Supercharging vs. Stroker Kit

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07-08-2003, 07:53 PM

#46

Fastest928

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header design is dependent on so many variables...valve sizes, air flow, curtains, lift, overlap, stroke, bore, rpm range, exhaust system details, etc, it is best to start with a specific objective, install a header/exhaust system and then see if the data matches the result and tune your model.

We choose the tube diamter, length and merge point based on using 3-5 928s....and found the "average" spot for gratest area under the curve!!

Did the same for 5.4 - 6.5 l engines..

We have over 2000 dyno runs for exhaust testing for the last few years.

Marc
DEVEK

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07-08-2003, 08:28 PM

#47

karl ruiter

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How much power are you after Noel? Its possible to get about 300hp out of an O.B. 16 valve car with a combo of euro cams, port, MSDS headers, and bigger valves. I have an article that details this from VW Porshce mag in 1985. I'm not sure if this is the level of performance you want but it should cost you far less than 5K and be a very noticable inprovement. If you are interested email me and I will fax you a copy.

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07-08-2003, 10:04 PM

#48

Noelracer928

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<blockquote>quote:<hr />Originally posted by Hans SerVaas:
Here's an original and the most cost effective solution. Sell your car, search ebay for an s4, buy the s4, turn the ignition key. Aproximately 0-60 in 6.2 sec, and as we all know topend of 176mph. I bought my 89 s4 with 84k mi on it, in perfect condition, with every option, including the baby seat, heated lumbar seats, etc. for $10,700.

Just a thought.<hr /></blockquote>I posted earlier that wasn't my best option. Let's say I buy a s4 for $10.700 put another 12 or 13 grand into the car bringing it mechanically up to date. I just put 5k into my 928 making sure it is mechanically sound plus it has a unique body kit (take a look.) And let's say I have to spend another 4k - 6k for a good body kit and 6k for paint so a total of est. $34000 all said and done. I just cannot justify that right now.

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07-08-2003, 10:27 PM

#49

bcdavis

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Well, it looks like unless you want to do it yourself, an s2 supercharger kit is not ready yet...

So you can build a stroker, run nitrous, or do a Chevy swap... Those are your main options...

Buying an s4, or swapping in an s4 engine, will cost you quite a bit, and you will not see a huge power increase...For someone who has a US s2, and they want a little more power, I agree that it is cheapest to sell the s2, and add that $5K to that, and buy an s4. But if you love your s2, and it has a body kit, etc, then your options are more limited...Headers and euro intakes will not get you an amazing boost in power, the way a stroker or supercharger will.

If you can find a used block from a wrecked car, or buy a totaled car, you could build the stroker one step at a time, in your own garage, as your time and wallet permits.

Nitrous is a quick fix, but it will not give you extra power all the time. And, like all the other options, you do risk an engine catastrophe. And if that happens, you will be in sad shape, if you cannot afford a new engine at that point...

The American V8 swap is also pricey, but you have the benefit that once you pay out the cash for the conversion parts, if you kill the American V8 engine, there will be many cheap replacement engines out there to choose from...

If I were you, I would just save my money, and wait, and eventually build a stroker or do a conversion to American power...

Until the superchargers are proven on older s2s, I would be hesitant to spend $8K on one, and then have my engine grenade, and then have to pay another huge hunk of cash to build a new engine. That is why the American V8 conversion is tempting. Either that or the stroker. I want power that is either reliable, or cheap to fix...

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07-08-2003, 11:19 PM

#50

Rufus Sanders

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Noel, First, are you considering joining us on our July Drive? Second, isn't the real difference between stroked and blown engines is weather you want to push or pull in extra fuel/air?

Blown motors need to be tighter, and able to deal with extra psi of compression. People start with 7:1 just so they can blow it at 11:1,when actually 10.4:1 is all that's called for. These motors are being forced to swallow and contain more than designed for.

Stroked motors actually allow for more space and are actualy larger motors in the end with theoretically less stress. (any experts please jump in and correct me.)

For that reason, I'd go stroked, and simply because that is what the state of the art in race engines is, not blown. - Ruf

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07-08-2003, 11:34 PM

#51

ViribusUnits

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What do you mean by stroked engines are the state of raceing today? F1, CART, IRL, and Top Fuel drag raceing all run blown motors. NASCAR is the only major league that I know of that runs a NA engine.

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07-09-2003, 12:54 AM

#52

Rufus Sanders

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Well, like I said, correct me if wrong, but i seem to remember FIA banning turbocharged motors in F1 years ago because it didn't represent the state of the art in auto engineering anymore.

I'm more of a Formula 1 person instead of a NASCAR, NHRA person, but yes, those series are stae of the art too. Too bad none of us can take a 3 mile oval or a 1/4 mile straight to work every day - Ruf

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07-09-2003, 01:07 AM

#53

ViribusUnits

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I'm sorry. F1 and IRL does not allow a turbo.

