Fuel enrichment with a blow through setup

YEAH!

thats why i'm thinking the smaller carbs have a better chance, because the 'vacuum signal' which is really a pressure differential between the hat and the manifold, will be greater and they will operate more like stock. the YF is especially good because the 'metering rod' which is really a needle jet, is directly tied to the throttle position... and needle jets are super easy to tune, just chuck them in a drill and spin them against sandpaper to gradually reduce diameter and richen them in the ranges you want.

i'm thinking that a stiffer spring on the power valve and drilling out the 'jet' passage will give you some tuneability to that, at least in the 2100 autolite. I don't know jack about holley but i'm thinking it might be time to learn, as the info for holly tuning under boost seems to be more readily available. I have a 2300 on my boat and its a nice little carb when the damn electronic choke decides it wants to turn off.

coming from the motorcycle world, there is a lot more tuneability to most carbs than just swapping out the 'tuning' parts, holes can be enlarged, slides can be cutaway, needles can get turned down... might be as simple as some kind of externally adjustable air bleed leaning it out under boost.

obviously i still have a lot to learn about carb tuning, but i'm getting closer to figuring out how much i don't knwo.

MechRick":1kqlhdb2 said:

It's tough to get a turbo blow-through to work on the street. I've tried.

After 3 different carbs and a multitude of jet changes I figured out that the problem is in the way the enrichment circuit works. Power valves and metering rods work on the pressure difference between the intake manifold and the air pressure above the carb. The problem is at part throttle you can have significant boost with enough pressure differential to force metering rods or power valves into the lean position when the engine needs enrichment. Smaller turbos make this even worse.

One thing I would have liked to try is to reference the power valves/metering rods with underhood air instead of the carb hat. It would have required some clever plumbing to do it though.

I ended up running the carbs fat to compensate, not good for economy. All my street turbos were EFI after that. Solves all the problems.

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Some guys have all kinds of problems with blow through carbs on street cars, no doubt and there is a ton of advice on the turboforums from guys that have been there and done that and have made their stuff work on the street and very well at that. I for one have no problem with the part throttle boost thing at all and in fact my setup makes no boost at all unless it is under load and at full or very near full throttle. I did however have a few problems to work through with the fuel system and the car now drives great at the current boost setting and gives great performance and economy. EFI is great if you can afford it and make it work, but it is far more complex to the average old school grease monkey like me. I am a bit gun shy of that stuff and decided to work the bugs out this way instead. 8)

Really guys there is no need for anyone to be discouraged by the supposed complexities of blowing through carburetors. They are very simple devices really and almost every problem can be addressed and made to work. Jets will have to be changed, things will have to be modified and fabbed up, there will be some trial and error to make it work, but some of us find satisfaction in that kind of thing. Absolutely no disrespect to the EFI guys of course.

I was very inspired by Linc's project guidelines of working with what he had and I was basically trying to take over where he left off. He was not far away from making his setup work very well when he disappeared.

First Fox":igwl2ebd said:

Jets will have to be changed, things will have to be modified and fabbed up, there will be some trial and error to make it work, but some of us find satisfaction in that kind of thing. Absolutely no disrespect to the EFI guys of course.

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None taken.

I just chimed in because I've been there. For a drag car, or a hot street car that only sees weekend duty, blow-through carbs are fine. For those seeking the cool dual nature of small-displacement turbos (power and economy), you may run into trouble. I was disappointed with 20 mpg. When I went EFI, that jumped to 28 mpg.

My one regret was not referencing the power valve on my Weber to atmosphere....

Funny you mentioned the mileage as I just did another test on my weekly commute thus week. The last tests I did before the turbocharger my mileage was 31.5 mpg. I was so so stoked but was almost certain I would lose a bit with the turbocharger due to the restriction in the exhaust. I was wrong. Our Detroit area winter grade 87 octane gasoline just netted me 32.6 mpg. No male cow feces either guys, just reporting what I get for mileage.

Again, this is highway mpg and a 400 mile commute without using any boost. My cruise AF is about 14.2 and I will lean it out a bit and retest as I would mind cruising at 15 or so.

Btw, would love to hear about your atmospheric power valve idea rick. Not sure what you have in mind or how it would but I do appreciate new ideas and discussions.

http://www.ihpartsamerica.com/forums/ca ... build.html

That shows the underside of the power valve, and the bleed holes in the non-vacuum side of the power valve diaphragm. The power valve needs to be referenced to the same pressure as the exhaust valves in the engine (rich/lean is determined by atmospheric pressure). Almost all of them reference float bowl pressure, which in a blow-through setup is higher than atmosphere.

My idea is to plug those bleed holes in the underside of the power valve and tap a new hole for a tube that runs through the carb housing, to reference atmosphere instead of boost.

First Fox":8rbqe33n said:

Our Detroit area winter grade 87 octane gasoline just netted me 32.6 mpg.

