Supercharger vs. Turbo
 

Here's the deal: about a year ago i supercharged my 86 gxl. it was great and tons of fun...till a few months ago when i blew an apex seal...so anyway, im at a cross roads. im goin (if nothing happens) to pick up my motor tommorow. it will have a fresh rebuild and large streetport. for about the past month i have been thinking about how much time, money and effort has went into this "project" and i began to look at it all pesimitically. i mean yes, i personally think its pretty badass to have such a unique car, but at the same time, for what i have put into it, i could be making near 375hp instead of ~265whp (what i am projecting it will be with the addition of my street port and the new headers i bought). so my question is, what would you guys do? give it up on the eve of victory for more power? or keep it? also, i have already thought of keeping it for now and reinstalling everything once the motor is back in, then making my decision based on how much of an increase i see with the port work, but in reality, the car has been down for a few months now, and i think that if i put it all back in, i wont have the heart to take the car off the road AGAIN to do a turbo project. your thoughts and opinions are appreciated.

turbo.

Turbo.

Go turbo, I will help you out by buying your supercharger set up! :)

turbo.. (big one too)

hahah ^ lol haha

I'm confused about one part, you said you'll be making 375hp? Is that with the port and supercharger?

Put it back together, run low boost and save up for a nasty turbo setup. Turbo cars are much more fun IMO

haha, wow, this is kinda 1 sided!

blackedoutfc3s: NO. i was saying that with the amount of money i have dropped into my current setup, i could have a 360~375rwhp turbo car. before i blew the motor i was making about 220rwhp, since then, i have got headers and a test pipe (to go along with my apex'i catback) a large street port and other misc. stuff that should put it at around 265whp. im confident that it will make over 250, but above that, its just speculation since theres really not much for me to go by.

thanks for all the input guys, i look forwad to more!

Ok, that's what I thought you said, but couldn't quite make it out. My input is now changed...

TURBO

haha, sorry if it was wriiten akwardly. im no shakespeare.

either way, i dont think it would be possible to put down that much out of this s/c. i think where i am now is about its cap (safely) unless of course you had a bridged motor or something. now if i had one of those big whiple s/c's that make like 17 psi, it be a different story!

Was it Aaron Cake that coined "Supercharger, the most expensive way to make 200rwhp on an RX-7"?

well i guess i should start diggingthrough my hard drive for my pics of this setup, it has LOTS of extras. its not a bad setup or anything, i just want more power (my cousin has an 87 supra that he just put a t3/t4 hybrid in and i gotta keep up with the johnson's!). it will be perfect for someone that doesnt wanna have to mod there car (its practically bolt-on thanks to all my custom work :) ) and is a HUGE upgrade from an na. on stock ports with no mods, it will make about 200rwhp. throw in a full exhaust and a nice tune, your looking at close to 240.

he wasnt lying....but seriously, there are alot of perks to this s/c. its a centrifugal type, unlike the camdens, so it is made for higher boost levels (i have the upgraded impellar which flows at 1200 or 1400 cfm, i cant recall, and i hit 12 psi on it twice. for obvious safety issues (no intercooling and 550x4 injectors) i normally limited myself to acout 8~9psi, but could easily and consistently hit 10+. the main advantages of this s/c over a turbo is that boost is near instant (i starting building boost at under 2k) and it builds incredibly linearly. if you are looking for a good upgrade to your na and not gobs of power (but plenty fun mind you, i puled on an automatic 350z), its a great option

Turbo.

Do it.

yea i pretty much already sold before making this thread, i just wanted to see what other forum memebers thought haha

to make the kind of power you are wanting from a rotary i would say turbo it.

torque from SCs are nice but rotaries are happier with turbos.

next question is, did you determine what caused the failure and plan to fix it before putting it back together as it was?

yea, the torque was nice....haha

im pretty sure that it was a combination of 3 things: high compression rotors, lack of intercooling (these two combined make HOT HOT air, which can cause preignition as we all kno) plus the lack of timing retard under boost (was running stock NA ECU w/ an safc). to correct the problem i had TII (low compression) rotors instlled when it was rebuilt. i also was searching for an intercooler solution and was pretty set on water/meth injection, and lastly i got a TII ECU which i was gonna (still am btw) rtek.

evryone is saying turbo, but it looks like you have a 6port.

