BOTLFED

Feel free to add anything or correct me if I'm wrong.. Hopefully this will be helpfull, correct and added to the sticky turbo stuff thread, if helpfull and correct... ha ha...

The first thing on the list was to get rid of the chock horn that would hurt the air distribution over the top of the carb when using the bonnett.



I used my 14" chop saw (overkill), mini grinder, die grinder and file to get it some-what decent..





Next was to plug the choke linkage hole that would allow boost to exit from the carb.



I used a small screw and some JB Weld to plug the hole.. It shouldn't come out, ever..



Now, onto the solid floats.. Most fuel bowl floats are hollow and can/will collapse under the added pressure inside the fuel bowl.. Just think, for every PSI of boost the turbos create, that much boost has to be ADDED on top of the current fuel pressure.. For example, my mechanical pump runs at 8PSI, on 10PSI of boost, the pump puts out 18PSI of fuel pressure to keep the turbos from pushing the fuel out of the carburator.



You can see that the floats were cut a bit on the bottom.. This was done so the jet extensions wouldn't interfere with the travel of the float.



Although the jet extensions are NOT neccissary for a blow through turbo setup, I believe they are a great help.. Even on N/A cars.. When your car is accelerating, the fuel in the rear bowl is forced away from the jets, so the extenders make sure that there is always fuel available to the jets.

Lastly, with the addition of extra air being brought into the system (ie, the turbos), we must add an increased amount of gas. Now, there are a couple of ways to do this, one is to put larger fuel jets into the primaries and secondaries, or to add a fuel injector somewhere in the pressure side of the turbo system that activates at 100% duty cycle when a certain PSI is reached.

Now, I've chosen to replace the jets in the carburator as opposed to adding the injector because it's a lot more work and I'm not real concerned with fuel economy or street manners. The jets I chose were 85's for the primaries and 95's for the secondaries.. I'd rather have the motor run really rich than too lean.

Here she is, all back together.. You can also see my WOT switch for my nitrous kit.. I don't think I'll need to hook it back up, but you never know I guess..



One other note I guess I would like to make, would be the throttle shafts can sometimes leak air/fuel under certain conditions.. These conditions all depend on the amount of PSI you are running and the state of your throttle shafts.. On a relativley tight set of shafts, you can probalby get away with 15+/- PSI without any problems.. There are a couple ways to avoid this.. One is to completely box in the carb and the other is to pressurize the throttle shafts.. I won't go into them, but they're out there, you just have to search..

Cheers!

Twin_Turbo

iTrader: (25)

Nice work

It may not be necessary but if you have fuel/air blowing out psat the throttle shaft you might want to consider grinding a small grove on the shaft and drilling the housing for a small hole so that it conencts to thre pressure, that way the fuel can't be blown past the shaft and out of the carb.

Guido

I'll leave this one for a couple days to get some feedback before I sticky it with the turbo post.

A suggestion. Submit this to the webmasters to make it a tech article. It would be really helpful in case someone cones along looking for the information!!

Greasemonkey

Nice write up. Almost makes me wanna dump all this TPI stuff and put a carb back on it. Almost.
Also, FWIW I'd planned on trying to do an update for the turbo sticky this weekend, so if anyone has any good links to anything turbo related PM me and I'll put them in.

Jester

No offense but that stuff isn't really worthy of a tech article. Chopping off the choke tower and changing floats is described in every one of the 1001 Holley books out there, even just for NA purposes.

If you really want to make your info useful you need to go into more detail. Describe and diagram at least one or two of the ways to pressurize the shafts or make an enclosure. Alot of blowthrough guys end up messing with the PVR's too...should go into that.

TwnTrboZ28

What about adjusting your air bleeds? I know that if you make them smaller, you will have a richer mixture throughout the rpm band. I have heard that piano wire would work very well for this.
I have not personally tested this, but will in the near future.

bhaas

We also need one for an Edelbrock Carb. No one ever seems to use those in blowthru setups. So far mines working good. Still goes lean though. But I got bigger jets to put in today so we'll see how that goes. When I get it right I'll post what I had to do and maybe add both articles together. That way people have a choice.

