Simple way turbocharge a gas engine

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wayno
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Simple way turbocharge a gas engine

#1

Post by wayno » Sat Aug 03, 2019 7:51 pm

I learned something very interesting today, I was at a car show that has invited Datsun owners with our own area to park, we had 16 Datsuns, and there were 12 roadsters, 2 Z's, a 510 and a 320 truck, they highlighted British cars this year, 26 of them showed up, a lot of american sheet metal was there also, even a 2019 Corvette was there, it is for everyone.
I was walking around and seen a big truck with a turbo on a stroked 383(350 block with 400 crank), it had a 700/750 double pumper carb and a box on top of the carb that had a tube that went straight to the turbocharger, this confused me as when people do it this way the fuel cannot get out of the carb because of the boost pressures inside the carb throat so I went over to the guy and asked him how it worked.
He had a normal Carter electric fuel pump, the diaphragm type with a vent hole in the top, it has to be this fuel pump with the vent hole, he drilled a hole in the box on top of the carb(3" X 6" X 8" box) in the back and threaded it for a fitting for a quarter inch inside diameter hose, this went to a tee, one side of the tee went to the Carter fuel pump back by the tank, he drilled the vent hole in the top of the fuel pump for the hose coming from the tee and threaded it for the same fitting that the box had and connected them together, the other end of the tee went to the auto transmission, he drilled/threaded that vacuum device on the transmission to except a valve stem, the end that you fill up a tire with, I suppose one could just tee the hose and put it very close to the transmission, this stupid valve stem is the blow off valve for the transmission vacuum devise, some how the boost in the vent hole on top of the Carter electric fuel pump makes the fuel pump push the fuel to the carb with more force, or making it work harder to create more pressure so it over powers the boost and his truck runs great, at least that is what he told me, it looks real nice and unfortunately I forgot to take a photo of it.
I do not know if you would need this valve stem blow off valve with a manual transmission, seems like it may be needed, and valve stem as a blow off valve seems crazy to me, and remember it has to be mounted on the threaded end like one is trying to inflate a tire with the boost.
Normally one has to make a box for the whole carb to fit in, this was way simple without holes for throttle cables, fuel hoses and other such things and worth looking into if you try to turbocharge a gas engine with a carb, if you have a 4spd then it may be as simple as a hose going to the top of the Carter fuel pump with a vent hole in the top as the connection, he kept saying it had to be the type with vent hole, only that Carter fuel pump would work.
I forgot to ask about the distributor mods if there were any, I will likely see the guy there next year.
Last edited by wayno on Sun Aug 04, 2019 12:28 pm, edited 1 time in total.
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Re: Simple way turbocharge a gas engine

#2

Post by DRIVEN » Sat Aug 03, 2019 8:34 pm

I'll probably have to reread that a few more times and sketch it out before it makes sense. My grandpa did the carb box thing back in the 50s for a Paxton on a Chevy 265. My uncle has the whole setup in a box somewhere.
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Re: Simple way turbocharge a gas engine

#3

Post by wayno » Sat Aug 03, 2019 10:13 pm

It really doesn't make sense to me either, I just don't see how adding boost to the vent side of a Carter electric fuel pump can make it overcome the boost issue.
The way I understand it is that when a carb is under boost the venturi that makes vacuum to pull the fuel out of the bowl is under the pressure of boost, so air that is pressurized would rather go into the carb bowl via the venturi and carb vents than pull the fuel out of the carb bowl via the venturi, if the whole carb is under boost like when inside a box, then the bowl is under the same boost as the throat of the carb, so the venturi works properly again, it creates vacuum and pulls fuel out of the bowl.

Keep in mind that when I figured out my turbocharger out on my diesel engines which have a venturi to control the throttle, I had to put the vent side under boost also to get the throttle body venturi to work properly again, boost on both sides of the diaphragm cancelled each other out and the venturi in the throttle body worked properly again, it works great.

Maybe this is how it works, think of it this way, the vent side of the Carter electric fuel pump diaphragm sees boost, and the feed side of the fuel pump also sees the same boost because the boost from the running engine is trying to push the fuel back into the tank via the venturies and carb bowl vents(pressurizing the bowl not allowing fuel in the bowl), now if there is as much pressure/boost on the diaphragm on both sides, then they cancel each other out and the carb works like it should again as there is as much pressure pushing the fuel onto the bowl as there is trying to push it out of the bowl back to the tank, they cancel each other out.

What I don't understand is how it works, the only way I can think of to test this is to buy a Carter fuel pump, apply 10lbs of pressure to the vent, then have the fuel pump pull gas out of a open jar, then have the feed hose going to a closed jar with a lid on tight(hose going to the carb) piped to 10lbs of boost also(so the jar has 10lbs of pressure in it and the vent side of the fuel pump has 10obs of pressure), then turn on the fuel pump and see if it will fill the jar, then try it without boost on the vent side of the fuel pump, if a fuel pump only puts out 4psi fuel pressure, then it should not be able to fill the jar that has 10psi of pressure pushing back, does this make sense?

I think the key here is the fuel pump, boost is not always the same, it goes up and down depending on rpm, so if the pressure on both sides of the functioning fuel pump diaphragm are always the same, then the fuel should flow like normal for that pump at whatever PSI it is set to run at.

I asked the guy how he figured this out and he shrugged and said I am an engineer.
Last edited by wayno on Sun Aug 04, 2019 12:33 pm, edited 1 time in total.
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Re: Simple way turbocharge a gas engine

#4

Post by DRIVEN » Sun Aug 04, 2019 6:46 am

Any chance he's just messing with us like with all the useless gauges and valves on the urinals at Cornelius Pass Roadhouse? :rofl:
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Re: Simple way turbocharge a gas engine

#5

Post by wayno » Sun Aug 04, 2019 9:16 am

I do not lean on or touch vehicles at car shows except my own, they are all so clean and shiny and I don't want to leave my hand print on the nice fender, I was able to see a "Y" where the turbo exhaust feed was before it entered the turbocharger, so both exhaust sides of that 383 V8 were feeding that turbo, it looked clean but I didn't follow both them hoses to where they ended, I just approached him and asked how it worked and how did he over come the boost on the carb issue.

