Twin charged bp

[dueces]

I doubt it. A roots blower is just a fixed ratio air pump. An m62 pushes 1.0 liter/rev. If that 1 liter is of 15 psi, it will compound it, I would rather the turbo so more of the work, because the more you make the blower do, the more power you loose to drive the blower. If you give the turbo a '7 psi' jump start, it will take nothing to finish spooling to 20....

[bhearts]

I doubt it. A roots blower is just a fixed ratio air pump. An m62 pushes 1.0 liter/rev. If that 1 liter is of 15 psi, it will compound it, I would rather the turbo so more of the work, because the more you make the blower do, the more power you loose to drive the blower. If you give the turbo a '7 psi' jump start, it will take nothing to finish spooling to 20....

For you, it'd be like driving your turbo with a 3.8l engine. Half again the displacement

[dueces]

Yes that's the pretty solid theory behind it. So if you wanted to get technical, you would roughly want a turbo sized for a 2.4L, so like a 6262 or 6266 would even be better. They are great turbos for 2.3L and 2.4L 4g63 engines, and would spool just as quick on your 1.6L. Only problem is those turbos like 600+whp, which I'm assuming you won't be shooting for, haha.

[ZephTheChef]

Yes that's the pretty solid theory behind it. So if you wanted to get technical, you would roughly want a turbo sized for a 2.4L, so like a 6262 or 6266 would even be better. They are great turbos for 2.3L and 2.4L 4g63 engines, and would spool just as quick on your 1.6L. Only problem is those turbos like 600+whp, which I'm assuming you won't be shooting for, haha.

Glad to hear some actual firsthand experience. My setup is going to be a lot different from yours in my intended use of the supercharger.

My setup is *running* but I have a massive boost leak at my adapter plate for the larger supercharger, that I need to redo. The new plan is I'm going to swap to the TVS blower while I'm going to the trouble of building the new adapter intercooler. I am going to put the smallest pulley I can find on the thing with the goal of making stupid boost immediately to spool the turbo, and bypassing it as early as possible to take the load off the engine and let the turbo do it's thing. I would think belt slip is less of a concern since I will never be spinning the loaded supercharger past probably 3000rpm or so which results in lower supercharger rpm than even a stock pulley at 5000rpms (granted, my rotors are also considerably longer and heavier than the stock M90). I am predicting 20-23psi on my 3.8L as soon as I snap the throttle. That gives me an effective displacement of something like 10L to spool that turbo, which is a 1000hp or so unit. So theoretically it will have spool characteristics even better than a stock 3000GT VR-4, which make peak torque around 2500-3000rpms. (300hp from 3 liters...but the turbos are really more like 400hp when maxxed out, so for size comparison to my big single, I have more effective displacement compared to turbo size). Essentially, when wide open throttle I should never have less than 20 pounds of boost, and have a theoretical maximum boost of around 80psi in full compound, max effort mode. Of course, that will never happen in the real world cuz I'm not trying to guarantee parts breakage, but I should be able to run an efficient 30psi on the turbo up top without problems.

[ZephTheChef]

I did a fun proof of concept the other night. Flashed in a 1200rpm rev limit so I could hold the throttle wide open at "idle" to confirm that these superchargers do in fact make boost from ANY rpm and don't have to wind up as some people seen to be convinced of. Sure enough, it started blowing a considerable amount of pressurized air out the back of my adapter plate where I suspected my boost leak was. At 1200rpm. Freaking awesome. Can't wait to get the leaks fixed and repeat the same experiment with an accurate map sensor reading and the TVS blower to see how much boost I can make from say 800rpms, lol. Theoretically with a fixed displacement supercharger withba fixed drive gearing to the engine, it should be the same boost from literally any rpm, with minor considerations for rotor leakage at low rpms and different VE at different rpms.

[dueces]

I'm going to try and find a post for you to read.

Do not, I repeat, DO NOT use the supercharger to push most of the air! The supercharger takes more and more power to drive it, and I also would not bypass the blower either. The two units should be used together, I will try to find a good thread by Tony the tiger over on hondatech, or wherever it was. He explains it really well. Give me a few and I'll post it.

[dueces]

Here is the link, read what Tony the tiger posts. He had a 580whp twincharged camry....

http://honda-tech.com/forced-induction-16/twincharging-setups-2861610/

[ZephTheChef]

I'm going to try and find a post for you to read.

Do not, I repeat, DO NOT use the supercharger to push most of the air! The supercharger takes more and more power to drive it, and I also would not bypass the blower either. The two units should be used together, I will try to find a good thread by Tony the tiger over on hondatech, or wherever it was. He explains it really well. Give me a few and I'll post it.

Have seen that post and read it, and many many others. The premise of not bypassing the blower is based on having valve overlap, and thus higher intake pressure than exhaust pressure to help get all the exhaust out of the cylinder...and probably on lack of ability to adequately intercool the supercharged air.

