Need help finding power

#1

Need help down on Power.
Down 17hp. Car history- purchased my car from D. Hickey in the SE region engine built by Richard Bratton. Group 3 Dyno’d the car and got right around 144whp. Dave thought the car needed the AFM changed out. I ran a few events and really noticed a power deficit at the last Summit Point Event with all cars pulling away bus lengths on the straights even on the rolling start and me getting the jump.

Here is the uncorrected with no smoothing. Compared to other Spec E30 graphs done on this same dyno it is really jumpy and has a significant drop off of power in the 4.5k to 5.5k range. All other graphs showed power flatten a bit but never dropped off. We adjusted the A/F up and down with only 3-4hp change and left as below. Also swapped DME with no change in HP or behavior. Second graph shows smoothed and SAE corrected. The humidity was reading 25% and actual was 85% appears that should up the correction by 4 or so, making it 142hp if we are generous. It was noted that the car did not feel as responsive or smooth as others on the dyno. We checked tires and pressure and also checked to make sure rear when were rotating freely. Nothing or concern was found.

dyno1
dyno1.jpg1582x922 208 KB

Dyno2
Dyno2.jpg1578x888 178 KB

When I got the car back I did the following maintenance items-
Compression test - 146-149 (across the board on fresh built Honda C30 saw 160s)
Leakdown test - 2-5% (on fresh built Honda C30 same 2-3%)
Changed Plug wires
Changed Cap/Rotor/coil
Changed Fuel and Air filters
Changed Oil
AFM changed out on dyno and then adjusted spring load (current one rebuilt by BAV in 2018, New one from them this month, and older unit)
Checked valves .009 intake and .010 exhaust
Replaced crank position sensor (checked Gap)
Checked voltage of the TPS at the DME (closed, partial, WOT)
Checked other voltages per Jim Levie’s troubleshooting guide
I cant stomp test as the engine lights on the dash is out
When running the fuel pressure is right around 41 and never drops
Engine temp was 180ish and oil temps in the 170 range (iirc)
Also pulled plugs and all looked good. No cracks etc.

Next steps
Check coolant sensor voltage again and make sure DME see warm/hot motor. I read a bunch about this and sounds like at WOT the only thing the DMR looks at is the temp sensor.
Get OBDI reader and see if any codes
Redo compression and leakdown test
Pull front cover and check timing markings

Looking for any help/guidance so I can figure this out.

#2

Ok finally have time to write.

Head is the no 1 power part on our cars. A fresh head & cam and with the right gaps will get you in the 150 ball park. Now if your data is correct, then you should be fine.

TPS is the second choice. I would open it and clean it. The issue with the TPS is when there is oil, it can easily infiltrate or bind to the connections. Example: I had a “good” one go bad when the engine was hot.

Third is coolant level/ temp sensor. The engine has 3 states from experience: cold, right temperature and hot. I have personally been fighting a water leak that was recently found to be the thermostat housing 3 bolts neck not being torqued down and would leak when the thermostat would open. My engine dynoed 159hp when happy. But at some points during races, when the temp sensor was not happy, it would feel like you are currently feeling the car at around 140hp. It has been very consistent with the water levels and temperature of the water. Bleeding is also a big must. Car would be down on power untill it “burped” itself, since the air get easily trapped right next to the water temp sensor.

Finally O2 sensor has some say in all of this. A bad O2 sensor will screw with any partial throttle. This is why I wouldn’t suggest messing around with the AFM. Both are partial throttle tunning elements. Being able to make good power there is also important.

Hope this helps.

#3

Thank you. Mach9ne shop found two wxhaust valves that need replacement. Also intake valve guides. I will check and verify other items. Good to know too hot is also an issie with the temp sensor. I found the ohms to be a bit out of spec showing warmer that it really was so replacing it.