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Old 02-19-2015, 01:35 AM   #1
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Default Want my 45.1HP back . . .

Hi All, Long-time reader, first-time poster.

I have a '97 LeSabre rated at 205HP at sea level. Unfortunately I live at ~6,500' above sea level. The math I've done has me at 159.9HP at 6,500'MSL and 77 degrees F. The difference is very noticeable.

Disclaimer: I don't intend to go (much) over the factory 205HP. It'* a good daily driver and I want to keep it that way, just want my 45.1HP back that I enjoyed when I lived on the West coast.

So, off the top of my head turbocharging fixes this, give or take many details. Theoretically if I have very little boost I'd end up at same very little boost at the Eisenhower Tunnel (11,000 feet) and the beach (0 feet). Problem is it'* complicated and guaranteed to be a lot of custom work.

The other option would be supercharging, and fortunately give or take details, this is fairly easy and common on the 3800, and there are a zillion donor cars all over the place for everything I need to do this. Surprisingly cheap too.

Before going much further: I'm likely keeping the car forever, and it is coming up due for some transmission attention and a few other things but is overall running great, even at 6,500'. I'm thinking towards the end of summer I'd want to drop the whole works out, split the engine and transmission, and give each whatever attention I finally decide on by then. I'd like to keep as much of the car original as possible, while also adding and improving here and there.

So . . . looking for some subject-matter knowledge here: Are supercharged engines affected by altitude like naturally-aspirated engines? Reading around it seems that everybody has an opinion, there are many opinions, and my summary would be "the supercharger'* volume is a constant related to engine speed and ambient air pressure therefore it would be effected by altitude" but an experienced engine/performance/etc. person would likely know more about this than me.

Also I'd like to be able to go to lower altitudes and not worry about compression or 4T60E transmission issues, hence the turbo possibility.

Experience level: I'm okay but learning at welding, pretty good mechanically, and very familiar with reading/understanding OBD2-related stuff. Basically some of my dad'* 40+ years as a heavy-line GM mechanic rubbed off on me and I used that as my foundation to expand.

Random idea: Maybe there would be a way to add a wastegate to a supercharger?

Okay I've typed enough. If you survived reading this far then you must be interested.

Thoughts?

Thanks!
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Old 02-19-2015, 06:53 AM   #2
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1. Supercharged engines are also affected by high altitudes. This is because the air is thinner. Thinner air = less to combust with = less power.

2. You can't simply supercharge a non-supercharged car. Yes, the blocks are the same, but the short answer is no. You would be better off transplanting both the engine and transmission out with a L67/4T65-HD

3. Superchargers already have a wastegate valve.

4. Yes, putting a turbo in requires custom fabrication of the exhaust and the turbo. This also requires tuning of the computer and bigger injectors. It would be simpler to just swap engines.
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Old 02-19-2015, 02:58 PM   #3
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While the power isn't there, does it help the gas mileage that there is less drag with the thinner air?
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Old 04-06-2016, 02:05 AM   #4
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Hi Tech II, Sorry for the very-extended delay. I think the thinner air, if it has any effect improving fuel economy, would be easily negated by pumping/friction/parasitic losses revving higher to do the same job. Right now I see about 23MPG on 85 octane and 27-28MPG on 91 octane. I have a bit of lead in my foot.

(Yes the octane ratings are lower way up here and in most of Colorado. Less atmosphere=less combustion pressure=lower octane rating necessary for preventing detonation)

When I lived near sea level I got better fuel economy, unless I "hurried" through a tank, then I got worse. The engine had a much easier time of everything down there.
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Old 04-06-2016, 04:41 AM   #5
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Hi Mike, sorry for the delayed response. Soon after my original post my job wound up tight for a long time. I understand the sentiment of [just swap for a supercharged engine/trans], and yes it might be easier depending on the donor parts. I'm a bit sentimental so I'd just as soon keep as much original as possible.

That having been said:

Everyone who has friendly advice: I've had a lot of time to ponder this subject, often around 39,000 feet. I've also had a chance to drive a few Expeditions with the 3.5 EcoBoost in various places. What a marvelous engine. I know I'm speaking blasphemy here at GM world, but they did good over there in Ford Land with the EB.

