Throttle response from 3K! Ouch!
 

I did some testing with fellow forum member Heiko and his new 74mm throttle body. His car (same as mine 2000 S) is really quick and accelerates amazingly well! Well I now know what I have been missing with the 74mm. The time in his car really accentuated the throttle response issue that I am having.

In 3 or 4th gear at 3K it seems like it can take up to 3-5seconds to get over 4K! At 4.5K things wake up and seems fine but it is all too late! At 3K, I would look over at H and say I am “flat” (pedal to the floor board) here… and his reaction would usually be dismay…

Could my used TB be defective? Is there a vario-cam problem? Is there an intake or exhaust acoustic problem?

Heiko’s car is pretty much stock with the exception of the TB and intake plumbing for it. The plumbing is potentially “smoother”. His engine is better maintained..

Mine is modified much more:
short snorkel
rougher prototype intake tube for the 74mm TB; 3.25” dia. rather than 3”
secondary cat by-pass pipes
stock S by-pass muffler (worse flow?)
softronic tune
leaky spark plug tubes/older plugs
older air filter
5w40 oil….heavier

I am wondering if the stock tune works better with the characteristics of the 74mm TB. Any thoughts?

To my knowledge, and that's almost NIL, when you do A/F mods to a motor you need to get the ecu custom remapped or you'll suffer in either low, mid, or high range (or all). Needs a dyno, a few runs and an experienced tuner able to read and remap A/F curves for your given set-up.

Just a guess mate

Sure true..... A/F tuning on these cars is quite involved. The DME should be able to compensate for more air

The implication here is go back to stock in the same areas and see what happens. On the exhaust side this means more back pressure to boost scavenge velocity......put the 2nd cats back in....arrrrrrgh! Stock muffler!

Snork up the intake.....I am using a larger dia. intake duct than everyone else I know of...3.25". This would have to go down to three.

Stock tune...

I suppose if anything were amiss like an MAF sensor I would see codes.

Then start timing the changes in engine acceleration with a stop watch...or camera

I'd start with the intake side of things, and check the MAF. It seems a more likely culprit than the exhaust tuning, which as I understand your setup to be, shouldn't cause a massive dead spot. There's a lot of flow dynamics in the intake path so that air hits the MAF in a way that is in accordance with the rest of the system. Turbulence/swirling could be a factor.

You could be right. It might be that I need a snorkel back in to give me this. But it is so far down stream of the MAF and in front of the filter... That I wonder.

I have my own snorkel in there now ....here is a picture of it versus stock. It is a big difference!

http://986forum.com/forums/uploads01...1381172610.jpg

It may be that my intake pipe is to turbulent.

If you are experiencing hesitation, replace you air flow meter. Its not your throttle body, and it isnt a modification you need.

Could be...it's old but there is no code...just had an emissions check and they now read the ECU

It's more of a bog ...like you are in the wrong gear rather than a stutter or hesitation

Jay, your car is not slow... it just seems to have some bog in mid range...
When you put the bigger intake pipe in did you move the MAF? Also did you try the other map? We'll have a look next time you come over when we have more time:-)

H...

The MAF has never been touched or even.... breathed on wrong! I averted my eyes when working close to it!

If everything is working as is my guess would be the predefined map. With the custom exhaust and modified air intake your only bet to get it right would be for someone to create a custom map on a dyno. Hard to justify the cost though.... At least in my opinion, especially if you don't track it anymore.
Your car is absolutely mint and looks and sounds great...
Heiko

Oh
My
God.

Are we really trying to reinvent the wheel here? Bigger pipes, different maps...

how about you borrow your friends air flow meter insert and see how it goes?

There are days when I would love to go back to the mini 1" stock headers, restricted cat converters, the excessive back pressurized maze-designed exhaust system. Not forgetting putting back the stock map tuned for retarded ignition and low grade petrol AF curves - and of course putting back all the emission restrictions that the manufacturer hides in the oem mapping. What else... oh yes, almost forgot to put back the motorcycle size TB back in there!

Not reinventing the wheel. Just making ourselves a Porsche car (instead of a DOT restricted vehicle).

My wife used to like the car before... she hates it now ;) To each their own!

I am all for it. My boxster has a 996 3.4 engine, headers, a full exhaust....I love making a porsche drive like a real porsche.

What I am against is using tuning the ecu as a bandaid to fix an existing problem. Hesitation on a stock engine is a fuel metering or vacuum issue, and needs to be resolved before any further modifications...and most likely the air flow meter

Yes I doubt I would custom map it. Don't need to pull past on the back straight at CTMP at present...not driving at all

It may that the stock map has more adaptation capability than the one I currently have loaded. I have heard the comment that the stock is really pretty good with coping with changes...

My modified one may be optimized for the stock S TB which is 68mm

Oh yes thanks! Glad you like the sound!