Vacuum pump for brakes

[Nate Crisman]

Preface: this is for a dragstrip-only car that goes to the track on a trailer.

I'd like to start a conversation about running a vacuum pump for the brake booster. I was able to get a few 1.4 launches out of my 16g/auto car on the stock converter last season, but I had a hell of a time keeping the car from creeping forward. (It didn't help that I had the boost set well past 30psi). I would say that pretty much all of my runs I was simply letting the brake go as soon as I felt the car start to overcome the brakes, which are oem single piston 90-91 calipers).

My "procedure" for staging:

• lighting both bulbs
• shift to neutral
• free rev to build max vacuum of about 21inhg
• pushing the brake pedal (still stock)
• waiting for revs to come back to idle
• shift to L (I use the oem shifter with the "kiggly manumatic mod")
• let off the brake pedal to leave

My plan for this season is to prep the car to run DST class at the shootout, and will need to be able to stage and get up on the converter quickly (without nitrous) as it's a pro-tree situation. Obviously the car needs to be up on the converter before breaking the stage beam which completely negates the whole "max vacuum" procedure listed above. I need to be able to bump in with the foot pedal.

Im thinking of buying a vacuum pump, running it switched of the brake pedal switch. As for vacuum lines, are you guys running the pump in a T with the factory line to the intake manifold w/ check valve? Im considering plugging the intake manifold and simply running the vac pump straight to the brake booster.

Any suggestions on a specific pump that works well?

Has anyone done any calculations on single piston vs dual piston stock brakes to determine which offer the most clamping force? (heat issues are not involved on a cold brake set)

 

[burkgonzo]

I am new to the Auto world, I will be following this. Never had to have to stall a converter.

 

[GDNF2ET]

I'm gonna give this a try..I don't see why it would'nt work, plus its simple..
Booster vacuum problem with big cam - Third Generation F-Body Message Boards

 

[Nate Crisman]

I found this analysis of oem 1g 90-91 single piston vs 92-94 dual piston front brakes:

Ok, because it's a healthy discussion;

Assuming some basic controls; leg input pressure, front pad Cf, rear rotor dia, rear piston area and rear pad Cf, as well as all being calculated in 'static' form here's what you get.

The controls:
Leg 70lbs
Cf .40
Rear Rotor 9.0
Rear piston 1.5
Rear Cf .40


The single piston on a 10.06 rotor nets 82.0%
The twin piston on the 10.85 rotor nets 82.3%

Yes, I think the total % is too high but the difference between the two is the issue. It changes the same if we go to a 10" rear rotor for example.

Now, if you change the MC you retain the same %. Only you ALSO chang the feel and leg requirements as well as the operating pressures.



So,what's all the fuss on the 'big brakes' over the single? Sorry guys, the total brake torque is the same. But man I know it's different! I agree. I also understand that if you do the 'big change' you are also doing new pads and likely SS hoses as well. And maybe the bigger MC.

Let's suppose this is what you do; the hoses firm up the feel, the pads appy more bite and the MC requires more leg. As a general rule a 10% increase in piston area in the MC will require a 10% increase in leg required. This is the 'better feel' you get.

But I know it stops better! Perhaps, but it's more due to pad choice as well as the ability to modulate the pedal better with the lines and bigger MC.

What's the difference in the part and why do it? The larger caliper has twin pistons. This in turn places a better load on the pad. The pad in turn bites the rotor better. And if you check the pads (I could not) and find the pad is taller and narrower this also adds to the 'pad radial height' and nets a bit more 'effective diameter' as the book calls it. All good things.

Now lastly, if you do the pads, the hoses and the MC you get better feel, firmer pedal and more bite. And a bit more RADIUS to work from. And perhaps a bit more mass, but not a lot.

Still all in all it's not a bod deal. However it does not create more stopping power all things being the same.

 

[Car Cannibal]

The vacuum pump and the canister are different, in your case you're already doing the neutral blip so you don't need the canister or vacuum pump unless you're releasing the brake pedal before the launch. The canister is a great way to have max vacuum during times where you're at WOT and need to slam on the brakes.

