BAM! Twin Turbo S4 557 RWHP, 540 RW ft-lbs

[sonett3]

Fabio you need to put on the manafolds from my brother and use the GT turbos on them .

[Herr-Kuhn]

I can say these turbos would feed up to a maximum of about 750-800 HP and that would be it...you'd be pushing them very hard at that power level. I figure my flywheel power is somewhere about 625 HP if you figure 75 or so HP loss through the driveline. I never bought into the the fixed 15% driveline loss figures used...I think it overstates things quite a bit. With the right chargers and a large enough engine I would think that 1000 HP is possible, but at that point you have a missile that only a handful of drivers could manage on a track.

I'm not sure I would want too much more power than this on a street car. It's a lot more than most people can handle effectively. You have to be on your toes with these kind of power levels because it can get you into trouble real fast. Sometimes I swear the gas pedal is sticking beacuse I swear I lifted off earlier and the car is still pulling...it all happens very fast and you have to be careful. I'm really glad the 928 has a very solid suspension and is of decent weight...it helps to make the car streetable for sure.

It would be nice to build a track 928 with monster meats out back and a race TT system, but I'd question if it would be competitive against 911s and highly race prepped 951s.

[rhjames]

I would question the move towards lower CR and upping the boost, unless you have gas/octane concerns-----you can probably compensate for that with water injection or knock sensor/computer controls...?

I am curious though, on what numbers you case the comment that superchargers won't keep up with your turbo's (?)

I am not criticizing your work by any means, John, just asking the questions that any good consumer would before making such an important (and large) purchase........

What I would like to see is this:

A blown 928 of similar specs with a blower from each of the current suppliers (you, Murf, Dave Roberts, Carl Fausett, Mark Robinson, etc), strapped down on the same dyno, under the same conditions, for a serious non-biased comparison.

Then it comes down to a matter of ease of installation (and removal for the whiners in California), hp/torque #s (who has the most?), and lastly.....price.

That would put everything into perspective.


-Russ

[Normy]

Originally Posted by rhjames

I would question the move towards lower CR and upping the boost, unless you have gas/octane concerns-----you can probably compensate for that with water injection or knock sensor/computer controls...?

I am curious though, on what numbers you case the comment that superchargers won't keep up with your turbo's (?)

I am not criticizing your work by any means, John, just asking the questions that any good consumer would before making such an important (and large) purchase........

What I would like to see is this:

A blown 928 of similar specs with a blower from each of the current suppliers (you, Murf, Dave Roberts, Carl Fausett, Mark Robinson, etc), strapped down on the same dyno, under the same conditions, for a serious non-biased comparison.

Then it comes down to a matter of ease of installation (and removal for the whiners in California), hp/torque #s (who has the most?), and lastly.....price.

That would put everything into perspective.


-Russ

I think that's a good post Russ.

First of all, due to all the plumbing, a turbo will always be somewhat more difficult to install than that belt-driven supercharger. And that is certainly an issue in California. I don't live in California.

As to horsepower and torque? Turbosuperchargers use exhaust energy that is normally lost. The increased back pressure is a negative, but no where near the negative that a belt-driven supercharger causes. I read somewhere, in one of the car magazines...that the Eaton supercharged 3.8 liter V6's that Ford and gm produced for a while used upwards of 60 hp at full throttle and max RPM! The supercharger folks are having trouble with their belts all the time- ever wonder why? Because these belts are being asked to transmit nearly as much power as one of the original Ford Escort's had at the crankshaft. Hell, even a typical automotive air conditioner will use 10-12 horsepower, and it only compresses a tiny amount of gas. The long and short: a turbo will always make more power than a supercharger.

Negative of a turbocharger? It works when it wants to work. My brother has a 1.8t Jetta, and it has a small amount of lag. I read that these were lag-free, but that's not the case. My own airport-car Jetta GLX with a very-cammy VR6 engine runs just like it. And they are a pretty good race too: they weigh the same, and the power is about the same too. The thing is...the GLX would make a FAR better autocross car because the power curve is completely predictable. My brother's turbo, despite the tiny size of the unit, still needs a moment to wind and if you have the car just balanced going into a curve, the sudden increase of torque will tend to cause the car to react underneath you. My VR6 doesn't do that.

