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This seemed like it might be a little open-ended for the question thread. I'm running (or, well, about to be running) a small fast-spooling turbo (GT2860RS) with a small hotside on a relatively big (3.0) engine (because gently caress top end I want to build boost backing out of my driveway). Currently only set up for 8 PSI and no boost controller because I want to shake out bugs first, but unlikely to go past 10PSI in any case. I'm inclined to take the wastegate signal from the intake manifold. My thought is that the turbo's likely to spool up so fast that if I take the signal from right after the compressor, I'll start popping the gate before the intake manifold is under pressure (especially because the tubing run from compressor to wastegate is about 4".) My charge pipe right now is only about an 18" straight run of 2.5" silicone, so it seems like any backpressure shock from the throttle plate against the turbo isn't really going to be that big a deal (compared to someone who's running five feet of intercooler plumbing at 15+PSI.) Does this make sense? Alternate suggestions?
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Oct 3, 2014 14:24
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| # ? Apr 28, 2024 09:27 |
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There are a few different places to source reference pressure, usually the best is at the compressor since its has the quickest response time. You'll be 'cracking open' the wastegate really quickly (lowering the chance of spiking and such), but you'll have a softer response from the turbo. Electronic boost control using the compressor boost reference is probably the best way to manage boost pressures, though there are pressure changes (temperature related) in the charge cooler and into the intake manifold that may cause erratic power output as the charge cooler heat soaks and the temperature of the air entering the intake manifold rises. I would not recommend putting it on the intake manifold, wastegate actuators are not meant to take vacuum at all, and would likely have some sort of erratic spiking as you transition from manifold vacuum to pressure as the wastegate diaphram and line has to go from vacuum, pass atmospheric pressure, and then be at positive pressure, where feedback regulation occurs.
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Oct 3, 2014 17:37
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I've never had a wastegate failure due to vacuum. Spiking can be a result of inadequate wastegate preload or inadequate wastegate base spring pressure. A lot of the aftermarket turbos might come with the cast compressor boss but are likely not drilled and tapped for reference. Also, why the undersized turbo? Lag in modern engines is almost nil with a properly sized setup. You're doing more than choking the top end, your high exhaust backpressue is going to make for an inefficient and underwhelming setup.
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Oct 4, 2014 09:06
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Pretty much what they both said. Also it makes it easier to plumb and shorter vac lined to do it off the compressor. Generally the most common way of doing it, and all that I have ever seen on oem setups.
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Oct 4, 2014 09:31
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Really appreciate the responses, guys. It's not a modern engine - it's a VG30E, lol. This turbo's actually about the same size as the ones on the stock 87-89 turbo models. Basically I am trying to recreate what Nissan did on the later z31s with the small early-on turbo, just with a technically better turbo at higher boost, higher compression to start (the engine is originally NA), a less restrictive exhaust setup (2.5" straight pipe right from the turbo back, no cat), and a few other minor supporting things. My GT28 has a T3 exhaust housing - I have a .63 that fits it but I bought a .48 just to take the idea to its logical (and agreed, maybe too backpressure-y) conclusion first. The turbo's been relocated up top so if the .48 is choking out just too early I can upsize without any major downtime. I've always run wastegate signal off the compressor housing up until now but I was wondering with the really small hot side, like I said, if maybe the intake manifold might be worth trying in this specific case. That said I have a 7-inch run from compressor to wastegate and from the mani it's about 20 inches. It's 15 minutes' work to change so I may try it both ways... edit: typo 1st Edition ADandD fucked around with this message at 17:16 on Oct 4, 2014 |
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Oct 4, 2014 12:12
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Take the source after the intercooler but before the throttle body. Install a cheap EBC system to keep the waste gate closed until you hit target. Edit: oh, no IC. Then just take it off the compressor. You still don't want it in the IM.
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Oct 4, 2014 16:07
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It's off the compressor. Thanks guys. Intercooler will probably go on in the spring once everything else is sorted and running (car's running and has had a couple test drives but I have no downpipe, I'm just dumping from the turbo under the hood) and I may revisit destructo's suggestion...
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Oct 6, 2014 22:19
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