[vinesy92]

Basically I'm interested in a blow thru carby set up running dual fuel. I know EFI is the right way to do it, but it costs alot to tune and set up. And I'd rather a carby set up.

It would be intercooled, running around 10psi of boost. Is this possible to run on LPG, then say run a boost controller and when using petrol lower the boost, to stop it pinging?

Thanks

 

[patrol_maverick]

I think a draw-through setup would be more reliable if you're using the standard carby. If you're going for a blow through setup, normally you would need the carby inside a sealed box. Gas injection would be the ideal way to go.

 

[vinesy92]

I was thinking something like a holley 350 or a weber carby. A gas injection set up would be good.

Will a carby like just sitting there 95% of the time with only air going through it?

 

[sutto]

yeah a draw throught setup would be ideal, it also mixes the air and fuel really well before it enters the motor. the main problem with a blow thru setup with a standard or unmodified carby is leaning out. as the Psi/boost can overide the fuel presure form the bowl and push the fuel back throught the jets but you should be able to get away with a little boost this way but not 10psi. you could try and find a factory turbo carby like a 12A rotary turbo these carbs are equevalent to a 650 for memory.

 

[bigcam]

Blow through you must pressurise the fuel chamber and for every pound of boost you need to add a pound of fuel pressure to keep a positive pressure on the back of the jets. (as said above)

however you have restricted yourself straigh away to blow through by adding an intercooler. You cannot safely run a draw through with an intercooler, as the fuel charge is delivered prior to the charge going through the intercooler in a draw through system, fuel vapour will condense inside the intercooler, one backfire and you will have an aluminium bomb strapped to the front of your car..

 

[vinesy92]

Okay so a better option is a draw through set up. Which carby could be used? Side draught weber? SU? I've just never seen one done on a patrol and definately noone running duel fuel. Most seem to use EFI.

Would the LPG need to be plumbed in pre-carby or after the turbo?

I haven't bought anything yet, cracked the head on my GQ on saturday.. so going through ideas of where i want the car to end up.

 

[BeNos]

i think really straight gas is going to be the easiest and already done before. then you dont have the hassles of trying to get a carby to work with it and you already have the gas tank.

 

[MikeH]

<snip> I know EFI is the right way to do it, but it costs alot to tune and set up. And I'd rather a carby set up.
<snip>

Blowing a motor up costs a lot too.
Dyno time costs a lot too.
Time spent messing with it and cobbling together a boost-retard and mapping your distributor the old fashioned way costs a lot too.
You want cheap power go with a cam, extractors, decent carb (not holley) and a bit of tuning. you can make pretty decent power out of the TB42 with a bit of a tidy up.

I challenge you to find a daily driver of any make running the combination you propose on pump fuel. Unless you have a good mate who knows blow thru backwards I'd just wait and save up for a bit longer.

 

[vinesy92]

I didn't want to run straight gas, as if it runs out of gas then you got to tow the vehicle and not everywhere has LPG.

Mike i think your right. I went reading abit about the draw through set up, they seem to lag and have a lot more issues. EFI would be the best and most reliable. Sigh!

Thanks Anyway

 

[MikeH]

have a look at all of the work done to my toy.
A well set up NA carby TB42 is hard to keep up with.
By well set up I'm talking balancing, head work etc.

 

[ls400x]

Blow through carby facts:

You don't need to have it boxed for it to work (and will make it a w*ore to make the many jet size changes that you will need to make throught it's development)

You will need a 1:1 fuel regulator and a fuel return line

You will need an efi fuel pump capable of the flow rate required at the maximum pressure anticipated (determined by your boost pressure plus the original na fuel pressure)

You should replace all existing rubber fuel lines with efi rated pressure ones and clamps

Suck through = fail, even more so with an intercooler (unless you feel that a large quantity of stioch mixture air and fuel stored in the cooler and piping waiting for a backfire through the inlet is low risk). Also the fuel condensing and pooling over the huge surface area involved along with the fuel falling out of suspension due to it's inertia going through the compressor are both serious problems.

Your stock ignition system will cope for a mild boost pressure

Vacume secondaries will give you gief if you deceide to use the stock carby

A holley with mechanical secondaries and non-collapsible floats is the best bet, not to mention that more people now how to work on them than any other carby.


I have personally done 2 blow through setups now and it is not worth the pain. My reccommendation would be to shop hard for a secondhand aftermarket computer with the features that you will think you will use after serious research along with a wideband O2 meter like innovatemotorsports sell, combine with a few later model bits like inlet manifold, injectors, fuel rail, reg, throttle body, tps, iac, cas. It will be far far better and likely to cost less all in (a lot less unless you feel you can have a serious go at getting the jetting right yourself) and be quicker to get on the road again. Maybe even buy a complete efi 4.2 and build it along side of your carby one so you only have to take the car off the road for a short time?

