Brake servo with Throttle Bodies

[steve-V8s]

If you fit throttle bodies and therefore don’t have a plenum where do you get the Suck from to run the brake servo ?

[spend]

I have a 'balance reservoir?' that links via small pipes into all the manifold ports downstream of the butterfies. This also has links for fuel reg, vac, as well as idle air valve..

[350Matt]

Apparently the vacuum off just one cylinder is enough to run the servo so you can tap into the nearest port.

the Editor of PPC magazine had this dilemma as well and thats how he sorted it ( addmittedly with a 5 ltr ford lump on a mild cam)

[dnb]

I believe TVR used the same idea for the AJP8.

[steve-V8s]

Good point I hadn’t thought about the fuel regulator, suppose that effectively needs the same feed as the servo. Just looked at the throttle bodies on a modern 4cylinder bike and they have a tiny pipe (probably about 2.5mm id ) coming off of each header, they are all linked together and feed the pressure regulator.

Would think if you start linking all the headers together with a pipe that is closer to the size of the servo feed it would negate the benefits of having them separate. Diesel cars seem to use a vacuum pump as they don’t have a plenum.

[scoule]

My Lotus Excel (2.2 N/A on sidedraught 45's) just has a take off on one port for the servo.

[spend]

Many diesels have a pump off the alt. My Disco has an electric pump under the air filter BTW.

The link pipes are narrow bore, vastly different from a shared plenum

[rev-erend]

I link of just 4 of the 8 cylinders for my TB's.

[Simon Says]

scoule said:

My Lotus Excel (2.2 N/A on sidedraught 45's) just has a take off on one port for the servo.

Never had problems with lack of vacuum on a 1720cc X Flow Ford with 3/4 race cam drawing vacuum of one runner on the side draught manifold(much smaller bore&stroke)and a 3500 rover servo(bigger than the TVR item);) i know on very lairy cammed yank V8 motors they sometimes used vacuum tanks but that is an extreme measure some settled for Toyota Hi-ace/Mits Shogun alternators with the vacuum pump on the rear of the unit,problem solved.

Edited by Simon Says on Friday 16th October 19:43