double throttle body modification idea
 

Couldn't decide where to post this but it applies to guys with big singles (and duals) as opposed to stock 3rd gens and twins.

I'm currently in the process of having an engine built by CLR Motorsports in Miami. They're road race guys and the owner gave me what looks to be a very good idea. Most end up removing the secondary set of throttle valves behind the throttle body in a quest for more airflow. I believe the original system was designed to allow for a smoother throttle response with the small twin turbos that spin up quickly. If you go to a single turbo, that's out the window.

For more top end power, the primary ports are often modified and enlarged, killing velocity at lower rpm levels. I am in the process of reinstalling the secondary set of throttle valves and working on a system that will keep them closed until a predetermined pressure point, say 3-4psi. This will divert all airflow through the primaries until that set psi point. Those with large primaries may benefit from the increased velocity and a better bottom end. Naturally one will have to experiment with the right pressure setting in relation to their port and turbo size.

Now I have my system back on the UIM and noticed when installed, they're essentially kept open. Applying vacuum to the vacuum pot closes the valves as would happen when the car was idling (better idle quality?). It's been soooo long since I've had these hooked up, I cannot remember if the vacuum pot was ever hooked to one of the many solenoids under the UIM. If I were to just hook it up to a vacuum source, the valves would open fully as soon as I went to zero degrees vacuum and probably sooner (not sure how much force is needed to open them fully).

What I'd be looking for is some sort of a Hobbs switch, preferably adjustable by psi (for testing) to activate the vacuum pot into opening the secondary throttle bodies. But one would need to keep vacuum applied to the pot up until the point where it's slammed open. I'm assuming that would be the job of a solenoid/vacuum chamber combo. It all sounds sort of complicated but there has to be some sort of integrated pressure switch that combines all of the above. I've just started searching but as of yet, I have not found just such a device. I can locate a 4psi Hobbs switch easy enough, but I'm not sure where to begin in regards to the solenoid. Perhaps one of the stock solenoids has this capability? One could wire the Hobbs switch in-line with that solenoid and associated stock plug and it would simplify the system greatly. He has apparently done this with great success and combined with negative split in the vacuum areas (chew on that for a while!) which tapers off as we approach boost will help to make the car much more responsive down low and through the bottom of the midrange. Ideas/links appreciated!

If you run a second set of throttle blades but keep them closed untill 3-4psi but dont do anything to the main blades on the throttle body and the tps your probably going to end up with a tuning head ache. In addition the pri/secondary injectors are staged and your probably going to end up pumping fuel into the secondary but with no airflow.

Obviously it can all be tuned out, but what a pita thats going to be.

Even with low rpms, say 100cfm I cant see that barely enlarging the pri runners is going to make such a noticable difference that you need to go to this extent. The 100cfm is 1.66cf per second. The amount of material your remove from pri is a SMALL fraction of a cf. I cant see that its going to make more than a tiny fraction of a second difference.

If your really intend on blocking the secondaries for a longer period of time why not try to reconfigure the way the main blades open and just set them up to be more delayed. The secondary blades are delayed anyway, you can pull the throttle cable and watch the pri blade open first. Why not try to reconfigure it so that the secondary is even more delayed.

If your going to do it the way you described then I think using a Hobbs switch would be fine. Just hook everything up just like stock but instead of it going off a computer controlled solenoid just have a pressure switch that opens and allows pressure thru to activate that actuator that controlled the 2nd set of blades. You need to get a good quality one that reacts fast.

Anyway, let us all know how it goes, Personally I'll be gutting my runners out to be larger and putting on a single big ass tb. More air flow and smoother less turbulant flow.

BTW - Have you ever stomped on the gas when the car was kinda cold and those stock sec set of blades was closed??? NOOOOOOO power at all. I think your going to kill your bottom end setting that up to have nothing till 3-4psi. But thats just my .02 you guys try it out and see, maybe it'll work good.

Stephen

Good points steph...I'll need to work on the secondary injector transition point. I did think about the fact there wouldn't be any airflow to pick up the seconary fuel injector's input but I figured I'd need to map the point when they come online. And you might be right about delaying the secondary runner throttle body openings. Apparently he's tried it and it works using the double throttle.

