white_lightning

I live at 3450 feet above sea level in Calgary AB Canada. I want either the Brenspeed Stage 0 Edelbrock E-force or the Whipple Ho kit from lethal performance.

I noticed that Brenspeed has a little disclaimer about the boost level saying that boost will depend on elevation and rpm. I've seen dyno sheets and other posts saying that e-force advertised at 5psi might climb to 6-7psi at 6k RPM so I think i understand that aspect. BUT my question is will 5-6 psi at sea level ( brenspeed is at sea level so i assume that's where they rate it) be 3-4 psi at higher elevations or will it be 7-8 psi at my elevation.

I've never seen this question posted I hope you MF'ers can help me out.

Vapour Trails

It's not hard to calculate.

Pressure at sea level is 14.7 psi. The overall pressure is the boost + the atmospheric pressure. Boost is defined as pressure above atmospheric.

So 10 psi boost at sea level is actually 24.7 psi (overall).

Calgary atmospheric pressure is about 12.7 psi, so at 10 psi boost, the overall pressure is 22.7 psi. This would be equivalent to running 8 psi at sea level.

So you will lose about 8% overall boost (and power) vs. sea level. (22.7-24.7)/24.7. Keep in mind, it's not that the blower makes any less boost, it's that the air coming into the blower is not as dense.

Notice how it effects N/A cars more. (12.7-14.7)/14.7 = -13.6% power vs. sea level

hammeron

i like Vapours explanation, it breaks
it down very nicely.

white_lightning

Forgive my slowness I think I get it.

For Example - 6psi at sea level on a blower will effectively be lower boost here at 3500feet maybe 4 or 5psi. However my engine is seeing the same boost EG: 6psi ( therefore same stress) as those vehicles at sea level however my power will be less.

With this explanation it would seem there are no implications when travelling. Say I go to Vancouver BC; I will have more available HP's with the "same" psi of boost? Will a boost guage pick up on this?? or does it see the boost going into the engine.

I knew that higher altitude affects HP. Same reason that my stock GT ran a 14.70 in Calgary AB, Vs. a friends Bone stock GT in Toronto ON running a 14.0
I ran a calculator and a 14.7 is pretty much = to 14.0 at sea level.

thanks for your help

Cusp

I have wondered if super chargers did the waste gate trick like turbo chargers do. Where you can set the desired boost level and the waste gate maintains it from sea level up to the maximum ability of the turbo system by closing the gate as density altitude increases.

cummins cowboy

the cool thing about having a blower at higher alititude is you can just swap to a smaller pulley to make up for the power loss. the other thing is most cars you will likely face off against will be N/A they will be down on power and you can be putting out sea level power with a pulley change. I live at about 5k elevation and this is something I have thought about.

I drive a dodge diesel, with turbo of course. my truck will just about waste anyone going up the high altitude grades we have around here even pulling a trailer, those gassers are gasping for air right before we crest the top, whereas I am at 30#'s of boost pulling past them like a freight train.

back in WW2 the P51 mustang was first made with an allison NA engine, the plane did ok at low altitude but was outclassed at high altitude it wasn't until the supercharged merlin did the plane become what it needed to be. it was the supercharger that made it work

Vapour Trails

No, the overall stress would be less as well. The stress is created by the power generated, and you would be creating less of it at higher elevations at the same boost level. Running 10 psi at your elevation would be sustainable in my opinion.

SCCAGT

This was going through my head with op. Superchargers, being belt driven, will only pack in the air that rpms allow. So the same physics rule applies in vapours post. Turbos do not have the same rpm restrictions. S/C's use a bypass valve that dumps the extra air when vaccuum is present. As opposed to a waste gate that bleeds it off when boost gets to whatever level it's set to open at. I wont claim to be any kind of expert in this area, but would believe there would be losses associated with elevation changes. Just in much smaller amounts compared to s/c. Spool time would increase a little due to a lack of air flow through the engine.