McGehee/Forza Supercharger Install!!!

Finally got the boost gauge in today (the previous boost gauge was DOA but replaced under warrantee). Yep, I've got PLENTY of room to go up... only hitting 5-6 psi at redline right now!

I like the gauge -- electronic with sender, records peak, you can put in a peak warning if you want, is bright white for daytime, and amber if you're running your headlights. I took Tommy's suggestion and put it in the glove box/coin tray. When power is off, the gauge is blacked out completely, so it's very unobtrusive. And only $79! www.prosportgauges.com though I bought mine from www.deftracing.com
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A better look at the gauge, displaying the "SHOW PEAK" function (I'm hitting a peak between 5 and 6 psi)
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I replaced my center console clock with a Prosport digital A/F gauge, and I changed out the oil temperature gauge next to it so that they'd match. Like the boost gauge, they're "blacked out" when you don't have the car running. But they look great when powered up. The oll temperature gauge showed a perfect temperature match to the stock gauge when I first changed it over (with the car warm), but it's actually more functional than the stock gauge since it has finer measurement and shows you temps below 140 degrees as you're warming up.

The A/F gauge does "double duty"... it always shows your A/F ratio as colored bars around the periphery, and the center can show the A/F as a number digitally or you can have it show volts.
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Hi Chris:

A non-supercharged engine works with negative pressure or as we commonly say, 'vacuum' (piston/ring action pulls air through), and the supercharger pushes air through at positive pressure, or as we commonly say, 'boost'. The "boost gauge" is really just a pressure gauge that shows what your engine is seeing at the manifold/plenum as it ranges from negative pressure (vacuum) to positive pressure (boost). My supercharged engine still functions at vacuum except at higher rpms and higher load (strong accelleration).

To get more psi, I will simply change the pulley on the supercharger to one with a smaller diameter (about $80 from Vortech) to make it spin faster as it is belt-driven off the custom 6" pulley at the crank. I already have a smaller pulley in hand, and hope to change it out next week.

"Max" for me is either when I reach the limit of the clutch being able to hold the torque, or I start blowing out gaskets from the pressure or start getting valve float. I fully expect that my stock clutch would go first (at least I hope so), and my target as such is to work the psi amount to get me to around 350hp as measured at the dyno to stay within stock clutch limits, and do it by staying well under around 15 psi as a target maximum. The HP and psi should be "safe" numbers, though some will say the stock 308QV/328 clutch can take you nearer to 400hp.

The boost gauge just lets me know where I am as I'm working up towards my hp and psi targets without hurting anything, rather than just guessing from Scott's calculations (which appear to be high as far as pressure associated with the particular pulley sizes with this supercharger model). In the current circumstances, after exercising the car aggressively to redline through multiple shifts, the max incoming fuel-mix pressure the engine saw was (only) +5.5 psi, yet we know from my dyno run it's still giving me over 300 hp. Mark E was right on the money with his correlation between my hp and the amount of boost I'm currently using. So the question now is, what will it do if I double the boost?!?

Don't worry... most all of this was new to me too!

 

I think we're going to be fine on the the fuel *flow*, but we'll see what the stock CIS can do regarding A/F ratio. Larry has tuned my new WUR fuel regulator to the rich side of spec, so that should help. The new non-lambda fuel distributor should help that too. My mechanic had another idea... use the WOT switch as a secondary trigger for the cold start injector to add fuel during hard accelleration to also improve the A/F ratio. Anybody tried that? It sounds like it should work!

 

Right.

Nope, it's really just for setting up and optimizing the system initially. Once you've put on your "final" pulley, you wouldn't need it. For example, with my current setup, I know where the max (peak) pressure is ALWAYS going to be -- +5.5psi -- and that's not going to change until or unless I change something in the system like the pulley. Unlike the tachometer, I wouldn't be using the pressure (boost) gauge in real time to adjust my driving in any way. I do plan to leave the gauge in with the "warning" set to about a 3 psi overboost condition (3psi higher peak than wherever I intentionally decide to stay) just in case something were to go seriously wrong, but that's highly unlikely.

added: I see Mark beat me in answering this already!

 

FYI, my next pully swap should put me right around 8 psi at redline...

 

It *does* datalog for later playback or graphing... I wouldn't really know what to do with it, but I presume my mechanic (or you experts) would.

 

If I can impose on you a bit more... if I'm getting 5.5psi from a 3.60" pulley, and we're expecting aprox 8psi from a 3.25" pulley, what pulley size would give me aprox 10psi, and what size would give me aprox 12psi?

 

Thank you, I appreciate it. Vortech makes pulleys for the superchargers in diameters ranging from 5.0" to 2.6", but of course it has to be properly matched to the particular blower and crank pulley size (and yes, mine is 6.0"), but that does give plenty of flexibility.

Here are some of Scott's pulley/psi calculations, and it's a reasonable presumption that they are at the supercharger itself based on Vortech's data/specs and that they don't account for the actual reported "air-pig" nature of the 308 (which may be why my 3.60" pulley is NOT making near 10psi at the plenum):

3.1" = 20psi
3.125" = 18psi
3.25" = 15psi
3.33" = 13psi
3.4" = 11.5psi
3.48" = 11psi

 

The Vortech V9-G is rated at
Maximum airflow: 800 CFM
Maximum boost pressure: 20 PSI
Absolute maximum impeller speed: 65,000 RPM

 

The Electromotive XDI-2 shows the MAP sensor values in Kpa, but I guess all I have to do see how it moves relative to maximum (whatever that number in Kpa is) to know where to pull back the advance.

Scott's planning in write some new XDI-2 advance maps and email them to me to try out at my next dyno session. I can't get into the shop schedule this coming week (a 246 Dino that's been sitting for 2 years is my mechanic's current priority) but we're set for getting my work done during the week of the 25th.

Meanwhile, I'm still having fun driving it!