Eagle2000GT

If you are cruising and not accelerating the motor is operating in vacuum. It doesn’t matter how much boost the supercharger is generating. I once cruised at 5000 rpms in third gear for a brief moment. (Can’t do it too long because it will pump the oil pan dry.) The vacuum gage showed vacuum not boost. Open the throttle to accelerate and the gage immediately went to boost. Boost was being generated but it wasn’t being used.

This is an incorrect statement. The by-pass valve is held open by vacuum. A spring closes it when vacuum decreases. The butterfly valve in the by-pass valve opens and closes exactly opposite of the butterfly valve in the throttle body. I have worked the throttle manually under the hood and watched the by-pass valve partially close and then reopen. It is true that the pressure will take the path of least resistance. That path is not through a mostly closed butterfly valve in the throttle body but out the mostly open by-pass valve. When the throttle is open the opposite is true. Then the by-pass valve is closed and the path of least resistance is through the throttle body.

I’ve run my system both ways and it makes no difference. It is called a by-pass valve if you “recirculate” the air. It’s called a blow-off valve if you vent to atmosphere. It’s the same valve either way. (Note: I run a blow through MAF which allows me to vent to atmosphere.)

You are absolutely correct. A centrifugal supercharger generates boost in proportion to rpm. Mine generates 1.8 psi at 2500 rpms and 8.9 psi at 6000. It always does this regardless of speed or throttle position. But this doesn’t get past the throttle body to the manifold unless you are accelerating. Whether this is at 60% open throttle or 80% open throttle probably depends on how much boost you are generating. It will be different for a supercharger generating 20 psi from one generating 9 psi.

You are running a Vortech at around 380 rwhp so you probably have 9-10 psi at 6000 rpms and probably have a similar boost curve to mine. If I go wide open throttle at 2500 rpms my boost gage will immediately read 1.8 psi and then start increasing with rpm. Partial throttle might see 1 psi or less. A slow acceleration will stay in vacuum and never see boost. At 5000 rpms I can see a larger amount of boost at partial throttle than I see at 2500 rpm.

But you can accelerate without ever letting boost into the motor. A closed throttle causes about 17 inched of Mercury (vacuum). If you are driving for fuel economy you then slowly accelerate shifting when the vacuum/boost gage reads 10 inches of Mercury (vacuum). I have done this and slowly accelerated to 70 mph never reading boost on the vacuum/boost gage.

jmn444

so here is my question of the day...

running average 295's, nothing super sticky, with a turbo (i'm assuming similar characteristics to a centri) pushing around 7-8psi which should break the 400rwhp mark in my '07 4.6L, if I were to floor it in 1st without dumping the clutch, would i be spinning thru 1st gear? or would the power build in a way that should keep it planted fairly well?

2nd question, assuming that it would stay hooked fairly well, is it also safe to assume that dumping the clutch at 3500+ would smoke them easily?

I've never driven a turbo/centri car, but leaning towards trying a turbo in my SGT... still researching the options though. I prefer to hook and go over the instant smoke show of a roots, but also want to know smoking them is still "easy" to do intentionally with the turbo/centri setups...

Eagle2000GT

Smoking the tires is not a problem. I'm running 315/35-17s Sumitomo HRZs @ 25 psi tire pressure. I cannot go WOT in first from a dead stop, slow roll, or at 25 mph without breaking the tires loose and hitting the rev limiter. If I launch at 1800 rpms and go half throttle the tires spin and then latter grip but I cannot go WOT and have the tires grip. I cannot shift to second early without spinning and bouncing off the rev limiter (i.e., shifting at 4500 instead of 5800). For some reason if I run it out to 5800 the tires grip better. I cannot under any circumstances just go WOT in second in a corner. The tires break loose and the car goes sideways.

I could put drag radials on it but I drive 20,000 miles per year but I don't want to buy new tires every six months so my solution is throttle control.

jmn444

That's good to know! I will likely stick with my turbo plans then, as I will always be on street tires anyway.

ShadowDrake

I'll add my dyno sheet here from earlier - A/F was a little rich, it looked like a diesel :P but better safe than sorry.



I have 245/45-17 tires and first gear is out of the question. Second gear holds just fine when ambient temps are ~50 or higher... as long as I'm going in a straight line.

Grip is more about suspension setup than tires! You can have the best tires in the world but a terrible suspension setup and still not hook up. My car isn't set up for traction, it's set up to look nice. It's lowered too far with springs that are too stiff to give me adequate weight transfer - thus my lack of traction.

Edit: Switched links for picture.

Furinox

I recently switched from a vortech t-trim to a ported eaton and I like the eaton much better for my driving style. My car is a daily driver and I like to be able to instantly make full boost rather than having full boost right before I let off the gas. The car is much more fun to drive now and actually seems quicker while normal driving around town, while the vortech seemed slightly slower than stock when not flooring it if that's possible. Again, just my perception after having both.

teej281

Im talking about the whipple 2.3, not the 3.4. The 2.3 is a pretty BA little blower id say. My buddy on 17psi is making 560rwhp with stock exhaust manifolds, and that was on one of those 85* days we've been having here in south central PA lately on i'd like to say the 3rd run. So his blower and engine were already hot from previous runs and they made some adjustments to his tune and he came out with 560rwhp, but it definitely feels like 580rwhp i'd say. So yea, the 3.4 has its place in certain setups but you need to be cranking that thing to like 23psi or higher for it to be worth it to switch to it over the 2.3. And for a blower thats half a liter smaller putting out close to the same power with less boost, i'd say the whipple is better than the KB, but thats just by my reasoning. All in all, its better than an eaton. lol

To Furinox: Why the switch? And whats the current setup right now

Furinox

I didn't like the way the vortech worked/built power. Right now I have a ported eaton with a 2.93 upper and 4 lb lower.