PorKen

Maybe because of no correction factor?

326 rwHP is 30 more than I'd expect for a S4 5-speed w/X-pipe & stock chips (290-ish DynoJet)?


Especially odd since the internets say that Mustangs often read lower than DynoJet as well.

victor25

Here is a chart from a 5spd with stock exhaust and 5 psi boost. Does this help?

ptuomov

I may have been talking about roots type blowers in drag cars. Twin screw and centrifugal are more efficient in that they require less pressure for the same density and waste less in heat. Apologies if I've spread misinformation on this.

This thread was posted when I was knee deep in the euro zone debt crisis, so I missed it. Hence the slow reaction.

I did a little spreadsheet with a lot of assumptions about the compressor and intercooler. I got about 30 hp loss from that as well. For the transparency's sake, here's the math:



If you find errors, please point them out!

I am assuming 100% mechanical efficiency for the Rotrex and the belt drive. In reality, there's more losses there but that's not a double digit number of hp in any case.

I can't quite get the engine to produce 450 crank hp in my spreadsheet though. That doesn't mean that it doesn't produce 450 crank hp, it just means that there's a discrepancy with my simple model and that number.

At 12 AFR and 0.45 lb/hp BSCF a normally aspirated engine requires 2.45 kg/h of air to produce 1 crank hp. In the above spreadsheet, I fed it 1100 kg/h, which would produce 448 crank hp before the supercharger losses. If the supercharger consumes 28 hp, then we'd be at 420 crank hp. This 1100 kg/h is also consistent with the 28 hp compressor power requirement.

Another way to skin the car is just scale up the stock motor power by the pressure ratio and subtract the power required to run the compressor: (14.7+6)/14.7*318hp - 28hp =420 (crank) hp.

This probably just indicates that there are some more speed secrets for me to learn.

SMTCapeCod

Is the S3 notional project dead?

victor25

Holy cow man.... your math makes my brain hurt!!!
Honestly all I know is what the dyno tells me. We can do math all day long, but there are so so many variables to consider... altitude, temps, humidity, exhaust back pressure, cat status, compression status, the intakes ability to flow air evenly over the cylinders and flow in general, type of fuel & octane, timing advance... and on and on and on...
I will make an appointment and put my car with the stage 2 kit on the dyno in a couple of weeks. The car will look as pictured above in post #402. With a 70mm pulley, on a 5spd, with stock exhaust and 93 octane shell gas in the tank. This is a good shop and these guys know what they are doing. They are the ones that did the later dyno sheet, and I believe there dyno is pretty spot on. cool???

jeff spahn

I have the VCB stage 1 and really don't care what the HP is. 420, 450, 5000, who cares. It has the go I want now. Spins the tires in 1st and 2nd and that means I have plenty of power with 285's on the back. I only want a 5 speed auto now (Calling Dinsdale!) with overdrive so I can cruise on the highway and get 25 mpg or better so I can go farther on a tank. Then it will be a super duper GT car for me.

ptuomov

If that supercahrger meets your needs, it works. No argument about that.

I am just trying to understand how these things work and what power they make, etc.

SeanR

I wish I had an answer for every person that asks me what HP I'm putting down. People sure look at me funny and dont really don't like to hear "not sure, it was 316 stock". I need to get mine to the dyno someday soon. I've been saying that for almost two years though. I figure if I can spin my 295's at 60 when it kicks down it's doing ok for me.

DKWalser

Kewl. Burning rubber at freeway speed is super cool.

Question: The knock on this kind of supercharger is that, properly scaled, it doesn't reach maximum boost until the RPMs approach redline. That implies that there's not a lot of boost (and increased HP/torque) at 2,000 RPM; there's not a lot of low-end grunt gains compared to a twin-screw supercharger (or a spooled up turbo). So, to make the most of this type of supercharger, you have to keep RPMs in the upper-half of the range. This might make the power band seem very narrow. Do you feel that in your street driving?

I've not driven a car with this kind of supercharger. I have driven other types of boosted engines. (A positive displacement supercharger, like a twin-screw, feels like you've gone from a small block to a big block engine. Just more power throughout the range. A turbo can have a little lag, but once it's spooled up -- unless you let RPMs drop for an extended period -- it, too, just adds more power throughout most of the RPM range.) So, I'm asking for your experience. Is the theoretical problem a problem in practice?

hacker-pschorr

The only way the numbers mean anything is if you have a before and after on the same dyno using the same correction factor.

Unless you do that, the results are still going to come into question.

Or stick with DynoJet's for the "final" numbers. At least in my experience they are the most consistent across the board.

Any brand dyno will work for tuning, especially one with a brake system. But trying to compare dyno to dyno... forget it.

Those should not come into play unless something is wrong with the dyno. That is what the correction factor is for.

I've had my car on the same two DynoJets in every kind of weather conditions. Some days in a balmy, humid shop with all the doors open and other times in the dead of winter (again with the doors open.....yes we are crazy).
The results are exactly the same.

Blaming dyno results on weather patterns and posting fuzzy math crank HP is the kind of stuff I expect from Carl, not you guys.

You have a good product in the works, stop muddying the water with this marketing BS.

ptuomov

Here's another question. I may have misunderstood this, but is the intercooler air to air with the coolant air supplied by the smog air pump? Or has that configuration changed?

jeff spahn

I notice more power from about 3000 up. I don't take it to redline all that often so I can't really comment on redline. Have done it before to spin tires while moving but that's not my style. I just like having more power.
Perhaps when this engine craps out I'll scrap the whole thing and put in a small block chevy with a twin screw or a 4.6 ford with a twin screw or even a GB stroker. I don't know. I figure this engine will last a long time so by then my thoughts may change.

victor25

HAHA... Believe me Hacker, I agree, and I'm really trying NOT to muddy up the water!! I am just trying to answer as best I can in simple terms. And there are no Dynojets in my area.

I completely agree the best thing is a straight before and after with the same car on the same Dyno. Thats what I tried to do with the original posted Dyno, but look at what a mess that has turned into!! We have a few people that are installing kits soon both here and over seas. Hopefully I can arrange a before an after with one of these people.
One guy in Sweden has just finished a very cool setup with an aftermarket engine management system running MAP, and fully water inter-cooled. Basically a stage 3 if you choose to call it that. Hopefully he will run it on the Dyno soon and I can post the results. Its a very cool setup and a beautiful car!!

SeanR

Looky what showed up today

Mongo

I must have missed it, but what does this kit retail for?