I reality he described what I did to make the turbos work on my vacuum throttle diesel engines and I didn't tell him about that till after he told me what he did to make it work on his gas engine, and he kept mentioning the Carter fuel pump with the vent on top, only that one would work, no other pumps would work, only that one.
And that valve stem, who would think of using a valve stem as a blow off valve, I cannot blow on a new one and force air thru it with my mouth, but that is how you fill your tires, I have never heard of such a thing before, but it makes sense if they start opening up at 7lbs of pressure as that is what he told me when I asked how much boost he was using, 7lbs.
The guy was a total stranger to me, I believe he won an award at the show for his truck(he was parked right up front at the meet headquarters), it was a nice clean truck although I don't remember a lot about it as I was interested in the turbo piping not that huge truck, I also asked about his valve covers, I didn't recall Chevy having a 383 marked valve cover but he had them, he looked at me and said it was a common modification, I asked if his 350 block had a 400 block crank in it and he said yes although I didn't even know if that is even possible and still don't, I mentioned that most manufacturers would not even be interested in making such a thing with such a small demand, and he looked right at me and said it was likely that at least 10 of the vehicles at that show had done the same modification to their engines, if that is true then there likely is a large enough demand to make them valve covers with a raised 383 in them, I wish I had taken photos now.

I am not sure if I have a way of testing a system with just 7lbs of pressure, will a glass jar even hold 7lbs without blowing up, it probably will as I have installed a valve stem in my pump sprayer and put a 100psi in it, but tires and pump sprayers are made of plastic and expand and contract as I watched my pump sprayer container expand.
I wonder if it is possible to turbocharge dual SUs if one pipes the vents of the bowls to boost, I like thinking about stuff like this.
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Re: Simple way turbocharge a gas engine

#6

Post by jtinluvr » Sun Aug 04, 2019 12:19 pm

I find hard to believe there is such a fuel pump, but there is a lot of stuff out there I am sure I don’t know about. Generally, a fuel pump will put out a set pressure and that’s it, unless you can vary the voltage and either speed up or slow down the pump. Not sure how pressuring a vent can increase pressure, but again it may be possible. Most of the time on boosted cars you would use a boost referenced fuel pressure regulator that is set to provide a lower pressure under vacuum conditions and increase as the engine goes from vacuum to pressure. The fuel pump never changes but the regulator adjusts to let more pressure through. On the 383 Chevy, this is a pretty common upgrade to the 350. I built one maybe 10 years back for a split bumper RS Cameron I had. IIRC, it’s a 400 crank, 350 rods, and “custom” pistons. You can buy new cranks for this combo pretty inexpensive these days.

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Re: Simple way turbocharge a gas engine

#7

Post by DRIVEN » Sun Aug 04, 2019 12:38 pm

383 has been a mongrel build for 40+ years. Early ones were 400 crank with turned down mains along with 400 rods (slightly shorter than other SBC) and 350 pistons. You also need to grind the pan rail in a few strategic spots for rod bolt clearance. You could either consider it a stroked 350 or a small bore 400. You could also use the opposite combination of parts with main bearing spacers to build a 377 -- essentially a big bore 350. They were popular in circle track applications.
Now days, there are tons of aftermarket 383 crank manufacturers that just drop in. Custom piston choices let you use 5.56, 5.7, or 6" rods. Lots of 383 crate motors available too, even from GM. But GM never offered a 383 in a production vehicle.
The "383" valve covers are likely just Chinese Ebay pieces.
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Re: Simple way turbocharge a gas engine

#8

Post by wayno » Sun Aug 04, 2019 1:06 pm

So far then everything the guy said about the engine was true, it's a common modification/upgrade that I didn't know about, he didn't say anything about the rods or custom pistons but I didn't ask either, I just guessed on the crank.
He said it had to be that common Carter fuel pump with a vent on top, he mentioned that several times.

This is the best I can explain on how I think the fuel pump works, if both sides of the fuel diaphragm see the same amount of boost all the time then basically the fuel pump has a new sea level, the fuel pump cannot see any pressure difference as both sides of the pump diaphragm are under the same pressure even though everything outside of the pump housing is at a different sea level, so the fuel pump runs like normal, as the boost goes up and down but nothing changes as both sides of the diaphragm see the same pressure, so the fuel pump doesn't need to create anymore pressure, it just runs like normal.
This is all my opinion after thinking about it for a day, I didn't see it run when the show/meet ended as I was hurting by then and just wanted to go home, I even forgot my chair, again I asked how he figured all this out and he just shrugged and said he was an engineer.
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Re: Simple way turbocharge a gas engine

#9

Post by wayno » Sun Aug 04, 2019 1:16 pm

I really have never known much about small block Chevy blocks, never had the money to build one myself.

I know more about L blocks than any other engine I have ever owned, and there are others that know way more than me about the L block, so I really don't know that much, just what I have done myself.
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Re: Simple way turbocharge a gas engine

#10

Post by Laecaon » Sun Aug 04, 2019 10:05 pm

Just did a little looking around.

Definitely seems to work on the GM Mechanical fuel pumps. Add boost reference above the diaphragm. The chamber above the diaphragm must be sealed off from the crankcase. A sealed operating rod is also required so boost pressure does not escape into the crankcase.

I cannot find a single reference to an Electric fuel pump being used this way.

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