my Scion FRS has 2.0L Subaru engine Rotrex supercharger

[turbosmart44]

Hey Guys, So I am building a new engine for my FRS . I wanting to try and figure out what kind of WHp it would make with a new larger compressor ?? I don’t know how to read compressor maps very well!!
I made 355 rear whp @13psi at 7450rpm with the C-30-94 supercharger and it’s maxed out with small pulley any smaller and it’s a heat pump . The Company has a kit so I can upgrade to a C-38-81 it flows more cfm and will make 17psi at 7450 rpm on my engine so an increase 4psi! My new engine will also be a 2140cc instead of 1999cc/2.0L . Cause of a stroker crank!
If I attached a picture of the old compressor map that made 355whp@13psi and the bigger compressor map below that makes 17 psi. Can any one tell me a estimate around how much power the bigger blower will make with and without the extra140 CC stroker motor ??Thanks and happy holidays

 

[AlexLTDLX]

Sorry for the delayed reply. I can tell you from experience simply increasing displacement without increasing induction flow will net no improvement in horsepower; assuming you're induction limited (most engines are). You'll see an improvement in low end torque, and your hp RPM peak will go down a bit. Here's what happened when I tried it: back when I was playing around with a Jaguar/Eaton M112 supercharger, I first had it on a 306 ci small block Ford. The blower made enough power to split the block in half - the car ran 10.5x @ 127 mph (oddly, pretty close to where we currently are with the electric turbo). Since I had exceeded to power handling capabilities of the factory blocks, I decided to step up to an aftermarket block - specifically, a Dart Iron Eagle Sportsman block; which allowed for more bore and stroke. So I went from a 306 cubic inch engine to a 363. I made no changes to the induction. I went back to the track and ran... wait for it... a 10.5x @ 127 mph. The only difference is instead of shifting at around 6,250 rpm, the car was now nosing over just past 5,000 rpm. I know that's probably not what you want to hear, but it makes sense if you think about it.

As for the blowers... I'm going to make a bunch of guesses based on experience and math. It looks like you're currently making about 420 crank hp. Your blower is currently flowing about .31 kg/s; and the impeller should be spinning around 85,000-89,000 rpm (calculate the pulley ratio and the internal step up and tell me how close I am - I'd like to know). You're definitely not in what I would call the "heat pump" range - I've been there (the Whipple was so far off the map I had to guess) - you're actually in a pretty good spot, but you are closer to choke than surge. Looks to me like you're inside the 65% efficiency island (for comparision, my Whipple was in the 50% region).

You can get to 17 psi with either blower, and I don't think you'll see a huge difference in power. What you will see is more low-end torque from the smaller blower - since centrifugals need rpm to make boost, the smaller blower will see more rpm sooner. There is a point below which centrifugal efficiency falls off a cliff; the smaller blower will pass that point sooner in the rpm band, because it has to be pullied more aggressively; thus more torque.

That said, looking at your dyno plots, the current blower is performing exceptionally well - you've basically doubling your power on less than twice atmospheric pressure. It looks like the boosted pulls were done in 5th gear (vs. 4th to the N/A pulls); so even though there's supposed to no difference, there usually is by a few numbers. Even so, your current blower is performing well - it's about 30 rwhp higher than I'd expect it to be. If you were to pulley it up to 17 psi, you'd see about 400-410 rwhp (about 490 fwhp). That would put you about 95,000 impeller rpm and right on the edge of the map (but still inside the 60% efficiency island). Remember, your car spends very little time at or above peak hp. You'll have a fatter torque curve.

If it was me, I'd do the stroker and have the induction mildly ported (head, intake, etc). You'll be close to maxxing out the blower, but I believe the smaller blower will actually out perform the bigger one at this power level. If you want to push beyond that, then I'd consider the larger blower; but not now. With the bigger blower, you'd only gain 10% efficiency, but that will only really show up as 10% lower intake charge temps - so if those aren't an issue (i.e. you have adequate charge cooling), then there's not much peak gain to be had, and you'll be giving up power lower in the rpm band. You definitely need charge cooling at these boost pressure BTW; unless you're running E85 or something similar.

