GoRideSno

Gregg,
My roots system fits under the hood. I'm pretty sure the centrifugals do too. Mine will soon have an AW intercooler that sits in the V, and it will still fit under the hood. I could do a complete install of my system in one day since I have already done it. Most other people would take 2 days to do it. I recently re-installed my whole system except for the crank pulley in less than 3 hours. It would have only taken 20-30 min more to install the crank pulley if I had to. It won't fit any 2 valvers though.


Randy,
I refuse to answer, on grounds that it may incriminate me.

Chris,
Yes I used a blower that I salvaged from a Jaguar. It is an Eaton M112. I could eaisly fit a new MP112 from Magnuson or very easily swap to a Whipple twin-screw type blower. The dimensions of the Whipple are nearly the same as the Magnuson/Eaton. The Whipple would cost about $1000 more that the Eaton, give cooler charge temp and take less power to drive. It also comes in several more sizes with 2 larger sizes that the Eatons, meaning much more power potential.

If I had a 5-speed I may have just gone the route you have. I will PM you and I look forward to your decision.




Andy K

PorKen

Gregg K - GoRideSno had it easy in that the thirstytwo valvers have the intake holes toward the 'V', versus the sexteen valvers which have the spark plug holes closer to the 'V". So the original engines require a bit more thought.

GoRideSno - what difference would the 5 speed have made?

Gregg K

I am dying to hear a 928 blown engine. Can anyone even verbally describe it? Am I acting like a dunce? Don't make me do an install just to hear one. Altho, I'm slowly starting to think about how fun it would be to do a custom design.

GoRideSno

Porken,
You don't really need the widened power curve much at all with the 5 speed because it is easier to keep the RPMs where you want them. So the roots has no major advantage with the 5 speed. The centrifugal has the advantage of having lower discharge temps, and less parasitic loss due to drive power. They are capable of making more power than the Eaton Roots (move more air) on the top of the RPM range. So it would have been just as good and 1000x easier to bolt on one of the available centrifugal kits if I had a 5 speed.

When considering supercharging an auto v/s a 5 speed, the automatic has two major disadvantages. The autos have less gears with which to take advantage of the peak power, and it is harder to get the autos in the right gear to take advantage of the peak power. So it would be nice to be able to widen the power curve in order to more easily take advantage of the peak power. The roots and twinscrew do this by adding power at low and high RPMs since full or near full boost is available just off idle.

I haven't researched it that much but the twin-screw could be the best choice overall. The general buzz is that they have lower discharge temps and low drive power loss like the centrifugal, but have just as much lowend boost as the roots.




The 2 valvers would not be that hard. I would take two 944 intakes (which would bolt right up to the head generally speaking) and cut them about in half. I would then fasten them to a plenum via welding or hoses that the blower is blowing into. It would look about like the stock intake spider. The reasons for using the 944 intakes v/s cuting up the stock intake is that the 94 intakes are readily available and cost about $30 each. Some even have a six rib pulley near the engine on the crank pulley which would simplify the design even more. Somebody send me a 2 valver and I will do it!!!! The challenge would be relocating the air flow meter I think, but I really don't know much about the OBs.


Andy K

Z

They can vary a lot. It depends on the supercharger used for the particular installation. Some can be quiet enough that you wouldn't really notice anything too different from stock at idle and low throttle. Others definitely leave no doubt that there's something different about the car, even when it's just idling.

I think that there may be some misconceptions about the centrifugal and where it makes boost, especially in relation to the automatic transmissions. The before and after dyno runs of Lagavulin's car were started at around 1,600 RPM. The charts clearly show the centrifugal supercharger already making boost at that 1,600 RPM point. At that point he's already making over 20 ft/lbs more rear wheel torque than stock. That RPM is below the stall speed of the automatic's torque converter. In other words, the centrifugal would be making boost at any time the automatic car is at full throttle. The worst case situation for the automatic would be at just above the torque converter stall speed, but even in that situation you'd already be making some boost. In higher gears the transmission will downshift, causing the RPMs to be up where a lot of boost is being made. When the gas pedal is floored while in higher gears, in my automatic the RPMs never drop below about 4,000 RPM with the upshift, so big low end boost wouldn't be an issue in those gears. A roots style supercharger would increase the amount of boost at the just above torque converter stall speed in first gear, but what are you going to do with it? One reason I changed the cam timing on my normally aspirated automatic car was to reduce the amount of wheelspin I was getting off the line. Even in second gear, with the centrifugal superchargers both Lagavulin's and Tim's cars could use more traction, even though they both already have good sized rear tires and limited slip. What are you going to do with more low end boost when first gear is already nothing but wheelspin?

