I'm curious to see what the pedal ratio is on a 3rd gen throttle pedal and how it compares to my 2nd gen, since I have a 1985-88 style throttle body.

Possible to get a measurement from the attachment point of the foot pedal on the rod to the pivot point of the rod on the firewall?

Then a measurement from the firewall pivot point to hole on the rod where the cable attaches?

Thanks!

 

I am assuming your are asking because you have an overly touchy pedal. You need the 89+ TB and cable to correct that.

TPI, Q-Jet and TBI all had the same pedal on the 3rd gens. Later TPIs got a throttle eccentric cam on the TB and matching cable that was more progressive acting. IIRC 85-88 had the same throttle cable end and geometry as a Q-Jet or TBI and 89+ had the eccentric. I used the early TB setup with the stock Q-Jet throttle cable on my G-van and a cable for an 85-88 F-car on a C1500 using the stock pedal. The pedals free height and travel was unchanged carb or TBI to TPI. Whatever the distance for a Q-Jet was for the cable to fully open it is the same as the TPI.

I have used the factory older pedals on numerous swaps in numerous platforms including LT and LS. GM did not change that geometry. GM went to various shapes of throttle eccentrics and even put a lip attached to the throttle blade to block flow at low throttle angles on some engines to tame the off-idle jumpiness.

 

Yes and no I guess....

I recently rebuilt the throttle body with new bushings and all of that and what happened was I didn't wind the return spring up sufficiently when I first re-assembled it. I then drove the car and noticed how much nicer the throttle felt, but the problem was that it wouldn't let the throttle blades return fully, so the idle would hang up.

I experimented with some external springs to see if I could solve the idle hanging problem with as minimal extra spring force as possible, but by the time the idle hanging went away, I was pretty much back to the full strength spring.

I ended up taking the throttle arm back off and winding the spring up fully, so now its back to where it was before the rebuild. Which is not the end of the world necessarily as I"ve had it like that for the last 34 years.

I wouldn't say it's jumpy either... I've dialed in my AE and throttle follower such that I don't have to press the pedal down that much for normal take off. But it'd be nice to reduce the amount of force needed to push the pedal.

I do like the linear feel of the throttle (vs say, a progressive linkage), so if I can't lessen the return spring force, I thought maybe I could increase the leverage at the pedal.

 

That makes sense. I think if you make a ratio change at the pedal though it will defeat what you trying to accomplish. To get less tension on the pedal would require a longer throw on the pedal end and that will make the pedal travel longer. Honestly part of the reason I went DBW on my 383 recently was that I like being able to dial in the throttle map.

 

What system did you use?

 

Factory GM pedal and TAC module from an 01-02 DBW 8.1L, an 87mm Hitachi ETB0024 GenIV throttle body and the same P59 I was already running. I went 24x at the same time and changed my base engine tuning from a 2005 DBC L31 350 to a 2005 DBW LQ4.

 

Ok, yeah that's not going to work for unfortunately with this old cable-driven TPI throttle body.

 

I have seen several LT1 guys build adapters to put 90mm 4 bolt LS throttle bodies on LT1s.

 

I figured it out... and the throttle feel is absolutely perfect now.

It was a negative cascade reaction effect from something I did many moons ago...

So recall that idle air manifold I did attempting to duplicate the LT1 manifold's cast-in idle air passages...18 years ago(!!!).... attempting to combat the terrible A/F distribution nature of these Miniram/LT1 style manifolds...

https://www.thirdgen.org/forums/diy-...ram-split.html

It did the trick on getting rid of the split BLMs. But the extra air that came in through that contraption requires that the throttle blades be essentially fully closed. With the return spring at full strength, it never presented a problem and I simply got used to the level of effort it took to push the accelerator, figuring that was basically "stock".

What I didn't realize was that I was getting away with that because the spring was overcoming the engine vacuum wanting to keep the blades cracked open.

Also at that time, I didn't S_AUJP with open loop idle, and I hadn't conceived of the idea of putting 10% bigger injectors on cylinders 1-4 (replicating GM's fuel tailoring on the SEFI LT1's).

Fast forward now, with the accidental finding about the throttle spring I posted about, and realizing that the engine vacuum is what was causing the problem...

It dawned on me... if I have the throttle blades cracked open, then there isn't so much vacuum force to overcome since I'm not trying to fully close the blades anymore.So then I thought... do I really need this idle air manifold anymore? I've been running open loop idle, so no more split BLMs. And my A/F mixture has been normalized on the fuel side of the equation by putting 10% bigger injectors on cylinders 1-4 (whereas before I was attempting to do that normalization on the air side).
So I unhooked the idle air manifold, open the throttle blades (actually quite a bit) to get the IAC and TPS reset... I then loosed the spring by about 1/2 turn. With the throttle arm now screwed back on after the rebuild, it's a snap to get in there and adjust it (one advantage of not welding it back on... the red loctite is super secure)

Boom... absolutely perfect. I know the engine isn't necessarily performing any better, but the seat of the pants feel is much better (basically what your brain thinks the car is doing relative to how far down you think you're pushing the throttle).

Sometimes you just have to back track through modifications to realize that the problem you're experiencing now is a result of something you did a long time ago... lol

 

A fringe benefit...

The idle and very-low throttle feel improved by disconnecting the idle-air manifold. I think what was happening was that I was now overcompensating for the low-throttle A/F distribution problem. With the 10% bigger injectors on 1-4, there was no need to be balancing out the airflow anymore. Most likely cyl's 1-4 were running too rich.