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Location:
Montrose, VIC
Registered:
May 2002
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Turbo/blow through carb
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Tue, 20 January 2004 06:56
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Hey all
I've got an upcoming project of turbo'ing an Alfa engine. The guy that owns it insists (much to my VIOLENT PROTEST!!!) on keeping the carbs - DCOE 40 Webers. I understand the basics, just wondering if anyone has got specific experience with making these mongrels work with boost? Thanks guys! 
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Location:
Brisbane
Registered:
February 2003
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Re: Turbo/blow through carb
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Tue, 20 January 2004 10:20
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you'll really want a carb made for turbo blow thru - otherwise you have to seal the bushes around the butterflys, fill the floats with foam to top them crushing, work out how to block off all the vents without confusing the crap out of the carbi, etc ...
can you get an EFI setup off a similar series motor?
or use designed-for-blow-thru carb - in an earlier thread, someone said the mazda made one?
or stick the webber infront of the turbo - means you can't really run an intercooler (imagine the results of a backfire) but at least the carbi's will work as designed and will run rich enough under boost.
or buy some new hardware from speedtechnology or similar who make TBs that fit DCOE manifolds.
do a static test for the owner, get a carbi full of fuel bolted to a table, attach air line to hose from your vacuum cleaner and then duct-tape one end to the carbi - turn on air and watch fuel spray everywhere, light petrol for show and suggest to owner that's what'll happen under the bonnet...
otherwise good luck ... 
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Location:
Montrose, VIC
Registered:
May 2002
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Re: Turbo/blow through carb
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Tue, 20 January 2004 12:26
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Yeah, I understand the basics of it, and for now the carbs must stay... There's NO way I'm doing anything suck through, and the carbs are already there. There are factory EFI parts available, but I have to set up the carbs and convince him first that's all  Besides, I've always bagged out carbied turbos based on seeing OTHERS cars, I want to play with one myself so I can badmouth them with authority 
Surely someone's done this!
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Location:
Brisbane
Registered:
February 2003
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Location:
Montrose, VIC
Registered:
May 2002
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Re: Turbo/blow through carb
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Wed, 21 January 2004 11:41
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Well, suck through is not an option:
1. The turbo isn't suitable
2. It's gonna be intercooled
3. The ALFA (not fiat! hah!) already has twin sidedraft (40 DCOE) webers, and they're staying right where they are. Going to be making up a reasonable looking plenum, and I've already got the fuel system (pressure reg, pump, etc.) sorted - you don't need a rising rate reg, just a 'normal' one set to 6 psi above plenum pressure is fine! As far as I can see, all I need to do is pressurise the tube going to the float chamber, and also run a hose to the diaphragm on the bottom of the carb, then spend hours on the dyno with a box of jets trying to get the mongrel thing to run. Just looking to see if I've missed anything, and if any other poor fool(!) here has done this 
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Location:
Brisbane
Registered:
February 2003
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Re: Turbo/blow through carb
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Wed, 21 January 2004 14:00
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| mrshin wrote on Wed, 21 January 2004 21:41 |
<snip>
3. The ALFA (not fiat! hah!) already has twin sidedraft (40 DCOE) webers, and they're staying right where they are. Going to be making up a reasonable looking plenum, and I've already got the fuel system (pressure reg, pump, etc.) sorted - you don't need a rising rate reg, just a 'normal' one set to 6 psi above plenum pressure is fine! As far as I can see, all I need to do is pressurise the tube going to the float chamber, and also run a hose to the diaphragm on the bottom of the carb, then spend hours on the dyno with a box of jets trying to get the mongrel thing to run. Just looking to see if I've missed anything, and if any other poor fool(!) here has done this
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fiat/alfa/schmalfa .. they're all landfill for olive tree groves.. 
seriously now...
accel enrichment (can't quite remember how the weber does this) may need serious work?
don't forget the blow-off valve?
timing? is the motor decompressed? if so then you'll need more advance than standard at idle, but less total mechanical advance (otherwise you'll detonate from excessive advance on boost) - you could try to find a vacuum advance unit from an older turbo dizzi that responds to both vacuum and boost.
if motor is at factory compression, you;'ll definately need some kind of boost retard - and probably a modified curve as factory mechanical and vacuum advance curves will result in pinging/detonation. plus see prev para about a dizzi.
water injection - helpful in controling pinging/detonation?
a fire extinguisher for when the gaskets in the webers give up from the pressure?
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Location:
tallahassee FL usOFa
Registered:
May 2002
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Re: Turbo/blow through carb
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Wed, 21 January 2004 17:41
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Lotus did this(blow through) 20 years ago with one of theirs, and the factory/engineers said they would NEVER attempt it again.
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Location:
Montrose, VIC
Registered:
May 2002
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Re: Turbo/blow through carb
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Thu, 22 January 2004 10:49
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We're changing the engine to a recent rebuild one, and it's only 9:1 compression. Going to give the dizzy a recurve, as well as fit it with a vac advance/pressure retard unit, and set it up on the dyno. Plus it's going to be intercooled, blow off valve, etc. - all the needed crap.
Italian cars landfill... Well, yeah I'm not exactly into them myself, although they DO have some good points, they're just buggers to work on...
I have heard of the Lotus effort, and I know they weren't brilliant - hell I'm not exactly big on this carb/turbo idea, but I'm at least willing to give it a go for the owner's sake. And the car already has an extinguisher
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Location:
Finland
Registered:
November 2002
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Re: Turbo/blow through carb
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Thu, 22 January 2004 11:10
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For some odd reason in Finland here are quite many cars going around with turbo/carb setups and I mean blow through setups. Propably some weird relic from the eighties.
