non-sequential and lag
 

I know there's a lot of posts about this, but it's hard to find clear information about the lag experienced when people go non-sequential. In older posts many people say that "if your car is heavily modded the lag should not be that bad." I'm thinking about going non-seguential b/c lately I'm having trouble building full boost (always about .06-.07 bar from where I should be), and I'm worried that more problems will just keep coming. So with my mods (in my sig), do you guys think I would have noticably bad lag if I went non-sequential?

-Matt

non-sequential tends to "lag" appx. 400 rpms. Mine normally hit 11 psi at 3200~ rpms(It's been awhile so don't quote me)

You should be fine. It pulls so much harder mid-range you wont care about the few more rpm that you have to wait.

double post deleted

I went NS because I was also having boost issues.
I did the poor man's NS conversion. I think I get more lag than most: 14 psi by 3800 rpm consistently.

Either I did something wrong in the conversion or the HIGH FLOW CAT is causing the additional lag.

Not too familier with the "poor man's" non-seq. Does this cause more lag than the "normal" non-seq mod?

Nope, it's the same. jpandes numbers are pretty much what you can expect if you look at the dynos of the NS people. I've seen many people "claim" less lag but I've never need a dyno sheet to prove it (on stock twins).

IMO, fix your boost problem. NS is not a fix, just a work-around and it doesn't guarantee that you still won't have a boost problem.

Not to frighten you away, but I don't get full boost til just over 4000 rpm. The only flow mods I have right now are the intake and downpipe, though. With your mods, I'd put you somwhere in the 37-3800 rpm range for full boost.

But really, how often do you need that much boost any lower than that? If you're racing someone, or pushing the car hard, the engine never falls below 4krpms anyway, so why worry about lag?

I say just do it, I couldn't be happier with mine, and thats with a lot more lag than most.

911gt2
i'm glad to hear your description of your boost pattern since i have the same mods and my car is responding exactly the same as yours. i never had the car working properly with it hooked up sequentially and i was considering going back to sequential just because i'm not sure what i am missing. can you think of any reasons why i should switch back in your opinion?

Why you should switch back to sequential? The only reason to switch back is for low end response. Which is really nice. I loved having 10 psi at under 3000 rpm, it felt great.

But the stock sequential system is just way too complicated IMO. There is what, 120 feet of vacuum hose, and 30 odd solenoids? Something will break eventually. It's just not worth the trouble to keep it going the right way. I've never felt it work completely correctly, because I had a secondary boost issue from when I bought the car (~7 psi, dropping off to redline). But I've been told that when it works, it's awesome.

Do a search sometime for "low secondary boost" or "sequential issues" or something like that, and see just how people have issues with the system. Not worth the trouble.

Then there is the issue of reliable boost. Every time I hit the gas I see 10 psi. No matter if I let off and hit it again, let it build slowly, don't build at all 5k rpms, then drop the hammer, it makes no difference. With sequential, wierd things happen. If you keep the car at part throttle, then hit it, sometimes you get really slow building boost, sometimes, it spikes, theres just too many wacky things to go wrong. With a full exhaust and non-seq, you can hit full boost by 3800 rpm, which is not very long to wait.

Long story short, don't go back.

Thats very true, it might not fix your boost problem. It didn't fix mine the first time around. But that was because my secondary turbo was blown. If the issue is with one of the many feet of vacuum hose, or a solenoid or actuator that controls the seq system however, it will fix it.

I thought of it as a simplification. There is a seq system simplification diagram around, and I felt this just took it one step further.

I see the non-seq as a poormans single turbo. The twins effectively function as a single in non-seq mode, but you don't have the issues of finding a turbo, manifold, new dp, intake, BOV, IC, piping, and ECU to control it all.

It is a workaround, but it's also a workaround for future boost issues that the seq system WILL have. I don't know, think of it as a reliability mod too.