The folks with supercharged 928's who autocross ALL prefer the Murph kit. Why? Because the way that the boost comes on causes the LEAST disruption. It is very progressive, and comes mostly at the top of the power curve. But the guys who don't autocross? They prefer the 928 Specialists kit, since it means INSTANT power. The one criticism I could level at the Porsche 928 is that compared to a Mustang or corvette, it feels weak off the line, the power coming when the cams come alive a second or two later. Well, Specialist's kit takes care of that in a hurry and makes the car into an utter hooligan! These cars respond like nothing else and they are happy to display their accelerative prowess and their ability to spin the tires at nearly any speed.

Yeah, but possibly too suddenly; an independent rear suspension such as what is installed on the 928 can't transmit to the ground instantly anywhere near as much power as a beam-axle. The result is massive wheel-spin or even "wheel- hop". Yuck...!

I personally prefer turbos. I don't autocross [yet...], but I had a turbocharged VW Scirocco, and I just loved the way that the car accelerated once the turbo started to spool. The way that a turbo car comes alive is very intoxicating- your car is now your "personal roller coaster".

-Being a non-boosted, totally naturally-aspirated-type so far [but having a bit of experience with the drug known as boost via the Scirocco], I have to say that I don't understand at all the HUGE arguments that went on over on Rennlist regarding what was the best way to boost your engine. What the hell? Both were doing the same thing- forcing air into the engine...exactly as Kuhn has done.

What's with all the rancor over method of boost?

N

[Herr-Kuhn]

RH...All you have to do is look at the dyno sheets. 70 extra HP upstairs on the same boost pressure on the same engine is quite a bit. Only one other supplier has boosted to these pressure levels on the S4, and we all know who that is. I don't want this to turn into an online bashing contest so I'm not even going to put up the comparison graphs. Anybody with a computer can do that on their own.

I'm just clearing up 4 years of confusion and being decent about it, that's all. 4 years ago we were all told that the Dynojet was the measuring standard...any now you see the results when you strap a twin turbo 928S4 to one.

There are a lot of other benefits to turbocharging too...but of course to each their own.

[Herr-Kuhn]

I'll also add that a short or easier installation time is the last reason to make a purchase decision.

It's not like you need a PHD to install it.

One thing I laugh at is the numbers quoted for installing a small block into a 928...there is a lot left to interpretation in some of those numbers, so I see your point. This situation is different as the motors stay in the chassis. Myself, I don't mind working on the floor on my back...in many ways it is easier than bending over the car all day.

[Fabio421]

Herr Kuhn.......you've got mail.

[njsharkfan]

That is amazing!!!

Great work. Just amazing numbers. Now you need an HP gauge like in the Veyron.

[blown 87]

Originally Posted by Herr-Kuhn

With the right chargers and a large enough engine I would think that 1000 HP is possible, but at that point you have a missile that only a handful of drivers could manage on a track.

That is good work John, but my guess is that there are a whole lot of drivers that could not handle what you got now.
Not sure if I could or not, but it would be fun to try.

[928sg]

Awesome numbers John...... any guestimates on price? just ballpark numbers?

[lizard928s]

this really makes me want to finish building my setup.

[Herr-Kuhn]

Thanks guys...I'd really like to give some price numbers now (trust me it is close), but I have some final confirmation to do with my suppliers. I'm really hoping by January to have things ironed down. As you can imagine there is quite a bit of labor time in all of it. It's a very different animal then the other systems...for example, you have to pull the entire exhaust and install new from the heads, but then again you don't have to touch the crank pulley or the intake whatsoever. It's all a give and take. Also, I'm planning on all new pieces for the fuel...this includes injectors, MAF, chips, and a new fuel pump...the fueling is so very important...you've gotta feed this thing when you put it on the boost bottle.

I am toying with the idea of giving the first person a totally free installation on the system. I realize I would have to get some systems out on the street to "spread the word"...then it would not just be me up on the twin turbo podium.

[shaaark89]

can you also post the sae corrected numbers?

[Darien Nunn]

John, CONGRATS!!!!!

