How to stop boost spike on twin turbo
 

I've had my RX-7 for about 2 months now and I bought it knowing I would mod it with lots of bolt on's. The car stock was slow, so I figured I'd start by making it breeth better, so I added an Intake and cat back. The car felt much faster right away. Then I got some gauges, boost, air/fuel, and pyrometer all essential to a turbo car. Then I notaced a big 14-16psi spike when I first hit the gas in the low RPM. I know this was bad since the stock ECU is set to 10psi and does not adjust the fuel to compinsate for extra boost, when I would spike I'd run lean. So I came to the forum for help. People sugjested a boostcontroler. So I made the manual boost controler and hooked it up. No matter how I set it, 5psi or 15psi I would always get that 14-16psi spike in the low RPM. The boost spike is caused by the increased airflow to the primary turbo. The turbo spools up much quicker than stock and since the wastegate is closed while it is spooled up full you get a spike. Some people say that they never get a spike with similar mods to mine, but I can't see how you wouldn't get a spike unless you have an upgraded ECU or EMS cause then the wastegate would open sooner.

But anyway the cure I found is to run a non-sequential set up. I did this and now I have no spikes except when I shift but even then it's like a 1 or 2psi spike over my set boost of 11psi. The transition is nice and smooth no jerky switch to the secondary only to get a sudden burst of power. Just the same full power from 3500 to 8000rpm. I've heard you can still get boost creep but I haven't really tested for that yet.

This set up is also safer too. I spun my car right around one time when I first got it cuz the secondary kicked in and I was going around a corner in the rain, I didn't expect the sudden power I'm just glad that there was no one else on the road. Also trouble shooting the turbo system is simple now since you only have like 4 vac. hoses. The darw back to the non-seq. system is turbo lag. The more stock you car is the more lag you will have(non-seq. should not be done on a stock car since you won't really have a spike). I plan on getting a full exhaust cuz I've read that with a dp, mp, cb, and intake the non-sequential is the same as stock spool or better. I planed on doing these mods anyway but now I won't have to get an EMS first and thats good cuz I can only spend about $1000 a year on my car so it would set me back quite a bit.

NOTE: *** when taking off vac. hoses from under the pressure chamber(off the solenoids) be careful it is really really easy to break off the solenid nipples(I learned the hard way, but I didn't need the solenoid anyway). I recomend sliceing the side of the hose on the solenoid to loosen it then slide it off, don't twist it that's how they break. *********

- Here are some good sites that give you info. on non-seq. turbo setup.

this one tells you how to do a FULL convertion
(very involved)
http://www.scuderiaciriani.com/rx7/how-to_turbos.html

this is a simple convertion (the one I did)
http://www.dontbearikki.com/id49.htm

I also recomend having a hose and turbo diagram, makes it easy to see whats what.
http://www.rx7turboturbo.com/robrobi...ages/hoses.gif
http://www.rx7turboturbo.com/robrobi...chargerBig.jpg

this gives you a simple vac. setup, you don't have to do this but if you hate vac. hose then with a non-seq. this is all you need!!
https://www.rx7club.com/forum/showth...non+sequential

I hope this is helpful, I've been given so much help from this forum it's nice to offer to finally it back.

Re: How to stop boost spike on twin turbo
 

All the information you posted is good to know EXCEPT for this. If you are in a turn, in the rain, IN AN FD... by no means should you be on the boost enough to transition hard into the secondary turbo. You were asking for that one. Be careful.

great write up. explained well. i'll refer back to this when the time comes to break the link..

Yea I realize the mistake, I'm much more careful in the rain! I was tryin to do a little fish-tail thats why is was reved up so high:D I don't do stupid thinks like that anymore, I just go 150mph down the highway but nothing stupid:cool:

Excellent information!

My friend is having a similar problem.... He has been having boost problems for a number of months now (instead of 10-8-10psi, more like 7-2-3psi). Came to the conclusion that the exhaust must have been blocked in some way, and sure enough when pulling the CAT's off - both had collapsed (all other pipework and vacuum lines have been replaced).

He has now purchased a complete new freeflowing exhaust system (with no CATs - as they are not required on a 1992 model car in the UK), and I know
from experience that this can instantly cause boost spike problems.

Upon testing it today, all of a sudden boost is now 10-15-9!!! just a slight spike there.

