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Boost: more, earlier, then vent to atmosphere? Limits of S62, etc

4K views 17 replies 7 participants last post by  Redshift 
#1 ·
For those who run superchargers...I run the 92mm pulley on the ESS kit, runs about 8.5-9.0psi at redline. Needs further tuning and meth, but still decent power.

I wanted to run more boost, so was thinking of welding a couple blow off valves/wastegates to the plenum and then venting anything above 10 (11, 12, whatever) to atmosphere and of course tuning for it.

Vortech says just putting a smaller pulley on won't get me there because it will still not make max boost til top RPM, and while I realize it's somewhat linearly building from idle through redline, I would have to think that going to, say, an 82mm pulley would hit 9 or 10 psi earlier in the RPM range, then you can keep it steady from there to redline.

Thoughts on this?

Further, what is our current level of knowledge regarding safe boost limits on S62? The M62 guys are starting to push higher boost now, 14-16psi and maybe more soon. It stands to reason that, due to lower compression, S62 won't stand up to quite that much, but I wonder about 10 or 11 or even 12 - and then venting excess out.
 
#2 ·
I have seen S62s take 20 psi. The plenum will blow before the motor does, unless you go metal or CF reinforced. Has to be a sleeved motor IMHO.

The technique you describe of increasing boost at lower RPMs--using a "pop off" valve that opens when a certain PSI is reached to evacuate pressure rather than a "blow off valve" that is normal open and only closes at a designated boost pressure--is controversial on this forum, but is IMHO well founded and a great way to build pressure faster and more efficiently. The CA Automotive supercharger kit for the E39 M5 employs the pop off valve that I use--designed by Mr. X and super simple: spring keeps the valve closed until certain pressure is reached, and that pressure is adjustable with a simple retaining screw. Beautiful form and function. But plenty of people will race in here to tell you how stupid it is to run such a valve, etc. But I can tell you that it works exactly as one would expect.

--Peter
 
#3 ·
Thanks, Peter. I don't want to do any internal work on my engine. I will run 50/50 meth for safety and cooling. Street use only.

I do have the metal early style plenum and have solved boost leaks up to about 12psi but can go further if this project seems realistic. I have a local indy shop excited and ready to help me take on some of the work including the aluminum welding and the custom tuning.
 
#5 ·
I probably will. But now I'll be burning through $300 275/30/19 tires at twice the rate. Michelin is getting super stingy on warranty so I may have to switch brands in that case!

Peter, where can I find more info on these valves? Would I want to run two, one as a backup for safety? I wouldn't want one to fail and all of a sudden get a 20psi spike.

Also, do you happen to know offhand the crank pulley size on the ESS kit? I want to be sure I don't overspin the blower which is a V3Si and has a max RPM of 52,000.
 
#6 ·
LOL. Yeah, you need to go R-comp!

Look them up on the CA Automotive website.

Don't remember the ESS crank pulley size (6" maybe?), but you can overspin that little ole' V3Si by about 3k rpm without incident (and probably more), so long as your car doesn't hang out at max rpm all the time and you change the SCer fluid regularly.

--Peter
 
#12 · (Edited)
For what it's worth, I had your exact process sketched out for my car as well. It was only when I found that I literally am at the maximum RPM for my blower that I was forced to abandon it. Spin the hell out of your blower and just bleed the pressure off past 8 or 10 PSI. I'm hitting 10.5PSI at 7k RPM and so far it's been with out a hitch. If my Rotrex would let me do it, I'd already be cranking my CFM through the roof.
 
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#13 · (Edited)
Its a solid idea, but remember that part of what makes boost safe at higher RPM's on this engine is that it has a far lower VE there. If you bring that boost to lower RPM's your cylinder pressures will climb. On this engine 10 PSI at 7,000RPM maybe yeilds 380lbs-ft of torque, but that same boost at 4,000 maybe yeilds 500lbs-ft. Its more stress on the engine and drivetrain. You may find your clutches slipping too.

If you are doing it, the best way is to keep a traditional BOV and then add a wastegate. Both valves will double up as a blow off valve when you drop the gas at redline and the wastegate will ensure boost stays in target.

Now, another thing to remember. 10 PSI on a stock engine versus 10 PSI on an engine with a better exhaust are different things. The latter being more load on the engine and therefore closer to its limit.

Its a fun project but you're going into more dangerous territory here even though you're not increasing peak boost.


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#15 ·
Popcorn on lap. What rpm is your blower doing now? Can you post a boost curve? I forget if yours data logs. Definately get your meth installed first. You can mirror mine or go all out auaquamist.
 
#16 ·
No boost logging ability. Not quite sure on RPM as I don't know the crank pulley size. Yes, for sure meth first. Thinking of AEM's setup and will be talking to you soon about mounting options, using the windshield washer reservoir, etc.
 
#17 ·
Keep us updated. I installed the ESS kit in '09 and went with the 92mm pulley and water meth soon thereafter. I recently picked up a 88mm pulley which I plan to install and have the car re-tuned. I also have a S54 car. What's going on with yours?
 
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