How to go from a single turbo set-up to sequential twins?
 

I really don’t know how serious I am, but I'm thinking about going from my current single (GT3574) set-up to sequential BNR’s. I really miss the fun of the stock sequential system on the street and think the BNRs are a great option for fast spool and good power (close to, or over 400 rwhp).


What parts do I need take to go from a proper single-turbo set-up back to the sequential system (besides the BNRs obviously)? I don’t care about emissions, just the vacuum lines and solenoids that are necessary to get the sequential system up and running again.

search simplified sequential. you may want to look into a custom set of solenoids or a brand new set of OEM ones.

you will need at minimum:

charge control
charge relief
turbo control vacuum
turbo control pressure

you'll need to have wiring for this. if you cut up your harness that will be a problem. you'll need a form of boost control for the precontrol and wastegate actuators. you'll need to modify your intercooler piping and you'll need a new downpipe and exhaust modifications.

you will need to remove the blockoff plate for the rear turbo oil drain, and you'll have to make sure you have the oil and coolant lines

Who did your single turbo conversion?

This may be a first on this forum but I totally see where your coming from. Ive been down the big single rout before so theres a very good reason my current FD is staying twins this time.

Why not change to a smaller more responsive single? You probably wouldn't miss the twins as much if you had something like Apexi RX6.

Thanks for the reply's.

Thanks arghx, I'll search for simplified sequential and see what I come up with.

I've thought about that too. I've never driven in an RX6 FD, so I really have no reference for how it feels. New BNRs are pretty cheap (all things considered), and a used RX6 is hard to find and the kit is usually pricey.

This is my second FD and I bought it with the conversion. My previous FD had the twins then I went single on that one too. I'm sure I can bring the car to my local mechanic with a set of BNRs (JPR) and he can get it all sorted, but I am curious exactly what is needed as I will likely do the work myself.

Depending on how soon you're planning on doing this...

I have a pair of used (but pretty good condition) BNR's, and the old solenoid system that Rob Bailey (Saxyman) was putting out before he disappeared.

I'll be selling both of them when I return from Afghanistan this summer.

Well at what RPM do you get 10 psi?

The reason I ask it's because I have short piping, short manifold with a GT35R (T3 1.06 hot side) and I get 10 psi by 3200-3300 RPMs. Not as good as the sequential but I certainly don't miss it

It would certainly be easier to switch to a smaller, more responsive single. You have a T4 turbine housing with P trim turbine wheel. A T3 GT35 kit would definitely build boost more easily.

Good thing is most of the parts you'd need to go back to twins can be had quite cheaply. And, I'm sure you can easily sell your single turbo setup and come out money ahead.

One option if you're feeling enterprising is to buy a JDM long block off Ebay for around $1800 or so. Get all the turbo bits you need and then sell off the rest - you can easily make money on that deal, and get some other nice stuff for your car like a low-mileage tranny.

Basically, to just get the twins on, you'd need the turbos, manifold, oil and water lines, rear intake pipe, y-pipe, intake, and intercooler piping to go to your IC setup. You'd also need the stock BOV's unless you can re-use your current BOV. If you're going sequential, you'll need the sequential solenoids and make sure you can plug it all in to your harness, if the engine harness has been hacked up and the extra plugs removed you'd need a new harness.

It's a big job for sure. But, there's nothing like the response of stock twins :). Love mine!

Dale

Thats the idea :nod:. Ive been reading a few more threads on simplified sequential and this is certainly not looking like a simple job. I like the idea of buying a longblock for all the bits I may need and selling the rest.

Im not sure if my harness has all the conectors in place or not, when it warms up a bit outside I'll check. I know there is one or two open connectors, but I don't think they are all there. A new harness is probably a deal breaker for this idea, thats a little more work that I wanted to deal with. Maybe I'll let that decide whether to go forward on this or not.

Matt, keep in mind a lot of these JDM longblocks come with blown turbos, just to name one of the frequent problems with them.

Also, if you plan to road race the car in the future, twins aren't really the best option--- from the standpoint of longevity, reliability, and heat management.

If I were you I'd recommend a smaller single for the quick spool, along with lots of other little things to help response and keep the heat to a minimum. PM me, I'd be happy to chat w ya over the phone more about it :)

Post some links to the threads on simplified sequential that you've found informative. It would make this thread pretty useful for somebody going down the same road.

Thanks Rich, I'll give you a call if I start to take this more seriously.

Since I got ignored I'll ask again :) : At what rpm are you seeing 10 psi?

I honestly don't know. I'm seeing full boost (16psi) at 4300 rpms I think, maybe a little higher. I would guess 10psi hits at 4k +/- 100 rpms.