Basically, I've been considering going non-sequential for a while and this boost problem just made me consider it more seriously. If I'm going to have to go through all of my vacuum hoses and solenoids etc, why not do the conversion now. I'm not necessarily looking for it to fix my problem, but diagnosing the problem may get so intensive that I might as well go ahead with the coversion. I'm still not convinced that it's what I want to do, though. If I can be convinced that I will gain some more power and not be bothered by an unreasonable lag, then I'll go for it.

People have claimed that it gives a lot more power in the mid-range (like racerfoo above). Is this simply due to no pressure drop durring the transition, or is b/c of something else?

That's opinion, not fact. I know several owners (including myself) that aside from user error, have never had a problem with the sequential system.

The only problem I've ever had was my own mis-routing of two lines to the UIM when I was fixing another problem. I can't complain much as that was the first time I ever removed and reinstalled the UIM myself and I should have checked with the vacuum diagram first.

So, that makes almost 7 years of ownership without problems. Take a look at a dyno chart, you only loose with the poor-man's NS compared to the standard sequential setup. You do gain with the full-NS in the higher rpms as you have slightly better flow. So if that's what you need, that mod with worth wild.

IMO, doing NS with the twins is a waste. If you want a single turbo, get one. Basically, you are getting the lag of a single and keeping the heat of the twins. A loose-loose situation if you ask me.

Yes, you don't gain more power you just have a different power curve (with the poor-man's NS).

same here....don't get full boost till like 3600-3800 rpm..... it was worse before i dropped the efini y pipe. i am full non-seq. it lags but not too bad....14 psi by 3800. k

And I know several thousand that have had issues. Taken a course in statistics lately? Numbers are not in your favor.

I called the non-seq twins "poormans single" for a reason. It'd cost upwards of $5k to get a properly functioning single, with all of the hardware and software needed to do it. It cost me about $5 to do the poormans non-seq. It's a taste of single without all the work and money. You call it a loose-loose situation, I call it a win win. Cheap, yet effective. To each his own!:)

I'm no statistician either, but I know that people who are content tend to tell one person about it, people who are not content tend to tell 9 people about it. So you may find that your analysis is off because you have mostly heard the negatives. I have had three FD's over the past 8 years and never had an issue with sequential. Care and precaution seems to do the trick for me.

I get 17 lbs by 4000 on bnr stage 2s...I hate it. I have the full non seq. Worst thing I ever did! Stay seq! If I'm just cruising around town...my car is not quick..its a dog. Its either a dog or a missile, there's no middle ground.

mcf has it right. This is a trouble-shooting and technical forum. Of course you'll only read about people having problems as they will be asking here for help. Why would they post if they didn't have problems?

That's like going to a support forum for a product, and then not wanting to get the product because there are people in a "support forum" with problem. :rolleyes:

However, as mcf said, "care" is #1. The sequential system typically fails because of vacuum or solenoid problems which can be remedied by going non-full NS. Both problems are typically caused by heat from the underhood temperature. Any other problems usually will carry over to NS.

With proper care (and proper work done to the car), there shouldn't be problems at all with the sequential system. Do it right the first time so it doesn't need to be done again basically. So, if your headlights go out, are you just going to remove them instead of fixing them? ;)

Going NS to fix a boost problem is the wrong reason, IMO.

I don't understand any of these replys. 15lbs by 3600 & 17lbs by 4000rpms ...what's wrong with that? If transition takes place at 4500rpms, that means in sequential you are at 10lbs at 4500 on a stock 7. I was at 15lbs at 4500 (modified) sequentail. How many lbs are you boosting at 2800 vs at 3000?

If you can describe parallel as slingshoty then I can understand the drawback because that is not streetable to me. As far as loosing 400 low end rpm, that will happen with a single. Basicaly you are tading low rpm for reliability (same as single).

If both turbos are online then aren't you hitting full boost in parallel sooner then you would in sequential waiting for the transition?

Doesn't parallel change the power curve from high end to midrange, which is where all the power in a "non" ported engine is anyhow?

