 it makes now is way more than I need..
I'll be running an inlet restrictor for 95% of the time, so gearing it up to make more power only to choke it down with a restrictor isn't much point...
The reason I chose a rotrex in the first place is because it is the easy button for extra power/torque.
I only needed 40-50hp more than my nat asp motor was making, but that meant bigger cams, port work and running a higher rev limit to get there, all which shortens the lifespan of the motor.
This way I get to the power cap I needed, get way more torque than the n/a was going to give me, and it will (hopefully) last a long time, cos its not getting revved to the moon all day long...
And on the one event a year I do that isnt limited, I can still just pull the restrictor and run it unleashed, and 240whp is plenty in a 1000kg car..
VERY interested in how this is all working out for you. I too am in a power restricted class. At 2600lbs (lots of ballast) I can run 189WHP and decided the rotrex was the way to go for track reliability and budget. Like you, I feel the WG method of bleeding boost is adding a layer of mechanical complication I don't want to deal with on the track. So that leaves running a restrictor, sizing up the pulley, or running a combo of both. I'd love to hear what you have settled on and why. Does sizing up the pulley do essentially the same thing as a restrictor, or does one method (or combo for that matter) give a flatter power curve in the midrange?
VERY interested in how this is all working out for you. I too am in a power restricted class. At 2600lbs (lots of ballast) I can run 189WHP and decided the rotrex was the way to go for track reliability and budget. Like you, I feel the WG method of bleeding boost is adding a layer of mechanical complication I don't want to deal with on the track. So that leaves running a restrictor, sizing up the pulley, or running a combo of both. I'd love to hear what you have settled on and why. Does sizing up the pulley do essentially the same thing as a restrictor, or does one method (or combo for that matter) give a flatter power curve in the midrange?
Thanks for any insights!
it’s working very nicely.
a simple restrictor deals with the power just as I wanted.
neither method would give a flat midrange.
A larger blower pulley just reduces power everywhere. Weaker bottom, mid and top end
The restrictor just chokes it up top, so bottom end and mid range is similar to without a restrictor but top end plateaus off considerably.
so just size your restrictor according to the power cap you want.
My restricter is just a simple ring cut out of 10mm acrylic sheet stuffed into the intake pipe. 75mm OD, 43mm ID. It begins to affect output from about 4000.
no doubt you could make that a little higher if you made a proper radiused in/out restrictor, but for me a ring worked perfectly, and my car is almost never below 5200 anyway..
unrestricted it makes 8psi at redline in a linear fashion . = 240hp
restricted it makes 4psi linearly up to about 4000 and then just flatlines. = 177hp
it’s working very nicely.
a simple restrictor deals with the power just as I wanted.
neither method would give a flat midrange.
A larger blower pulley just reduces power everywhere. Weaker bottom, mid and top end
The restrictor just chokes it up top, so bottom end and mid range is similar to without a restrictor but top end plateaus off considerably.
so just size your restrictor according to the power cap you want.
My restricter is just a simple ring cut out of 10mm acrylic sheet stuffed into the intake pipe. 75mm OD, 43mm ID. It begins to affect output from about 4000.
no doubt you could make that a little higher if you made a proper radiused in/out restrictor, but for me a ring worked perfectly, and my car is almost never below 5200 anyway..
unrestricted it makes 8psi at redline in a linear fashion . = 240hp
restricted it makes 4psi linearly up to about 4000 and then just flatlines. = 177hp
YMMV
Thanks for the info! Few more questions if I may:
-How far away is your restrictor from the inlet of the rotrex?
-What pulley setup are you using? Are you still 145/105 to hit those numbers?
-What do you mean properly radiused? Like something that has a gradual reduction from 75mm to 43mm opposed to just a plate with a 43mm hole in it?
-What negatives do you foresee if you went with a small SC pulley for getting more power in the low-mid range and shrinking down the size of the restrictor hole to make your HP cap? Can the restrictor be too small?
01-03-2021, 07:55 PM
Rotrex'd NB1
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