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Re: Viggen Turbo Theory/Replacement/Upgrade Strategy Posted by thetallguy [Email]  (#1698)  [Profile/Gallery]
(more from thetallguy) on Sun, 13 Sep 2020 07:55:39
In Reply to: Re: Viggen Turbo Theory/Replacement/Upgrade Strategy, md2boys  [Profile/Gallery]
, Sat, 12 Sep 2020 18:14:01
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I try not to be a proponent of "upgrade creep" where the usual assumption is upgrade=more power/ torque. I apologize if my suggestions lean toward that trap. If its city driving and throttle response you are looking for, then going larger compressor much larger AR would not be the correct direction. Generally, the idea for more performance includes a desire for more power and better throttle responce across the entire RPM range. The issue with larger turbos is that you move the power band upward but its further "up" in the RPM range for the simple reason that it takes more heat to turn a larger compressor wheel to a higher pressure/more lbs of air per minute. Good engineering can improve this situation somewhat but requires (sometimes) extra components and cost. The twin scroll turbine housing with a progressive inlet, ceramic exhaust and turbine coatings, stainless tubular twin scroll compatable exhaust manifold, stainless turbine housings, ball bearing turbos, cams, timing, individual intake manifold throttle bodies, 1/2 shafting or 1/4 shafting of throttle butterfly, separate wastegate(s), larger exhaust diameter, fuel injection into exhaust manifold while off throttle, high flow/no cat, better intake for turbo, better heat management of intake to head, and last but not least, the variable AR turbine housing are all efforts toward improving lower RPM engine response which do not come stock. The variable AR turbine housing being the most costly but "probably" the best all around solution for both response and power. If you are looking at just better throttle response then the fuel injection into the exhaust manifold (pre-turbo) while off throttle would probably be "best" but probably lacks turbo longevity and is questionable for emmissions.
What we, as Saab owners, have which improves throttle responce is the T7 software (which supposedly "learns" the drivers style and anticipates fuel/boost requirements), the recirculating "blow off valve" (helps maintain turbine wheel speed when off throttle), a fairly efficient exhaust manifold, and a very well designed turbo with a very good internal wastegate. True upgrades to the recirculation valve will yield better throttle responce-the idea is that the strength of the spring should be just enough to retain a cosed seal while off throttle/under vacuum but open fully when coming off boost to release the pressure backing up behind the throttle plate because the throttle has closed (while under braking/gear shifting). The pressure must vent somewhere and if there is no recirculation valve it will vent back through the turbo compressor essentially slowing down/stalling the wheel. The turbine, at this particular moment of time, has less heat (because you are off throttle) and therefore offers no "help" to offset this situation (hense the idea of fuel injection imto the exhaust manifold while off throttle). When you get "back on the gas" there is poor response because the turbo has lost its speed and must re-spool. The blowoff/recirculation valve allows the pressure to vent back into the intake and allow the turbo to maintain "speed". I sometimes wonder if the aftermarket valves are actually "more better" because you only get the choice of three springs. My experience with the stock "hooter" valve indicated that the spring is just about perfect for the application because it "hoots" just as the pressure transitions from very low boost to a vacuum. I would say that this would indicate a perfect "match" between just (about) enough spring pressure to insure that the valve opens at the soonest opportunity and therefore maintains the highest turbine speed possible. While I would prefer just a tad bit more "spring" and no hoot. I perceive that this is probably an optimum setting. The aftermarket would probably disagree. I also perceive that the orientation of the 9-3 and 9-5 recirculation valve is incorrect for longevity. I prefer the 9000 orientation with the air venting directly over and around the seal in a mechanically balanced and better flow path than the stock side venting scheme. Some people have reported this improves throttle response...I could not tell the difference but I liked the idea of it. The stock side vent side loads the diaphragm which is not a good situation for longevity. Bosch added a weight to the base of the diaphragm sometime in the '80 to, I suspect, address diaphragm "flutter" which translates to the hooting noise the stock valve makes...this weight further adds to the side loading so anything which can be done to improve this situation is good.
So, returning fully to the question of throttle response: airflow throught the throttle body which includes streamlining (does not include porting to a larger diameter), 1/2 shafting or 1/4 shafting butterfly, head porting, intake cooling, ceramic coating (Swain Tec) the exhaust and turbine housing, and the addition of an aftermarket "popular" meaning best matched recirculation valve are the easy ways to better throttle response. The harder ones include stainless tubular manifold, twin scroll turbo with ball bearings, and external wastgate. Holset makes the variable AR turbine turbo for deisel trucks. I have been waiting for a aftermarket controler for these turbos to retro onto a four cylinder...so far only a few experimental units have surfaced- as near as I can determine. There would be virtually no lag with this type of system...kind of what I am holding out for. The ceramic coating of the turbine housing probably is a bad idea if you are going for longevity.
All of the above suggestions could be interesting father/son or grandfather/grandson types of projects (pardon my sexism). I will close with the follow observation: The Magflashlight is a fully o ringed housing with internal measurements which exactly matches the external measurements of the stock recirculating valve and spring "cylinder". Because you can use the base to retain the vent tube separate from the diaphragm a fully adjustable blow off valve can be made using the stock Bosch valve by sectioning it up. This unit allows changing out the spring and diaphragm and, as already noted. it is also fully adjustable. I know this is possible because I built one in 2000 for my 9000 from a Mag light that suffered battery leakage. My "mag" valve currently has 200K miles. It is also possible to make a recirculation valve the same way which would be fully adjustable.So, I could post pictures of this (the blowoff valve) if there is any interest but perhaps it would be better to let you "figure it out" as a project.
, Sun, 6 Sep 2020 09:06:57, Wed, 9 Sep 2020 17:14:35, Wed, 9 Sep 2020 05:27:11, Sat, 12 Sep 2020 18:14:01, Sun, 13 Sep 2020 07:55:39 <-- Viewing This Message, Tue, 1 Dec 2020 20:25:48
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