Shad Laws

Hello-

Well, for auto-x, there is something to be said for low rpm boost and no lag... that's true.


I don't think it's quite as simple as you think :-).


The stock ECU isn't going to cut it. Even at 10psi, the AFR will be all wrong. This is because you've removed the turbos, so 10psi of manifold pressure will flow more air through the engine, making it go quite lean.

A sidenote: you may think that since there is more airflow through the engine for a given manifold pressure, you'll make more power, right? Well, not really. It's true that the combustion process will produce more power, but you also have to deal with the supercharger robbing that power before it can ever get to your flywheel. In the end, it will be a net loss...

To be fair, that's almost a point in favor of turbos... it's much easier (and cheaper) to change turbo boost than it is supercharger boost. Turbos need as little as a software change in the ECU, whereas superchargers need new pulleys and belts.

That's hardly a fair comparison. If all you want is near-stock psi and power output from turbos with an emphasis on low rpm boost, then the stock sequential system is great... and costs you $0.

If you want to compare a badass single setup with big boost to an equivalently badass supercharger setup with similar power output, then that's different. I'm not sure which would be more expensive... they're both pricey to do it right.

Not quite. As far as solenoids and vacuum lines go, a single turbo (or twin parallels) are a near-tie against a supercharger. There still needs to be some stuff to deal with cruising (i.e. not using the blower), blow off, etc. Of course, a sequential turbo system is a great deal more complicated.

The intercooler is optional?!?!?! C'mon... have we not learned anything from this thread? <sigh> An intercooler on a roots supercharger is MORE required than it is for turbos, not less. An intercooler on a twin screw supercharger is about equally required as it is for turbos. You can't get somethin' for nothin'! The inefficiency of the roots blower will bite you in the butt.

As far as couplers go, well, I'd like to see you build an intercooled supercharger system for an FD with no couplers. Possible? Yes. Likely? I don't think so. And skipping the intercooler on an inefficient roots blower in a car that it notorious for overheating and detonation is a REALLY bad idea.

Forced induction is tricky dude... no matter how you cut it. There's no free lunch here. The sequential twin turbo setup is clearly the most complicated, but all of the others are comparable. If you want easy, I'd recommend porting the hell out of the engine and ditching forced induction altogether :-).

Please understand, I'm not trying to "take sides" here. There's no reason that I personally love turbos over superchargers. In fact, I have nothing against them. However, many of the folks in this thread seem to misunderstand them. In particular, they think they're better than they really are. Maybe it's because the grass seems greener on the other side or something...

Take care,
Shad

Shad Laws

How useful is low rpm boost on an FD?

Just something else to ponder... with my sequential system in cherry shape (i.e. NO cracks in the manifold), I can get a full 10psi at just 2000rpm. It's pretty cool. But, let me tell you... the power down there still sucks. And that's with no extra porting... the factory engine just doesn't make much at 2000rpm even with boost.

That said, below 2700rpm, there is still notable turbo lag. A supercharger would definately help out here big time. IMHO, this is the main reason to put a supercharger on an FD. If this isn't a major concern, though, then I'd focus on dialing in the stock sequential setup into 100% working order. You'd be surprised how well it works when all 87,540 of it's little parts are in good shape :-).

Take care,
Shad

marix1521

i know of one place that has SUCCESFULLY supercharged an FD. It's located in Jacksonville, AR. I can't remember the name of the place, but i'll try to find it. I met a girl at starbucks in Little Rock with a VR FD and that's where she had her motor built.

Prôdigy2nd

iTrader: (3)

well how bout this..... best of both worlds?




Yes a RB26 TT and SC'd fricking sweet i'de say, only thing that would make it better is a screw type blower, becuase they tend to give a little bit bit more power advantage than a Centrifugal blower, which would be the ultimate set i think. incase i've reposted i'm sorry but i was not really wanting to read through all 4 pages so i read through the first 2 instead. and i'm not realyl gonna get into this "debate" but just thought i'de toss in my 2 cents.


Prôdigy

SamuraiSam

best of both worlds??? no.

I am lazy so I am just going to type a few points instead of a long thread (clubsi exhausted me earlier lol)

-How does a turbocharged rotary require more maitenance than a supercharged rotary?

-Did you read all the posts?

-A turbo that small is FAR too small for your car. Turbocharger sizing is not based off pounds per square inch. If you dont want to sift through hundreds of pages of matieral (and also learn a ton about forced induction), you can visit http://www.turbobygarrett.com/ they give a nice little tutorial on sizing turbos.

94MazdaRX7

Until someone does it I guess we will never know and we will just have to read everyone's speculation instead.

