hyperion

iTrader: (2)

All,

First, I want to be clear that I mean no disrespect to anyone on the forum, but I've been pouring over the archives on the perennial discussion of single vs twins debate and I've found the subject of lag a bit lacking. Here is where I am:

I've got a '94 R2. The stock motor is doing okay, and the stock twins are blowing a bit more oil than they should. I am think about a rebuild path. I am looking for a streetable car in the 400 RWHP area. For this, the best choices seem to be:

Singles: GT 35/40, Apex'i RX6
Twins: BNR stage 3, M2

So here is my delimma: I've read about a billion dyno sheets and comparisons, but those don't tell the story I am interested in. Making boost at 3200 RPM is not the same thing as good throttle response. Dyno charts (usually) can't tell you about responsiveness. 3rd gear pulls put much more load on the car than 1st and 2nd gear. Torque vs. RPM says nothing about Torque vs. time.

I've been running around with a high-boost single turbo car (not an FD) for a while and I am really getting to the point where I believe that throttle response is the most important thing in life. This might not be true on the racetrack (big sweepers, and you know each turn before you get there) or the drag strip but it *is* true for most street driving when you need to react quickly. Just look at how WRC cars are set up: high compression ratio for better response.

I am unwilling to sacrifice responsiveness for big power. I know that it's possible to get ~350RWHP on the stock twins with extensive upgrades to everything else. So, finally, here is my question:

To those who have actually done a turbo change firsthand, are there *any* turbo upgrades that match (or better) the throttle response of the stock twins across the entire RPM range? I love the way that you can just stab at the pedal to get the car to rotate in a tight corner--this is what I want to preserve. I want to have decent pickup off the line without slipping the clutch. For a turbo car, the stock system has excellent driveability. Let's keep it that way.

I've heard that the BNRs in parallel have great response. But how great? As good as the stock twins? Don't show me a dyno plot--tell me that you've compared it back to back yourself. This is a seat-of-the-pants kind of thing (unless you've done a bunch of low-gear dyno runs plotted against time instead of max torque). Are the M2's better? I'll sacrifice the top 30HP that I only see 5% of the time for extra response that I use every time I get into the throttle.

What about the 35/40 or RX6? Or something I haven't mentioned? It's all about the throttle response--stock twins or better! I'm looking for guidance. Thanks for your time and indulgence,

-ch

Kento

I'm bumping this because I'd like some answers to his questions as well... well, hopefully, anyway...

Wargasm

This has been gone over a million times and I think the answer is that the stock twins or modified twins are the BEST, with small singles such as the RX-6 and T04E close behind.

Brian

maxpesce

In ARTGUY's absence I'll say that (imho) Sequential Twins will give the best throttle response and that of the available twins the M2 ball bearing units are possibly the best for quick response.
for each setup (stock, 99+ RZ, M2, BNR stage2/3) Non Sequential will be less responsive than Sequential

ZoomZoom

iTrader: (2)

Although I personally like a single turbo on and FD for not only its unbeatable power potential but for its simplicity. Like many Stock twin owners I had the ever present boost gremlins. Not only do I make more power with a single turbo but I never have any fluctuation in boost. I always get whatever I dial in. I also was sceptical about losing low end for top end performance and really did alot of research trying to find the best solution for my problem. First of all I knew i didnt want a huge turbo. Second I wanted to remedy my turbo control issues and really wanted to simplify the stock sequential system. Going non-sequential was an option but it has even more lag than a single turbo. I wasnt really held back by budget so i went with what i thought would be best. A Mid sized ball bearing single turbo. I have the GT3540 with the 1.06 A/R. It has a bit of lag, but sparing you a dyno sheet it makes only 5 hp less up to 3300 rpms and then really buries the stock twins all the way up to redline. I dont miss my twins even in stoplight to stoplight driving. If you do decide you want to keep a more stock car then it gets no better than Mazda Stock 1999 model Twins. These make 25 more HP at the same boost levels on the same motor. They can be run at higher boost levels than the stock 93-95 twins as well. They are a more efficient new design and are proven well beyond hybrid frankestien turbos like BNR's and M2's twins. Keep in mind price and what your getting in return. Both BNR's and M2's require a core. The Mazda 99 spec twins can be found with low miles from some sources here and will provide you with your goal of 400rwhp. Thats about thier limit so you may or may not reach 400. A single turbo will assure that you do it and at a lower boost pressure than twins. The Apexi RX-6 isnt really capable of 400 RWHP but it has great response as its smaller and ball bearing. The Garrett GT3540 will make 400 RWHP easliy. Also there is a smaller Model that would probably spool up even faster and still make 400hp for you. It has I believe a .87 A/R. This might be even a better choice for you. As far as anything else your likely going to have considerable lag (compared to twins) or not be able to reach your HP goals. Try to score a ride in a car with some of these set-ups. That will definatly make up your mind for you.

