RB26 with a supercharger.. opinions?

[onethirtyone]

so at first, I thought it would be really cool to do an RB26DETT with a supercharger that's on a clutch, so you could drive with the SC off, and have fun with the turbos, but when you hit a track or wanted all the power, just turn the SC on. well, due to physics, current state on engine technology, and my own knowledge base (which i don't think is all that great to begin with), i don't think i'll be able to do that. i got close to figuring it out, but alas, i've ditched that one. so here's my new idea; ditch the turbos on the RB26, and use a twin screw supercharger, with an electromagnetic clutch system (like the air conditioning in a car) so that it's still an on/off thing, but without the added complexity of having turbos in there as well. i would like to this setup for a few reasons;

 

1) twin screw because it gives great boost for all engine ranges.

 

2) you could cruise around town if you wanted, without having to try and wrangle huge amounts of HP, but if you took it to the track (i intend on doing both both), you could flip on the SC and have some serious fun.

 

3) i also thought it would just be really different, and kind of cool..

 

with that being said, i would like opinions on the matter.. and FYI, i HAVE thought about doing ball-bearing turbos that spool quickly, but again, there's no on/off system, that you could really use, AND, twin screw superchargers (if i remember correctly) can begin producing boost well before even the ball-bearing turbos.

 

thanks!

[emoximuu]

Sounds like a tuning nightmare. Turbos do have an on/off switch, it all depends on your foot.

[onethirtyone]

why would it be a tuning nightmare? i mean, Mercedes Benz does it, but i think they use a roots SC. so the biggest issue would be a bypass system for air to get through to the engine when the SC is off.

and couldn't i have a piggy-back ECU that only comes on and adds input when the SC is turned on.. i mean, wouldn't that work? or am i missing something? like i said before, my knowledge base isn't exactly extensive, so that's why i'd like opinions, and maybe a little help..

[emoximuu]

You could do a stand alone and have different maps for changing on the fly. Thats the only way I can see it. The RB runs a low compression also, you'd have pretty crappy gas milage and response from it with out the charged air. I think Power Enterprise has done a few twin charged systems for your original thought. I think the RB they did was pretty insane. I'll see if I can find the mag.

[LoneStarS30Z]

It was to my understanding that RB26's were twin turbo for a reason, like most other twin turbo engines being sequential. In lamens terms, no lag down low and power throughout the powerband as the other turbo kicks on.

 

I would venture in saying supercharging a non-turbo RB25 before ever de-turboing a RB26, which just seems really awkward even saying.

[onethirtyone]

actually, i just looked it up, and MB uses a twin screw SC for those systems.. so couldn't i just adapt the MB system for the RB? i mean, maybe just buy a MB supercharger with the clutch system, and install it on the RB, and wire it to a switch in the car, and to the ECU? and for re-programming the ECU, could i use a MB ECU, or would i just have to try to re-program one for an RB to closely match the MB one in regards to the SC? i don't know much about ECUs, so this is where a little help would be appreciated..

[onethirtyone]

ok, and so with an RB25, how much power can those take? i mean, i don't plan on putting 1000 HP through it, but i'd love to have the option of 6-700 HP.. and with a good enough intercooler system, could you use a SC with higher compression ratio and still get like 600 HP or would i really have to get low compression pistons?

[LoneStarS30Z]

Well it seems this is actually possible, crazy. I have no idea what kind of engine management would power this thing, but maybe I can find more through some digging. That being said, I can only imagine how expensive of a project it'd be.

 

[LoneStarS30Z]

ok, and so with an RB25, how much power can those take? i mean, i don't plan on putting 1000 HP through it, but i'd love to have the option of 6-700 HP.. and with a good enough intercooler system, could you use a SC with higher compression ratio and still get like 600 HP or would i really have to get low compression pistons?

 

 

I don't think you'll see that much power coming from a supercharged alone L6, or else it'd be done to death to avoid boost lag. Maybe there's some crazy example somewhere of one, but I've only ever seen turbo'd RB's making that kind of power. Upgraded twins would net you 500hp with proper supporting mods, the single turbo monsters are the one's that put out huge numbers at the cost of some boost lag.

 

But once you start talking about number's as high as 600-700hp there's alot more to the equation than simply what kind of forced induction you want.

