Jim bailey - 928 International

SteveM " Maybe there is one solution that would put a lot of this stuff to rest:"
But Steve , where are the turbos and the nitrous ?? The fact that you can buy polished blowers is to me an indication of why some people add them to an engine , as is the option of quiet or loud (many choose loud)and the question everyones asks the owner of a blown car (whose hoods seem to be often open ) is " Wow , how much horsepower does it make ? " . I am happy that there ARE options to the , bore and stroke it to 6.5 liters .........spend $20-30,000 . Besides all I ask is for another 100 horsepower for the very brown 1980 .........Yea right like you ever have enough or too much ! everyone should just do what they want to their own car and have fun with the car .....it is not about transportation after all . I would mention that there is a diminishing return as you spend more and more money to gain performance . Double your outlay , typically gets you far less than twice the performance increase . Now I need to go practice my reaction times ...... go on the last yellow ?

SteveM928

On the air cooled six cylinder stroker motor that gets mounted in the back of the car.

Very true. There are some of those nice shiny blowers around that are completely hollow and mounted on internally stock engines. Much easier and cheaper to look fast than to actually be fast.

Depends if you stage shallow or deep.

Jim Nowak

" And that is about where it really falls, 1 psi boost at about 3300 rpm. "

Maybe something is wrong with my ATI Procharger P1SC centrifugal blower because at 3000 rpm I've got 5 psi and at 6000 rpm I've got 10 psi?

mspiegle

you're running a smaller pully

Jim Nowak

"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."

I was referring to this logic and pointing out that it does not match what I see on my car. Since I have 10 psi of boost at 6000 rpm, according to John's assertation, I should only have 1.25 psi of boost at 3,000 rpm. That is clearly wrong.

GoRideSno

SteveM928,
I appologize I don't have time to read your entire posts.

I see where you posted a link that said something like Murphy dyno chart at 8psi. I am taking you word that there was one there.
Now please post one of my car at 8 psi. OH Wait you can't because I have never dynoed my car at 8psi, silly me for asking you to do that. possibly you need to read a little more of ththread you posted a link to.


As far as a lot of Centrifugal SCs being sold, there are a lot of ricer wings and coffee can mufflers being sold too.

I like Centrifugal SC's just fine. I like Tim and Lag and the other Cheese heads too. I've given them lots of compliments and meant them all. Maybe I'll come up with a centrifugal kit. I could probably do it in a week or two. Mayeb that's what I'll have to do to get a 1/4 mi time form a centrifugal SCed car. I'm Just Keeeeding! But seriously would you like to pre-order?

Andy K

GoRideSno

I found one! This a link to Quick Carl's before and after time from when he first put his system on his car. Great Job Carl!

Andy K

Old & New

The CS curve can be altered to look more like the turbo curve with certain simple mods to the system, but it is not my story to tell. I *am* chomping at the bit for a certain individual in Wisconsin to get this nicely developed and onto my dinner plate, though.

John..,

Will you puleeeese post a dyno of your car so there will at least be some yardstick to compare CS to turbo?

Even though the boost rolls on very sharply with turbo, isn't there some correction that needs to be mentioned due to exhaust backpressure? What would the curve look like if you subtracted out the backpressure?

Lizard928

Old &new, what is a CS, do you mean SC

Old & New

"Centrifugal Supercharger"

Lizard928

ah gotcha

GoRideSno

Ok let's see,

Since we dont have a HP figure for my car with it's current setup we can figure it wth the math you suggest above. I agree these are generally accepted figures.

We need a baseline:
we'll use the only 928 I have found posted with the 1/4th and rwhp posted.
Quick Carls '78 Supercharged 5 speed. 13.6 sec 320rwhp stock weight of 3197lbs maybe 3380lbs with driver

My car, 87 twin-screw supercharged automatic 12.4 sec, Xrwhp, 3550lbs stock weight add 200lbs for driver 50lbs for big H20 tank I had in the back of the car, and 35 lbs for SC and periferals 3835lbs total.

Ok,
My car is 1.2 seconds quicker so that gives me 120 HP.
My car is 455 lbs heavier so that gives me 45.5 HP.

320 (Baseline HP)
+120
+45.5
= 485.5 Wow! And I only thought it had around 400rwhp.

485.5 RWHP on only 8.8psi and a very small prototype IC. No wonder Whipple claims their SC is the most efficient of any kind.

And since 1/4 mi times are such a variable form of measuring HP we must assert that if Carl made a descent run (not much wheel spin, good shifting etc) that the final HH result for my car could not be lower but only higher. (baring that huricane force winds behind me, or the track I was running was down a steep incline)

Now to get a fair comparison to other dyno charts we must adjust my RWHP since it is an automatic. We need to multiply it by 1.03 to 1.05 to be able to accurately compare it to a 5 speed. We'll go mid way and multiply by 1.04 and get 509.8.
Now let's not forget we need to adjust for the chip, exhaust and cool water running through the IC of the car that made the 525rwhp run at 14PSI.
I'm tired so someone else can do that.

I hope everyone realizes this is all in good fun.


Andy K

BTW I am pretty sure I am pretty sure I am making around 400rwhp.

SharkSkin

Keep in mind also that the early 5 speeds aren't exactly designed for speed shifting in the 1/4 mile.... I would expect AT to have some advantage there.

John.

N/O I posted the tts dyno results last year, like I said on 8 psig the car made 353 ft-lbs at 3700 RPM and 302 HP at 4800 RPM, that was with a very rich mixture and 2 degrees of timing pulled out. Go out to 12 lbs and it made 382 ft-lbs at 4800 RPM and 366 HP at about 4900 RPM. These are Dynojet rear wheel numbers straight off the graph. Remember on the street I have more cooling air for the A/A intercooler and the car will make even more boost in the real world. I'd say it is brushing 380-390 rear wheel on the street.

Before I touched anything the car was capable of 13.6 @ 114 MPH, that was with a 20 year old intercooler and fuel management on 8 lbs of boost. The new enhancements allow boost much earlier, but I am still on late 70s technology turbos. Big deal, 5 lbs at 3000 RPM, in the high gears I can make 10 lbs by 3000 RPM at a gate setting of 12 lbs. Before you go comparing to other cars, let me make it very clear this car has had zero head or cam work and is breathing through a totally stock 4.5 liter induction system. Do you suppose I could make more with a set of Euro heads and camshafts...I have a set now, maybe I should try that?

The exhaust back pressure doesn't rob nearly as much HP as does the supercharger.

Old & New

John.,

I was talking to John..

If you have a set of euro heads and crankshafts, of course you should try that if you want to... no need to get your panties in a bundle.

Thanks for your info, though.