Technical How long should a throttle cable be?

Non-stock application (SBC in 37 Chevy) that has about 7” from firewall to carburetor throttle cable bracket. Right now what’s on there has a pretty big U shape to it, seems to be quite a bit longer than necessary. The only custom throttle cable dimensions I can find are in Lokar’s instructions, they say 2” of slack, but that’s for their custom cable.

 

It depends. As long as the bends aren't too tight, and there is some slack, you can use any length. But it will look better with the correct length cable. The relative location of the ends, makes a difference, as it affects the angle at the ends of the cable.

 

Sometimes a longer cable with slack works better.

 

I have a 10 foot throttle cable in my V8 Corvair. Runs from the throttle pedal through the firewall,into the trunk for a sweeping turn.Then through the tunnel to the engine compartment through a bracket and attaches to the Carb. It is a Lokar custom cable
You can see the cable ,bracket and attachment in this photo

 

If it's a tight u it's too long. Too many bends and it'll bind. What led to me doing a burnout in my 53 when I tried to pull it out of the shop after I put the engine in lol

 

As long or as short as it takes to connect the carburetor / throttle body to the throttle pedal.
I recently bought a car that the cable is "about" (never actually measured it), 4+ ft long !

See it connected to the pedal, then into the trans. tunnel. Then back out of the shifter hole, through the firewall, and finally to the carburetor. I can take about 12" or so inches out of it, but, it actually works ok as is, so, for now, it stays.


Mike

 

As long as needed to connect the accelerator pedal to the carburetor PLUS enough to compensate for the engine's movement in the motor mounts. A lazy bend is preferred.

 

I kinda lean toward as straight and direct as can be rather than a "pretty big U shape"........
but with enough slack to allow for engine torque or soft motor mounts, etc.
It sounds like someone was too lazy or skeered to re-trim the cable.

 

use the 3 bears system to work out lengths, not too long , not too short, just right

 

Probably should have done this in the first post. Here’s what I have now.



Firewall to carb bracket is about 7”. Cable is a few inches longer than that. To my eye, the U bend looks too tight, I’d like it to be closer to straight, but I know it needs “some” slack to account for engine movement.

How much is “some”?

 

Pegasus Racing has a lot of cable fittings and makes custom length cables. They are very easy to work with. https://www.pegasusautoracing.com/keywordsearch.asp?KeywordStart=Throttle+cables&KeywordButton=Go

 

I'd pull the inner cable out.
Cut the sheath 3 to 4 inches longer than a straight line.
Install inner cable and hook it up.
Test for smooth operation and full throttle opening, best appearance.
If not perfect, outer sheath may need additional shortening, an inch at a time.

 

In general the best practice is to use largest possible bend radius for any hoses or cables. Not sure what the minimum bend radius is on this style throttle cable but I’d agree it’s probably too tight on the ends of the cable (against firewall and bracket.)

But what does too tight mean?

The short term concern would be if you think you’re getting a lot of resistance/ hard to push or hard to return. If that’s the case I’d replace immediately because of driveability and likelihood of premature wear. If not I wouldn’t worry too much about it.

Long term you’ll get some wear on the rubber liner, but I wouldn’t be too concerned of the steel cable breaking. Eventually without the support of the rubber liner your gas pedal probably won’t return properly and be floppy. As long as your return springs on carburetor linkage work well there shouldn’t be any stuck throttle concerns in the short or long term.

but there are plenty of cut to length throttle cables on the market if you want to upgrade/ correct it at some point

 

you want a cable that's 1.5" shorter than what you have. But since it's an OEM cable, the odds of finding one are small.

I expect that what you have now will not cause any problems.

 

I'm not sure if this one is causing problems. I got looking at it because it sometimes feels like the carb isn’t returning all the way when the pedal is released. Not a lot, just a little. Like going down the road with no pressure on the pedal at 30 MPH, where you’d expect the car to slow down.

It’s not the pedal. I don’t think it’s the carb. So I’m looking at the cable and thinking that the U bend is too much, that I’d like to see it bent less. I don’t think this one can be easily altered, so I started looking at universal cables. Found several, but no solid recommendations on how long they should be, except for the Lokar docs.

 

In the "Way back then" when all that my budget could afford was the "junk yard parts house", I used a throttle cable from some Mopar product that was too long, but with an approximately 6" loop (& carefully greased with speedometer cable grease) worked perfectly for almost 10yrs, when I sold the truck. Sure, it might have not been up to "show quality", but it did the most important thing : IT WORKED!!

 

You should be able to make the universal cable almost straight between the firewall bracket and the carb bracket. It will have an adjustable ferrule on at least one end to make it slightly longer or shorter.