Warren928

This reliability issue is well covered territory. Im glad you chimed in here Z because I think we're on the same wavelength. Its an old statement but a street driven boosted 928 is not under the stress of boost most of the time, only under boost.
I agree with bcdavis about the mileage factor. Several hundred hours of reliable operation on a completely stock boosted engine is equal to 20-40,000 miles. It sounds like Z was even saying 30,000 and results we're unoticable on the engine.
Again, the results shown so far are that 1) an engine with a severely corroded head gasket failed its gasket. I've seen non-boosted cars blow gaskets for the same reason. 2) 13 psi may be too much boost for the stock head gasket since there was a failure, but that could also be from the cylender walls being unsecured (no deck plate or liners) or detonation.
I also havent heard of one engine grenading from boost either on a 928. Only gaskets thus far.

Warren928

What attitude are you referring to Marc? Also, please produce some engines that have grenaded from a SC install (properly done) so we can all see the evidence of SC engine failure you speak of. Its one thing to speculate in order to create fear of the unknown, it another thing to have failure statistics to back it up.

bcdavis

Actually, if I had money to burn, out of curiosity alone, I would like to see what the weak link in the 928 engine might be. I would like to take a stock engine, and increase boost and fuel exponentially, until something gave way. In one way, having those head gasket failures are probably a good safety valve. When you start pushing too much boost, the head gasket gives way before the pistons do. But yes, I have not heard of any cars having a catastrophic mechanical or structural failure with a proper air-fuel mixture. Projekt928 cars? Yes. But those were acknowledged as not being a good kit or a good install. They had lean conditions.

Fastest928

Mike,
Prove me wrong. And better yet, how about accepting my challenge of a peak hp dyno pull for 5 minutes? You can even pick the HP range?

Highest average hp wins.

Marc

blau928

BC and Warren,

It is detonation that causes the head gasket to fail, not the pressure of the air charge entering the engine. The detonation can be designed out, and if it is not, it does not matter what kind of gasket you use, it will fail, or you will smash off a ring land and cause internal failure. 13psi by itself is a meaningless number, unless you know all the operating parameters of the engine, and can account for this with measurements at specific points in the operational cycle of the engine. I mentioned to you earlier, the PSI number is meaningless. You can move more air CFM and have a lower PSI reading on the gauge if you have a system designed with LESS RESTRICTION....!! Ask any qualified automobile engineer that has worked in forced aspiration engines.... Drag Racing to F1, it does not matter... Hell, ask a qualified Diesel engineer, and you will undoubtedly get the same answer...

The cylinder pressure is only part of the equation, figuring what events in the combustion chamber caused the pressure spike is where the forensic detail and analysis is key. I seriously doubt that any of the sellers of the kits have data logged all the multiples of combustion cycle event parameters and tested to see where failures are caused, and when this happens in the combustion cycle.

On another note, the entire operational cycle in the combustion is calculable physics, down to the cylinder pressures and variances due to spark timing across the crankshaft rotation.. YOU DO THIS IN A PROPER DESIGN PHASE.....! Not by guessing that X psi, or by turning up the pressure until it fails..

While I think you guys mean well, I think you are missing the point, and guessing about what happens as a result of "boosting" the engine.

On internals, Rods usually fail from RPM related issues, as the rotational (inertial) forces are much more than the compressive or tensional load placed by supercharging. Compressive forces from the cylinder pressure will break the crank journal before the rod, unless the bearing goes. Then all bets are off. How do you tell which caused the failure then....? When you have a burnt piston, spun rod bearing, and broken crank journal...? Oh, let's not forget that the gasket also went...?

Pistons will fail due to detonation, if you don't believe me, ask any indy car mechanic, or drag racer that run forced aspiration in their engines. Hell, for that matter, call any car manufacturer and ask them. Actually, ask PORSCHE, as they have many years of experience with forced aspiration engines. To say that the internals will not break at this power level is not accurate.. If the entire system is designed properly to begin with, then no, not likely. But, the 928 as far as we know, was not designed for this..................