Get a RTek, T2 pressure sensor, AFM, and tune for 12psi and call it a day.

yes, i do have a 6 port. like i said previous, i already have a TII ECU (and the pressure sensor and afm) that i was planning on rteking. also, i dont believe it would be safe to run the boost level. originally, the s/c is meant to run 6psi. with the upgraded impeller, its supposed to hit 9psi. the reason i was able to hit 12 was because i had a smaller pulley (for those not familiar with s/c's, smaller pulleys are upgrades since the cause the s/c to spin faster in relation to engine rpm) BUT, i heard from 2 others with this s/c that it isnt safe to run anything smaller than 3.75" pulley as it will over spin the blower and cause it to fail prematurely. the 3.75" pulley with the upgrade impeller is only capable of about 10psi, so therefore i decided to only boost 8-9. that and the fact that i still had high compression rotors and no intercooling at the time.

even so, at 12 psi with all my other mods, i dont think that i would be able to break 300rwhp on this supercharger. the reason being that the characteristics of superchargers would not provide that kind of power versus a turbo at the same psi. however, this is strictly speculation, im not a physist. also, the rotary just seems like its designed for a turbo. it produces so much exhaust volume relative to its engine displacement that it will get good spool out of a large turbo that other piston engines with similar and even more displacement could only hope of getting to spool in a much higher rpm range.

I love this board!
 

Most Supercharger threads end with a blown engine.

Touch always STARTS his thread with a blown engine!:lol:

Good Luck!

haha, you made that comment last time, but its so true, i believe this is like the third thread that has begun with: "ok, so i had a s/c'ed gxl until i blew an apex seal.."

...and the beat goes on!


Heh heh.

haha, but in all seriousness, thats not true jackchild! with the proper ems (most importantly being the ability to retard timing under boost), and cooling of some sort (intercooler or aux injection) you'll be fine, even with high compression na rotors, altho TII wouldnt hurt.

If you were happy with the performance, keep it as-is and save your time and money for something more worthwhile.

If you want more power, go turbo.

If you want something unique, try out one of those new Eaton TVS superchargers.

No, that is for an inefficient Roots type blower. A centrifugal supercharger should have the same efficiency as a comparable turbocharger at the same psi. Belt drag would reduce the power a bit, but the exhaust should be more efficient and make up for some of that loss. Your lack of an intercooler hurts.

Yes

It very likely to lead to detonation, but is less likely to lead to preignition.

BOOOOOST IT!:lol:

Then your SC setup will be a unique and special thing...just like all those other SC setups...

Take this statement the way it is intended- if you prepare your engine-fuel, charge temp and timing - the way the successful turbo guys do, there is no reason it won't work. All you need is $. If you cut corners or get boost happy, you will pop it another time.


The weak link is................................................ ...................




.......................you.

Good Luck!

TWINCHARGED?keep you low end torque and a nasty top end,the best of both worlds.

joeylyrech: in a perfect world: Definately. personallytho, i just dont think im that talented nor am i financially endowed or patient enought to pull that one

Your problem was not the 9.4:1 rotors, Aaron Cake is running 13psi on a GT40R on his. 10+psi with no intercooler, NA ECU with RPM based fuel controller, stock timing and 550s is a ticking time bomb. With the TII rotors you are limited to a turbo upgrade for anything over 250whp.

With a supercharger you are WASTING a unique characteristic of the rotary engine, the stronger exhaust pulses. You have already done all the work to rebuild the engine, finish it off and throw a big turbo on it.

Yeah, I don't know about that. The easiest and most effective way to get HP from an N/A is to free up the exhaust. With a turbo, all you are doing in putting a cork in the exhaust. I had this conversation with someone alot smarter than me and he was convinced that with enough time and $$, a supercharger could be made to perform better than a turbo. Although he wasn't going to foot the bill :hahaha:

Oh, this is coming from a guy that has made 960 BHP on a 13B:icon_tup:

I agree, 110%

Yeah, strong exhaust pulses but you're bottling them up with a turbo.

I say keep the SC and here's why.

If you were to go turbo you would need at the minimum a turbo, manifold, wastegate, intercooler and EMS.

If I were you, this is what I would do. Keep the supercharger. Get a REAL EMS. Motec would be nice, M6/800 and make sure there is enough fuel in terms of injectors. Then I would add some AUX injection. See where that leads you. I bet with the AUX injection you'll be able to get alot more boost and do it safely. You won't have to worry AS MUCH about popping another motor, & the motec can safely retard igntion timing based on boost level, or even better, EGTs.