He will now look into the links you have posted - many thanks.

wait, ther eis a porblem here, you aid 'non-sequential ' set up and then said the transition is smooth, ...if you are running non-sequential , then ther IS NO TRANSITION!!!!! hehehe, but i know what you ment, in the stock transition rpm range

also, be careful in thinking that you dont need a computer mod just by keeping the boost down to 10lbs....froom what I was told, mods will 'open' the pipe so that the airflow at 10lbs is more that the 10lbs stock....so you need more fuel even at the same boost level...consult the forum expers on this though, I am no expert.

I totaly agree. Since I have more flow there is more air in that 10psi, just like if you have a smaller turbo and a bigger turbo both running the same boost there is a big difference between the two in the amount of air being pushed to the engine and also a difference in power. However I don't beleave that there is too much of difference between a non-seq. and a seq. at least not enugh to damage my engine. I run on the rich side anyway so I think it will be ok. I do plan on getting an EMS as soon as possable but I want a dp,mp first so I can just tune the car with it's max flow(I think thats more worth it than tuning an almost stock car now). By doing the non-seq. now at least I can drive the car till then without risking boost spikes. If I could do it again I would have got an EMS first. Thats a great way to avoid problems, if you know what you are doing.

But wait I just remembered the non-seq set up is the same as when a sequential is running at like 5000rpm. once both turbos are running it is the same as the non-sequential so the stock ECU should have the right fuel

THERE IS NO DIFFRENCE BETWEEEN SEQ AND NON SEQ INTEH AMOUNT OF POWER IT MAKES. teh non seq will always be less. unless u otherwise mod the car.

Yea I beleave I said that before, the more stock your car is the more lag. But non-sequential is a must do mod if you have intake, cat back, dp, mp or a combination of them and you want to keep the stock ECU. Otherwise you get boost spikes.

12-12-12 here.
3" turbo back exhaust - no cats, straight through muffler
FMIC
PAC intake
... and a LOT less pre-spool :)

The car still has so much kick at 4500 that it's starting to fry my clutch :)

-pete

Yeah but now you have increased airflow below 4500 rpm due to both turbos running. I don't think it'll hurt the motor but you never know.... I run the Apexi PFC and so have no spiking at all.

the spikign can be eliminated if u get a boost controller and do some rerouting with the hoses

had a manual boost controller no change in the spike. How would a boost controller make the ECU tell the wastegate to open sooner? what kind of rerouting with the hoses are you talking about? a vac. hose siplification? why not just go non sequential? Why do not like steady power? why do they like a little jump off the primary, then a dip in boost, then a spike then power? why not just have power through the whole powerban and 4 vac hoses!!!

I have come up with a method that doesnt need solenoids anymore, but still is sequential and doesnt get boost spikes!!! instead of having a waste gate and pre control solenoid, i took the hose going to solenoid and looped them right to the bleed. Heres the trick, you have to get two more resriction pills that are in the beginning of the pressure side hoses of both controllers and put them in the looped hoses that are now constantly bleeding! I also hooked abv directly to manifold vac just likr arv. Works much better than with solenoids. Leave sols hooked up and get no error codes. Who could ask 4 more?

do you hear a constant hissing sound?

Lots of good information that I can refer to once I get an FD. Nice post.

I love it how when people can't figure out the stock sequential system, they go non-seq :rolleyes: I've known a few guys go non-seq. They hated it and went back to seq :p: I know a guy that ran mid 11s with the seq system, so it can't be all THAT bad.

I use to have the big spike you are talking about. All I did was adjust the prespool control and I added a $35 Dawes Devices valve, and I was back in business.

Flybye --
Are you saying I don't know how the seq. turbo works?
If you read the whole thread you'd see that I have already tried a manual boost controler and I know exactly how the seqential system works. I studied the seq. system for a long time to learn what is going wrong with it. I found that there was nothing wrong with the system itself it was the ECU not opening the waste-gate soon enough that caused the spike. You must understand that the intake I put on my car has about 4 times the surface area of the stock air filter. Thus the primary would spool up way to fast since it was getting 4 times the air. Even with the manual boost controler in it's lowest possable setting I would get a 14psi spike which would settle down to 5psi. I reviewed my intalation several times and found that it was hooked up right acording to Robb's web sit. I don't have the money to get a programable ECU yet to corect the wastegate problem and geting the stock ECU re-tuned is a waste of money since I would have to get it tuned every time I do a mod. Also the car now has only 4 functional vac. hoses with the non-seq setup making the turbo system simple to fix if there ever was a problem (not likely). The person who said they hated the no-seq. set up must have had stock or nearly stock cars cuz it does suck then. In your defence I've heard of people fixing boost spikes on stock or nearly stock cars with the manual boost controler. But I've found it to be a very inconsistant way to fix boost spikes on my FD. Sometimes it would spike other times it wouldn't I'd rather have some lag till 3,500 than a blown motor and once I have my full exhaust I should have almost no lag. If your going to mod your intake and exhaust for the max possable flow save yourself a blown motor and go with no-seq, a programable ECU, or both.

