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Take a look at this pic, a 1.5ltr twin turbo Ferrari V6 from the 1980s, a championship winning car.



Exhaust ports on the inside of the V like a Ford/Foyt- Interesting

Twin turbos and a HUGE wastegate- Interesting.

Bottom wastegate port attached to turbine housing- VERY interesting.

What do you guys make of that? From logs I've seen, backpressure rises when the wastegate opens too?
 

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I played with something similar on my car running a tiny EVO3 16g turbo (48mm, 42 lbs/min). It ran a 10.31 at 130 mph. I first moved the pressure source from the side of the Tial V44 wastegate gate to the top port, so I could use boost pressure to clamp the WG shut (internal flapper was welded shut). I could run any back pressure I wanted to, up to maxing out the 5 bar sensor at 60 psi with 20 psi boost. Ultimately running back pressure at around 45 psi to a boost pressure of 19 psi at redline gave me that record setting pass. I eventually plumbed the boost controller in between the turbine housing and the wastegate to try lower back pressure values but never got around to running the car like that, I swapped on a 61mm turbo instead for a local race (8.89 at 152 so far). I'll probably get back to this in the fall, I'd like to see a ~10.1 out of that turbo. I may also try it on the 61mm turbo as well or whatever I run next.
 

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Discussion Starter #3
[email protected] on a 16G, jesus!

I'm confused though still, what is the advantage of backpressure controlled gate?

And what about backpressure when the gate opens? Does it rise when the gate opens? Thats what I''ve seen, but tbh not seen many.
 

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The WG opens as back pressure gets up there, not the other way around. I could see how it might look that way though. BP would keep right on rising to unproductive levels if the gate didn't open, as seen in the example I gave above.
 

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So, what would boost pressure do? I'm having back pressure issues now, 15psi boost and 35psi back pressure. If I tried this and got the back pressure to open at say 20psi, what would manifold pressure be? I would think the boost woul be way lower?
 

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I wonder if they used BP to control the gate for a safety control. Make all the boost you can make until X back pressure to keep the head gaskets on and max power before Excessive BP killed the power.
 

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I played with something similar on my car running a tiny EVO3 16g turbo (48mm, 42 lbs/min). It ran a 10.31 at 130 mph. I first moved the pressure source from the side of the Tial V44 wastegate gate to the top port, so I could use boost pressure to clamp the WG shut (internal flapper was welded shut). I could run any back pressure I wanted to, up to maxing out the 5 bar sensor at 60 psi with 20 psi boost. Ultimately running back pressure at around 45 psi to a boost pressure of 19 psi at redline gave me that record setting pass. I eventually plumbed the boost controller in between the turbine housing and the wastegate to try lower back pressure values but never got around to running the car like that, I swapped on a 61mm turbo instead for a local race (8.89 at 152 so far). I'll probably get back to this in the fall, I'd like to see a ~10.1 out of that turbo. I may also try it on the 61mm turbo as well or whatever I run next.
So you could make the same intake boost with different backpressures when the side port on the wastegate was hooked to the turbine housing? Do you think you could have lowered backpressure to 20psi to get it to 1:1 ratio?

Thanks
 

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Nope, there's no magic here. If you reduce back pressure you reduce boost, for a given combination. Where this comes in is when back pressure is rising 10 psi for every 1 psi of boost. ;)
 

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Pressure is pressure. Doesn't matter where it comes from. Kinda like money.
 

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Nope, there's no magic here. If you reduce back pressure you reduce boost, for a given combination. Where this comes in is when back pressure is rising 10 psi for every 1 psi of boost. ;)
Bringing this back up from the dead!

My combo, 421SBC S400-75mm. Car has about 40psi of back pressure (max hold) and makes about 16-17psi and the gauge is very erratic on the intake side. With the wastegate lines off I can make 15 pounds of boost at 3200rpm on the transbrake if I wanted it to.

So it makes boost super quick and gets the turbo moving pretty good. I "think" the high back pressure comes as the turbo just gets driven up in rpm as I go down track. From what I can tell from trans brake tests back pressure to boost pressure stays right at 1:1 up to about 4000rpm and 12-13 psi.

I wonder if moving the waste gate to reference the back pressure at 30 would still have enough exhaust energy from this big engine to maintain 15psi of boost?

And Pete, what is the reasoning on the gate location angle on new white car ya'll are doing?
 

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I have a similar issue with a similar turbo. I tried lowering backpressure and it just lowered boost. I figure that it takes that much pressure on the turbine to move that much air through the compressor. This is why a larger turbine is needed. If it was on a smaller engine it would take more boost to achive the same power. If it took 15 psi on your motor to make say 800 hp and 40 psi backpressure. It may take 40 psi boost to make that same power on a smaller motor making 40 psi backpressure. It is moving the same ammount of air. In other words it take 40 psi to move 800 HP though said turbo weather it be at 15 psi boost or 40 ps boost.

My concern with a larger turbine and housing like the 96mm 1.32 housing is how much it will kill that part throttle power and how easy it comes up on boost. IE I don't want to have to go full throttle to make boost. Still might try it though having a cork in the exhaust like that can't be good for part throttle N/A power. Maybe it will come up into the boosted power easier with less backpressure and larger turbime that puts more leverage on the shaft.... Maybe I think to much LOL.
 

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Unless there is a mismatch between the compressor and turbine sides, getting up to 2 or 3:1 exhaust to intake pressure might be a sign that you're using up the compressor. As you run it to the edge of the map drive pressure goes way up.

Dropping the back pressure to 30 psi might result in a loss of boost, but the car might go faster or at least not lose anything.
 

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It is definitely maxed the compressor wheel! I'm making probably 900rwhp out of this thing on the 421 at 16-17psi. I haven't seen a S400 map, but I'm sure I'm on the very bottom/right of the map!

I have the hot side piping off and am going to redo it, it is leaking in a few spots and am going to go from 2.5 to 3" crossover and with a 3.5" merge from a 3". I'm hoping this helps a little as well.
 

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I have the hot side piping off and am going to redo it, it is leaking in a few spots and am going to go from 2.5 to 3" crossover and with a 3.5" merge from a 3". I'm hoping this helps a little as well.
You will find that this is a waste of time....does nothing to help the problem.

What turbine wheel/housing do you have?
 

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It is definitely maxed the compressor wheel! I'm making probably 900rwhp out of this thing on the 421 at 16-17psi. I haven't seen a S400 map, but I'm sure I'm on the very bottom/right of the map!
Yup, that makes sense. IIRC at that PR the map ends at around 90 lbs/min. I was at the same point on my compound turbo setup with it.
 

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Done told you how to fix this a dozen times. 3 inch stroke crank.

Hehehe
 

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IMO best way to fix it:

Put the BW 80mm compressor wheel with a John Deere cover on it and clip the turbine wheel a few degrees.

You will pick up around 300 HP and have less BP and much lower IATs. You are over-speeding the 75 based on your earlier statements.

Spool time will not be affected enough to notice.

This is from personal experience on a DTS engine dyno.... not pontificating like others here.

Good luck to you.
 

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Glenn. He cant run the 80. 76mm inducer limit in his class.
 
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