Jump to content
HybridZ

Blow through turbo, again...


Guest JAMIE T

Recommended Posts

One thing that I have found in my research is that you have to have more air pressure in the floats than in carbs. Here is a picture of my box and vent tubing for the floats. The HSK intake has baffels to increase the float pressure.

 

These are SK Racing carbs. My set up is using a supercharger in lieu of a trubo.

 

Carb_Box_1.JPG

 

I figure that I will loose about 1 PSI of boost through the intercooler and piping. I will be running a stock Subaru WRX intercooler, it should take care of 10 psi of boost. So will have to bleed off some of the excess pressure to the floats.

Link to comment
Share on other sites

  • Replies 82
  • Created
  • Last Reply

Top Posters In This Topic

I had come to the same conclusion when I was drawing up the idea a few years ago and planned to utilize the stock airflow meter(not electrically connected) as a one-way valve just after the intercooler discharge from the turbine so turbine air will only flow one-way and the supercharger discharge would not surge the turbine due to the one way flow. When the turbine discharge builds enough to open the flap on the air flow meter, they will both provide boost.

Link to comment
Share on other sites

  • 1 year later...
I will also be utilizing the blow through carburating setup on my 1979 280zx L28 super/turbo project as soon as my parts arrive. I am going the Demon 650cfm blow through route with a clifford 4-barrel intake manifold. I will utilize a 2 inch carb spacer with a 3 inch tall carb hat with two 2 inch inlets. One for the TO4e turbine discharge, one for the paxton novi 1000 supercharger.

 

I am currently running 280zx turbo factory injection with RB26DETT 440cc low impedence injectors with a n/a air flow meter which I installed on the turbine discharge side just prior to the manifold inlet(this allows for the flapper style air flow meter to open upon boost instead of opening depending on air intake demand). Also have a bosch boost sensing fuel pressure regulator to up the fuel pressure upon every pound of boost. That way my turbine intake is clear for the custom cold air intake. ARP head bolts are used to hold the P90 head on with the 1.5 mm steel head gasket direct from Japan. Not fond of the stock fuel injection manifold, looking forward to the 4-barrel blow through Demon set-up. More to follow when I get it all on-line...

 

Well here is the latest on project 79 ZX that has been on the back burner for sometime due to job hunting in this great economy.... Finally found a job, home with a garage (my priority in home purchase) and can now continue my Frankenstein project Z (hence the stitches you may see up close) Enclosed are the latest pictures over the weekend mocking up the clifford manifold, T04e, Demon, new head and carb hat. Now that most of the mockup is done, I will take the intake manifold off again, relocate the internal wastegate on the T04e since the bracket holding it was contacting the bottom of the intake manifold in its current location. Should have a test fire and if that goes well, a test and tune at Top Gun Raceway in Fallon sometime September or October if all tests are a go. Depending on how this works out will determine if I will still add the paxton supercharger in tandum to the mix. After all, this car is just for fun and by no means a daily driver.

bt turbo z_thumb.jpg

bt turbo z1_thumb.jpg

bt turbo z2_thumb.jpg

bt turbo z3_thumb.jpg

bt turboz4_thumb.jpg

dodge ram 280zx and mustang in garage_thumb.jpg

Link to comment
Share on other sites

  • 1 month later...

Why not put the whole carb set-up in a custom built plenum so that pressure is equalized?

That's how Maserati did it (but with only one, progressive, carb). The priciple is the same: fewer air pressure differential problems; i.e., boost carbs and all as an environment...You would want noncollapsible floats here...

 

I have a later model Biturbo with efi so I can't say from personal experience how the blow-through in a box works on the road (my fi Biturbo hauls a**, though)

DAW

Link to comment
Share on other sites

Corky Bell would agree with you Tony, quote from Maximum Boost, "Are blow-through carb systems technically and functionally workable? Yes. For some heavy-hitting evidence, drive a Lotus Turbo Esprit or a Maserati Bi-Turbo."

Link to comment
Share on other sites

Well finally started the Demon blow through set up, did some adjustments to the floats, primary/secondary idle screws and air fuel mixture screws, holds an idle well. Did about 10 power test launches in the drive way in first gear and the rear tires that would get a slight chirp with the past fuel injection set up went up in smoke until I ran out of driveway. Figured after that, well its road test time. Got out on one of my county roads and gave it a mild launch at 1500 rpm then slammed the pedal to wide open throttle. Shifted to second gear at 7000 rpm and then the engine surged, suspected vapor lock. Stopped car, looked at the float windows and as I suspected from the engine reaction they were empty, no fuel. Back to the garage again adjusted the fuel pressure regulator to the maximum pressure setting, tried the same drive again and vapor lock a second after shifting to second gear at W.O.T. Back to the garage again, laid a bunch more burn outs in first gear to cover the driveway with multiple black streaks to celebrate that its alive after several months of planning. I ordered a much larger carburator fuel pump that will deliver what this demon needs to feed the Frankenstein. The bad news, didn't get it tuned in time for the last Top Gun drag race of the year. The good news is it runs real strong until it runs out of fuel. Another test drive to follow installation of the higher volume fuel pump.

