Attn: ben wright

[TGemi1]

hey dude i've sifted through hella posts of yours in regards to turboing etc. i'm supercharging my gem, motor is recon 1600 block and recon g200 head. I am going blow through setup but i dont no which carb would be best suited. For fuel i will be using a vl commo pump and a malsappi fuel regulator. can u give me a run down on the best carb to use for this setup,and what mods i have to do to presurise it etc.

chris...

[SHEEL]

hey chris,
i'm not ben but can answer your questions.
allthough i would advise against using a carby with your setup, this is what i suggest you do...

don't use a vl pump for a start, the pressure is too high and the reg wont bring it down far enough, you need to use a LOW Pressure HIGH Volume pump, like a holley blue, go to an injection or carby specialist, they will be able to find one for your application.

malpassi reg is the way to go, make sure when u but it that you specify it's for LOW pressure, as there are a few different models.

the carby you need is from a turbo citroen or lancia.
its a WEBER DMTT34 or DMTL34
it is DESIGNED to be blown through any thing else will not work as the boost pressure feeds into the fuel bowl and blows the gaskets in the carby.
you can source this carby from a euro wrecker if you are VERY LUCKY, they are rare as rocking horse shit.
the other alternative is buying an aftermarket model which i believe is a DMTR34. it is basically the same just with a different part number, these units are costly though. i think they go for around $300. if you source a second hand one reconditioning kits are available and cost about $75.
the DMTT carby has the same dimensions as a dmg34 like off an XF falcon, which by memory are slightly differrent to the dgv weber. this means u need a different adaptor plate to fit it. redline have an adaptor to suit but it is universal for a few models, this means that it is blank and you need to drill and tap holes for studs to suit your car.
you've got my email if u need to ask me more don't hesitate.
hope that helps you.
sheel
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[Frederick Stienheld]

Sheel don't you need a fuel pump that will output boost pressure + ~4 psi ??
In which case you would be after a high pressure pump.

[Ben Wight]

Hey Chris, its Ben Wight by the way, wright is wrong.

Anyway, i think the VL pump and malpassi is a good combination, I see Sheel doesn't think so becasue I guess he couldn't get the pressure low enough, but that simply means the return line to the tank is too restrictive. Becasue those efi pumps flow a lot of fuel when the system pressure is low, you need a very large return line, or two small ones. I would recommend running the factory return line and the 'pollution' line in parallel to double the flow, you just have to put a fitting in the tank in the boot for the pollution line to return through.

I have only used downdraught webers, but I know a lot of people using Holleys. Webers are easy, I have run both 32/36 and 38DGMS, both with no actual 'boost' mods except correct jetting, and they worked well. For your setup, I would recommend a 32/36 and tune it to suit, that way you get the mech secondaries and seperate primary circuit, and you can tune the primary for cruising, and the secondary for power. ie. richer.

You might want to consider efi though, as these days, you wont save a lot of money sticking to carb, maybe only a few hundred if you get a cheap efi setup and computer. the ease of tuning is well worth it.

Ben

[TGemi1]

can get hold of an efi manifold, just gotta understand all the conversion, what boost u reckon i could run with my enigne?

chris...

[SHEEL]

i ran the two return lines with the VL pump to the tank and the fuel pressure was still too high, it was about 6psi on idle, close but not right.
with the low press high vol pump the pressure on idle is around 3-4 psi, right where you want it. and the malpassi closes the return as the boost rises resulting in the fuel press rising in direct proportion.
trust me dude i have actually DONE THIS!!!

i have also seen a holley used in a blow through configuration and it worked sweet, but it costs around $300 to have the internals modified to handle boost.
the 32/36 carb works well in a TURBO application as BEN has siad, BUT i never got mine to work with the supercharger despite having spent many hours and around $1000 on pump, jet, float, regulator combinations.
there is too much boost pressure for the carby to handle in the primary circuit. When you are coasting along at 80km/h with a turbo car there is no boost.
but superchargers are different! there is a small amount of boost which puts tremendous pressure on the carby as it needs to escape from somewhere! i found that the gasket sealing the feul bowl blew out continuosely and the B.O.V was always open except under hard acceleration. the car ran very rough whilst cruising and idleing, it was flat out or nothing!
I believe that using a holley or the weber that i specified in the previous post will rectify the problems for the primary circuit. However, u may still have problems with the BOV being open constantly, which isn't a problem in terms of the cars performance, it just sounds gay!
i believe to fix this problem u need to fit a second throttle body in front of the blower to restrict airflow into the blower whilst the engine is in partial throttle conditions.

that is my theory, i haven't tested it but i read it off some old forums where people had fitted sc14 blowers to various cars, it seemed to work for them. i know it sounds funny but if you think about it there is alot of method in thier madness!
Like i have said before, no desrespect to ben, he knows his shit! but his experience is in turbo applications, which differs from supercharging.

that being said you also asked about pulley size, i had my pulley made the same size as the toyota pulley. It ran 5 PSI.
i also calculated that with a g200 head on a 1600 the compression ratio is approx. a mega low 7.7:1 as compared to the normal 8.3:1 which is already low.
i think you could push 10 PSI on a tight stock bottom end.
with 10 psi compression at full boost would be around 10.7:1
which is comparable to a N/A g200 with a g161 head on it.
to achieve this boost u have to calculate how many revolutions the blower does compared to one revolution of the engine.
the formala to calculate this is in the R & D forum in a post titled "the lowdown on supercharging"

hope that has helped you, sorry about the huge post.
sheel
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[Ben Wight]

Yeah Sheel, I have played with a Malpassi on a friends car with a VL pump, and we got 6psi as well, which was fine in his case. I cant remember if it would go any lower, but I often run the 32/36's at 6 psi with no dramas. I haven't used a malpassi on my own cars though, I modify factory efi regulators, its a bit cheaper.

I dont know what sort of low pressure-high flow pump you used, but you might find that although it worked well in your case, with say a base pressure of 4psi, and 5psi of boost, giving max fuel pressure of about 9psi, it might not work well at higher boost levels, as the pump might max out at say 12psi for example. I know some pumps do, but I also know a guy running a holley blue with a malpassi with over 20psi of boost and no dramas, so a Holley blue seems a good high pressure pump as well. I dont know about flow at that pressure though. Some pumps, might be carter, dont like more than about 15psi of fuel pressure.

I would guess that typically, an efi pump will outflow a low pressure-high flow pump at around the 15-25psi of fuel pressure range.

Anyway, thats all history hey, no more supercharger. What engine setup you running now?

Ben

[SHEEL]

i've moved away from the fuel problems by changing to straight gas!
as soon as i get my tax return (anyday now) i'll be puting my to3 turbo on!!!
when its finished i hope to see some 12 sec time slips or less. an engine with the same internal mods as mine, built in melbourne, currently runs 10.6 sec 1/4 mile times and is daily driven. that car is my bench mark. if i can achieve anywhere near what he has and still have a reliable package i'll be happy.
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