10thAEWHiteHeat

iTrader: (4)

So there isnt much left i can do before i rebuild my motor aside from going big turbo or getting a standalone. I know that some people port the wastegate on their turbos to get better turbo response and efficiency (which was what i was gonna do). However, my mechanic suggested instead to cut the "flapper" in the turbo out and that would help me hit full boost faster. Then i could add a little more boost if i wanted (I'm at 11 lbs right now). What do you guys think of this?

need RX7

iTrader: (4)

No.

K-Tune

iTrader: (26)

porting the wastegate helps control boost levels, it doesn't do a damn thing for response.

if you're talking about removing the twin scroll door(s4 only)...sure go for it. i have a j-spec manifold that i modded to eliminate it.

need RX7

iTrader: (4)

Oh yeah, didn't think of that. When I first saw 'flapper', I thought he meant the wastegate flapper. I was like "uhhhh...... no. very bad."

10thAEWHiteHeat

iTrader: (4)

^^I believe that is what it is.. Well my goal is faster boost, and (if its not the shortcut to a blown motor) like 13lbs of boost. So will that help build boost faster?
And yes i know that more boost equals more stress yada yada i just need the motor to last about 3-4 more months more before i rebuild but i am fiending for more power LOL

Lewk_FCRX7

Probably not more effort than it is worth - a standalone computer + tune is a far better option... I was running a stock ECU, made 160rwKw @ 12 psi, then I installed an E8 - had it tuned and made 202 rwKw @ 11 psi! a 42 rwKw power gain.

I'm not familiar with the s4 turbos but it sounds like there is a flapper/two path arrangement to increase exhaust gas velocities at lower engine rpms (converging - diverging nozzle). So by removing the flapper and allowing the exhaust gas to flow through a larger opening, you will get lower exh. gas velocities and ∴ your turbine will have less kinetic energy emparted on the wheel = less turbcharger rpm and slow boost reponse!

I may be wrong though - I am just theorising.

Cheers

- Luke

freemanrx7

Buy a blown s5 turbo and just use the hotside and manifold. Combine these items with your turbo and be done with it. As you boost higher you will have a larger wastegate to let out boost.

joeylyrech

iTrader: (11)

a stock turbo above 12 psi is not a good thing to do,at those boost level the turbo is moving hot air (the air gets hotter)and instead of getting a nice cool charge on the motor you get a hotter one and this combine with stock injectors and ecu equals to a blown motor.

K-Tune

iTrader: (26)

leaving the stock twin scroll device installed will make for quicker response as long as it's working properly.

10thAEWHiteHeat

iTrader: (4)

well my injectors are not stock.. i have 720CC secondaries, and i have an FMIC to help the hot air.. is it still not a good idea to boost above that? So the best route would be to get an S5 turbo? I guess that make sense.. Good for maybe an extra 15 horsies? Lewk I understand what you are saying but i will be going Microtec after my rebuild shooting for 280 to 300whp i would rather rebuild and then get the standalone. What does a used S5 turbo go for?

arghx

iTrader: (3)

do yourself a favor

If motor-wise your car is running decently right now, save the money you were planning to spend on an s5 turbo upgrade for something more useful. Got any electrical problems inside the car? Maybe some broken interior pieces? Broken antenna mast? Fix some of those. You spend your time inside the vehicle and you will definitely enjoy it more if it doesn't look and feel like it's falling apart. A swap to an s5 turbo is not going to make a huge difference if your s4 turbo is working fine and you already have an FMIC and all that stuff.

For engine performance, save your money up. If you don't have a big budget, get a hybrid. This will be just fine with an Rtek 2.1 no matter some people here are saying. I have many hours of tuning under my belt on FD's and FC's and I will say that standalones are a lot of bullshit and are not worth it for smaller turbo upgrades on an FC. You can control fuel and ignition with an Rtek just fine, and people are dynoing in the low to mid 300's with them. Standalones require a lot of tuning to get that stock-feeling stock throttle response and driveability, not to mention the monetary expense and the wiring (even if you go Power FC there is some wiring). Go all out for the standalone if you do a full T4 turbo with a 4" inlet and/or you plan to run bigger than 1000cc secondary's.

10thAEWHiteHeat

iTrader: (4)

^^ well the plan is rebuild and push as much power out of the stock turbo, and then upgrade to something like a BNR stage4 for 400+whp. The car is in great electrical and interior shape and the exterior goes into the bodyshop in like a week. Thanks for the useful advice but i have considered all of that. I am just curious to see what the car can do with a stock turbo, motor, and computer before i do my major work.

KhanArtisT

iTrader: (2)

You can boost more but the extra boost coming in will probably be canceled out with the hotter intake charge yielding little or no gain in HP.

