Blow Through Carby Set Ups...Disadvantages?

[astro boy]

so i'm thinking of going the blow through carby route on my a15 project.


the biggest reason i want to go this way is for cost, i can pick up a cheap manifold, FMIC and a carby with hat.

the rest is pretty cheap and straight forward i guess?

just asking advice and opinions from people who have had experiance with them.

my main concerns are engine temps, reliability, how they come onto boost, how the carby responds and how they go when off boost??

the motor itself is built tuff and ready for it and i have a T25 off a ca18 which i plan to use..thoughts?


any advice welcome.

[td42gq]

I had a Gemini once (that's probably a nasty word around here but anyway) It had a modified g200 (2 litre) log style manifold and a turbo of similiar sort of size that you are refering to. It had a blow through style carby of some sort off a renault or peugeot (can't remember what model off the top of my head) and it went extremely well.

I did approx 50,000km with that setup and found it was no problems once it was setup initially. The biggest problem I had was when I was orginally setting it up I wanted to run 10psi+ but during the setup stage I found with the biggest available jets for that type of carby I could only get about 8psi out of it before it became to lean.

I guess where I'm going with this is try and choose a carby that is quite common and uses the same style jets as other models that require more fuel flow. There were options I could have gone down to overcome jet problems such as resizing or custom made but it all became to hard so I just stuck with what I had. Other than that it was a good setup reliable and only very minimal tune changes where required to keep it running well.

I hope that helps
Aaron

[NME308]

Hi There,

I run a 650 double pumper holley carby in blow through format on my 3TC with T25G S14 ball bearing turbo and somewhere between 15 and 20lbs boost depending on whatever lights my fancy on the day.

It is my daily transport and I have no issues with engine temps (even when it still had the shagged original radiator) and it is pleasant mannered to drive. With a bit of tuning it now comes on boost almost seamlessly. Off boost driving is totally fine and achieves 9.4L/100km fuel consumption on the highway. Down the quarter I flogged my mates BA GT falcon last weekend by 1.1 seconds and was a poofteenth quicker than another mate with a tuned etc LS1 powered VU commodore ute all on 175/13inch street tires.

My point here is you are on the right track as it is all doable DIRT CHEAP and can be reliable - I forgot to mention I did the 1200km trip to Dubbo on the Easter long weekend and flogged it in the motoring events before driving the same 1200km home without a hickup!

I love to see old skool stuff blowing people's minds i.e. hardly anyone seems to know you can sling a turbo on an engine without using an ECU!

Cheers,
Jason

[astro boy]

cheers lads.

it definitely seems like a worth while option as i wish to keep my ride as period correct as possible.
i'm surprised more people aren't running these setups. it's so piss easy.

i'll be running a twin barrel down draft webber jetted for a 2L, with my motor being only 1500cc in displacement i think this should be sweet, there is also room to move with this particular carby as well.
unfortunately i'll have to use the standard inlet manifold but meh...cheap.
the obligatory VL fuel pump, electronic ignition with a strong spark and all will be good.

thanks for the feedback.

[astro boy]

oh and whats a cheap option for piping??

[td42gq]

Personally I would use alloy, easy to work with and fairly cheap to purchase. If you have a Tig welder or know someone who does than it is no real problem. If you don't have a Tig than you could also use stainless steel, tends to be slightly more expensive and harder to work with imoa but does the job and is easier to polish if you want that sort of look.

If you want to run alloy and can't weld it, Richard at A.R.E. use to do welds for $30 each. Not sure if that's still the case as I haven't had to pay to have them done for awhile. He is at Brendale (Brisbane) not sure exactly where in Qld you are but that may be close for you. One thing to consider though is his price is based on nice neat cuts and ready to go. He does excellent work but it can be expensive if you pay him to do everything.

You can use mild steel it is very cheap and will do the job but you will have to have it coated - HPC or something similiar otherwise it will rust so personally I would go with something else

Aaron

[NME308]

oh and whats a cheap option for piping??

I am using mild steel exhaust tube for my intake piping and even though I spray methanol pre turbo I have no signs of rust at all.

Cheap and for someone like me with limited exotic welding experience - effective!

