Lagavulin

330 rwhp / .85 = 388 crank hp

First let's see what 388 crank hp does with Mark's 7-8 psi using the same setup mentioned earlier in the thread:

388 crank hp @ 7 psi = 500 rwhp
388 crank hp @ 8 psi = 524 rwhp

Quite a bit over his target of 440 rwhp. How much boost must he run to hit his target?

388 crank hp @ 4.0 psi = 427 rwhp
388 crank hp @ 4.6 psi = 442 rwhp
388 crank hp @ 5.0 psi = 452 rwhp

The key term here is 'race'. 4-5 psi is not that much boost; however, there has been no testing whatsoever where the engine is run WOT for 45 minutes. I think it would be a stretch at this point to say that the setup would be 'race dependable', even at such low boost. Maybe it would be, but at this point in time, there's nothing to substantiate any track-racing related claim. I don't know, maybe Tim might have a different take on this, but I doubt it.

We do plan on running Road America as many times as we can this year so that we can firstly have fun, and secondly test. But those future plans do nothing to help you make a decision now.

That's good! The centrifugal is an excellent unit, and especially excels at producing power between 3500 RPM to redline (..race-rpm), with no drop-off in power delivery.

blau928, how much boost do you plan on running? Have you done/plan any short-block mods? I'm glad to know you're using Corky's calcs for your project.

Tim Murphy

Mark, you need to clean out your mailbox.

Email me and we can discuss options. I would be happy to work with you to get a setup for track use. 5-6psi would net you an additional 100-125 rwhp.

blau928

Hi Lag,

I am planning on starting at .5 bar on the 5L motor and going up to .7-.8 bar adjusting to afr of 12.5-12.75 : 1 on street 91 octane in CA. When I am done with this, and all the bugs have been worked out, I will raise to 1 bar on race gas on Sundays.

I also plan on building a 6L motor, and using the same setup and using 1 bar on street 91 octane with the internals... Pistons etc modified. Still calculating and trying to get accurate info on head volume in the S4. So far, I think my static compression ratio will yield 8.75-8.9 : 1. Powerhaus does this all day long in 951's, and gets 400 rwhp on 93 octane at 1 bar on their 3.0L 4 cylinder. My 6.0L motor will be double their's, so my target should fall in at 750 rwhp if the theory is correct. However, I do not know yet, as I have not built the thing as yet, and dyno tested.

Block mods will include modification to solve #6 oil issues at high rpm. I also plan on Carrillo's with ARP bolts, and ARP head studs, and some head work 968 intake valves. This should be my winter project once I am done with the 5L and observed the system over the summer and fall.

There is a guy in Germany that claims to modify the block to solve the oiling issue, and DEVEK claims that the ACCUSUMP anf their mods also runs very well. I have been in the DEVEK car on several tracks, and it has not had oil probs going left.... My car will have an ACCUSUMP at least.

I am also looking at the effect of a cam on boost effective compression pressure in the cylinder, similar to the Miller cycle engines, and still researching.

If you want to know more, send me an email, and I will send you a hit list.

Cheers,

Lagavulin

Quite a comprehensive list of things to do!

Have you seen this thread?

https://rennlist.com/forums/showthre...ce+compression

Starting the thread, I was not aware of the Miller Cycle until gbyron suggested to look it up. It turns out that the principles are similar, but one really needs a positive displacement blower to make the Miller Cycle work, if that is what one is after. I was not per se as I'm trying to avoid any additional low-end power production, but it's good to know that 'my' idea is sound in principle, and already proven by others.

I was simply looking for a way to lower the effective/dynamic compression ratio other than by tearing the engine down; instead use a camshaft which hangs the intake valve open longer.

Addtionally, with the bigger cam I was hoping to attenuate the over abundance of low and mid-range torque production, and move it higher in the RPM band where there's greater hookup. Well, I got the new cams installed, and unexpectedly, the mid-range hits even harder than before, and it pulls harder on top as expected.