To answer all of your questions:
The difference between hitting 15 lbs by 3600 rpm, and 17 by 4000, is entirely dependent on flow mods. With a full exhaust (dp, mp, cat back) the turbos will spool a lot quicker. The guy who hit 17 by 4000 had a few less flow mods (say, a high flow rather than a MP) than the other guy. The twins function as a single when in non-seq mode, so they both need to spool up together, which takes longer.

Non-seq is far from slingshotty. I experience a "boost building" sensation, which basically involves a growing smile on my face as the gauge climbs to 10 psi. Even with a full exhaust, power is far from instant in non-seq mode, and it is more than streetable.

With both turbos online, as I described above, it takes longer to spool them up, so no, you're not getting full boost before you would when the were seq. In seq mode I got full boost at about 3krpms, then I should have had re-full boost after transition. The idea behind sequential is that you have one turbo thats small, easy to spool, but has a low flow capacity. The second turbo needs much more exhaust to get it spinning, but has a much higher flow capacity. So the first one comes on very low in the rpm range, but loses it effectiveness somewhere around 4500rpm. So the second one is calibrated to spin enough at 4500 rpm to achieve 10 psi, and it can create that just about til redline. The faster the engine spins, the more air/unit of time it needs, so the turbo with higher flow capacity comes on later in the rpm range.

Non-seq makes them both spin all the time. So they take longer to spool, but you don't have the transition period in between, but you have to wait longer for both to get going.

Non-seq moves the power curve, but not to lower rpm range, it squishes it up into higher rpm range. Because it takes longer to hit full boost, the power curve moves up.

Let's let the number do the talking.

https://www.rx7club.com/forum/showth...hreadid=212547

Trying non-seq with most bolt ons, I found very good response going wot at 3500 rpm or above .. not doggish. But that is not likely at 3k or below. With seq'l, I hit 10 psi at 2400 rpm in 3rd ... valued by some like me.

Mid range with simple non-seq is better due to lack of transition near the torque peak.

non-seq is inherently rmore reliable by simplicity, and results in less manifold thermal cracks due to more uniform heating.

Exactly. Even getting boost at 3800 rpms NS verse sequential at less than 2400 is a huge difference. The numbers don't look so far of at a low range, but over 1000 rpm difference is more than enough for me. I'd rather not get beat off the line by a Neon. ;)

As I said, the poor-man's NS mod is great if all you want is top end power. But switching to it because of a boost problem is the wrong reason IMO.

However, saying that it's eventually going to fail is like saying your tires will eventually need to be replaced. It's a mechanical system that like anything else in the world, can break. That doesn't mean it's worthless.

I have never been beaten by a Neon. I have also not been beaten by my brothers 2003 WRX. Nor have I have I been beaten by my friends modded 91 DSM (15 psi). Both of those cars have a little something called AWD, which happens to give them an advantage out of the hole. (Ok, so I lost off the line, but caught up really quickly) Keep in mind my car runs stock boost levels, and has very few power mods.

I don't consider 4k rpms "top end." That is actually dead in the middle of the rev range. And thats when I get FULL boost. it builds from about 3500rpms or so. And it'll spool much quicker with the rest of the exhaust.

I understand that all things mechanical break at some point, but why not replace the broken piece with one less likely to fail? When your stock tires popped, did you replace them with factory rubber? Or did you get Z-rated tires with a 3 yr/50,000 mile warranty?

Did you bypass your AST? Same type of thing. Some might argue that it's there for a reason. Other see it as a fault in the stock cooling system, and get rid of it.

My point is, take two cars, on seq, and one non-seq. Full exhaust on each, and take them to a track. They'll run dead even in the quarter, and dead even on a road course. Why? When a car is being pushed, it's never below 4k rpms anyway, so why have the power available there, while walking on thin ice with reliability? Do you ever race anyone from under 4k rpms (aside from the launch)?