If after all that is done you are still lusting for more power, then go turbo. You'll already have the EMS and the AUX injection and really just need the turbo.

That's what I would do. And for what its worth, I have a turbo setup :suspect: and I'll be building boost and be around full by about 2k too:p:

thanks titanium, you are always helpful. i was l;eaning that way at first, but the thing is, even with all the intercooling in the world and an awesome ems, only the motor will be able to take the extra boost. the s/c will physically max at at about 9~10 psi. which is limiting.

also, thats an awesome spool. full boost by 2k!

hmmmmm, & forgive my lack of knowledge when it comes to SC's and the different types, but if the SC maxes out @ 9-10, would it be possible to put a smaller pulley on and get more boost?

I really believe that it was the factory ecu that popped your motor. I think a different EMS and some good time spent on the dyno would net you some more RWHP. Not to mention the chemical intercooling not only allows you to advance the timing, but by lowering the charge temp I would think it would have benefits onto itself.

What do you want to accomplish?
 

It's not really how much horsepower you get, but when you get the horsepower. If you're going racing on a track or setting land speed records on a multilane, then you should go turbo.

If you're trying to beat out the other guy between stoplights, the torque usually comes on earlier with a supercharger. The SC will give you an advantage in the stoplight drag race.

Either way, more boost = less reliability.

With all due respect to Aaroncake, who truly is my idle for his well thought out explanations, 200 horsepower delivered earlier in the powerband is better than 500 horsepower late, because, often times, your not going to get to that point quickly enough to use it.

More importantly, there's always somebody with more boost. But judging from this thread, the guy next to you isn't going to have a supercharger.


sisyphus

Your idle should be around 800rpm, I think there's a problem if it's Aaron Cake.

:D

Well, if you really want more power, then you should probably go with a turbo. But since you have a 6-port, that is far from a straight-forward process. If you think you can deal with the power, keep the s/c. If you get an intercooler and a proper EMS, then you should have a nice, solid car.

turbo peak+rotary peak= heaven

Superchargers have a redline, and become less efficient as they approach the redline, so you can only change the pulleys so much before bad things start to happen. Unfortunately, I am not familiar with the operating parameters of the supercharger in question.

I agree. However, the EMS and proper tuning cost a lot of money for working class people, and the typical speed-density EMS needs to be retuned as the engine wears.

No, the centrifugal supercharger mentioned in this thread has a slower torque rise than a typical turbocharger, Roots supercharger, or Lysholm supercharger. It is basically a belt-driven turbocharger, which does not really kick in until the higher engine rpm's. The advantages of the centrifugal supercharger are its good efficiency and easy driving (no or low boost) in the lower engine rpm range, as well as the 'attached' feel of the engine rpm-based boost rise which is typical of all belt-driven superchargers.

Regarding spool times, I think many have forgotten that you were running NO intercooler, I sure did. With my crappy 1.5 to 2.5" piping with the front mounted stock TII intercooler and the extra bend from the TB being on the wrong side my car
hit full boost at ~3000rpm and Aaron's first setup at 2500rpm so I would say that spool times with the two setups are similar.

Do you have a map for the SC? I would be surprised as to how efficient it really is past the 9psi that it was meant to be run at or what the boost limit is.

I always thought that the reason SC setups weren't common was that our engines don't make enough torque to spin a big supercharger. American V8s use SCs to convert their unnecessarily large amounts of torque to useful power and the drag from the SC has little effect on the engine. If you drive an FC with the AC on they drive like crap. A bigger SC with more interia would put even more drag on the engine, but I'm curious as to how this will compare to a similar sized turbo with the lack of backpressure usually created by a turbine.

idle = idol to me in this sense

Ah, so it's not just a matter of changing a pulley AFTER a certain point. It becomes, crap, need a bigger SC.


To an extent. Some EMS's have an autotune feature that automatically adjust injector pulses and timing based on set inputs.


I sincerly pray that this is a typo :icon_no2:

Regarding spool times, I think many have forgotten that this is a centrifugal supercharger, which is not designed to make max boost until engine redline. Quoted from 'teh internet' so you do not need to rely on my statements which appear to be ignored on a regular basis:

"Typically, a centrifugal supercharger will make it's maximum (quoted) boost at the engine's redline rpm and nearly nothing at 1500-2000 engine rpm. Boost builds exponentially with engine rpm, meaning that boost comes on very quickly in the upper half of the powerband."
http://www.superchargersonline.com/content.asp?id=21

Yes, and just like with turbochargers, a bigger supercharger will generally have a higher boost threshold. Matching a centrifigual supercharger to an engine is almost like matching a turbocharger with no wastegate to an engine (which was the old school method BTW).

