Marshall

Hey guys,
I was looking at the powerbands of stock and modded non sequential twins versus singles over on Brian's site http://www.catenet.net/dyno.php

I was doing comparisons between Boostn7's and SPOAutos cars against many of the T-78, GT3540, and T04S cars. Though the single usually did better in peak numbers, I was astounded by the shape of the power curves. The non sequential stock/modded twins just blew them away until very high rev ranges where the single would barely peak on by. The track times from some of these cars backs this up as well -the twin cars are running as fast as many singles with 50 hp more.

So, can anyone explain why the restrictive stock exhaust manifold twins have a much nicer plateau shaped power curve and alot of these singles are pretty much linear?

matty

uh oh

Marshall

Here is an example:
http://www.catenet.net/graph.php?car...1&SUBMIT=GRAPH

All three good running cars. Not mean as a flame, I'm just curious where the upper mid mange boost comes from.

matty

when drag racing, you are above 6k rpms more so then u are below it, so i would thing that the singles that we are talking about are faster then the twins.

rynberg

Marshall, you just discovered why so many otherwise modded cars stick with the twins. As I have pointed out (in the single turbo forum no less!), most singles at 15 psi don't make the same power as the twins at 10 psi until about 3500 rpm. The bigger turbos are even worse, as I've seen T-78s not make the same power until 4000 rpm. That's way too long for me, especially since mine is a daily driver. FWIW, my mechanic had a full T-78 set-up, got sick of no low-end, and went back to the twins -- 99 RZs.

apneablue

I am getting close to an rebuild and will upgrade the turbos at the same time...Ihave been leaning towards upgraded twins...this thread is making me lean that much more on the twin side than single... ...

Can someone explain to me why running the BNRs parallel is better than running them sequential?

cover8

The stage threes spool too fast for sequential control...spikes would probably be uncontrollable.

Marshall

Yeah -but look closer and you'll see some not making the same power until 6600 rpm! I would think getting rid of all the 'restrictive' exhaust manifold stuff would show gains everywhere, but it just doesn't happen.

As for shift points, the 1-2 and 2-3 shifted at 7500-8000 rpm will put you into to low mid 5000 range -meaning some of these single cars would fall back and pull even in 2nd and 3rd in a drag race.

rynberg

Well, I was referring to stock twins at 10 psi, not upgraded twins running at 15 psi. But I fully agree with your points. To me, a larger single just doesn't have acceptable low-end power for daily driving. As a weekend fun car or for road racing, I can certainly see a smaller single (TO4E or Apexi RX6) being very enjoyable.

The real advantages to going single turbo are simplicity, more room in the engine compartment, and lower intake air temperatures at high boost.

sexxy7

Marshall, that's cool as hell!! Thanks for posting the link!

Marshall

Thank Brian (Wargasm on here)! He did an awesome job with the site. I'm just thinking out loud

artguy

who told you this?

I run ball bearing twins and get full boost by 2800rpms...i have no issues with uncontrollable spiking.


its just not true.



j


the single guys like the simplicity...the lower heat...the space in the engine bay...etc....

the modified twin crowd want more low end and daily drivability than the singles offer....though the rx6 seems decent enuff that way....going single also costs more cash in most cases.

a lot of the single guys want more than the twins can give them as far as peak power goes. they are a die hard crowd. For every one that would switch back there seems to be twenty that would never switch back to the twins.

it will be interesting to see how the ASPEC twins work out. Those should put down a lot more power than the sets currently on the market.

I want to see someone run the stage 3 bnrs sequentially. though..i doubt anyone will do it.


personally...i like to tear around town...most of my driving happens on the first turbo...i like the response...the other way i like to play is on the freeway...just drop it down and go...i have decent enough power gains from 4500 and up to rock most cars on the street...which is good enough for me...well at least til i run across spoautos one day and get beat at that game. around town though i have been very happy with the m2 set....ive run it seq and non seq...and i will always stay sequential.


j

LAracer

I'm pretty sure that the non-seq twins give a broader power band than a single because it takes less energy (i.e. less rpms) to spool 2 small turbos than it does to spool one big turbo. The quicker a turbo spools, the better the low end power and the wider the power band. Three smaller turbos would spool even quicker, but then the restriction cause by complicating the manifold might kill any benefit from the quick spool. I think at two turbos we're pretty close to the point of diminishing returns.