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I believe you. My best non-turbo Mustang got 25 mpg. The turboed car consistently got 27-28 mpg @ 70 mph. I think it's because the turbo recovers some of the lost efficiency of the combustion process. At cruise, my turbo setup made a few psi over atmosphere. The exhaust gasses are still expanding when they leave the engine, that normally wasted energy can be recovered. Supposedly that is how Smokey Yunick's hot vapor engine worked...

Just a quick word, I know my name is all over the forum lmao, so I hope ya'll don't mind Butttt... when it comes to power valves...

remember to REMOVE the check ball if your carb is equipped. YEah they prevent backfires from damaging the power valve, by momentarily causing a really lean condition (sealing off the power valve) in a boosted engine this could be a real problem. versus a blown power valve which in my neck of the woods is 11 dollars. and will cause your engine to run rich... rich > lean!

and until you get into slightly higher boost levels i dont think you really don't need to boost or atmospheric reference a power valve.. in fact I had never heard of atmospherically referenced lol. I know of a guy running 30 psi on a litle four banger with a stock power valve and with just drilled PVCRs. Just grab a LOW numbered power valve, hog out them PVCRs a bit, and start tuning. Since they basically work off of a pressure differential anyway, which should be maintained.

If you wanna get real intense look into the CRUTCH system, which uses a 12v air pump to open the power valve on command.

and little tip if you can find them, grab a few little brass hex plugs, as small as you can. and drill + tap those in. Then you can build your own power valve "jets". If that seems sketchy, wait until you overdrill the metering block, because if you don't good on you! but if you do, all hope is not lost I have a few kicking for if i mess up, Im not positive if theres anythign behind them that it will mess up, but I was led to believe there wasnt as long as you make there the caps are shallow enough so you dont drill into the main wells opposite wall.

Just hoping to help! -Brandon

Just another update guys for the benefit of anyone that may want to utilize one of these carbs for blow through.

I tried turning the boost up again and of course it was leaning out so I figured I would try to modify the carb a bit more before installing the meth injection. Although there is a ton of info and experiences from people who have modified holley 4 barrel and 2 barrel carbs for boost, I havent seen a single thing online about this one barrel carb except for what Lincs200 had done, and he didnt write much about it or seem to understand how it works as it is pretty different in design than the other Holley's. So after litteraly having this carburetor apart 30 or 40 times, and paying attention to the insinstruments while driving, I found a problem that I was able to address.

While under vaccum and light boost the powervalve in this carb works fine, but over 5 psi or so it would close from the boost pressure in the bowl and and lean out. I was able to correct this by boost "assisting" the powervalve. I say it this way because it is not necessarily boost referenced as the original function is not affected and it still operates on engine vaccum and as such it stays closed at high vaccum but opens at around 2 inches of vaccum. What I did was drill a passage to the top side of the valve and run a boost line to it to force the valve open during higher boost. Now with pressure equalized on both sides of the valve, the original spring in the valve can do its job and keep the powervalve open. Works like a charm.

I opened the PVCR to about .090 and also had to reduce the air bleed to about half its original size. These mods have gotten the a/f to safe levels up to 12 psi, but still are not perfect. I will update again when I get it better and can turn the boost up some more. 8)

Just sent this video to a member here and thought a few of you guys would dig it. It is just a short video of my wideband and boost gauges during a measured quarter mile on a closed road. I took the vid on my phone for my own benefit so I could look closely at the gauges after my carb tuning so the quality is bad, but it sounds pretty cool and I thought Some of you guys may like it.

After going over the video a few times with a stopwatch it comes very very close to what the gtech on the windshield indicated: 14.20 ish at 92 mph. This is not top fuel funny car fast at all of course guys but I am still pretty happy with the fact that this is a 200 inch nearly stock engine with a ONE barrel carb running 87 octane gasoline, and during this run never exceeded 4000 rpm. Its is also an incredibly driveable car that commutes 180 miles one way and nets 31 plus mpg.

Ford inline six. 0 - 90 mph, 12 psi: http://youtu.be/d5eNTz0MAwI

Thanks for posting the video. Impressive!

Looks like it still runs lean as the boost increases.

Have you added a boost referenced fuel pressure regulator?

Oh yeah it is boost referenced. I have enlarged and modified the PV in this carb more times that I care to remember and have snuck up on the enlargement so as not to over richen it because if I do, it will be very difficult to fix it. It is a but leaner than it should be while boosting but there is no sign of detonation and it runs great. I will drill it a bit more one of these days and lower the AF a bit more, but I am not too worried about it. It took a LOT of tuning to get it where it is now.

I believe as it sits now, the PVCR is drilled to .090 and it has a 65 main jet. The HSAB is also reduced with fine wire. Before the HSAB mod, it would lean out in a linear rate with boost and after that it leveled out quite a bit.