So my goal is to reclaim the 45.1HP I've lost by living at 6,400' . I've decided that I'd prefer turbocharging it for a few reasons. The car is nearing 210,000 miles and still runs great. The transmission shifts just as it did 120,000 miles and 14 years ago when I bought it, so clutches/bands/TC etc all seem good. Here'* my thinking:

- Engine has a few hard-to-reach odds and ends that need replacing, the power-steering pump is starting to whine, and the AC compressor is shot . . . all of which would be easy to replace with the engine out
- Transmission needs TCC solenoid, shift solenoids (while I'm there), and a few other minor things done . . . all of which are in the side pan and need to be replaced with the transaxle out
- For the cost of a battery box and some fat wire the battery can move to the trunk (maybe I'll get a sealed box and ventilate it outside), now the turbo has a home where the battery was
- While engine and transaxle are out, what a great time to run more pipes, hoses, wires, etc.
- Leave everything stock, like injectors, cat, fuel parts, etc.
- Cleverly pull feed exhaust from right behind the catalytic converter and outlet O2 sensor
- Cleverly deliver post-turbo exhaust to the remainder of the factory exhaust system
- Cleverly feed factory air-filter box across the bay to the turbo
- Run turbo compressed air through intercooler in front of condenser, from passenger side to driver side (some cleverness routing pipes will be needed here too)
- Feed intercooled air to factory MAF which is on driver side
- Oil pressure sending unit is already ~18" away from battery tray, so "T" in and I have oil supply
- Oil pan is ~12" nearly straight down from battery tray so good return path with no concerns with needing to add or maintain an extra pump

Questions I have:
- Can I set this up such that I always deliver (when spooled) 14.7PSI just like at sea level, such that the turbo has nothing to do at sea level and "keeps" me at sea level when I'm higher?
- Can I set this up such that the wastegate is open (no boost) until the engine is warmed up? I'm thinking something that opens/closes vaccuum based on coolant temperature or somesuch
- Suggestions for turbo unit? Should I go just barely big enough or go too big knowing I'll spool a little slower and the turbo will never be working very hard therefore last longer etc.?
- Journal or ball bearing turbo?

I bet you'll never see me put racing stripes, extra badges, sporty aftermarket rims, a spoiler, or a radio that'* more visually entertaining than the music it is playing. You won't see me on Youtube doing big smoky burnouts.

I will be swapping for some Bonneville sway bars and 16" rims and 225/60-15'* for a Park Avenue that only the most die-hard triple-shield fans will notice aren't stock. I might add a small boost gauge inside. Otherwise I want to blend in.

The way I see it some turbo lag is fine and will make the transmission happier. It will also keep from adding traction issues from a dead stop. I just want my power back along with less shifting and revving and etc. that it has to do now.

My goal would be to start taking things apart end of summer.

Thoughts?

Last edited by CathedralCub; 04-06-2016 at 04:42 AM. Reason: Mis-edited the first time
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Old 04-06-2016, 05:47 AM   #6
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It'* time for another RG long crazy time consuming thread!!! Take your restroom breaks and go grab a snack.

The point of this is to educate on how altitude plays a role on how much air can enter your engine. You really need to look at the attached spreadsheet to understand how these numbers work. For comparison sake, I am going to just assume 100% efficency and not factor in any losses to backpressure, heat, etc.

The purpose of forced induction is to get more air into the engine so we can make more power. We commonly refer to this as boost. It is typically measured in pounds per square inch (psi). It is a misconception that at sea level we are at 0 psi. This isn’t outer space! We are actually at or near 14.7 psi. This varies a little depending on weather conditions so just assume a perfect day by the ocean. When we refer to boost, we want to know how much pressure we are running over this amount. Therefore 6 psi of boost is 14.7 + 6 = 20.7 psi ambient. Everything is referenced to ambient pressure at sea level.

You need to print the attached chart up and look at it while reading the rest of this.

At sea level as stated above, we have 14.7 psi. If we want 6 psi of boost, we need to have 20.7 psi ambient pressure. This is a 40.8% gain over ambient. Desired boost pressure should not be considered in psi but rather in a % over ambient. If we want 6 psi, we really just want 40.8% gain in pressure. You get the point. The rest of the examples assumes we have a fixed ratio of 40.8% more power than stock at that altitude which equals 6 psi at sea level for comparison sake.