Link to comment
Share on other sites

YOU NEED A EFI PUMP! I have done many of these gotta have it. aeromotive 13301 is the best bang for the buck reg. I have 4 of these under my belt in the Rotary world which is alot harder to do than a boinger motor. Dont piss with anything but a efi pump. You will run dry either in 2nd or the top of third and ping bang boom! its why these setups get bad names.

 

 

 

P1000711.jpg

 

 

th_movie_01_01.jpg

Link to comment
Share on other sites

"Shifted to second gear at 7000 rpm and then the engine surged, suspected vapor lock. Stopped car, looked at the float windows and as I suspected from the engine reaction they were empty, no fuel. Back to the garage again adjusted the fuel pressure regulator to the maximum pressure setting, tried the same drive again and vapor lock a second after shifting to second gear at W.O.T."

 

I agree with yerbetten! You need something that will produce at least 3.5 psi more than the boost level you intend to run. I know a kid in AZ that was going through L28ET's like there was no tomorrow runing a Holley Red...everytime he got to 12psi of boost, BOOM the thing ran lean and detonated to death!

 

Holly only produces 15psi at best conditions! HE was overpowering the fuel pump with boost and the air was going backwards down the fuel line!

 

This is the same scenario with yours. If you look at the Lotus Esprit Photo I posted, you will see in the lower right hand corner a small pressure regulator, that is what you need. It will reference boost pressure and keep fuel pressure a set delta-p above it to prevent gradual running lean as boost comes on...

 

This was a very common occurance in the VW world decades ago---there was a misconception that you couldn't run boost more than 2-3 psi because 'the fuel pump won't keep up'---wrong. They are sealed on the VW, and you can vent boost to the lower chamber of the fuel pump to make the mechanical unit boost regulated to 3.5 psi over boost pressure on them, no problem! But if you don't they only make aroudn 5psi terminally and once you hit 2-3 psi you start running lean. Do it hard run style and you blow air into the tank! (Or at least stop it from entering the carb at all as the pump can't overcome the air pressure!)

 

YOU GOT LUCKY THIS FAR! IMO you're running on borrowed time, runing dry on a turbo causes exactly what yerbetten stated: "ping bang boom!"

 

That's just about all the warning you will get one of these times. Could be the next time, the time after, but eventually it WILL happen if you don't get a pressure and flow capable pump. Most carb rated pumps are only good to 9-12 psi because they are terminally rated to produce 12-15psi. EFI pumps are great because they're everywhere flow like crazy at 20 psi, and are quieter than most carb pumps. Hell, a stock N/A pump works GREAT! (Cheap, and readily available, too!)

Link to comment
Share on other sites

Take it from Tony and myself get the efi pump. Dont listen to books or others who feed the rumor mill it has to be done. Nothing in this world is harder to tune than a stock nikki carb on 15 psi boost on a rotary engine. I did it i nabbed 260 rwhp on a 2,600 lb car. With a stock fc turbo. With the twin scroll actuator in place. I had full boost at 1.5rpms traction wtf was that till mid 3rd. It also got 4 mpg on the boost :) and launched 4 foot fireballs on decel i love rotaries for every green piece douche there is me driving a rotary :P

 

I also hope to god that dizzy is locked! IF NOT LOCK IT NOW! FULL OPEN! i have seen to many tards lock them closed and if the weld breaks the dizzy jump's 17 degrees 0_0

Link to comment
Share on other sites

Take it from Tony and myself get the efi pump. Dont listen to books or others who feed the rumor mill it has to be done. Nothing in this world is harder to tune than a stock nikki carb on 15 psi boost on a rotary engine. I did it i nabbed 260 rwhp on a 2,600 lb car. With a stock fc turbo. With the twin scroll actuator in place. I had full boost at 1.5rpms traction wtf was that till mid 3rd. It also got 4 mpg on the boost :) and launched 4 foot fireballs on decel i love rotaries for every green piece douche there is me driving a rotary :P

 

I also hope to god that dizzy is locked! IF NOT LOCK IT NOW! FULL OPEN! i have seen to many tards lock them closed and if the weld breaks the dizzy jump's 17 degrees 0_0

 

I agree, that's kinda what I was getting at.

Link to comment
Share on other sites

Thanks for the advice, I was very fortunate that the lean condition from the vapor lock didn't take my engine out. I can attest some of that to the cold 9 heat range ngk iridium spark plugs and 110 octane race gas. I currently have a bosch boost sensing fpr however, it cannot do its job without a pump that puts out enough pressure for it to regulate at boost. I had originally run the factory efi pump dialed down with the regulator however, it gave out during my first start attempt a few weeks ago. If the fuel pump I have already ordered does not supply enough fuel pressure, an efi pump will the next pump ordered and installed. It can always be dialed down with the regulator and the excess sent back to the return line.

Link to comment
Share on other sites

Good point on the distributor. I cut my plate to allow reverse rotation so underboost the breaker plate moved backwards and retarded timing. I think I was set at 24 total under 10psi of boost. That was pretty agressive, I ended up dialing it back to 18 and could run on normal gas then.

 

I got 5mpg on boost as well...17 in daily commuter duty though. Not bad for as heavy a foot as I have.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...