Presentation and questions Fiat 131 Abarth volumetrico

Competition engines and ancillaries - general discussion
tmvolumex
Posts: 165
Joined: July 7th, 2006, 12:43 am
Location: USA
Contact:

Re: Presentation and questions Fiat 131 Abarth volumetrico

Post by tmvolumex »

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
Posts: 13
Joined: September 16th, 2016, 11:58 am
Contact:

Re: Presentation and questions Fiat 131 Abarth volumetrico

Post by Heli1996 »

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
Posts: 13
Joined: September 16th, 2016, 11:58 am
Contact:

Re: Presentation and questions Fiat 131 Abarth volumetrico

Post by Heli1996 »

The car was tested again today. Main jet size increased from 195 to 226.
IMG_5300.JPG
IMG_5300.JPG (1.65 MiB) Viewed 28142 times
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.
IMG_5306.JPG
IMG_5306.JPG (1.51 MiB) Viewed 28142 times
Hope this is interesting.
Brgds,
Simon
GC 133
tmvolumex
Posts: 165
Joined: July 7th, 2006, 12:43 am
Location: USA
Contact:

Re: Presentation and questions Fiat 131 Abarth volumetrico

Post by tmvolumex »

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
Posts: 165
Joined: July 7th, 2006, 12:43 am
Location: USA
Contact:

Re: Presentation and questions Fiat 131 Abarth volumetrico

Post by tmvolumex »

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
Site Admin
Posts: 5039
Joined: June 18th, 2006, 9:31 am
Location: Bedford, UK
Contact:

Re: Presentation and questions Fiat 131 Abarth volumetrico

Post by Guy Croft »

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
Posts: 13
Joined: September 16th, 2016, 11:58 am
Contact:

Re: Presentation and questions Fiat 131 Abarth volumetrico

Post by Heli1996 »

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

Brgds,
Simon
GC 133
Heli1996
Posts: 13
Joined: September 16th, 2016, 11:58 am
Contact:

Re: Presentation and questions Fiat 131 Abarth volumetrico

Post by Heli1996 »

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
Posts: 165
Joined: July 7th, 2006, 12:43 am
Location: USA
Contact:

Re: Presentation and questions Fiat 131 Abarth volumetrico

Post by tmvolumex »

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
GC_31
Heli1996
Posts: 13
Joined: September 16th, 2016, 11:58 am
Contact:

Re: Presentation and questions Fiat 131 Abarth volumetrico

Post by Heli1996 »

IMG_0034.JPG
IMG_0034.JPG (31.04 KiB) Viewed 28117 times
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!
IMG_0035.JPG
IMG_0035.JPG (678.23 KiB) Viewed 28117 times
All the best,
Simon
GC 133
Post Reply

Who is online

Users browsing this forum: No registered users and 27 guests