Shorten accelertor travel (GTD)

FredV · 01-07-06, 05:48 PM

The pedal unit on the GTD is not the best we can find on the market but i am trying to shorten the travel of the accelerator pedal.

Why ?

To be able to use it while i am braking, you know this little gas given between two gears to avoid wheels blocking during the braking phases (usefull also with dog type boxes).
Today the accelerator is much higher than the accelerator when the brakes are on, which prevent to press the gas with the heel.

So my question is: does anybody made this modification on his GTD ?
I am using a 750 single Holley Carb, and i must say that the butterfly travel is quiet high. [img]/ubbthreads/images/graemlins/bash.gif[/img]

Andy Besic · 01-07-06, 06:09 PM

High Fred,

You can hook the cable up to different points on the carb actuating arm as well as the clevis onto the accelerator lever. This will "speed up the action" on the butterfly movement, just be careful to have a physical stop at wide open. I have also adjusted the brake pedal clevis to "raise" the brake pedal to a point that at full brake pressure it is at the same height as the throttle. You can then use the side of your brakeing foot to match-rev downshift.

olfrjf · 01-07-06, 07:29 PM

Hi Fred, i have done some little modifications on the throtle pedal since i have bought my car, i send you a PM.

regards
Olivier [img]/ubbthreads/images/graemlins/smile.gif[/img]

Jim c · 01-08-06, 02:00 AM

Fred I dont know what a GTD pedal set looks like but I fixed a similar
problem on another GT40.

I made a bellcrank & linked the pedal to the bellcrank via a rod.
The swivels & ball sockets i used 3/16 cable ends from morse cables.

The throttle cable then attached to the bellcrank.
By moving the cable or the link on the bellcrank changed the pedal ratio.

All the circles on the drawing are pivot points.

hope it gives you an idea.

jim

Malcolm · 01-09-06, 07:30 AM

I have a GTD with a Holley set up. I have adjusted my GTD pedal box to allow better operation. I made a little bracket to allow a throttle stop to be installed. This is adjustable so moving the zero throttle position forwards or backwards. I have aligned it so that when on heavy braking with my foot equally on the throttle (with clutch in) rpm is 4000 so allows for easy down shifting. No blipping required just stamp on all pedals!!!! The throttle stop itself is a long 8mm bolt with two nuts either side of the bracket so I just screw it back or forward. Obviouly set up with throttle cable disconnected.

Hope this helps

Canuk40 · 01-09-06, 04:01 PM

Malcolm makes a good point about the relationship between the brake and throttle pedals. Fred, you should consider changing the starting point of the throttle travel rather than shortening it to get closer to the correct alignment of the pedals.

Shortening the throw will quicken throttle response which will have an adverse effect on balancing the car in a corner and smooth application of power on exit. Street drivability will also suffer. I preffer a longish throttle pedal to prevent over controlling the car. Most production car pedals are a bit too quick, gives the impression of more power when it's really just a more aggresive throttle tip in rate. With a GT40 you've got REAL power so no need to play games. Hope this helps...

Cheers

FredV · 01-09-06, 05:11 PM

Guys,

As usual you are a great help and i thank you very much for your different advices.
I must agree that a short travel will occur a hardest control, especially on wet roads.
In fact my goal is to have the gas under the brakes, the travel was not my priority, i confess that my title was not so good ...

Jac Mac · 01-09-06, 05:34 PM

Hi Fred. When fitting up any cable throttle assy I find it easier to make up small grooved wheels or pulleys which are fitted to the pedal/pivot- carb/spindle [check out any late model car throttle cable] By changing the dia of wheel @ either end you will be able work around most of your travel problems. this will give you a constant rate of travel. Also makes life easier for the cable where it enters/exits the conduit.Regards Jack

Russ Noble · 01-10-06, 02:53 AM

Excellent tip jack. Simple, easy and obvious!![img]/ubbthreads/images/graemlins/banana.gif[/img] I can't believe I haven't used it!! [img]/ubbthreads/images/graemlins/banghead.gif[/img]

Whereabouts down south are you? Are you building a '40, or just doing bodies?

