[Tom Vaught]

Well, STEELCITYFIREBIRD, I need to mind my time better. I put in an hour typing my first post on the new subject and then got involved in more HOME type stuff and the PY Board timed me out. I lost all of the info in the post.

Twice now this has happened. Need to figure out a different process but if you do the post a couple of times it looks better each time you do it. Just more wasted time lost.

That being said, I AM writing a book.
The book is about what I learned from the different bosses I worked for in 40 years.
Many are VPs in Ford today. Most were lower level "WORKING MANAGERS" when I worked for them.
They all 'Did Good' over the years "moving up the ladder".

The book is NOT a "Tell All or Bash all" type deal.

I am about finished with the 1st 75 bosses and you can have multiple bosses on any project.
Engine Guys, Chassis Guys, Fuel System Guys, etc.
They all get a "Salute" (just like the military) even though you do not work DIRECTLY for them.
I worked for RESEARCH and interfaced/ directed the other organizations on how to limit the mistakes and have a good product at the end of the day.

But back on the Boosted Engine info later.

Tom V. (FORMER) Senior Engineer for all ECOBOOST PROJECTS in the world.

[Tom Vaught]

Well Today, I am NOT going to type for an hour to have the Website lock me out and destroy my hour's worth of effort. Going to do shorter posts but more of them. Will try to break the Boosted Carb info into the same carb circuit "chapters" that I did for the Naturally Aspirated Holley Carbs.

So initially we are going to talk about a "Old School" 1960s "Draw-Thru Turbo Carb and its modifications.

1) Rebuild the carb with new gaskets, .120" needles and seats, and 6.5" Power Valve on the front metering block and a 8.5" Power Valve on the rear metering block. (JUST LIKE STOCK).

Remove the Carb Throttle Base Plate and remove the "Anti-Backfire" spring and ball. Thread the hole (from the top side of the base plate just enough to install a short set screw in the former passage. When the carb main body is installed on the throttle base plate the set screw is trapped and can't fall into the engine. So now you have made your first "Draw Thru Carb" Mod.

Because you plugged the carb "Anti-Backfire" spring and ball drilled passage you also removed the Power Valve Signal from the intake manifold to the Power Valve Cavity in the main body. So now the Power Valve has no signal to tell it to stay closed and the spring on the Power Valve will keep it open all the time. This will not affect idle at all but will cause the rest of the circuits: Transition, Main Circuit to run rich.

So A bit later I will have some pictures and info on how to correct that deal.

Tom V.

[Tom Vaught]

I decided to start from the beginning and discuss a simple "Draw Thru Boost System" first.
The most simple one is the Roots Blower with the Holley carb on top of the Blower and the Blower attached to the Intake Manifold.

But, this is the street section and we are talking about Boosted Engines so we will do simple first.

A street car is different from a Race Vehicle in that the Race Vehicle does not care a bit about Fuel Economy and Air/Fuel Ratios higher than 12.7 to 1. But a Street Guy would like to have the Big Blower with the carb(s) on top and still be able to pass the gas station occasionally without stopping.

The way to do that is to have the carb(s) Air/Fuel Ratio a bit leaner under light load just cruising down the road. More like 13.5 to 1 Air/Fuel Ratio.

You are not going to get those Air/Fuel Ratios with Power Valve Plugs in the Carb(s) and Big Jetting in the Carb(s).

So you need to dial in the engine to run under light load (with smaller Jetting and with a Power Valve) that enriches the Air/Fuel Ratio when higher loads and more fuel demand is required.

The way that a Street carb (without a blower works) is there is a passage in the base of the carb that is connected to the Power Valve Vacuum Cavity that releases the vacuum applied to the Power Valve Diaphragm and lets the Power Valve open.
It gets that Vacuum Signal from the intake Manifold. No need to explain the different Power Valve Numbers or the point where the spring over-powers the vacuum and opens the valve. We already know that deal with Holley carbs.

Problem is Now we have a Supercharger stuck right in the middle between the carb and the intake manifold. So the vacuum signal to the carb is not the correct one.

So the fix for that is to change where we get the signal from. Not in the normal location but BELOW the SUPERCHARGER (back at the intake manifold point again). Will post "the fix" in the next post.

