im sure this has been touched on before but i couldnt find any definitive answers from searching. anyway, i was on the highway today and a guy in a "roushe 2" mustang came up next to me and wanted a go. first run we both slowly led into full throttle... i.e. i was at full spool (on the twins) when we had at it. i pulled on him the whole way and ended up gaining a car length or 2 on him by the end of the run.

second run, i started out from closed throttle to full open (roughly same RPM, same gear). however, this time it took a second or more to build full boost. at that point he had a lead and there was no way to catch up.

first question... are my turbos operating properly in seq mode? (what i mean is... does everyone else have some amount of lag from closed throttle-> WOT at say 5000RPM's? i was under the impression that the pre-spool actuator was supposed to take care of this... however maybe that is just regarding spooling the secondary BEFORE the transition.

basically my question is.... is pre-spool supposed to be active for BOTH turbos past 4.5K? if so, can i manipulate that manually? i understand however that you wouldnt want to be pre-spooling all the time while youre crusing down the highway at partial throttle. can someone help me sort this out? im a bit confused with the seq system. thanks, heath

 

Only the secondary turbo gets "pre- spooled" just below 4500rpm, So if your above 4500 both turbos are "online" and will lag if you let them spool down. Next time do a rolling start in third at about 45 mph... You'll smoke him (Not that I'm advocating street racing)

 

45 mph is a horrible place to start a race in 3rd gear. Perhaps you meant 2nd gear.

I don't understand why you would start a race with the throttle completely closed. Normally it would be at least partially open to maintain your speed.

You want your secondary turbo to spool to a level just below your max psi on the primary turbo. Any more than that will give you a spike at transition (bad).

 

Ya I was talking out of my butt...... I don't know crud about drag racing.

 

Prespool only works from 3k-4.5k, and if you punch the throttle then you'll still see a little build-up time for the primary to get going. I notice a steady build for about 1s when in 4th on the highways. From 4.5k up, you'll have even more build-up time. Not many tricks out there to avoid the rotating inertia issue.

Dave

 

Not sure if you got your question answered completely so I thought I would take a go.

Most of the pre-spool convo is centered around the second turbo, which comes on line as everyone said. A little boost from the first turbo is bled off to spool up the second in advance of it coming on line. This is controlled by the pre-spool acuator (nopt sure if this if the right term). Anyway, the amount of prespool on the second can be altered through the amount of restriction in the pre-spool control line. The factory has an orifice in the line, which they call a pill. The more restriction the more the pre-spool, which can lead to a spike at transition.

Now, there is a give and take with this. The more that is bled off, the less boost there is available before the transition. It is a balancing act against the boost level, and with a manual boost controller, it will change somewhat day by day depending on outside pressure and temperature. You can see a difference from morning to afternoon even.

Prespool on the primary is a different animal. There is no pressure reserve to bleed from to prespool it. I think this is what you were wanting to get at. That is a function of engine RPM, engine load, and the boost controller. Obviously, with enough revs, the boost will come up.

Just reving the engine is not enough engine exhaust flow to really cause some turbo RPMs. There needs to be a load to develop pressure on the turbine side of the turbo. Since mine is a auto, there is this nasty lag at a dig. Still thinking about how to make this work....sorry...the engine is not known for much idle torque, which equates to a lack of spool on the primary at low rpms or load.

Just thinking out load, I wonder if a line lock is the solution, or something like that. Any way the engine could be loaded would prespool the primary and then it would be ready at launch with moderate pressure across the primary's trubine.

Perhaps there is someone that has worked on this probelm here???

 

RotorMotor : check out this page
https://www.rx7club.com/showthread.p...hlight=perfect
it is Damian's write up on how to manipulate prespool. I used it when I was sequential and it is very effective.

 

sounds like you were locked in twin mode at mid-rpm. if you eased up to say 3800 in 3rd, go wot you start strong in primary, transition at 4500. Say your again at 3800 in 3rd and go clutch in and rev to 6k for some reason. Unless rpms drop below 3200, you are locked in twin mode (non-seq) now, with some lag. To unlock it, let rpms drop temporarily.

Starting in primary only, trans will be 4500 at wot, or 5000 at say 75% throttle. Very light throttle and non-seq is triggered above 5500 rpm.

 

really. very interesting... thank you for that. ive never completely understood why the turbos behave differently under those different situations. thanks once again... this will help me alot. -heath

 

there is also a time-out for getting seq'l back, and these things vary based on gear selected. Best to carefully practice.

 

i wasnt aware that the ecu was aware of what gear i was in. may i ask how things change depending on gear? adn what you mean by a "time out for getting sequential back"? in what situation would you loose it?

i remember reading a play by play grid/chart of what our turbos are doing at various loads and rpms. anyone know what im talking about? i cant seem to find it. -heath

 

I hate when I'm driving through the town/city and the car gets stuck on parallel mode. It gets loud and laggy, so annyoing! Im going to do damians boost setup in a short while once I get my IC and injectors so I can run 12 lbs. Thumbs up !