Drewster67

Lagavulin -

I know the feeling (heart pumping) - It's such a rush. Makes you want to do it again.

Take it to the RED. (Safely)

Z-Thanks for the information.

Peace.

Rufus Sanders

Erik, Lang, Z, you guys are right. I see the light now. Of course quotes from Mark D. are gospel anyway.

So 600+ crank HP is just mind numbing for a street car. It really makes me wonder if you Green Bay Boost Boys are now on the edge of the envelope, and the California Stroker Boys are old school. Guess the writing s been o the wall for decades since boost replaced displacement back in the 40's on aircraft.

And the "in traffic" example puts it in perspective. I'm still finding it amazing that I can have any traffic slot I want with my 82. If there was a whole 400 more hp there, someone would be in trouble somewhere and I'd probably be personally involved.

I'm gonna keep up with this as long as you guys keep reporting on it. It's the most fascinating stuff going on for 928s. - Ruf

John..

For the record, there were 5 Bastards produced....two remain.

PeteS

Well, the big auto manufacturers seemed to pretty much quit going with the larger and larger displacement stuff back around what, 1970? More and more I see where they're going to supercharging now. Ford, Jaguar, Mercedes, Chevrolet, at least one Japanese manufacturer I saw an ad for, and possibly more already have supercharged vehicles out.

Lagavulin

Although increasing displacement can be considered ‘old school’, there is no question it remains as a viable ‘modern’ horsepower option. Look at the two valve, pushrod Gen-3 Z06 small block, that's defintely old school compared to our 'sexy' four-valvers, but it's kicking some major ***.

You can increase an engine’s horsepower by one of three ways. Make it spin faster, increase the displacement, or force more air into it.

Although three entirely different approaches, but when you get right down to it, they all accomplish the same thing in the end which is burning more air/fuel (‘X’) in a fixed amount of time (‘Y’) versus the original engine.

If we make the engine spin faster, it is able to make it’s additional horsepower by completing more revolutions in that given amount of time 'Y', which allows it to gulp in ‘X’ amount of air/fuel, burn it, and push on the crankshaft.

With the bigger displacement engine, because it now has bigger ‘lungs’ to breath through, it too can gulp in ‘X’ amount of air/fuel in ‘Y’ amount of time at the original engine’s max RPM.

Finally, with forced induction, the original engine is forced-fed ‘X’ amount of air/fuel in ‘Y’ amount of time while spinning at the original engine’s max RPM.

All three of these engines will produce roughly the same amount of horsepower since they are all burning the same amount of air/fuel in a given amount of time. Of course, the power and torque curves will vary, but I’m not going to address that here.

Let’s now look at the economics surrounding each choice.

Spinning an engine faster is very expensive to do.

Increasing the engine’s displacement is expensive to do.

Comparatively, forced induction is a drop in the bucket compared to the other means of increasing horsepower.

For example, there's a brand new stroker motor that's putting out 499.6 rwhp. In order to reach that level, it has a carbon fiber intake which by itself, costs $4k, and the installed cost is more than double that.

For the cost of the installed carbon fiber intake alone, my car is putting out the same amount of horsepower! And I haven’t even mentioned the cost of the engine itself which alone costs $20k+.

What I’m getting at is, if you have a street engine which is in perfectly good shape, there is NO NEED to tear that engine down and bore and stroke it to get more power. Put a blower on it instead for 1/4 to 1/3 the cost!

On the other hand, if your engine is toast, or if you race and class rules prohibit blowers, then spend the $big bucks$ to bore and stroke it. If I were rebuilding an engine, I would seriously consider a stroker since I’m rebuilding it anyway.

In the past, BMEP has been brought up as it is a form of a measurement. But really, how useful is it? Both sides can use it to their 'advantage' and get nowhere fast.

If you look at it for what it really is, BMEP is merely a ratio of the amount of horsepower produced divided by the engine's displacement in liters. Looking at it another way, it is a measure of how efficient an engine is, i.e., how much work can be had from the available displacement?

If you keep the displacement the same and increase the horsepower, the result, the BMEP, will be higher as in the case of a stock block supercharged 928 engine; that engine is now more efficient as we are way exceeding 100% volumetric efficiency by cramming more air/fuel molecules down it’s throat.