Edited January 12, 2011 by LoneStarS30Z

[Canadianz]

OneThirty,

 

The supercharged RB sounds interesting on paper. I guess it comes down to what your goals are, if you want a small displacement engine that feels larger then a supercharger might be the ticket. If you are looking for a responsive turbo engine the other route might be a RB30 with a rb25det head and a single like a Gt 3071R or something around that size. That way you have a bit more displacement to get the turbo rolling.

 

Im reading this book right now and I really like it its called The Turbocharging Performance Handbook Its about 20$ on Amazon.com.

 

As well the same author has a book on Performance EFI Tuning Which I think will really help out on how you can go about managing a twin charged setup. The author actually covers a twincharged MR2 that has a corolla v-6 so I think that book would be ideal to wrap your head around the concept.

 

My advice is to write down the goals and then the easiest and simplest ways to accomplish them. I often get so excited about an idea (especially cool ones like this) that I forget why I am doing it.

 

Any how best of luck, its definitely a do-able project but it will require alot of planning.

[onethirtyone]

good point. and i've actually seen that pic before.. but the biggest problem with the way I wanted to do it, was the fact that on the top end, the turbos would be X HP, while the SC when on would be adding even more at the top end. then it became an issue with the wastegates operating at the right boost levels, with the "right" levels changing. the setup in the pic is probably more just for normal twin-charging.. that's my guess..

 

so then if it's usually just like a single giant turbo for huge numbers, how is it that some of the more extreme mustangs get crazy numbers, close to 1k? i mean, i know the shelby's use superchargers.. do they do a twin charging setup? i thought the biggest issue would just begetting a SC big enough to push that much air..

cause i also definitely planned on doing things like cams, chips, intake, exhaust, all that kind of stuff to help push a few more numbers here and there..

 

and like i said before, i'm pretty sure i've seen built RB25's with i think like a 10:1 compression ratio. with something like that, could i just put a SC or turbo on it and use a really good intercooler/radiator to keep it all pretty cool? cause then i would have all the low end and gas mileage of a high compression engine, but then the high end of a forced induction engine?

[onethirtyone]

thanks for the advice, Canadianz.. my goal is definitely a smaller engine that feels like a larger displacement. to be honest, a lot of the stuff about forced induction bothers me. like boost lag, and not having much of a low end with things like turbos and the like. maybe that's because i've never really driven a car with turbos, but, i like the behavior of an NA engine a lot better. but i realize that without forced induction, i can't really get an NA engine to produce the numbers like a forced inducted one. that's why i like the idea of the twin screw SC a lot better. boost happens at a little over idle, there's not as much lag (at least i'm pretty sure, but i could be wrong), and there's not as much of a surge of power, when the boost kicks in. it behaves a lot more like an NA engine, from what i've heard.

if i'm wrong, please let me know, because i don't want to spend a bunch of money on this and find out it's not at all what i was thinking. from the research i've done and what i've heard, a twin screw SC's power curve looks a hell of a lot more like an NA engine than a turboed one.

and i think i'll definitely have to look at getting those two books! they sounds like they'd be very good, and right now, i'm about to have a lot of time for reading and research..

[onethirtyone]

so i did a little bit of research.. and it looks like the RB25DET has a fairly high compression ratio for a forced induction engine. so then with that, could i take off the turbo of an RB25DET, use a twin screw with an intercooler, and just do that? i mean, cause then with a 9.5:1 (i believe that was the DET, and the DE was 10:1) compression ratio, that wouldn't be bad at all for mileage or response, because that's as high as a lot of NA motors these days, and with a good intercooler, i could keep the air going in nice and cool, so couldn't i do that?

it would have the responsiveness of an NA motor because of the high compression ratio, but the overall power of FI.. or would that not work at all? i mean, i would build the hell out of it to begin with, to make sure it could handle lots of power..

[ZT-R]

that is the dumbest thing i have ever seen on this forum. 1st buy a Z, then buy a rb, then worry about a twins and a super charger... if you drive the car with the factory rb26 you will soon realize you have bigger issues than a lack of power. and its "roots style"

Edited January 13, 2011 by boostedh23a1

[jakeoster]

There has been ALOT of talk about this on the Internet. So far the only person I have ever seen that actually came through and twin charged an RB (and got it to run) is trying to sell his project as it was turning into a nightmare and a money pit he said. It was in a commodore I believe.

 

It seems like a good idea and probably would work awesome if you have the time, money, and expertise to see it through.