KevinK2

"To those who have actually done a turbo change firsthand, are there *any* turbo upgrades that match (or better) the throttle response of the stock twins across the entire RPM range?"

If you insist on equal or better response below 3k-3.5K rpm, then you must stay sequential twins ... search about 99 spec, M2, and BNR stg2 (not sure stg3 is seq). Early transition with the PFC will help save some torque loss at 4.5-5k.

hyperion

iTrader: (2)

Great responses, everyone. This is helping quite a bit. So if response is to be maintained, then I've got to stay sequential. It's kind of a shame, as it appears clear that the big gains on the stock configuration come from deleting the sequential components. But I understand the tradeoff.

Regarding upgraded sequential setups, is the M2 just a bearing change? Or does it have upgraded housings like the BNR? And on a related note, are the 99-spec RZ's the ultimate way to go? I'd love to hear more opinions.

Thanks,

-ch

hyperion

iTrader: (2)

Oh, and let's find out if anyone is running the BNR Stage 3's in sequential!...

-ch

Swolbynos

Where is a good place to find the 99 spec turbos?

rynberg

Jesse Lau at www.4jspec.com He's a stand-up guy.

Or you could race just two auto-x's a year and get the Mazda Motorsports (now Mazdaspeed) discounts.....

maxpesce

The M2's use completly NEW Garrett Dual Ball Bearing cartridges mounted to a remachined stock exhaust housing,
The BNR's use stock Hitachi cartridges w/ updated dynamic oil seals and new larger secondary compressor wheels on the stage 2's (both compressors w/ Stage 3)

artguy

thanks max...ya saved me some breath.

the m2s have two wheel sizes available..both are larger than stock...i actually had mine customized and went with a larger than stock primary and the biggest possible secondary that would fit in the housing. that kind of response is how i prefer to drive my car...freeway bursts and off the line throttle response.

the m2s are far better than stock when it comes to the throttle response. I was very very happy with that.

the bnrs have an overall larger powerband running non sequential...but below 4000 rpms the m2s have them beat on response..something like 40lbs of tq and 25rwhp difference at 3000 rpms...granted Id lose in the quarter mile to someone like stephens monster machine...around town its a lot of fun.

throttle response is immediate...especially compared to stock twins....or the stockers running non seq.

the garrett cartridges are gt30 ballistics...dual ball bearing...they came completely cherry and take a beating daily. no leaks...no problems. be sure to get the restrictor pills (included in the price) if you run them...do not run them without the pills...they need less oil than the stock shaft bearing twins.


good luck


j

hyperion

iTrader: (2)

j

Hmm, your setup looks about 15HP shy of what I'm hoping for. With the DP/MP and M2 turbos, have you had any issues with boost spikes or creep? There seems to be a bunch of problems on the board regarding creep with the twins, so I am interested to see how you've solved this problem. I'd like to retain the PFC boost control...

Would you expect the BNR stage 2's to perform similar to the M2's? Stephen's car is running the stage 3's which are bigger, clipped turbines.

Thanks,

-ch

rynberg

You don't have boost creep when you are running 16+ psi......

BTW, why do so many people prefer the PFC for boost control? Any aftermarket controller will give a more consistent response and work better. Just my 0.02

artguy

the m2 has better throttle response due to the ball bearing design. plain and simple

the m2s and bnrs running sequential compare well...the m2 set gets the jump early but the bnrs pull pretty even when comparing kwiks and my dyno sheets....you cant compare stephens non seq to mine really...its two different beasts...he sacrefices some down low response for that wide powerband and smooth delivery that non seq brings. his car is a beast.

my car is not finished tuning...dig up my dyno sheets and you will see...past 5800 rpms it is running pig rich and you can see the power falloff...i am flying out BADOG to do some tuning with me to finish it up in july. I should hit the 400 mark with another round or two on the dyno.

the stage three wheels and the m2 set with the larger wheels are of similar diameter..bout as big as will fit...literally...the wheel design is different...the bnrs are mitsubishi (boosted7 pointed this out i believe) and the m2s are Garrett Gt30s.

if you are wanting to run seq the m2 set is your option...if you dont have the cash for it..yer best bet is to go non seq with the stage threes and give up some of that response for that big *** power curve.

i dont have issues with spiking...or creep...Im using the pfc to control boost. peak boost will vary slightly...i have it set to 1.10 bar for the high setting and the most I have seen it hit is 1.13 bar.

i was using the profec b...Im selling it as Im having success with the pfc....though early on I did not and picked up the profec.


j

hyperion

iTrader: (2)

j,

More great info. I want to stick with the PFC for simplicity--I don't need any more gagets in the cabin right now, so it's great to hear that you're seeing success there. When I get closer to tuning I might plead for a peek at your PFC maps just to get a good baseline for my car. Our setups will be similar, the primary difference being that I will be trying a V-mount configuration up front, and I am planning on retaining my high-flow cat.