On the other hand, a stroker engine's BMEP will pretty much remain the same since adding more displacement produces a corresponding amount of horsepower, thus the ratio remains more or less the same. However, the number also suggests that it's also less efficient than the stock block supercharged engine. What that means is that a more or less ‘brute force’ approach is used by upping the displacement, but not much was done to increase it’s volumetric efficiency.

Does this mean any one of the two is more reliable than the other? Not really as both load the block in different ways.

No one ever acknowledges the higher piston speeds and thinner cylinder walls inherent in a 6.4L stroker which Z has repeatedly pointed out. Those additional loads are present even at idle. However, there's no disputing that the stroker does have a beefier bottom end.

On the other hand, the supercharged engine experiences it's additional loads only under boost since the engine's internal factory geometry is unchanged. Likewise, it has thicker cylinder walls, and piston speeds and cylinder wall loading by the piston are the same, unlike a stroker.

If the stroker builders ever get their normally aspirated engines to 800 crank hp like the 26psi Red S4 already has with an entirely stock bottom end, you can be rest assured those beefy bottom ends should survive too; just watch out for cylinder 4 with stock head gaskets and fuel rails. Who knows, maybe by that time, that trail-blazin’ Red S4 might be well over 1000+ crank hp if the stock bottom end holds up.

My point being, BMEP can be argued both ways. And likewise, it appears that Porsche WAY over-engineered the 928 engine, especially the '87's.

Rufus Sanders

Lang, Nice lesson in Hp improvement options. I think the cost/Hp factor is the most impressive thing about blown engines, as you mentioned. The other thing that really intrigues me is that a large displacement engine is heavier because it has to capture more space and surround it with metal. A blown engine simply does more with less, but must be strong enough to hold the forces of more explosive power.

It' s just so elegant, no machining or pulling the engine or anything like that. The only issue would be the shape of the torque curves, as you say, and where a guy wants his power to be on the curve.

Makes ya wonder if anyone from Porsche is watching...And who is the person with the "26 psi" car?- Ruf

John..

The 26 psig car sounds like a bomb to me. 14 psig is even over the safe limit for 10:1 compression. Sure it works, but longevity is questionable. Nice to see some pushing the limits though!

Regardless, it is good to see that when something goes out, it is the head gasket that has been the point of failure.

I'll know what to expect when I turn my dial too far. In all seriousness though, I may stop the dial at 11-12 psig....it may be all my system will support because of the tight manifolds and long runners to the throttle body.

BC

Whats a safe limit? What determines that? These two cars went through a headgasket each because of LEAN CONDITIONS brought about by the fuel pump flow, as well as the delivery of the fuel rail. These guys put some mondo pumps and some 1 diameter fuel rails with two *front and rear* fuel sources to the rails, and we won't even be in the same county when the put thier foot down, and they will be bullet proof.

These engines have essentially a Webbing GIRDLE holding that crank in. The heads have the pERFECT combustion chamber shape for boosting, and the manifold *controversy* is pretty damn perfect for boosting.

Here is what Z has been trying to say, as well as many others, including Lag just now, in a round about way:

A short block for the 5.0 motors is 1500 or 2000 tops, used. Burn a piston? Scratch a bore wall? Either re-bore it and have it recoated like (john) did, or buy a new bottom end, deck the head, and slap it back together. Put a better head gasket on there, and make sure you have fuel, and your back on the road in weeks.

After being without my car for a year now, I think I like that idea a hell of alot more then building some stroker and driving a damn chevy or honda for all that time.

Otherwise, turn the boost up and buy a short block and build it bullet proof while your driving the car.

EXAMPLE:
I think Jim Nowak is a great guy, and he has a very mean boosted mercedes... But why did he need to make his mercedes faster then an S4? Because Lucky or whoever has been building his motor for what seems to be half a damn decade. Thats just insane, and totally unacceptable.

