924Board.org

[leadfoot]

I was thinking of just plumbing it back straight into the bypass return, not even bothering with a wastegate.
http://wolfems.cart.net.au/details/106577.html
I might be able to manage a few close ups...
Leadfoot
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

[endwrench]

Interesting. So you think you may be able to use the blow-off to control boost. I have never actually run mine without boost reference. I wonder at what boost it blows off? I'll have to try this and see if it is below the 10 lbs I am currently running. If it is I can experiment with a bleed valve and see if I can "control" it. Thanks for the idea!!

Wonder if it will still do its intended purpose though and bypass off throttle? I did just fit a second bypass so they may open in stages if I let the other control boost. Will be interesting to experiment with if I can ever get a #*!$ starter to last more than 3 startes before failing!!

Todd
_________________
'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....

[Andrew NZ]

[Paul]

On a turbo that type of boost control may cause the turbines to over rev....
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

[Andrew NZ]

[Paul]

I'm not saying it's bad, but one must take other measures to avoid having the turbo overspeed and explode!
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

[endwrench]

[leadfoot]

This is what i was thinking...

Run the intake manifold output to the boost solenoid.
Run the wastegate line to the bypass valve routed back to the sc intake...
Run the bleed output of the solenoid to the bypass valve routed back to SC intake...
So at open throttle bypass valve is closed and there is a direct connection between air bleed and sc intake depending on bleed setting. This can be pulsed at any stage to regulate boost in the higher stages to smooth boost limiting.
Then boost solenoid is then set on boost cut mode 2, being valve position only and at 10psi (max level) for example the valve goes into position mode setting and opens the wastegate line (normally pulsed closed to bleed off air) this will be the definitive limiting setting as it overides the PWM of the air bleed line....
This will mean that instead of having a valve that open and closes fully at limit, it will be able to go from pulsed output the fully open back to pulsed output with a bit of luck...
Leadfoot
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

[endwrench]

Ummm, maybe I'm being a little thick (just spent a 12 hour day hooking up an MS to a customers vehical) but you completly lost me at the mention of a "wastegate". What wastegate? Can you draw me a diagram? Or just explain what you mean by wastegate. I find the whole concept very interesting.

Also remind me, is your TB before or after the SC?

Todd
_________________
'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....

[leadfoot]

TB after SC...
My bypass valve will operate in normal condition, at closed throttle bypass back to the intake... in regards to the boost solenoid,
Normally there are three lines to it...
1. intake manifold...
2. wastegate...
3. air filter...
My system would be refered to as closed loop, using a reference signal from intake manifold as control.
So instead of connecting the number 2 wastegate line as I will not be using one I can still use it to vent as the valve position can be set according to overide command. I will bleed air via the number 3 port but at the same time I should be able to bleed through the number 2 port as I can set the;
Overall trim % (I'm thinking this would be regarded as sensitivity)
PWM frequency- relationship between valve open/close times
Valve position - 0 closed / 255 fully open (would normally control wastegate actuator)
AND
Set a master overide valve to the valve position on line 2 as a function of boost.
It may require a bit of fiddeling with the settings but my aim would be to have a high frequency high load regular setting at the approach of max psi, say .5 psi below max and use the overide valve position to vent at max.
This is all if I don't get my pulley sizings right though... Food for thought though... does it make sense??
Leadfoot
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

[endwrench]

Ahhh. Now I get it! I probably don't understand completly enough to critique your thinking though. It does sound like it will work however. Here's hoping you blow your pulley size calculations so I can see if this is going to work or not!!

Todd
_________________
'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....

[leadfoot]

So the manifold came out a treat... as some food for thought, the throttle plate is only 6mm thick, enough to hold up for my project but might want to be thicker for a high psi application...
The main plenum is made from thin wall 80mm tubing and is approx 400mm with the end caps being 6mm allowing for a good thickness to tap the vaccum/boost fittings.
The slight bellowing of the diffusor is just my shoddy prep skills, I got a bit sick of the rasping noises from the loose piece and decided that I would clean it up after welding.
The only other thing I would change is the way the runners are mounted, if you cut the runners flush and use a flat strip to mount the runners you can get this welded before mouting the main plenum. This would give you a nicer finish inside the plenum.
I'm pretty happy with the end result and no I'm not flow benching it.
As a side note the plenum has a slight lean forward from front to back as this is keeping with the design of the origional manifold as the runners are of different lengths, you can see from the top view that the number one runner kinks before the 90 degree bend and the number four runner is almost straight, therfore when they bend 90 degrees to obtain the same lengths they made the plenum higher at the back, this is not the case with the N/A manifold.
Leadfoot
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

[endwrench]

Well, give yourself a nice pat on the back! Job well done!!

Can't wait for you to get this mounted up and running. You'll be the first here to do it (on a street car). This is close to my plans except I don't plan to use the original intake. I'll be using steel unless I get a tig welder before then.

I hope you plan to run the original SC pulley at first. I would really like to see if there is an actual reduction in boost pressure as compared to the NA head. This should be true in theory.

Off topic: does your setup give you more boost on cold days? I have noticed nearly a full lb more boost compared to this summer. Does this make any sense?

Todd
_________________
'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....

[leadfoot]

thanks...
there's something nice about polished aluminium, mind you it takes forever to do...
Yes I will be using the same pulley, for the reason you stated and I also want to see what duty cycle the injectors are running before any upgrades.
The only other factor will be that I will be using a new SC inlet and outlet manifold... the inlet was definately restrictive, it's going from a 60mm tube (which was the same size as the car it came off) to an 80mm, the oultet i'm remaking at the same time as I came up with a better design. I also run a boost gauge pre intercooler so I can verify any changes there too...
Do you happen to know what your psi figures are pre and post intercooler??
As for psi increase in cold whether ... I can't really give you any figures there, I know I picked up boost with my bypass valve return open to air so with that acting as a restrictor it's hard to tell.
Leadfoot
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

[endwrench]

No, I don't have pre and post IC boost readings yet. I do have to pull all my plumbing for paint soon and I plan to place test ports in at that time including the air intake tube. I'm running 75mm intake and 58mm pressure side.

I do know I was running 4lbs boost when I installed my IC and it was the same after. No perceptable lag either.

I might also note I had to install a second blow-off valve after moving from 6 to 10 psi. The noise was deafning before I did. This also seemed to cool my IAT's. I never see more than 25°F rise above ambient. I actually rarely see ANY rise. I am having a little trouble keeping my engine cool on 90°+ days though .

What throttle body do you plan to run? I'm a little scared of running anything too big as it is already very difficult to modulate the throttle at lower speeds.

I know what you mean about polishing aluminum! I don't have the patience for it. Very time consuming.

Todd
_________________
'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....