That's my two cents, hope it helps.

 

[turbosmart44]

Yeah thanks for the update and I appreciate your thoughts!!
so I’m running E85 and my stock compression is 12:5.1 with between 24-27 degrees of timing. Between the E85 and the high compression is why my power levels are higher than expected. I have both port and Direct injection . In the dyno I only rev the car to 7450 but later on I raised the rev limiter to 8000 and put on a inch taller tire in the rear so I could pass the finish line in 4th gear instead of nosing over 2-3 car length cause of hitting the rev limiter. I went from 105 mph traps to 112 mph and finally got into the 12s!! But after raising the rev limiter that’s when I would start to see Intake temps at 180-190 3 rd and fourth gear is when it had more time and load an would happen. Before raising the rev limiter I was only hitting 115degrees at the en of the track. If I remember correctly at 8000 rpm the compressor speed was 101,550 rpm. That’s when rotrex recommended going to the bigger blower since I was at The chokepoint of the smaller blower.

I am going to do some porting work and increase valve size by 1 mm on the intake not too sure if I’m going to change the cams but I may since stock cam Shaft really drop off after 7500 rpm . Another thing is my compression is going to be dropped down to 11:7.1 so I will lose some thermal efficiency but at the same time my blower won’t have to work as hard between the compression drop and stroker crank . But I’m thinking that with the extra cc and lower compression I may have to bump up to 17 pounds just to get back to we’re I was !! I may just end up going with the turbo but I will see what the supercharger does before I switch set ups because I am wanting to make around 460-500whp horsepower and I don’t think the centrifugal supercharger will get me there only drawback is I live in California and the supercharger kit is carb legal turbo kit is not so do I want to go fast or do I want to pass smog LOL. My hope is to run 10.80-11.50 with a 2800 pound car!!

I will attached A document of my stock cams lift and duration and some options that I have. Would be awesome to get your thoughts on what cams will work best for me to make peak power all the way to 8000 RPM instead of 7500?? I believe that the HKS cams are designed mainly to use with a Centrifugal supercharger and extract 10 to 12 more horsepower at the same RPM as stock cams. the other ones are from piper cams and I don’t know much about them there’s not much literature out there

 

[AlexLTDLX]

So if you're spinning 101,550 impeller rpm at 8,000 engine rpm, it means you should be around 93,000 impeller rpm at your hp peak - but the map shows about 5,000 impeller rpm less (more or less in the "meat" of my guess). I'd be very surprised if you you're not seeing belt slip - in my experience all blowers have some degree of slip, and it shows up as black dust in the engine bay (sometimes it's hard to spot if there's not much - and you're not seeing much.) If you're not running a charge cooler (I'm assuming you're not), your IATs are likely the result of sensor lag. They are much higher in reality. When you compress a gas, there's a calculatable rise in temp. Try this on-line calculator:

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racingcalcs.com

Even with some slip, you're approaching the max rated rpm of the small blower anyway - something I hadn't take into account in the previous reply. Personally, that doesn't bother me as I haven't owned a supercharger I haven't overspun. My Eaton M90 had it the worst - rated to 11,000 rotor rpm, I was winging it close to 20,000 rpm at the shift.

Even with E85, you'd gain a lot from an intercooler - the charge would be denser, boost would go down, power would go up. Plus your tuning winodw would be larger. An A/W intercooler can't be beat, esp. for dragstrip use. The intercooler in a dragstrip environment functions more like a heat sink - there's not enough time to reach thermal equilibrium. Heck, try what we used to do back in the day on Fox body Mustangs (my LTD is a Fox body, too - I've done the same thing). Before a pass, put a bag of ice on the intake to get it as cold as possible. Then make a hit. Your IATs will go down and your car will be faster. Read the short paragraph after the list of stuff in the first post of this thread. Bob Cosby was legendary in the early years for getting those cars to run fast (for the time) with little to no mods:

https://www.stangnet.com/mustang-forums/threads/bob-cosbys-12-second-recipe.853108/

