WonkoTheSane

iTrader: (2)

For the past year or so, I've been following every thread I could see about a turbo NA project, or a supercharger project, etc.. Now that I've graduated and gotten a real job, I'm looking to spend a some money on my Rx-7 this winter, including some form of forced induction, some minor, remaining suspenion things, and probably a bit of bodywork. Obviously this thread is about the forced induction. All of the supporting mods have been accounted for with either decision (better cooling, intercoolers, more fuel, etc). Tuning compliemnts of a LM1 and Megasquirt, on a local dyno. Here's my observations, and I'd like anyone with an experienced/informed decision to help guide me.

Now, my problem stems from the fact that I have never dealt with any form of forced induction hands on. I've read all about them, of course, but that's a poor substitute for hands on experience. So feel free to correct anything blatently stupid that I say I am also planning on adding a 50-75 shot of nitrous, just because I've always wanted to play with that.

Either of these are going to be done on my streetported NA engine, which has about 10-15k on it since the rebuild, and I have the luxury of working for a CNC machining company, so i can stay after hours to work on some adapter plates and things for myself..

I was initially thinking of supercharing it, and here's why: I can get ahold of an eaton M90 (roots type) supercharger for damn cheap (< $250), and I have the abillty to fab all the mounting brackets and such. What I was hoping for was a nice, 6-8 PSI boost level, giving me approx 225-250 at the wheels, and a straight power band, from gas to redline. Now I know that there have been some spotty results from supercharging, and a lot of unknowledgeable people claiming its the holy grail of power, but I'm not seeing much result except for SonicRat's Whipple. I don't quite have the money for a whipple yet.

I guess the question is: Is there a reasonably priced supercharger (read: =<$1500) that will give me the performance that I want, or should an intercooled M90 be able to do what I want?

Now, everyone has thought about turboing. And there's tons of different ways to do it, and I'm more than capable of doing any of them. I know that turbo offers the potential for higher levels of power, but I don't know what a good turbo would be to go with for a NA block. Should I stick with the stock turbo setup, just adapated for my block, or should I be looking at an aftermarket turbo? I will admit that my knowledge of different turbo types is almost non-existant. I recognize the names of different types, but i really don't understand the technical differences.

With this setup, I'm willing to sacrifice some lower end power for an easier achevement of my 225-250 RWHP goal, but I'm trying to avoid that laggy feeling. I'll probably run about the same boost level (6-8 PSI), at least intially.

So: Honest, no bullshit assesment: Will a supercharger cost-effectively reach my goal for about the same price as a turbo? I'm not looking for anything too crazy yet, and if I were to build up a monster, it would be a big turbo'd beast on a separate engine.. I'm looking for a fun winter project for a few grand.

Thanks for any creative insite. Again, I'm not looking for a NA to forced induction tutorial or anything, i've read tons of them, juat an honest assesment of the situation.

SonicRaT

iTrader: (6)

Mmmk, for 250rwhp figure this:

Obviously a new clutch
injectors, for that i'd go with 550/720's
SAFC (i'd also suggest getting a TII setup as far as ECU/AFM/ETCU goes, but you can run on the NA if you like)
Walbro pump
Exhaust (obviously)

Now... an Eaton M90 isn't quite a good charger, expect to rebuild whichever one you get, then comes the fabbing of pulleys/idlers/belts/etc, (expect $150 at the absolute lowest just for that). Yes, it will hit 250rwhp, @ around 9psi or so, expect a decent intercooler though, and possibly some charger porting, and perhaps even an upgraded outlet/inlet plenum. It's not exactly the route I suggest, since i HATE the M90, it's horribly inefficient. If you really want a super, go the twin-screw route, such as 88IntegraLS, or find an old paxton kit.

Turbo, alas, is better. You can size it so you have damn near just as much torque as a supercharger, and more power. Yes, low-end will suck (but honestly, how much are you really under 3k rpm?. For 250hp, you could EASILY get there with a BNR turbo, and have the ability to go a lot further if you chose.

either can be done for the price range, it's just up to what you want to do.

BklynRX7

From what ive read, seen and researched for ym own interest I woudl say that turbo chargers are the easier, and have a much better cost/benefit ratio than superchargers by far.

I mean, turbo charging a n/a, including ems is costing me under $1000. Ill be pushing approx 10psi, hopefully more and making hopefully close to 300hp. Now compare that to a decent custom twin screw setup or god forbid the $3000+ carb only commercial kits and youll see that youll be spending alot more for quite a bit less. Sure youll be unique but how often do people who speed past you and laugh stop at the light and give you props for being unique.

