John Boggiano

For almost as long as I can remember, my 964 has had a characteristic, small step in the power delivery. It only occurs at full throttle, beyond about 5250rpm. It is accompanied by a distinct change in engine note and I have always assumed it was due to the resonance flap operating.

Quite recently, the step (and accompanying change in noise) disappeared, although I couldn't detect any loss of performance. During an extremely thorough 'service' at Unit 11, everything was checked and given a 100% bill of health. The hammer shows the res flap is OK, and I can hear the 'click' of its 'test' operation when the ignition is turned on. There is (apparently) nothing wrong at all. And yet, the step is still 'missing'.

Any ideas?

Andy Roe

Pull your seat forward a bit so you can press the throttle all the way to the floor! j/k!!

LouZ

My 964 has a sweet spot at 3800 R's. It is quite noticeable and almost feels like a downshift. Then the power really comes on.

Smokin

Mine kicks in about 4000 - 4500 (Depending on which gear I'm in.) and pushes me back in the seat. I feel it almost every time I drive it!

jimq

I thought all older 911's had a power step at around 4000 rpm. Seems my other 2 had it also.

citychap26

Mine really kicks in at 4000, I also have a chip, decat, stainless steel exhaust and cone airfilter

Colin 90 C2

the step was much nore pronounced with the stock chip. It almost felt like the car was gulping for more fuel.
Now with a custom chip, it is much smoother, though still there.

CHASE

Back in the day I think this was referred as the engine was " coming onto the cam " or something like that. Mine has this surge also around the same rpm.

John Boggiano

So does anyone have any ideas why mine has gone AWOL?

a964man

Yep, i know what you mean there is a definate step in the power at about 4000 rpm and then another higher up the revs at about 5750rpm which i only notice at full throtle in third, forth, and fifth gear it was doing it quite a few times when i followed you the other day dosen't another injector come in or something, I'd like to know what is happening,

Cheers
Andrew

DaveK

If we're talking about 4K rpm - then yes, mine used to until I had it chipped by JZM several years ago. Then the kick disappeared.

I am almost certainly going to return to stock chip when it's serviced there in May.

JAMES J

CHASE.....I remember saying the "when the Cam's cut in".....Around 4k it's bye..bye
Jim

John Boggiano

It's Andrew's 5750rpm step that I mean. It's very like a VTech engine, for those that know them. Much more than a 'coming on to the cam' feeling, like Andrew said, it's almost like an extra injector firing, or like an extra cylinder suddenly cuts in.

I wonder if my res flap is a bit gummed up, even though it does operate.

andrew911

It could be gummed up.....Garret 376 has a post right now about this....good timing! the title is "cleaning out the intake system... "- you may have to search if it's off the page....

Andrew, I don't think there is any other injector that comes in on the 964- it's just the combination of higher revs w/tune of engine plus the change in the intake resonance. My beetle does have an extra injector though (the "5th injector"), which I believe is used on startup to supply more fuel- like a choke on a carb to increase the fuel to air ratio, but it's such a primitive fuel injection set up its more like a cross between a carb and a modern fuel injection system

springer3

My 86 300E has a 7 th injector for cold starting, but it does not kick in for extra power. I only count 6 injectors on the 964 engine.

I definately feel the two changes in WOT engine output, first at 4000 RPM, and the second one as the redline is approaching. It would be interesting to know which one is the flap opening. If it is the upper one, John may have a bad resonance flap.

Have you tried a top speed run to see if you have lost a few MPH? Your avatar implies you have the speedo wound up all the way at least once.