The A/W intercooler in my car with the Whipple would melt 10-15 lbs of ice in a single pass! Listen to the audio in this video - before the pass you can hear a ton of ice knocking around inside the water tank (it was my center console/arm rest - so it's right under the camera); at the end of the pass you only hear a few pieces left. And that's a 3 gallon tank that I'd literally pack full of ice, with just enough water to circulate (I'd turn it on before the burnout):

BTW, that digital meter next to my soda that goes flying when the car launches is the water temperature in the A/W system. You can see it's at 38.7 degrees F just before launch.

Keep in mind, I'm a V8 guy, so the next few points are from that perspective (the previous ones I feel are universal). I'm surprised you're not timing limited, even on E85, esp given your compression; DI and all not withstanding. For the cams, I'm afraid I'm not going to be much help. Your engine is a completely different beast than what I'm familiar with, and you're in an RPM range none of my V8s even came close to. And actually, one of the first things I notice is that there's no info given on weather the duration figures are advertised or at .050 lift (both pieces of data help us V8 guys know how "big" a cam will act and how aggressive the lobes are). I know several great cam guys in V8 world, but none the world you're in.

You have some choices to make - and much of it is outside my world of experience. You're already at what I consider higher boost, high RPM and high compression. I'm sure an A/W intercooler would help quite a bit. If you're sensible and not like me (I built my own A/W intercooler, even the core), you can check out https://www.frozenboost.com/ - just go a bit oversized for your goals. It's always better to have a bigger motor, esp. when matched with better breathing. I do know that the bigger blower will cost you some low rpm torque, but that's not all that important in a drag strip scenario.

If you want maximum efficiency, and extreme ease of removal to keep the smog nazis at bay, well - you know what I'm going to suggest, right? An electric turbo powered by a TP Power motor and a Speedmaster P2. I'm putting together just that setup right now to play with it. Just today I ordered a VESC to control it (along with $3,000 worth of MGM controller/LMT motor for my Vortech setup).

 

[turbosmart44]

So I’m running a air to air intercooler. I got my temps mixed up from my data logs from time attack/track day that was 100 degrees during the summer. My drag numbers are at around 80-85 degrees after my burn out and they are between 114-120 at the end of the 1/4 mile on an 80 degree day. On cold days / night runs I’m around 50-60 after burnout and 75-90 degree at the en of the track. I’ll attach my data logs from an 80deg day that was a 12sec run below

 

[cmoalem]

Ice packs work nicely with A/W intercoolers... for drag pulls.

@AlexLTDLX what is your take on this ? is the A/C compressor robbing more power than what you can gain with refrigerating?:

Kincaid Performance Inc.

Run ice cold intercooler temps with our Killer Chiller heat exchanger designed to piggyback the vehicle's AC system.

killerchiller.com

 

[AlexLTDLX]

Turbosmart - the first question that comes to mind is where is your IAT sensor? But it looks like everything is working pretty well.


Cmoalem - there are some OEM applications that use that trick too. Typically, they're not running while the car is at wide open throttle and under full boost. It's a thermal inertia thing. And if I'm not mistaken those killer chillers look a lot like heat exchangers that you'd find in like Volvo trucks and even some boats. Stainless steel is a horrible material for heat transfer. I don't think any a/c system has any hope of keeping up with boosted temps at least based on my experiences with air to water intercoolers. The volume of air is just far too great.

 

[turbosmart44]

It’s in the intake manifold by my 4 bar map sensor. My car is tuned using Mass air density tune. It only uses the MAF sensor during idle and cruise as soon as it’s making boost it uses the map sensor. If I was only 9 psi with a stock pulley the MAF sensor can be used but once above 9 the scaling is no longer accurate.

 

[AlexLTDLX]

That makes sense. I really think you're doing pretty well and you seem to be on top of things. I'd do the stroker first (since you're doing that anyway), and then see how the small blower performs and see if you want to upgrade to the big one (or e-turbo - you know I have to put that in there...)