Inliners International Forums General Discussion Hi Performance 2bbl Turbo Carb Mods

I was looking into the possibilty of modifying a Holley 350cfm 2bbl for blowthrough. Ive read a few site and here si what I can come up with as far as carb mods.

- Block off the choke hole
- Epoxy the main well and idle well plugs
- Nitrophyl floats
- PVCR Enlarnging if needed (which I dont see a need for on a near stock 6)

Am I missing anything else? Seems pretty straightforward. Not looking to make major power just add a bit and be diffrent.

how much boost on what size motor? that will also help dictate which carb to use. i question tha the 350cfm is not enough. revved at full boost mine is using closer to 700cfm, but that is only a educated quess. you may want to go to a 500cfm 2bbl. turbo's really wake them up. tom

Yeah its a 250 and were looking at 6lbs max boost. So maybe a 500 2bbl would work much better

Ive located a Supra ct-26 Turbo that just needs seals. If the price is right I may pick it up.

Air density increases in a linier fashion to pressure increases (Bournulli's Law). To save you the time to study Bournulli, if you double the pressure, you double the flow. If a carb has enough airflow for a N/A configuration, it'll allow enough airflow in a pressurized application. This is not as true for a draw-through as it is for a pressurized carb because you can't change the pressure of the atmosphere.

As a side, I managed to obtain 15+lbs manifold boost in a drawthrough with a single barrel carb on a 250.

Yeah then 500cfm should be close to enough really. What type of turbo did you use for drawthrough? Anything special?

What I tried to tell you is a "500" isn't needed, a 350 is plenty of carb as it will flow over 700CFM @ 1 atmosphere of boost.

The carb I used was an SU, with 2" throttle plate. It makes for a very simple system using the early Buick turbo. The only difficult part was the learning curve on the fuel curve, having to make my own metering rods. I built it nearly 20 years ago and my stepson has it still.

Ok I see what your saying now. Thanks alot for the info.

[QUOTE]Originally posted by Greybeard:
"Air density increases in a linier fashion to pressure increases (Bournulli's Law). To save you the time to study Bournulli, if you double the pressure, you double the flow."

The density to pressure relationship is correct. However I believe it is more directly derived from the Ideal Gas Law and the related Boyle's Law. Bernoulli's Law is usually applied to pressure and velocity relationships, and the resultant pressure drops. Density is used in Bernoulli's equation. Pardon my clarification, not trying to be a wise guy.

I believe you'll find the Ideal Gas law and Boyle's laws to be expansions of thought related to Bournulli's observations.

In any event, Bournulli directly discribed the effect of increasing pressure creating a linier increase of volume through a fixed size opening.

Quote "Ive located a Supra ct-26 Turbo that just needs seals. If the price is right I may pick it up"
What size is the Supra engine?
I would think that turbo would be too small for 4.1 engine.?

It came off a 3.0L Inline 6 in the Supra. This was also reccomended by the guys at Turbonetics as a Good Match For a stock 250ci Inline 6.

I actually found a good usable ct-26 singel scroll for $75. I may jump on it.

[QUOTE]Originally posted by Greybeard:
"In any event, Bournulli directly discribed the effect of increasing pressure creating a linier increase of volume through a fixed size opening."

Bernoulli's Equation:

Pressure + 1/2(Density)(Velocity Squared) + Pressure Head = constant

For a fixed orifice, the pressure drop across an orifice is proportional to the square root of the velocity. Four times the upstream pressure yields twice the flow through the orifice, provided the downstream pressure remains the same. This does not take into account the change in density for a gas such as air as the pressure changes.

winter, your answer does not directly help with the question stated. is the carb big enough? believe me i like science and engineering, but let's be reasonable. tom

Well I found a recently rebuilt 500cfm that should work came off a running car was just to big for what it was on. And ill remove the adjustable jet block from my 750dp and stick it on there for easy tuning.

RevOD & Tom,

In lieu of someone answering your questions who as installed a blower in a blow-through carburetor application, I will attempt to respond as I have the book "Street Supercharging" by Pat Ganahl. The book contains two pages concerning blow-through applications. The following is from the two pages.

A carburetor correctly sized for the same normally aspirated engine will work. Enlarge jets 20% to start.

Paxton Superchargers recommends a 500 cfm carb for engines up to 305 cid.

Leaning out at full boost is discussed, noting that the secondaries on a four barrel carburetor can be jetted richer to compensate.

Fuel system supply pressure must exceed the pressurized carburetor bowl pressure by 3 psi at full boost.

Make sure the throttle shaft bores don't leak. O-ring or drill sealing air channels in the carburetor body if necessary. Or place the whole carburetor in a sealed pressurized box.

You've probably already done so, Googling under "Supercharger carburetor" gives good results. Holley has a line of carburetors specifically for supercharging use (not sure if they include blow-through applications).

come on winter. your just trying to stir the pot and are not helping anything with replies like this. we have a bulletin board full of helpful people. i can understand wanting to prove your point, but i feel this is beyond. tom

As you all will NOTE I removed a few of these Posts. I feel where getting a touch off topic. and Before things lead to bashing OR what not.Lets justtry to keep things simple and on track.I would hate to have to close this topic.
So let not get to Overly technical here Ok ??

Thank You.

So back to what mods need to be done. See the post at the top. I have a 500cfm Holley for it. Is it necessary to mill the choke horn off?

RevOD,,,

It is not necessary to mill off the choke horn.

I do think if you can put on a stubstack for it ,it will flow better, than just milling off the choke horn.

You are looking for better airflow?

MBHD

No I just didnt want to mill the horn off if necessary so if I ever wanted to go back to NA with a choke it would be there.

RevOD,,
in that case,, then just leave the choke horn alone.

MBHD