You need more clamping force, example would be a 4 wheel line lock. Since we don't have a Transbrake you need to consider a stronger braking system, you can start at the fronts with the dual piston caliper and use the Emergency brake for the rears with your current launching method and see what that nets you.

Here is a chart on braking force.
http://www.classicperform.com/PDFs/BoosterBrakePressureChart.pdf

Todd says 70lbs of leg pressure and the charts is set at 100lbs so that changes the pressure figures. Also the Turbo models come with a 15/16th bore and I don't remember the booster size.

 

[Nate Crisman]

I cant use a line lock. The issue is that I need to be able to let up on the brake pedal in order to bump into the stage beam after gettin up on the converter. You can't light both bulbs on a pro tree and THEN get on the converter as you only have .5 seconds before the tree comes down. So I need to be able to spool up with only the prestige bulb lit, then lift the brake pedal to creep into the stage bulb and have it hold on reapplication of brake pedal. A vac pump is the only thing that is going to work.

From what I get out of my above post, the point is that single piston and dual piston stock calipers have the same clamping force, so 2 piston calipers are not an upgrade for staging.

 

[99gst_racer]

Nate, I've seen this one used on a couple different A/T DSM's and several other A/T cars: SSBC :: 28146

 

[GDNF2ET]

Here is a pic of the brake fitting coming off the stock intake..Would it make a substantial difference if the threaded end was drilled out larger ?
What part does brake fluid play in brake pressure ? I've read that diehard racers change their fluid often..I've never changed mine

 

[HighPSI TSi Guy]

I use the vacuum pump paul mentioned. It is not instant, but is generally at full vacuum by the time I am fully stalled (about 6 seconds). It will take some practice to master creeping on the stall, but it is doable. Just get the timing right and you should be good.

 

[Car Cannibal]

I wasn't implying to get a line lock, just the clamping force it would give that you need recreate.

I have a vacuum pump on a different auto, how much vacuum are you seeing HighPsi with yours?
The thing to keep in mind with VP's is that if the pump pushes less or the same " as your current setup than it's not going to create any NEW clamping force, just allow you to maximize your current system. If the pump was to push say 30" then we have a different scenario.

New fluid and SS lines couldn't hurt.

Here is something I found on NASCAR and Brembo 6 piston calipers. (towards bottom) I didn't see anything about 1 piston brake calipers.
Brembo - Brembo in NASCAR

Have you tried the emergency brake while brake torquing and creeping up to the 2nd beam? There was a slick setup that converted the emergency brake into a torque arm that was for sure not going to allow the rears to move once pulled up on.

 

[-red97rum-]

The SSBC unit is a little bit cheaper if you go through Summit.

SSBC Electric Vacuum Pump Kit - Summit

Has anyone ever heard of this one? Summit - Hella Street Vacuum Pump

It's more than $100 less than the SSBC. I'm just wondering if it has enough power to pull enough vacuum when trying to stall.

Here's a couple more:

CVR - Clay Valley Racing

Summit Racing Electric Vacuum Pump - Looks exactly like the CVR but advertised as Summit.

I was looking around online some more and stumbled across a pump manufacturing company named GAST MFG. I've read that ambulances and big RV's use vacuum pumps from this company to assist in braking. The price isn't really any cheaper but it could be another alternative so I figured I'd post it.

More info here: Miniature 22D Series

Can be purchased here: Brenner-Fielder.

It shows as a non stock item with a 13 day lead time... so that sucks.

 

[Nate Crisman]

I use the vacuum pump paul mentioned. It is not instant, but is generally at full vacuum by the time I am fully stalled (about 6 seconds). It will take some practice to master creeping on the stall, but it is doable. Just get the timing right and you should be good.

How is your pump hooked up? I can see three different ways to run a vac pump:

1. T'd into the factory hose after the check valve
2. Factory hose removed and the pump run directly to the booster
3. The pump run inline with the factory hose.

Would the third option work similar to a compound turbo in that the pump could possibly increase the vacuum over whatever the inlet vacuum is?

Im also wondering if these pumps could be cranked up via use of a "fuel pump voltage booster" like the Kenne-Bell Boost-A-Pump?

