Geo

First of all, I wasn't talking about fabbing up a NA header, I was talking about fabbing a manifold for a turbo set-up. Fabbing a manifold for a turbo set-up is much easier than a decent NA header. I know of people who have made 400 hp to the wheels of a 2 liter daily driven car with a log style turbo manifold. Second, just because you cannot do something yourself doesn't mean you can't go get it made for you. I weld like a monkey but I made my cage myself for my race car. I just had someone else do the welding.

hacker-pschorr

The 1987 928S4 running 22psi through a modified 951 intercooler (converted to air-water) is nothing short of a rocket. He has stock 9" tires on this car with LSD. He's still driving this car to work up here every day - once the snow flies he will park it.

He's running a Paxston supercharger.

I don't have any current photos of this engine to post at the moment.

Geo

Well if you're going to make a theoretical comparison using a poorly packaged turbo installation vs a well packaged SC what do you expect?

Or tell me there is no real exhaust backpressure with a SC?

Or try to make a point about how good a SC because of how a car equipped with one didn in Speed GT?

Those were one wrong statement and two very bad examples. But you're right, I'm losing patience for this whole debate so I should probably just back out. The debate is starting to drift into other things.

hacker-pschorr

Geo,
This is getting silly - with enough money, anything can be made. Ever see Jay Leno's 400hp Ford Festiva? - that was without the NOS.

That was not the point. I was trying to make a point that a supercharger setup designed from scratch is much simpler than a turbo setup to not only to design but to also install in a kit form for the "average" person (meaning no specific specialties when it comes to cars). My main reason was the header design / construction. I still stand by that.

Legoland951

I believe both the SC and turbo have their own applications like others have mentioned. I am more familiar with a turbo so I like turbos due to familiarity. I can't imagine the turbo not having more backpressure from the exhaust port back to the turbo than a SC car since the exhaust pressure, momentum, and kinetic energy is the ONLY thing that spins the turbo. A simple analogy is trying to blow through a straight straw compared to a straight straw with a fan in the middle of the straw. There are no restrictions from the exhaust port back to the tailpipe in the SC where the turbo exhaust impeller IS the restriction. Also, the exhaust port is the hottest part of the entire engine bay by far. You can get an infrared thermometer and measure it yourself. I would imagine that is why the intercooler is used in our 951s. Gas laws state Pressure (p) x Volume (v) = number of gas molecules (n) x R (gas constant x temperature (t). If you lower the temperature, you decrease the volume so you can cram more air in the same amount of space (increase air density). In other words, intercoolers are much more necessary for hotter intake air temps (as in our 951s). I can't imagine a supercharger reaching a fraction of the temperature of a turbo because the belt would probably melt. How does the supercharger heat up the intake air temperature comparable to the turbo?

Superchargers are driven by a belt with much more moving mass/parts compared to turbine blades, therefore taking more power away from the engine generally. In the case of a 928, its probably a better choice because its no fun working under the hood of an S4. I find it easier to work on a 951 than an S4 (probably because I work on a lot more 944s than 928s. The 928 V8 is a very wide engine and its the reason why I personally prefer a SC kit for that car because there is just not that much room by the exhaust manifolds. With the SC, its probably like working on an n/a with another pulley (god forbids - a smog pump).

All in all, whatever makes you happy is what you should get.

Geo

Fair enough. I just disagree. I personally don't think you're getting my point, but that's OK too.

I should have known better than to get into this holy war anyway. I personally don't care because I know the folks I get my info from are as good as you'll find. Furthermore, I neither own a forced induction car (anymore) nor do I make kits to make one. I don't have a dog in this hunt and basically it's not worth the aggravation and this sort of holy war argument is not why I'm here. So, if I've been out of line with anyone, my apologies.

nine-44

OK, that's it, everyone must now go do their homework twice! John, you have my permission to skip this assignment, lol. I was talking with a buddie of mine last night while we were covering my designs for my plans. He was telling me about one of his Audi buddies doing a 5000 turbo swap into a 4KQ. He took a KKK K-26#6 to a deisel shop here locally that deals with alot of turbo related stuff. The guy pulled the K-26 apart in like 10 mins, looked it over and told him that the turbo was junk, anchient technology and wasn't even worth bolting on and for 200 bucks he would build a frankenstein for him.

There are quite a few anti lag strategies listed in various books, the better designs listed in the Forced Induction Performance book that also has the graph of the 951 turbo vs SC are what I'm looking into.

