coltboostin

iTrader: (1)

Have you even come near to maxing out your current set up?

fdracer

you are misinformed about the surging on those tt cars. what you've seen is a common problem with big twins, which is often misconstrued as surge. the turbos are actually fighting each other. boost pressure is not static flow, it comes in pressure pulses. picture the pressure pulses as sine waves and you'll realize that at certain frequencies flow from one turbo will be at peak amplitude and will meet flow from the other turbo at it's trough at the point where the two tracks merge. a portion of flow from one turbo (at positive pressure) will move back up the intake track of the second (at negative pressure) causing it to slightly surge, i.e. backspin. this goes back and forth between the 2 turbos, which is manifested by a sort of shucking sound which most can hear on big twin cars. this phenomena of conflicting pressure pulses is exacerbated as you go with bigger and bigger turbos.

there are alot of ways to alleviate this, but it sounds like you're not technically adept enough to run big twins at this point in time. save yourself the headache and either go with smaller twins or a big single or you'll have a lot of driveability issues, plus you'll probably blow your turbos.

Marcel Burkett

Nope , cant do so if the exhausts are too small .

Well this one is COMPLETELY NEW ! ,I honestly dont know how to respond !!............ need to get more technically adept !!

Howard Coleman

iTrader: (6)

i considered fdracer's concern prior to designing my twin setup...

i digitally monitor exhaust backpressure and do note that it is clearly in impulses... (of course---- power strokes out the exhaust)

this may manifest itself in an uneven spinning of the turbo mainshaft and compressor wheel: result impulsed compressor dynamics. obviously it is a question of degree.

having 12,000 miles on my twins and making over 500 (not totally tuned) hp i can say that neither surge or any type of interplay between the turbos has been an issue. i hear no weird noises other than about 80 plus pounds per minute wizzing into my engine at 18 psi.

as to the surge issue Marcel, it is really all about the left line on the map and two 35r turbos should work o k. they are not much different than what i run surge wise. i have no surge.

just make sure you have a different gearbox, rearend and axles as you will shred all 3 if you get it tuned.

bobby freeman did have surge problems. that was because he initially ran HT300s. they have a really more eastward left side line. he is now, or last i spoke to him, running HT200s which should work.

good luck to you whatever you decide,

howard

Howard Coleman

iTrader: (6)

oh, one other thing... at 800 rwhp your E shaft will deflect and your rotors will gall your endplates so you will need a center main bearing. someone in australia does the mod.

BTW, i am not kidding.

howard

dubulup

Good God...never have I been happier that I only have money for one turbocharger at a time. the list "could" never end

Marcel Burkett

**** , this comment ^^ was meant for this vv ;

Marcel Burkett

But why would I make 800+ Hp with twin 35's ? don't we see 1000- 1300 hp + capable turbos make 600 to 680 rwhp at around 30 psi boost ? I would much prefer to make the power at lower boost , so volume is important , but 800 ! I doubt it .

GoodfellaFD3S

iTrader: (213)

Sounds to me like you might want to think about adding another engine rotor

mr2foryou

I agree, another rotor and twin 35Rs or even 40Rs would be nice.
Either way, good luck with whatever you decide. Honestly I would say stick with the 13B and do a GT47R. I am seriously contemplating getting Sean to make me a GT47R kit this year.

Dee E.

GoodfellaFD3S

iTrader: (213)

The 40R doesnt have enough pull for youat 15 psi?

In 40 degree ambient temps about a month ago, my 500R felt so strong at 15 psi on 1st/2nd/3rd gear redline pulls, I knew that I was finally done. If the car ever needs to be any faster, I'll just turn up the boost and run c16

CarbonR1

iTrader: (2)

I am not an "authority" nor am I a "highly respected forum member, ie 3000posts" but it seems like there is a lot of stupid forum information going down on this thread.

I see such poorly matched turbos to applications here, that it makes me wonder if anyone cares about what their engine is doing before 7000RPM.

I mean, a GT47R kit?? Are you kidding me? Yea if your target boost was 50psi @8000RPM, that'd be a good choice, but something tells me you don't want that much boost.

The simple idea that is being overlooked is that you want the smallest, yes smallest! turbo that is capable of efficiently flowing your air flow/pressure at peak load/RPM when your air flow requirement is the greatest. If you want to flow a 13B-REW at max of 25psi at 8000RPm, then you want the smallest turbo that can flow that volumetric flow rate (given a bunch of parameters like volumetric efficiency). Anything more would be overkill and would greatly sacrifice response and low end power.