Cart, and top fuel drag raceing do though.

I'm more of a Nascar guy, so this isn't my home feild. You got me.

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07-09-2003, 02:08 AM

#54

TAREK

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<blockquote>quote:<hr />Originally posted by Rufus Sanders:
Well, i seem to remember FIA banning turbocharged motors in F1 years ago because it didn't represent the state of the art in auto engineering anymore.
- Ruf<hr /></blockquote>Rufus, are you sure this is the reason why turbocharged motors were banned?

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07-09-2003, 02:31 AM

#55

urnotthesameina928

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Tarek I believe they moved away from turbo charging as things were getting too fast too soon for the handling technology they had available at the time.. and were looking for a more level playing field for all entrants.. If a 1.5-litre turbocharged car were produced today, as was the case up until 1988, it would be a great deal faster than the contemporary 3-litre cars. However, contemporary cars benefit from significant technological progress, allowing them to exceed the speeds of the 1988 turbocharged models, despite the fact that these were able to rely on over 1200 horse power in qualifying.
Todays f1 engines produce around 800+ horsepower and can propel these cars over 220mph.. Dave

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07-09-2003, 04:55 AM

#56

LT Texan

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<blockquote>quote:<hr />Originally posted by Noelracer928:
[QB
If not 170mph+ where do you think then? Most of the stuff I can do myself. I,ve been rebuilding engines for quite some time. Granted I've never rebuilt a whole 928 engine (just the top end) but I have enough know how to get the job done correctly.[/QB]<hr /></blockquote>I think Marc answered this question. Devek "3-pack" cam, big valve heads and exhaust system. 50-60 rwhp. I think this gets you past EuroS territory. But not up to 170 top end. I believe that needs the S4 aero package.

Solid rebuild+hotrodding=fun!

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07-09-2003, 10:23 AM

#57

Lagavulin

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Warning, this is a long post!

<blockquote>quote:<hr />By Brendan:
If you run an aftermarket ECU with a supercharger, then you can finitely control those AF ratios, and NOT have a problem.
<hr /></blockquote>Tim has proven that an after market ECU is not necessary.

<blockquote>quote:<hr /> By bcdavis:
Some of the most successful SC cars out there, did rebuilds from the ground up...
<hr /></blockquote>Are you referring to 928’s? If so, which ones?

<blockquote>quote:<hr /> By Rich9928p:
I wouldn't consider supercharging an engine unless the lower-end was refurbished, rod bearings as a minimum. All of that extra HP has to get out, and sometimes the pistons don't stop at the bottom of the stroke ... they keep go'n out the bottom of the engine! This cost needs to be added to a supercharge budget. <hr /></blockquote>On a healthy engine, there is no need to do any of this.

<blockquote>quote:<hr /> By bcdavis:
It's hard to say if these SC engines will withstand the test of time. They are making a lot of power, but will these engines last ten years, or two?
<hr /></blockquote>That is the question, for sure. However, according to the experts in the field, they say that a properly setup engine will last.

Please try to keep in mind that boost does not kill an engine, it’s detonation. If you can keep detonation at arms length, you will not have a problem with a supercharged engine; it’s that simple.

<blockquote>quote:<hr /> By Brendan:
The 928 engine management system is the FIRST to go if you want to make sure you don't blow a stroker OR a boostard up. Very simple. If you are going to spend 15k on a stroker or 10k on a boostard, would not not spend 2500 on a ECU? <hr /></blockquote>Because it’s not necessary. Tim as well as Devek and The White Car have proven that the stock system works well. Use that $2.5k for some trick wheels or an exhaust.

<blockquote>quote:<hr /> By John:
In short, if you blow it and don't want to BLOW it, keep the boost below 10 psig.. <hr /></blockquote>There is no need to stay below 10 psi if everything is accounted for and adds up right. For example, on a 10.5:1+ cr engine, your advice is sound as the numbers say do not do it. However, on anything less than 10:1, one is being overly conservative and otherwise missing out on 'safe' horsepower detonation-wise.

<blockquote>quote:<hr /> By John:
I know of at least one Callaway 944 running on 12 psig with 8:1 on machined cast pistons....but that is in the winter, when the air is cold, he runs 10 psig the rest of the time. <hr /></blockquote>With that low of compression ratio, assuming proper air/fuel management, and efficient aftercooler, he can safely run way more boost than that and not worry about detonation.

Obviously, people are focusing upon the reliability issues again, and I don’t blame them given the novelty of ‘highly’ boosted (..a relative term for sure) centrifugal supercharged 928’s. Not to mention the cost of a 928 engine rebuild...

It goes without saying that the Devek stroker motor has a proven, well documented history behind it, and everyone should take their hats off to them for making it possible for anyone to run it with confidence under their hood. A Devek stroker motor’s reliability is indisputable.

