Forced Induction with Autolite 1100?

[Crustang to Mustang]

I have been reading about forced induction projects that utilize the 1bbl carb and was wondering what the cons (and possibly pros if there are any) are to this vs a 2bbl as well as how you set up the 1bbl carb for blow through.

 

[powerband]

I'm an advocate for any coherent modification but here's my $ .02 :
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THREE important carbureted' 'blow-through' forced induction considerations are :
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1) the NA fuel supply to typical carb bowl is usually @ 5-7 psi (Weber a little lower) BUT with boost, fuel pressure needs to be raised equivalent to normal pressure PLUS boost. At 0psi boost (run and cruise), fuel supply is @ 7 lbs to carb from pump, at @ 7psi boost the fuel pressure needs to be @ 14 psi to keep it flowing into not out of carb ...
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2) Conventional Power Valve operation on carbs adds fuel with drop in intake vacuum under acceleration or WOT. Boost thru carb obviously needs OPPOSITE Power Valve operation - opening max with intake pressure not vacuum. Some way to operate carbs' PV with boost pressure is needed.
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the universal Holley 4Bbl Carb ( '4150' ) has a lot of info available on Forced Induction mods ( googl e "hangar 18 mods') and readily available parts, jets and aftermarket unique operating Power Valve made for boost application.
The Holley 2300 2Bbl carbs are universal as well and are 1/2 a Holley 4Bbl so all the mods work on it as well.
1100 1Bbl can of course be modified but starting with a 350 CFM Holley #7448 (2300 series) 2Bbl is likely a shorter route.
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Blowthrough Carb How-To

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3) Draw-Through Carburetors setups don't need carb fuel bowl pressure compensation but where Blow-Thru boost makes carb CFM act LARGER than at NA, Draw Thru needs huge NA to boost CFM capability . Early BOP Draw-Thru setup used a unique ThermoQuadrajet 4Bbl with EXTERNAL PV control from intake manifold pressure switch - vac/pressure xover and Draw-Thru necessity huge non-boost to boost CFM rating of 280 to 900 CFM !.
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Nevermind turbo INTERCOOLERS - BOP draw-thru on 250 Bernoulli Effect' from intake needed coolant circulation HEATING to prevent plenum icing ! ...
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the Vortech supercharger on the current 250 uses modified Holley 7448 350CFM thru a simple 1 X 2 adapter .
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Hav efun
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[aussie7mains]

To add my comments, IMO draw through is easier, the carby does not know any different to NA application. As to the sizing of the carby/mixer in my case (LPG) although it is rated at 400cfm, which would seem too small for any great power, what happens is that the supercharger can create a much higher DP across the carby than the test pressure use to arrive at the CFM rating. I have a dual needle manifold pressure gauge on my car so I can see the DP across the supercharger and the carby. From my observations when driving, the moment the manifold pressure rises to jsut above atmospheric, even on small throttle openings, the suction on the carby increases noticabaly. IMO I would NOT use any centrifugal type of compressor for a street application, with one exception, a turbo that is FULLY integrated like the GM setup on the Equinox, and this ai almost impossible for any of us backyarders to achieve. Positive displacement superchargers deliver the best drive ability, torque is available at any time by just opening the throttle, you have virtually a much larger NA engine available. Draw through has one advantage over a blow through, that of latent heat from the vaporisation of the petrol, as stated above. I dont have this effect because I run LPG where the fuel is vaporised externally to the engine, however the knock resistance of the fuel means I have no problems with detonation even with 10-12 psi and 9:1 CR. Ill chuck up a picture for those that have not seen my setup before.

 

[Crustang to Mustang]

Well, I didn't want a draw through turbo setup because I don't really care for how they look (I understand if some people think that this is a stupid reason, they are a lot harder to organize under the hood, but also my brother-in-law has an intercooler that I can have so I was planning on using that. I haven't fully decided whether I will T/C or S/C it but those were just some thoughts.

 

[pmuller9]

As you know the carburetor needs to increase the fuel flow under boost.
The Holley carburetors that have a power valve can easily be modified by drilling the passages that sit behind the power valve to a larger diameter.
The PV passages can also be drilled and tapped for screw in restrictors that are used in the Quick Fuel carburetors.

The Autolite 1100 has a built-in power valve that consist of a spring loaded piston with a rod that extends down to a valve that uncovers the PV passage to enter more fuel just behind the main jet.
I'm not sure how you would go about increasing the PV fuel passage with that setup or how you would even get access to make modifications.