You and BC asked to "bolt on" stuff to a stock engine and see what happens. Well, have any of you asked if the designers of the kits designed their systems to work with additional items you wish to bolt on...? Warren mentined NOX, and still dhas not answered what type of system, wet or dry... Nor has any calculation been shown as far as how the density ratio and chage temperature will be affected..

It just takes one miscalculation, and the engine will be destroyed. To say that you guess that the cylinder will be fine because a weak gasket failed under similar conditions, is not something IMHO that will lead to a successful long term outcome for the engine. Granted, the used engine replacement is a very good economic option.

However, when you run your 13psi, how much air will you be moving, at what density ratio, what timing sequence (retard/advance), how much fuel, at what pressure, and at what ambient air temp..?
I could go on, but it seems that you guys are really missing the point some of us are trying to make here.....

In addition, Warren, Andy Keel's kit is the only one currently available for the 85-86 model...... In addition, you have not defined the operating parameters of your car.... I know you have engine experience, but the car will break when you just "bolt on" stuff and take it to this power level, and, unless proper diagnostics are done, when you install another used engine, and not solve the problem, it will happen again...

Z

As far as how many engines Tim murphy has gone through, I always said, I do not know, nor why they failed. However, when we spoke last year, he told me "a few." I also think Tim has done an excellent job in developing his system, and contributed significantly to the 928 community.

W and BC

While Marc Thomas and I have our differences in design on some components, I agree with him on many many things.. It's a question of when the engine will grenade.... I am not doing this for a living, and do not intend to. But the science does not lie... Oh, and I can say in his defense, that Marc has some experience rebuilding blown SC engines... Ask Joe Dyer with the white GTS. It has been rebuild a time or two....

Come to think of it, maybe I should keep my big mouth shut.... Again, I wish you all luck, and thank you for your contribution to the community. It is appreciated..

Thanks,

bcdavis

My point in encouraging this kind of exploration, is because I think that a majority of 928 owners are not going to want to drop $20K into building a new engine, built for power *and* longevity. Most people seem eager to drop 3-10K into a supercharger kit, and let it rip. Is it smart? Probably not. But since that seems to be the way people are headed, I would like to know how the stock motor will handle the boost, if set up properly. Since most of the kits out there now seem to have addressed the detonation issues, it seems like the question now, is reliability. They aren't blowing up left and right anymore. So I am in favor of anyone who wants to push the envelope, and see what the *stock* internals will take, without having to build the motor for boost. That way people will know how much power they can extract from the stock motor, before they need to look into building it with lower compression, stronger rods and crankshaft, etc...

GoRideSno

As it stands today I have 124556 miles on my 87S4 automatic and the last almost 13k has been supercharged ABUSE. The engine has never been opened and I have never replaced a head gasket. I don't mean just hard testing I mean severe and intentional ABUSE. Boost has ranged from 4 to about 10psi. I've MADE the engine knock so severly that it sounded like a snare drum. I recently did a compression test and I can't imagine any car doing any better than the results I got.

Andy K

bcdavis

Why was it knocking?

GoRideSno

Like I said it was intentional. Just turn off the intercooler pump at 8.5 psi and start climbing a few thousand verticle feet up a canyon for 10+miles in 90+ degree weather and it can be emulated as this is what I did. If an engine was going to go from detonation at those boost levels then it would have happened then.
Another time an injector wire was completely severed so ther was very little fuel going to the cylinder and this caused knock as well. Once too I was given and 87+ throttle switch which is backwards of an 85-86. When I hit full throttle the injector duty went to idle specs at around 5 psi......no problem.

Andy K

Z

To clarify, there have been 928 engines that have blown up from boost beyond just head gaskets, and that includes by both supercharging and turbocharging, but not Tim's car or any cars with the kit that he sells. One supercharger install on an S4 was done by a shop that kind of specializes in turbo instalations on import cars. I wish I had more of the exact details on it and what all it was that actually broke, but that one blew up to the point of requiring a new block.

Don't count on it. Even if the head gasket did fail before something else did though, it's not necessarily going to save you. If the head gasket goes and enough coolant then gets sucked into one or more cylinders you may very well be looking at new pistons and/or a new block. Don't assume that blown head gaskets only happen on boosted cars either. There are a couple of people that are ocassionally on this board could tell you normally aspirated stroker motors can definitely blow head gaskets as well.

