Hey guys I am debating whether or not to go single. I understand the logic behind turbocharged engines and all that, but I like to be somewhat different. Now most of my friends are into the single turbo thing and I think that is cool as hell, but I am leaning towards upgraded "true" (non-sequential) twins. I'm just asking the question so feel free to help me out. What are the pros and cons on each, which has a better efficenecy, what uprgade kits are kick@$$. Lets lay it on the line.
Thanks

 

I'm having the same problem. Either upgraded twins, or go with a Rx-6/motec. From what i've heard the Rx=6 is great for its fast spooling, and claims to 400-450(?)rwhp. Thats the way i'm leaning right now, because of past problems with the vacuum lines. CJ

 

Personally, I like the idea of "Twin Turbo". Just like people associate RX7's with rotary engines (although some have dumped V8's in them), I associate twin turbos with them.

Even though you would probably get a heck of a lot more out of a single, I would go for the upgraded twins myself, but I'm not into dragging.

 

My main goal is to have good power. Plain and simple, I will drag my car if the oppurtunity presents itself, or when me and the boys decide to go to the strip. I would much more prefer to use the car on open track days and stuff with an air of road racing to it. But again I just want overall power, (not to be confused with mind blowing 710HP pulls, more like 450+HP at the ground. So to get there, would it be more cost effective to just upgrade the twins? Or incorporate a huge single? To tell you the truth I dont really know of too many upgrade kits for the twins, and are all singles HUGE? Maybe a not so large single can do it? Let me hear your input, thanks all.

 

I'm new at this, but has anyone done a large single turbo with a smaller helper turbo? What would be needed to complete this set up and would it be pratical? Is it considered a single or twin or none of the above?

Thanks

 

M2 sells upgraded ball bearing twins: http://www.m2performance.com/pturbo.htm . They're supposed to be capable of 400+ RWHP. The Apex single kit is supposed to be very good in the lag department, and it's not too big, but its limit is about 450 RWHP.

 

I have non-sequential turbos and love them - it acts like a small single. If you are going to spend the money get a good single - T04E or S, Apexi RX6 - they spool quickly and produce very good power - they are also around $3K and up. M2s ball bearing TTs are great from what I heard and produce quick power. I've seen upgraded twins for like $1800 - hooking them up non-sequentially might be a cheap way to get 400 at the wheels and keeping things simple and cooler. You get more hp in the midrange having non-seq. set-up but don't know of anyone hooking up upgraded twins non-sequentially - good idea for a cheap single.

 

I tried to get an answer to this on the mailing list, but didn't have any luck. I'm trying to find out if going true non-sequential is any different (flow/performance wise) than when the stock sequential system falls on its face after running over 4500 and letting it fall back down slowly. For example, in 4th, run slowly to 5500 or so... let it fall back to 3500. Stomp on it and blah.... twin mode.

I just can't see how you could get more HP in the mid-range, as most people with non-sequential twins say the power really doesn't come on until 5k. Unless something changes...

The main reason I ask it I have a set of blueprinted turbos sitting in my garage. They have been modified for non-sequential, but I'm not sure I want to leave them that way. I was planning on sending them off to Turbo Specialties to have them worked over.

Just rambling....

-Matt
'93 Touring

 

I get full boost by 4K in 1st 2nd and 3rd and about 3800-3900 rpms in 4th and 5th. I've been having some trouble with either an failing ignition coil or double throttle and my car only runs strong sometimes - getting fixed soon. But when it's strong - it hauls. If you have most of the bolt-ons (full exhaust, street-port) the non-sequential will work better. I think Brian Goble??? somethink like micromanx.com has a dyno run with his non-seq. FD compared with 2 other modded seq. FDs. The non-seq had more hp and torque most of the way through the powerband. There are too many complications with the stock system. Going non-seq only cost me $75 to do the full conversion since my engine was out for rebuild. With upgraded twins it would be very interesting what you could get out of a non-seq. setup - probably some strong numbers.

 

I'm probably straying off topic here, but I have frequently seen the term "true twin turbo" to describe a twin turbo set up which doesn't operate sequentially. I guess I just don't understand why people call it "true" twin turbo...as if sequential twins are "fake" twin turbos

My sequentials are getting their feelings hurt

 

Interesting... Even more so than dyno sheets, I would like to see some 20-50, 30-70, 60-100 runs done with one of the new turbo timers that measures those times via ecu inputs (as opposed to gtech style units). A couple of sets with each non-seq and seq... same car, same day, same driver.....

I agree that the stock system is a mess if something is wrong, but when it's working, it is hard to beat. At least on the streets....

-Matt

 

Go single turbo, 1/2 as much stuff to buy, 1/2 as much stuff to fabricate, 1/2 as much stuff to break, lots more space, easier to work on and a lot easier to tune with just as much power as a twin setup with the right single turbo setup...