On the other hand, there’s not much history to draw upon with respect to the supercharged 928’s. So, we are forced to resort to well founded prognostication gleaned from experts within the forced induction community such as Corky and Graham Bell, and apply those principles to our 928’s.

The following is a post I made in an earlier thread. Instead of reinventing the wheel, I'll reuse it since it's important to keep these principles in mind when envisioning how an engine perceives the loads induced upon it by doubling the horsepower thru supercharging:

<blockquote>quote:<hr />By Lagavulin on 5/29/2003:

I do think the longevity issue people are mentioning is a bit over-done though.

For example, doubling one's horsepower equates to double the internal stress, right?

Wrong, and here’s why:

Firstly, lets assume the engine is optimized: air/fuel and timing are spot-on, and a good balance of compression ratio/boost temps, so that detonation won’t be a factor. In other words, the engine was supercharged the right way.

To start with, the greatest internal stress on a engine occurs at max RPM on the exhaust stroke at TDC when the tensile strength of the connecting rod is tested to it’s max as there are no compressive forces whatsoever to help decelerate the piston's mass as it reaches TDC since the exhaust valves is wide open, offering no resistance, or compressive force. It is here where a rod will more than likely come apart, not under a compressive load such as the power stroke. You can picture in your mind that when an object is experiencing a tensile load, that object is trying to ‘fly’ apart whereas in a compressive load, that same object is being ‘packed’ together. Thus, it is known that a connecting rod can handle much higher compressive loads than a tensile one.

With that said, the max RPM of a normally aspirated engine is usually the same as it’s blown counterpart, so the tensile loading of the connecting rod will remain the same.

Now for the loading upon the crankshaft.

Once the charged is ignited, the cylinder pressure will continue to rise until it reaches it's peak at approximately 20 degrees after TDC (..on the power stroke), and is exerting a max compressive load first on the piston, and is transferred to the rod, bearing, crankshaft, and finally bearing.

Now lets supercharge that engine so that it’s horsepower is now doubled, and again let’s measure the peak cylinder pressure where the compressive loads are greatest. One would be quite surprised to find out that the peak cylinder pressure has increased by only 20%, since all the extra air/fuel does not burn all at once.

Because of that, by the time the crank rotates to 90 degrees after TDC, there’s still ‘tons’ of air/fuel mixture remaining to be burned and subsequently used to push upon the crank at such an optimum leverage point. It is at this point in time where most of the massive amounts of torque is generated in a supercharged engine.

So we doubled our horsepower, yet only increased the peak load on the bottom end by only 20%; that's a nice surprise! <hr /></blockquote>One must admit it does look promising. And as you can see, beefing up the bottom end is not necessary at stock RPM’s. As Z stated earlier, a beefier bottom end is required only if higher RPMs is a prerequisite.

However, Corky minces no words when he states that yes, one must pay the price for the additional loads imposed upon the system, and he speculates that engine life will be compromised by 10%. That’s not too bad, although not as good as Devek’s documented 1-2% decrease. Nonetheless, I do find it perfectly acceptable for a street driven car, especially since a properly maintained 928 engine is expected to last 200k miles.

<blockquote>quote:<hr /> By bcdavis:
I would think that a stroker would be MUCH more reliable. <hr /></blockquote>I agree the stroker should be more reliable (..less parts and their associated weight to worry about), but not by as much as people are assuming. Hopefully for all of us in the 928 community, smart supercharging will prove to offer unprecedented bang for the buck, i.e. dollars per horsepower, along with the proven reliability of a Devek stroker.

I feel very good about it's chances, but as the saying goes, time will ultimately tell the truth.

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07-09-2003, 10:47 AM

#58

LT Texan

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<blockquote>quote:<hr />Originally posted by Lagavulin:
Because of that, by the time the crank rotates to 90 degrees after TDC, there’s still ‘tons’ of air/fuel mixture remaining to be burned and subsequently used to push upon the crank at such an optimum leverage point. It is at this point in time where most of the massive amounts of torque is generated in a supercharged engine.
[/QB]<hr /></blockquote>Interesting argument. How do you prove it?

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07-09-2003, 12:06 PM

#59

Carlos

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Personally I like the supercharger. I think it is just as safe if done well. It is undoubtedly much cheaper & simpler. Besides, it takes more than just a stroker to do this <a href="http://www.raceworks.com/inside_the_ride/gillig1/stream1/default.htm" target="_blank">http://www.raceworks.com/inside_the_ride/gillig1/stream1/default.htm</a>

Or this <a href="http://www.raceworks.com/inside_the_ride/gillig1/stream2/default.htm" target="_blank">http://www.raceworks.com/inside_the_ride/gillig1/stream2/default.htm</a>