throttle respons on turbo engine
 

just a curious thought what is it that affect the most at our cars slow free rev throttle respons?

my car has LW flywheel, ported heads, cams and frankencis so i can adjust the fuel good, but it has that boring slow free rev feeling.

i am guessing the low CR and timing is one thing.


also curious how much difference in spool up is a shorter exhaust manifold and a modern twinscroll turbo make?

A modern turbo will transform the throttle response..drastically.

yes i know

I wanted to discuss the technically complicated parts of cis turbo porsches that makes just this engines so remarkable slow free reving

The air meter plate is not the fastest reacting when you compare to something like ITb's. Removing back pressure will improve throttle response, such as replacing the OE muffler with a free flowing muffler or Zork tube.

I have a C2 turbo with CIS and recently a modded fuel head.
My Turbo is a RUF K29 (Pig).
My modification list is linked below.

My C2 revs so fast both free rev and under boost - I have had to set my soft touch rev control below
stock limit. The car Revs so fast it will fly past redline before you know it......I hit the soft touch rev limiter so easy and it sounds like gunfire and sets the Cops off.

http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/767012-forced-deal.html

Many things can help the engine rev faster. Light weight engine components, lighter car, shorter gears, higher compression ( more power not under boost) , newer style turbos. You get the idea. Even though I have longer gears, I have all the other items I listed, probably why I can jump from 70-100 in less than 2.5 seconds. Not bad for 45 year old car.

My 930 is set up like the one above with similar performance. Checking my EFI data logs, it revs from 3000 to 6500 rpm in the stock 4 speed 1st gear in 1 second. So that's about 25-53 mph in a second.

I suspect he’s asking about revving the engine in neutral, and asking why it’s not snappier. And for that I’d suggest that the CIS trap door air meter and the heavy flywheel are probably the main contributors. The turbo can’t matter at this no load condition.
Turbokraft had posted an IG of one of their EFI builds and it had insane throttle response. Sounded like a motorcycle. Clearly they addressed whatever the reasons the stock ones are a bit ponderous.

6 throttles will solve your issue. ITB's. They give the Sport Bike Throttle response..... But get out your checkbook.....

I think it may be these cars need the equivalent of an accelerator pump that dumps some fuel down the the intake when the throttle is mashed. Like 4 barrels have.

My car is EFI and I can adjust the acceleration fueling to add in extra fuel for up to 2 seconds when the pedal moves above a certain velocity or when the manifold air pressure changes above a defined threshold. My engine revs pretty quickly in neutral (or anytime, for that matter) :)

Maybe there is a way to accomplish something like this with the CIS system...

Turbo engines are NA engines when reeving to red-line in neutral. A map log should read more or less zero on pressure readings from back-pressure / boost when reeving in neutral on a turbo engine unless the muffler or intercooler is filled with dirt or intentionally mismatched. Throttle response is when the throttle is let open in neutral (or clutch engaged). All other scenarios when gears are engaged and driving is no longer throttle response.

For quicker and fast throttle response these are the main factors:

1) Piston travel (stroke) - keep as short as possible
2) Air volume between throttle(s) and inlet valve - keep as low as possible
3) Weight from rotating parts linked to the crank, i.e. crank, flywheel, clutch, rods, pistons, rockers, valves, fan, alternator, pulleys, etc. etc. - keep all rotating mass as low as possible
4) Compression, static and dynamic (cam profiles) - keep as high as possible
5) Ignition timing - keep as close to MBT (Minimal advance for Best Torque)
6) Fueling, among others correct acceleration enrichment etc...

The turbo spinning with no inlet resistance in neutral have no noticeable change or impact on throttle response

Muffler will affect throttle response. If the car has a stock muffler remove it and see what happens.

My top three are
CIS
Muffler
Flywheel

CIS is always injecting, so fuel is always burning. When you do a throttle blip, there is combustion on the way up, and on the way down.

Muffler - the back pressure, as discussed

Flywheel - heavy to begin with, and the rubber donut makes it worse.

ported heads and bigger cams can also reduce it.
cam timing is another
turbo is a biggie.

It's just one of the many drawbacks of that terrible CIS system. My throttle response was drastically improved by converting to EFI.

The OP stated that he has a LW flywheel, ported heads, cams and frankencis.
What were your heads and manifold ported to ? Typically opening up your intake and heads will gain top end power but give it up on the other end. Which cams are installed ? If SC that should help some on the low end. Which exhaust and turbo ? As stated those are going to be the game changer.
A free flowing exhaust and a modern turbo transforms these cars. I’m not at all versed with FrankinCIS but perhaps there are low end gains to be had with tuning.