The question sounds dumb, but there is more to take into account than the obvious. Let me start out with an example. There are Evos that make 23 psi, fall to 18 or so at redline. That is pretty good in my opinion. These people then do a pressure test find that their throttlebody seals leak at like 3 - 5 psi, and some people find leaks at the couplers, injector seals, etc…
So if the car is still making 23 psi, falling to 18 psi, how would fixing the boost leak help you make more power? Would the turbo just have to work less to get the same results? I don’t see how that would affect power output. Could it be air leaks result in lost air post-maf, so the mix is more rich than it needs to be?
I don’t think the tune cares how hard the turbo is working though, nor does the turbo itself. It may produce more heat working harder, but I don’t think that is the big factor here. One would assume its because you would make more boost after fixing the leaks, but I don’t think you would make much more, since that’s already cranked up pretty good.
when you talked about the evo psi drop…wasnt this taper tuned for from the factory?
i see what you mean by the turbo working harder… producing more heat…but not effecting power…
wouldnt the turbo just keep up with the leak to produce the psi the vehical is tuned for?
I had some boost leaks in my Grand National. In my case my EGR was leaking a lot of boost. Before I fixed them I would get some knock retard at part throttle and sometimes at full throttle probably because the leaks were messing with my fuel pressure. After I fixed them I had none under all conditions. I think my MPH went up from 104 to 107.
If it’s a map sensor car, the turbo will work harder to achieve the same boost. This will increase the pressure differential across the hotside, elevate EGTs, which will hurt power, increase knock, pull timing, etc.
On a MAF car, you’re actually losing air mass, so your injectors are operating on the condition of X cfm, while in reality, you’ve got .95X CFM. So you’re going to run rich. Now couple this with the above issue and you have a serious problem.
When you’re speaking of the boost tapering at high RPMs, it’s simply because the OEM turbo can’t produce the CFM demand that 22psi at 7000 RPM requires, because it’s so far out of it’s efficiency range.
Forget the taper, I was just showing that it was a normal taper, and not any lower than it should be, due to a leak. It is a maf car, so I assume its partially caused from the air mass loss, like newman said. I suppose a back to back test would be required to see if the psi actually went up after fixing said leaks, but I really think its going to be negligible. Kinda a neat topic eh?
The boost leaks probably aren’t going to be enough to cause much overall pressure loss, but are most likely to hurt you because of the loss of metered air.
I’ve been doing a lot of research to maximize my setup this year, and I am finding a lot of tweaks I can do, I am hoping that the results are going to show at the track :tup:
Couldn’t resolving boost leak issues increase spool time even if it’s only 100 RPM? If there is a boost leak, it MAY be a vacuum leak as well which can mess with idle and such.
I chose to respond to your post because you posted the most correct info. I just want to clarify a few things and add some others.
To clarify, the turbo will spin faster to get the CFM into the intake manifold that results in x psi than it would if air wasn’t leaking out. I know you know what you mean when you say the turbo has to work harder, but some people don’t.
The turbo has to flow more CFM and operate at a higher pressure ratio because some of the air is being lost. This reduces the turbine and compressor efficiency, resulting in hotter charge air which reduces power and makes the engine more prone to detonation and heat related damage. See thread on how intercoolers make you power for how charge air temps are related to HP output.
To clarify another point, whether a car uses a MAF, MAP, or both to determine fuel/timing outputs, the turbo will spin faster to maintain boost pressure in the manifold.
You’re correct about the MAF base tuned car running richer overall due to a leak, but also remember that if the leak is on one cylinder, that cylinder will run richer than it should and if there’s AFR trimming hapening or you retune the car because you think it’s just running rich, the other cylinders will be running leaner than you’d want them. This assumes you’re trimming/tuning off a wideband that’s reading post collector(s).
Another issue is that MAF based cars make timing decisions based on calculated load determined by airflow, rpm, intake air temp, etc. With a leak the ECU will “see” less calculated load than actual so it will run more ignition timing than it should assuming the ECU is tuned so as load increases, ignition timing advance decreases. This coupled with the hotter air makes the engine more likely to detonate. EGTs AND CHTs will increase because of the leak and a hotter engine and combustion chamber is more likely to detonate.
A boost leak in certain specific areas could cause other issues. For example, a leak at the MAP sensor, in boost control lines or other critical area would have other severe consequences resulting from overboosting, underfueling/overtiming advance, etc.
Boost leaks are far more of an issue than most people realize.
And to clarify the last point, there are ways to reduce that tapering which are generally imprudent, because they involve pushing the turbo WELL out of its efficiency range as well as pushing the pre-turbo exhaust pressure much higher than it should be in relation to intake manifold pressure. This assumes the car has a proper boost control setup to begin with.
I know this post has been sitting dead, but we’ve been too swamped at the shop for me to respond to tech in a while. Sorry…
An aside, towards tapering due to running out of efficient areas: A small amount of pre-turbo water injection can compensate for “overloading” the compressor wheel. Once the water flashes to gas it brings down temps in the compressor, as well as slowing down the wheel - yet you don’t lose any of the air mass.
The key is to keep the water well atomized going into the compressor inlet and using a (generally) very small jet/nozzle, as too much can cause: extra stress on the shaft; impellar blade pitting; and even “bogging” it down.
The method & tech has been around for eons (rally cars, indy cars [google "ring of fire], endurance, etc), hell alot of the revered DIYers (GN guys for example) have done it for over a decade… but alot of casual (street, street/strip) people are afraid of it because of “internet knowledge” they read about.
Now, a fair # of 2.3T guys on stock turbos (smallish IHIs & T3s) use preturbo water when running past the generally excepted turbo limit (18# & 20# respectively), and so I read up on it and gave it a whirl as well. Admittedly, I’ve only used it once because at the time I was running out of steam @ 22#s (T3 60/48) as the turbine was a bit small. There was a signifigant difference in IATs & spool time. I did not have EGT available to me at the time. This was with an old Starion FMIC. After (only) one season a 10x monicle showed no pitting of the compressor wheel, and there was still no noticable axial shaft play.
One of the major downfalls / concerns is that the water will condense to liquid in the intercooler (its possible) as both water & intercooler are cooling the charge, but this is hugely application dependant obviously, and comes back to nozzle choice, what PR you’re running, what your w/water IATs are, among other things - so as with anything do your own research before imparting on any new mod / DIY.
