LS Engine Throttle

[crafty]

I have a 90mm UMI throttle body.
www.umiracing.com/news/documents/U.M.I.90MMThrottleAssembly.pdf

This cable operated and cable wraps around a cam, which opens the throttle slowly, and gets progressively faster as you open the throttle, giving a more sensitive throttle response down low.

The problem is that the Ultima throttle setup gives 40mm of pull on the cable. The UMP throttle body needs 60mm.

There's not enough room to extend the pedal end to get more movement.

I was thinking of either:

A. Remaking the cam for 40mm of cable pull.
B. Doing away with the cam and attaching the cable to a lever of the correct length for 40mm of cable pull.

Have any of you guys had this problem, and how did you get around it?

[steve_d]

Remaking the cam would be the route I would take. An alternative is to take the cable to an unequal length crank then a short cable to the cam. I use the term crank as that is the easiest way to describe it but it could just be a single arm with the main cable connecting to the arm and the TB cable connecting to the same arm but further out giving increased leverage.

Steve

[BigAl1]

I designed my throttle pedal to match the cable pull on the LS1 F-body throttle body - CAD says I have 58mm of pull. I would recommend looking at the pedal again.

[CanAm Dave]

I agree with Steve. By far the easiest way would be to make a bellcrank which would convert the 40mm you have to the 60mm you need. Remaking the cam would be the best and cleanest way.

[Builder]

Have you contacted UMI to see if they have a 40mm crank?

[tblackey]

Funny you should ask. I remade the bell crank. I havn't tried it yet, but my prototype is circular. I want to see how this works. Also much easier to fab up. I would see about 60% throttle before. Your numbers seem about right.

Bill

[gtrclive]

Had a Road Race thorttle lingage on my modified holley, found it alot better than
the normal version slower opening at first then opened the 4 barrels faster....
Well worth it....

[gtrclive]

But be carfull, the mapping my be done on the throttle position, so this would make a new map a must !!!!

[davefiddes]

Craft is running a supercharger which to my understanding means you have to run speed-density. Only normally aspirated engines can run alpha-N.

[crafty]

This will not affect tune whatsoever. The throttle position will still be.....the throttle position.

The bell crank idea has crossed my mind also, but it will be a bit messy and I'd rather not introduce more "trouble spots" between my right foot and the throttle body.... there's a possibility of breaking/getting stuck etc.

Allan/Bill - do you have any photos of your solutions?

[jschwartz]

Crafty has a GM mass airflow system that we re-mapped for the SC. As stated, throttle position will still be relative. Today I checked the latest production 90mm throttle bodies that I have in stock, they need about 40mm travel to WFO, I'm sure we can switch the linkage out. Email me a pic of the linkage side view.
Jeff

[tblackey]

Here are two pictures:

http://home.pacbell.net/tblackey/img_
http://home.pacbell.net/tblackey/img_