Technical SBC boost / vacuum gauge - help!

Hello,


I am looking for a bit of advice.
Someone told me I need to get a boost gauge along with a fuel pressure gauge, as I got a small block Chevy with a GM 671 blower.


I have an original 2 5/8 Stewart Warner green line Vacuum Inches gauge from 0 to 30. I am thinking of using this gauge, with setting the 15 as 0, or do I need to get a boost gauge instead?


I would prefer to use the Vacuum Inches gauge, as the boost gauges look to modern.
Just wondering if anyone would know.


Cheers,Matt

 

http://www.summitracing.com/search/...-chrome-analog-gauges/gauge-type/boost-vacuum

Are these vintage-looking enough for ya?

 

might look into a boost reference fuel pressure regulator too...and possibly a boost reference timing control box

 

Referenced regulator is for a blow through application.

 

if you had to go new, maybe this?
http://www.egaugesplus.com/uploads/8/5/2/4/8524701/5116245_orig.jpg?232

 

http://www.antiqueswordsonline.com/new-an-original-british-ww2-aircraft-boost-gauge-new

 

Old boost gauges show up on ebay every so often if you search "manifold pressure" or you can get a memory kit http://www.summitracing.com/parts/atm-3230/overview/ and mount a small gauge remotely.

 

do you use boost refenece power valves instead..?

 

Yep.

A referenced regulator would up fuel pressure incrementally with boost on a pressurized carb.

A referenced power valve would be wide open under boost and act normal at cruise and idle. Not necessary on a blow through since the whole things under pressure.

 

I think the wheels are to big it would alter the gearing, oops sorry ive gone off topic as well

 

Ok.
Below is the vacuum gauge I have.
With the memory kit you mentioned, would I be able to set the 15 as the 0, with the 0 as minus and the 30 as plus? I am not quite sure what the kit does?
Also, where would the other end of the cable go. I am not sure what I need to do to the blower case as there is nowhere I can attach it.

Cheers

 

I have no idea if the gauge would work properly like that but it would never read vacuum with a memory kit because it has a check valve inline.




The fitting on the right with the one way check valve goes in the intake manifold, Tee to gauge and release button on other end. You can mount the button on dash with a hose or hardline if you want.

 

Thanks for being patient with me.
Would this mean that I would not be able to use the vacuum gauge as a boost gauge then?

 

A boost gauge shows both vacuum and pressure on the same gauge. Most boost gauges available have a more modern look to them, like the Autometer pictured. I prefer the old Stewart Warner gauges as well, but they did not make a boost gauge. The best thing to do is actually use two gauges, one vacuum and one manifold pressure, which will show you the same readings, just on two gauges instead of one. New Stewart Warner vacuum and manifold pressure gauges are available everywhere, but I prefer to find the older ones, but visually they are pretty much the same.

 

Don't know about the vacuum gauge idea. I've also used a small fuel pressure gauge like this on the engine with the button tee and valve right on the back of the intake.

 

Using two gauges does sound like a good option. I have not seen any vintage manifold pressure green line gauges. I am thinking of getting a second vacuum gauge and noting underneath what each ones measures, you reckon that might work? As I really don't like the look of the modern boost gauges.

 

Yes I know you can do this, but I would like to have the gauge in the car.

 

I think the manifold pressure was only available in Stewart Warner's "classic" series. like the one that I pictured. You cannot use a vacuum gauge to read pressure. They are "mechanical" gauges. Simply put, the vacuum gauge works by air "pulling" on it, and the pressure gauge works by air "pushing" on it. Only a true boost gauge will read both.

 

They did make a green line "Custom" manifold pressure gauge in both 2 1/16" and 2 5/8" at one time. Might see one or two a year on ebay.

S-W "Custom" gauges part numbers:

360-DD 2 1/16"

691-P 2 5/8"

 

pressure gauge below blower , vacum on carb base , you cannot use a vacum gauge as a pressure gauge as it will try to make the needle move CCW off scale , as the movement is determined by the bourdon tube inside the gauge as the suction causes it to expand . and when you apply pressure it will try to collapse it and damage it . a dual range unit is set up to have a negitive atmosphere applied to it . with 2 gauges its easier to see if there is a problem developing with in the blower as the pressure will drop from wear of the lobes .

 

I will have a chat with my mate Merv, who is building my engine and helping me with my car, to see what the best way forward is.

Thanks for everyone's advice, it's much appreciated.

 

That Auto Meter 2401 doesn't look too bad, but I'd like it better w/ a white pointer if I was trying to mix it in w/ some '60's SW gauges.

Most of the Boost gauges out there reek of the "hey, look at my turbo" type of design. Going w/ the two press/vac gauges may be the best option for a vintage look.


Later, Kinky6

 

Hi

Thanks for that yes it is one of the best gauges. It looks a lot like this moon one, don't know if they made it for them? But I cannot find it anywhere!

 

Why not explore aircraft gauges a little more many ed find a matched pair of vacuum and boost gauges that have the right look even if they don't exactly match it other gauges

 

only a very small amt of time will the boost gauge show anything but vac.. press. gauge may look like its broken most of the time as the reading will be 0 on a streetdriven car

 

Judson boost gauge. This came with a car I bought. They make a repos on ebay but bring your wallet this the repop is $350 but you can choose your face and bezel it has modern internals.



Posted using the Full Custom H.A.M.B. App!

 

Hi Rory, yes I've seen that gauge, they are mint. They originally were in a few cars in England, like the TVR. I've seen the repop ones on ebay, I've heard they are fake and that they are not made by the actual company. But I don't know this for sure.
As I already had your Moon and Eelco tank of you, if you would like to send the gauge to the usual address, that'd be great! I would keep that gauge safe if I were you, they go for $1000 plus.
I hope all's going well with your project.
Matt

Thanks, I'll bear it in mind.

 

What about tracking down one of the gauges from a late 50's Studebaker Hawk with a factory supercharger? I'm pretty certain they were made by Stewart Warner. I've seen them on that auction site from time to time.

 

That one looks lovely. I didn't know about those yet. Do you know what size it is?
Cheers Matt

 

I believe the Studebaker pieces are 2 1/16 like other SW gauges.