Carb box?

[Anonymous]

I was talking with a friend if mine about turbocharging our 300L6. We were basically discussing the problems with fuel requirements under boost with a carb.

Long story short, he was telling me that a sealed carb box would be the way to go instead of the top hat/bonnet style. Reason being that the sealed box would equally pressurize both the inside and outside of the carb, resulting in the carb not "knowing" it was under boost. This would eliminate the problems associated with the PV and lean conditions under boost.

Now he is a pretty smart guy and I'm still learning all I can about blowthru set ups. what I would like to know is if he is or correct or partially correct or what? I understand his point of the carb having equal pressure both inside and out, but is it that beneficial?

What are your comments/opinions about this? I'm here to learn!!

 

[XFlow_Fairlane]

it is the same exact thing.

people run a box so they can not have throttle shaft leakage and still run a choke....thats about it. you still need a solid float and the fuel pump mods to make it work.

 

[Anonymous]

1 ) We were basically discussing the problems with fuel requirements under boost with a carb.

2 ) Reason being that the sealed box would equally pressurize both the inside and outside of the carb, resulting in the carb not "knowing" it was under boost.

3 ) This would eliminate the problems associated with the PV and lean conditions under boost.

4 ) I'm here to learn!!

1 ) I have founfd the needle and seat to be a big restricyion. What carb are you looking at? The Holleys have available a .130" needle and seat!!! On my Holley model 1946 (1 - bbl, stock '82 Mustang) I have to add another fuel circuit since the single stock needle and seat just couldn't keep up.

2 ) The only places this is true are where the gaskets are, and any port that is "external".

For instance, in my turbo 200 thread you will see things like the "bowl vent" that normally goes to a charcoal cannister is plugged off. Other ports were threaded and screws installed.

3) Absolutely, positively NOT TRUE.

There is more than meets the eye. The power valve gets its signal from the manifold anyway, and a box won't help.

4 ) Welcome!


The only thing the box helps eliminate is throttle shaft seals (has not been a real problem for me) and gaskets from blowing out (not a problem either.

Having "been there and done that" I can think of NO good reason to box any carb.


This might help, too:

http://www.turbomustangs.com/forums/for ... forumid=13

http://www.turbomustangs.com/forums/for ... forumid=15

http://www.turbomustangs.com/turbofaq.php

Good luck!

 

[XFlow_Fairlane]

the only reason to do it I think is to keep a choke.


I am looking at getting a man choke kit for my carb and just using it to have a high idle control to help with warm up in the winter.

 

[Anonymous]

Thanks everyone for your replies.

Linc's 200: Thanx for the TM links. I actually started looking around there about 2 wks. ago. What a wealth of info!!!

I didn't think that the carb enclosure would make it much easier than a carb hat. The one thing I do like about the enclosures is that you can run a VS carb. Which I think is a plus because the vehicle I would like to JYT is also my DD (I really don't like MS or DP).

However, the difference in price between the enclosures and top hats is sickening to say the least.

I have been doing a lot of reading up lately (here & TM), and still I do not fully understand what is needed to prevent leanout conditions. The spark can be controled to retard under boost, however, you can't exactly tune your a/f ratio on the fly.

So, how do you go about setting up a carb that supplies adequate fuel under boost with out having rich conditions at cruise? (This is where me and friend differed about the advantages of a carb box)

 

[rust collector]

I don´t get this

Why would the box let you use a choke?
If I understand these things about right, the choke is removed because it disturbs the air, and makes it hard for the carb to meter fuel like it is supposed to?

Turbulence, I guess

Please, say I am wrong(if I am??) but let us know why...

 

[XFlow_Fairlane]

you remove teh choke on a bonnet carb because the linnkage for the flapper will blow TONS of air out of the hole. also there is a vac port on the side of the choke (I think this is just for pulling in hot air on an autochoke?) that needs plugged. if you run a box all of this is enclosed so that the choke will function and not leak boost all over the palce.

 

[rust collector]

Thanks! 8)

 

[Anonymous]

So, how do you go about setting up a carb that supplies adequate fuel under boost with out having rich conditions at cruise? (This is where me and friend differed about the advantages of a carb box)

Has nothing to do with a box.


You jet for cruise and drill Power valve restrictions for boost.

I went one more - and added some extra fuel by alcohol injection. Doesn't come on until over 10 psi.

The problem with BIG boost (over 10 psi) is you have to start adding more fuel by other means.

 

[Does10s]

The problem with BIG boost (over 10 psi) is you have to start adding more fuel by other means.

???

We've been running 15lbs. of boost for over a year now. Yes I've jetted up a bit to accomidate the increase in power but we don't have any extra means of adding fuel.
We are still running fat, but that just means we're still running safe. It also means that we still have more power to make when we want just by lowering the jet number.
I basically have the car tuned to run at sea level. But we are never even close to that. We always race at least around 4000ft. D/A.
Oops! I think I hijacked the thread. Sorry!
Will

 

[Anonymous]

1) I've jetted up a bit to accomidate the increase in power ...

2 ) We are still running fat,

1 ) That is where the fuel comes from.
2) There is the problem...

It is difficlut to make a car run good power under boost and good gas mileage at the same time. I think you said in another post you were getting around 10 mpg. That's pretty bad, even for a 250.

If you were trying to make the car run efficiently at cruise (good mileage) you would run out of fuel on big boost unless you employed some mods. For now, you are just happy to be running over-jetted at cruise to have enough fuel under boost.

 

[XFlow_Fairlane]

Doesn't will also have a 4.10 gear or something crazy like that and a loose converter?

 

[Anonymous]

Doesn't will also have a 4.10 gear or something crazy like that and a loose converter?

Used to - has 3.55's now, I think.
Converter is a 3000 RPM if I'm not mistaken.


I can make a 302 get better than 10 MPG even with 4.10's and a 3000 converter, though!

 

[Does10s]

Almost correct.
3.50 in the rear.
3500 stall in the converter.

And we're getting in the neighborhood of 15mpg or so.
We used to have 3.89s in there. Before that was 4.56s!
The thing was screaming down the interstate! It cruises real nice now.
A tighter converter would help with the the ET/MPH and the MPG!

And Linc's you're right. We've made a compromise on the fuel economy to have a safe and effective tune up.

Later,
Will

 

[hasa68mustang]

so you mean to tell me you are running low 12 and getting better gas mileage than me???? oh well maybe mine will go up with a turbo...

 

[Anonymous]

so you mean to tell me you are running low 12 and getting better gas mileage than me????

speed, power and mileage.....

It's because he has a Holley 350 and you have that darned 500....

 

[Anonymous]

Nice thing about a carb box is you never have to worry about blowing the top gasket out of your carb and spraying fuel from the floatbowl everywhere....
Not that anything like that's ever happened to me personally of course *s*