Boost gauge question....

[Hart_Rod]

I just installed an Autometer 3301 boost/vacuum gauge on my 383 with a vortech supercharger. I have a question about normal operation of the gauge. At a steady 60 mph/2800 rpm/4psi boost, the needle flucuates so fast you can barely read it (+/- 3 psi). I'm new to superchargers and this is my first boost gauge, but that just doesn't seem right. I installed it exactly like the autometer instructions said and used the port that Vortech recommended. Do I have a leak? Any suggestions? OBTW, it's in the in the same port that goes to my MSD 6BTM box. Thanks in advance.

R/

[1FAST68]

I have done a bunch of blowthru procharger stuff. Where exactly is the gauge hooked to on the engine. If it is showing 3psi driving normal sounds like you have it above the carb, it will never show vacuum.

What is the setup? carb, fuel inj, and does it have bypass valve.

[Hart_Rod]

Originally Posted by 1FAST68

I have done a bunch of blowthru procharger stuff. Where exactly is the gauge hooked to on the engine. If it is showing 3psi driving normal sounds like you have it above the carb, it will never show vacuum.

What is the setup? carb, fuel inj, and does it have bypass valve.

It's connected between the supercharger and the carb (outupt of the supercharger). I'm not to worried about it not showing vaccuum, but should the need be bouncing around so erratically?

[1FAST68]

probably, it could be compressor surge sounds like there is no bypass valve

I put the boost gauge on the intake manifold so I could see the pressure in the motor and not above the carb. Also I used a bypass valve that dumped boost when driving normal so the supercharger was not is a bind.

[Hart_Rod]

Originally Posted by 1FAST68

probably, it could be compressor surge sounds like there is no bypass valve

I put the boost gauge on the intake manifold so I could see the pressure in the motor and not above the carb. Also I used a bypass valve that dumped boost when driving normal so the supercharger was not is a bind.

What did the bypass valve do for your drivability? I was told I didn't need one, but what would you sugges? My MSD is connected to the same line, what problems will/could that cause? Do you have some pictures of the bypass valve and where you connected the boost/vac line? Thanks for all the information.

R/

[1FAST68]

Originally Posted by Hart_Rod

What did the bypass valve do for your drivability? I was told I didn't need one, but what would you sugges? My MSD is connected to the same line, what problems will/could that cause? Do you have some pictures of the bypass valve and where you connected the boost/vac line? Thanks for all the information.

R/

The bypass valve helps ease the load on the supercharger under normal driving, it also helps flooding issue when you suddenly let off the gas. The valve should be located between the blower and carb, it operates off of vacuum, so when driving normal you have vacuum and it opens the valve, dumps unwanted boost. When you floor it you loose vacuum and it closes and sends all the boost in the engine.

As far as the MSD boost retard line, it needs to be on the intake also, otherwise you will be retarding the timing under normal driving because it will see boost between the carb and blower.

Another note, fuel pressure should rise with boost, so you should have a fuel pressure regulator with a vacuum line connected between the carb and blower.

I will have to email you pics, they are too big to load here if you want.

[Hart_Rod]

Originally Posted by 1FAST68

The bypass valve helps ease the load on the supercharger under normal driving, it also helps flooding issue when you suddenly let off the gas. The valve should be located between the blower and carb, it operates off of vacuum, so when driving normal you have vacuum and it opens the valve, dumps unwanted boost. When you floor it you loose vacuum and it closes and sends all the boost in the engine.

As far as the MSD boost retard line, it needs to be on the intake also, otherwise you will be retarding the timing under normal driving because it will see boost between the carb and blower.

Another note, fuel pressure should rise with boost, so you should have a fuel pressure regulator with a vacuum line connected between the carb and blower.

I will have to email you pics, they are too big to load here if you want.

I looked on the back of my intake (Edelbrock RPM Air Gap), the only vaccuum port I see is right under the vortech airbox and there is no room to add any fittings. You can send pictures to robhartley@aol.com.

[1FAST68]

Is there a way to get a line off of the bottom of the carb below the throttle blades and get it out of the box?

[1FAST68]

what kind of carb is in the box??

[Hart_Rod]

Originally Posted by 1FAST68

what kind of carb is in the box??

QFT 750 Blow through carburetor.

[1FAST68]

I would hook to a port below throttle blades on the base of carb and put a bulkhead fitting in the box. You could T off that on the outside for MSD and boost gauge.