The hardest thing about matching a small displacement/high revving/high power engine is that your flow needs are vastly different at low RPMs and high RPM/high load. generally to achieve this match with a single turbo, you will undoubtedly sacrifice low end and response.

CarbonR1

iTrader: (2)

Do you mind explaining this in more detail of how you came about this information?

Howard Coleman

iTrader: (6)

i do agree that the way to size a turbo system is to settle on the power you want to make and then run turbos that peak, plus maybe 10% at that airflow. for instance two GT35s would make 120 pounds per minute. that works out to 904 rw rotary hp.

the fd trans is good for 500 rwhp if babied a bit. the rear end and axles around that level too. the E shaft is good for 750.

of course traction w 335s at 24 psi is non-existent over 600 rwhp in virtually any gear.

so take your pick of poison here.

my point however is that if you want to make 600 rwhp then you shouldn't be trying to power compressors that can make 900. it will cost you everywhere under 600 hp.
it costs hp to swing un-necessarily larger wheels.

i do agree w CarbonR1 on the cost of running too much wheel.

OTOH, if you want to make 900 hp... that's cool too as long as you understand what goes along w the turbos.

howard coleman.

matts85rx7

One large turbo would be better, a large gt42 ball bearing would most likely lag the same, and hit 3 times as hard.

mr2foryou

I mean, a GT47R kit?? Are you kidding me? Yea if your target boost was 50psi @8000RPM, that'd be a good choice, but something tells me you don't want that much boost.

Not to undermind anything that you may be saying, but if ErnieT is making the boost and power he is making at said rpms; then I think I could live with the spool of the smallest(if there is such a thing) GT47R with the same portwork in the motor and maybe even a small shot of nitrous to help it spool a little sooner. I mean, I don't really think it would be so terrible. I would certainly be planning on running 30+psi on c16.

It might not work out, but I wouldn't mind trying. I know that I could sell the turbo to one of the supra guys on supraforums if it don't work out and just get a 42R. I would kind of just like the in your face factor when I pop the hood too.

PS. Steve Kan is running a GT47 turbo on his drag car. Not with a 20b either.

Dee E.

mr2foryou

Yes, my car does have enough pull. But I am not even running 15psi right now. Only between 11-12 because of my leading coil. I know on around 28-30psi and full tank of c16, it will probably make me **** my pants. But only time will tell. I think I am going back for my final tune in a month and see what Ray(PFS) can get out of it.

Dee E.

mirabile

Very well put.

Marcel Burkett

Well I did some more checking and it turns out that the 35's are physically larger than the 30's , so I guess I'll be going with a pair GT3076's so that it would be a direct "exchange" with the 71's and I wouldn't have to change my manifold or intercooler piping.
They should do the job easily ! I remember the pink TII from Japan with a pair of HKS 3037S turbos (that are the exact same as the 3076's) and a bridged motor making 600+ RWHP (I think) and running in the 9's , I also came across a for sale add for a british FD using the same turbos , claiming to be making 900 RWHP and running low 9's .
I assume that since the 76's use the same turbine section as the 71's , I'll need to step up the housing size to .86 , but how do you think the 1.02 a/r would work ? but what if I can have a custom turbo done up using the 35R turbine section (68mm) with the 76R compressor , I should benefit from the larger turbine , but how do you think the spool would be ?

GoodfellaFD3S

iTrader: (213)

In my opinion, you need to decide if you have a street car or a drag car. I've driven Steve's car on a few occasions, and while it's very fast, it's not a reliable, streetable car. He has like 4 other FDs as well, so the drag car pretty much sits and collects dust. For the longest time he ran a 66mm turbo, comparable to your 40R. If he has a GT47 sitting on the shelf it's news to me, but I don't believe the car has ever made a pass or a pull with that big of a turbo.

crispeed

Never had that problem. Plus I know of a lot of people at that power levels and higher still on the stock stuff.
It's not the horsepower that will cause the shaft to deflect.

Zero R

iTrader: (1)

35R's are no good for 25psi on a well ported rotary you will be a bit off the rightside of the map. I'm not guessing either J/k, if your saying maybe a 40R that would be different. 35R's are great for 20psi or less after that they are too inefficient or there are better choices.

-S-

Marcel Burkett

If used in a dual configuration ? ......stop teasing and tell us more !

CarbonR1

iTrader: (2)

Hence 35- 40 frame size I mentioned.

Howard Coleman

iTrader: (6)

you are definitely on the wrong side of the curve above 20 psi w a gt35r. OTOH, you can make 60 pounds of air at 65% efficiency at 20 psi times 2 turbos if spinnable will make your 900 rwhp.

the operative word in the title of this thread is "crazy" so we aren't off topic anyway.

hc