GLHS

A good friend of mine who races SCCA told me that removing the secondary throttle plates from the throttle body causes a HP loss and a velocity loss.

Have any of you guys dynoed a TB mod and got a gain?

Just trying to get broaded range of views.

I know most of the poeple here feel this is a great mod, but all the cars I have raced with this mod has lost to my un modded TB.

SaabGuy

I can see a loss in tw, but not HP. Not sure though.

seventhgear

my car has it levi and guess what ?? u feel a run through the rpm's better but i dont know if it freed up n e hp... i dont see how it would give u a loss but i dont see how it would give u more also.....

Jimmy325i

Why would removing a restriction from the air passage create a problem? Most vehicles run single butterfly TB's and single chamber plenums. The secondary block offs are there to prevent the secodary air passages from being used at low throttle positions. I can see where it will cause a lack of bottom end torque. Mine sucked *** on the bottom end against a stock exhaust unmodded TB car when I had just done it. But now that the motor is ported it needs that extra air to breath. (and she pulls harder down low now than any other 7 I've been in short of the 3rd gen)

I took all the vac lines off my engine when I rebuilt it so it would be a major piece of work to swap the unmodded TB back onto my car. (I have an extra)

Funklord

the secondary throttle plates are there to smooth out throttle response, so its less jerky... taking them out increases throttle response, making it more responsive than the average driver can handle, but great for someone who knows how to drive.

GLHS

Jack, didn't you do your TB mod after you got the engine rebuilt? or before.. You may be noticing the rpm response increase from something else..

This guy knows his ****, he even makes his own pulleys...

Also every car I have seen with this mod has been slower than stock.....

dre_2ooo

I thought the TB mod just increased (quickened) throttle response, not add hp...

seventhgear

after..... but waaaaay after... about a month or 2 ago

GLHS

Maybe you noticing the engines power more quickly now that the engine is broken in fully and has loosen up some..

Jimmy325i

I'll second the jerkiness factor on the TB mod. I plan to make a very cammed throttle pulley for the single butterfly TB when I get to that point. (get the initial opening to slow down a bit so its easier on passengers in traffic)

I had headers and full open exhaust when I first took my secondary plates out. My engine rebuild was done a couple mo's after the mod. Up top my car was a real contender with just the basic mods. Now that its ported and a hybrid, it's downright devistating to the competition. (but there are people who think I'm bragging when I say this. I just want others to know whats possible without forced induction)

GLHS

Please explain what "a very cammed throttle pulley" is?

GLHS

Please explain what "a very cammed throttle pulley" is?


You do understand when you say cammed, you refer to a more aggresive opening and closing?

Jimmy325i

I'm fully aware of what a cam is. and it can be formed in such a way as to delay the onset of the throttle cables pull, not just to accellerate it. Look at a holley sometime. There's all kinds of cams avalible to dial in mechanical secondaries and to tweak the primary's rate of opening.

I plan on going to an 80mm single blade TB from either a performance mustang application or some other stock TB of the same size. When I do this I will want to slow the opening rate of the TB (initially) so that the engine isn't forced to take too much air in at too low an rpm thus preventing the intake velocity plummeting causing a bog.

GLHS

I wanna see when your done, its hard to think Mazda didn't try the single style on the RX7 and didn't like the results they got, or they would be single big bore now.

Just thoughts.

Jimmy325i

Keep in mind that the stock arraingement keeps the secondaries blocked off at low temps and forces the engine to breath through a single 45mm TB utilizing less than half its flow capacity on the bottom end. Once the TB mod has been done it brings other changes to the functionality of the two chamber intake plenum.

Once the primary ports have been enlarged the intake velocity through the primary side of the intake manifold will increase and possibly plateau. This causing an uneven flow of fuel/air from either side of the rotor in the intake stroke.

My intention is to even out the balance between the two halves of the intake runners (with the exception of the 6 ports) and hopefully free up some more power in doing so.

I can only imagine that the dual chamber intake plenum was utilized for emissions and fuel consumption reasons. Any carburated rotary uses a design similar in functionality to what I am proposing. The main difference is that I will keep the long runner intake manifold as it has benefits of its own worth free power.

GLHS

You do know about volumetric efficency?

Are you aware the amount of CFM the rotary pulls?

I personally think, unless you have a large port bigger than street sized. You will lose 40% of your lower end from loss of velocity in the primarys through out the entire power band. The primarys are basically as large as they need to be untill you get around 230 hp range..

You should well under that hp range.

Ran a couple of cars with ported engine with tricks like yours, and they all got beat at the track, by me. Not saying I am special, just saying they were slower than I.

Jimmy325i

Well, I figure that I'm at or near that figure as it is. (hp)

My primary ports are easily 50% larger than stock and my secondaries are as large as possible without compromising the oil seals or the 6 port opening. (or radically changing the overlap)

GLHS

So you are saying you have ported the engine, but did no port matching to the manifolds?


when you ported the engine, do you follow someones template or your own idea?

I appears to me you have effectivly killed all your lower and made a 100% top end machine.

Aaron Cake

iTrader: (1)

So does anyone here actually KNOW why there are secondary throttle plates? No? Well, I'll tell you.

They are there to keep you from going to wide-open-throttle when the car is cold. There is a small thermo vacuum valve that prevents them from opening until the engine has warmed up. That is their purpose in life.

Removing them usually results in better throttle response, very little to no HP gain (unless they were stuck) and frees up space in the throttle body for porting/smoothing.

bingoboy

hopefully guys in the forum know not to go WOT until the engine is warmed up...hopefully.

Jerk_Racer

I know that when I was removing the butterflies and other junk off of the TB it would not give me any power, but better response. Boy howdy! Did it ever! It might feel like more power, but that's just the response. I highly suggest doing this if you also have a T2.

Cammed pulleys? Do you think a 944 piece could be made to work? They came this way from the factory from what I can tell. Maybe somebody that has had some firsthand experience under the hoods of these cars would know better?

Jimmy325i

I heavily ported the lower intake manifold where it matches the block. I know I've mentioned this several times before.

My car pulls just fine down low. I can start in 2nd if I want.

NZConvertible

By opening only the primary ports at small throttle openings the port velocity is kept high, improving fuel atomisation and mixing. This gives more torque down low and improves drivability, economy and emmissions, but allows maximum airflow at full throttle. This concept has been used by Mazda on rotaries from the first Nikki carb (in fact pretty much all engines with 4-barrel carbs) right to the present-day Renesis.

NZConvertible

You need to clarify which plates you're talking about, plus they have two purposes.
The #1 secondary plates sit below the primary throttle and operate conventionally apart from not starting to open until about 1/4 throttle. The #2 secondary plates sit upstream of the #1 plates and stay closed until the coolant reaches ~140degF to stop you romping on a cold engine, but they also have a dashpot that stops them snapping open and causing a stumble from the sudden change in airflow. These are the ones that are removed during the TB mod.

Capn' Wankel

So if your secondary throttle plates were stuck shut then you would have more torque down low? My engine and everything is stock except for an aluminum flywheel and a S/S clutch....... Like GLHS was pointing out, because my engine is bone stock would I even flow enough to warrant opening up the secondary throttle plates at all? Even if I got the freeflowing exhaust that I hope to have soon would it still breath so much better as to warrant a neeed for more flow at higher rpms?

GLHS had his secondaries stuck for a while on his ultra lightweight N/A killing machine and he ran a 15.3 with minimal mods. Now that he brings this post up I am very curious as to whether having working secondaries as a benefit or whether it would just decrease the velocity enough to slow down a stock engined N/A 6-port.