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9201

[VintageLambo] vacuum from an engine

Espada Tech Site

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Hi folks, In ref. to the current discussions about the vacuum available for the brake boosters : The more capacity of the engine ( and the less valve-overlaping ) the more air flow is being pulled into the engine, of course also in relation to the speed of the engine. However, the vacuum build up in sufficient "power" as to use for a brake booster can only be achieved at closed or almost closed carb/injections butterfly valves. When running flat out the butterfly valves are fully opened and vacuum is at the lowest. Ok, you dont need braking power just then, but when you do what happens ? You let go the accelerator and stamp on the brakes. When letting go the accelerator the butterfly valves snaps closed with the engine still running fast, thus high vacuum is generated fast, however not fast enough, then it is a good thing that the Lambo"s do have the vacuum reservoir. You save precious braking meters with this arrangement. The vacuum build up in the reservoir was actually made when runing slowly or at idle ! Furthermore, the vacuum-reservoir is good to have around should your engine stop dead and you need braking assistance. So, vacuum is generated because the engine is trying to suck air into the cylinders but is restrained by the butterfly valves being CLOSED. Nothing to do with venturi. This leads to the question often poping up : why does american V8 muscle-enginee seem to have more vacuum than the exotic multi-carb engines ? The answer is simple : because most american V8 are fed through a single or double body carburator or butterfly, whereas the exotica have individual butterfly valves per cylinder. This means that whilst the americana does leak through only one butterfly valve, the exotica is leaking through 12 valves ( as they are actually joined through the vacuum-pipe !) So in the V12 every time one ( and small size ! ) piston tries to "suck" up a vacuum, air is leaked through by 11 other butterfly valves. If you are really hungry for lot of vacuum then you can either : add a separate pump ( electrical or belt driven ) or fit a single carb to your V12 ! got it ? By the way : high vacuum ( by the engine ) may on the other hand suck up oil ( from piston-clearances and the valvestem guides ) causing the dreaded burnt-oil-smell. regards Lars ---- Original Message ----- From: lamboguy To: VintageLambo@yahoogroups.com Sent: Thursday, May 20, 2004 4:16 PM Subject: [VintageLambo] Re: another dumb brake booster question Hi Paul et al, ......... But I have a question. A long time ago I heard somebody say that one of the reasons we have low vacuum is because of the short stroke of the V-12 400gt motor. Is that true? Is that a major or minor contributor, or is that just wrong? Thanks, Fred Yahoo! Groups Sponsor ADVERTISEMENT ________________________________ * * * Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service .

 

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Last modified: 12th January 2020