great! Thank you for that, I’ll give them a call tomorrow, and maybe try that before anything since I’ll have to wait a little bit for warmer weather anyways lol

 

I had that on my OE secondary and solved it with a 1/4 turn of the return limit screw which controls the closed throttle opening. Probably could do the same on your primary butterflies.

 

ordered a cable 6” longer than my previous one, and wow they were fantastic to deal with. Great quality, fast turnaround AND they answer their phone lol buuut bad news is, it still does the same thing no change at all here is what the bend thought to be a point of failure now looks like…

 

That sucks.

 

Post a photo showing the entire throttle-cable routing. This dilemma intrigues me and I may be able to offer some more insight if I can see the whole cable all the way from the firewall to the pulley.

 

I am more than willing to listen to any insight you may have lol I even drilled a small hole in the butterfly to see if that was it and it didn’t do a thing. The haltech is telling me ~15lbs of vacuum at 2000rpm and ~20lbs at 2500rpm.

 

What I'm going to do here is assume 5-lb of force (this estimate is probably low) to be overcome at the pulley from the return spring, vacuum from some BF offset area, and/or friction on the shaft. I'm then going to assume a coefficient of friction in the cable, say 0.1, and calculate the required cable tension at the firewall to overcome the 5-lb at the pulley. The total angle change in your photos over the entire cable length is approximately 360-deg, i.e., 2 pi (6.28) radians.

Here it is:

load at pulley = 5 lb
e = 2.718
CF = 0.1
Angle = 360 deg (6.28 rad)

Tension at firewall = (tension at pulley)*e^(CF*angle)

So T at FW = 5*2.718^(0.1*6.28) = 9.4 lb

So the tension at the pulley is almost doubled by the bends in the cable. and if the CF is 0.2 (unlikely), the tension at the firewall increases to 17.5 lb. The tension at the firewall is proportional to the tension at the pulley. Double the tension at the pulley, and you double the tension at the firewall.

This could be your problem, even with the new low friction cable, and if the tension at the pulley were higher it would be even worse.

 

that’s a whole lot of maths but I follow you on it lol so If that is the case then it sounds like my only option to fix this issue specifically would be to have a different throttle cable set up? And the reason it’s not an issue on OEM, is the smaller butterfly’s opening/ closing at different times so not near as much surface area all at once?

 

Here's a study of P-P cable friction with various degrees of bend in the cable. They determined that the tension ratio for 360-deg bend in a plastic-lined cable (your situation) was ~1.75, which is similar to what I calculated above.

 

I can't be certain that this IS the issue, but it very well could be. And what you said about the OE setup vs your current setup is logical. If you could have a cable routing with less angle change it would certainly improve the situation.

If you could fab a bellcrank setup at the firewall or at the pulley to cut the cable's total amount of curvature in half (down to 180 degrees) the cable tension ratio would go from almost 2 to ~1.3, so that would be a major improvement. If you eliminate all the bends, the ratio is 1.0.

Bellcrank definition from the web:
A typical 90-degree bellcrank consists of an L-shaped crank pivoted where the two arms of the L meet. Moving rods (or cables or ropes) are attached to the ends of the L arms. When one is pulled, the L rotates around the pivot point, pulling on the other arm.

Also, having the arms other than 90-deg apart, or of unequal length can change the leverage so opening from closed would not require so much initial cable tension. We have bellcranks like that on my pushrod racecar suspension.

 

so call me crazy, but maybe you unbolt the gas pedal and go stand on the left of the car, so the cable is straight, and see what it does.
or maybe try a stock throttle body, just to see if it changes anything

 

I would try to check if the 'stickiness' will happen in neutral, because if it happens in neutral then you should be able to move the disconnect the cable and move the throttle blade by hand. If it still stick without the cable connected, I would look closely at the linkages and springs, or maybe think about drilling holes in the blade. Before drilling holes I would check if there are spare blades available in case you dislike how the car behaves with a hole drilled in the throttle blade.

 

How about an electronic "drive-by-wire" throttle setup ? That would totally eliminate the curvy throttle cable.

 

Still think you should be aiming for around 100/150mm bend radius to get something half decent based on the old OEM installations you used to see. You must be around 50mm at best. A cable run around the front of the engine, somehow under the TB snout/elbow possible? The addition of an aftermarket throttle wheel or being remade, still seems the most elegant solution to me if you persist with this.

Just on the routing too, the stock RHD cable is above and in front of the brake master, it's common enough for those to melt, I wouldn't expect a long life for the cable as it runs now - if you do happen to solve the throttle stickiness issue.

Likewise the hydraulics - looks clean, but really too exposed to radiant heat for my liking.

 

That all makes really good sense, especially the heat/melting warning. I melted and froze solid a P-P cable to my racecar rear swaybar by running it too close to the exhaust without any shielding.

Another thought would be, if it's possible, to rout the cable directly over the top of the engine to the top of the pulley (might be possible to rotate the pulley 1/2-turn on the shaft to get the cable attachment point where it needs to be), reducing the total bend angle to ~90-degrees. At 90-degrees, the force ratio is only ~1.17, minimal capstan effect, and the cable would be ~half as long. The cable sheath bracket might be able to be attached to the top of the manifold.

 

Thank you so much to everyone with their time, effort and great advice. At this point I’m just kinda fed up with it and plan on going the DBW route. If anyone wants a rotary works cosmo tb let me know I can cut ya a deal lol

 

You're welcome. Good luck with whatever TB you choose. I enjoyed thinking about what caused your issue and how to potentially solve it.

 

i think we didn't do a good enough job eliminating potential problems. the cable should be good, because its new, but other than that everything else is still possibly a problem.