Marshall

Yeah, I can't wait to see the A-spec twin kit run. A nice fat powerband and a 450+ peak should net some 130 mph passes.

mb7

All this talk about the modded twins is making want mine back bad!!! Come on Bryan ready for them stage 3's

mb7

Check out the curve of this Rx-6 and the BNR Stage 3's.
http://www.catenet.net/graph.php?car...1&SUBMIT=GRAPH
They are alomst identical. That Rx-6 looks like it is tuned good as hell. Maybe I'll get one of those next, after I see how much tuning is left in the BNR 3's

Joker

j-spec twins

apexkw

rx6 baby....plenty of low end power....top end leaves some people wanting but i like it. its not crazy power like the big singles, but its got enough *** to kill most cars. the drivability is nice two. i have full boost @ 3000rpms.

|aFk| LiMiTz

what is this a spec twin kit of which you speak? Sounds familiar and sounds nice..I am thinking about upgrading..got a price quote? Thanks

Joker

same as the type rs/rz japan spec fd twins rynberg posted about. boosts at 2500 rpm making for very sensitive throttle response. sr motorsports used to sell the type rs/rz j-spec twins brand new for $2599, but i think they were on clearance late last year. the new price is probably closer to $2900, $3500?

ttpowerd

Its not finished yet, or so I hear....



https://www.rx7club.com/forum/showth...hreadid=139378

es

I am one of those single converts that would NEVER go back! Most of the guys around here that I know have singles, & wouldn't go back.

I used to love the seq twin setup when the car was a daily driver, but either way that first turbo wouldn't give enough to pull from a stock GT Mustang out of 3K RPM. The quick spool just wouldn't make up for the torque disadvantage. Once the #2 came online it would all be over, but by that time (4500 RPM) my GT3540 is quickly becoming more impressive!

The Aspec twins do look like a cool setup, & should provide a very impressive band, but at the cost of cluttering up the engine bay again. And my whole point is that when you want power you put the car in a gear to make power regardless.

redrotorR1

The ASPEC twins don't look very sequential. In fact, if that picture is correct, there's no way to run them sequentially. So, no, they are not the same as the RS/RZ twins. I have the RZ's and I absolutely love them. Boost comes on at ~2200 rpm, full boost by 2500 rpm. Running 13lbs of boost on my setup ... it feels faster than some of the single setups that I've driven/ridden in. But, not nearly the top-end pull as some of the bigger singles that I've ridden in.

Different strokes for different folks. I auto-x and time trial. I need low-end response. And straightline acceleration is kinda boring, IMHO. Taking turns super fast ... now that excites me. On the other hand, I've done some fun runs with a T-88 RX-7 .... he destroyed me. Not walked, but RAN away from me at 90-130mph. Stoopid fast.

Back on topic, the design of a turbo requires proper balancing. With larger singles, the compressor wheel is so big that a larger turbine wheel MUST be used; hence the longer lag. But, if you want a real definitive look at the difference in power between single vs. twin turbo, look at the area under the curve. That should tell you something about how much power each setup makes.

artguy

red rotor...do you have dyno sheets you can post....id like to see your low end power band.


the aspec twins are NON sequential...good observation there. we are on the same page with what we want out of a car...zoom zoom...more than BLAST OFF at 80mph. too bad we have the cake and eat it too.




j

SPOautos

Yea, but thats not a very good comparison between twins and GT35/40......what would it be like racing a Mustan at 3K with the 35/40.....prob about like it was or worse than twins. You should have races the Stang at 4500 or higher no matter what turbo you have.

BTW guys....check out this comparo graph I was looking at yesterday......

http://www.catenet.net/graph.php?car...1&SUBMIT=GRAPH

Course maybe there were tuning issues involved with that T78, I dont know but its from RP so I figured it would be better than that.