The only thing lacking with a turbo is a low end. I have driven a SC car before and you can feel the pull all the way through to redline. too bad it was a v8 so the powerband was come and gone in a blink (scoffs at 6k redline). Felt good though.

Im no expert, im just sharing what I came up with when I first pondered forced induction

WonkoTheSane

iTrader: (2)

Hmm... That's what I was sort of leaning towards... Thanks for confiming it, guys. Where is the best place to start pricing BNR turbos from?

Tech_Greek

The turbo to N/A really isn't that bad if you've got a real job, I live with my parents so mines going through rather quickly...SonicRAT's awesome and will actually be helping me with this skittle and has been for the past month.

I'm going to be using an S4 TII Turbo, Manifold, etc...Yes not the best turbo BUT I got it for horribly cheap and it has no play from what I can tell so it's perfect for my swap, a BNR Upgrade is in the future...

Superchargers are fun...but terribly expensive on Rotarys imho...but that's my 2 cents from what I've gathered...a turbo's just as nice and gives a better feel that the rotarys known for anyways (that 4k-8k rpm pulls you to your seat instead of breaking your neck and drive train on take off! )

- Tech

SpiffyD

a stage 3 BNR turbo goes for about 750-800 on rx7store.net i think? pending on what stage you want though

iSP33D-for-J3SUS

Turbo.

I asked the same thing awhile back: https://www.rx7club.com/2nd-generation-specific-1986-1992-17/centrifugal-supercharger-vs-turbocharger-419397/

iSP33D-for-J3SUS

WonkoTheSane

iTrader: (2)

Yeah, I'm thinking that I'll just go with TII manifolds (ported and spaced appropriately, of course), but since I finally have some cash, i'm going to do this right the first time Although I'm thinking about going to two indivdual throttlebodies.. I forget the brand, cause i"m pretty tired, but I was thinking about eliminating the stock mazda TB and going straight through those....

88IntegraLS

The only supercharger worth putting on is a lysholm type or centrifugal, IMO. Roots types aren't worth the trouble (adding a supercharger is very time consuming) - power gain versus detonation threat is small with roots type.

I'd turbo it unless you really want a challenge. I supercharged mine for the sake of supercharging it, I absolutely didn't want the turbo power response and sound. If all you want is performance, turbo will pretty much always be better IMO on a rotary at least. Considering there are ready made turbo manifolds out there, doing a turbo swap looks much easier than adding a lysholm charger, which is the only type that can compete with turbo's torque curve.

Summary: one more vote for turbo, unless you're totally in love with supercharging.

Tech_Greek

A turbo is defintley bolt on so far, no real hard stuff.

Supercharger here I come custom fabbing lol

k-rok

im doing it right now, and i raise the BS flag on this comment

Tech_Greek

lol how so, it's bolt on for me, everything's come off a TII...

RETed

M90 sucks.
Getting it to break 200 at the wheels will take a lot more time, trouble, and money - i.e. intercooling.

Any of the centrigual units is EXPENSIVE.

Turbos are proven and relatively cheaper, especially if you start to look at that SSautoCRAP / Master Power stuff.

All the SC dyno's I've seen don't show a low end advantage - maybe cause the time element is not a factor on the dyno charts?
Garret GT35R on a 13B is a lot of fun and power - it's costly though.

Cheap will bite you in the ***.
How much are you willing to spend?


-Ted

k-rok

are you using TII intake and stuff?

Tech_Greek

Yep

WonkoTheSane

iTrader: (2)

I don't have a set budget right now.. I'm thinking that I'll probably try to keep it under $4000, which will allow me to get the suspension bits that I'm missing, too.

Now, keep in mind with that price that I'm an engineer with a full CNC shop at my disposal

What's the average cost of a GT35R?

SonicRaT

iTrader: (6)

$1300, toss in about $400-500 for a decent T3 manifold (unless you adapt to a cast manifold, in which case think $300ish), then a good wastegate (again, another $400), so damn near half your budgets gone just off the turbo! That's the turbo I had/was going to use, I've since picked up a GT42R, but I'm starting to think it's a hair too big... Oh, and you're absolutely gonna need an EMS, and a TII driveline for that thing... They can support ~500rwhp, a bit past your goals

WonkoTheSane

iTrader: (2)

I figure the MegaSquirt should be a fine EMS for me... and the TII driveline was one reason that I wanted to stay at a more conservative 250HP.. Well, that and I didn't really budget for a 500 HP monster, as nice as that would be, I think that's overkill..

That's why I'm thinking your suggestion of the BNR might be more within my budget/requirements..