viperbob

I had an oil leak coming from my breather cover on the engine. In order to fix it, I had to take EVERYTHING off the top of the engine. So while I was there, I decided to modify my throttle body. Porsche did a weird thing here. Those of you that have had your intercooler off my have noticed the large chunk of aluminum between the intakes. This has two large round ports that then run into the intake manifold on either side. The lower port is slightly smaller in diameter than the upper one. The lower port you would think would be a resonance chamber linking the two sides of the intake and smoothing the airflow. Well it doesn't do anything. Inside the throttle body this port is completely sealed from each side by an aluminum wall. So with a little machining, you will see that this is now opened up.

So what effect does this have? By opening this up, it will allow for additional HP gains over 5200 RPM while potentially sacrificing a slight amount of power in the mid-range. At 5200 the TT starts losing power related to the intake. This mod allows the engine to continue building power. From tuners that have done this with before and after dynoing, they have seen an additional 50+ HP at 7000 RPM. I'll post back as soon as I get the car back together and I drive it. Just thought some of you might like to know a little more about your cars....

jrgordonsenior

Thanks Bob,

Aren't you supposed to be getting ready to instruct a HID light DIY?

And why is your engine so clean?

ca993twin

Damn you Bob. Everytime you do something like this, I start salivating. I'm gonna have to start saving my pennies.

Would this mod work more effectively if you had cams that were more suited for high rpm power?

jmreiser

Hi Bob- Fascinating. In the non-turbo 993, all the resonance plumbing is important for different operating ranges, but in the twin turbo, at full power / full boost, the air is all pumped in there under pressure by the turbos, so all manifold space is immediately filled. I would be very surprised if you can get anywhere near 50 hp on the stock car with no other changes.

50 hp is fairly easy to get with these engines with other modifications, especially changing the ECU programming. But since the stock rev limiter is at 6720 rpm (+/- 20), I think it is safe to assume the tuners (running 7000 rpm) that you refer to have obviously made other modifications, no?

You ARE referring to the intake manifold plenum, not the throttle body itself, correct?

Very interesting.

Jean

Bob, most of the stock or slightly modified cars with K16s or even hybrids on this board will be limited by the size of their turbos that will not flow enough cfms beyond 5500 rpms with their 28 lb compressors, according to my engine builder, a large TB and modified intake are good for a few hp provided the engine is tuned properly for the change and balanced with cams and turbos.

Your car has modified K24s and you might benefit some at the higher range but I would be surprised if it is more than 10-15 hp, raising your limiter to 7200 RPMs might give you more than that with these turbos (I am sure you have it there already ) It would be great if you could do a back to back run on a dyno and let us know, this sounds very interesting, thanks for sharing..

Rassel

Ah, very interesting!
Didn't really think too much about it until Jean mentioned the RPM range. So I had to read it through twice...
Do you know if the GT2 also have this issue?

Jean

Rassel what I meant is that IMO, as jmreiser mentioned, the limiting factor are the turbos rather than the intake on street cars.

I am not sure if this was your question, but the 993GT2 race versions had huge compressors from the K26 series that continue flowing beyond 7500 rpm and 1.2 bar of boost helped by an extremely efficient intercooler, therefore a restrictive TB or intake will have an impact on its performance.

Rassel

Jean,
I'm following you perfectly. My first thought was, why did they design it as they did?
Then I noticed your answer about the RPM limit, and had to read bobs note again and noticed the high RPMs he mentioned.

Seems like you had the same thought as I did about the GT2 with K26s, that is actually the reason why I'm asking

viperbob

I too was skeptical of HP gains. I found a couple of different respected folks that gave me the same info on the mod and some gains they have found. I unfortunately do not have a recent dyno as a before to compare. I was not really planning this upgrade. It just sort of happened when I found an oil leak. I will do a dyno run soon (when I found the oil leak I was putting my cats back on as it is smog time). I will do one with the cats on and then one with them off.

You are correct Jean that with the larger hybrid K24s that I have it may help me more than others. I may use it though with some other folks and see how it affects their cars. If it works, and logically it should have some effect, it may be a cheap upgrade.....

nman413

Does this mean my car is going under the knife again? My car is going to end up with the most power obtainable using stock turbos

ruffy

wrt the oil leak...
anything to report there?

jmreiser

Has anyone done a before & after dyno run on this change?

I am sure we would all be interested, whether the engine is stock or not, as long as the dyno run is before the change, then after the change, with other mods noted, and no other mods introduced for the dyno run. With others reporting this, hopefully someone has done a back to back dyno run on this change. Who knows, maybe it's really 100 hp.

In a non-turbo engine, we are sucking through a collection of straws, pipes, and chambers. Airflow is crucial and every nuance matters. But in a turbo engine on boost, we are inflating a tire under pressure. Does it matter if there is an obstruction halfway around the tire? No, it will inflate anyway. Will it inflate faster or slower? Not much difference either way, if anything it might even inflate faster, since there is less turbulence from the flow recombining across the wall just removed. The air flow is going to smash into itself from opposite sides after the mod.

crossdrill

pictures measurements. my engine is in the shop right now.
also does any one done k-24's the idiot that send me the turbos from germany
send them for 996, terefore i cant use the turbine housings. any ideas....

Acropora

Bob,
What does your butt-o-meter have to say about this mod?
Is there any hard data from the tuners that noted 50hp available yet?

jmreiser

Buttometers are misleading for this sort of change because there is a different amount of fuel (weight) in the car before & after, the air temp changes (direct influence on the ECU cutting or adding fuel & timing), etc etc etc. Headwinds, up/down hill, etc.

Stopwatches don't really help unless you have a private airfield or somewhere that you can really open it up and leave your foot flat to the floor for a long time, long enough to make the inaccuracies of starting & stopping the watch small compared to the total time. If human reflex on the stop watch is 0.4 secs of reaction time, or 0.1 sec of imprecision, you will need at least a 25 second test to get the stopwatch error down to 2%. Then add back the variables above, and it is still highly subjective. Oh and you'll also run out of gears if the thing is making any kind of power.

Dynos are really the only way to know. Sorry, I wish there were an easier way. Maybe something in-car with GPS and an accelerometer, but we still need a way to manage the rest of the variables above. Not too likely.