Cheers,
Jason

[andrew_mx83]

i believe the weber will need some modifications if you wish to run it blow through.

OR you can build a sealed box the carby sits in, and pressurise the whole box with teh boost ala lotus esprit turbo.

["Z" UTE]

I
I guess where I'm going with this is try and choose a carby that is quite common and uses the same style jets as other models that require more fuel flow. There were options I could have gone down to overcome jet problems such as resizing or custom made but it all became to hard so I just stuck with what I had. Other than that it was a good setup reliable and only very minimal tune changes where required to keep it running well.

I hope that helps
Aaron

Carby is ultra important, I have seen some total stuff ups with guys using blo thru. Some carbies will just not take boost pressure, Get that right and jetted correctly, and it should be sweet. Water methanol (even Metho) injection to cool the air post compression, and all will be good.


cheers Chuck

[Hurricane]

what carby are u thinkin or runnin? holley or webers?

suck through is by far the cheapest setup ive done over blowthrough or efi.

dan.

[wrench]

Yeah i have to agree with the suck through idea, it seems to work easier and a lil better. I have seen people have problems with blow throught setups with carbies. I done a suck through SC14 setup on a datsun 1200, used a 1 3/4 inch SU carb, worked great. Yeah i understand the blower doesn't create the same heat as a turbo. But if you are going to do a suck through turbo setup its a good idea not to use a intercooler as you will get fuel welling up in it as it gets too cool, methanol idea is much better. I'm making at present a suck through turbo setup for one of my old XE falcons, using a old T03 off my old MX10 soarer i had and a 34ADM weber 2 barrel off a 4.1 falcon on my 3.3 engine. Even with 7psi it should light a fire under its arse, coz stocko it just doesn't cut it lol.

[Hurricane]

im my eyes suck through has/is cheaper to setup and do.
but i would rather run a blow through holley or webers,
u can run a cooler then, dont have pressurized fuel in the piping that would see boost, looks better, u pritty much just need to run solid plactic floats and run more fuel pressure in the carby when on boost, so say 15psi fuel for 10 - 12psi boost. and make sure the seals and gaskets in the carbys are ok.


i think there is a 600 holley marine carby that is good to put boost straight into it with no mods apart for jetting. that would be my pick if its not to pricey.

also i just use exhaust piping for the boost piping, and tig or oxy it together, remember u dont want any leaks as it is both the fuel/air mix that will leak out.

dan.

[ToyTA22]

As andrew mx83 said best bet is encase carby in box and use a low pressure manifold sensing fuel reg. We used this system on hot rods using a Mustang/paxton style blower a number of years ago, which is what was used on about 1970 Ford Mustangs. Fuel pressure will need to vary as boost increases to compensate for pressure in carby throat. It isn't that difficult.
A good book which covers that idea Turbochargers by Hugh McInnes. Think spellings correct, I had a copy but it grew legs and ran away with somebody else otherwise would lend it to you.
All the best & hope you get it working.

[astro boy]

cheers for all the advice, i have been slowed down by needing to upgrade the fuel lines, almost complete though. i have a rising rate fuel reg to go on.. havent figured out pressures yet but the boost will be kept fairly low, certainly nothing over 12psi, most likely not over 10. i'll have to just work out the fuel pressure in tuning.

i have a nice pressurised hat to suit my webber but alas it needs beefing up. i'm thinking thin copper gaskets?? or do you think i should just use good ol gasket paper??
not quite sure how to hold the pressure.

i'v also made up the pipe from turbo to cooler, tapped in some turbo oil and water lines.
i think until i get it running properly i'll just use some hose from cooler to hat, dodgy i know but my mate who made up the piping has gone away for 6 wks... i just can't wait that long.

exhaust also needs completing, it currently just dumos behind the firewall haha.

[Hurricane]

so ur goin with a blow through weber, what type are u using?

is the hat ur talklin about just one that sits ontop of the carby?
if so all ive every used is paper gaskets with no proplems.

as for runnin hose from the cooler to carby hat, it should be fine as its only air pressure/vacum it seeing, even radiator hose would work if it really came down to it