B230ft Power Curve Issue

Hey everyone I'm home sick today and thought I would worry about my car some more.

I drive 88' 745, b230ft, t cam, m46, lh2.2, td05-12b up to 11psi with an mbc. Newer tune up, newer fuel pressure regulator, recently cleaned injectors, O2 sensor reads 0.12V-0.88V, timing at idle is dead on, few months ago confirmed in tank pump was working while replacing the submerged fuel hose, running a genuine n/a main fuel pump in good condition, newer fuel filter and fuel sock. Haven't checked fuel pressure. Engine is also pretty worn out with lots of blowby and over 258K miles.

I've noticed something lately while running through the gears more aggressively than I normally do. At 3500 rpm and above the power seems to hit a plateau. I would think that this range of engine speed would be where the power wakes up. I know torque might start going down but hp should be picking up right?

Am I looking at a boost leak? When I installed the n/a main fuel pump I was told it should flow plenty for my application, maybe I need a turbo main fuel pump? Something else I'm not thinking of?

Any help is appreciated. And this isn't my biggest worry right now but thought I would ask

Normal, and all things considered pretty respectable. T cam turbo cars have a great big powerband, even for an old-school turbo, around 2500-5300ish rpm.

The only way you'll improve on that is by using a ball-bearing turbo or a head with more valves.

edit: and variable valve timing

Possibly a partly clogged cat?

It's also possible you're running short on fuel, which would be a bad thing for the motor. An AFR gauge would be good, even if it's one of those wonky NB things.

Hey thank you fellas.

JohnMc: thank you for the suggestions. I should have added that I have a 3 year old cat back exhaust and a gutted cat.

Woodenpudden: thank you too, but I'm a bit confused as usual. Are you saying its normal for the power to flatten out around 3,500 rpm's? Sorry for my confusion. And likely different but looking at curves for b230f engines it seems hp increases up to around 5K rpm

Thank you

Barring any other issues such as a boost leak or fuel. The T cam is very good for what it is. However, it is normal for the power to flatten at around 3500 rpms. The torque starts going away and while the hp is still trying to build a bit from about 3500-5000 rpms not much more is going to happen.

Since your car is a manual. You can get more high rpm power without a big loss of low rpm power by using a cam like the IPD turbo cam. Then also consider a chipped ecu. That would give you a nice jump in power while still keeping good road manners. An adjustable cam gear is also a good part of the setup. I recently added these parts ot a 89 740 turbo. It really woke up the car and made it how Volvo should have sent it to us. In my opinion.

Hey thank you dl242gt.

Looking at my last post I hope it didn't come across wrong, I'm just genuinely ignorant. Thanks again guys.

Surely. The M cam in the n/a cars and the T cam in the turbos are conservatively designed to work great with an automatic right off of idle and easily pass emissions. They are very well designed for what they are. The give back for that is a loss of torque above about 3500rpms. A turbo helps with the turbo cars.

It felt like I got a new engine with power everywhere when I put the enem cam in my turbo.

Check the intake hoses between airbox and turbo, they get soft and collapse when boosting

And perhaps I read into the original post more than was there. I was thinking you were noticing a marked drop in power over that RPM, but reading it again you say it just feels like it plateaus.

While the engine does make more HP at higher RPMs, it's not making more torque. And torque is really what you are feeling. You can create and destroy torque by changing a gear, so it's not a great measurement of 'power', but in a single gear, accelerating up through the RPM range? You're not going to feel the car pressing you more into the seat as the HP goes up the curve, you're really going to just be feeling that torque curve. And the torque does plateau and start to drop off past that RPM range, at least with a T (for Tractor?) cam.

The T cam was made with a somewhat paranoid eye toward emissions - making sure the turbo didn't 'blow' any fuel-air out the exhaust if there was any valve overlap? or maybe they just wanted to minimize turbo lag by encouraging early spool with a stump pulling low rpm torque cam. And many of their cars were sold with automatic transmsissions, which can't really utilize higher RPM's anyhow.

Excellent stuff guys. Thank you much for the great explanations and options. I value having such a great community here.