My problem can be explained with an example:

In 4th gear, if I start going WOT at 3k RPM's, the boost will creep to 8psi by 4.5k RPM's, but then it begins falling right after this... Down to 6 or 7psi by redline.

BUT, if I start WOT at 5k RPM's in 4th gear, the boost will quickly spike to 11psi and will hold it until 6k RPM's or so before dropping down to 8psi or so by redline.

So the amount of psi I'm running isn't dependant on RPM's, but where and (how long) I'm in the power-band... Why?

Another example, if I start slow in 5th gear at like 2.5k RPM's and begin WOT, the boost will MAX out at 5psi by 4k RPM's and just stay at 5psi until I let off... WTF?

The Rx7 in question is a s4 TII
-rebuilt using 9:4:1 rotors
-streetported
-TO4B hybrid turbo with heavily ported WG (new flapper welded)
-CS DP/MP bolted to an Apexi GT series cat-back exhaust
-K&N drop in filter
-MBC
-Greddy type-S BOV
-Greddy 720cc injectors
-Walbro 255lph fuel pump
-Apexi S-AFC

The S-AFC is pretty much untuned, but I actually might be taking it to be dyno tuned tomorrow.

If anyone knows what could be causing this strange boost pattern please inform me, lol. Right now I'm thinking there are several possible reasons; untuned with gobs of fuel, MBC is too weak to support the flow of the hybrid, WG actuator arm needs to be shortened, twin scroll is getting in the way (somehow) or...?

Also, tomorrow I'm buying an EBC. Will this help?

Thanks,

 

I would suspect that you are running a BIT rich in the higher engine loads (the final example), higher r's and at higher boost.... That'll cut down on exhaust pressure and, thus boost!

Boost normally drops off at higher R's, but, MAN.. you didn't take the twin scroll flapper out??? I would suspect that as a culprit as well!!!

If there is no tension on the wastegate arm when its in the closed position.. that'll effect spoolup a bit as well...

 

why would removing the twin scroll result in a drop in boost?

it shouldn't, mine didn't... it actually boosted too much, hitting up to 16PSI+.



i still say it is a weak WG actuator spring or wastegate problem. no leaks in the intake pipes?

 

thanks for the answer YearsOfDecay, pretty much what I suspected.

Anyone think an EBC will help?

The previous owner of the turbo and safc was able to hit 13psi consistently and dyno'd at 247whp at 11psi... Using his exact MBC, that on HIS setup was set for 13psi makes the boost pattern that I used as an example (11psi max etc.)... Weird huh?

 

No, I don't suspect any leaks of any sort... Everything's pretty much the same as it was before the turbo and fuel mods install. I'm pulling a solid 11 vac. press. at a 750RPM idle. There's just not too much that could go wrong in terms of a boost leak...

Karack, do you think an EBC will help?

I'm going to go buy one (retail) before I get my car dyno tuned tomorrow.

Also, what should I do before I dyno (if at all)?

 

I just realized that I'm a n00b... lol. There's so much info to be had just from searching.

Tomorrow I'm pulling my turbo, wiring open my twin-scroll, 'shortening' my WG actuator arm installing an EBC and frikkin' getting my car tuned at a local dyno...

I hope everything goes good... I should be asleep right now, lol.

 

check that WG flapper while you are in there.

 

An EBC wont help :-/. The best that can be done is buying a closed loop EBC and help sustain a boost "above stock" By using a bleeder valve.

I think your setup would be great R-tek territory.

Mine does something similar. Runs 6psi all day in 4th gear when you reach 7.2K+ the boost drops to 4psi and around 3psi at 7.8k, 1st 2nd and 3rd run 6psi evrywhere.

 

when it was on my car it boosted fine. no problem... 13psi from about 4.6k till 7.5k.
I did have a 3" TID that would help a little with the boost fall off.... well it did on mine.
it might just be tuning.... but there has to be something else involved... i mean could it really be that rich?

 

I remember seeing something (in my searching) about a 'boost controller actuator'...? I've never heard of it (it's part of the stock system?) and it's supposedly on the oil-filler something blah, blah side of the motor. Supposedly, you can't reach 'full' boost if it's busted...?

What the heck is this?

BTW, I'm about to start the turbo removal etc. in about an hour.

 

you gonna make a TID before you dyno?

i dunno about that boost thing... shouldnt have anything to do with this.

wire the twin scroll open,
check the wg door is still how it should be and closing correctly,
make a TID.

 

Im having the same exact problem. I have a stage 1, I can boost all great at 6psi and holds fine.


I tried cranking it up to 15, it would only goto 9psi and slowly drop until 6psi.

So if I had the car tuned better, it would hold 15 better?

 

tuning makes a huge difference. adding a 3" tid was the best thing to help spool and to keep boost from falling off.