The only reason a boosted car will become a bomb is when there is detonation. Detonation happens from fuel ratio and lesser issues. These two cars had head gasket problems (probably) because of the inherent design of the S4 fuel rail, and the way the fuel is delivered and pressurized. This will be fixed, the headgaskets "beefened", and they will be back on the road having fun and blowing anything with *FOUR WHEELS*, excepting a few 400,000 exotics, and *MOST EVERYTHING* with two wheels.
***

...The first 8-9k I get for this car after I get it on the road with my EFI system is going straight to Tim Murphy. Another 500 bucks (off season) and I get Z and Tim to come out to San Diego and I will have 550 to the wheels in a weekend.

Gregg K

I'd like to add something that is really not too useful, but it's reminiscent for me.
When I first contacted Ak Miller to discuss turbocharging, back in the early 80's, I'll always remember what he said- "An engine is just an air pump."

I haven't been following the train of posts, and suppose the use of copper gaskets has been posted. I use a copper gasket on my Norton Commando. Using the sprayon Coppercoat, and flame annealing the gasket, AND remembering to retorque the heads after about ten minutes of use, I found copper to be THE way to go.

John..

I'm not saying the work isn't impressive, because it is, but there have been issues with detonation, this is obvious. Read any of the texts out there. If you want the motor to last, there are safe guidelines and all I am saying is 26 psig on 10:1 compression is waaaaaaaay on the ragged edge....specifically if the motor was designed as a normally aspirated unit. Run 100+ octane and you might have a margin of safety, but on 91 or 93 pump gas, there will be issues.

I run 21 psig on 9:1 in my Audi, and that is pushing the limit as well....but that car has a very strong forged lower end and is as bullet proof an engine as just about anything out there....yes it is a better engine to add boost to than any 928 engine going. The factory rally cars made over 600 hp on less than 2.3 liters. It doesn't have free standing towers like the 928 does, so the integrity of the deck surface is much better.

Yes, I could have turned the dial on my 928 with the stock bottom end, but there was too much risk, especially after talking to both Devek and 928 International about blown up Callaway engines with broken ring lands. This isn't and won't be just a Callaway problem. You guys seem to think those cast pistons are indestructible....just wait. Strengthen the head gasket too much and the next weak link is the ring land of the piston. I'd prefer to pop a gasket any day of the week. There is a reason high performance turbocharged engines use forgings. Continue to add too much boost and the forged pistons too will fail.

You can have detonation and a good air fuel mixture....it all plays together, air temp, ignition advance, compression ratio and fuel mixture. Detonation is not just a function of air fuel ratio or lean conditions....it is far more complex.

I'd suggest picking up the book "Maximum Boost"....it is very informative, to the point with no BS.

If it was me, I'd play it safe and keep boost levels down around 10-11 psig. There isn't a boatload of difference in a car making 490 HP to the wheels and one making 520 HP to the wheels.

I'm on 8:1 and I'll be keeping it sub 14 psig at the mainfold....granted the combustion chamber is more prone to detonation on the 16 valve cars.

Over 550 to the road on the street....I'd challenge you to find any back road where it can be effectively put to use. That kind of power can only be put to real use on a track or dragstrip.

I'd also mention that the bottom end on the 928 isn't as robust as you might think. For example the 944 uses the same number of mains....and 1/2 the pistons. Nonetheless, both are good designs that hold up well over time.....assuming you don't go too insane with the boost.

BC

"Forced Induction" by A. Graham Bell is where many are getting thier info from.

Callaway did them wrong. Didn't your 928 come from Callaway with a non-adjusted twin turbo system? Meaning that they didn't change any part of the car for the added HEAT STRESS that the turbo makes? Didn't the cam have a barn door maf? Callaway broke a whole bunch of 928s by doing the process incorrectly. Obviously, you are doing it correctly with your signal processing and the MAf you are using. Thats good....

Sure, 10:1 is high. But the 26psi guy didn't break any piston ring lands, or have any issue with the free-standing tower. He blew a head gasket on number four because of a lean issue caused by the fact that that cylinder is the farthest from the fuel line intake. All the other injectors were using the fuel up before it got over there (this is the assesment so far).

And I would assume this guy is driving this car like a bat out of hell. I would have to think so with 800hp of whatever he has.

bcdavis

Time will tell...

Those with 26psi may have engines that last only 3 years.
Those with 10psi may have engines that last 6 years.
Those with Strokers may have engines that last 12 years.
Those with stock engines may last 24 years.

Who knows?

Time will tell.

