Engine Performance?

[Edelweiss]

Originally Posted by Steve@Rennsport

Hi Dirk,

I too, have experienced the very same things with that cam when the headers/muffler are wrong.

Not many people understand how sensitive these engines are about exhaust systems.

So true Steve, and we hear the same - " an exhaust can't make power "

But yes it can, ant when the TDC lift goes up the difference from a very bad to a very good exhaust concept is so huge.

Primary to secondary length / diameter - collector design and reflector to absorber.

It can make an engine alife or kill his good spirit.

Best reg.

Dirk

[Walt Fricke]

Crash
How about changing the graph so RPM instead of speed is shown? I think that is more useful, and the software allows making that change from the data stored from the run.

Looks like a 3d gear run?

The ends of these runs look like either a rev limiter kicked in, or you took your foot off the throttle, not that the engine just wouldn't rev any higher. What was the deal there?

What fuel did you use? If detonation is a suspect, running some 116 octane fuel ought to help see if this is happening, or if it is some mismatch in intake/exhaust resonances.

[hdrockerroller]

Originally Posted by Walt Fricke

Crash
How about changing the graph so RPM instead of speed is shown? I think that is more useful, and the software allows making that change from the data stored from the run.

Looks like a 3d gear run?

The ends of these runs look like either a rev limiter kicked in, or you took your foot off the throttle, not that the engine just wouldn't rev any higher. What was the deal there?

What fuel did you use? If detonation is a suspect, running some 116 octane fuel ought to help see if this is happening, or if it is some mismatch in intake/exhaust resonances.

Yea I was thinking rev limiter too. Do have an MSD ignition, they have programable rev limit.

[Eagledriver]

If you're only reving to 6100, that explains your lack of power.

-Andy

[crashmy911]

If these Pistons are higher then 10 5 to 1 compression I would need race gas? What do u guys think these would come out as?

[crashmy911]

The engine only went through two pulls on dyno and then was shut down.

[crashmy911]

Just looked at cam timming. Cams are off some. Left side at 5.92 and right side at 5.91. Going to try setting them closer to 5.6.

[Walt Fricke]

1) If you can't post a dyno sheet which has RPM across the bottom, how about you specify the gear you were in (if 6100 was where it shut off, I'm guessing 4th, but no one should have to guess), the ring and pinion, and the ratio for that gear (or, if a stock transmission, which one), along with your rear tire specs.

2) I'm dubious that a changing the cam timing by that amount is going to make much of a difference, but it might. Just be sure you are checking for full throttle butterfly opening.

3) At one time I thought that if you got rid of a rev limiter apparently set at 6,100, you'd get that HP you think you should. But looking at the graphs again, I guess not - since the HP falls off with the torque fall off, rather than continuing to rise as it typically does with race motors and race cams at those rpms (the increased revolutions more than offset the fall in torque), something more serious is going on to kill the breathing.

4) By all means post the new dyno results. I wish I could time my cams within 0.01mm of each other side to side! Anyone who can do that surely can set them to 5.6 without too much trouble.

[crashmy911]

Walt my readings where fast so I'm sure they aren't perfect

[crashmy911]

[crashmy911]

Stock gear box.

[crashmy911]

It's a electramotive tech 3r system

[fred cook]

Which heads are you using on this 3.0 engine? If the ports are small, that could be the restriction, especially with the 48mm ITBs.

[fred cook]

About 2 years ago I built a 3.3SS engine for my SC. It is using 10.1:1 Mahle pistons, KN Engineering 100mm cylinders, 964 cams, Carerra twin plug heads, Electromotive XDi direct fire ignition, CIS induction, etc, etc, etc. As you can see, it is quite similar to the engine in your car except for the intake system. However, my engine will pull like crazy up to the ignition cutout at 7500 rpms. So, it does seem that your engine is restricted somewhere. There is an old saying among hot rodders that the horsepower is in the heads. Since you have the big (48mm) ITBs, hot cams, and direct fire ignition, you might consider the following: 1) Ports in the heads are too small or not matched to the intake diameter, or 2) you are not providing enough amperage to the power for the direct fire coils. If it's the first, it's a case of trying to pull air over a ledge that is causing non laminar flow to the intake ports. The intake size and cylinder head port size should be the same for good flow. If it's the second, then your ignition system just can't supply the spark intensity needed to make power at high rpms. The coils should be operating off of relays that pull current directly from the battery. As a general rule of thumb, expect to need 1 amp of current for each 1000 rpms. So, your system would need to provide 7-8 amps to each coil pack for max power. Happy hunting and good luck!

[crashmy911]

Thanks Mr Cook. I've got early sc heads. The ports where enlarged to mate with manifolds

[crashmy911]

Car at new tuner in Maryland. Behe Performance we will see what he can do with it.

[camgrinder]

I would expect to see a 5500 RPM and up powerband with those cams in a 3.0 litre at 10.3-1 compression. Looks like 5500 RPM is around 75-77 mph on the graph?

Going from 5.91mm to 5.6mm on the cam setting is a little over 1 degree on the centerline. And the wrong direction (retarding them) if you are looking to pick up the hole in the powerband.

Did you try adding fuel? Not saying its a cure, but with these cams the a-f is probably going to end up in the low 12's.

[Walt Fricke]

Crash

The early SC heads are the big intake port heads. They require the larger intake manifolds.

You can open up the ports on the later US heads to match the early/Euro head ports.

But you wouldn't want to try to open up the later, narrower, manifold runners. You could probably do that down at the port flange, but that won't do any good with the air flow out of the air box, where everything needs to be larger as it was on the early SC and the Euros.

If you port matched the smaller port runners to your larger port heads, that might be part of this puzzle.

Perhaps you just misspoke? And you have the larger intake ports and the proper runners to go with them?

[crashmy911]

Heads are 78sc heads. Cams are at 5.7 and 5.8. Best I could do.

[crashmy911]

Tuner has gone to bigger injectors. We will see next week what it will make. Tuner also found problem with TPS sensor.