I've just recently completed a TII conversion in my 87 gxl. Car seems to run excellent, good idle at around 800 rpm with a strong vacuum, and is smooth with no real hesitiations. Only problem that has happened recently that i've noticed was that the boost drops at around 5500rpm and starts decreasing to about 5 psi!!! before i hit redline. I am boosting at 10 psi and i mainly notice the boost dieing in second gear. (although it drops in each gear) By the way i have:

j-spec s5 TII engine
greddy fmic
walbro fp
hks intake with custom honda TID
hks super seq BOV
emissions removed ACV, BAC
TB mod
ported wastegate on s5 turbo
Manual boost controller from boostvalve.com (ball and spring type)
apex n1 dual exhaust
racing beat downpipe

Before installing motor, I checked the turbo and it seemed in great shape with hardly no play. Any thoughts on what it might be.

Thanks,
Chris

 

vac leak check everything twice

 

I know that when completely stock, the boost starts to drop around 5500, but I thought that was supposed to go away with the exhaust opened up?

I don't know, it could just be the stock turbo.


how do you like your greddy FMIC? I'm thinking of getting it.

 

it's pretty normal. maybe not quite that much though. mine drops after 6000 or so to around 7.

the stock turbo is too small. it's ment for a stock engine and lower spool up.

what's between your downpipe and catback? a cat? or mid pipe?

 

That is typical, like Scott_89t2 said. The stock turbo just cannot flow enough for the higher rpms - even the S5s. You should look into a hybrid turbo, or something from BNR. The upgraded stockers will hold boost until redline, and make a fair bit more power .

 

mine dropped off even when I had a full exhaust, and now that I have a cone, it drops but less.

 

Doesn't the ECU do that? Because isn't that the reason why a lot of people buy FCDs???

 

What FCD's do is "trick" the ECU into thinking you aren't running higher than the preset boost level. Without the FCD, it cuts off fuel to the rear rotor and hence the bucking. With a stock turbo, you cannot keep the boost at a preset level above 1.0. It'll start dropping about 6000 or so to .7 or .8. It's due to the small exhaust wheel and small wastegate. The only way to defeat that is a full turbo upgrade with a larger exhaust wheel.

 

By the way, having an FCD doesn't give you a safe boost level above 1.0 in terms of fuel. It leans considerably above 1.0 with stock injectors. I would highly suggest re-wiring the fuel pump and get bigger secondary injectors. When you drive at night, hook up a wire to the fuel pump and see what voltage you are getting. I'll bet that it's below 11V.

 

Stock turbo, more than likely, wont hold boost til redline. I dont think it even holds boost in bone stock trim.

Its a common "problem" and the only real cure is to get an aftermarket turbo.



This is a very common subject. Please search next time.

 

Thanks guys for the info! I will definitely check again for vacuum leaks but i doubt it.

Scott, after the downpipe I have a 2.5 inch midpipe/custom straight pipe that connects to the apex n1 duals. Usually the boost tends to drop around late 5000 rpm usually around/near 6100 rpms to be more exact. I guess it seems to be more of a normal issue and might just have to go with a hybrid turbo.

BigRetardhead, the intercooler works excellent and is very INTIMIDATING to people. Overall it is a great mod and really havent seen no signs of overheating. Will try to get pics on the forum.

Now what do you think would be the best: a hybrid turbo or a full to4. Money isn't really an issue but as long as i can keep the factory ecu? What i am looking for is just a bit more power to get my power band deeper into redline area, therefore, if a hybrid turbo is good for the money and will do the job, than that it is.

Chris
87 GXL into s5 turbo conversion

 

It doesn't.. my S5 TurboII doesn't even hold 5.5 psi (my max boost) all the way to redline with a full exhaust and a cone intake. Isn't that sad?