Hey if u r serious about going back to twins, I got allot of twins parts and soleniod plus I got the color diagram, I see u live NJ which means u r local you can feel free to come by look at the parts and make me and offer and take them, btw I also got a pettit blue pritend turbo I got back in 99 put 5 k miles and then I swap it for BNR stage 3 non seq step up, I am currently making 391 rwhp at 16 psi, and 7 psi 343 tune by ENZO, and I still got my air pump and power sterring working. pm
Khris

thanks for answering I was thinking that this may be a case of this 'may be good for you but not for me' kinda thing. yeah 4300 for 16 psi is quite a high threshold. My high boost is 15 psi and I see it by 3500. I think the easiest route is just to change the turbo as someone else suggested.

wow, that sounds very laggy. I think it would be much easier for you to just swap turbos. My 35r with the 1.06 t4 housing makes 10psi at 2800rpm. Also, Sean has said the BB version of your turbo spools as fast as a 35r, maybe you could just buy the chra?

That would certainly be an easier option. I'm still not ready to make a move but I appreciate the help.

This may seem like a dumb question to some of you but, is there a single turbo option that would equal or slightly exceed stock performance through the RPM range, i.e good low end and large enough to provide stock or slightly more than stock boost at the upper end? I just thought that maybe because of turbo technology improvements over the last 10-15 years something like that might exist. I know everybody is looking for more power than stock but is there a turbo that would still make 10-11 psi at the top end while spooling as fast as the stock primary. A good simple single for stock like performance. I realize that answer is probably no.

to4e

To the OP....

I would reconsider going back to twins. If you are single & you're not liking the "lag", then I would consider revising your setup. There are many things that can be done to make it all gravy & avoid the horrid mess that is the sequential system.

You can see my relative setup & numbers from my signature. I will tell you brother, I DO NOT have any complaints about lag. The thing spools almost as quick as the twins. In fact, it's barely noticeable. Builds boost FAST & hard. My car is solely a street machine and it does it VERY well. I am also using a MBC so I could likely gain a few 100 rpm spool time with a quality EBC.

The key is turbo size and spec, engine port, & intercooler setup. All of my parts match very well & I did it specifically to build a fast spooling street car without the heat & reliability issues of the twins.

Simple, smart, fun ;)

http://sphotos.ak.fbcdn.net/hphotos-...7_891470_n.jpg

if you really want response, you can go a little smaller than most people do. For example you don't have to get the 1.06 A/R GT35. They do have smaller hotsides that are more common on 4 cylinders.

A 57 trim To4E spools just as fast as the stock twins on a well built engine with a good tune, and doesn't run out at the higher rpms.

I bet the OP has an engine compression issue, I recently dynoed a stock port FD and had 22psi by 3400rpms!( 4th gear).
P trim 1.15 T4 GT35R

Why a compression issue?

low compression is possible (albeit not likely), but there are so many factors here. Besides the turbo itself, the exhaust manifold design, boost controller setup, intercooler setup, porting, and so many other things will affect spool.

Due to the time and trouble involved I really think you should switch to a turbo with a smaller T3 hotside first, and only if you aren't satisfied should you go down this route. That will give you the transient response you want. Then you can set up the boost controller to give you midrange punch by running higher boost in the low to mid range and letting it fall off in the mid to upper rpms where the engine is more prone to knock. This type of setup is very common on 4 cylinders (Evo, STi) making broad midrange torque.

moehler as you can already tell from this thread a boost threshold of 16 psi by 4300 RPMs is way out of the norm.

Here we are talking about BB, piping, port jobs, manifold designs, switching turbos, low compression engines... When in fact the largest contributor of spool time is the turbo itself (lol). Funny I just realized that we seem to be under the impression that you have a healthy turbo. As you stated yourself: you bought this FD with the conversion already done, meaning you don't know the history of your turbo. Shoot for all you know you could have a T-78 (No just joking ;) but I'm trying to make a point).

I'd say take out the turbo and have it inspected.

Let me get the car out and again verify the spool. It may be closer to 4k (it's definitely over 4k). There really is no evidence that the turbo has a problem, it really just has a large hotside, it's non ball bearing and is built more for top end than mid-range power. 4-4.3k makes sense for that kind of turbo (it put down 504 rwhp at 17.5 psi).

well shoot, there's your answer right there. No need to verify anything. Whenever you get around to changing out to a different turbo (if you do of course) come back and update this thread. As I'd love to hear your experience of a top end car vs a midrange one.

Low compression = slow spool, but 500rwhp @ 17psi indicates a healthy motor. Although there are a ton of dynos that rear stupid high. I would do a compression test to rule it out, takes all of 10 minutes...

You are using the same turbo I mentioned, but this one has a 1.15 and hits 15psi by 3k rpms...

Yeah on another dyno (but with old, bad plugs) it did 478 rwhp at 17.5 psi. I had a compression test last year and it was perfect. Hopefully it still is, but there is nothing that indicates otherwise.

I think I'll just switch to a smaller single turbo when I am ready to make a move. It actually is a lot of work to get back to the twins (and money since I want BNRs). Thanks for thehelp guys :icon_tup:

someone correct me if I'm wrong, but a gt35, especially at 17.5 psi, shouldn't be capable of making 500 whp. methinks you haz a bigger turbo.

It's a 3574...

Bump for update!

http://www.a-spectuning.com/html/products/gt3574.htm

Also, after reviewing my original post I forgot to add that I have a T3 35R.