[Hart_Rod]

nm

[Hart_Rod]

Originally Posted by 1FAST68

I would hook to a port below throttle blades on the base of carb and put a bulkhead fitting in the box. You could T off that on the outside for MSD and boost gauge.

I just remembered that there's a port that comes through the box that goes to the tranny modulator. Do you think this would work?

[1FAST68]

Originally Posted by Hart_Rod

I just remembered that there's a port that comes through the box that goes to the tranny modulator. Do you think this would work?

yes

[Hart_Rod]

OK, I hooked the gauge up to the same port that the tranny modulator is connected to. The gauge now is more stable and shows about 14 hg of vaccuum at ide. I took it for a test run and and got on it a couple of times, but nothing real hard. The gauge would go to zero but I don't think it went positive (boost) for very long. Is this geting closer to the way it should act?

[1FAST68]

Originally Posted by Hart_Rod

OK, I hooked the gauge up to the same port that the tranny modulator is connected to. The gauge now is more stable and shows about 14 hg of vaccuum at ide. I took it for a test run and and got on it a couple of times, but nothing real hard. The gauge would go to zero but I don't think it went positive (boost) for very long. Is this geting closer to the way it should act?

Yes, you will have to go wot for it to show boost. Now you are getting a true reading of what is in the engine and not on top on the carb.

[Hart_Rod]

Originally Posted by 1FAST68

Yes, you will have to go wot for it to show boost. Now you are getting a true reading of what is in the engine and not on top on the carb.

Cool. Where did you get your boost adjusted fuel pressure regulator? I think that is the last thing I need to add to have all the parts in place prior to taking it to be dynoed tuned.

R/

[1FAST68]

I have used a mallory 4309 regulator for below 15lbs of boost, but I don't know what your fuel pump is. Hope not a holley blue style!!

My 1rst setup I used a mechanical edelbrock pump that had the clockable bottom. I drilled and tapped the top of the pump for a 1/8 nipple and ran a vacuum line to it. It would raise fuel pressure with boost then, but I only had 8lbs of boost back then.

If you run your fuel pressure at 7lbs and have say 10lbs of boost that means you will need 17lbs of fuel pressure and another 5 to overcome pumping loses and g force in the line, so 22lbs of fuel pressure at wot.

[Hart_Rod]

Originally Posted by 1FAST68

I have used a mallory 4309 regulator for below 15lbs of boost, but I don't know what your fuel pump is. Hope not a holley blue style!!

My 1rst setup I used a mechanical edelbrock pump that had the clockable bottom. I drilled and tapped the top of the pump for a 1/8 nipple and ran a vacuum line to it. It would raise fuel pressure with boost then, but I only had 8lbs of boost back then.

If you run your fuel pressure at 7lbs and have say 10lbs of boost that means you will need 17lbs of fuel pressure and another 5 to overcome pumping loses and g force in the line, so 22lbs of fuel pressure at wot.

I currently have a holley black pump and am running 10 AN lines front to rear. PSI is set around 7.

[1FAST68]

How much pressure will the black pump make?

I would call vortec and tell them the serial # on the blower, they should have a record of what pulley combo it was sold with and what boost it should put out. Also ask them about the fuel system, I am not that familiar with the vortec box. I assume it works the same a the procharger hats I used to run but I don't want to assume anything on your engine and give you the wrong advice.

I hope I have been helpful. I have had 6 centrifugal blower setups and learned the hardway.

[Alex1]

Nice set up, is it the YSI? or an S or T trim?

I prefer the Vortechs to the PROCHARGER - more reliable. Do you have better pics of your set up? I'm sure the guys here would like to see.

I noticed you have a blow through carb - do you have a wideband set up? I thought one was supposed to use a regular carb in the enclosure - the blow through cars are for the set ups where the carb is not enclosed.

But if it works..

[Hart_Rod]

Originally Posted by 1FAST68

How much pressure will the black pump make?

I would call vortec and tell them the serial # on the blower, they should have a record of what pulley combo it was sold with and what boost it should put out. Also ask them about the fuel system, I am not that familiar with the vortec box. I assume it works the same a the procharger hats I used to run but I don't want to assume anything on your engine and give you the wrong advice.

I hope I have been helpful. I have had 6 centrifugal blower setups and learned the hardway.