Until then KILL THIS THREAD!

Shad Laws

Hello-

<sigh> See, that's the part you just don't get: this isn't speculation. It's physics.

You aren't the first to think of putting forced induction on an engine. Neither am I. Everything I've said here is OLD news. It's a chapter of engineering that is pretty well figured out. I'm not saying that every little detail is 100% known - there's always something else to learn. However, I am saying that a heck of a lot more is known than you think and present yourself in this thread.

I'm trying to share some of it with you in a straightforward, unbiased way, and you toss it off as speculation. That's nearly insulting. Ah, whatever. I give up.

End conclusion: superchargers are NOT better than turbos. Turbos are NOT better than superchargers. They each have their own pros and cons. Just because it isn't commonplace to supercharge the rotary doesn't mean that it's the answer to our prayers. The grass isn't necessarily greener on the other side...

For more information, go buy one of the billion books on forced induction design. They'll all say the same thing, but maybe you'll trust the source more than me. After all, I'm just some idiot on a web forum, right? :-)

Take care,
Shad Laws
-BS in ME with Honors, Northwestern University
-MS in ME with >4 GPA, Stanford University
-Previously founded and ran company to engineer and manufacture high-end aftermarket engine components for aircooled Porsche and VW engines
-Currently working on PhD in ME, Stanford University, working on developing by-wire technologies for future automobiles and building prototype by-wire cars from scratch

Sgtblue

iTrader: (16)

Why?
You may not have appreciated what the others had to say... but I did. I'm just a simple civil servant with an under-graduate degree who found it pretty interesting and informative. Especially when contrasted with the latest "Can I swap this engine?" or "It blew up!" threads.
To Shad, neit_jnf, Kento and the others, thanks for your time.

scotty305

iTrader: (2)

Just to keep this debate going (because it's much more interesting than "I crashed my FD" or "which BOV?" threads), there are a few people who have installed superchargers on FC's. Here are a couple people who used the Camden kit:

pianoprodigy made 230 whp @ 6psi in his FC. He has also owned a single-turbo FD and a Corvette Z06. I imagine he would have some useful insight for you.
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/230-whp-supercharged-vert-complete-dyno-car-video-sc-comparisons-431570/

https://www.rx7club.com/rx-7-audio-visual-lounge-143/1987-supercharged-fc-457752/


The Koenigsegg supercar uses a twin Rotrex supercharger system, as outlined here:
http://www.koenigsegg.com/thecars/en...?engineering=2






94MazdaRX7, have you autocrossed an FD with a healthy twin-turbo system? I took about 4 events to get used to the powerband, but the car doesn't surprise me anymore. My car is mostly stock, with a downpipe. I'd still like to drive a single-turbo, supercharger, and a V8 swap, just to see how they compare.


-s-

Jager

iTrader: (10)

It depends on the charger and the engine for instant boost. Most drag racers aim for a powerband. Its why V8 rx-7's run quicker 1/4 miles then a rotary of the same horsepower. Its all about where torque is put down over the best powerband.

BryanDowns

iTrader: (2)

A much simplier answer to your quest for power down low is an LS1 swap. I know I'm going to get attacked for saying it... but it really is. You'd probably come out about the same in terms of money spent as well. Because the engine control system wasnt designed and built in a shop, but by actual engineers who had warrantee, emmissions, longevity, and a host of other factors involved, I can almost garantee at the very least the engine itself will be more reliable as well in the 350whp range you are wanting.

Food for thought.

side note: pretty much any aftermarket FI setup on the FD is going to be less reliable than a "new" seq oem setup. Now, a 10+ yr old seq setup not in perfect shape... thats a different story as you'd probably be better off w/ a single turbo conversion on low boost. As you all know, LOTS of stuff to break in the seq system, and 10+yrs of heat baking and usage will break alot of stuff.

94MazdaRX7

The reason why I say kill the thread is because there are some people in hear that think they know everything about everything when the supercharger hasn't even been tried on the FD. Just because Shad has a degree doesn't make him the TURBO/SC guru that he thinks he is no offense but just because your have a degree doesn't make you an expert. I am looking for an AUTO X application not ultimate power which IMO a supercharger would be more reliable and cheaper then a single turbo or a problematic seq setup. Shad you have given alot of good info and I appreciate that but until there is a comparison done for what I need your info is still just speculation.

I work for Gulfstream Aerospace as an Senior Eelctronics Technician and deal with engineers on a daily basis and they do know alot on paper but when it comes to putting the theory into an airframe and making it work they are lost. Paper is one thing reality is another.

