Presentation and questions Fiat 131 Abarth volumetrico

Competition engines and ancillaries - general discussion
tmvolumex
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Re: Presentation and questions Fiat 131 Abarth volumetrico

Post by tmvolumex » Mon Mar 06, 2017 8:36 pm

Simon wrote: "My plan is to spin the Volumetrico blower at 8000rpm at 6000 engine rpm and control the boost in the manifold with a modern dump valve. I can change the maximum boost by changing the spring in the valve and I have three to choose from."[/i]

Simon,
I assume that your Volumetrico still has a carburetor ahead of the supercharger and is not fuel injected. That means that the boost you plan on dumping, will be a mixture of fuel and air. If you use a dump valve that dumps in your engine compartment you will have a fire or explosion in your engine compartment.

Do not use a dump valve with a air and fuel mixture to control boost pressure, you will burn the Volumetrico to the ground.

Tom McGaffigan
GC_31

Heli1996
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Re: Presentation and questions Fiat 131 Abarth volumetrico

Post by Heli1996 » Tue Mar 07, 2017 7:22 pm

Hi Tom,
That would spoil my day. Thanks for the excellent advice. The setup for the pop-off valve is for it to vent in to a breather pipe that is about 30in long and passes down the bulkhead and vents underneath the car. I am actually using the dump valve as a higher quality pop-off valve because the vacuum pipe on the top of the valve that dumps the charge on the over-run is not connected. I will be sure to plumb the vent pipe in so it vents to a safe place.

Brgds,
Simon
GC 133

Heli1996
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Re: Presentation and questions Fiat 131 Abarth volumetrico

Post by Heli1996 » Tue Mar 07, 2017 7:32 pm

The car was tested again today. Main jet size increased from 195 to 226.
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Max advance increased from 26deg to 30deg only increased max power by 4hp so we backed it off to 26deg.

The results were not as good as expected but then this is a completely standard engine with standard carb, standard cams, no porting or gas flowing and a standard cast exhaust manifold so I am not complaining.
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Hope this is interesting.
Brgds,
Simon
GC 133

tmvolumex
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Re: Presentation and questions Fiat 131 Abarth volumetrico

Post by tmvolumex » Tue Mar 07, 2017 8:07 pm

Simon,
Your carburetor is feeding air and fuel to the supercharger, this mixture is then forced into the intake manifold and then into the engine cylinders. On "overrun" the throttle is shut and there is minimal air and fuel getting to the engine thus there is no boost. In fact, it creates a strong intake manifold vacuum with a closed throttle. I would not vent the high pressure fuel and air mixture anywhere. The "pop off valve" on the intake manifold only comes into play if the engine backfires. Without the pop off valve, a backfire explosion in the intake manifold can force the manifold or supercharger off the engine. The stock Volumex and Volumetrico pop off valve valve opens with a backfire. The relief occurs at 14 PSI, it is not a dump valve.
Tom
GC_31

tmvolumex
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Re: Presentation and questions Fiat 131 Abarth volumetrico

Post by tmvolumex » Tue Mar 07, 2017 8:12 pm

Simon,
You do have some nice torque out of that baby.
150 LbFt at 1,500 RPM and 177 LbFt at 5,000. That is a tree stump puller !
Add a Weber DCOE, some cams and exhaust and it will rev also.
Great looking car.
Tom
GC_31

Guy Croft
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Re: Presentation and questions Fiat 131 Abarth volumetrico

Post by Guy Croft » Tue Mar 07, 2017 8:39 pm

that jetting is way off and will wreck your engine. Timing likewise.

ALL WRONG.

Whoever is doing this is way off the mark.

You need to come and see me.

GC
Guy Croft, owner

Heli1996
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Re: Presentation and questions Fiat 131 Abarth volumetrico

Post by Heli1996 » Tue Mar 07, 2017 10:24 pm

Hi Tom,
Got it thanks. I will fit the pop-off valve overhauled innards back in.

Brgds,
Simon
GC 133

Heli1996
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Re: Presentation and questions Fiat 131 Abarth volumetrico

Post by Heli1996 » Tue Mar 07, 2017 10:27 pm

Hello Guy,

Gladly come and see you. Maybe we can talk about GC overhaul and race prep of a 125TC engine too.

Brgds,
Simon
GC 133

tmvolumex
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Re: Presentation and questions Fiat 131 Abarth volumetrico

Post by tmvolumex » Wed Mar 08, 2017 12:38 am

Simon,
If you did not have any innards in the pop off valve as you said, quite a lot of your fueled boost was going out that valve and out the pipe that you installed. I am surprised that the smell of raw fuel was not apparent. You were lucky that there was no fire.
Tom
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Heli1996
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Re: Presentation and questions Fiat 131 Abarth volumetrico

Post by Heli1996 » Wed Mar 08, 2017 8:04 pm

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Seriously Tom, I checked out the Forge Motorsport Valve and the yellow spring I had fitted opens between 15 -23psi. Higher than the 14psi of the pop off valve. Absolutely no smells of fuel vapour I am glad to say.

Drove to car to work today and the wheel centres finally arrived!
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All the best,
Simon
GC 133

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