Tom Vaught

[Tom Vaught]

The Holley "Draw Thru Carb" Modifications will primarily be made in three places: The Metering Block side of the Main Body of the carb, the Metering Block of the carb, and the Throttle Body side of the carb.

The Metering Block side of the Main Body of the Carb

Attached is Picture #1 of the carburetor

The Picture was taken from a Web Image

STEP #1

"A" is the Holley Carb POWER VALVE CAVITY. "B" is the signal passage normally used for Ported Spark on the Throttle Blade Base of the carb. "C" will be a machined channel that you will add between the Spark Port Hole and the Power Valve Cavity.
After we machine the channel "C" (from "B" to the Power Valve Cavity) we will plug the"B" hole with a recessed plug so that the Spark Port is no longer able to function.
Whether you choose to Mill or Cut the slot, the end result is that the Power Valve Cavity is now connected to the bottom of a backwards "L" in the metering block "D" (picture 2) then to what was the Ported Spark vacuum port.
We will also install a Plug in location "H" so that the Power Valve no longer gets its signal from the carb base mounted on the inlet to the supercharger.

The 2nd Picture Shows the Primary Metering Block
STEP #2
"D" is the Holley Carb Ported Spark Passage (many times that passage is not drill at point "E") but occasionally you will have a Holley Carb that has a functioning Ported Spark System (and Passage).
So the idea is that we will use the Ported Spark Passage along with the machined groove over to the Power Valve Cavity to now have a new Power Valve EXTERNAL SIGNAL to the Power Valve

The 3rd Picture Shows the Same Primary Metering Block with the drill in the passage (that needs to be drilled to inter-connect with "Opening F"
The new port that will be used "F" (picture 3) many times has a small tube (3/16”) pressed into it as a Ported Spark Vacuum Advance source for the distributor. Some Metering Blocks are already tapped for a 1/8" NPT thread that uses a nipple as the hose connector. In some cases you might have to finish drilling the passage and connect slot “D” to Port “F”. Use a #39 .099" drill for hole "E" (picture 2) with the drill in it. If there is no tube in port “F” then a 1/8 NPT tapped hole will need to be machined to allow a nipple to be installed to connect the vacuum hose to.

Primary Metering Block Passage "F" will now supply the signal to the Power Valve. It will be connected with a “T” hose fitting to the same hose as the Blower Boost Gauge (from the intake manifold uses. uses.

The Last Picture Shows the bottom of the Carb Main Body. It shows the Spark Port Passage "G" plugged with a socket head plug. It also shows the Power Valve Signal Passage "H" also plugged with a socket head plug.

So to summarize:

1) We have removed the signal to the Power Valve from underneath the carb base to a remote location source
2) We have blocked the signal to the Ported Spark Channel (from the Ported Spark pick-up hole in the throttle blade base).
3) The Power Valve Signal is no longer at the supercharger Inlet but at the Intake Manifold Inlet

The Power Valve will now close when we have higher CRUISE vacuum ond open properly when we have high pressure in the intake manifold.

The Supercharged Holley Street Carb will now be able to have better F.E. Because:
A Functioning Power Valve System vs a Plugged Power Valve Circuit and Larger Jets.
Smalled main Jetting under Cruise Mode so better Fuel Economy.So to summarize:
Better drivability as the engine will not be Pig Rich when it needs to be moderately fueled traveling down the road (not the race track).
If the Power Valve Channel Restrictions and Main Jets are properly selected the Engine will run the same times on the Drag Strip but will have much better Fuel Economy on the street.

Tom V.

[Tom Vaught]

So yesterday talked a bit about the Mods for a Draw-thru Roots Supercharger Carburetor.
Several Carb People (including Holley offer the "Supercharger Carbs" with the mods already done.

Will talk a bit later about Draw Thru Turbo Stuff.

Tom V.

[Tom Vaught]

Will Post up a couple of Pontiac Draw-thru Turbo Pics initially just to get people up to speed on what we are talking about.

In the First Picture you can see a basic carb Plenum "mini manifold" designed for a Rochester 4 BBL carb.
It has water heat capability and pressure taps for different signal pick-ups under the carb. The Part is Aluminum
and It used a small outlet opening flange that bolted onto the Turbocharger Compressor Inlet Housing.