My buddy Nelson just snagged one of those Gast 22D pumps off ebay (cheap...due to the seller misspelling vacuum and the auction getting no hits). Seems to be about 5lb in weight and small. I think it might be able to find a snug home on his car under the brake booster on the firewall.

BTW: that Hella brand pump at summit lists 29inhg as the maximum vacuum compared to the others that are showing between 19 and 22inhg. Wonder if that's a typo or not?

 

[Car Cannibal]

I've yet to see a vacuum pump over 23" but if that links correct than it's a nice improvement.

Here is something we're going to install later this Spring on a DSM, it will be the closest thing to a line lock or beyond a Hydroboost system while using the factory braking system.
ECI Brake Pressure Multiplier

 

[GDNF2ET]

I've yet to see a vacuum pump over 23" but if that links correct than it's a nice improvement.

Here is something we're going to install later this Spring on a DSM, it will be the closest thing to a line lock or beyond a Hydroboost system while using the factory braking system.
ECI Brake Pressure Multiplier

I looked into that, seems you have to add one for each wheel...

 

[-red97rum-]

BTW: that Hella brand pump at summit lists 29inhg as the maximum vacuum compared to the others that are showing between 19 and 22inhg. Wonder if that's a typo or not?

Yeah I saw that too. I'm not sure I believe it would when it's half the price of some other popular pumps.

 

[Car Cannibal]

FWIW, the ECI has a newer version coming this Summer and can run the whole braking system off of one unit.

 

[Nate Crisman]

I've yet to see a vacuum pump over 23" but if that links correct than it's a nice improvement.

I'v tried to find out more info on that hella vacuum pump, but haven't been able to find anything at all. I may just have to buy one and find out by testing it, and since it's on the cheap side of the vac pumps available, there's not much to lose if it ends up only the same as the other pumps.

 

[johnnytsi]

I picked up an OEM Audi/VW pump to try. $30 from my local pick-a-part. I haven't had a chance yet to hook it up.

 

[Car Cannibal]

Hey Nate, I checked out your engine mods and am stumped on how you're only seeing 21" of vacuum on the Neutral Rev. I have FP2's and get a solid 24" and you have 264 and 272 HKS. I'd assume you could get at least 24" like I'm seeing but....

Did you degree them?

BTW, did Mitsubishi ever make a Hydroboost braking system?
It's possible that can bolt on and the braking force would be improved by a bunch.

 

[Nate Crisman]

Hey Nate, I checked out your engine mods and am stumped on how you're only seeing 21" of vacuum on the Neutral Rev. I have FP2's and get a solid 24" and you have 264 and 272 HKS. I'd assume you could get at least 24" like I'm seeing but....

Did you degree them?

BTW, did Mitsubishi ever make a Hydroboost braking system?
It's possible that can bolt on and the braking force would be improved by a bunch.

Actually, I just went back to look at the DSMlink log, it's saying -23.1 inhg, so it's pulling more vac than I thought. (I was previously going off what I saw on autometer mechanical gauge)

My cams are installed with stock gears...no degree effort. Maybe this year I'll luck into a set of adj cam gears to experiment with.

 

[-red97rum-]

Did anyone give this a try yet?

 

[talont3t4]

Any updates?

 

[e85_4g63]

This might be a stupid question, but why can't you just use the E brake with the foot brake? (I didn't see if your already doing that or not, what about making an adjustment in the tune, is that possible?)

 

[ed1380]

I picked up an OEM Audi/VW pump to try. $30 from my local pick-a-part. I haven't had a chance yet to hook it up.

I hooked one up to my boost gauge and got 20in of vacuum
http://www.dsmtuners.com/forums/bolt-tech/421486-diy-cheap-vacuum-pump-launching.html

 

[ElectronVTEC]

I have that same Audi pump hooked up in my '97 auto. Works like a champ. I have a switch in the line that goes to the relay from the brake switch to shut if off when I don't need it. I did a few quick tests on it about a month ago and it does help quite a bit. I'm on stock 2G brakes with Hawk pads FWIW. Spooling my 3065 to 15 psi, it held the car steady. If I turn it off, as soon as I hit about 8 psi, the car starts to creep forward.