I think it is cool that some people are going for MAXIMUM horsepower.
While others are going for power with reliability...

The people who push it, will show us what the weak points are.
If the ring lands eventually break, then we will know that it is unwise to boost it that much.
If the head gaskets blow, then we know that boostards need o-rings, or copper, etc...
It is all yielding better data for those of us who want to boost horsepower later...

All this experimentation is taking all the "voodoo" out of boosting the 928...
Soon we will know what works, and what doesn't...

I think the biggest test, is seeing if the stock internals will take it.
If they can take the boost, with proper fuel management, and a better head gasket,
then that means it is not necessary to build a forged internals engine like Markus Hutchinson.
We can just bolt a supercharger onto a stock block...

If that turns out to be true, and reliable, and successful, I think we will see a lot more people jump on the bandwagon...

BC

I would much rather have 550rwhp for 4 years then 300 hp for 24 years.

24years? We'll be talking about buying an "good condition" '08 928 and why its computer keeps blowing just like those "classic" 89S4s did back in 2003.

Z

Lots of numbers have been thrown around, and apparently at least some have been mixed up. Nobody said the 26psi car has 10:1 compression. In case anybody's wondering, nobody said that 26psi was as far as the boost is planned to eventually go either. It's very true that there isn't a boatload of difference in a car making 490 HP to the wheels and one making 520 HP to the wheels. There is a good bit of difference in one making 490 to the wheels and one making 600hp, 700hp, or more to the wheels though.

As far as the strength of the cradle, all I can say is that I haven't ever heard of that being an issue with a 928. The Kelly-Moss engine dynoed at over 700hp, and apparently that crank is still where it's supposed to be, even though I'm guessing that horsepower was at a pretty high RPM, since it's naturally aspirated.

Is 550rwhp too much for the road? I guess that depends on the individual. There are people out there that say the same thing about 200rwhp. There's a twin turbo Chevy in the area whose engine's been dynoed at 1,100hp. There's also a boosted Mustang around here that's dynoed around 980hp with a .030" over 5 liter engine. These are cars I pretty regularly see on the street, or in a parking lot somewhere. Sunday I'll be at a Buick dyno day where there should be Grand Nationals making 700hp or more from the V-6 engines in them. The owner of a local shop drives an Impalla SS with a centrifugal supercharger on it that dynoed over 740rwhp and 690rwft/lbs. That was without using the nitrous it's set up for. There's yet another shop in the area offering twin turbo and supercharged Vipers. The twin turbo does 950rwhp and 1,150rwft/lbs, while the supercharged does only 870rwhp and 970rwft/lbs. There are turbo Supras running around here making 900+rwhp, and doing mid 9 second quarter mile times. At last years national Supra event the top dyno run was over 1,120rwhp with 930rwft/lbs. Those Supras aren't too shabby for 3 liter six cylinders.

I suppopse I might be wrong, that the 928 engine is just way too inferior to ever come even remotely close to making big power, and is probably best for just being recycled to make soft drink cans out of. Maybe time to get rid of the no-big-horsepower-potential 928 clunker? But what to get instead? Buick, Chevy, Dodge, Toyota, Ford... seems like there are just so many much better options for big power out there.

Supra 1/4 mile times:
http://www.suprastore.com/top2514miles.html

National Supra event dyno results:
http://vegas.supras.org/v02/index.htm

Turbo Supra dyno chart:
http://store5.yimg.com/I/supra_1746_19980986

Boosted Vipers:
http://www.supervipersystems.com/Upg...iii.html#chart

Grand National smoking tires on the dyno:
http://grab.orsm.net/update20030709/insanebuick.wmv

In the past I've asked racers about the implications of putting a supercharger on a track 928. I've recieved answers that were basically like "you could, but then you'd have to run in the class with those 700+hp guys". How silly of me to think that a 5 liter 928 engine could ever make as much power as some variation of 3.X liter six cylinder 911 engine.

BC

Yes Z, I did forget that the 26psi+ car has closer to an 8 or so CR with the 951 pistons. I was mis-representing that if I referred to that in that way.

When you recycle your no-big-horsepower-potential-928, just send it over to San Diego. I need an auto for my wife that I can break....I mean Break In.