I'd say I already have if we're going to use the milage method of reliability. The only 600 crank horsepower 928 engines that I can think of that have gotten mentioned would be Marc Andersons, Joseph Fan's, your's, the Kelly-Moss car, Tim's, Lag's, the 26psi car, tomboyea123's, Marcus', and probably Tom Falkenburg's, and Blown Beast's. Of those, the the supercharged 5L liter ones would be Tim's, Lag's, the 26psi car, tomboyea123's, Marcus', and Blown Beast's. Those have significantly more miles on them than since having made 600 crank horsepower than those stroker cars mentioned, unless you're counting milies that they were towed by trailer. Louie and Don's cars should both be in that 600 crank horsepower stroker group, but neither of those are finished yet.

You mean like the challenge you proposed for Wichita, and then you didn't even show up for?

Fastest928

Mike - The only relibility test I that will demonstrate "SC is as reliable as stock" is a multi minute test at peak hp for at least 3-5 minutes. Prosche tested each 928 engine far longer than that...every 928 engine that went off the line!

Mike - ever hear of the term "accepted"? NO ONE accepted my challenge, I doubt anyone will. And it was for a run on a Superflow chasssis dyno...one that can apply a brake load for a period of time.

I never saw a dyno sheet for the Kelly Moss engine or Tom F engine, or the 26 psi engine....where are they?

Marc

bcdavis

I don't really recall anyone accepting your challenge either.

But I think that now that there are quite a few properly-running SCed 928s on the road,
it will only be a matter of time before they are proved to last just as long as your strokers.
I could be wrong. But only time will tell. I don't think a peak hp dyno run will really prove anything.
The fact that Andy has been thrashing on his car is good evidence that the engine is
pretty damn strong. It will be a few years before any real conclusions can be drawn.

Z

I'd be interested in what kind of chasis dyno that you use for those tests Marc. DynoJet, Mustang, and Superflow don't even have the capacity for that kind of test at those power levels. Kind of gives the impression that it's not particularly useful to very many people.

As I recall, Tim and Lag both said that they were planning to be there in Wichita, Carl was there, and even John showed up in Wichita inspite of a blown head gasket on his car. I can see your point on thinking that no one will ever accept your challenge. I think the owners of those cars in the list I mentioned would prefer to operate them in a real world manner, rather than some kind of foot to the floor while strapped in one place type of test. Maybe you can get some of those guys that participate in those burnout contests to join you. You know, where they try to do a brake torque burnout until the tires blow up. It sounds like just the kind of thing that some of those guys might have an interest in.

Maybe the Superflow has a high enough capacity for that kind of test back when you did it, if you did, but it doesn't for the power that's being produced by the cars in that list I posted.

Okay then just leave those off of the list then if it makes you feel better. The Kelly-Moss one is a stroker engine, so it would have only helped your claim if anything. Tom's car is both a stroker and supercharged car, so would be on both sides. The 26psi car probably has more miles on it at the power level mentioned than all of the strokers at that power level do combined just by itself, but even that one's not needed to make the point.

Speaking of producing dyno charts, it's been asked before but you've never responded. What about a dyno chart for that Bob Devore stroker engine that you've brought up on multiple occasions? I've asked a number of people that have been pretty involved in the 928 community for a long time, and none of them have apparently ever seen a dyno sheet of it either. What ever happened to that engine, and how come no more have been built since then? I know you've said that they "got tired of breaking cranks" or something to that effect. I wonder how many of those stroker cranks ended up getting broken? That all sure was a pretty long time ago. How long before you were associated with Devek was that engine built anyway?

Tell you what though Marc, maybe there would actually be some kind of dyno shootout this time. I'm guessing Mark Anderson, Joseph Fan, and hopefully some of the other high power cars will be at the PCA Road America Labor Day weekend event again. The shootout could be then at a dyno in the area. Who knows, Superflow might even design and build a dyno that would be capable of your kind of test by then. Come on out, hit the dyno, and then put the cars out on the track. Sounds like it could be a great 928 weekend, with a lot of high power cars there. I'd love to see Don H. come back to Road America, and that would be a great time for it. After the experience with having the timing belt failure and bending all those valves on his Devek stroker motor after only running a few laps there, I don't know if he'd be too anxious to return though. I know his rebuilt stroker motor isn't done yet, but I'm sure hoping he gets it running soon and comes back out, and the same goes for Louie. I don't think I would have ever had the patience to wait as many years as Louie has, and still be motivated to work on getting the engine built. That individual throttle body intake that he came up with does look great though! The sight of that alone would be enough to scare some of those 911 types there. Has he come up with some kind of a hood scoop or something to be able to fit a hood on the car with it yet?

