View Full Version : GT4 Questions about engine

01-05-2005, 11:03 AM
Hi Sorry to be a bother but i need assistance from anyone with gtfour.
im trying not to make it a winge session but yeah.

I recently bought a st185 gtfour, stock except for a kn pod filter, bov (taken off atm for RWC) motor was reco'd bout 10,000k ago buy dalton automotive but i forgot to get the receits so i dont know the specs but i remember he said it had new cams and forged pistons

the car is very nice to drive but i am a bit confused about its behaviour.

It pull ok from about 3,000rpm to about 4700-5000rpm but power dies after this i dont expect to rev anymore than 6000rpm with a stock ct26 but i thought it should atleast get to 6000 easy? , Should it?

I have also noticed that when im on boost Witch seems to top at 7-8psi the car has more torque at 1/3 to 1/2 throtle than it does at full , though in first gear it is better at full throtle?

there is a screw on the AFM that i havnt touched it looks like it is screwed in completely what does this screw do?

there is a thing near the firewall that has a 1'4in hose connected to the plenum it has two other small hoses coming out of it and a big black screw with a spring on it what is this thing?

I noticed a round tube type thing under the front bumper pointing forward with a plug with two wires on it but the wires arnt hooked up to anything what is that thing for ? and should it be hooked up?

the hose that goes to the MAP sensor has some type of restrictor on it, its white and it looks like a filter why is that there coz it doesnt look factory

Sorry bout all these questions all in one thread

How should a stock st185 perform, and if i up the boost what is a safe limit to up it to ?

I much appreciate any help on these question


01-05-2005, 03:56 PM
1. Stock the cars power band drops out around 6k, so that behavior is somewhat normal (as long as it isnt like the car is hitting a brick wall)

2. i boosted to 8psi on a stock CT26, so that is also normal. Crank it up with a boost controller if you want (no more than 12 psi)

3. the cog/screw in the AFM controls the sensitivity of the measurement if air, or similar. Basically adjusting it adjusts the A/F ratio somewhat - best to leave it alone.

4. ive just realised im trashed and i dont think what i am saying is correct. ill leave now


01-05-2005, 09:18 PM
1. Stock, you should have power upto around 6000rpm, you should be holding boost all the way to reline at stock boost. The CT26 has never been known as a turbo to hold its boost/airflow above stock boost

2. Stock boost is anywhere from 7psi-11psi, unless you have an aftermarket boost controller

3. the cog/screw is the AFM spring adjustment, but that should be inside the black casing, the one outside it is something different again.... AFM, best leave it alone.

4. that is the A/C idle up adjustment, adjust this is idle is to low when aircon on

5. those wires could possibly be there for the stock foglights, some didn't come with them, depends, need more info

6. that white thing is not a restrictor, its a filter. Leave it there, its designed to filter out the crap from hitting the sensitive MAP sensor.

Hope that helps.

01-05-2005, 09:47 PM
hrmmm... That white filter thing going to the map sensor is definately from the factory,But i removed it so i could tee on my boost guage. i think i'll go put it back on now! :D

I'd get your timing checked too. a 3SGTE should go to 6k quite easily, but power will drop off after about 5k as you said. also on stock psi (from memory) it still might drop .5-1psi after 5k up to 6k+. thats pretty normal for a ct26...

Also has it been serviced recently? eg. ignition parts, filters and oils. what engine oil are you using?

Ohh. And welcome to the boards!:D

01-05-2005, 09:57 PM
gt-4's are pretty restricted top end, crap stock exhaust ect, so they don't like to rev out much stock, my old 4th gen stock for stock wanted to rev way higher than the gt-4 stock, doesn't take much to unleash that extra power tho

01-06-2005, 06:09 AM
Hi Fellas , Thanks very much for the answers about my car it sounds like its all normal so i am happy!! :-) I think i will check my timing i think it was somthing like
10deg BDC or was it -10deg BDC? the oil is Penzoil 10w30 is that the right stuff?

You guys are legends!! Thanks and happy safe driving to you all


01-06-2005, 11:03 AM
i really hope it wasnt -10deg BDTC, that would make ur car run like shiiiiiiiit! :hehe: