Gretch

89 GT power in an 80 weight class..........That is a huge gain. Wishing for anymore is "eyes-bigger-than-belly" syndrome....

Just do it.

James-man

Carl definitely has the right idea by suggesting dividing horsepower by weight for comparison's sake.

Assuming that the feel of HP is the real goal, the same HP in a lighter car will feel faster and more powerful.

Having a lighter car to start off puts you at a HP advantage from a performance perspective. Anyone care to run the numbers to show what HP a 1980 needs to run in order to feel like a stock S4? The 1980 will probably feel even quicker at this target HP due to gearing as you will run through the gears faster.

You can ball park with ( curb weight of 1980 / curb weight of 1987) * 315 HP = ???? hp

Any hp beyond that point is the gravy that we would be looking for.

928fan4life

Michael - the fastest car I have been in was a bmw 850ci. Not sure what the specs are on it but it had very nice pickup and would be happy with that pickup all the time.

Carl - Point taken. I kinda thought you guys would be able to get more outta the car if there wasn't the fuel system restricting it. S4 power would be pretty sweet! What is the weight difference between my year and an s4?? Would s4 power keep up with a bmw 850ci? Just wondering, because I have been in the 850 and know what the pickup and power is like. That way I have something to compare the s4 to.

928fan4life

If I were to throw on a euro throttle body, will that effect the way the supercharger setup works??

mspiegle

850csi cars are nice.... but I would have to say that a 320hp '80 would be a good deal faster.

In fact... he should correct me if i'm wrong, but the whole reason Andy started making these kits is because he couldn't catch up to one of those on the freeway with his S4. Most of the decent BMWs seem to do very well at higher freeway speeds. My friend has a bone stock '99 M3 and I was surprised how much slower I pull awy from him than other cars.

bcdavis

Doubt it.

Once you create pressure in the intake maniford, it tends to eliminate most of the issues of flow restriction.

The idea of doing a ton of head or intake work on a boosted car is kind of a waste of money.

Cameron

I tangled with an 850 a couple of times in my ex '90 S4. The 850 has about 300 hp in an almost 4000 lb car. It is not fast. In fact, the tested 0-60 time is around 7 sec. I knew that going in, so was not worried. Same result both times - before we cleared the intersection, he was seeing tail lights.

GoRideSno

It wasn't a race and, it wasn't a matter of what car was faster. It was a matter of driveability with the auto trans and wide gearing. It was extremely heavy traffic moving at around 85-90mph. I was just wanting to catch up to this car to take a look at it. At 85-90mph in the S4 auto you are hitting the rev limiter in 2nd and then the shift to 3rd leaves you at around 36000 rpms where a stock S4 only has around 132RWHP. While I struggled with just trying to accelarate at all in the heavy traffic, the 850 just kept motoring along happily minding his own business whipping in and out of traffic, increasing the distance between us. This is when I became absolutely certain that just just having a higher peak HP # wouldn't help that much. I knew that for my car to really be faster it would more available power everywhere, making it more driveable than it was stock.


TAmons,
You have done some very interesting and very original work. I am very impressed with your ingenuity.

Andy K

Herr-Kuhn

Let me give you a word of caution on centrifugally supercharging the 3-spd automatic car....major boost lag, especially off the line.

With a turbocharger you can be cruising at 15 in hg, boot it hard under a heavy load and you will have full boost in less than 1 second. I do not believe you would be at all happy with a centrifugal supercharger on your 3-speed automatic...the first gear is simply too wide. A 5-speed in the lower gears can somewhat cover for the centirfugal's inabability to deliver mid range boost, but the characteristics are still there and it gets worse as the gears go higher.

I have the 3-spd auto in my twin turbo and it delivers a very nice mid range punch. This car has done 0-60 in 5.2 seconds on a very crude state of tune and I expect it could do better long term with more tuning. The tip in torque is simple awesome, and mid range to high end is where the turbocharger really shines. I have done zero head or cam work to this car and I expect it would run a 1/4 mile somewhere under 14 seconds, perhaps lower. Myself, I am not a fan of the 3-spd AT, my first one could not hold the torque this engine is now producing. The one I have now is working well, but I would buy a 5-spd next time. Plus the 1st gear is too damn wide. Imagine if my 3-spd auto can pull 5.2 seconds 0-60...how fast would a 5-speed car be? Remember this is a 4.5 liter I am talking about, the lowest power 928s ever made. The 3-speed 80 928 was 8.5 seconds 0-60 stock, so you can see what a dramatic improvement the turbochargers made. My system is quite involved and intricate and is intercooled. When I do things I go all out. Could I make a cheap setup, of course, but why? Nobody is going to get rich selling forced induction kits for the 928.

