All Small Six Are Twin Turbos Too Much?

[aussie7mains]

The Eaton M90 flows 520 cfm with 10 lbs of boost at 12,000 rpm which would be around 5,000 engine rpm.

What do you think would work for a carburetor?

The airflow calcs give actually a bit higher CFM at free air delivery, but this doesnt consider any volumetric efficiency losses, in any event, its enough. I would use a Weber dcoe45, or a 2inch SU.

 

[pmuller9]

The airflow calcs give actually a bit higher CFM at free air delivery, but this doesnt consider any volumetric efficiency losses,

The VE is just over 80% at 10 lbs of boost and 12,000 rpm on an M90.

I wouldn’t want to boost limit the supercharger by creating a high vacuum at the inlet with too small of a carburetor.

 

[aussie7mains]

The VE is just over 80% at 10 lbs of boost and 12,000 rpm on an M90.

I wouldn’t want to boost limit the supercharger by creating a high vacuum at the inlet with too small of a carburetor.

Thats true enough, but remember that the suction of the blower can create a lower pressure than the DP used to rate the common carbs. Its interesting that only the USA made carbys are rated this way. my mixer has a 60mm throttle bore plenty for my setup. Delorto SU do not give cfm ratings. As I said mine has a rating, and theory would have it that its too small, but it does not limit boost in any way I can tell. Im seeing manifold pressure above atmospheric even at tiny throttle openings, and I have a pressure point on the suction side and its rarely lower than 5 inches Hg. I have a manifold ABS pressure gauge from a ww2 bomber, it has two needles. so I can watch both, its facinating to see what is going on, it wasnt what I expected. A bit of research into LPG in the USA shows that its not that rare, and the average price seems to be about the same as here,$1 per litre or $4 per gallon. Its listed as 104-112 octane on the site I found.

 

[pmuller9]

Thats true enough, but remember that the suction of the blower can create a lower pressure than the DP used to rate the common carbs. Its interesting that only the USA made carbys are rated this way. my mixer has a 60mm throttle bore plenty for my setup. Delorto SU do not give cfm ratings. As I said mine has a rating, and theory would have it that its too small, but it does not limit boost in any way I can tell. Im seeing manifold pressure above atmospheric even at tiny throttle openings, and I have a pressure point on the suction side and its rarely lower than 5 inches Hg. I have a manifold ABS pressure gauge from a ww2 bomber, it has two needles. so I can watch both, its facinating to see what is going on, it wasnt what I expected. A bit of research into LPG in the USA shows that its not that rare, and the average price seems to be about the same as here,$1 per litre or $4 per gallon. Its listed as 104-112 octane on the site I found.

Good information!

That is one of the reasons for using a 4 barrel carb.
The majority of the time the engine is operating on just the primaries.
On a 500 cfm square bore carb, the primaries are only 250 cfm with throttle bores that add up to a 56mm throttle body equivalent.
If you use a spread bore carb, the primaries are even smaller if that would be useful.

The OP expressed the desire to Drag race where the secondaries would come into play for max boost at max rpm.
The 4 barrel carbs are rated at a 1.5 Hg depression so a 500 cfm carb would have a WOT depression of around 1.5 Hg if the M90 is pulling around 500 cfm at max rpm.

The next reason for running on small primaries is the throttle response is much more controllable rather than having a larger throttle plate opening off idle.

The other reason I was suggesting the 4 barrel carb is the 450 to 650 cfm carbs are relatively inexpensive.
You can get 450 to 650 Holley factory refurbs between $200 and $300.
Since this is a budget build this would be a point of interest.

 

[sixtseventwo4d]

. I do understand that its not widely used in USA, which is a puzzle to me, could you give me some rundowns on its availability and cost for you guys.

It was promoted here for a while, it mainly enticed companies that provided work vehicles. They were attracted by certain incentives to buy new vehicles equiped for lpg; and breaks along with lower maintenance. They also needed their own pumping stations along with trained personnel, qualified to dispense the fuel. Between the federal tax or exemptions thereof, which is usually a bite in the ass; DOT and other governing bodies ( like TRRC ) you are never done with fees, filings and permits. And they are closely scrutinized. Let's not forget the insurance that must be maintained also. I don't see a pay-out for an independent or a franchise pumping station.

 

[Crustang to Mustang]

I was hoping to use a Holley 500cfm 2bbl... Would I be able to modify the stock log for a 4bbl?

 

[pmuller9]

I was hoping to use a Holley 500cfm 2bbl... Would I be able to modify the stock log for a 4bbl?

You did not read what I wrote in post #14

The carburetor does not go on the intake manifold if you are going to use a supercharger.
It has to mount on the inlet of the supercharger as a draw through system.
The outlet of the supercharger is what connects to the intake manifold.

 

[Crustang to Mustang]

You did not read what I wrote in post #14

The carburetor does not go on the intake manifold if you are going to use a supercharger.
It has to mount on the inlet of the supercharger as a draw through system.
The outlet of the supercharger is what connects to the intake manifold.

I'm sorry. I read it but having no knowledge whatsoever about superchargers, I didn't understand. I'm trying to see past what I picture in my head because I've never even seen a supercharger in person.

 

[pmuller9]

I'm sorry. I read it but having no knowledge whatsoever about superchargers, I didn't understand. I'm trying to see past what I picture in my head because I've never even seen a supercharger in person.

That’s ok.
Ask whatever questions you need to ask to help yourself make the best decision.

 

[Crustang to Mustang]

How would I go about mounting the blower to the block?

 

[pmuller9]

How would I go about mounting the blower to the block?

It's done on the driver's side with a bracket that bolts to the driver's side of the block.
If the blower has carburetors, the bottom of the blower outlet cannot be lower than the top of the intake manifold so the fuel can't puddle.
Everyone else doing a block mounted blower uses fuel injection at the intake manifold so the blower can sit very low on the block.

Here is Clintonvillian's block mounted blower on a 300 six with fuel injection.

https://fordsix.com/threads/m112-300-build-for-the-56.81597/post-640953

 

[Crustang to Mustang]

The only problem that I see is that with a 250ci (with a 1bbl carb and a stock air cleaner) in a '66 Mustang there is about 3/4 in. of clearance between the air cleaner and the hood...