John..

The shadows of my garage, now that is cool

Jim bailey - 928 International

Andy's street legal BFG drag radials will be delivered here tomorrow once mounted to some 8x16 rims he plans on some more 1/4 mile "dyno runs " But he will be busy for the next few days getting 11-12 manifolds ready to ship . Carlsbad raceway is a possibility and near sea level , maybe I should run the very brown 1980 as well see what those 194 horsepower 225 ft lbs of torque really will do ..............

bcdavis

Yeah!

Get a *before* time, then go back there after the supercharger, to compare the improvement...

slate blue

I thought the Devek car ran a 12.4 and not a 11 anything. The trap speed was the same as one I had seen and as such I would have thought that 11 something was a typo. Maybe the gearing was changed? anybody really know?

SteveM928

Tim Murphy 8psi dyno chart
I told you I've been watching some of this stuff for a while.

Maybe, but definitely not from me. You can fairly closely calculate the 1/4 mile performance that a car should be capable of by using a dyno chart if you know some of it's specifics, like weight and gearing. I can get a pretty good idea of what my car as it's equipped should run in the 1/4 mile if it had only Marc's engine as a change just based on his dyno chart. You can't calculate out a dyno chart from a 1/4 mile time slip like that. You can also use the dyno chart and some of the other information available for the specific car you have to calculate a reasonably close top speed. A 1/4 mile time slip isn't going to do that either. Marc's selling power, not 1/4 mile times. Professional racing teams all spend a good amount of time working on dynos. Except for drag racing teams, none of the other professional teams spend any time at the drag strip.

That again enforces my point about using drag strip results to try and accurately compare the two supercharger systems. Are drag radials going to increase the engines power? If 1/4 mile times are what's being sold, do any kits come with drag radials included?

The dyno automatically corrects for the weather conditions it records when a dyno run is done. The altitude of the dyno location is entered in when it's initially installed. That's about it as far as "lots of correction factors entered into the machine", and is all that's necessary. How many variables are encountered when someone states that a car ran XX.XX@XXX.XX in the 1/4 mile? If you're lucky, there *might* be one correction made for altitude and that's it for that 1/4 mile run.

There are also very clear reasons why so many aftermarket centrifugals are being sold compared to other forms of forced induction.

You make it pretty obvious that you haven't closely loked at some of the dyno charts that have been posted in the past with statements like those.

Being a turbo guy, I'm very surprised you even brought much of this up John. I can dig up some information showing Porsche's test results in comparing supercharging to turbocharging on a 944 if you want. It makes it very clear about that response on the road stuff you're talking about, but I'm guessing you won't be very happy to see it.

I know it may sound like I'm kind of bashing Andy to some, but I'm really not. I just think that if any real comparisons are going to be made in regards to what's actually being offered by different people, they should make those comparisons using standards that are as close and standardized as possible. If you want to do drag strip comparisons about the best you'll probably be able to do would be to get Andy and George Sunnen's car out on the strip against each other, with both having the same tires on them. Until then, using 1/4 mile results for direct comparisons of the different systems doesn't make too much more sense than comparing to that 10 second Honda that someone mentioned before.

Jim bailey - 928 International

SteveM.."Except for drag racing teams, none of the other professional teams spend any time at the drag strip." ........You will not find them using a dynojet style inertial drum dyno much either .
SteveM .."very clear reasons why so many aftermarket centrifugals are being sold compared to other forms of forced induction." ........correct mostly because it is relatively "easy" to hang one out in front of the engine and not because of any superiority of the design . I just think it is nice that Andy has significantly increased the performance of his S-4 . Has he made the most horsepower ? NOPE has he made enough ? maybe ? But you have to admit he is having fun . I want to get him back on the road race track for another day of burning up tires and brakes .

mspiegle

If those really are his times, those are indeed damn quick! Too bad this is a supercharger discussion.

jorj7

Sounds like a parts supplier talking , not that there's anything wrong with that.
Just encouraging our addiction to speed.

John..

Yes, there are lots of CS being sold in the aftermarket, but I can also buy a cheap set of tools or a good set of tools. Get the picture? The CS is so popular becasue it is the simple way to get some boost, that is it. By no stretch is it the best. Talk to the serious tuners and experts out there, they will all tell you it is at best an ametuer approach. How long does a CS last compared to the far less complex turbocharger? I'd lay you money no CS will go 200,000 miles.