Burned valves and turbos on a 928? My Callaway has 22+ years of turbocharged use and still has the same seats, guides and valves. You don't have to be pegging the boost all the time to make the car run well. Valves have not been an issue. There are other turbo 928s out there with lots of miles as well so you should ask those guys for some feedback before assuming this is a problem.

You want to do some of your own fab work? I can sell you the manifolds and get you on your way. With a 3-spd AT I see two viable options, turbocharge or positive displacement supercharge. Either option would do what you are looking for. I would not be too concerned with a peak HP number, but rather with the ability to make the car perform better in the range in which you drive. This is the reason OEMs use positive displacement superchargers or turbochargers for forced induction. Remember, a centrifugal will only make full boost at the redline, while the turbo will be on the wastegates by 3,200 +/- RPM and has the least parasitic drag on the engine.

In my mind the chioce is clear, but I'm sure others will disagree. It doesn't matter to me that I sell someone a kit, but I think you need to be informed with the facts before you make a decision and the CS would be last on my list, specifically because of the gear ratios on the 3-spd AT. Perhaps the screw SC would work best with a 3-spd AT, I would like to see that setup.

I would ask to see before and afterreal world performance data with whatever you purchase. Dyno charts are not the only thing that matters and a peak HP number is the last reason to purchase a kit. If you want to really do it right, I suggest a good forged piston as this is the weak link in the 928s engine.

GoRideSno

Amen Brother Kuhn, Amen. I just keep getting poorer, no kidding. Lucky for me I think I only have one set of pullies that is unaccounted for so maybe I can recover financially for a while before torture my checking account by selling more.
Welcome back, and sorry to hear about the wife.

Andy K

928fan4life

Michael - If a 320 chp 928 could walk by a 850 that is a perfect amount of power for myself right now. I was impressed with the pickup and quickness of the 850.

bcdavis - thanks for the info

Cameron - Do you know what kinda torque the 850 has?

Andy - What is the weight difference between an s4 and a 1980 like mine?? Did I also read that correctly when you said the s4 has 132 rwhp stock?

Herr-Kuhn - Thanks for all the info on the turbo chargers. I will have to read more info about those.



All the info you guys are giving me is great. I am getting a free 101 in superchargers and turbos. Alot of good info. I know that with the supercharger I could get around 275 rwhp but what kinda torque would I be looking at? the more I talk about this the closer I am getting to just getting a SC

IcemanG17

fan
If you are looking for 850Ci like performance, there are many cheaper options. The first that comes to mind (other than S/C) is a Euro "S" motor..with 310hp & 295 torque (underrated) it is a serious performer & can be had cheap if you find a wrecked one to pull the motor out of....I'd bet if you had 300rwhp even with the 3 speed you would be quite pleased!

bcdavis

It's another one of those financial questions.

Sell the OB, and get an s4, and be happy with the 300+ horsepower,
or spend $4,000 on a SC, and get the OB up to 300+ horsepower.

I'd say that the two things to consider, is that the s4 can remain fairly stock and still put down good numbers.
Whereas if you do the SC, you will have a custom car, that will need to be well-tuned, etc...
Although the benefit of the SC, is that if you blow the engine, you can get an OB engine
pretty cheap. And if you break the timing belt, no problem... Whereas if you break a timing
belt on a s4, it won't be cheap to fix...

drnick

what are the 310hp euro motors worth? mine is coming out soon and im wondering whether to strip the heads and induction to sell. there is the small isue of shipping but..

928fan4life

I was looking at going the s4 route but I like the earlier cars because they are easier to work on and I don't have to lose sleep about worrying if my timing belt is going to break. I was thinking of doing the euro s motor swap but the chances of finding one close to me are not good and shipping would be quite a bit. So that is how I have come about looking for a supercharger, I am just doing some looking into it to see the pros and cons and the numbers of a supercharger.

So to make sure I get this all right........A supercharger will put me up around the 275 rwhp range which would give me a decent ride. I still would like to know the weight of the various years of 928s and the torque that a supercharger would add to my car. Also, does anyone have a supercharger installed on a 16v car yet? If so, What kinda numbers is it putting out?