As it turns out, my car is nothing but a great big science fair project, and I'm having lots of fun learning the things I need to know to make it work.

BC

Thats pretty much what I have decided for my S4 Richard. Get the boost and the fun going and THEN build the other motor in the spare time.

Have you thought about traction? Not the 1/4 mile time hooey that has been discussed here - I a1m talking ab out somehow puting 750rwhp (north of my own goal for 6.6L) to the pavement?

I will be doing a DTA ( www.dtafast.co.uk ), so I will actually have the ability to add traction control.

I guess these guys with over 500rwhp in the 928s are having wheelspin above 40mph when they are pushing the car - so how will we keep traction with 600 to 750hp?

If you get any info on that german guy that modifys the block, could you share?

BC

....Uh, Lag, did you dyno yet? Do you have any idea of what power increase you got from the GTS cams? Or was it just exhaust cams?

More info. Start a thread.

Brendan

bcdavis

Sounds like some awesome engines coming down the pipeline!

Woo Hooo!!

blau928

Hi Lag,

I did not see the thread, but did some research on the Miller Cycle principle. I am using a positive displacement blower, the Autorotor MX 422, which tha KB guys have used to make over 700rwhp on a Cobra. this fits with the Miller Cycle's needs for higher boost at lower RPM to offset the valve staying open longer.......

Brendan,

My system is designed to function differently than the centrifugal. Boost is a function of throttle position, more than engine speed. KB has lots of write ups on their site, so I won't bore you again. However, I can adjust the ratio of the throttle lever opening to somewhat compensate. In addition, I know that I will have to learn to drive the car all over again with this much power. Yes, traction will be an issue, but it is all in the learning process.

As mentioned earlier, I have been in the DEVEK 6.5L race car and felt the traction on slicks 11 inch or wider spin when the power was on. Another reason that I used an automatic for this project. With this much power, traction is only a side issue. More critical are drive line components. The torque tube on manual 928's have 2 bearings, vs 3 for autos. In addition, the autos can handle 700-800 lb/ft of torque all day, while the manual may destroy itself.

I am also thinking about reducing the final drive ratio from 2.2 to 1.9 or 2:1. I was after a big fat torque area under the curve, with the ability to keep it flat across the band.

We shall see how it turns out.

SharkSkin

I thought it was the other way around???

SteveM928

I've been kind of wondering about that too, especially after reading the following on that Kenne-Bell web site:

"The 2.2L Kenne Bell/Autorotor has made over 700rwhp on a Cobra at 26psi - reliably - and an incredible +700 ft/lbs of rear wheel torque at a mere 2,500 rpm and holding the 700 ft/lbs all the way to 5,000 rpm. That's enough to twist trans input shafts, fry clutches and snap IRS half shafts."

Tony

Wasted? Explain?

IMHO, You have the priorities wrong. Add LSD, not a 5 spd. WAY cheaper and more beneficial than doing a full ***** 5spd conversion.

To each his own.

hacker-pschorr

IMHO, a 5-speed is only a performance advantage in road racing where exact gear selection is crucial. I know a few drag racing junkies that swear by using auto's at the strip.

Like Tony said, to each his own. I for one prefer a 5-speed no matter what.

mspiegle

The Automatic transmissions are just fine.... as Hacker-Pschorr said, you'll just lose a little precision and a little efficiency. In drag racing, the AT will save you time.

Jim bailey - 928 International

Drag racers running in bracket racing where they dial in a E T and must not do BETTER , like the consistency of automatic shifting and "automatic " launching with a high stall torque converter loading up the engine to the SAME rpm for every launch . For road racing with corners you want consistent engine braking in all the gears and the ability to select and hold the "appropriate" gear in a corner which is only possible with the 5 speed . However in my opinion , until the car is being driven at nearly 10 tenths the automatic is probably faster for most people .

mspiegle

@Jim
The coolant gods are once again on my side.