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Discussion Starter · #1 ·
Hello guys, after I swapped out the exhaust for a wide-bend 3" all the way with a 3-in-3-out cat and magnaflow muffler and an ATP Ultimate Wastegate, I've been thinking the seat-of-the-pants test has been failing ie. not quite as good as before the swap, which makes no sense. Some of you have been telling me that it's not as torquey which is a good thing, but then, how is it good? The car doesn't seem as fast as it was. There are a few things I want to ask, for those of you who may have experienced this problem or might know something about the physics of it all.

I'm pretty sure it's all turbo-related, so here are my questions.

The first thing that crosses my mind is that I've at the same time upped the max boost on the turbo, which is the stock Garrett (T3?). Although my APC has been pissing me off because I haven't been able to get rid of boost taper even with all the mods possible (max boost mod, Dan's boost-taper mod), I've raised the max boost to about 22psi, and the base boost is at 11psi (held there by a Forge actuator). Now, I'm no rocket scientist, but I'm pretty sure the turbo is working outside of its efficiency range, even though it's popping all my vac lines! :eek: But, what does this mean? Should I be experiencing better boost at, say, 17psi, or even 15psi, than I should be at 22psi? The taper puts the max boost back down to about 15psi, but by this time it's too late to tell what's going on... And if I remember correctly, turbo charts mate boost level to horsepower (approx related to flow lb/min)...should I get a turbo that has 22psi (or more) as the centre of its efficiency at roughly 200hp? I know mating a turbo is quite the science, but I need somewhere to start...

The second thing is I have heard that Chuck's new ELH's are producing quite the stir, and that one experience is that they lowered boost threshold by 500rpm, which sounds pretty amazing. Would this make a difference in what I'm experiencing?

Third, would a lightened flywheel help here? Because the engine's rotational mass is reduced, it spins up faster, producing exhaust gasses faster, and thus the turbo spools up faster too?

Lastly, external wastegates. If I look into a new turbo and Chuck's ELH, perhaps this would also help?

I think she's feeling a bit under the weather lately and her self-confidence is lacking a bit...perhaps some shiney new parts will make her happy! :cool:

li Arc
 

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I asked a similar question in the past, search for my posts. More boost, i.e. more psi does not always equate to more hp. Breakin5Speeds has experienced more hp with less boost (psi) by putting on a turbo that can flow more air. At 22psi all you are doing is creating massive amounts of heat (with a stock turbo) which robs you of hp and creating more backperssure towards the exhaust ports, thus restricting your air flow even more! It seems most people are running 15-19psi boost. Also check threads by Allessence. She is able to run higher psi than most and have an effecient engine. I have yet to figure out how she does it, perhaps it is just plain ol girl power (no insult intended Jen). Turbo curves relate inlet pressure to outlet pressure or the absolute difference between them and it is hard to equate that with mainfold "boost" pressure.

pierre
 

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I'm just guessing here, but I think Jen may have also done some head work to her engine.

I think anything about 20psi is way out of the efficiency range of a stock T3, but I had mine running 26psi for a few weeks and it definately felt crazy fast compared to the 18 or so psi I have now.
 

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Discussion Starter · #4 ·
Well Dan, that's the thing though...it used to feel crazy, before I swapped my exhaust system. It's almost making me thing I made a mistake, but somehow logically it shouldn't be. I might try to tone it down to about 17 or so, and then try running it from there...I've got a pretty big 3" thick FMIC, but for all the heat the turbo is creating it's probably not doing too much. I left in 2.5" piping all the way though.

I'm still contemplating on a new turbo in the spring or summer. Most Garrett turbos seem to hit the sweet spot at about 1 bar boost, or about 15psi. I haven't seen many (save for something like the GT35) that keeps that spot until around 20-25psi at least.

I'm wondering, the straighter vertical the graph, the faster the spoolup? I'm pretty certain the shape of the graph is just as important as the plot itself...?

I'll check your previous posts Pierre, I'd still like to find the root of the problem instead of just covering it up too!

li Arc
 
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