Slide throttles...info needed

[HawgRyder]

I am up against the wall with my 69S...the MFI throttle assemblies are corroded to the point of not idling down (runs at 3500rpm when hot).
So....I am considering building a set of slide throttle plates to replace the old s##t.
Anyone with ideas of experience in this area muchly appreciated.
The design I have so far allows me to bore the set from 32mm to 46mm.
I am thinking of about 38mm for the 2.0L in the car.
Maybe too much?
Thanks, Bob

[HawgRyder]

Bump....no one with any suggestions?

[911pcars]

Thinking of fabricating from scratch or modifying the existing stacks?

Either way, I imagine it's a big job. Unless you like to machine and fabricate, it might be easier to buy. Why slide valve? If not in a racing mode, they tend to stick (not good in the open position).

What's wrong with regular throttle valve-based housings like TWM?

Sherwood

[HawgRyder]

Sherwod...Was thinking of complete fab for the units.
The reason....the old throttle bodies are so corroded where the butterflys touch the side of the bore, that the gap is large enough to pass air to run the engine at 3500 rpm!
I thought about over-boring the hole to get enough room to press in a silicon bronze sleev, then re-bore back to original size....but not enough meat in the sides of the casting to allow this.
I would have to bore them out to more than 44mm to clean them up and this would be too big for my little 2.0L .
Sooo....new metal all around is the best solution.
As for the sticking...not a problem....ball bearings to float the slide on....teflon to guide the slide....and a positive return for the linkage (gear and rack).
It's not that big a job....the main unit containing the slide...the support columns to the head with the correct flange....and somthing to guide the air in...either horns or tubes to a filter holder.
I have the machine shop...the material...and no money!
I can't afford to buy these things....so build is the only answer....unless someone wants to donate a pair of throttle assemblys....LOL.
Bob

[BURN-BROS]

Whats your application Bob. I would go smaller for slide valves and take advantage of increased port velocity. I want to say 36mm for the 2.0. take some pics when you do it!

[911pcars]

Bob,
Sounds like a worthy project. After your prototype is complete, why not go all the way and make a bunch of them. Slide valve throttle bodies, as you know, are not that plentiful. Engineer it so you can change bore and/or venturi dimensions; make it universal (e.g. single, multiple throats w/interconnecting linkage, etc.), to increase the vehicle applications. Or if just for the flat six your ROI should be fine.

With some research, you should be able to come up with a state-of-the-art unit.

Sherwood

[kenikh]

What are your plans for the corroded throttle bodies? I might be able to use them for my future 2.8L project. PM me if interested in dumping them.

[HawgRyder]

Sherwood....my thinking exactly on the design....making them interchangable as far as size is concerned.
I was not thinking of any other application other than Pcars...the spacing between the bores is probably different for other engines (118mm for our engines).
Kenik...the units are broken down (dissassembled) right now...and the reason for the slide idea is because one of the units has a big crack in the housing where the flange meets the upright tube...probably an air leak.
The corrosion is extensive...from sitting with the throttles closed for more than 10 years I think.
It must have been galvanic action between the alauminum core and the brass butterflies.
If this slide thing works out...you have first grab at the remains...I promise.
As to making more of them....good idea...can I get rich doing it?....LOL
I am keeping the design as simple as possible with hopefully...many pics to accompany the build.
I will make the measurements available as soon as the design proves out (actually works)....
Bob

[Vapors]

Sombody must have a set of working drawings and material list for slide valve set-up for a 911 engine. I would like to machine a set for myself also. Help us out. Thanks

[Eagledriver]

The other part of this equation is matching the pump to the slide valves. Does the airflow through the slide valve increase at the same rate as a conventional butterfly? You might have to have the slides move at a variable rate to match the pump output.

-Andy

[HawgRyder]

Had not thought of that one Andy.
You have something there...in the original setup, the throttles and the pump are connected by a rod (the 114mm measurement).
I will have to match the throw of the original lever (length and stroke) to the new system.
If I set uo the new linkage with the same dimentions, I should be OK for the matching of air to gas, and adjust the pump for the ratio through the RPM range.
Bob

[350HP930]

Keep in mind that you also need to come up with a way to calibrate the throttles too.

[HawgRyder]

I had thought that using a 90 degree lever assembly would simulate the closed to open action of a regular butterfly.
Translating that to a gear and rack to open the slide.
At least I am getting ideas from you guys....things I had not considered or had forgotten about....this is good....thanks to all.
Bob

[2guard]

I've also been desiging some slide valves based on the same rack action. The old lucas slide injection was based on this design. Look at this diagram...

[Walko]

If you decide to make a set as a prototype and then market them I woul dbe interested in a set.

Michael

[Tim Walsh]

Is this a streetcar or a racecar? From everything I've heard slidevalves have a tendency to stick from dirt and grime that builds up in a streetcar. Since a racecar gets much more maintence and squeezing every ounce of power out of a more is critical, it's much more applicable to them

Frankly, this sounds like a pretty big job, you should be able to get your throttle bodies rebuilt for around $900. It's not cheap, but it's like having a new set of throttle bodies.
http://eurometrix.ws/

[HawgRyder]

Tim...I have been to that site before and the problem is the corrosion.
If the bores could be cleaned up oversize or re-bushed to original spec, then I would go ahead and do it myself.
The corrosion is where the galvanic action has taken place in the bore where the throttle plate touched (or was close to) the side wall.
The difference in metals created the problem, and the erosion is like having a trench dug around the edge of the plate.
In one of the bores this trench is over 2mm deep.
The thinking and designing continues.
Bob

[svandamme]

bump .... any luck with those slidevalves?

[HawgRyder]

I have the parts in various stages of build.
The slides themselves are the easiest part...just a flat bar with the correct holes and spacing.
The housings are partially done....I am experimenting with bearings for the "floatation" of the throttle bar.
I have 6 bearings holding the bar up (from the bottom of the housing) and 4 bearings to center the bar int the chamber.
I have indented a piece of rack (straight gear) into the side of the slide bar.
This will be pushed by a 90deg piece of gear I have to cut down.
I figured the gear had to have the circumference equal to the total movement of the slide (through 90 degrees).
To make the gear smaller, I have cut down a full circle into just a 90 deg piece (approx) keeping the hub intact.
The slide works so far, and has about a .0002" clearance at the bottom and sides.
So far I have been working with aluminum but am considering making the slide out of Delrin to make it more slippery.
I am not sure how the Delrin will hold up to the heat of the manifold.
That's the progress so far.
As to making a bunch of these....had not thought of it seriously.
Bob

[svandamme]

got any pics?

oh , and that mfiwdp .. is there a website? and where do i sign up?