Volumex Set Up Question

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Andy007
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Re: Volumex Set Up Question

Post by Andy007 »

Now the project is finished, today i have made the first tests on street. The car has a lot of torque a makes simply 7000 U/min. Blower ratio is 32/21 with weber 40 DCNF (28mm venturies) self made alloy inlet manifold (between carb and blower) , ported head, 124 spider exhaust cam ( timed at 114) and 130 TC inlet cam (timed at 112).

At 800 U/min the pressure is minus 0.2bar ( negative 2.9 PSI) , at 4000 U/min the pressure is only plus 0.1 bar (+1.4PSI ), this is not enough boost ?

What is my mistake ?

Kind regards Andy
tmvolumex
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Re: Volumex Set Up Question

Post by tmvolumex »

Andy,
It sounds like you either have a bad boost gauge or you have the gauge connected between the carb and the supercharger not between the supercharger and the engine ie to the intake manifold.
More serious that that though is a post I made a few days ago on this list. I am reposting it below.

I just noticed on your Feb 25th post that you are using a Lancia Integrale head gasket. It better be for the Delta, with the intake and exhaust on the same sides of the engine as the Fiat engine you are building or your engine will have severe detonation and overheating issues. The Integrale has "reverse port layout" compared with earlier Fiat engines. Because of this, the cooling holes in the head gasket are reversed on the Integrale gasket.

I had hoped to catch you before you mounted the head.
Tom
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Andy007
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Re: Volumex Set Up Question

Post by Andy007 »

Hello Tom,
thanks for your fast reply. I think i have found the problem. There was a big sharp in the line behind the dashboard. Now it goes to 0.65 bar negative boost (9.4 PSI ). But in my opinion it must go to positive boost ?

The gauge ist between blower and inlet manifold head.

The cooling galeries in head gasket were opened.

kind regards Andy
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tmvolumex
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Re: Volumex Set Up Question

Post by tmvolumex »

Andy,
It sounds like you have located your boost gauge problem.
With the gauge connected to the manifold between the supercharger and the engine (INTAKE manifold) it will indicate intake manifold vacuum and boost. The intake manifold can only go positive pressure (boost) if the supercharger has something to pressurize. At idle with the throttle closed, the supercharger does not have anything to pressurize. Under closed throttle, the CARB manifold has vacuum (negative pressure) and so does the INTAKE manifold. Opening the throttle gives the supercharger something to shove into the INTAKE manifold thus building boost. Boost will be developed in the INTAKE manifold if the engine can not accept the amount of air the supercharger is delivering to the manifold. Porting, big valves, flow work etc increases the flow of the head and boost readings will actually come down with the improved breathing of the head. The engine will make more power as the boost is actually making it into the combustion chamber, making power, not backing up in the INTAKE manifold.
Under full throttle conditions and under load, a good indication of a well matched blower, head, cam and exhaust system is if the boost is flat (stays constant) after around 4,000 RPM. If the boost continues to rise after 4,000 RPM you have restrictive breathing and or restrictive exhaust. If the boost drops off after 4,000 RPM, you have a restrictive air filter or too small of a carb / chokes.
Tom
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tmvolumex
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Re: Volumex Set Up Question

Post by tmvolumex »

Andy,
One more thing I can not tell for sure, but from your engine picture, it looks like you may have a sintered auxiliary shaft pulley. If the pulley has an oval hole for the dowel pin then you have a sintered pulley. If this is the case, you need to read Guys post on this. I have reposted a portion of Guys post below.

“The best auxiliary driveshaft pulley is the early solid steel or plastic one. The later sintered one with big holes in it has a different offset and should be used with auxiliary driveshaft shortened 1.5mm. When this is done the step on the hub on the rear of the aux d/s pulley may rub on the aux d/s housing seal and thus - either leave out the gasket and use silicon sealant or - machine 1.5mm off the hub. It is imperative to check the alignment of the aux d/s flange with the cam pulleys and the crank nose pulley that drives the belt.”
Tom
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Andy007
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Re: Volumex Set Up Question

Post by Andy007 »

Tom,
thanks for your advices. At the moment the gauge line is broken, so i can test next week the pressure with a new gauge line. This is the reason of changing the place of the gauge instrument, so that the gauge line does not sharp.

The aux pulley is changed to a plastic one after the first start of the engine, because i need a aux pulley with guide in front, now the cam belt runs exactly in the middle of the cam pulleys.

Tom, this is my self made alloy intake manifold, what do think about ?