All just my opinion..

 

[jonsey850]

I have heard that blow through set ups use a ridiculous amount of fuel also after the jetting is done.

EFI set would be the go do it properly and get a good after market ecu (haltech ect), save so much messing around and elliminates things like air flow meters and oxy sensors. A decent EFI/turbo setup would not be cheap though for a 4.2 i would say about 6k+. Also clutches arnt cheap either.

 

[vinesy92]

Hey mike do you have a dyno figure of your TB42? It would be nice to know. Are you using the standard carby?

Basically a blow through carby set up wouldn't work effectively, especially involving LPG. .

 

[MikeH]

1: havent got one
2: havent got a carby either.

I said I have trouble keeping up with one. I run a stock TD42 with a bunch of custom stuff bolted onto it.

I dont know in detail what was done to it, but it's all sensible common stuff because of the class rules they run it in. About the most exotic you could go with it would be an offset crank grind and the smallest undersize commonly available big end bearings to stroke it slightly. I strongly suspect they didnt go to that expense.

It all depends what you want to spend and how much you can do yourself. Also if it's for comp use and they let you run methanol you could get some pretty serious power cheaply.

 

[UR-50-LO]

Blow through carby will be fine so long as you only run the single boost level as you can't really adjust the fuel to compensate everytime you change the boost level unlike EFI. Use a 350 boost referenced Holley with a carb hat attached & a 1.1 Malpassi regulator with something like a T04E turbo (internal wastegate is fine for such a mild setup). If going dual fuel you can have an Impco 225 which has a 3" inlet/outlet in your piping between cooler & carb or turbo & carb if not intercooled. Be realistic with your expectations, only run a mild 10-12psi and she should be sweet...You could also consider going for a draw through system as it would be easier & cheaper to setup and as only running low boost the incoming fuel/gas would do a good enough job of cooling the intake down, otherwise adding water/meth injection on a hobbs switch isn't too hard...

ETA:
Alot of people will shake their head at a carby turbo system now that EFI is so easily available (no denying that EFI has it all over a carb & is my 1st choice also) BUT back in the day Peter Wherrets Mitsubishi Sigma, Daihatsu Charade, Holden Strata 6 cylinder, Ford 250 Xflow XE's, Ford 2 litre Escorts and many other Rotary, 4, 6 & 8 cylinder factory & aftermarket kits were all carbied & turboed. Go to the states and that is all they use over there, big carbs & big turbo/superchargers. Many years ago before the EFI rage we used to muck around with them including mates 10 second 202 LH Torana & an 11 second 13B RX3. I personally had a 12 second 12A set-up that used a boxed 55mm webber & T04 turbo built by David Broadhurst. It later went onto a 13B but I never heard anything of it again!!!

 

[vinesy92]

Mike its not for comp use. Im rebuilding the engine to be balanced, cam, slight head work. nothing to major, mostly need it to be reliable.

Spending 3k+ for a engine rebuild, then 6k+ for a EFI turbo set isn't really what I'm after..

Running a carby set up, I'm only after low boost. About 6-10psi tops.

 

[Steelo]

Bit old now I know but am interested in this also for my rb30, not after a comp 4b just an everyday 4b that has a little bit more power with 6 to 10 boost. I know there's all the VL Condomadores & Skylines out there but just want to keep the carby set-up.
Thanks

 

[Snapper Trap]

Mike its not for comp use. Im rebuilding the engine to be balanced, cam, slight head work. nothing to major, mostly need it to be reliable.

Spending 3k+ for a engine rebuild, then 6k+ for a EFI turbo set isn't really what I'm after..

Running a carby set up, I'm only after low boost. About 6-10psi tops.

Just saw your post so here is my update :
Blow through Turbo TB42 done and dusted!!! Man this thing will peal your ears back, Bring on the kiddies with there HSV's
This thing steps out big time form mid 2nd and pulls like a bus load of school boys there on.
It's Done , It Works & and it kind on fuel running 10psi Boost is more than enough for street, Tried 25psi and heaps of woe with Pinging.
Stuck it back to 10psi and love it.
Yee Ha
[email protected]
Photos avaible.

 

[Steelo]

Just saw your post so here is my update :
Blow through Turbo TB42 done and dusted!!! Man this thing will peal your ears back, Bring on the kiddies with there HSV's
This thing steps out big time form mid 2nd and pulls like a bus load of school boys there on.
It's Done , It Works & and it kind on fuel running 10psi Boost is more than enough for street, Tried 25psi and heaps of woe with Pinging.
Stuck it back to 10psi and love it.
Yee Ha
[email protected]
Photos avaible.

Pics don't seem to work, any chance of putting some more up of the engine & set-up?
Ta

 

[Snapper Trap]

Trying to add photos, Some things have changed since the photos ie: Inter Cooler is now in the bullbar as I dont go off road and have no need for a winch.