Which, on a totally unrelated note, is a question I had: how bad is the smell with DP/MP combo? I would LOVE to sack the airpump, but I've heard that it makes your garage smell like hell. :P

But back to the question at hand: it sounds like M2 with big compressors is a great (if expensive) combo, and just what I'm looking for. I am also assuming that if I broke down later and converted to non-seq that I would see performance similar to the BNR stage 3's?

Anyway, thanks for the great advice! Keep it coming,

-ch

artguy

you wont want to use my maps unless you go with the hybrid setup Im experimenting with...all cars are different...i had another m2 fuel map on my pfc and it ran like ***...i tuned it myself after that.

the smell is bad...it stinks.

good luck

j

hyperion

iTrader: (2)

j,

Edited: I found your dyno sheets. Very cool. How much did your hybrid conversion cost you?

-ch

artguy

i got lucky....didnt cost me a thing...it was an experiment...if it failed Id end up with junk...if it didnt Id end up with response and high end power gains....it definitely didnt fail...but there were some questions about running two diff size turbos and having the stronger have "blow by" back to the primary....once we finish tuning we will have a better idea of what the results are...Id have definitely had more power running both compressors large...but i must have response...cant go without it...so thus the experiment.

i didnt ever figure out how the cosmo twins (diff size compressors) get away with the idea..they also have a Y pipe right? perhaps there is a valve or something...i dont know...but my car feels damn good so I cant complain.

I do still want to see it put down 400 though. will know in the end of july once it goes back on the dyno with the crew out here. Im selling my profec b and my J&S knock Safeguard and picking up ignition and tires instead.

j

ZoomZoom

iTrader: (2)

Seeing you live in California I dont see how you would be able to rid yourself of the airpump. This would also limit your turbo choices when it comes to single turbo upgrades as very few allow you to retain the airpump. The smell and Noise are very prominent when deleting the emissions gear. As far as your horsepower goals 15 hp would'nt be felt in the seat of the pants meter. But you free up alot of power when ridding yourself of the emissions crap. Tuning is the key to making power. There are alot of ways to skin your cat. Twins making 400 RWHP is a challenge but can be achieved. 400RWHP with a single turbo is expected and is fairly easy to attain reliably. 400 RWHP on twins make more heat than a single turbo so you have a few downsides with intake temps as well as having those turbos red hot bolted right to the side of the motor. It has its negative effects. Weigh whats most important and make your decision.

hyperion

iTrader: (2)

j,

With regards to asymmetrical turbo sizes and "blow by" to the weaker turbo, I think I can shed some light on the subject. First, it's useful to note that even identical twin parallel turbos will not have the same performance characteristics. I bet if you carefully tested a twin parallel system (such as a 911TT) you'd see a 2-3% variation from one bank to the next.

So why don't these cars, and those with higher asymmetry (like your FD with modified M2's) see one turbo stalling the compressor of the other and pushing air back through the intake? Well, it has to do with a simple fact of fluid flow--namely, that there is no flow without a pressure differential, and that fluids (air, in this case) always flow to the point of lowest pressure.

Both turbos in the system are regulated to the same pressure, but let's say that there is a slight difference in pressure between the smaller and larger turbo of about 1psi. Now, if the throttle were completely closed, the larger turbo would indeed (slowly) stall the smaller compressor and drive air backward and out the intake. (of course, as soon as the throttle closes the bypass/blow-off valve releases and the turbos lose their exhaust energy.)

BUT, when the throttle is open the engine does not present a "closed volume" to the turbochargers. On the contrary, the engine actually presents an alternating vacuum and closed volume as the ports open and close. This, by the way, creates the intake pulses that companies like Porsche use to increase volumetric efficiency by varying the length (and therefore the resonance) of the intake tract.

But I digress. The point is that even if the larger turbo runs at, say, 17psi while the smaller at 16psi, the engine might present only 5 psi (average) of resistance. Both turbos will drive 100% of their flow to the point of lowest pressure (the intake).

A great way to visualize this is to think about the following: cut two holes in a cardboard box--you blow into one hole while your friend blows into the other. If the box is sealed tightly, then the stronger of the two will force air back into the weaker. But cut a third hole in the box and all the air will rush out that hole, and neither will feel any "blow back". Of course, as you progressively cover the third hole with your hand, at some point there will be blow back, but it would have to be almost completely closed. To connect the analogy to real life, at WOT the hole in the box is almost completely open.

So I wouldn't worry about your setup at all. You might run into problems if the differential gets too big, but I don't think you're even close right now.

-ch