yemodat

Hello from little ol' New Zealand!

Long time lurker but finally have an issue that has me stumped. My freshly tuned motor is very down on power - 125kw on a hub dyno or 167bhp at the wheels. It's a Dynapack dyno if that makes any difference?

I have a 1999 JDM AP1 with a relatively fresh approx. 1,500km (930 mile) motor in it. The relevant mods to this situation are:

1. AP2 retainers and valves
2. Mugen headers, J's Racing test pipe
3. Berk 3" single exit exhaust
4. OEM airbox, new OEM filter
5. 4.77 FD with Cusco 1.5 way LSD

This motor used to be supercharged and was tuned on the same AEM ECU but had a few issues after overheating. It was stripped down back to NA. New headgasket, timing chain, AP2 valve guides, retainers, pistons + rings and the big end bearings were replaced.

The car has a number of other cool mods on it but its not relevant for the purposes of this thread.

Pre-tune dyno run with factory ECU:
My tuner was not able to get a clean run with the gearing as the JDM ECU has a 180kph speedcut and got a measly 100kw output before he hit speedcut in 6th gear. The gearing was too short in 4th or 5th he said to get a good power reading. He expressed concern that the reading was low but attributed the fact it was so low because of the gearing as he could only hit approximately 6500rpm before speedcut.

Initial ECU electrical gremlins:
The first issue we came across was the ECU had a faulty 5v circuit as it was reading 4.8v when all sensors on the same voltage rail were plugged in but as each sensor was unplugged, the voltage would jump up around 0.2v each time. Further the MAP sensor was incorrectly reading at 80kPa instead of 100 kPa. The tuner recommended repair or replacement and said he was confident that it was fixable. This was remedied late last week and the tuner was satisfied the repaired ECU was fully functional and able to be tune the car.

Dyno tuning:
I received a call yesterday indicating that he had done the bulk of the tune (minus the cold start and road test) but the car only ran 125kw. I have not received a dyno sheet so don't have the torque readings or when it made peak power. He proceeded to check:

1. Compression - 200psi across all four cylinders
2. Timing - he said it looked like the timing was right and the car didn't feel like it was missing in any odd places or spluttering
3. Unbolted the exhaust and intake to check for external restrictions - ended up losing slightly more power when the exhaust was unbolted but no change otherwise

He's confident its not external to the motor. He said he managed to find approximately 30-40nm of torque across the mid-range and the motor pulled strongly. VTEC engaged and was distinctly noticeable.

Prior to my tune, I was driving this car around on the factory ECU and the car felt strong and did not hesitate at all. I have a B16a Civic which is approximately 100kw and this is definitely faster than that Civic. Especially given that the S2000 factory ECU output 100kw at the wheels for the baseline would imply that the S2000 and the Civic would about as fast as each other which I know is definitely not the case.

Next steps:
I'm not sure what to do to be honest. I am semi-confident the motor is healthy but I can't say for sure to what extent it may be thus I have a couple of questions:

1. Valve adjustment - I don't know if these have ever been done, I will do this soon to Billman's specs. I doubt I'll find 25-40kw in this alone though.
2. The ECU - I don't think it's the repaired ECU at fault because relatively speaking, it picked up 25% more power from the factory ECU and that low baseline suggests it's mechanical rather than electrical.
3. Skipped tooth on timing chain - is it possible to be out but still run well?

Any help would be appreciated! I've included a pic for reference

HawkeyeGeoff

6500 rpm is kind of on par with the power numbers you're seeing. ~168 HP (for those of you that use imperial units).

See dyno:

s2000Junky

Compression seems pretty low at 200psi for a fresh engine, but that could just be the gauge. The engine recon was still done to factory 11:1 compression ratio? A leak down test may be prudent here. Id like to know if you are losing compression by some fouled up valves. But checking the valve lash first may be worthwhile. If you have some valves that aren't seating properly because they are too tight or bent, you will lose compression. Chances are slim you would run into any of these issues being a new engine, but ive seen stranger things. Best to do the basic mechanical checks next before you go too far down a rabbit hole.

yemodat

Thanks both for your contributions.

Should I do an valve clearance adjustment first or do a leakdown test first?

s2000Junky

Depends on whats more easily accessible/cheaper for you. If you can do both yourself, id start with the leak down to tell me if there is a problem, its also cheaper to have done then a valve adjust if you are having someone else perform these task. If you can do the valve adjust yourself but have to take somewhere for a leak down, then that may change order for you. the valve adjust if quite far out of spec may be enough to tell you thats the culprit, if close enough to spec, then your doing a leak down anyway to rule out any further issue, say with bottom end.

That aside, its possible your off a tooth or more on the cam timing. Rebuilds can always be subject to builder error.

yemodat

I've ordered the 10mm jam nut valve adjustment tool from Amazon and will tackle the valve adjustment job myself.

I will probably do the adjustment at my friend's workshop which has the correct air tools to perform the leakdown test.

If I am off a tooth on the cam timing - will the car run at all? I was under the impression that if you skip a tooth the factory ECU wouldn't read the timing and not start.

s2000Junky

It likely wouldn't have skipped a tooth, but rather installed that way/wrong initially, but should be verifiable once you pull the valve cover off and clock the motor to tdc and see where the cam timing mark lines up. I couldn't say for certain if/how well it would run, but considering timing gears and offset keyways have been used on this motor/any motor for more/less int/exh cam overlap with smooth running but altered power curve results, its a possibility/theory to rule out. Anything is on the table in my view once someone cracks open the engine and starts monkeying around/rebuilds.

afzan

a local tuner here (dynapack) uses 4th gear for ap1 and 5th gear for ap2, not sure why you tuner is insisting on 6th gear? I'd try the comparing the OEM JDM ECU vs your AEM in 4th/5th gear and see how they compare

s2000Junky

True, 4th is most common, sometimes 5th, what ever is closest to 1:1, but neither 4th or 5th is for our car, its either under or over. 6th gear makes no sense to use on ap1 or ap2, it way over driven.

yemodat

This is all very valid points - perhaps he needs to rerun it in 5th? I think its down on power regardless.