Warren928

I agree that rods fail due to RPM. Its good to have your rev limiter in place for such an occasion. Again I agree with the pistons statement too. Obviously I would run it rich until adjusting for optimum air/fuel mixture.

I would disagree with the design statement because I believe the 928 engine has alot of good attributes in stock form that work well with boost. 13 psi stock I think is the upper limit of what a stock engine (with cometic head gasket) can handle for extended periods of time. If you read my statement a couple pages back you will see what my plans are.
NOS systems are all quite similar for my 928 but I would use a WET one that could take advantage of any advanced electronics that could help timing, mixture settings and engine longevity. Jets for fuel and NOS are usually pre-chosen for these kits based upon engine displacement and are matched to deliver an even air/fuel boost and will not cause detonation on its own effect.

You say the 928 engine will blow apart with this setup at 600 hp. Okay, explain why there are several 5.0 L 928's running around from Tim Murphy kit already with 600+ chp and havent blown anything. Obviously there is no serious design flaw with running 600+ hp or somebody in the murphy group would have grenaded an engine. Those engines arent substantially different from my 86' 5.0. In fact, when you compare the results of Supermodel kit installs between the S3 and S4 there hasnt been much difference in HP for the identical setups. Is it luck that those engines havent blown? I doubt that, its more to do with the same safeguards, system checks and tuning required to make the engine run within safe parameters.
Can Joe Dyer be included in the statistics? Not until it is clarified exactly what kind of kit he had and the events, guage readings,symptoms that led up to the grenade twice, and the parts broken in the grenade. Its easy to blame the SC in that event, but we dont have any hard data to go on right now and therefore it could be several other causes for death.

blau928

Warren,

Please see my comments in <<..>>

Your Quote "I would disagree with the design statement because I believe the 928 engine has alot of good attributes in stock form that work well with boost. 13 psi stock I think is the upper limit of what a stock engine (with cometic head gasket) can handle for extended periods of time. If you read my statement a couple pages back you will see what my plans are."
<<Warren, PSI has nothing to do with the amount of air mass you can move into a chamber, there are other variables that must be taken into consideration. PSI is measured as resistance to flow, and until you understand this basic but extremely important point, you will NOT have a correct understanding of the way a forced aspiration engine works>>

"NOS systems are all quite similar for my 928 but I would use a WET one that could take advantage of any advanced electronics <<which one?>> that could help timing <<how and when?>>, mixture settings<<at what point in the compression cycle or RPM band?>> and engine longevity.<<how?>> Jets for fuel and NOS are usually pre-chosen for these kits based upon engine displacement and are matched to deliver an even air/fuel boost and will not cause detonation on its own effect."
<< This will change when you go from Vacuum to positive pressure, as the density ratio of the charge will be affected due to the heat of compression versus ambient air temperature. Another point I have made several times. Density ratio has not been addressed. In addition, NOS will create a different spark requirement, and due to its volatility, could definitely detonate from the air charge temperature. Again, leading to detonation>>

"You say the 928 engine will blow apart with this setup at 600 hp. Okay, explain why there are several 5.0 L 928's running around from Tim Murphy kit already with 600+ chp and havent blown anything."
<<Tim has told me personally that he has blown a few engines while developing his systems. In addition, there is no 600HP S3 Centrifugal kit or Twin Screw kit, "bolt on," on stock internaled S3. If there is, SHOW ME....!>>

"Obviously there is no serious design flaw with running 600+ hp or somebody in the murphy group would have grenaded an engine."
<<Wrong, see previous reply.>>

