bigacuralvr

So, I have the 2.37" Pulley on my 2nd gen S/C, and am only boosting 5psi, even as full throttle, all through the RPMs.

It only has about 7k miles on it, maybe a little more.

Its on a 99 4Runner Limited.

I have checked the gauge, and tried another, and both read 5psi.

Could I have some lines hooked up wrong? It pulls well, and runs very smooth, and doesn;t idle bad at all....

I get no ping at all, could it be a smaller pulley made to reduce ping at higher altitude??

(I know, the URD kit is on it's way, I have just about the ammount saved for the unit.)

Any help would be great!!

Thanks,
Brett

Greedy

I don't think that 5 psi at your altitude is that odd. With the stock pulley, I was only running 7 lbs. and I am at sea level. You may want to check for a leak in the boost tubing somewhere and make sure that the hose is not getting pinched inside your gauge pod when you are pushing the gauge back in. How much vacuum are you reading when at idle?

bigacuralvr

I don't have vacuum, only boost. (Soon to be changed).

I hooked up a Defi straight at the boost port, and it was 5psi too.

rimpainter.com

I am not a math guy or anything, but it seems to me that lower atmospheric pressure at higher altitudes would mean lower boost. 5psi seems about right considering the stock boost is 6.5psi at sea level. Here is a page that goes through the math...http://www.2-stroke-porting.com/altiden.htm

I show Broomfield at 5300ft ASL or so. Does it make sense after looking at that link?

mt_goat

I think most boost gauges will just read the difference between the intake and the atmosphere, not absolute pressure, so the boost gauge will read the same at any altitude. Your actual boost will be less though at higher elevation.

Digger33

I am in colorado as well. I have the 2.2 and my boost gauge reads about 8-9. But the advanced MAP sensor in the ftc reads only 5psi, at full throttle. I went to evergreen and it dropped half a psi to 4.5. I would assume with the stock pulley your not even getting the 5psi, probably only about 3.5psi at 5000ft. It's just the elevation and it sucks. Go up to 10000ft and you will probably only be getting about 2psi if your lucky.

HaveBlue

I ran a "9 lb" pulley from EL Prototypes for a while. At this altitude, I only got 7 PSI and a whole lotta extra noise and heat. The only benefit was slightly snappier throttle response. Unfortunately, up here in the clouds, our superchargers don't produce as much power as they do at sea level. I read somewhere that out SC'd trucks produce the same amount of power here as an NA'd truck does at sea level. So, it's good that you're getting the URD fuel kit, but I wouldn't bother with a larger fuel pump or anything. You won't need it at this altitude.

FWIW, that's also why I was asking if a larger MAF would produce any noticeable results at this altitude. I figure with the thinner air, it won't make a difference.

mastacox

Its true that the air is much thinner at altitude, but nevertheless a supercharged engine will do much better than its N/A counterpart at higher elevations. I'm quite sure my supercharged engine outperforms a N/A engine at sea level hands down even taking into account my altitude losses.

Here are a few little facts for ya:
Air pressure at sea level: 14.7 psi
Air pressure at 3000 ft: 13.2 psi
Air pressure at 5000 ft: 12.2 psi
Air pressure at 7000 ft: 11.3 psi
Air pressure at 9000 ft: 10.5 psi

So, running a 2.2" pulley (approx 9 psi boost, yes?) ASL nets you air that is prssurized to about 23 psi. Now, say you're at 5000 ft with the same pulley; the drop in pressure (and therefore air density) will have a detrimental effect on how much air your S/C can pull, so I'd say total boost from the S/C will decrease by about 17% to 7.5 psi (I'm assuming a linear relationship, but I haven't looked into the actual fluid mechamnics yet, it could be more). That, paired with the fact that the atmo. pressure is lower, means now you're only putting 19.7 psi into your engine (equvalent to about 4 psi of boost ASL. Go to 9000 ft, and you're down all the way to 17 psi total air pressure in your engine (2.3 psi of boost ASL). (EDIT: by the way, a stock 6psi pulley based on my claculations should be pushing about 4.97 psi at 5000 ft...)

The fortunate thing is, you can make up for this by pushing more boost! (Disclaimer: run more boost at your own risk, because too much of a good thing CAN be bad...) This is a common practice by drag racers running at a high-altitude track... At 5000 ft if you run a 2.1" (11 psi) pulley, you will be able to push about 21.5 psi into your engine, you're almost back to sea level! The problem is, if you plan to go BELOW 5000 ft, you might have to replace the pulley with a 2.2" one to make sure you don't over-boost your engine when going down into thicker air again (too much boost without water injection will lead to very high EGT's). Anyway, that's how that works...

As for going without a fuel pump or other things, even at altitude you will be able to get into lean-out conditions, as well as a significant amount of ping, which is definitely why you will want a URD kit.

bigacuralvr

Yep, The URD kit is coming right after I get the AllTrac put back together!!

Thanks for the help/input guys, I was just worried something was not working right. But it is!

Brett