RSAErick

Well, after removing the air box to give me more room to remove the foam engine insulation, I decided to keep going to get things 'cleaned up'. What a surprise!

The first thing I noticed was that the air flow gate must have terrible air flow characteristics. I also noticed that it was relatively dirty, with a residue that doesn't come off very easily, if at all:



So I decided to keep going, and take off the intake 'elbow', and then the throttle body. Wow, what an oily mess!!! Take a look at what it looks like:

Throttle body side 1:


Throttle body side 2:


I spent some time with carb cleaner and brake cleaner getting the oil and gunk out of all of these parts. The throttle body actually turned out looking pretty nice.

I also took some measurements of the throttle body bore size, and noticed that it is slightly smaller than the next piece in line - the part that takes the air to each bank of cylinders. That leads me to think that this thottle body might be a good candidate for boring out a bit.

Does anyone have any thoughts on how well optimized the intake side of these engines are? As an inexperienced observer, it certainly appears to be less than optimal.... but what do I know?

Maybe a throttle body rebore could actually yield some results?

Chris M.

I have a relative that bored out the throttle body on his 993 but I don't know if it's the same part or not. It's a 95 so I guess it's as similar as it can be (non Varioram). I'm surprised no one else has chimed in....

c

RSAErick

I'm surprised too, Chris. I searched the archives and came to another post, where I asked a similar question in 1993. Wow, time flies. HERE it is.

Anyway, I was not thinking of upgrading the air flow sensor, but instead simply removing an air flow restriction by matching the inside diameter bore size of the throttle body to the next piece in line.... whatever that thing is (?). The TB seems appears to be a couple mm's smaller in diameter.

I wouldn't expect much improvement, but why not remove any flow restrictions that you can?

garrett376

I'd be wary... it reminds me of what it looks like on Weber IDA carbs when you look down their throats - the chokes on those things are tapered inwards so they look like they close up the intake bore by a couple mm's, but the design is necessary to develop a certain pattern of airflow. I'd be curious what the result would be, but wouldn't want to do it on my own car!

Chris M.

Sounds like Adrian pretty much answered the question in that old thread. I'll try and find out exactly what was done to my cousin's 993 and get back to you. Maybe he has a remap or chip or something else. I know the car's got 350hp and the only other mods I can think of are racing headers and racing clutch but I know there's more.
c

RSAErick

Thanks Chris. The only problem is that Adrian never answered the post from 'jhill', who knows a fair amount about air flow. Plus, it is my belief that a throttle body rebore could be done to remove the restriction from TB to the next flow area, rather than to simply increase the volume of airflow. Maybe I'll give a try and see. I don't really want to pay for a before and after dyno, though, so my results will most likely be inconclusive.

RSAErick

Point taken. Maybe I'll jump on the grenade and give it a try.

dutchcrunch

Erick,

while you are in there you should look down the short intakes and see if the gaskets are deformed as i have removed my intake also to clean it out . my intake gaskets were buldging and after i remved them found them to be soft and mushy. look at my post under injector service on the 964 board. the new gaskets are 993 part numbers and are green in color compared to the black ones that were installed. if you do find them bad let us know if you could. the gaskets are cheap too. if you have the left and right intake runners removed you can look down the short intakes ( the ones that hold the injectors ) and look down them, if you see buldging rubber that looks deformed taking away from the roundness of the intake bore, most likey they are bad.

dutchcrunch

i posted pictures of the gaskets

RSAErick

Dutch,

I believe that THIS is the post with pictures that you are refering to. Those gaskets look horrible. OK, when/if I bore my throttle body, I will probably check mine out too. If nothing else, I think that those would qualify as a "flow restriction". We don't want that!

Thanks for sharing!

dutchcrunch

Erick,

those are the gaskets, they were bad .

I heard that if you bored out you throttle housing you could lose lower end power and get alittle more breathing at the top end. some people complained about losing the smooth idle to full throttle transition. but hey you only live once and if the money is not a problem try it. my intake is diiferent i have the alumunm intake withe the steel throttle housing. i think the later set up is a little better and also smoother in the intake also.

could you let us know the condition of you intake gaskets when you inspect them? can not wait to get mine back together and see if there is any difference. started of by wanting to clean injectors next thing i know i am replacing every belt on the engine, removing entire intake and cleaning it out, painting fan, replacing every intake boot , and while i was in there did a real good hand cleaning to the top of the motor too. it was easy removing everthing but now it time to put it back together. I am glad that i replaced those intake gaskets mostly as they were the biggest problem and just a matter of time before they failed.

good luck with you car.

dutch

Red rooster

The thing to keep in mind is that air will easily flow from a small diameter pipe into a larger one .The reverse , large into small is a bad news situation.With the throttle body the diameter has been made slightly smaller to accomodate mounting tolerances on the plastic housing.The trick will be to find out what the mounted situation is.As a suggestion how about a piece of card with the four bolt holes put between the body and manifold as a template.Open the throttle and mark the body internal diameter.Remove the body and check how accurate the plastic is .This will also give a guide to how much can be bored out of the body and how big the new throttle disc needs to be.
Hope this helps.
Geoff

Chris M.

Erick- my cousin reports that he's got a custom chip to deal with all the various mods he's done but whether or not this is absolutely necessary is still unknown I guess.

c

Jeff Curtis

The reduced chamber in the "throat" of the throttle body actually acts as a "choke" and these are things that you change in carburetors for different airflow characteristics. If you change this, by boring it out...my opinion is that you're messing up years of German engineering!

A restriction caused by the aforementioned bore difference would cause increased air velocity whereas you would wind up with more flow if you opened it up...the sensor wires can only sense airflow and adjust fuel/ignition as necessary...if you increase airflow to the point where the sensor cannot compensate for the additional air - it's possible you may wind up with a screwy running 964...I dunno, personally I'd like to hear from someone who has performed this "modification"...as boring out the throttle body on my 911SC didn't seem to do much in the way of performance.

Just my "two cents".

chancecasey

Larger at any point in the system is not always better for many reasons.

As cross section decreases, velocity (and therefore inertia per cross section area) increases. The most important thing to know about intakes is that the intake valve is open often times through almost half of the compression stroke, because that's about how long it takes the increasing compression to overcome the inertia at the intake port.

The relationship of velocity at throttle body to velocity at intake valve is incomprehensibly complex due to resonances and turbulence patterns resulting from pipe shape, increases and decreases in size, distance, and material between the two. It would be impossible to predict what a change at the throttle body would do to the velocity or volume at intake valve.

Further complicating things, the optimum velocity/volume setup changes with RPM, which is why we have things like resonance valves and variorams.

Complicating things even further, if we held the velocity/volume setup contant because we know it yields the most air/fuel going into the cylinder over a given range of RPM, that RPM range also changes the turbulence patterns, which can change a "good" fuel dispersion to one that splatters liquid fuel all over the cylinder/piston surfaces ("bad").

I think it's a roll of the dice unless you have a lot of experience doing such things. I'm pretty sure even Porsche still uses prototypes and smoke in addition to whatever fancy computers are involved, the math would be too unworkable for the system as a whole I would think. From what I've heard and read, the intuition is about as accurate as a coin toss when it comes to intake tweaks.