What are the main changes from the last dyno? Can you post the AFR log?

[Herr-Kuhn]

Tom, I think the SAE is like 542 WHP/527 TQ. I just got the STD and uncorrected numbers. I used the STD last time so I am trying to stay along the same path as before...so the car picked up 40 RWHP and like 35 ft-lbs or so. We had one run with 550 ft-lbs and like 549 HP. Boost settings were not changed from September...I made changing the boost settings on my car a pain in the ass for a reason. My air-fuel is still not just perfect...it's amazing how much time the tuning can suck up. We had the top end at about 12:1 after a lot of runs (probably 10), but is is still rich in some places down low...probably in the 11s or so. I'd love to have the dyno to myself for a whole day!!!

Hey, I can't tell you all my tuning secrets . All kidding aside, I will say the last time on the rollers she was terribly heat-soaked and still very rich upstairs. The better ambient conditions did help. You have to remember I run air to air and this makes it very tough to cool the charge when it is 100F and you have almost no cooler airflow because you are strapped to a treadmill...it's totally different on the street because by the time she is pounding boost you are well over 50-60 MPH and the cooling is then very effective. With an air to water the cooling at low speeds or while stationary would be much better...it's all a trade-off. I wanted simplicity of A/A and I already have 2 additional electric pumps for the TC water circuit run delay and the oil scavenging system. Both have been bulletproof...I think my water pump is the same the SC guys use for the H20 charge coolers. A mighty powerful little Swede!!!

It was still quite rich (low 11s) in September when I pulled her off the rollers...my thought was it would lean out in the winter and colder weather. It ended up pulling down harder on the load maps and the cells were still very, very rich...so we pulled and pulled the fuel down and it then came on full song. When I rolled it on the dyno Saturday morning it only made 492 peak HP (too rich)...after tuning we got the 557 number (with me standing there with my fingers crossed), all by getting the air fuel correct upstairs. It's AMAZING to see the difference that a couple degrees of timing and correct air-fuel can make on a turbo car. I've cranked the distributor on an L-Jet just 2 degrees and seen a full 40 RWHP! I did not touch my ignition this Saturday.

Darien...I didn't get the a/f log charts. I have some more cold-weather mapping to do on the warmup and I want to put some more fuel in on tip-in to minimize the potential for detonation. The Shark Tuner is such an amazing piece....there would have been no way for me to take advantage of this hardware without it (except for maybe going MoTEC or Haltech or similar). John Speake is an incredibly intelligent man and I'm sure Nicklas is also well deserving of credit here too. The fact that we have a tool like this developed for such a specialized market, well it is a very unique situation to say the least.

For those of you still running FMUs...I would strongly recommend you step up to a set of chips for your car. The throttle response is incredible and you can run the system at a low pressure to allow for maximum fuel flow from your pump(s). I've toyed with the idea of renting out the Shark Tuner, but it's an expensive tool and nobody ever treats it like it was their own so I will probably just not go there.

Any more questions, just ask and I'll be glad to answer as best I can.

Thanks,
JK

[Herr-Kuhn]

Wanted: Wide Steel Fenders for the rear of my car and a set of MASSIVE tires... I should just get a GTS and sell this car off...this way I could fit bigger meats!

[lizard928s]

John, have you measured the EGT in the manifolds??

[Herr-Kuhn]

All the tuning has been done off of air/fuel and the knock sensor status. I keep the fuel around 12:1 upstairs to make sure there is some extra cooling capacity in the charge. Peak power is supposed to be made at 13:1, but a 12:1 mixture is safer.

[lizard928s]

I fully hear you there John,
I have full standalone in my 81, (86 32V engine) and will be twin turboing it as well, just a one off build.
I was just curious if you had measured the EGTs to see what they were at with this boost level and at this AFR,
Actually peak HP is made around 12.5:1, peak torque around 13.1:1 (though that does vary with who you talk to)

Couple other questions though
How much total advance are you running at this amount of boost?
What type of a knock count are you seeing at this level?

[icemang17]

John
Great work........ Yet another excellent "boost" option for us 928 owners!! That kind of power in a driveable motor....that just SO sweet......