 

The reason you can get more mid-range out of non-seq is because both turbos will be blowing hard by 4000 rpms. Witht the stock-setup on a modified car, the stock-sequential system still prevents the secondary turbo from coming online, so you're still running off of only the primary turbo until the changeover at 4500 rpms (and as that approaches, the power levels off (or even drops on some cars) since the primary turbo cannot support those power levels by itself.

With non-seq, you'll just have smoothly increasing power from the start...but from low rpms, boost will build more slowly than the stock-seq setup (it's not really lag...the boost needle is moving...just not as fast).

With stock-seq, you'll have great low-end response, and then the flat spot in the mid-range as the power levels out (or drops) just as the transition approaches...then you'll have a big blast of power (spike) at the transition, and then it will level out and resume increasing power.

Top-end is basically the same on both.

Each setup has it's own advantages and disadvantages...I like having more mid-range power since I am on the street 99% of the time and I have modified my driving style to keep the rpms/gearing where I can have good power available when I need it. I do miss the great stock-seq low-end response...but for me, non-seq has too many advantages for what I like.

If you can, drive a car that is non-seq and see what you think...that's what convinced me (after one run too :)

Here's a few links...
http://www.micromanx.com/goble/rx7/p...3/nonseq3.html
http://www.micromanx.com/goble/rx7/p...3/compare.html
http://www.micromanx.com/goble/rx7/projects.html

I don't have any Xmph - Ymph times...my guess (from experience owning/driving both) would be that non-seq would have a slight advantage....unless you required both drivers to be in the same gear and setup the starting speed so that the rpms were around 2000-2500.

If the gear was whatever the driver wanted, the non-seq driver would be in a lower gear. If the speed was so low that both drivers are in first gear...even in non-seq, first gear at 2000 rpms is just like stock-seq on my car...instant power and instant wheel-spin. :)

After the first gear shift, it's all basically the same since both turbos are both blowing all the time.

[the above paragraphs are just my thoughts...I am not saying one setup is better than the other, just trying to point out what the advantages and disadvantages are for both setups...hopefully so people can make better decisions based on what things they like/dislike for their power delivery and setup. Drive both and decide for yourself if you can. I was never planning on going non-seq...I was against it actually...but finally my stock-seq failed me and even 3 experts (including jimlab) couldn't figure out the problem. So, I rode in a non-seq car and then I had to have it :) ]

 

I wish it was that easy.... The town I live in in Northern California now has 2 rolling smog stations. What does this mean to those of you living in the rest of the world? A couple times a week they park one of these things on the side of a street. A cop stands in front and waves cars over to the station. They pull your car on the back of a truck, run it on the dyno, smog it, and do a visual check. If you are lucky, you leave with a warning or a clean bill of health. If you aren't lucky, they impound your car....

A single turbo, especially with no air-pump, is going to fail... plain and simple. Minimum of a $500 fine, +ticket, +impound fees, etc...

-Matt
'93 Touring

 

Thanks for the reply.... I suppose the only way to decide is to ride in a car with similar mods to my own with the non-seq mod done. I just think that when the stock system falls on its face at 3500 after going over the transition point and dropping back down, that is the same as non-sequential.

I agree that it's probably the easiest way to fix a sequential turbo problem though.

I think I will most likely go with the sequential turbos modified by Turbo Specialties to allow more flow. I like not having to worry much about rpm....

By the way, nice site.... lots of good info.

-Matt
'93 Touring

 

I'd move to a hill billy state if I were you... HKS makes a single turbo manifold that allows you to run the airpump, stick a To4E on there with a A/R .84 exaust housing and run a aftermarket catilitic converter witth the stock port... If tunned correctly you should be good for smog and over 350-380hp at the wheels.

 

Yeah, singles are great and huge power but not everyone has $3K laying around plus different piping for the IC and tuning - it could easily be $3500-4000 for a new single. I have the poorman's single and it's possible to get 360 or so rwhp safely out of a non-sequential setup without breaking the bank. When my turbos go - I'll get a single. But my turbos are brand new for the most part and so is my engine so hopefully I can get some mileage on them. I would like to find out if anyone ran the upgraded turbos - whether PFS, Petitt or M2s non-sequentially to see the power numbers.

 

When you were saying true twin turbo, I took it as putting on somthing like 2 x TDo5's or somthing, not keeping with the stock turbo's....

 

Changing over to non seq isnt going to add but a few hp if any unless you upgrade the turbos. I'd either go seq or single. The reason most people go nonseq is when thier rats nest is in a huge mess and they dont want to trouble shoot and fix the prob, they just rip it all out. There is a seq turbo system simplification mod you can do on RobRobinettes web site that removes the entire rats nest except for a few silenoids and some vacume line. I just got done with it and will have everything back together as soon as I get a few free hours to finish. This leaves the system in the seq mode (which is what I wanted) and gets rid of the head aches. I dont know why more people dont do it unless they just didnt know it was available or they thought it was to hard. Once I got to the rats nest the removal and rerouting of junk took about 3 or so hours and with the diagrams I printed it wasnt hard. I'll take a few pics and report on it in the next week or so.

Anyway, if you dont want seq I'd go single.

Good Luck,
STEPHEN