My first primary port job was left almost stock, very small, as the Cosmo runners were big to begin with. Secondaries were quite large, really big. Wanted to keep velocity at vacuum and low boost high for good bottom end and midrange. Worked well enough but Carlos is now going to port the primaries as they should be, nice and big. The negative split may be enough to get around a loss of low rpm thrust, who knows. Owners of first gen cars can try the negative split effect by hooking up the vacuum advance to the trailing spark only. Using this plus the double throttle trick should get rid of that lazy low rpm feel inherent to rotaries and help spool larger turbos in the process. I'd like to keep it as simple as possible but forcing all the air through the primaries sounds promising. It'd be like a variable intake manifold in theory without taking pressure wave effect and all that other nonsense into account. I suggested the 3-4psi point but one may need to set it lower. Time to hit the Datalogit list and figure out the injector transition point!

The stock ECU kept these secondary butterflies closed up until the engine was warm enough by way of one of the rat´s nests´solenoids (look up how it works on the factory shop manual).

I got an idea for you: imagine a hose made into a T where one end is connected to the secondary butterflies´pot, another end is connected to a vaccum port on the LIM by way of a one way valve allowing vaccum to pass but pressure to keep out, and a normally closed solenoid run by the Hobbs switch connected to the third end. Now, you can also have a vaccum acumulator feeding the vaccum signal, so that each time the solenoid went back to its normally closed position there would be inmediate vaccum available to close the secondary butterflies.

Let me know how it works out for you, it does sound like a good idea

Ahh...good idea! I'll have to dig through my box of solenoids to see if I have an applicable unit.
Michel

why not make it rpm activated? secondary injectors come on at around 3k or so. . . just make it come on at that point. . . OR have them slightly opened at all times. . . that would allow air to flow through and HOPEFULLY atomize the fuel in the secondary ports.

this is a great idea. . . and could GREATLY improve low end driveability/torque if done right. . . keep the ideas rolling!!!!

great idea michel!!!!

paul

We're working on it :-) It's pretty much a done deal. Just have to get the engine back in, break her in and then tune on the dyno. Carlos has it all figured out!

dude, im so interested in this. . . i have an extra manifold laying around, and i will DEFINATELY be working on this later on!!!!! GREAT IDEA!!!!

paul

Did you remove the double throttles already? No need for an extra manifold. Just the extra throttle plates, an adjustable hobbs switch, one of the stock solenoids and a vacuum Y or T. The rest is going to be adjustment, tuning, dialing it in.

my blades arent going into my manifold anytime soon. . . i hogged it out. hahahaha.

here are some things to think about when doing this. . .

if you have the blades COMPLETELY closed until the desired point of opening there are two things right off the top to worry about. . . of course, the injectors. if there is no air getting to the secondary injectors, then the fuel wont atomize correctly in the secondary ports and youll have fuel dripping into the combustion chamber and thats not very good.

another thing is. . . with the blades completely closed, the compressed/moving air will back up and cause some uneasy flow characteristics on the primary port on the TB. turbulence BEFORE the combustion chamber is obviously bad. hahahaha.

so, there is a solution to this. . . simply keep the blades cracked at all times. that way, there is air getting to the injectors for atomization and it relieves the pressure at the TB.

now, heres something i thought about. what if a solenoid was wired into the secondary fuel injectors? that way, when they come one. . . the blades AUTOMATICALLY open up. the only thing i dont like about this is that secondary injectors come on ALL the time. . . no matter the boost level.

so, i go back to the idea to keep the blades cracked a small amount before opening and continue on using an actuator/solenoid to open them up.

this is niiiiiiiiice.

this way, we could keep velocity up in the primaries while cruising and running up in the rpms while staying out of boost. . . i reeeeeeeeeaaaaaaally like this.

paul

Sweet idea! I love this type of idea.

I'm currently working with an idea involving a stock seq. sys. solenoid inline with my MBC to keep the WG closed until almost max boost then slam open. This would give the MBC response like an EBC, with the cleanlyness and ease of operation of a MBC.

I still have my double throttle stuff too!!


Maybe you could tie in on the intake side of the turbo and run vacuum through the solenoid, and have the pressure switch cut the vacuum supply. (was this already discussed? I ran through this pretty quick)