Andy
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tmvolumex
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Re: Volumex Set Up Question

Post by tmvolumex »

Andy,
I would put a radius on the underside of the top plate. IE radius the underside of the oval hole edges where the carb mounts. The fuel air mixture has to turn a sharp corner under there. Given the lack of space between the inner fender and the supercharger on a Fiat 124 spider you manifold looks OK. Radius's are better than right angles but given that superchargers breathe much better than pistons going up and down inside cylinders I think you should be able to meet your goal of 170 hp (crank)if you have a good flowing head and exhaust. Your drive ratio is 1.52 to 1 vs the stock of 1.3 to 1 and at 9.0 PSI of boost. Remember, boost is an indication of what is not getting into the engine. I dont think you mentioned what size and type of exhaust you have? That will make a big difference. are you going to chassis dyno the car?
Tom
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Renier RSA
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Re: Volumex Set Up Question

Post by Renier RSA »

HI Guys

We are also building a VX motor. I was asked by my engine builder what is the boost at 2500 rpm up to 5000 rpm.

What size carb you ended up using. People are recommending DCOE 45 but with a smallish venturi. (I think 27mm venturis) What is the advantage using a 45mm barrel fitted with such small venturis – can one rather use a 40DCOE?

Can any one of your shed some light? (BTW I actually intended to create a fresh post but as it is related I slipped it in here)

Thanks
Renier Nelspruit RSA
Andy007
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Re: Volumex Set Up Question

Post by Andy007 »

Exhaust system is 4-1 Header and only one straight thru silencer at the end, diameter 2" (50,8mm). no catalytic converter.
Now driven 300km , very tourqey in each gear, lambda goes a little bit rich.
Making the radius in the manifold in a few days, good advice Tom, thank you.

kind regards Andy
cstorry
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Re: Volumex Set Up Question

Post by cstorry »

Very nice manifold work Andy.

It looks very much like the stock 124vx manifold.

You should definately get +'ve boost pressure under load as Tom has indicated. I did on my VX spider : )

Chuck
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Guy Croft
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Re: Volumex Set Up Question

Post by Guy Croft »

A very nice informative thread - well done all!

G
Andy007
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Re: Volumex Set Up Question

Post by Andy007 »

Now i have made some tests with the car. The acceleration 0-100 km/h ( 0-60 miles ) is very quick ( i beat a Mercedes 230 SLK Kompressor with 193 PS ), so in the region 7.3 -7.6 seconds to 100 km/h.

Problem: when i pull the pedal full down in 5. gear from 100 km/H ( 60 miles ) to full speed, Lambda goes at 7000 U/min from 0.87 in one second to "lean".
I think the fuel pump give not enough fuel to carb ( needle valve 2.5mm ) and the fuel goes down in the carb.

Better to use Bosch injection fuel pump ( on stock )with pressure regulator to 6-7 psi and fuel return line to the tank or Facet pump ?

Distributor is Fiat 131 Marelli , centrifugal advance is 25 at 5500, i think it is very retard. Better to use Marelli SM 807 CX, max. centrifugal advance is 28 at 3600 U/min ?

any advice ? Thanks Andy
cstorry
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Re: Volumex Set Up Question

Post by cstorry »

Andy

A popular tuning change on the original volumex spider cars was to drill and mount a return pipe in the stock carb and use a fuel pressure regulator inline.

This was done on my car and gave good results. G+B (in Germany) sells a kit of parts or you can likely buy them from a tuning shop.

Sorry not much help on the other points:
- I have the Bosch part number somewhere for the stock 124VX fuel pump (it looks like the FI pumps but I presume it is not)
- I also have the pressure setting for the regulator from G&B but will have to look that up

Chuck
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Guy Croft
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Re: Volumex Set Up Question

Post by Guy Croft »

No way do you want an injection pump. Those things shove out 45psi plus and that is for injectors and high pressure boosted intakes. Your carb is operating at atmos pressure in the float chamber not 15psi overpressure.

You should look up the delivery from Facet pumps before ever contemplating anything er, 'more powerful'.

For example - the lowest output interrupter type is 36 US gallons per hour. If your engine needs that much gas something is wildly wrong but if you need more pressure at the carb go Silver Top comp spec or Red Top. Much over 4.5psi pressure with engine running and the needles will simply never shut so use of a fuel pressure gauge and if need be (only!) a regulator can be pretty important.

An electric pump MUST be located in the boot so it's pushing not sucking as the latter causes fuel boiling in the low pressure line on hot days at even relatively low altitude.

GC
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