At 1000 ft above sea level we need to figure out what 40.8% greater than ambient (14.18 psi) is. 14.18 X 1.408 (40.8%) = 19.96 psi. That’* a loss of 3.575% pressure from sea level. This is what a mechanically driven supercharger will yield if it is designed to provide 40.8% more air (6 psi at sea level). There is less air to begin with at higher altitudes therefore less compression. The percentage increase stays the same but the boost pressure does not. Your mechanically driven supercharger’* boost gauge will now read only 5.26 psi since it is set to sea level while a turbo’* will still read 6 psi. A turbo has the advantage by .74 psi.
A naturally aspirated engine loses 3.538% pressure at this same elevation over sea level. An exhaust driven turbocharged engine will get a total of 20.7 psi absolute or a 0% pressure loss since the wastegate is calibrated to sea level or a fixed spring pressure.

At 2000 ft above sea level we need to figure out what 40.8% greater than ambient (13.67) is. 13.67 X 1.408 = 19.247 psi absolute. That’* a loss of 7.02% pressure from sea level. This is what a mechanically driven supercharger will yield if it is designed to provide 40.8% more air (6 psi at sea level). Your mechanically driven supercharger’* boost gauge now reads 4.55 psi while a turbo’* will still read 6 psi. A turbo has the advantage by 1.45 psi. A naturally aspirated engine loses 7.01% pressure at this same elevation over sea level. An exhaust driven turbocharged engine will get a total of 20.7 psi absolute or a 0% pressure loss
since the wastegate is calibrated to sea level or a fixed spring pressure.

At 3000 ft above sea level we need to figure out what 40.8% greater than ambient is. 13.17 X 1.408 = 18.54 psi absolute. That’* a loss of 10.435% pressure from sea level. This is what a mechanically driven supercharger will yield if it is designed to provide 40.8% more air (6 psi at sea level). Your mechanically driven supercharger’* boost gauge now reads 3.84 psi while the turbo’* will still read 6 psi. A turbo has the advatage by 2.16 psi. A naturally aspirated engine loses 10.41% pressure at this same elevation over sea level. An exhaust driven turbocharged engine will get a total of 20.7 psi absolute or a 0% pressure loss
since the wastegate is calibrated to sea level or a fixed spring pressure.

At 4000 ft above sea level we need to figure out what 40.8% greater than ambient is. 12.7 X1.408 = 17.88 psi absolute. That’* a loss of 13.624% pressure from sea level. This is what a mechanically driven supercharger will yield if it is designed to provide 40.8% more air (6 psi at sea level). Your mechanically driven supercharger’* boost gauge now reads 3.18 psi while the turbo’* will still read 6 psi. A turbo has the advantage by 2.82 psi. A naturally aspirated engine loses 13.606% pressure at this same elevation over sea level. An exhaust driven turbocharged engine will get a total of 20.7 psi absolute or a 0% pressure loss
since the wastegate is calibrated to sea level or a fixed spring pressure.

At 5000 ft above sea level we need to figure out what 40.8% greater than ambient is. 12.23 X 1.408 = 17.22 psi absolute. That’* a loss of 16.81% pressure from sea level. This is what a mechanically driven supercharger will yield if is designed to provide 40.8% more air (6 psi at sea level). Your mechanically driven supercharger’* boost gauge now reads 2.52 psi while a turbo’* will still read 6 psi. A turbo has the advantage by 3.48 psi. A naturally aspirated engine loses 16.8% pressure at this same elevation over sea level. An exhaust driven turbocharged engine will get a total of 20.7 psi absolute or a 0% pressure loss
since the wastegate is calibrated to sea level or a fixed spring pressure.