In the Second Picture you can see a complete 301 Pontiac Turbo Engine.
The Driver's Side Exhaust Manifold feeds exhaust gas under the engine to the Passenger Side Exhaust Manifold.
Exhaust flow from both banks flows out of the passenger side manifold thru the curved pipe and into the turbine
housing of the T-3 Turbocharger.
The Exhaust Flow drives the Turbine Wheel which is connected by a common shaft to the Compressor Wheel.
At 40,000 Compressor Wheel RPM the Turbo has enough Mass Flow at 7 psi of pressure to increase the HP of
the engine a moderate amount. The 301 Engine acts like a 400 cid engine.

The Mass Air/Fuel Flow goes out of the turbo and enters the intake manifold and then into the cylinders.
It is a "Wet System" like a normal Carburetor installation except that the Turbocharger is forcing more
air/fuel mass into the engine vs a typical carb installation.

The mods to the carb are minimal as the carb is at the inlet of the system just like the carb is at the inlet
of a normal 4 BBL installation. The carb just need more airflow and fuel flow capability to supply the additional
mixture to make the power of a 400 engine using a 301 engine. Simple really, and was done by the Turbo Aftermarket
people for many years prior to EFI or Blow-Thru Carb systems. Not a Holley System but it would work exactly the same
way with a Holley Carb Installed

Tom V.

[Tom Vaught]

Next Step is a Blow Thru Configuration, again low boost, so we will talk about the Studebaker Avanti R3 engine with the belt driven compressor and the AFB "Boosted Carb in a Box".

Starting with the passenger side of the vehicle, Pic #1, first we see the Air Filter peeking out of the shiny silver deflector air cleaner housing. The Air Cleaner has a nice LARGE air inlet tube with a short length over to the Orange Colored Part (which is the Paxton "Ball Drive" Supercharger. The Ball Bearing "Balls" in the drive system created a "step-up ratio" so that the supercharger impeller rpm was much higher vs the engine rpm.
There was also a Large Crank Pulley and smaller Supercharger Drive Pulley "Step-Up Ratio in the design.

So at the end of the day, at 5,000 rpm you could make about 7 psi of boost pressure inside the Carb Enclosure.

The Blow-Thru AFB carb was installed inside that enclosure. It is the Aluminum Box shown in the second picture Pic #2.

The "Clamshell Box" was held together under Boost Pressure by 4 long Bolts that went from the Intake Manifold to the Top of
the box. See Picture #2.
You can also see the Accelerator Pedal rod attached to the lever on the enclosure. The Lever hooked up the the AFB Carb Lever
inside the enclosure. You can see the short hose coming off the discharge side of the Paxton Supercharger and where it is
attached to the enclosure inlet nipple with a hose clamp. (Pic #2)

You can see the fuel line and fuel filter but cannot see where the line enters the lower half of the enclosure to feed the AFB Carb Fuel Bowls.

The Fuel Bowls used brass floats with an expanded foam material inside them (to keep them from crushing under boost pressures or they had small brass support rods installed inside and the rods soldered to the float walls from the outside.

So now we move into another part (not visible on this enclosure). An Air Bylass Valve that was a simple plate that moved upward under higher air flow rates and sealed the box for higher than atmospheric pressures from the supercharger.

The valve was open under idle conditions to allow a smooth flow of air into the carb without having to pass thru the supercharger. So now you know the basic parts of the early Paxton Blow Thru Carb System.

Vortech Engineering, who many years later bought Paxton Superchargers, and still owns the name came out with their own
Supercharger Enclosure. See Picture #3 and Picture #4 (which shows the whole assembly of parts). Their system/Enclosure
is designed for a Holley Carburetor so we finally get to a Boosted Holley Discussion. More on that tomorrow.

Tom V.

[Tom Vaught]

Finished Shoveling Snow Early so had some exercise and back to my Favorite Subject.

Now I am going to Post some images of different Carb Bonnets (vs Carb Enclosures). You can see the progression fromthe early pieces (1957) to the modern stuff (2018). So I will post the pics and then modify my post with words. This is the first batch of Bonnets. We will number them left to right 1,2,3,4,5.