I doubt that an S5 turbo will actually end up making more peak horsepower compared to an S4 with the twin scroll removed. As far as I know the only difference is the divided manifold, lack of twin scroll and twin chamber wastegate design. It will probably lower the boost threshold and reduce boost creep if you have any.

Porting the wastegate has to be one of the most misunderstood mods in the RX7 community, lol. And the bigass twin scroll flapper on the S4 turbos is known to become a restriction at higher RPMs so I would remove it unless you need all the response you can get. Tip for removing it: hit it with a hammer.

Oh and stock S5 turbos go for anywhere from $100 to $300 plus shipping.

arghx

iTrader: (3)

If you are looking for 400whp, a hybrid turbo is not going to do it, generally speaking. You will need at least a T04S turbo (which is essentially a BNR stage 4 but with a bigger compressor housing and turbine housing) with an aftermarket manifold requiring an external wastegate. Other options are the Holset HX35 and GT35R if you have more money. You need to start looking at the single turbo forum.

Practically speaking, the stock turbo will get you 250rwhp max. You might be at 230-240 now already. You can gain more horsepower from a change in the weather than whatever mods you have left. Trust me man, I've been there... if there's nothing wrong your current setup, don't waste your time and money dicking around with stock stuff anymore, not with your horsepower goals.

francogt1

iTrader: (2)

if you port the wastegate , the flaper wont close it good after that to seal the hole, right?

i will have to fab a bigger Flaper as well am i right?

S4 stock turbo

arghx

iTrader: (3)

http://www.aaroncake.net/RX-7/s4wastegate.htm

read the writeup

10thAEWHiteHeat

iTrader: (4)

so remove it? Well i need a mojority vote here lol. I hit 11lbs in 3rd and 4th gear sometimes 12 for a second. But I want earlier boost, to hold boost, and more boost if its not too much to ask lol.

RotaryRocket88

iTrader: (7)

What kind of boost controller are you using? If it's a bleed-type MBC, you can improve boost response by switching to a ball & spring MBC or a EBC.

You're not going to be able to make the stock turbo hold peak boost constant. It'll always decline up to redline due to the compressor and turbine sizes. The upgraded wheels and clipped turbines on BNRs and other hybrids can help, but it won't hold say 12 PSI the whole way.

10thAEWHiteHeat

iTrader: (4)

yeah thats what i thought.. i was considering a manual boost controller. My car runs on boost creep so i don't get the same boost levels in every gear. Will removing the flapper and adding a boost controller give me the boost level i want in every gear and eliminate creep?

arghx, i have seen well ported motors with stock turbo and standalone get upwards of 260without breaking 10lbs of boost so i figured i could get closer to 300 with a sick motor and like 13lbs on the stock turbo. And i thought BNR had a stock port stage 4 go 400whp? If thats the case a ported motor should make more than that right?

Aaron Cake

iTrader: (1)

The stock turbo will never give you 300HP. Never, ever. It just can't flow enough air. When you spin it up to where it theoretically could, the intake temps skyrocket and the turbochargers lifespan goes down dramatically. 260-275HP is about the limit on a perfectly tuned system.

arghx

iTrader: (3)

260rwhp? When a good stock turbo setup will get you 235-250? 15whp is nothing for forced induction cars. You can go to sleep and wake up the next day and your car will gain 15whp from a change in weather alone. Don't waste your time trying to get more power than what you have. You can try and port out your wastegate and it will help your boost curve a bit (if you then set up a boost controller properly) but you need to just save you

The car that did 400whp had a Cosmo 13B-RE, which has bigger intake ports, higher compression, and a better intake manifold compared to the s4 motor. Even with a full T04S 60-1 (essentially BNR stage 4 wheels in more efficient housings) it will be tricky to make 400whp at 14-15psi. J-rat got around 350rwhp with a reman s4 13bt and BNR stage 4. That doesn't mean the BNR stage 4 is a bad turbo, it's just not suited for your goals.

freemanrx7

IF you can find a blown s5 turbo you can combine it with your good working s4 coldside. The whole idea is finding one cheap and using yours.If you do a hybrid down the road an s5 is better because of flow+wastegate. The s5 does have a twin scroll sort of.

freemanrx7

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/twin-scroll-removal-746913/page2/

eage8

iTrader: (9)

if you're running 13 psi on your stock turbo it's not going to last long... before you raise the boost, take off your intake and try to wiggle the inside shaft of the turbo, how much this moves says how dead your turbo is, it's dead when the fins touch the sides...

basically, all you have to do to get what your after is get a electronic boost controller, like a greddy profec B spec 2. you can raise boost, and it'll come up faster because the boost controller will be controlling the wastegate.

I don't recommend running that kind of boost on a stock turbo, I would say 10 or 11 psi is maxing it out.

arghx

iTrader: (3)

when you put a boost controller on top of a wastegate that already can't control boost, it will make creep worse and your boost pattern even more inconsistent as ambient conditions change.