As we can see from this trend, the percentage of power loss between a naturally aspirated engine and a mechanically supercharged engine is close enough to be considered the same. This is what SAE corrections on dyno’* is designed to compensate for. They are basing the results at a certain altitude (and temperature but it won’t be discussed here) and try to get their results back to sea level on a perfect day. This is a set standard and makes numbers from other dyno’* easy to compare. This correction value is based on a set % for altitude and temperature. This is fine for naturally aspirated of mechanically supercharged vehicles but isworthless for exhaust driven turbocharged vehicles. This is because mechanically driven superchargers are boosting to a certain set ratio of air greater than what the engine is actually sucking in. An exhaust driven turbocharged vehicle is set to reference pressure to sea level. At higher altitudes it just works harder to get that pressure back up. It has to work harder since there is less pressure to start with. It’* like climbing a ladder. A supercharger is like a person climbing up a ladder from the bottom. His goal is to only climb a certain way in total distance. The turbocharger is like climbing up a ladder to a fixed elevation only it doesn’t matter if you startedout on the ground or 10 feet under ground. You still climb to the same spot. The total gain is different and calibrated to a fixed, known location. Got it! This is why you use SAE corrections for naturally aspirated and mechanically supercharged engines but not for exhaust driven turbocharged engines. Correction factors for turbocharged vehicles will basically be the same as giving you some free boost. That'* cheating the numbers. It may be great way to sell more product but it isn't an accurate representation of how much power you put down. The greater the altitude change, the more inaccurate it becomes.

In reality, there is some differences that offset the effect of turbochargers holding boost at higher altitudes. First off, the turbo is working harder since it has to spin faster. This creates more heat. we also have an average loss in temperature of 3 degrees F over every thousand feet in elevation rise. While these will affect the final numbers from sea level a small amount, they are nowhere near as off as the SAE correction factor for turbocharged engines at altitude. We may also run into the problem of the turbo getting too far outside it'* efficiency range spinning at these speeds. Differently sized turbos will have different efficiencies so we can't jsut get a set standard for this either.

The next time someone tells you that you need to use SAE correction for a turbocharged engine because it is the "standard", laugh at them, tell them to go do their homework and to just go ahead and print up your uncorrected dyno sheet (turbo cars) so you can leave.


Altitude Air pressure (in. Hg) Air pressure (psi) Loss as referenced to sea level
(psi)
Sea level 29.92 14.7 0
1000 ft 28.86 14.18 -0.52
2000 ft 27.82 13.67 -1.03
3000 ft 26.81 13.17 -1.53
4000 ft 25.84 12.7 -2
5000 ft 24.9 12.23 -2.47
6000 ft 23.98 11.78 -2.92
7000 ft 23.09 11.34 -3.36
8000 ft 22.23 10.92 -3.78
9000 ft 21.39 10.51 -4.19
10000 ft 20.58 10.11 -4.59
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Old 04-06-2016, 09:03 AM   #7
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Two points, and although they might sound negative I raise them with your best interests at heart.

First, there is no way you get 4 to 5 MPG improvement by switching from 85 to 91 octane. Higher octane fuels prevents pre-ignition. Running 91 octane in an engine that runs fine at 85 provides no benefits, it just costs more.

Second, if your overall objective is to keep your car forever, leave it alone and live with the lower horsepower at higher elevations. I think your calculations of a loss of 45 HP are way off the mark because they don't consider the MAF sensor and the ECM which adapt to the decrease in ambient air pressure. I also think the modifications you are contemplating could shorten your car'* life span. We had a member on the forum who modded his car for higher HP and ended up chasing a spark knock issue to the point where he eventually gave up and put the car back to stock.

You live in the mountains. Drive slower and enjoy the view.
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Old 04-06-2016, 01:56 PM   #8
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Hi Mike, Thanks for the info. This is the kind of thing I'm looking for. I need to learn and research well in advance of actually trying to do anything like this. While it will be a bit of a hobbyist'* adventure, I'm serious about it working well when it is done and want to eliminate undo/redo as much as possible.

What I'm gathering from this is that (for my purpose) I'd be well advised to choose a turbo large enough that it won't be working terribly hard at 11,000' (at the Eisenhower Tunnel) and even less hard at home.

From the information above I'm gathering that I want to go with something larger than necessary and let the wastegate keep it spinning slow. The question I have is: Can I calibrate the wastegate for 0PSI of boost at sea level, and end up with 2.92PSI boost at 6,000'MSL and 4.59PSI boost at 10,000'MSL etc.? Maybe it needs to be calibrated to 0.1PSI at sea level so it has something to measure?

Regarding temperature, I'll be leaving that detail out of my figuring. If I was building a race car I might have my engineering team run simulations, but I'm not and don't have an engineering team. So I'll spitball it with the assumption that temperature won't affect my plan too greatly, a slightly oversized turbo will not heat the charge air too much, and maybe oversize the intercooler by a bit. I'm not too far off-base here am I?

