Author Topic: Linkage slowdown  (Read 432 times)

0 Members and 1 Guest are viewing this topic.

Stangman

  • Hero Member
  • *****
  • Posts: 854
    • View Profile
Linkage slowdown
« on: October 12, 2019, 01:47:47 PM »
So was wondering. If I wanted to slow my car down because of no roll cage could I swap rear carb linkage and have rear carb not open all the way or is that bad for the motor.

cjshaker

  • Hero Member
  • *****
  • Posts: 3336
    • View Profile
Re: Linkage slowdown
« Reply #1 on: October 12, 2019, 01:58:40 PM »
I think the best way is to just limit throttle travel. There's no chance of running lean or damaging the engine that way. Don Fotti has done this pretty successfully on his '68 CJ. He slows his car down over 1.5 seconds, and has pretty consistent ET's.
Doug Smith


'69 R-code Mach 1, '65 427 MR, 2x4, 4-spd, 4.30 Locker
2 1965 Galaxies with 390s
1970 F-350 390
1958 Ford Ranch Wagon 390

Stangman

  • Hero Member
  • *****
  • Posts: 854
    • View Profile
Re: Linkage slowdown
« Reply #2 on: October 12, 2019, 03:07:47 PM »
Well that’s what I’m saying I’m gonna do but should I be figuring out how to limit both carbs or can I just do the back carb like I want to. That is the easiest way.

Drew Pojedinec

  • Hero Member
  • *****
  • Posts: 1851
    • View Profile
Re: Linkage slowdown
« Reply #3 on: October 12, 2019, 03:28:23 PM »
Just remove the hose that connects the VS

BattlestarGalactic

  • Hero Member
  • *****
  • Posts: 802
    • View Profile
Re: Linkage slowdown
« Reply #4 on: October 12, 2019, 03:35:56 PM »
That will not do it.  Trust me lol.  That would just cause random opening\closing as it tries to recover from the vacuum loss from that balance tube being unhooked.

I removed the vacuum pods and drilled small holes down the length of the rods. Now i could use tiny hitch pins to limit secondary opening.  Won't do much for 1\8 mile racing, but 1\4 is fine.

I also tried using tiny nuts(like 1\4-20) and slit them to slide on the rod and then drilled/tapped for set screws so I could slide them easily for adjustment.  I'll try to dig them up and get a picture.

shady

  • Hero Member
  • *****
  • Posts: 543
    • View Profile
Re: Linkage slowdown
« Reply #5 on: October 12, 2019, 03:50:59 PM »
A block under the gas pedal.  Plus that way, there is no strain on the linkage anywhere.
What goes fast doesn't go fast long'
What goes fast takes your money with it.
So I'm slow & broke, what went wrong?

Stangman

  • Hero Member
  • *****
  • Posts: 854
    • View Profile
Re: Linkage slowdown
« Reply #6 on: October 12, 2019, 05:21:09 PM »
Well I’m going to the track tomorrow and I need something to work at least just for the time being. Ya see last year almost to the day was the last time I was at the track and it was at this track and they stopped me right before I lite the second bulb and changed my dial in at the line. I had my exhaust on to slow it up and still dialed an 11.39. Then made me change it to 11.50. Now I switched to a medium riser 2x4 so I’m hopeing I’m gonna have to slow it up even more. My first pass will be all out then I’m gonna need to run 11.50 for eliminations. I will post my times tomorrow in the drag section. But I still want to be competitive in eliminations. Will it be bad for the motor if I just limit the back carb for tomorrow.

