Curious to know what, if anything, can be done to maximize the god-awful, low end power on an S5 T2. Money not an issue but on the original motor.

Things can be done like a half-bridge port to the engine, and smaller wheels I think most know of, but beyond that, I was thinking there must be something else that can be done (a new set of smaller turbos maybe? if so which ones would work best?). Also, please post how effective what your suggesting would be, for example how much improvement will the results show.

Making this thread so that with the suggestions we get, others looking to accomplish this task, could also use this thread.

 

higher compression rotors, a BOV that vents to atmos under vac.

 

sequential twins, custom geared transmission, 4.6 rear end....

 

do you have a stock turbo?

you could get a smaller turbo, or the same sized ball-bearing turbo that would spool faster, but it would end up hurting up top if you go too small, and it won't improve off boost performance, just reduce boost lag.

you could also get an electronic boost controller that will ramp up boost faster by holding the wastegate closed until the last minute.

 

Who needs low end power?

Rev the Bitch, they like it!

Or Get a V8.

 

neofreak had an S5 t2 back in the day that did more tq than HP on the dyno, it was like 220lbsft@3000ish, and it only did like 200-210hp something like that.

i think the only mod was the turbo back exhaust.

IMO its a waste of time to try and get more power under 2500rpms, you're only there in 1st gear...

 

On the track I would agree, but this is the most common gear on the road and the one that requires the most amount of work on these cars. I think a lot of people would enjoy driving their rx7's if it weren't for the lack of torque in the low end.


Some other idea? Say for example, is it possible to increase the amount of air and the speed that it comes in, maybe polishing the throttle body?

 

what exhaust are you running?

 

Stock now, but I do have the racing beat II exhaust waiting to go on. But this isnt about me, but rather for everyone, do tell what you have in mind.

 

higher compression rotors, as has been said(you can mill rx8 rotors to work, they currently are the highest CR rotors available at 10.0:1)
making sure the 5th/6th ports aren't stuck open
compression test the engine, a worn engine with low figures will have resulting less power at lower RPMs
an EMS will also allow you to fine tune fuel and timing better for more low end torque
as also said smaller turbos spool faster so the FD was the most reactive at lower RPMs of any turbo 7

in short the answer is: just live with what you have, it's not worth the amount of work involved just for a little more bottom end power.

 

Good last point, its just that I love the thing and its either make or break right now. The car is old and I think I might be selling it. If I was to keep it, I want it restored (mechanically not cosmetically, its pretty good as it is) however my purpose is street driving ability and reliability

The engine runs ok, and is slowing moving towards the low end of compression. So I was thinking of rebuilding the engine for drive-ability and durability or thinking of anything I could do to improve its road going factor.

 

perhaps it is just time for a rebuild then, the only time i would say that a rotary lacks so much low end torque that it's worth getting rid of means that it is probably hovering around 80psi or less or has another problem going on like a timing issue, worn plugs or vacuum leaks.

my DD has about 75psi because i rape the hell out of it but the top end still more than makes up for it, however it lacks that low end in part because of the baby chipper i have strapped to the side of the engine. it just turns into a total dog below 2k RPMs but above that as the dynamic sealing of the engine comes into effect it is just as zippy as any new engine. old school rotary drag racers just run their engines until starting fluid won't work to get them started, compression just affects idle and stoplight to stoplight type driving.

 

Some will argue this point, but the stock intake is restrictive and is not freeflowing. Fabbing a true ambient air intake with smooth runs will help with spool. It will also multiply the effect of a free flowing exhaust. These are the things a turbo rotary responds to the most.

That said, the S5 has an electronic boost controller built in, but with an aftermarket boost controller you will maximize the spool, then you can tune the boost curve overshoot.

These will all give you more 'boost under the curve' so to speak.

Beware, if you maximize the above you are going to need some additional fuel and a way to tune it.

After you blow the motor, you could rebuild with some of those N/A high compression rotors...

Good Luck!

 

I HIGHLY DOUBT the OP's car is running right. I have driven a bone stock s4 T2 10th anniversary with about 70k on it. It had no lack in low end torque, and the S5 is well known to have better low end. A properly running stockish T2 drives like a DOHC v6. It reminds me of at lot of the naturally aspirated DOHC 6 cylinders from that era (7M-GE in the Supra, 6G72 in the 3000GT), although you still have that boost feel.

Is your car even hitting proper boost levels? Is the boost control solenoid working right? What does the factory boost gauge say? It should hit 450 mmHg/60kPA/8.7psi peak @ 2500rpm and then fall to 375mmHg/50kPA/7.25psi at 4000rpm.



The s5 T2 starts to hit most of its torque band at 2200rpm. What are you complaining about? It's not gutless at all. Either you're driving a messed up car or you expect the car to feel like a supercharged V8. You don't need an aftermarket boost controller to make that low end either.