Regards

Bill Musarra · 01-10-06, 06:42 AM

I have wondered about some of these problems myself, and a lot of the questions I had have been answered. That being said, I am having a problem visualizing jacks solution. Could some pics or artist renditions be given. I have thought that some sort of bell crank setup(s) would solve the critical turn issues with a 40 setup, especially with a motor moved forward. With mutiple attachment points on the bell, the throtle could be "dialed in" to the desired travel lenght.
Another arguement against shortening the travel, would be pad wear. That would raise the revs over time(more than a non shortened setup) and cause the car to lurch forward when the clutch is released in the corner. Not a good thing I would think.

Bill

olfrjf · 01-10-06, 10:04 AM

Hi guys, this is the picture that i have send to Fred in MP.

i have put this part on the manifold, near the carb.
i have in mind to change the accelerator cable for two smaller....

Olivier [img]/ubbthreads/images/graemlins/smirk.gif[/img]

Malcolm · 01-10-06, 10:14 AM

With a bit more time now I can give a bit more info on my set up.

I use an 1980's F1 style throttle cable (£75ish) that uses rose joints for its connections. I have it coming to the Holley from the front of the engine as in a 40 this means it doesn't really get close to the exhaust so less likely to melt! It uses a 2mm diameter wire so is nice and chunky. Some people use cables designed for trucks as they are also good and rugged.

I picked the mounting point on the carb (a variety of holes exist as standard on a Holley) to suit the lenght of throttle travel I wanted so didn't need any cams or wheels. Used springs at both ends as in competition they like you to have two means of throttle closure!

I have kept a long throttle travel. I run telemetry on my car including a throttle position sender. The computer says (!!!!!) that I rarely go over 84% throttle opening. Even in competition. This is partly down to running a Holley and mashing throttles with Holleys tends to bog down the engine unless you spend monster time on carb set up. Also with my prodigious BHP output clearly a mere 84% is enough to keep those others at bay!

Just thinking about it, this means that on the front edge of my throttle pedal I have the cable coming in, a brake light switch, a throttle position sensor and zero poition throttle stop! Gee, it is getting crowded!

Jac Mac · 01-10-06, 05:40 PM

Hi Fellas, Bill I am a "newbie" at this computer stuff so posting a dwg out of my league at this time.Could fax dwg,s if reqd. Have a look at the cable / throttle assy on a Nissan 300zx[1990-]and you should be able to see what Ive tryed to explain. Russ, just on the nth side of gore[sh.1]. Are you the same Russ Noble that ran single seaters and or sports cars? Have set of molds for Mk1 W/body. Hope to develop Mk2 F/R parts[ Have a soft spot for F/E,s]. Will you be at SFOS, ask for me at white TVR. Jack.

Russ Noble · 01-11-06, 12:44 AM

Hi jack,

Yes the very same. 1600 Twin Cam Brabhams in the early '70's. SCANZ 2 litre sports/racing in the mid '70's. Van Deiman FF early '80's Then nothing til TR7V8 recently. You must be on Jack Ondrack's crew? I'm not racing SFOS this year, too busy building the GT40, but will be in the pits at Ruapuna and probably Levels this year and will look you up. At present no plans to go to Teretonga. Look forward to seeing you.

Regards

Mike · 01-11-06, 01:38 AM

Fred, do I understand that you are happy with your throttle ratios, but only want to reposition the pedal so you can heel and toe? i.e. have both pedals about the same level?
If so, have you considered using a threaded rod (like in Olivier's drawing above) with Heim joints to connect the pedal to the floor?/bulkhead? mounted bellcrank? Simply screwing the joints in or out changes the position of the pedal, allowing you to adjust it any way you like without affecting throttle ratio. Not sure how your pedal linkage works, but if the pedal connects to a bellcrank that in turn pulls on the throttle cable, this is an easy way to go. It works great for me.
Good luck,
Mike