I am not trying to make most of the boost with the supercharger. I am overdriving the shit out of it so that the turbo will spool as early as possible, and the supercharger will be bypassed as early as possible. There is zero valve overlap in my engine, so there is no point in having the supercharger running to get an advantageous intake vs exhaust pressure. The only advantage of running the supercharger is the instant boost response, and low rpm boost I can get out of it. Tony the tiger is absolutely right that trying to run high boost out of the supercharger will not make more power, but that is assuming
1) That you do not have adequate intercooling to cool the extra heat from the supercharger
2) That you will not be bypassing the supercharger thus creating lots of heat and parasitic drag up top
3) That you can take advantage of the pressure differential during valve overlap for better exhaust evacuation and a resulting cooler chamber

None of those things are true on my setup. I am running ice water through intercoolers after both the turbo and the supercharger. I have a stock cam and zero valve overlap. And I will be opening the supercharger bypass once the turbo is spooled (which I predict will be by 2500-3000rpms). With the bypass open, the supercharger will still be digesting all the air...there just is no pressure differential across it thanks to the giant "leak" created by the bypass, so minimal parasitic load (just friction and weight of the rotors) and no temperature rise. Granted, the bypass valve is probably not large enough to recirculate ALL the air, since it's really sized for idle/cruising...but I can deal with a minimal amount of compression/added boost from the supercharger...I just don't want or need 20+ psi all the way to redline.

[ZephTheChef]

My biggest concern now, is actually that my turbo (despite being well bigger than the power level I would actually want to run) is pointlessly small compared to my supercharger, and for my engine. I would be fine spool-wise with that turbo even with no supercharger. After actually plotting the engine demands on the turbo chart, I redline the turbo at 25psi at 6000 rpms. I may need a fancy programmable electronic boost controller so I can start with the boost "all-out" and taper it down to 20-25 towards redline so the turbo doesn't overspeed and disintegrate.

[MiltonHavoc]

Why not a B1 or similar, motorcycle procharger?

[ZephTheChef]

Why not a B1 or similar, motorcycle procharger?

My opinion is that prochargers are the worst of both worlds. Belt-driven parasitic loss, plus most of the lag of a turbo. Do they get the job done? Sure. But they don't eliminate lag like a roots style supercharger, and they aren't as efficient as a turbo because they are still crankshaft driven sitting there robbing horsepower. They also are relatively extremely expensive. M90s can be had all day long for $100 or so. The baby prochargers are like $1,800 just for the unit itself.

[bhearts]

If damkid can have v6 torque, there's no reason we can't do the same with a b6d or bp build

[bhearts]

My big question is, is there a way to mount the alternator in the front of the engine, factory ac location

[ZephTheChef]

So I'll elaborate on the plan a little bit, and some of the reasoning why...because I like to ramble and it was a good maths exercise for me to actually sit down and figure it all out. Feel free to ignore this book of a post unless you're super interested in why I did my setup the way I did. First off, a lot of this is perfect world math and hypothetical scenarios. I'm not so delusional that I don't realize there are countless real world reasons why I would not run this setup this all-out. This is strictly to compare theoretical limits of different setups.

The truly beautiful thing about these roots style superchargers is the "fixed" torque they deliver. They are almost like a torque regulator for your engine. The math on torque from a given engine is mostly only affected by VE and intake density at various RPMs. In a perfect world, RPM has no effect on torque produced, and since a supercharger is geared to the engine and increases in rpm directly proportionally, boost remains relatively constant within any practical rpm range as well, so the only variable is engine VE at varying rpms, and changes in charge temperature as the run progresses which is a non-factor during say a drag race with adequate air/water intercooler capacity. Low end torque is amazing in terms of useable powerband and flexibility with gearing, resulting in much better average torque to the ground.

Take my car for example, I re-did the math on my car to figure out how much torque I might have at launch (to see what gear I can launch in). Assuming zero help from the turbo, At 21psi boost (I will have approximately 1.4x the effective blower displacement as my old setup which made around 15psi) and 85% volumetric efficiency. That gets me 648 lb-ft of torque. It is going to take approximately 122 lb-ft of torque to spin the TVS...that changes with efficiency depending on blower rpm, but I did the math at 58% which I feel is a reasonable assumption. That would leave me with 526 lb-ft of torque going into the transmission, assume a conservative 15% drivetrain loss. Which gives me around 457 lb-ft to actually launch with by overdriving the supercharger to that extreme. Compared to around 200 ft-lbs that a NA 3800 makes. I could launch in 2nd with 26% more effective torque than I could launch in first without a supercharger (and that's not taking into account that the NAs have a higher compression ratio, so a truly comparable engine would make even less without boost). The kicker is, I am not launching at 800rpms, I'm launching at probably the 2500rpm or so stall of my converter, which may allow the turbo to build boost as well. In any case, for this comparison, we are going to assume it does NOT spool any faster than if the engine did not have a supercharger to first illustrate just the added torque from the supercharger.

