Wankel7

I have a '91 TII with these mods:
'91 TII - "RotaryR"
Atkins Streetported Engine
Apex N1 Dual
RP DP & Hi Flow Cat
K&N Drop in filter
Walbro High Flow Fuel Pump (255)
Water Temp, Boost, Oil Temp, Oil Pres
Haltuner Air/Fuel
HKS FCD
Apex S-AFC
720CC Secondaries
Koni Sport Struts
Greddy Turbo Timer

My problem is this. I will floor it in 3rd gear at 4000rpm it boosts to 11-12 psi. Then as it nears redline it will progressivly drop to 5-6psi. What gives? I have several guesses:
- It is getting to much fuel and drowning in it (Getting it tuned next week)
- Needs an upgraded intake to breath freely
- S-AFC says airflow meter peaks at 66%? What gives? Should be 100%?
- Any more ideas?
Idles rock solid and pulls about 13-14 " of HG at idle

Please help

James

Scott 89t2

the boost dropping is common with a stock turbo. the street port just makes it worse. adding a custom TID with a cone filter will help. but you will also creep more.

time for a bigger turbo

Wankel7

100% Humidty
Started in 2nd gear to finish in 3rd

Best of 5.7 seconds

How does that compare?

Tried starting in 3rd gear. 8 seconds. Maybe the streetporting has moved the power band up on the tach?

James

Chance

I was curious about this too. My airflow meter also peaks around 66%. I was under the impression that it should peak at 100% as well. Does anybody's peak at 100%?

Scott 89t2

this topic came up a while back and everyone said they only had in the 60's.

fastrotaries

That's why i'm dumping the stock system and getting a Haltech...the stock system is highly inadequate for that motor. Technology has gone above and beyond it's parameters.

I have a stock motor and it does the same thing. Even with a Profec B. The worst is that your torque curve really takes a dump. I really couldn't care much about peak horsepower as long as the torque went up and stayed there.

Wankel7

I was under the impression that the stock turbo would boost too much at the higher RPMs. Not fall flat on its face at the higher RPMS.

What mods do you have fastrotaries?

James

Josepi

Weell I just got done staring at my dyno sheet, and both HP and TQ fall off at 6300ish, while I kept it floored to 7k. all stock, just thought i'd shoot some info in here to help ya guys guess.

Judge Ito

Try to check your internal waste gate valve. I have had similar problems with customers cars. After carefull inspection, I have found the exhaust turbine to have many cracks right where the waste gate valve is located.

Judge Ito

Look into your exhaust turbine housing. It's a big Job, but its a common problem. You will have to take turbo off and split the turbine housing. Only go this way if e verything else has been checked. Like leaks in your intercooler make sure your clamps are tight, boost controller, etc,etc.

Wankel7

I hope to hell it is not that. That turbo is brand new with 1500 miles on it. But I will keep that in mind.

IF it is a boost leak...would it just have low boost throught the rpm range? Or could it be a line somewhere blowing off at higher boosT?

James

Wankel7

Well, I have helped out my problem a litte. Started screwing with the manual boost controler. I didn't think it was a problem cause the boost would initally go to 10-12 psi.
Now the boost only drops to 9 psi as it nears redline. I really wish I had an electronic boost controler. That ACV-R by APEXi is sweet.

However, my car is sure faster now that I have started working on the boost controler. I blew my first hose off under boost today At about 12psi it went WHEWWWWW and the engine died. Beleive it was the hose that went from the bov to the intake. And I also found my upper radatior hose about to blow off. Good finds today

James

Scott 89t2

I told you before the stock turbo is too small. it will drop off in everycar. and even worse with a street ported engine as it flows more air. upgrading your intake and adding a 3" TID will help. but you really need a turbo upgrade to get full boost in high rpms.

JohnL

The stock turbo will loose its efficiency at higher boost levesl... example: you can set your boost controller to 13psi, initially you may see boost hit 13psi, but as rpms increase your boost will gradually decrease.. this is normal with the stock turbo. You have to remember this stock tubo was designed to run at boost levels below 8psi. I have a compressor upgrade on my stock tubo and also have the waste gate ported. I have been told the turbo is good for 15-16psi. I am only boosting 10-11 psi right now, still tuning the car, however, my boost hits 11psi via Apex AVCR and stays at 11psi to redline.

Also, for those running full exhausts on stock turbo 86-88, you'll get boost spikes, possibly as high as 16psi, but this will drop drasticly as rpms increase..

Also, I am on my second exhaust manifold, and I am going to have to change it soon do to exhaust leaks, very small stress cracks, and the turbo also has cracks, this is very common with Mazda and I wish they would have designed a better exhaust manifold.