How much boost are you planning on running?

 

[awasson]

Excellent! Glad to find another recent discussion regarding boosting a small 6 because I think I will follow this path.

@pmuller9 regarding boost, what do you think is a safe bet for holding together under boost? I was following a guy on YouTube who turbocharged a mild 6 build in a 66 Mustang. He did a really nice turbo fixture by modding an EBay header to point forwards towards the battery location (he had relocated the battery to the trunk). I think it had stock pistons and not a lot of compression, a performance cam and a 2v carb on a modded big log. Unfortunately, he ended up blowing up his 200 with too much boost just north of 15 lbs.

 

[aussie7mains]

Its not just how much boost, its how often you use it. 12psi is usually plenty for a stock type of thing, and will wake up most engines. I can produce a lot more than that, but I find watching my gauges, that Im often well below that. I run all stock parts, Ive heard our pistons are better than US, this might be wishfull thinking. I have an advantage in that the crossflow head breathes much better than any or the log heads, boost cant make up for that.

 

[pmuller9]

@pmuller9 regarding boost, what do you think is a safe bet for holding together under boost? I was following a guy on YouTube who turbocharged a mild 6 build in a 66 Mustang. He did a really nice turbo fixture by modding an EBay header to point forwards towards the battery location (he had relocated the battery to the trunk). I think it had stock pistons and not a lot of compression, a performance cam and a 2v carb on a modded big log. Unfortunately, he ended up blowing up his 200 with too much boost just north of 15 lbs.

A stock 200 six can handle 15 lbs of boost providing the air/fuel ratio is correct and the ignition timing is correct for the boost level.

Starting with a blow through carburetor.
As you know from elevation changes, a carburetor does not compensate well for changes in air density.
You can get the air/fuel ratio correct for a given boost (air density) by increasing the fuel flow through the power valve passages.
As you increase the boost (air density) beyond that level you will see the air/fuel ratio get leaner, so the object is to jet the carburetor for the maximum boost and not go beyond that point.
Of course, the air/fuel ratio will be rich for lower boost levels.
As always, when working with carburetor tuning, an air/fuel ratio meter is a must.

Secondly is the ignition timing.
It is best to start with a conservative approach of retarding the timing one degree for each lb of boost.
Units like the new MSD Ultra 6AL Plus makes that an easy job.

The other consideration is fuel octane.

With everything in order, you will be surprised how much a stock engine can handle.

 

[awasson]

A stock 200 six can handle 15 lbs of boost providing the air/fuel ratio is correct and the ignition timing is correct for the boost level.

Starting with a blow through carburetor.
As you know from elevation changes, a carburetor does not compensate well for changes in air density.
You can get the air/fuel ratio correct for a given boost (air density) by increasing the fuel flow through the power valve passages.
As you increase the boost (air density) beyond that level you will see the air/fuel ratio get leaner, so the object is to jet the carburetor for the maximum boost and not go beyond that point.
Of course, the air/fuel ratio will be rich for lower boost levels.
As always, when working with carburetor tuning, an air/fuel ratio meter is a must.

Secondly is the ignition timing.
It is best to start with a conservative approach of retarding the timing one degree for each lb of boost.
Units like the new MSD Ultra 6AL Plus makes that an easy job.

The other consideration is fuel octane.

I was thinking about that after I posted about the guy with mustang blowing up his engine at a little past 15 lbs and it occurred to me that as you mentioned, a carburetor is not good at compensating for changes in air density and he likely went extremely lean and melted a piston or maybe he expanded a top ring and broke a land.

My top rings are gapped at .016" - .017" which is right in the pocket for a NA engine but for a boosted engine, I really ought to have a bigger gap. Using the calculation of .007" x bore, I get .026" for my engine which is 60 over. It probably wouldn't hurt to use ARP crank studs/bolts and ARP rod studs. I'm using ARP head studs on mine already.

 

[awasson]

@Crustang to Mustang I think based on what @pmuller9 was mentioning about carburetors not being able to navigate differences in air density, rather than an autolite 1100, you ought to look at a Holley single barrel sniper.

 

[pmuller9]

@Crustang to Mustang I think based on what @pmuller9 was mentioning about carburetors not being able to navigate differences in air density, rather than an autolite 1100, you ought to look at a Holley single barrel sniper.

The Holley 1100 Sniper is only good for about 150 hp with boost.

 

[awasson]

The Holley 1100 Sniper is only good for about 150 hp with boost.

Good to know. He ought to move up to the larger 2v version.