Let's compare that to a turbo only car with the same engine. I will give it the benefit of the doubt and assume it is equally capable of spooling the same size turbo I have at the same rpm, even without the supercharger's help but figure the average at a starting torque of a naturally aspirated car (which is higher compression, so would be higher actual torque than this car would really make, but since the only turbo 3800 dynos I have been able to locate indicate positive boost starts at 3500rpm and peaks around 4500, I will use stock NA torque numbers of 200 lb-ft to be more fair instead of the turbo dyno numbers of 100 lb-ft (which I assume was just lightly accelerating up to rpm before they punched the throttle on the dyno). I will omit the 500rpms of spoolup time from the average, for the sake of not doing a whole bunch of extra averaging that doesn't affect the end outcome much at all). I also assume torque will be equal between the two setups from peak torque to redline, and that the turbo spools at the same rate so peak torque occurs at 4,000rpm. I calculate average torque output from a stall of 2500rpm to be around 583 lb-ft on the turbo only car. Average on the twincharged car (without even factoring in faster turbo spool) is 721 lb-ft, or 23.6% improvement. If the turbo spools like I am predicting, and I get the bypass tuned properly, that could potentially bump the average up to over 1000 lb-ft depending on where it hits peak boost.

So why not turbo only? Apart from the above reasons, my car is also way left of the surge line of the compressor map on my turbo. Riding that left edge with my engine demand at varying psi (which would not happen in real life because it would spool at a higher rpm, but for the sake of calculating my earliest theoretical spool point without surge it's a valid thing to look at), I could make 5psi at 2000rpms, 8 at 2200, 12 at 2400, 15 at 2600, then it finally gets into the map and hits 28 at 2800, and 34 at 3000, and can pretty well go to the turbo's ceiling of 55psi around 3500rpms. That's a reasonably normal plot for a moderate power (for its displacement) turbo car. However, with a supercharger pushing air through my engine at 21psi in those early rpms it literally puts my engine demand into that compressor map from 1000rpm onward and allows for the turbo to be able hit its peak boost as early as 2200rpm without compressor surge (whether or not it will do this is a different calculation with too much guesswork involved to even bother). It makes it look more like a high boost engine demand line on an OEM turbo setup...the only difference is, the turbo is sized almost 3x that large.

It actually plays out really nicely with the plan to bypass the supercharger, because at 3000rpms, my fuel system will be tapped out in full compound boost and I am sure the belt will be in danger of slipping if not well past that point, so the supercharger bypass will have to open at that point or sooner but with the turbo already at or near max boost by then the 122 ft-lbs of torque I get back to the crank should offset the dip in power I take from opening the bypass for a relatively smooth transition, and the resulting lower engine demand keeps it inside the compressor map a lot longer. So if I were to get an electronic boost controller that I can set by RPM, and taper the boost off to keep it within the compressor map, I should theoretically have roughly the same torque output from full boost til redline.

So why not just run a supercharger only? Well, to make the same power on just the supercharger would put me not only insanely above the redline on the supercharger, but also would be at about 8,000 RPM on my engine due to the significantly lower pressure ratio. It also would plant me firmly outside the compressor map on the TVS blower, likely 50% or less efficiency if I guessed at an extrapolation, if it's even possible to get decent flow out of it at those points so far off the map.

So why twincharge? I will be solidly in the 68% efficiency of the turbocharger's map and be able to make enough pressure with the combination of the two to theoretically be in that sweet spot as early as 2500rpms, making 1,348 lb-ft of torque at that point after considering losses from driving the supercharger as well as drivetrain loss. IF I could build that on the line and launch with it, I could launch in 3rd gear and put down more effective torque than a C5 Z06 corvette launching in 1st at 4,000 rpm. 3rd would take me from 0-150mph so with my fat 4500lbs or so of car, running 10-something at 130mph there would be no shift taking place during an entire 1/4 mile. Yes, it's pretty sad that my car will likely only run low 10s if I were to run it all out...but that's what you get for driving a 4500-lb FWD tank. Oh, and that launch torque figure is without factoring in the magic that is torque converter multiplication...of which I believe I would have plenty early on considering the wheels wouldn't be up to stall speed until 60mph.

So just for grins, what is that perfect world max launch torque figure in first gear with 2x torque converter multiplication? 24,803 lb-ft of effective launching torque after all gearing (at something like 135 rpm, which to be fair is only good up to 1.1 mph at that gear ratio before torque starts declining, but it's a fun number to throw out there anyway).

Can we do this with a baby 4-cylinder? I don't see why not. The M90 is actually really well sized with a stock pulley to perform a similar, but scaled-down setup with a E3-16G-sized turbo on a 1.6L for a total output of 350-400hp with an insanely useable powerband.

[ZephTheChef]

My big question is, is there a way to mount the alternator in the front of the engine, factory ac location

As far as I'm concerned, alternator relocation will be so relatively easy compared to the rest of the build that it's not even a real issue.