OK, so I take a plane jane K-03 from a 1.8T audi and throw it on a 8HP Briggs and Stratton motor, with a matched sizing exhaust and intake so there are no step-ups or restrictions. I filed the cam to get rid of overlap then couple a Mikuni carb to the front, drawthrough. Interestingly enough I was able to play with it and got 2-4psi of boost out of a turbo that was about 10 times the size for the application. This was with NO load on the engine so I don't know how high it will boost to under "hard" boost loaded.

Also, I ran the same K-03 on a 16.5 HP briggs motor on my riding mower, just cuz I was board, and can get it spooling, I have not tuned it yet and have not had a chance to put an accurate boost guage on it either.

I have yet to test the throttle body added to the outside of the turbo strategy on a car, but I have read that an Indy car team's drivers didn't know what turbo lag was when other drivers talked about lag because their design eliminated it. That's Indy car tech vs Indy car tech, not Indy vs Ugo. It is within grasp and is also my current adventure. SCs are limited by their mechanical limits and efficiency restrictions due to design, turbos are limited by the closed mindedness of the builder of the system.

Bring a hard argument and I will gladly cave in to the SC bandwagon if you can prove your case and show me that they are not dinosaur pumps.

OH yeah, BTW, I have no real schooling in any automotive related subjects, engineering and whatnot. I only took general courses and welding in HS, that's it. Besides that I'm self educated and I try to be as open minded as possible.

turbo vs SC in short...eh, screw it, do the homework and you'll see, that is unless you don't want to see it. Have fun with whatever you run and prefer, I'll be on the drawing boards.

Remember, everything goes better with boost.

Geo

Lego, you're right, there will be greater pressure between the exhaust valve and the turbine wheel. I'm sure there are some issues here, and while I don't have the engineering knowledge to correctly address how this plays out in the mix. All I can say is I've never heard any issues over this in the past. My guess is that with proper sizing of the turbine wheel and housing, this is not a significant issue or you'd hear about it all the time.

The backpressure issue with a turbo that you do hear about is post-turbine. Backpressure there in the system has a major effect on performance. There is little difference here between the SC and the turbo. From my friend at Garrett "it's impossible to go too large on the exhaust for forced induction." Anything you do to reduce the exhaust system backpressure is a plus.

Tony

Im on stock engine mgt, stock 10:1 CR and 91 octane gas in Las Vegas...and 150K miles stock headgasket. I still have a full hot summer ahead of me next year yet!
Ive only got 800 miles and 2months or so on the set up.

Beside if you cant hook it up, what good is a gazzilion horspeower/TQ anyway? right now my power band suits my 4sp automatic with 2.20 gearing perfectly! It has really woken it up!


There are 5.0L 928s putting out over 550 rwhp on SC's now...but the guys doing it have a bit more experience with it.
Also, remember, this is a 928, not your familiar 951 that has seen forced induction its whole production run as it was intended.

500rwhp is my long term goal, but more so a performance range. ..its what ever i hit first. I tell ya this though, ITS ALL FUN!

Tony

Right now at my boost level this Supercharger isnt even breaking a sweat! Ford Cobra guys are running them into the high teens and even low 20s on boost.
Right now my set up is only seeing 12000rpm at 6000 rpm. The ford guys turn them upwards of 18000-20000K...and more!

Main barriers are first fuel delivery as you all know LEAN isnt good.
After that it probably becomes air flow restrictions in the intercooler.
All this has to be balanced with "streetablility" and in my case the environment where i live. Las Vegas in the summer isnt kind to ANY engine on 91 pump gas!

Legoland951

George, I am no expert on exhaust and I heard the same thing you mentioned about "the bigger the better" as far as the exhaust is concerned on a turbo car. I have a 3" straight one piece exhaust from the header collector back and the only thing I can complain about was the added weight for the huge piping. I am not even sure if its necessary for my 300 flywheel hp turbo S but in this case, its not how you use it. Bigger is better

Campeck

which is a better s/c design though?
a centrifugal or a twin screw?

944J

which turbo?

hacker-pschorr

Campeck,
Do everyone a favor and search the 928 forum for that answer. You will find no less than 10 threads ormore dedicated to that discussion. That is a more difficult question to answer than the Turbo vs SC question.

hacker-pschorr

Geo,
I -think- I got your point. I have nothing against turbo's, never have. But in my situation (and most 928 owners looking for power) the turbo vs SC argument leans a lot more in favor of superchargers almost on the basis of simplicity alone. The 3 main kits offered for 928's are so well designed and work very well and IMO very inexpensive. The percentage gain you could get from turbo's is not worth the extra effort for 95% of the 928 crowd. I give John all the credit in the world for the car's he has been able to build. If and when he has a full kit to offer, excellent - the more boosted 928's on the road the better.