427LX

  • Full Member
  • ***
  • Posts: 191
    • View Profile
Re: Linkage slowdown
« Reply #7 on: October 12, 2019, 06:05:26 PM »
Just run it on street tires!

cjshaker

  • Hero Member
  • *****
  • Posts: 3336
    • View Profile
Re: Linkage slowdown
« Reply #8 on: October 12, 2019, 06:35:36 PM »
Messing with the opening of one carb could affect AF ratios. On a dual plane 2x4 intake, it may not be drastic, but I don't like the idea of affecting AF at all. Potentially running a cylinder lean is not something I'd be happy with. Like Drew and Larry mentioned, you could stop the secondaries, but that is a on/off scenario, with no adjustability. I also don't like the idea of anything under the pedal. I suppose if it was solidly mounted to the floor behind the pedal, it would work, but again, how do you get any adjustment out of it? I'm curious why messing with the linkage on one carb is easier than just limiting the throttle?
Doug Smith


'69 R-code Mach 1, '65 427 MR, 2x4, 4-spd, 4.30 Locker
2 1965 Galaxies with 390s
1970 F-350 390
1958 Ford Ranch Wagon 390

Drew Pojedinec

  • Hero Member
  • *****
  • Posts: 1851
    • View Profile
Re: Linkage slowdown
« Reply #9 on: October 12, 2019, 06:46:51 PM »
Sorry, I was joking, shoulda put a smiley face.
  Just adjust your throttle linkage to not go WOT.  Or just rev to a lower rpm and see what happens.

wayne

  • Full Member
  • ***
  • Posts: 189
    • View Profile
Re: Linkage slowdown
« Reply #10 on: October 12, 2019, 06:51:16 PM »
Li














Limit the throttle i know three guys that do it that way it will run the some every time.










thatdarncat

  • Hero Member
  • *****
  • Posts: 1372
    • View Profile
Re: Linkage slowdown
« Reply #11 on: October 12, 2019, 08:43:40 PM »
I’ve been slowing my cars down for various bracket racing reasons for almost 30 years. Both to fit into certain classes, and at times to keep it under the NHRA rollbar limits, first 12.00, now 11.50. Some of the classes I run don’t allow gadgets like electric or air throttle stops, timed stops, etc., so I & some of my friends have used different mechanical ways of limiting full throttle, among other methods. I’ve also tried various carbs. I’ve learned some things that have worked well for me, and some things that didn’t make much difference. One thing I’ve found is it takes a pretty significant change in limiting the throttle sometimes just to make a small ET change. If you think about the throttle blades at full throttle standing straight up, you can get an idea how a few degrees slightly off full doesn’t have a big effect, but as the blades get closer to closed the effect becomes bigger quicker, so my point is just that it’s not a linear change, more of a curve. The same also can happen with the arc the carb throttle arm goes through. I remember reading your earlier posts, but I don’t remember all the details, but I think your car is running a pretty similar ET to mine, and currently I’m running a MR 2-4V intake with the stock BJ/BK Holleys. Going from 11.30’s to 11.50 won’t be too bad, but it does take a significant change. You didn’t mention if you were using the stock Mustang throttle linkage rod, but if you are, one thing I have done in the past to make a small 1-2 tenths change like that, was adjust the threaded throttle rod that connects to the accelerator rod at the firewall so that when your accelerator pedal is on the floor your carb linkage isn’t at full throttle. I use a small hairpin type clip on the pin, instead of a cotter pin, to make it easy to remove & adjust. Leave the linkage at the carbs alone. That will give you a measure of adjustment to fine tune it to a safe ET above 11.50. Here’s a picture showing the part I’m taking about adjusting.



As a more permanent solution, and to give me the ability to close the throttle more so I could slow down to 12.00, I fabricated this - I took an aluminum plate I already had on hand ( from a Moroso  throttle cable plate ), and drilled & threaded a hole for a bolt I can adjust, which the stock Ford 2-4V jackshaft contacts to keep from going full throttle. I recently ran this, and after a half dozen passes I got to 12.00, but it requires closing to less than half throttle to accomplish that. I keep a cheap caliper or small ruler with to measure the height I have the bolt adjusted to, and log it in my logbook.