The seqential system was made to work with the stock restictve air flow system because with a very restrictive system the turbo lag would be horable (full boost at like 5k). But with a free flow system turbo lag is greatly reduced. Infact I read at http://www.scuderiaciriani.com/rx7/how-to_turbos.html
that with a no seq. turbo and a free flowing air system, turbo lag is less then stock and more powerfull since both turbos are online. I bet the guy who runs mid 11's would run high 9's low 10's with either a single turbo or the no-seq setup.

When I was getting the spiking, I had a stock motor, intake, exhaust, DP, efini y-pipe. & jet-hot coated UIM (the coating gives it almost the same texture as geting a polish job). I was getting the spike because back then, people had also started to realize just how well the Efini y-pipe flowed :)

My transition boost went down a couple of lbs still, so I decided to then route additional exhaust from the 1st turbo to the 2nd during prespool. I finally got no spiking on the first turbo, but now spiking at transition became a little TOO high, so then I moved on to the Dawes Devices Valve. The best thing about their controller is the spring actuated ball check valve. You set it at the disered boost level, and if boost goes beyond that, the valve opens up allowing the wastegate to open. The only downside to this valve is that your boost may fluctuate a bit, but you can't expect miracles with a $35 valve. This system worked perfectly for me, and iw as able to fine turn the prespooler and the Boost controller to the point that I was able to get almost stock boost levels. Why didn't I just install the boost controller? Because then I would still have that minor dip at transition. After that, I got power greedy, and went to the PFC and MP :D

About the guys that went non-seq and hated it...
The first guy was the guy that ran 11s with ported motor, M2 ECU, full exhaust, IC, and running 14-15psi. He wired the system open for non-seq., didn't like it, and went back. Then he upgraded to a Haltech and he no longer had precise seq-control, and so he had to go to a FULL non-seq mode. He didn't like how it felt at all, and he ended up upgrading to a small single in which he is still able to get a good amount of boost low end.

2nd guy also has a ported motor. Has Pettit unlimited ECU, full exhaust, intake, IC, runn13-14psi. At the same time he dumped in the ported motor, he went non-seq. Even with the new engine, he didn't like the power band, and so he decided to go back to seq.

The 3 of us enjoy SCCA and track events, which is probably why we like our low end power.

Too many times (not ALL the time) I see the reason for someone to go non-seq because they were having problems with the seq system. IMO, I think it's a combination of people not knowing how the system works, people not knowing how to tweak it, and people just NOT wanting to deal with the rats mess and attempting to diagnose it. Hey, that's fine. If ya just don't want to deal with it, you don't have to. I just personally feel that the stock seq systems, although a bit messy, works pretty good. I've had problems with it. Bad hoses and sticky solenoids, but that never stopped me from trashing the entire system.

Did I consider going non-seq? Sure. A few of the people were happy with it, but I decided to try to tweak the stock system.

How did you send more exhaust to the 2ndary during prespool, no matter how I ajusted the prespool it made no difference. I used an air pressure regulator as a boost controler I still get a 1 or 2psi spike but thats just cuz the wastegate opens too slow and after that the boost stays rock hard at whatever I set it. Why deal with the stock system unless your car is mostly stock? with dp,mp,cb, and intake there is less lag and more power than the stock system. Tell your friend with the single turbo to get a ball bering turbo and see what the lag is like. I hear they make full boost at 2k and thats on a 4cyl. who knows on a rotary.

I manually adjusted the prespool flap.

Right cuz that one is ajustable but the wastegate isn't

Soooo, not true. Non-seq isn't a must do mod. A simple change of the WG pill will eliminate the spike on a mildly modded car, if the car is more seriously modded then you might have to change the PC pill too.

Plenty of info on pills on Rob R's site or Steve Ciriani's.

Jeff