Your statements on the 944, is that with a centrifugal or positive displacement blower? The inherently low mid range air delivery of the CS would rear its ugly head on the 4 cylinder for sure.

You think the dynojet is the best. Horse Hockey! It is a good baseline measure, that is it. Why would my car only put down 12 lbs on the dynojet and over 13 on the street? Because the dynojet does not laod as hard as the road. A real loading dyno is far superior and can get real word loads on the car.

You guys talk all this crap about the CS and how great it is. The fact it is can't hold a candle to the performance of the other setups. Let me go find that chart on the boost curve of the CS vs Positive vs Turbo....

John..

http://www.aerocharger.com/tech1.htm

Does this graph help explain the benefits of one method over the others? It is simple, really.

mspiegle

Don't top fuel cars utilize positive displacement blowers?

John..

From Cartech's website... Looks like there are some other experts that share my viewpoint. Read closely lads...



Why the Turbo?
For technical excellence and engineering judgment, we should all stick with the industrial leaders such as Rolls Royce, Porsche, Mercedes, Audi, Lotus, Mitsubishi, Toyota, Nissan, Saab, Volvo, and Ferrari. These guys are turbo adherents and lead the world in automotive engineering. Over the last 45 years, turbochargers have been essential in winning thousands of races with the diversity of Formula One, Indy Cars, and even the great endurance contests of Le Mans, Daytona and Sebring. Is the disparity between the abilities of the turbo and the SC that large? Yes it is, and here’s why.

Shape of the torque curve:
The centrifugal supercharger is fabled to offer huge low end torque advantages over the turbo. That is flat wrong, never had an inkling of truth. With a size compressor selected for, say 8 psi, the CS must turn at some specific speed at the engine redline to flow the air needed to produce that boost. It is necessary to understand that flow through these types of compressors varies with the cube of the shaft speed. In other words, doubling the speed of the shaft will produce 23, or 8 times the flow. Turn that around and clearly, the flow is 1/8 at half the engine speed that it would be at the redline. Basically, that means you have 1/8 the boost at half the redline. And that is about where it really falls, 1 psi boost at about 3300 rpm.

Please understand, that is what you get with the centrifugal blower, but we strongly suspect it is not what you either want or think you are getting with a supercharger. Wouldn’t it be a hoot if someone invented a way to let the same compressor wheel speed up relative to the engine so more low engine speed boost could be produced? Such a device exists and it is the turbo. The key to this great turbo performance benefit is that it can change speeds independently of the engine.

The net result is this: The turbocharger applied to the BMW M3 can produce all of it's boost by 3500 RPM.

bcdavis

Regulations require it.

They aren't allowed to run turbos.

ViribusUnits

John, something is wrong with that chart. The conventional turbo and centriffigal seem all right, the positive displacement, something is wrong.

The line from the roots blower SHOULD be nearly flat. Theory, and practice says the line is nearly flat. Why is it sloped?

SteveM928

According to DynoJet, their model 248x is the "Officially Licensed by NASCAR" one. That really doesn't necessarily mean that much though. All I'm saying is that if you want to fairly, accurately, and realisticly make comparisons of the different systems available, it should be done using the same type of test and it should minimalize any other variables to as great of an extent as possible. Don't like DynoJets? Fine with me. Have any of the different kinds of system cars got charts from Mustang, Superflow, or other types of dynos to post? The only even reasonably close to accurate comparison of only the power created by the superchargers so gfar has been the DynoJet charts that the various cars have posted.

I'd think that those guys that are building tube frames/cages, custom engines with non-production blocks, heads, etc. and are collecting prize money wouldn't base that much of their decision on one maybe being a little easier to hang on the front of an engine.

Very true. Again, I'm not downplaying Andy's setup and what he's done. Everybody will have to make their own decision on what they want. So far my wallet has stayed in my pocket. If I were buying something today, I know what it would be. I also know that not everybody is necessarily going to want the same thing. Maybe there is one solution that would put a lot of this stuff to rest:



It's a 5.0 liter engine with an ATI Procharger centrifugal's output blowing into a Paxton centrifugal's intake. The Paxton centrifugal's output then blows into a Kenne-Bell twin screw's input.

Yes John, you've posted that link before. I've got it saved in case I ever want to turbocharge my snowbobile. Two sources that sell turbochargers stating that turbochargers are best eh? Why the chart from a guy that just said charts aren't important, and that street performance was?

Yes. Mandated by rules stating that they have to.