Last edited by CathedralCub; 04-06-2016 at 01:57 PM. Reason: Replaced a "that" with a "than"
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Old 04-06-2016, 03:23 PM   #9
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Hi 2kg4u, I appreciate your comments, let me throw a bit more detail at you: My measurements are odometer and fuel fill to full, so today'* odometer minus last fill-up'* odometer then divide by fill-up amount. It didn't have this big of a gap when I used to live at lower altitudes. Looking through my OBD2 logs (collected by TorqueOBD2), with 91 octane I see about 5 degrees more timing advance at 80MPH continuous than on 85 octane. This on same flat stretch of road on my morning commute at about the same ambient. Quirk of my car? I don't know but the numbers are pretty clear. I wish I had readings from sea level to compare but that was a decade ago and OBD2 access wasn't so easy back then.

My posterior tends to agree that it feels a bit more anemic on 85. First time I noticed was when I traded with my bride for her Suburban for a couple of days. I had already run 91 for a couple of tanks to see if any perceivable differences. First day with it back while driving to work it felt tired. Not like 30% of itself but more like 80%. Thought it could be in my head then I filled up on 91 and it felt better. She had filled up while she had it and put 85. This is when it got interesting. I commute the same 75-mile route every day, five days a week (when I'm not flying around). Filling up about every 230 miles but alternating between 85 and 91 I got similar results (85 slow and lower MPG, 91 feels better and higher MPG).

Same test on my 95 Roadmaster, car feels a bit more spunky on 91 but no noticeable change in fuel economy. Same test on her Suburban, car feels the same and no noticeable change in fuel economy.

For what it'* worth, I have a mid-80'* 1-ton Chevy pickup with a QJ 4-barrel 350 . Back near sea level I could advance timing about 3-4 degrees without audible pinging if I ran 93 octane. Put it back to 87 octane and pinging would start up at WOT and pulling etc. Here in CO I have it advanced a bit off the end of the scale and run 85 octane all the time and never ever hear pinging, even towing 9,000 pounds uphill foot to floor. My belief here: lower cylinder pressures with less air available equals less detonation.

This (above) is why this subject became very interesting to me.

Regarding your second comment, I understand and that'* why I'm being careful. If all I did was drive quiet mountain roads at low speed looking at the beautiful scenery then I wouldn't notice enough of these things to care. But I don't. It'* either commuter traffic (with more and more Californians joining all the time, I told them to close the gate after I got here!) or it'* up and down the big hills on I70 with the lifted turbodiesels and other maniacs. The car does it okay (with lots of revving and shifting), but now I want to slightly modify it to make it better. I'm not looking to modify it for more power, but rather to give it the same power it would have if I was driving at sea level. I get that the PCM and MAF adjust for the altitude, but they only adjust the mixture. They don't add the missing air.

I can't answer for what the member that chased spark-knock did or didn't do to mod his ride, and I bet there are many more than one. Did he put in too-high compression pistons or heads? Maybe he milled the heads a lot too much. Maybe he put a small pulley on an L67 SC and bolted it to a L36? Maybe he had a Buick 455 running 87 octane and 25 degrees of advance? I have a friend that restored FWD Eldos from the 70'* and chased detonation and overheating issues on a 500ci caddy V8 for a year then found that the supposedly factory-stock replacement cam he had installed was cut wrong. I don't know. That'* why I'm researching this in advance, and my goal is only to achieve manufacturer-approved conditions, just at a higher altitude. And have something interesting to chat about in the process. And a neat thing to show grandkids someday.

It seems like every yahoo out there is trying to get 500HP out of everything, then when it blows up their friends yell "woooooooo" on the Youtube video of it and they say shucks and try again. I'm on a bit different direction than I've seen out there. Maybe my results will be something folks will talk about here. 45.1HP loss is nothing to shake a stick at. And gaining 45.1HP by doing anything to an engine is something that some spend thousands on. I hope I'm on a more moderate path.
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Old 04-07-2016, 09:05 AM   #10
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If your timing is advancing 5* when you switch from 85 to 91 octane, you are getting knock retard on the 85. The issue causing the knock retard may be more related to your perceived loss of power than the change in altitude. As stated in my previous post, you engine uses the MAF sensor and the ECU to adjust to the thinner air, and you are not taking that into consideration.
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