To answer your question Scotty yes this is my 2nd year Auto X in the FD and the car is amazing on the track when I have boost. I did run last year with the seq setup but kept having problems: with hoses so I changed them all, then one selonoid, then another, then a coupler, then another coupler, then a CR actuator. Basically I tore the UIM off several times replaced parts on several different occasions and am now seeking an easier more reliable means of forced induction. I loved the seq setup when it worked, but I just keep having issues.

SamuraiSam

Shad might not know 100x more than anybody else but he has done something that you have not done. He educated himself.

Until you have any sort of fact or proof to refute a single one of his statements you have nothing to stand on. The fact that you don't belive many of the FACTS just shows a lot of people that you are very uneducated on this subject. And thats what he has given, a lot of facts and some opinion - but mostly facts.

I am not trying to insult you or say you have a lack of intelligence but the smartest person in the world wouldn't know anything about forced induction until they did a bit of research, and you need to do more research. Once you do, you will understand a lot of what has been said in this thread, and you will probably apologize about your lackadasical attitute towards all of the information and suggestions that have been thrown at you in this thread. You have proven again and again in this thread that you are much less knowledgable about forced induction than many of the other people that have posted. If you did know much about the topic you wouldn't be saying things like "it is impossible to predict what would happen until you actually bolt a supercharger on".

This is extremely true. Look at any rotaries torque curve, they don't produce power down low. Making boost down low is still not going to produce much power down low. Sorry.

Anyways, I hope that you do take the time to pick up good books on the subject as both Shad and I have suggested you do, get a little better grasp of how things work, & i think a lot of things will fall into place and maybe you will believe...

Best of luck in whatever path you choose to follow, fellow car enthusiast.

Sam

Sgtblue

iTrader: (16)

If I might make one more suggestion....
It might be a bit early for you to give up on the stock sequential system. If an LS1 isn't for you, consider that for less than what you would have into R&D'ing a SC for the FD, you could remove that UIM one more time. Replace every solenoid and check valve with new, replace the vac hose with viton. Then install a BNR III with a decent SMIC and PFC. From what I understand, the BNR will easily give you reliable 350-ish rwhp along with all that you loved about the sequential system.

neit_jnf

iTrader: (17)

My turn!

Neit J.N.F.
-BS in ME with Honors, University of Puerto Rico, Mayaguez
-MS in ME with Honors, same as above
-3yrs working in Manufacturing of various automotive drivetrain components for Ford, GM and DCX
-Plan to enroll in a PhD in ME, Internal Combustion Engine Design, currently researching Colleges in the SE Michigan Area

KevinK2

"To answer your question Scotty yes this is my 2nd year Auto X in the FD and the car is amazing on the track when I have boost. I did run last year with the seq setup but kept having problems: with hoses so I changed them all, then one selonoid, then another, then a coupler, then another coupler, then a CR actuator ... "

There is a step by step logical way to first find if sufficient pressure or vacuum is getting to the several actuators at the right times. Lots of hoses, tees, and gauges. Someone did a good write-up. Once a problem is found, solenoids must be hot tested at pressure (another write-up).

If that is too much or getting old, a good medium single turbo (another forum) would offer an order of magnitude simplification, and adequate low end for 350 rwhp target. GT30R, rx6, T4/T3, come to mind. Those with internal wg are ok ( not the T3 type with valve pivot in the cover) as they allow a divided exh path dp for the wg and main exhaust ... more top end power. Having autox'd and mostly won for about about 5 years (other built car) I can't see how a good launch and keeping rpms up (well above 2700) would not match non-existant supercharger options.

chep ecu path would be a used pettit or M2. As others noted, SC would require major map changes to a PFC due to higher VE's with headers and no back pressure.

screw types and the new helical roots (eaton) build pressure along the compressor length, so simple recirc bypasses tend to superheat the air, even with local A/L IC. Really need a clutch. That said, my dad's 3.8 buick with an eaton sc ran great, like a big v8.

I modified a laggy old saab turbo (2L, T3) with timing and fuel changes, so that it took off with nill lag and big torque.

I agree an ME degree only means the potential to know the proper application of physics. Guys here seem to be spot on.

Kevin K
ME PE, (debadged when I missed my dues payment .... paying dues is more important than constantly consulting in the industry)
Used analysis and FEA modeling to design composite 3-spoke bike wheel (now the Hed-3) 10 years ago, but still used by Lance (and team) for time trial wins in the last tour de France.

poss

iTrader: (5)

Just because they told you what you didn't want to hear, although correct, they don't know what they're talking about....

I agree theory is different from reality, but they haven't been quoting theory and on top of that, this isn't a new, uncharted subject.