Z

By measuring and comparing the torque produced as the engine goes through it's cycle, you'd see where and how much torque was being produced in relation to the crankshaft position. Instead of a torque curve in relation to RPM, like you get on a typical DynoJet chart, you'd have a torque curve in relation to crankshaft position. Comparing that to measurements from a similar normally aspirated engine would show where in the engine cycle the torque produced varied between the engines. The shape of the torque curves would be different, with the supercharged engine having a higher torque peak further along in the engine cycle than the normally aspirated engine. You'd be comparing the actual shapes of of the curves, and not just the amount of torque being produed. A similar comparison of curves would be the way that GT cams have a higher second torque peak in the RPM range than S4 cams.

Noelracer928

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Dan Perez:
<strong> </font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">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.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">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![/QB]</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">That might be the way to go. Can I do those mods along with the stroker kit. And what is the S4 aero kit?

LT Texan

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Z:
...you'd have a torque curve in relation to crankshaft position...</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">A machine that measures torque at a certain crankshaft position? Create a torque curve from top dead center to bottom dead center on the power stroke? Torque curves for each engine speed desired to be measured? On a one cylinder engine (or would the results be jumbled)?

I am unfamiliar with such a machine

John Speake

Hi,
My 2 cents worth..... I've been looking at the LH ECU, and the length of time the injectors are open.

At max torque, they are open 10mS, at max rpm full throttle, they are only open 4.5mS. That tells you something about the volumetric efficiency of a standard 32v motor.........
this was measured on a GT ECU, on the bench with my test rig.

BC

Were you doing sequential injection Sterling? A graham bell suggests that with sequential there is no power increase from going that way unless you keep the duty cycle of the sequentially controleld injector between 60 and 70%.

Batch injection should rarely be run above 80% is also another point that he makes.

Normy

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> 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] </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">-In my reciprocating engines classes in college, they taught us that the max torque takes place around the 90 degree ATDC point, for obvious geometric reasons. They went on to say that typically, the exhaust valve opens around the 120 degree ATDC point for two reasons: 1. To give exhaust gases more time to exit the cylinder [better scavenging at high RPM], and 2. To reduce cylinder temperatures. It would seem to make more sense to keep the exhaust valve closed until BDC, but this apparently not only hurts power but raises temperatures. This all is the reason that turbo's can work- there is still a tremendous amount of energy in the freshly heated charge [at exhaust valve opening the charge is still burning], which also explains why turbo's typically increase fuel mileage if no other changes in driving style occur. Energy that is typically wasted is recovered to increase effective compression ratio = greater efficiency.

The long and short is that there is a tremendous amount of energy at the 90 degree ATDC point-

N!

LT Texan

I figure the highest cylinder pressure is the time just after TDC. Why? Well ignition happens BTDC and I figure the flame travels across through the chamber while the piston is dwelling at the top of the cylinder and before the piston has pick up much speed travelling downward and the combustion chamber is so small. So there is tremendous pressure as the piston starts its travel downwards.

As the piston passes about 20-30 degrees ATDC, I bet the pressure starts dropping as the volume of the chamber increases rapidly with the piston travel.

At 90 degrees ATDC, over 1/2 of the cylinder displacement is exposed and this expansion allows the pressure to drop significantly.

That’s the way I’ve understood it.

This makes me think supercharging will add lots of stress to the rod bearing at the beginning of the power stroke.

T_MaX

Anyone know the differances between the S4 and GT EZK/LH units?

John..

Personally, I think the big money programmable injection systems are overkill unless you are racing the car.

I'll reserve comment on my setup until I finally get it tuned in with the new MAF and signal conditioner.

chris928

"A machine that measures torque at a certain crankshaft position? Create a torque curve from top dead center to bottom dead center on the power stroke? Torque curves for each engine speed desired to be measured? On a one cylinder engine (or would the results be jumbled)?

I am unfamiliar with such a machine"

Regarding this statement, there is a machine that I used to run that could essentially do this. It was called a detonation engine which you could vary the CR of the single piston by raising or lowering the head with respect to the crank. This was to test octane ratings.

We placed a pressure transducer in the head to measure combustion pressure and observe knock on an o-scope. The pressure curve could be translated into a torque curve using the engine geometry.

Regarding the aftermarket computers, I think it is great idea. I've been looking at the AEM or Perfect Power (Ott is selling these).

Why, well I would like to have detonation control on my '85. Additionally, I need a way to controll the flappy on the S4 manifold I installed. I temporarily will be using an RPM switch, but an EMU could do it nicely. Also, I don't like paying the big bucks for OEM replacements (just paid $600 for a used LH computer as mine was bad). The EPROMS are past their half lives in these older computers and I predict you S4 guys are going to feel similar pain as me very soon. $600 would have put me a third of the way to a modern unit.

I recently tracked down some wiring issues that a PO had created (switched the TP wiring with the idle control). If I had the ability to plug in a laptop and look at all the signals, I could have saved hours.

Anybody who has troubleshooted the stock system should agree. Grab the manual and a multimeter and plan on some serious time away from family and friends.

I think the AEM and the Perfect Power are both under $1500. I don't know of any reason to spend the money for a Motec or anything of that price range (if sombody knows, let me know). Both companies have their software available to play with before you buy. AEM has tuner forums and a downloadable manual.