Personally, if I were you, and guessing you will be limited on the amount of time trials you can make, I would not start with your plan of making a full throttle run, and then slowing down, but I’d start with a significant amount of linkage adjustment first, to try and safely be under a 11.50 ET, and adjust from there. That will also keep the track from scolding you, and gaining unwanted attention immediately. My guess is your first attempt may still be too fast, but if not, it’s easy to adjust a little quicker if you want. What I would do is put a small piece of tape on the threaded rod, to mark where originally you had it, to make it easy to go back to your initial full throttle setting. You can also use the tape as a spot to measure from, and log the settings.

You may also want to consider some legal ballast. You can take a heavy truck spare tire, the biggest you can fit in the trunk, and secure it with the spare hold down. I’ve done it in the past when I’ve been away at a distant track, and just need to take off a half tenth, by using my tow vehicle or trailer spare. I carry my old Bronco heavy duty spare tire J-hook with to use as a hold down. It’s not NHRA legal to have loose ballast in the trunk, and it’s a dangerous idea anyway, if you’re in a crash, so be sure & secure it. As a more permanent solution you can add weight bars, or a weight box to the car, there are guidelines in the NHRA rule book. That can help you adjust the ET .1 to .3 fairly easily and consistently.

I like Larry’s secondary limiting ideas too.
« Last Edit: October 12, 2019, 08:53:12 PM by thatdarncat »
Kevin Rolph

1967 Cougar Drag Car ( under constuction )
1966 7 litre Galaxie
1966 Country Squire 390
1966 Cyclone GT 390
1968 Torino GT 390
1972 Gran Torino wagon
1978 Lincoln Mk V

Stangman

  • Hero Member
  • *****
  • Posts: 854
    • View Profile
Re: Linkage slowdown
« Reply #12 on: October 12, 2019, 09:19:18 PM »
I like the plate and throttle screw and obviously I won’t be able to do that by morning seems like a permanent safe way. Well gotta go to bed gotta get up at 4 am.

thatdarncat

  • Hero Member
  • *****
  • Posts: 1372
    • View Profile
Re: Linkage slowdown
« Reply #13 on: October 12, 2019, 10:49:20 PM »
One of the local Super Stock racers has a really nice mechanical positive throttle stop on his SS/L ‘64 Mustang 289. One issue with our first generation Mustangs is the firewall isn’t flat near the accelerator rod area, it curves & kicks out. His solution was a thick block of aluminum mounted to the firewall, contoured to the curve in the firewall, but flat on the side facing the engine, and threaded with a large adjustable bolt that can contact the accelerator rod that pivots on the firewall. Someday I really need to get a picture of it to give a better idea. Using the picture of my accelerator rod, I circled the area that contacts the bolt head. It’s a really solid solution, and easily accessible to adjust. Many of the Stock & Super Stock racers ( especially Super Stock ) don’t run their cars full out, especially at local track S/SS events. It saves on wear, and helps consistency by cutting down on wheel spin, unless they have a heads up race.

Kevin Rolph

1967 Cougar Drag Car ( under constuction )
1966 7 litre Galaxie
1966 Country Squire 390
1966 Cyclone GT 390
1968 Torino GT 390
1972 Gran Torino wagon
1978 Lincoln Mk V

cammerfe

  • Hero Member
  • *****
  • Posts: 1080
    • View Profile
Re: Linkage slowdown
« Reply #14 on: October 13, 2019, 06:56:59 AM »
Some years ago, when running Brother Lon's '67 Mustang/427 TP, we found that we'd lost a full second from the previous end-of-season runs. Yet everything seemed to be working just fine. After a  half-hour thrash, we discovered that the throttle rod mounted to the firewall was bent---probably when out-'n'-inning the engine in the off season, and the carbs simply weren't being pulled fully open. I strongly suggest the same sort of procedure (mentioned above by several) to slow yourself down. Doesn't hurt a thing and you'll go slower! ;) :)

KS