And we will start with Bonnet #3. This is a very early Paxton Bonnet (more like a coffee can with a nipple on it)
No Idle Air Vent on this one Just a hole in the top for the air cleaner stud to pass thru and hold the Bonnet to the carb.

Then we look at Bonnet #1. This one they Lowered the Inlet Nipple and put it into the side of the Bonnet vs the Top of the Bonnet. They were trying out different airflow to the airhorn concepts. More on this one in a bit.

Then we look at Bonnet #2. This Bonnet has the 4 holes in the top to allow Idle Air into the carb/engine (as mentioned before)
so that the air does not have to pass thru the Supercharger.

Now we go to Bonnet #5. This Bonnet has a much larger diameter and the inlet nipple is off to the side. It is an old Bonnet.

And Finally we go to Bonnet #4 which is a modern Paxton Supercharger Bonnet, which has excellent air distribution to the 4 boosters of the blowthru carb. The owner of C&S Carbs "ROGER" (who makes fine "Blowthru Carbs") has tested this bonnet (with his carbs) and has stated it had the best air distribution of any Bonnet out there. No Bias to any one booster.
Notice how the design of Modern Bonnet #4 resembles Bonnet #5 (from the old Paxton Supercharger days of the 50s and 60s).

Tom V.

[Tom Vaught]

One More Comparison:

Early Holley Bonnet Pic #1 with a HO Racing Turboforce Bonnet. Fits a Q-Jet not as Holley carb.

Notice the similar design. (Course the HO Bonnet had several other features in the design not so obvious.)
Craig H, Ken C, and Kern O had their act together.

[Tom Vaught]

Now that you have a handle on the difference between a Enclosure and a Bonnet I will tell you the advantages and dis-advantages of each.

Enclosure First.

The Enclosure fits over the carb, just like if you had a engine in a pressurized dyno test cell.

The carb linkage from the gas pedal goes thru the "Box" and attaches to the Holley carb linkage.

The Fuel Line from the Fuel Pressure Regulator goes thru the "Box" and hooks up to the carb fuel bowls.
A Boost Gage nipple allows a remote Boost Gage in the car.
The lid seals the carb inside the "Box" so there are no adjustments that you can make to the carb without removing the carb from the "Box" so the carb has to be dialed in pretty well naturally aspirated before you decide to run boosted.
But you do not need to make a lot of carb adjustments once you figure out the jetting needed to support the boost pressure/ mass air flow you are adding to the "Box".

Since we are talking about fuel pressure regulators you need a "Boost Referenced" Regulator. You also need a fuel pump capable of more fuel pressure and flow to support the higher HP. The "Boost Referenced" Regulator has a nipple on it that connects to the "box" so that if the pressure in the box goes up by 2 psi the fuel pressure also goes up by 2 psi.
So if you want the normal 6 psi to the Holley Carb Fuel Bowls then when you have 2 psi of boost, the fuel pressure from the fuel pump will actually be 8 psi but the fuel bowl vent/fuel bowl will be fighting that 8 psi with 2 psi of Boost Pressure so the Holley carb will actually still have 6 psi of fuel pressure setting the fuel level in the bowls. Right where you wanted it to be.
So if the boost pressure goes to 10 psi the box pressure will be 10 psi and the fuel pump will supply 16 psi of fuel pressure to the "Box".

Pretty simple, just like putting the carb in a pressurized room with the only real mods to the carb being bigger jets so the air fuel ratio is correct. No real air bleed changes, no big mods to the carb. You just want to use black floats as they will not crush under boost pressure.

Later we can talk about Holley Bonnet Systems.

Tom V.

[Tom Vaught]

When you put the Holley carb in a box you also give the incoming air an equal chance with feeding each Booster the same amount of air.

When you install a Bonnet on the Carb you now can drastically change where the airflow is going to the Boosters.

I am going to post up pictures of 4 different bonnet styles and then discuss each one a bit.

The first Picture of of a CSU Bonnet. Basically the bonnet inlet is aligned with the centerline of the crankshaft, the air enters the bonnet and smashes off the back wall of the bonnet and enters the carb boosters. The rear boosters get a bit more air vs the front ones but you can jet for that air "in-balance" under boost conditions.

