The Wife wants to go faster @ the Dragstrip - Turbo Build

[SUX2BU99]

That's so cool! Blow-through makes total sense. Don't blame GM though for trying draw-through on the very under-whelming turbo V8 Trans Ams. Turbo's and carbs had not been tried too much by the domestics prior to then, save for the turbo V6 Regal and Monte's of the late 70's and then the early 60's Olds Jetfire and Corvair. Speaking of, those Jetfires were pretty cool. Turbo aluminum V8, wastegate, alcohol injection (Turbo Rocket Fluid). Pretty far out there for early 60's.

Blow-throughs can benefit from intercooling and as mentioned, the shortest possible path from the introduction of fuel to the combustion chamber. About the only downside is the carb is postively pressurized, increasing the importance of gasket and orifice sealing.

[eventhorizon66]

Cool project.

But I have always been under the impression that carb'd turbo setups aren't popular because they are rather tricky to tune, as it is difficult to coordinate the fuel curve with the non-linear boost curve of a turbo.  Centrifugal blow-through setups, on the other hand, are extremely popular presumably because of a very linear boost curve.

[SUX2BU99]

You mean centrifugal blowers? They operate very similar to turbo (as opposed to say a roots or screw-type positive displacement blower) by building more boost with more RPM. I suppose a turbo would be more non-linear than say a Vortech blower since it's not belt driven but both are more inherently non-linear than a roots-type blower due to their centrifugal compressors.

[eventhorizon66]

both are more inherently non-linear than a roots-type blower due to their centrifugal compressors.

What I meant was centrifugals build boost with rpm without any need to spool up, making them easier to tune than a turbo.  Once they build boost, yes they do it in a "positive-slope" linear fashion, but the lag period creates a major hicuup in the curve.  Roots build boost in a "constant" linear fashion.  "Positive-slope" linear is what I meant in my previous post.  

[biscuit41]

Correct me if I'm wrong...  I believe that a boost/vacuum dependent fuel pressure regulator is used to increase fuel pressure depending on boost.  It increases fuel pressure depending on the boost pressure of the turbo.  The one that i had used for a fuel injected setup needed a fuel return line.  Not sure how you set it up with a carburetor...

[eventhorizon66]

Yes you would want a boost referenced regulator, but I am talking about the fuel curve that the carb delivers, not proper delivery of fuel to the carb.

[SUX2BU99]

both are more inherently non-linear than a roots-type blower due to their centrifugal compressors.

What I meant was centrifugals build boost with rpm without any need to spool up, making them easier to tune than a turbo.  Once they build boost, yes they do it in a "positive-slope" linear fashion, but the lag period creates a major hicuup in the curve.  Roots build boost in a "constant" linear fashion.  "Positive-slope" linear is what I meant in my previous post.  

lol  "postive-slope linear". Did you make that up? C'mon now.     I kid, I kid.   

[HAULIN IT]

Guys, Yes a boost referenced regulator to raise the fuel pressure as boost comes up is part of the equation. Of coarse there is much more to it with the "fuel curve" as was mentioned.
 People have come up with some pretty unique ideas for this...some include: one injector in the charge tube (with a pressure switch) that sprays at 100% once the engine comes into boost, fuel solenoid/jets from a nitrous kit & the most popular method...modifying the carbs "power enrichment" circut to flow much more fuel than originally designed. Some means of control (boost, co2, air, electric, ect.) seem to be the better working systems.
 I'm sure (as with anything new) there will be quite a learning process.
One BIG advantage for me & others at this point, is that (like this site) many people that have made the in-road are very willing to help.
 I've been building the carb for a couple months (hobbie time has been a minimum due to work, family activities & SNOW removal) with the help of some great guys. Here is a photo of the metering blocks, I paid a fellow (Brent Davis) to do them...He has been a big help to many with blow-through set-ups. I felt that for the money he charged, it was a good plan for my first attempt & also "gives" him a few bucks for something he likes to do, sort of a "Thank You" for being there.
 The power valves are modified & will be controlled by air, the restriction channels opened up conciderably...this allows a more "normal" jet to be used so the engine runs correctly out of boost, among other mods.
 That's all for now, Lorne

   

[eventhorizon66]

Can't wait to see how it works out for you.

[HAULIN IT]

With an hour here & there, I got the carb built! I can't take any credit for the designing/planning of what & how to make the carb work under boost. Brent Davis came up with pressurizing the power valve cavities that originally used vacuum to hold the power valve shut...now the air will push them open. Not much to look at & but let's hope it works!
 You can see in the photos (Red carb cleaner straws) where I drilled through the main body to make "air passages" & where the body is threaded for the external fitting for the air hose. Lorne
 

[84 chevy guy id]

 I built a blow through big block twin turbo setup for my 72 vette three years ago and it is working out good. I still need to do a little more tuning on the carb for off boost fuel economy but its very driveable and a monster with a measly 15 lbs of boost pushed through it. I am running an 8.5 compression 468 motor with a 4l80e trans and 3.08 rear gears. It makes enough power to blow the tires off at anything under 65 mph. Good luck with your project, post some videos when you get it going.

[HAULIN IT]

I got a couple boxes the other day...Somebody forgot to attach them!   Just kidding

 Got a few hours in planning, fitting, ect.

 Moving Along

 Getting Closer!


 Just about done!

 Need to finish the rear tubes when the 45* bends come, trim back the ends & install the collectors & V-bands. More pic's to come, Lorne

[team39763]

Nice looking headers you got there Lorne.

[VileZambonie]

Wait, I thought you were building this for your olds engine??

[84 chevy guy id]

Nice looking headers !! Where did you get all the piping, collectors, v bands, ect from?