"Those engines arent substantially different <<define this?>>from my 86' 5.0. In fact, when you compare the results of Supermodel kit installs between the S3 and S4 there hasnt been much difference in HP for the identical setups."
<<The kits Andy K has built on S3's have been dynoed at 500CHP, not 600CHP. 100 CHP is a LOT more, it is not that simple.>>

" Is it luck that those engines havent blown?"
<<Not luck, as Andy's kits have been based in a large part on some proven combination of parts. He switched to the Autorotor Compressor from Whipple and Eaton Compresors after discussing the compressors with me. I introduced him to Opcon, and recommended he use the MX 422 as it was more efficient than the larger Whipple 2300 in his quest for more power. In addition, his current intercooler is based on the Ford Cobra unit. The bypass valve as well, actually most of the kit can be found from the Kenne Bell Cobra kit. His Throttle body is a Porsche 928 S3 TB due to the intake.. Anyway, the calculation of this system on an S3 is different to an S4 due to the heads, as they are different. This includes valves and PORT SIZE... S4 heads flow more air, and have different ports which affects the air mass, flow rate, and intake temperature charge. Tim Murphy has not done a 500 RWHP Dyno pull with an S3, he did it with an S4. In addition, I believe the 556 RWHP pull was done with low compression pistons (8.5:1) cylinder rings, and some other mods. Granted Paul (Lag" has done 500+ RWHP with his stock setup and an RMB. Tim and I discussed the cylinder rings, as he and I thought the cylinder towers would deflect or balloon at this power level for an increased operation period. Although you have a thick wall block, the pressure spikes from detonation will ruin it just the same if you are not careful>>

"I doubt that, its more to do with the same safeguards, system checks and tuning required to make the engine run within safe parameters. "
<<I am unsure what you mean here, please clarify.... In addition, define "safe parameters.">>

"Can Joe Dyer be included in the statistics?" <<Yes he can, see below.>>

"Not until it is clarified exactly what kind of kit he had and the events, guage readings,symptoms that led up to the grenade twice, and the parts broken in the grenade."
<< Joe has a combination of a FAST kit and some things Munck engineered for him. I have personally seen his car, and know it was rebuilt twice at DEVEK. Warren, just because you are not familiar with some events, do not mean they did not occur....>>

" Its easy to blame the SC in that event, but we dont have any hard data to go on right now and therefore it could be several other causes for death."
<<Warren... Not buying it.... Joe has GTS with a Vortech blower and intercooler (similar to the MURPH kit), and it was cranked up to 11+ PSI per the tech working on the car, and it grenaded on a test run. This was after the engine fire the first time.. Detonation killed the engine, no bones about it, it was a fresh rebuild from the engine fire, powder coating and all.. As far as WHY there was detonation, no one has been able to say exactly, as the designer of the system is not trustworthy, did a poor job, and claims innocence. However, WE ALL KNOW THAT DETONATION IS CAUSED BY AN INCORRECT COMBINATION EVENTS IN THE COMBUSTION CHAMBER.....! As I mentioned earlier, Tim Murphy has done an EXCELLENT job with his kits.... One does NOT exist for an S3, (your car). You cannot compare the effects on an engine with one system to that of a differently designed system. You will have inconsistent data. Centrifugal SC and Twin Screw SC's operate at very different efficiencies at different parts of the powerband, depending on gearing, and the design of the entire system. It is incorrect from a proper engineering point of analysis to say that a "blow through" Centrifugal system pressurized at X PSI is to be compared to different a "pull through" Twin Screw system at X PSI.. Unless the restriction on the inlet and outlet sides of the systems are EXACTLY the same...>>

With all that said, I will reiterate again, and AGAIN, PSI is RESISTANCE TO FLOW.... The correct analysis would be to compare Flow rate of the air mass, or LBS/KGS per min and see what the effects are.. The amount of air and fuel burned per time is what makes power... An engine is an air pump as I mentioned earlier.... With your claimed knowledge of engines, it is surprising that some of the fundamentals are inconsistent with you analysis when you say 13psi is the max limit..... Max limit for how much air? How much fuel? at what temperature? using what cams? how much octane? I could go on, there are more variables......!

Sorry, I stand corrected.. You said you guessed, not analyzed and concluded... My mistake.

Regards,