Picture #2 is of a old style Extreme Bonnet with a Divider Wall horizontal in the flow path.
The idea here is to split the air flow into a upper air path and a lower air path and have the boosters all
get about the same airflow. Problem is if you can't mount it on the centerline of the crankshaft and have
to put the inlet facing the passenger fender than the split is left bank/right bank (not front or rear separation)
More difficult tuning for sure.

Picture #3 is our HO Racing Bonnet again. The air basically expands outward after the exit from the feed pipe and slows
down quickly and expands over the whole carb top. There might be a slight bias due to the inlet not being exactly on the centerline of the crank but not a big deal. The Bonnet also has a air flow vane in the roof of the bonnet to help direct air
to the Q-Jet Carb properly.

Picture #4 is a Procharger Bonnet and is low profile and the inlet faced slightly downward from the carb airhorn.
A nice piece if you have limited hood clearance and you can locate the inlet on the centerline of the crank and get
even flow to the carb boosters.

Most of these bonnets (except for the HO Racing unit can be pointed other places but the engine needs to be tuned
for that booster Air in-balance.

Equal Air Distribution is everything on a boosted bonnet set-up.

Tom V.

[Tom Vaught]

Today, going to talk a bit about Carb Tuning to match the airflow going into a specific Carb Bonnet.

The HO Racing Guys had a nice Bonnet Design for their Q-Jet Carb but the bonnet was heavy.

Heavy is not all bad, as I have seen thin wall Bonnets split apart under Higher Boost Conditions and people always get greedy when it comes to Boost Pressure.

Step 1: Whoa, 15 psi, scared myself and soiled my shorts.
Step 2: Ok, 15 psi is fun, but I think I will try 20 psi. OOPS, time to change underware again.

Step 3: Well, I am up to 38 PSI on the boost, making over 800 HP with my 4 cylinder 200 cid Pontiac Engine and maybe I ought to fix the drivability of the vehicle off boost and make it more fun to drive vs scare the crap out of myself.

Drive-ability is based on getting the air/fuel right at all of the load/rpm points and having a smooth transition between each of those points.
You can do it with a NA Holley carb and you can do it with a Boosted Holley carb, if you get the air distribution right so that the carb boosters are happy and all of the cylinders are making the same basic power per cylinder.

PROPER Air Distribution really helps in that area when using a carb system and boost.

With EFI you can tune each cylinder based on uneven air distribution and still get away with it.
Much harder with a boosted carb engine because now you have to look at the air distribution as a Systems Approach:

How does the air come into the Bonnet?
How does the air mass divide between the given Carb Boosters?
How does the Intake Manifold design distribute that air mass to the cylinders?

More on this later this afternoon.

Tom V.

[KEN CROCIE]

Hey Tom: Cudja post a pix of the nice H-O production bonnet as seen in Car Craft's Ludicrous Pontiac Power article of Dec 2009 instead of the lumpy experimental bonnet you show?

[Tom Vaught]

I posted before about the C&S Carb Guy who tested the Vortech/Paxton "Power Hat" on one of his Blow-Thru carbs he sells. The carb was a 850 CFM Unit. He said the "Power Hat" had GREAT AIR DISTRIBUTION to the boosters/carb.

I have posted before "Engineers do stuff for reasons" and in this case with the "Power Hat"
it is true. (THIS IS NOT A COMMERCIAL - THIS IS AN ENGINEERING ANALYSIS OF AIRFLOW THRU A BOOSTED HOLLEY CARB).

IF YOU GO TO PICTURE #4 IN POST 288, then you can see that the Paxton/Vortech Power Hat Bonnet has the inlet on the left side of the bonnet. The air comes in the bonnet and travels in a clock-wise direction around a "racetrack" inside the bonnet. In the center of the racetrack is a special air "Defuser" that separates the racetrack from the inlet to the carb/boosters.

So you say, if the air comes in and goes around the race track it is going to just make "laps and not go into the carb. That would be true BUT:
Look at the picture again.
If you draw a imagionary line from the Large P on the Paxton sticker straight down to the edge of the outer ring of the bonnet you would see that there is a dam in the racetrack so that the air cannot make "laps".