The factory control, engineered by guys in lab coats, already has a boost overshoot just like almost every other turbo car with OEM electronic boost control. There is a whole section on this in the SAE paper on the s5 engines.

 

I agree with previous post that quesitons how healthy and correct your car is running right now. A stock T2 has good low end torque.... for a rotary. Maybe in comparsion to other cars you have had it doesn't have good low end? Point is, my first thought after reading you intial post is there must be something not correct with your current setup.

As for how to improve low end regardless of your individual situation? I have this to offer. I have been driving FC's for the past 11 years. I have owned 6 total. 3 s4 NA's, 1 s5 NA, 1 s4 T2 and my current s5 T2. I have driven them from bone stock to wildly modified in both NA and T2 form. The most effective way to add VERY noticable low end torque to a T2 is to install NA high compression rotors when rebuilding it. I would not rebuild a street motor for a Turbo 2 without putting NA rotors in it. Night and day difference in the low end. The s4 T2 motor I rebuilt was so much more responsive with the 9.4 comp rotors. Turbo spooled faster and it was so much easier to drive at low rpms out of boost. From this point I would go with s5 NA 9.7 comp rotors in everything I rebuild. Even if you have a s4 I think it is worth it to switch out the entire rotating assymbly to s5 in any build to get the 9.7 compression. As long as you aren't trying to make over 350 WHP I see no reason not to. My current s5 T2 motor was built by the prior owner for high hp and swapped to 8.5 T2 rotors when rebuilding. It feels sluggish in comparison when I stomp it at low rpms.

Footnotes: HIGH COMPRESSION ROTORS will do the trick. Don't street port on rebuild and the low end will be even better. Open that exhaust and you are golden. It will drive great on the street and take off from a stop like and jackrabbit.

 

serrsly. i would rebuild and port op if u wanna make more power half bridge or full and up grade from there fuel ecu fuel cut disable ect ect. and since money is no object thats what i would do haltech sprint re also pretty cheap and should do what u want if ur feelin froggy get a sport 1000 but its about 500 bucks more but highly detailed fuel maps

 

More power with the bridge.... yes. More power at low RPM's?????? HELL NO. Your power band will be above 6k rpms.

To make more low end power keep the stock ports. Not to mention the bridge and half bridge will fail after time and F'up your enternals. Anyone who bridgeports their daily is looking for trouble. Far more people talk about BP'ing the daily than actually do it. It is impractical as possible on a rotary, short of PP'ing it.

 

im not saying go full bridge port a half bridge isn't so bad don't need a huge port just enough. i remember bcd saying how the 1st time he tried it he only did 1 about 1 inch and 1/8 inch wide and it was noticeable. said full boost kicked in at like 4300 and kept it to redline. don't 100% quote me on that but thats what i recall from the thread i read. but yes def get some n/a rotors will help alot sure u can get a n/a that just kinda quit for cheap. chances are what would be wrong is a coolant seal. -.-

 

Noted.... I just want it to be clear to the OP and anyone else looking for low end power that a bridge or half bridge is the exact opposite of what you should be doing and will kill low end power faster than anything else you could do.

 

http://www.zercustoms.com/news/ZEX-T...us-System.html

 

If you think the low-end power is bad on a S5 T2, then you either need to get your engine repaired or you need to come to the realization that a 2900lb car is not going to perform like a race bike.

 

Karack hit on it.

You need to remove the restrictions from the intake and exhaust. Then get an ECU you can tune as the stock ECU runs the engine ridiculously rich under load. AFRs in the 10s completely kill low end and turbo response.

 

That was me-but thanks for the validation!

 

so I should clarify two things

1) I understand that there are restrictions, the idea is to get as much info on trying to solve or bypass these restrictions to the best of our abilities and so this is a free thought forum so that we can brain storm ideas about how to try and overcome these short falls.

2) The low end power on the S5 T2 is horrible, a car with >2900 lbs, like a Toyota Camry, has a better low end, not just better but rather far better. I understand the limitations that are inherited from having a rotary engine, i'm not complaining about the rotary, I'm simply trying to conjure up a forum for ideas for a solution.

*thanks to all of those whom have contributed

 

im with the "its not running right" crowd here
my S5 TII engine with cleaned up stock ports, and S5 hybrid turbo on the dyno with the run starting at 2000 rpm was making 150ft-lbs by 3000 rpm and averaged 217ft-lbs from 2000-7000 rpm with a peak torque of 312ft-lbs at 5800ish rpm i was maxing out my primaries so that was with me letting off a bit around the staging point.
with a pull from 3500rpm it averaged 259ft-lbs from 3500 to 7000 rpm

do you have the restrictor pill in the vacuum line goin to the pressure sensor? make a night and day differance for low end