From the holley website:

http://www.holley.com/12-815-1.asp

Compatible with alcohol or methanol fuels
Flows 140 GPH (free flow)
Flows 120 GPH at 9 PSI
Maximum pressure is 14 PSI
3/8” NPT inlet and outlet ports
Fuel pressure regulator is required (Recommend Holley P/N 12-704 for gasoline & P/N 12-707 for alcohol)
Provides constant fuel flow with no pulsation
Has externally accessible pressure relief valve (max 14 PSI)
Rotor/Vane pump design is more tolerant of contaminated fuels
Not designed or recommended for use with fuel injection systems

I'm still waiting for Vortech to get back with me. Their customer service suxs......

Originally Posted by Alex1

Nice set up, is it the YSI? or an S or T trim?

I prefer the Vortechs to the PROCHARGER - more reliable. Do you have better pics of your set up? I'm sure the guys here would like to see.

I noticed you have a blow through carb - do you have a wideband set up? I thought one was supposed to use a regular carb in the enclosure - the blow through cars are for the set ups where the carb is not enclosed.

But if it works..

What's a wideband setup? It's an S trim. The truck already had the supercharger in it when I bought it. I don't know about the blow through carb, this is my first S/C and I'm just trying to make sure everything is setup correctly so I don't break anything. If you go to the following link you can read the story behind the truck as well as view a bunch of photos:

http://67-72chevytrucks.com/vboard/s...d.php?t=358692

R/

[Alex1]

Originally Posted by Hart_Rod

From the holley website:

http://www.holley.com/12-815-1.asp

Compatible with alcohol or methanol fuels
Flows 140 GPH (free flow)
Flows 120 GPH at 9 PSI
Maximum pressure is 14 PSI
3/8” NPT inlet and outlet ports
Fuel pressure regulator is required (Recommend Holley P/N 12-704 for gasoline & P/N 12-707 for alcohol)
Provides constant fuel flow with no pulsation
Has externally accessible pressure relief valve (max 14 PSI)
Rotor/Vane pump design is more tolerant of contaminated fuels
Not designed or recommended for use with fuel injection systems

I'm still waiting for Vortech to get back with me. Their customer service suxs......




What's a wideband setup? It's an S trim. The truck already had the supercharger in it when I bought it. I don't know about the blow through carb, this is my first S/C and I'm just trying to make sure everything is setup correctly so I don't break anything. If you go to the following link you can read the story behind the truck as well as view a bunch of photos:

http://67-72chevytrucks.com/vboard/s...d.php?t=358692

R/

A wideband 02 sensor, tells you if your lean or rich - it's a good tool for tuning, although you should always read your plugs. But it can help you out certainly if you're tuning it yourself - because you don't want to be lean under boost.

Definately worth it.

[1FAST68]

Alex1 is correct about the wideband and reading your plugs. Wideband setups are expensive tho, if you were here in east tx you could borrow mine.

I don't think your fuel pump is going to cut it. Unless you only have 2-3 psi of boost.

[Hart_Rod]

Originally Posted by Alex1

A wideband 02 sensor, tells you if your lean or rich - it's a good tool for tuning, although you should always read your plugs. But it can help you out certainly if you're tuning it yourself - because you don't want to be lean under boost.

Definately worth it.

Does this just install in the exhaust like a factory 02 sensor?

Originally Posted by 1FAST68

Alex1 is correct about the wideband and reading your plugs. Wideband setups are expensive tho, if you were here in east tx you could borrow mine.

I don't think your fuel pump is going to cut it. Unless you only have 2-3 psi of boost.

Thanks for the offer on the WB, . So you think the fuel pump just won't be able to apply enough pressure? What pump do you recommend? This is just a daily driver with an occassional weekend trip to the drag strip.

I finally got in touch with Vortech, :-/. They said I should have everything connected to a vaccuum source as you 2 suggested, . I've got everything connected to the same port that the tranny modulator is connected to right now, but I will rework everything the next time I pull the carb enclosure off. I think I found some manifold ports, but I can't get to them right now. They also said I needed the bypass valve if I was getting more tha n 5-6 pounds of boost. When I asked how much boost this setup should be putting out, they couldn't tell me and said they were all different, . So, what's the best way to figure this out without breaking anything? They also recommended getting a pressure or boost adjusted FPR. I'm assuming the signal for this will come from the same port as the boost gauge? I didn't realize all this supercharger stuff was so complicated, , .