The stock computer is acceptable, but the handwriting seems to be on the wall. If you want to avoid costly repairs and get a significant upgrade in the process, we should be considering this option.

Whoever is developing fuel maps currently will be very popular in the near future I'm guessing.

DoubleNutz

No question that bang for the buck has to be Supercharging it, not to mention the ease.

p@

bcdavis

Yeah, but he is talking about what to do for his s2, and there is not a supercharger kit out there for the s2s yet...

To develop one from scratch will cost as much as a stroker...

The stroker would be more reliable and maintainance free...

Z

www.tfxengine.com/4stroke.html
www.tfxengine.com/4strokecylinder.html

There's another chart of torque vs crankshaft angle on page 27 of:
www.luk.de/Bibliothek/Download/folien_zms.pdf
That author's name looks kind of familiar for some reason.

With higher resolution and the smoothing feature of the software turned down, you'd even see it on a DynoJet. Without even having an actual machine to take the direct measurements, curves of this type can be computer simulated and predicted for various engine configurations. If you know the engine RPM and ignition timing when they were taken, even by just looking at high speed photographs of the combustion process you can get a fairly good idea of when the peak combustion is occuring, and how long combustion takes place in relation to crankshaft position. I would have thought that a number of you that are planning power increases would have come across stuff like this in your research. You are doing research, right? If not, you might want to take another look at that picture of that connecting rod and oil pan above.

That would be true if the air/fuel charge burned all at once and almost instantly. That's not the case though. The flame front starts small, then grows in size and spreads through the combustion chamber, in pretty much the same way that a match flame starts small and flares up when you strike it. That takes time. At 6,000 RPM, the crankshaft moves 10 degrees in under 0.3 milliseconds. The air/fuel charge doesn't burn all at once, and takes time to reach it's peak burn.

I'm not sure why you'd think that a supercharged engine making 55hp per cylinder would put any greater stress on a rod bearing during the downward force of combustion than a stroker engine that makes 55hp per cylinder.

As was stated before, the greatest loads occur from high RPM, and occur at the top of the exhaust stroke. The faster the piston is moving, the greater that force at the top of that exhaust stroke is. The force does not increase at the same rate as piston speed. It increases exponentionally in relation to piston speed. The longer the stroke, the faster the piston has to go to cover that longer distance if the engine is at the same RPM. A stock 5 liter 928 engine, with a 78.9mm stroke, has an average piston speed of about 15.78 meters/second at 6,000 RPM. A 6.4 liter 928 stroker motor, with a 95.25mm stroke, has an average piston speed of about 19.05 meters/second at that same 6,000 RPM. A supercharged 5 liter 928 engine would have to be run all the way up to 7,240 RPM before it got to the same average piston speed that the 6.4 liter 928 engine sees at only 6,000 RPM.

That 1,000 horsepower four cylinder engine I mentioned earlier in this thread was 2.0 liters. It was based on a GM engine with an original displacement of 2.2 liters. They reduced the displacement by shortening the stroke.

The following web page kind of focuses on diesels, but goes into some of the same points I've made here.
www.bankspower.com/Tech_somuchtorque.cfm

Rich9928p

quote: 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.

&gt; On a healthy engine, there is no need to do any of this.

&gt;&gt;&gt; True, but how do you know if your rod bearings are healthy? I've seen SPEC 944 racers blow rods in almost every car that didn't have the rod bearings replaced prior to racing (and these are naturally aspirated engines). If you're going to supercharge an older engine, it would be wise to pull the pan and replace the rod bearings. It isn't that expensive and is much less expensive than replacing a whole engine after it blows! The rod bearings bear the brunt of the extra power.

&gt;&gt;&gt; BTW, 951s (944 Turbos) have the same bottom end as the 944. So it might be safe to assume that a 928 motor can reliably take the extra power too.

LT Texan

Z,

Thanks for the link. You absolutely learn something every day.

But what I wrote seems to be supported by the example in the graph on the link, that is:

Peak cylinder pressure (800psi) is achieved at 22 deg ATDC, and cylinder pressure drops dramatically with the piston movement down to 90 deg ATDC (about 100psi). Heck at 40 deg ATDC, it looks like cylinder pressure is already halved.

At 22 deg ATDC the piston has only moved downwards 3 or 4 mm. At 90 deg ATDC it has moved 44 or 45mm.

And I never wrote nor wanted to imply that a supercharged engine stresses an engine more than a NA one making the same power. But what I wrote was in response to Lagavulin’s comment that a SC’d engine’s peak cylinder pressure increases by about 20% so a SC does not tax an engine much. I just don’t know if I buy that. (Or maybe, that's just too easy?)

I think you should carefully consider piston speeds if you change the rod to stroke ratio in our engines. Stock 78.9 strokes with the 150mm rod length gives a very conservative ratio that could be safely decreased. But I think the rule of thumb on this ratio is 1.7 or so depending on how much rpm you want.

Also, I wouldn’t worry about average piston speed, but rather maximum piston speed. This is influenced by the rod lenght to stroke ratio and maximum piston speed in my stock engine occurs at 77 degrees after and before TDC where at 6,000 rpm I figure the piston is travelling at 25.6 metres/second.

I think I’ve lost the point of this discussion, but whether it is “when will a rod bolt stretch to the point of failure” or if it is, well whatever, I think we can conclude that engines are a complicated (and fun) subject.