j.kenzie@sbcglobal.net

Hi guys,
I'm cleaning up my throttle body connections and was wondering if I can eliminate my brake venturi, and just connect booster to manifold directly.
Thanks,
Dave

dr bob

The venturi educter is there to support vacuum accessory operation like cruise control and hvac when you are at high engine load for a while. Like autobahn touring at speed, when there is no appreciable manifold vacuum. Without it, you have accessory vacuum until the reservoir is depleted. The brakes may or may not be an issue in a boosted car. You get one or two stops worth of vacuum boost from the booster can. So long as the manifold goes to vacuum immediately on braking you should be OK. The connection needs to be downstream of the throttle of course.

ptuomov

No reason not to hook up the venturi jet pump correctly to help with vacuum in a boosted car.

j.kenzie@sbcglobal.net

On my 84 L-jet I was thinking of simplifying the TB connections by eliminating all except:
Fuel pressure regulators
Fuel Damper
Distributor vacuum advance
I would be eliminating:
A/C solenoid valve
Evaporative system
Brake venturi

Any obvious problems?
Thanks,
Dave

j.kenzie@sbcglobal.net

I could, but is there a large benefit?
Thanks,
Dave

PorKen

I always delete them for the sano look. Not often you can use full throttle more than a few seconds in the US of A.

Better to install an electric brake booster pump (in the fender) when turbo/supercharged, anyway?

ptuomov

I disagree. The system is there for a reason, as is the vacuum reservoir. There's no legit reason to delete it, and the factory doesn't add expensive parts in the system for the fun of it. Plus to the extent that the power vacuum and signal vacuum are connected, you don't want the signal vacuum being influenced by the power vacuum transitions in a home grown system.

PorKen

I think those venturi widgets are dorky. They're only on German cars for the most part, for Autobahn use, AFAIK.

Power vacuum and signal vacuum are not connected? The brake booster, climate control, and early cruise control, are distinct from the fuel pressure regulator/dampers and auto trans modulator which are directly connected to intake manifold pressure.

An electric pump, EG. from a diesel car, would evacuate the brake booster and stock vacuum reservoir more effectively. (They turn themselves on/off according to the vacuum level in the reservoirs.)

ptuomov

I drove the turbo car for 1000 miles on the US highways in one trip. 5th gear, low rpm, decent speed. Power vacuum was marginal at times.

The concern about confusing signal and power vacuum related to home grown systems.

j.kenzie@sbcglobal.net

Hi Ptuomo,
I think i understand that the jet pump works by flow from pre-throttle to post-throttle creating a venturi effect to enhance vacuum to brake booster and its connected devices. My question is whether it really works well enough to be valuable, especially with boost.
Thanks very much.
BTW if you think it really works well, I can easily reconnect it.
Dave

Hold On

I swapped to a small vacuum pump off a F250 ford diesel pickup. It cycles on and off as needed. I use it for cruise control and HVAC on my supercharged 16V. Works like a charm.

kombatrok

I've been running with no venturi and a much simplified vacuum system for over a year now, both highway and city driving with no complaints.

j.kenzie@sbcglobal.net

Hi,
That's the point where I have arrived at present. All seems well so far, although I have not tried all kinds of driving situations.
Thanks,
Dave

FredR

I would describe the venturi as a safety critical item and deletion of this item could quite conceivably cause a delay in brake function under certain circumstances- for instance when cruising down the motorway and you suddenly need max brake effort- not a time to discover the system is priming itself before the brake servo can work.

To be fair I suspect the difference is marginal but half a second [ for instance] can make all the difference in a critical moment. Another point to consider is whether dicking around with a system like this invalidates your insurance!

j.kenzie@sbcglobal.net

Hi Fred,
I appreciate your comments very much. I suspect you may be slightly exaggerating the importance of the power assist booster on the brake system. Remember the brakes are hydraulic and not connected to the booster except in a parallel way. You do not have a delay in braking without the venturi. You have a delay in the power assist feature if the vacuum storage vessel has been depleted for some reason. People who put high performance brake pads would probably see a similar increased effort in casual driving, but no delay in onset.
As to potential liability, that's whatever a lawyer can establish in a courtroom, not necessarily a real physical problem. So yes, I would be at risk for this and any other modification I have introduced to my car. Right now, I choose to accept that risk, but will re-evaluate if I sense any real problem arising. I will of course report any problems that I encounter, so others would not make the same mistake.
Thanks,
Dave