What looks to be leaning out at the shifts is actually just the returning from a rich condition as the accelerator pump shot being used up and it is then feeding only on the main and PV circuits for fuel.

First Fox":3gxncfvk said:

Oh yeah it is boost referenced. I have enlarged and modified the PV in this carb more times that I care to remember and have snuck up on the enlargement so as not to over richen it because if I do, it will be very difficult to fix it. It is a but leaner than it should be while boosting but there is no sign of detonation and it runs great. I will drill it a bit more one of these days and lower the AF a bit more, but I am not too worried about it. It took a LOT of tuning to get it where it is now.

I believe as it sits now, the PVCR is drilled to .090 and it has a 65 main jet. The HSAB is also reduced with fine wire. Before the HSAB mod, it would lean out in a linear rate with boost and after that it leveled out quite a bit.

What looks to be leaning out at the shifts is actually just the returning from a rich condition as the accelerator pump shot being used up and it is then feeding only on the main and PV circuits for fuel.

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I was looking more towards you going past 12 psi of boost.

I agree that it would be better if you didn't have to do any additional work to the carburetor since it seems to be working nicely at this level.

Similar to what you were suggesting in your first post, add a single fuel injector and make a driver where you can control the pulse width from the dash.
It wouldn't come on until you had a few lbs of boost.

Since you have boost referenced fuel pressure the injector should work.

I am only running a mechanical pump right now. The fuel system is not equipped for any kind of real pressure unfortunately. For now this thing runs and pulls plenty for me. The key words being: For now. I actually just purchased another car to use for my daily driver and may be a little more daring with the fuel and boost with the Fairmont and see if I can break it.

First Fox":6hxhiq9w said:

I am only running a mechanical pump right now. The fuel system is not equipped for any kind of real pressure unfortunately.

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Ok. When the boost is at 12 lbs, what is the fuel pressure?
I couldn't see the fuel pressure gauge in the video.

The mechanical pump is referenced at 1:1 with a 5 psi baseline. @ 12 PSI of boost, fuel pressure is 17 psi. The fuel pressure gauge is on the cowl.

First Fox":3gvvq6dj said:

The mechanical pump is referenced at 1:1 with a 5 psi baseline. @ 12 PSI of boost, fuel pressure is 17 psi. The fuel pressure gauge is on the cowl.

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Like this



Force Fed i6 Foxes Fore Eva


At 32.6 miles per gallon, it won't be long before you can save up for a bunch of these...http://www.mustangandfords.com/featured ... allery/#11

Yeah, you should see the interiour of this thing while driving at night. It looks like a cockpit, but with a touch of 1970s porn era Naugahyde. I love it.

I like this thread.

I am running an Oz 2V head, ported and polished, tulip valves. I want to run a holley 8007 (390cfm), it runs on 2bbl and then turbo comes in, the vaccum secondaries open up, it runs off the big ones in the back.

so need to modify the oz intake and weld in a 4bbl adapter plate.

running the duraspark2 with probabaly the MSD 6530 to control the timing /boost

my cam is the isky 256, 202@050, .450 lift, LSA 112
68 mustang convertible 200cu inch 7 main bearings
turbo and intercooled
the goal is about 15psi boost

the 63 dollar question is....

fuel pump: will the holley blue with fuel pressure regulator handle the fuel pressure for this?? i found this one on Ebay
<http://www.ebay.com/itm/220680754983?_trksid=p2060778.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT>

I hope it comes to fruition for you, and I certainly wish you luck on your build.

Your carb with vaccum operated secondaries will not work as intended at all unless it is modified and reworked. Any boost would actually CLOSE the secondaries and defeat the purpose of them. A mechanical secondary carb will be much easier to work with and are really pretty cheap. And even that will require some tinkering. Don't be discouraged though, blowing through a carb is very doable for those willing to learn the process of modifying and tuning them. Consider a wideband a necessary expense.

Good move on a more tunable ignition system. 8)

The cam looks reasonable for your expected boost level.

And the unfortunate answer to your 63 dollar question is "no". That pump will not work with the boost level you are planning. I believe the blue pump is rated for 14 psi or so? You have to keep in mind that your available fuel pressure must always be above your boost pressure. A holley carb needs to see around 8 psi of fuel pressure at atmospheric air pressure. That fuel pressure would need to be raised to 9 psi when supercharging at 1 psi of boost, 10 psi of fuel pressure for 2 psi of boost 11 psi fuel pressure for 3 psi of boost etc... In other words, if you intended to run 15 pounds of boost you need a pump capable of delivering 8 psi + the 15 boost referenced psi so it would have to be capable of 23 psi MINIMUM which is far more than the blue pump would produce. This concept is known as "boost referencing" the system, and is an absolute requirement. When you are making that kind of fuel pressure, a return style regulator is likely required as well.

Just food for thought. What you want to do is very doable. You just have to do it.