The air comes in the bonnet, goes around the "racetrack", is blocked by the "dam", the air packs up in the race track, and the only place for it to go is to pass EVENLY thru the Defuser and then into the carb inlet. Perfect Air Distribution.
You could have the air inlet pointed at the heater box (with a feed pipe attached) and guess what Perfect Distribution. Point the inlet at the battery, Perfect Distribution.

So where the other Bonnets need a LOT of tuning to find the sweet spot for decent air distribution, the Power Hat does it for you automatically.
This bonnet is not a Big Chief 2000 hp race deal but it is a great street deal and 1000+ HP deal.

So do not blame the carb for a crappy bonnet airflow into the carb , and there are a few offshore crappy bonnets out there.

Tom V.

[4zpeed]

Tom V: Step 1: Whoa, 15 psi, scared myself and soiled my shorts.
Step 2: Ok, 15 psi is fun, but I think I will try 20 psi. OOPS, time to change underware again.
Step 3: Well, I am up to 38 PSI on the boost, making over 800 HP with my 4 cylinder 200 cid Pontiac Engine and maybe I ought to fix the drivability of the vehicle off boost and make it more fun to drive vs scare the crap out of myself.

While I wasn't to interested in boost (never acquainted with it), I have to admit, the appeal is getting the better of me.

Graduation bought my son a 06 Stang V6 Pony Pack, was a bit skeert he might get brave.

Did some upgrades, tuner/cold air/headers/gears but still weak compared to the GT.

Recently he sais, "dad, the guys on the forums are talkin boost", I shy away (unfamiliar) and tell him "don't worry be happy".

Just luckily, I am enrolled in Tom V's Holley School of Thumb and we are now having a class on Boost!

That being said, obviously we can't have him out muscleing dad right?

So,
Step 1: Adjust Huggies and attend class.
Step 2: Aquire case of Huggies/talcum powder from E-but, er E-bay, sorry rash on my mind.
Step 3: Engage in learning burst, I mean boost damit.


As Always Much Thanks Tom, as he will be attending as well.

Frank

[Tom Vaught]

Originally Posted by KEN CROCIE

Hey Tom: Cudja post a pix of the nice H-O production bonnet as seen in Car Craft's Ludicrous Pontiac Power article of Dec 2009 instead of the lumpy experimental bonnet you show?

Tried to find a Pic of the HO Production Bonnet and a simple search on Wallace's site did not show the Turboforce stuff.
Maybe I looked in the wrong spot.

If you have a web link pic I will post it up as the Production version. I used the Pre-Production version because it compared nicely with the much older Paxton unit which also worked well. Here is a pic of Ken's "Bad Boy" engine with the HO Racing Production Bonnet on it.

Tom V.

[Tom Vaught]

Just to give you a heads-up on the boosted Holley Carb deal we will probably change 90% of the Holley Parts in some way to make it work.
So we will be taking it step by step just like the NA carb discussion.

Tom V.

[Tom Vaught]

Good Morning, We will start with a systems approach first because there are a lot of parts that interface with the Holley Carburetor.

The systems we will deal with on the boosted engine are:

The Air Inlet System (because it feeds the boosting device) which is now upstream of the carburetor

The way the Boosting device gets its energy to compress the air, either by a drive system to the boosting device or the Exhaust energy/plumbing to the boosting device.

The Turbocharger and its control devices which are the Air By-pass Valve and the Wastegate (in a Turbo Application)

The Centrifugal Supercharger and its Air By-pass system or air venting system.

And the fuel system needed to supply the correct air fuel mixture to the engine when using the Boosting device.

More on each one a bit later. Everyone of these subjects is covered very well in Corky Bell's two Books
The Books are worth every dollar you spend on each one. I have had a lot of boosting discussions with Mr Bell
over the last 15 years. He is located in Texas. Texans are good people.

https://www.barnesandnoble.com/p/sup...waAgx6EALw_wcB

https://www.barnesandnoble.com/p/max...oaAvTAEALw_wcB

Tom V.

[johnta1]

Tried to find a Pic of the HO Production Bonnet and a simple search on Wallace's site did not show the Turboforce stuff.

I used to host Craig's HO Turboforce stuff.
He got a website so he does his own hosting.

His site:

Original HO Racing

[johnta1]

Calculator to see how much to change jets:

Jetting Calc