Autotuning currently only works for a base tune, while the fine tuning still requires a professional. Which EMS has autotuning for ignition timing?

I always laugh at how many people ignore/insult me becuase I don't have a running car. Forget the fact that I have owned it for almost 12 years, have done more work than most of the little punks here can dream, and have dropped the equivalent of a third world country's GDP into it, I'm often ignored as well becuase I use proper grammar and don't drift

What about using a pop-off valve and a smaller pulley. Let the boost build quicker but maintain a set level. It seems like a mikeymouse way of doing it though.


It's not autotune for ignition, more like trim based on egt's. I;m still learning ALOT about the software. It's beyond me at this point. Motec M820 V3 though.

Yikes! and English major! I didn't mean that Aaroncake sits around! Typo is my second language.

sorry, i havent been able to respond to this thread, yesterday i was driving to pick up my engine for half the day and today i have been at work and im about to go to a wedding rehersal! i will address things more detailed later, but the one thing i want to touch on is when i said it physically wont make more than 9~10 psi. TTT is right that smaller pulleys=higher boost and evil aviator is right that after a certain point, the s/c becomes unefecient just like a turbo. what i was geeting at tho is that i currently have the smallest pulley (therefore highest boost pontential) that will work on this blower without causing it to fail. this particular unit (and i will have to find the post in the mustang forum i got this from [puke]) can only withstand 38000rpm (the s/c itself, not the engine of course). after this point, the planetary bearing is inevitably gonna fail after repeated exposure to this rpm. its just a design flaw i guess. i was passed on this info by a guy name phil garrott (spelling) that had the same s/c as me like 7 years ago. he found out the hard way by running the smaller pulley (the one i hit 12 psi on) and destroying the s/c. luckily it was still under warranty. when he took it to paxton to have it rebuilt they told him that the company (nelson) that was distributing the fc "bolt-on" kit was using a smaller than recommended pulley to increase desirability by saying that it could hit over 10 psi. phil then bought the correct size pulley and lived happily ever after. coincidently, phil told me that he heard nelson was having so many units come back destroyed that they released a "revised unit" that used the bigger pulley.

when i get home ill address some other things that were brought up (unless TTT or EA get to it first!!)

THANKS FOR AL THE INPUT GUYS! KEEP IT COMING

also, i was told that these are the boost stats:

small pulley (3.25") w/ standard impeller: 8 psi max
small pulley (3.25") w/ upgrade impeler: 11 psi (this is the setup that i hit 12 with, altho i was tempting fate)
revised, large (3.75") pulley w/ standard impeller: 6 psi max
revised, large (3.75") pulley w/ upgrade impeller: 9 psi max (what i ran after finding out i was tempting fate)

turbo.

john ny

ok, now that im home, i wanted to address what evil aviator was discussing. YES, centriugal s/c is like a turbo that is powered by the crank (or in this case eccentric) shaft via belts instead of exhaust, hence the signature.with this in mind, everything EA said is absolutely true in theory, but it doesnt fit with my experience. unlike what a centrifugal s/c should do, i seemed to build my boost rather quickly (like i said before). since i have never driven another centrifigal s/c'ed car, i can only compare to a turbo, and compared to turbo cars i have driven, the building of the boost is incedibly linear. i will admit that it did increase faster on the top end, but still much more linear than a turbo. in regards to the torque curve, altho i have no sheets to prove it (and pianoprodigy's dyno sheets seem to contradict what i have said and am about to say again) the bottom end torque seems excellent (at least on the butt dyno) altho it is not on par with roots type s/c (i have driven both a roots type powered miata and a roots type powered t-bird), it is leagues above an na and even a sock TII. i think thats all i had to say for now

turbo!!!!!!!! if i had teh money id get 2 rx7s and have one of each. that way both ur sides are happy! ^^

haha, yea, i wish i had the money for 2 fc's, let alone actually having 2 fc's. like i said before, i am pretty much sold on the idea of a turbo ( i kinda already was before i made this thread.) i am currently negociating with another forum member who is interested in buying my s/c with its extras. if he doesnt get it, its going to the f/s section, if it doesnt sell within the month, im just throwin that bitch back on the car!!