CMW

Z,

Outstanding reply. Which is exactly why my target range of 400-425 is where it is. With LSD and good sticky tires they are still going to break loose in 1st gear.

Also, if I remember correctly TM and Lagavulin did not modify the engine such as new CAMs, Pistons, heads, etc, correct?

Chris W

Z

Both Tim's and Lagavulin's cars have completely stock engines, with nothing done to the heads, cams, pistons, or anything else. Lagavulin's car even had the stock cats and all of the emissions control stuff on it.

GoRideSno

Z,
I certainly don't mean to say that the centrifugal dosen't make any boost down low. It clearly does.
In specific to the 4 speed automatic. I am really not concerned w/ spinning out in 1st gear, just don't give it enough throttle to break them loose. 2nd gear is where the party begins and where it ends.
Here is my view on the 4 speed automatic.
The boost v/s RMP discussion always seems to default to describing what happens in straight line acceleration such as on a strip or dyno v/s normal street performance driving. It isn't so simple in real world driving. Normal driving speeds here in the US vary from, about 30 to about 100mph. This means we start with only 3 usable performance driving gears. Since 145mph is the redline shift to 4th it is useless in street performance driving if you want to stay out of jail. Once you get past about 30 mph there is no getting back to first gear. This leaves you with only 2 gears, 2nd and 3rd. While performance driving if you do not pass ~88mph there will be no need to shift to 3rd. That means the vast majority of the time, during performance driving on US streets the car will be in only 1 gear, 2nd gear. It is 2nd gear's duty to get us from around 30 mph to about 90 mph with rpms ranging from ~2500 to ~6400. The closer we are to our max boost at 2500 rpm and 30 mph the more power we will have and the quicker we will get to that next shift point into 3rd where we will start again at ~90mph and 4500 rpms. May I add that a stock NA M28.42 has less than 140 crank hp at 2500 rpms. If I could get back down to 1st gear at say 45 or 50 mph then I would be happy without any sort of blower probably. But since I can't I gota make the best outa that good ole 2nd gear.

Chris,
I'll give you a call tomorrow.


Andy K

Old & New

Andy,

Good points, but remember that for many of us (who travel highways) the power demand begins at 55-75 mph. We are looking at traveling in fifth, and dropping to third or fourth for optimum gearing.

GoRideSno

Old and New,
I guess I should have mentioned first that I was talking specifically about the 4 speed automatic. What I am saying there really dosen't apply to the 5 speed. I am in favor of the centrifugal and 5 speed combo. I think that combo would be the most fun to drive. I wish I had a 5 speed. IMHO, the positive displacement blowers make the automatic more fun to drive though. I am going to edit that post to mention I am talking about the 4 speed automatic transmission.

Andy K

Old & New

Doh! I didn't pick that up, but I guess it would certainly make a difference, huh?

Z

The rear wheel horsepower and torque of the stock M28.42 is basically the same as that of the M28.41 at that 2,500 RPM.

I don't know. Maybe I've just gotten to used to my '88 A/T, and too out of touch with what others are like. Mine's making more horsepower and torque than most GT and GTS five speeds, so that could very well be part of it.

Lagavulin

Andy, you mentioned you were going to 1/4 mile the car, did you get a chance to yet? Are you going to run it on the dyno? Are you close to getting the intercooler installed?

Sorry for all the questions, but I'm interested; keep up the good work!

Gregg K

No engine mods? Ok, now I've got a project in my future. No engine mods? Yer kidding. So why lower compression and larger valves for turbo installations? I mean, if I can simply bolt on a really cool twin screw. (Bolt on to me means lots of custom machining and Autocad drawing, and engineering. But I long for that stuff.) I can't believe you are cramming more charge in the engine, and not either lowering the comp ratio, or something!

GoRideSno

Gregg K,
The S4 has the same combustion chambers and valves as the 959. So I would say that they are pretty well designed for forced induction. The pistons and compression ration may not be the best for forced induction, however there is a Lingfelter kit that uses pretty much the same blower as mine on the Corvettte Z06 which has cast pistons and 10.5:1 CR. It makes 5.5 psi and has NO intercooler.

Lagavulin,
The trip to the track got side tracked. I went for a cruise over some mountain passes instead. I am still running the prototype manifold. I still need 1 more part from the machine shop. After I get that and Switch to the Bell FMU then I will go to the dyno. By that time I may have the intercooled version done.

Z,
Yes I had gotten used to my automatic as well. What I found my self doing was not accelerating when I knew the car had no kick. For instance if was in second at 30 mph i would ease the car up to 50 mph then accelerate hard. Now i don't have to do that.


Andy K