@underpsi68 @bbi_turbos

What turbo do you think would be perfect for a Ford 4.6 liter DOHC studded b-heads with stock cams with a fully forged built engine 8.75:1 compression running boost controlled at 16psi under high load operation on 93oct fuel?

 

How much HP are you wanting and is this a race only or street/strip? I'm guessing if you're limiting it to 93oct it's a street car.

ks

 

650 hp to the crank. Street.

 

3 pages and still no straight answer. Just arguing.

The upper port on the wastegates is used to control boost above spring pressure, eventually exhaust manifold pressures get high enough that they overwhelm the wastegate valve and push it opened, this only happens above a certain boost beyond the wastegate spring rating. Example: you have a 10psi spring in your wastegate and set boost control at 15psi, everything works fine, you turn the boost up to 20psi and boost drops to 18psi near redline, the wastegate is getting pushed opened by exhaust pressure.
The upper port on the wastegate applies the pressure bled off by to boost controller against the bladder in the wastegate to counteract the exhaust pressure on the wastegate valve from the extra above wastegate spring rating.

So until you get your wastegates working at spring pressure don't worry about the upper ports.

Side note, the upper port works very well at stabilizing boost but you will notice many members on this forum having issues with boost control, they run compressed air or cooled exhaust gasses or what no to the "dome" of the wastegate (upper port), the problems people have are not wastegate related they are all caused by the Mac valve used to regulate boost through the ECU, the mac valve pulses opened and closed attempting to maintain a certain voltage at the map sensor (manifold pressure), this opened closed duty cycle does not apply steady even pressure to the upper port, nor does it maintain perfect boost. With manual boost control (not ball and spring style) you can double the wastegate spring ratings boost with accuracy, with electronic boost control the spring rating must be closer to the boost ran to maintain accuracy. Mac valves or 3way solenoid valve often have small passages I believe an inline reducer stuffed in the hose before the T between the valve and wastegate hose will greatly increase the efficiency of the boost control valve through the recommended 1/4"/6mm boost hose.

Testing your wastegates. You need to eliminate the Mac valve from the plumbing between the boost source and wastegates and if you are running 2 wastegates off one boost source signal (compressor housing nipple or charge pipe nipple before the throttle body/carb) make sure the T or Y delivers equal pressure to both hoses (is positioned to do so).
If the intake boost is wastegate spring rating than the wastegates are functioning correctly and the 3way solenoid valve is the issue, (plumbing, connection, setting or function.

Personally and logically I find it best to run the wastegate boost signal just before the throttle body, this makes the wastegate react to manifold pressure instead of compressor housing pressure, taking piping and intercooler losses out of the equation, the wastegate operates at intake manifold pressure which is what we set boost to, this brings spring to dash gauge pressure very close and makes regulating boost more accurate (if 2psi are lost between the compressor housing and intake manifold, your spring is 10psi and you have to use boost control to run 10psi you're actually loosing 4psi adjustable accuracy with a boost controller at higher boost, 2from the wastegate spring and 2 from boost control, above 16psi boost control is less accurate). The downside is if you blow a turbo pipe between the compressor and wastegate boost source nipple than the turbo spins without any wastegate control (which it does even when connected at the compressor housing) but odds of blowing the turbo increase slightly, so always build things to take 3times the boost and never do things twice.

I have a friend who has boost issues doubling the boost using an ecu controlled mac valve, I have started to look into it and I'm not digging the way the "mac valves" regulate boost it makes it very difficult for the upper port on the wastegate to aid in regulating boost due to the constant pulsing pressure. I think that the ultimate solutions is running something like a 5way valve and four preset manual boosts that all feed to the upper port, that would require 4 signals to regulate boosts from the ECU and only give 5 different boost rates as tuning options but would still allow progressive and rpm and gear based boost control while eliminating the inaccuracy's of electronic duty cycle boost control.

Although I build and drive new cars (1988's) I am old school and don't believe a computer should ever be connected to a car to control it, manual, mechanical and electrical, electronics are for kids toys, "bullet proof" is bullshit and nothing but eternity lasts for ever.

 

I can't tell you what to do - I can only tell you what I would do.

I'd work on eliminating all variables and then adding them back one at a time. I'd want to start with the wastegate(s) working totally independent of the boost controller and on the minimal spring. Essentially - answering two questions:
1) Are the wastegates mechanically functioning as they should?
2) Does the exhaust system give sufficient priority to the wastegate to allow it to effectively bleed off exhaust sufficient to control boost?

If those two things are not true - none of the other stuff matters.

So - the first thing I'd do is confirm that the valve in the wastegate moves freely. Pull the wastegates - push on the valve - does it open easily / cleanly? If not - fix that...

Then - I'd leave the boost controller disconnected and leave the hose off of the wastegate - make sure that there is no chance that there is any pressure fighting the valve opening. I'd put the lightest spring possible in the wastegate (google tells me that for the 39mm Precision the natural metal spring by itself should be 1.5 PSI). Maybe also run a temporary line to the lower port on the wastegate with a few PSI of air on it - to force the valve open. What do you get then? If it drops your peak boost - great - by how much? My guess would be that if the boost controller or spring configuration was the issue this config (no boost controller and the single tiny spring) should resolve it - and you can then change one thing at a time from there to find the issue.

On the other hand - if you still are getting 13 PSI (or at least "more than 1.5ish PSI) - then you can be pretty sure that you are dealing with an issue associated with the ability of the exhaust / wastegate to evacuate exhaust sufficient to drop boost below that level. If you want to prove that you could try replacing the wastegates with a chunk of tube (just direct pipe from the the wastegate input flange to the output flange). I'd expect this to drop peak boost "a bit" (and probably really hurt spool up) because a simple tube will flow more efficiently than gas through the wastegate - but if you do this and are still getting real boost - then your exhaust is not allowing sufficient relief of gas to the turbine to reduce boost to the degree that you want to reduce boost. If that is the case - you can decide whether to just live with it - or modify your manifolds to allow better boost control.

My 2 cents...