 

As boostedh23a1 said, focus on getting a running RB26 powered Z first 0.o

Edited January 13, 2011 by jakeoster

[onethirtyone]

ok, well, first off, thanks Boosted, for just trying to shut me down and calling my idea stupid. that's not going to work. i want to talk all the way through this fail so that i can learn. otherwise, i could just walk into something later that i could have learned from this.

 

secondly, i would really like to have ideas and plans on paper first, so that i know what i'm aiming for, and don't waste my money on like 4 different set ups.

 

thirdly, i know it's "roots style." just like twin screw is a style of supercharger. and i figured anyone who would be able to help wouldn't need me to put "style" after "Roots Supercharger" to know what i was talking about.

 

now, back to my actual issues.. i didn't really want to do so much a twin charging system, as something completely new. that's where my problem is/was. for my original idea, i would have had to have the wastegates operate at one level of boost, and then when i turn the SC on, have it operate at a completely different, higher level. the only thing i could come up with, is that i would have to have 2 boost sensors, and the lower one would have to be over-ridden once the SC was turned on. but i don't really know how to do that. so i've ditched that idea.

 

so now, based on what i've read/heard today, i was thinking still do the on/off switch supercharger, like a Mercedes Benz, but on an RB25. because it would have a high enough compression ratio to still have some get-up-and-go with the SC turned off, but i think with adequate cooling via an intercooler, i could run enough boost through all RPM ranges with a twin screw "STYLE" supercharger to have a lot of fun on a track.

 

so my biggest question right now is, can you run forced induction, with a 9.5:1 compression ratio, and still achieve high amounts of boost/power, if you had an adequate cooling system?

 

because if not, there's really no point to an on/off supercharger, is there? then it just becomes an argument of which is better, turbos or superchargers? and that argument has been going on for decades..

[jakeoster]

Well the one thing I noticed about a supercharged RB25 on YouTube, no turbo, is it is pretty loud. Since there's no turbos to quiet the exhaust down and coupled with a loud whine. You might want to take that into consideration if this is going to be a street vehicle as it would probably get the fuzz wondering =p

 

*I am no expert* just my thoughts...as I think superchargers are awesome and arnt bias against them.

 

You have to take into account the parasitic effect and since the RB doesn't make gobs and gobs of power in N/A trim like some V8s etc do that could be an issue. That's where the idea of twin charging comes in to kind of counter that.

 

What seems to stop people from doing the SC on the RB engines is that the cost per hp ratio favors turbocharging.

 

You seem to want a car that doesn't boost all the time and you only want power when needed...what you could do is use a little bigger of a turbo that favors a higher rpm power band and shift at lower rpms before you begin to build boost.

Edited January 13, 2011 by jakeoster

[Evan Purple240zt]

I have an HX35 on an rb25det and if I am driving normally I rarely see positive manifold pressure.

[onethirtyone]

yeah, the loud exhaust is definitely something to be cautious of.. my friend had a 91 jetta with a V6, with a 2.5" exhaust. and when he got into an accident, people swore he was speeding cause his exhaust was so loud.. hahaha so yeah, something to be thoughtful about..

 

and i definitely understand the whole parasitic thing with a SC. that's why i was thinking of a system like Mercedes Benz. an electromagnetic clutch, like on an A/C system. when it's off, it's just freewheeling. there's no resistance. it's ONLY when the SC is actually on that there's resistance.

 

and i thought about doing just a large turbo, but that's the thing. i want something that will help give a lot of low-end, as well. because if you want a street-tuned car, you're going to want more torque. for a track car, mainly horsepower. and that's what i like about the twin screw type of supercharger, is it will give you power at both ends. cause i'm not going to lie. i wouldn't use the SC ONLY on the track. i'd use it to have a little fun on the street as well...

 

and what is it about the turbos that give a better cost:power ratio? i just don't know.. i mean, i thought that superchargers were around the same cost as a good turbo, and the intake stuff probably as expensive as all the extra exhaust manifold stuff.. or am i wrong? is it that turbos push more air easier than Superchargers?

[mario_82_ZXT]

You're misinformed about superchargers.

 

Most have vacuum operated bypasses, so that it takes basically no HP to turn them on cruise/light throttle stuff.

 

The Merc electronic clutch S/C is for a small 4 cylinder engine, and as far as I'm aware, the larger ones (that would be best suited for this) do not use an electronic clutch.

 

Also, have you priced out an RB26?