Hello all. I have a 1987 745 with 264,000 miles on it and runs well. The question I have is that at times the engine will seem powerful ( for what it is - NA ) and at other times it will rev then all the sudden it will kind of lose power - it still runs smooth, just less powerful. It seems to happen a lot around 4000 rpm's on the highway. Is this anything to do with the hot/cold air intake system? I was thinking that if the flap shut off the cold air and went to hot, that would slow it some?

Overall the car runs very well, no oil consumption, 20+ MPG all around, shifts nice (except the 2-3 shift is soggy compared to the crisp 1-2 and 3-4)

Please let me know what you think.

I am also thinking of installing the VX cam and adjustable gear for a little more get-up-and-go. any thoughts of wisdom on that? The cam is used, so do I need to "break it in" in my engine? will it kill the engine with that many miles? Should I take the head off and do anything?

Thanks for your input.

Stefan

I am also thinking of installing the VX cam and adjustable gear for a little more get-up-and-go.

It is a poor value. in my opinion, it is a compromised with meeting emissions standards, giving a torque curve that is ok with an automatic, which it sounds like yours is... just don't expect a big difference, but if you're getting it used, it likely is a better value. On a standard trans use an a, b or unitek mini sport.

The cam is used, so do I need to "break it in" in my engine?

Nope, that only applied to OHV pre 76 engines, not 76 -0n OHC type.

will it kill the engine with that many miles?

Hard to say, in itself no, but if it encourages you to rev the engine way up, yeah it could. Most internal strains on an engine go up with the square of engine rpm- so if you say 2000 rpm gives a "wear amount" of say 4, at 3k rpm it will be 9, at 5.5k it will be 30...though, a few other aspects are linear so at 5.5k rpm it will wear only 2.75 times as much. These are quickie rules of thumb, not carved in stone engineering kinda comments.

Should I take the head off and do anything?

Probably not, though there's always the chance of a head fatiguing off a valve stem at those high miles. Replacing all the valves with OE quality is pretty hard to justify though. I'd leave it alone, but keep your revs down.

".....a 1987 745 with 264,000 miles on it and runs well...."

How many owners of other brands could even come close to making a statement like that? Yet it's not at all uncommon on the Brickboard.

You may have an intermittant exhaust restriction, like a muffler or cat guts are blocking the passage when you hit those higher RPM's.

The car has a new CAT adn a good exhaust -- so that is not it.

It still feels like sometimes it is good (power) then at other times it gets "choked" a little.

Yes i impress people with teh milage on the car!

:)

Check your induction system (airbox, vacuum lines, etc...) to be sure, but it sounds like you're just experiencing the Volvo M-cam power curve. Torque peaks around 3k RPM, which is what gives you that 'fast' feeling shoving you in the back. HP peaks up around 5400 RPM, but with the torque falling off, you perceive the car to be slower (and it IS accelerating more slowly.) There just isn't much power to be had up there with the M-cam.

The VX cam is supposed to cure this by maintaining the torque curve at a nearly flat level all the way out to 5500 RPM or so, keeping that 'push' going through more of the upper powerband. This makes the engine more flexible and well-rounded.

Before upgrading anything, fix everything first. An upgrades profit relies on a perfect engine. Check to make sure that your hot intake flap is not always stuck in the hot position-this can lead to a toasted AMM. Better yet, if you are planning on upgrading, why not do an airbox mod?

Rene