But see if this helps:
http://www.geocities.com/jharkola/1380turbo4.html
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Location:
Montrose, VIC
Registered:
May 2002
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Re: Turbo/blow through carb
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Thu, 22 January 2004 13:13
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Yup, that's the kind of setup I'm talking about. Also, I'm tending to get the idea that Dellorto carbs might be a better choice? IE better sealing around the throttles etc.? I have the option of using them instead of Webers, should I choose to. Anyone got much to say on this??? 
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Location:
Brisbane
Registered:
May 2002
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Re: Turbo/blow through carb
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Fri, 23 January 2004 01:00
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Modifying carbs for blow-through applications is a PITA. If it was me I'd be enclosing the carbs in a sealed box; much easier and neater!
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Location:
Newcastle, Hunter Valley
Registered:
January 2004
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Re: Turbo/blow through carb
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Fri, 23 January 2004 02:07
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what alfa is this? 33, 75, gtv?
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Location:
Montrose, VIC
Registered:
May 2002
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Re: Turbo/blow through carb
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Fri, 23 January 2004 06:57
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Alfetta with the 2.0l twin cam engine already sporting dellorto's
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Location:
Newcastle, Hunter Valley
Registered:
January 2004
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Re: Turbo/blow through carb
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Fri, 23 January 2004 13:10
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does anyone know if the webers on a flatfour alfa33 can be used as sid drafts? they are mounted like down drafts yet they have the dcoe pattern
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Location:
Montrose, VIC
Registered:
May 2002
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Re: Turbo/blow through carb
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Fri, 23 January 2004 13:15
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They'd be IDA webers, yeah? In which case, no, they won't like working sideways! Just take a look at the float and think about how it's gonna work the wrong way up. Whats the plan, anyway?
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Location:
Madrid - Spain
Registered:
August 2002
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Re: Turbo/blow through carb
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Sat, 24 January 2004 09:05
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Many people in Europe remove efi and install webber/dellorto type carbies, namely because they dan't have the same aftermarket efi gear we have here. Think about it, try getting big power gains using only the standard ECU, no affordable aftermarkey computers and no Japanese interceptor type computers.
That doesn't mean that it is the better way to go. They use carbies because they work well on N/A engines without the technology that they can't get easily. For a forced induction car in Australia, your crazy not to use the technology available here.
There are plenty of efi throttle bodies available that will bolt up to the webber manifold and do the job better, more efficiently and possibly cheaper in the long run. I have seen a Valiant 265 engine with these T/B's on it. It ran absolutly huge cams in it, bigger than the R/T race engines, yet was easy to drive and had heaps more midrange power.
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Location:
Finland
Registered:
November 2002
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Re: Turbo/blow through carb
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Sat, 24 January 2004 11:35
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| Quote: |
Many people in Europe remove efi and install webber/dellorto type carbies, namely because they dan't have the same aftermarket efi gear we have here. Think about it, try getting big power gains using only the standard ECU, no affordable aftermarkey computers and no Japanese interceptor type computers.
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So true! 
In Finland we have only one aftermarket computer maker and that's only maker in Europe that I know of, not saying that there aint others. Anyway, it's called Hestec and it's VERY good and popular in racing circles. It's also $$$$.
Here is also big markets for Dellortos and Webers, both European.
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Location:
Sydney
Registered:
February 2003
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Re: Turbo/blow through carb
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Sat, 24 January 2004 12:18
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damn i love alfetta's, they are so sexy, even if 99.99% of them are 99.99% rust
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Location:
Montrose, VIC
Registered:
May 2002
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Re: Turbo/blow through carb
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Sat, 24 January 2004 13:04
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Okay peoples, I KNOW that EFI is the way to go, believe me I've been jamming this down people's throats for years... Thing is, it just isn't an option in this case, and besides, I'm keen to try this blow through carb thing Surely SOMEONE here has set one up at some stage and can share a few pointers...??
Alfetta's sexy? All a matter of personal opinion, really
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Location:
Montrose, VIC
Registered:
May 2002
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Re: Turbo/blow through carb
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Sun, 25 January 2004 13:10
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c'mon peoples...
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Location:
Brisbane
Registered:
May 2002
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Re: Turbo/blow through carb
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Sun, 25 January 2004 13:24
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Dude, I think if anyone knew anything they would have said something by now. Most people here are smart enough to use EFI!
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Location:
Madrid - Spain
Registered:
August 2002
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Re: Turbo/blow through carb
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Mon, 26 January 2004 10:31
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The only thing I can help you with is that Carbies are pretty sensative to fuel pressure and that boost pressure will quickly have the fuel going the wrong way through the jets.
I know there have been some successful turbo carby cars done,so it deffinitly aint impossible, It will take some work to get it right though.
Whats the guys objection with changing to efi??
Maybe it might be worth talking to Webber. Chances are they may have already solved most of your problems and can provide the required equipment.
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Toymods Vice President
Location:
Sydney
Registered:
May 2002
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Re: Turbo/blow through carb
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Tue, 27 January 2004 04:12
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Lotus ran blow through Dellorto's with a water to air charge cooler in earlier Esprit's. They were sealed from the factory to suit boost so if you could find some of these I'd assume you'd be off to a good start.
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