Brad...

Apeiron

Do they have solid floats for Edelbrocks?

bhaas

I don't know for sure but I think (maybe) they make some for marine applications. I haven't got to the point of needing them but when I get this straightened out I'll find a source for them and put it in my tech article.

Brad...

BOTLFED

Jester: No offense taken... The reason I wrote this the way I did, was because this was exactly the info I wanted to find when I was researching my blowthru project... I hadn't planned on it being a tech article, just a link inside of the sticky "turbo stuff" thread...

I guess I should have stated that this article was a list of the bare minimum mods required to start and run a blow through system.. Maybe if it had in-depth details on tuning various aspects of the carb, then it could be worthy of a tech article, but as it stands now, I would be just as happy if it was part of the "turbo stuff" thread.

My friends and I are planning on renting the dyno for the day in the spring, so maybe after that and a few trips to the races, I'll be able to write a usefull tuning guide for a blow thru application, but until then, this is all I have..

Cheers!

Apeiron

That's kind of an interesting question then, how much boost can you run before you risk collapsing a brass float?

bhaas

Between 15 and 22 psi somewhere in there.

Brad...

BOTLFED

Yea, that sounds reasonable.. We installed a brand new holley blue on my friends mustang that was faulty, which caused 17psi of fuel to hit the carb...

None of the non-return style holley regs would work with it.. I had to dissassemble the carb and bend the float arms back into place and I could see that the floats were starting to collapse..

It wasn't too bad, but bad enough that if we had of run the pump for more than a couple seconds that it would have caused way more damage...

Cheers!

bhaas

BOTLFED, we're talking about boost, not fuel pressure. I'll bet that carb didn't like that 17 psi though. Fuel everywhere. Well I went out for another test drive. Noticed gas was leaking from the halfass hose and hoseclamp trick so I went and got some -an fittings for the stock fuel lines I'm using, that easy task turned into a nightmare and now it's pouring down and rain. WTF????? Now I have to wait. Got a better check valve from the junkyard. Lots of those on Fords. Even got me a rail of fuel injectors, but the injectors just push in. Not sure if I'll be able to use them. They came off a Ford Escort or Fiesta, couldn't find any turbo cars and those were just laying there so I got them. The numbers on the injectors are FO3E-A2B if that means anything to anyone.

Brad...

bhaas

Went out in the rain anyway. Almost T Boned some *******. Jerkoff pulled right out in front of me and stopped. He/she could have made the left turn they wanted. I locked 'em up turned the wheels let off and turned right. Didn't even get sideways and I wasn't speeding, going about 35 mph. Anyway, that was a close one. The checkvalves I got at the junkyard work great. I had to use 2 of them cause with just one, the pump had no breather. I was at 12 PSI. Good thing I got two of them and one still had tons of hoses and T's hooked to it. Good thing, cause I needed to T in one more. So, now when I'm not in boost, it can breath through the one and under boost it closes as it sees pressure. I is happy. I did get into a little boost and the fuel psi was going up like it should and I wasn't going lean. I won't know for sure till I can get on some dry pavement and all the *******s are inside. The checkvalves I got hooked up look silly right now, but I'll clean that up now that I know it works.

Brad...

BOTLFED

Bhaas, pressure is pressure

Good to hear you got it working right.. I get to take mine for a blast tomorrow... It's supposed to be +4 tomorrow.. Kinda wierd since it was -30 a couple days ago..

Cheers!

bhaas

Wow +4 Nice and toasty I might get to the track Sunday (weather permitting) they said. Opens at 8am. If it ain't raining, I'm there.

Brad...

BOTLFED

That's pretty sweet man! What are you planning to run for tires?

Cheers!

bhaas

My tires are crap. Cheap Les Scwab tires. I also need to put my 9" rear in to. But that's not gonna happen before Sunday though. I have to work today and tomorrow. I'll be happy with 12 secs. for now. Still got some work to do yet. It'll be fun.

Brad...