Thread: Bad engine? Opinions requested.

Long story short, by '91 SE-R race car (NASA PTE) seemed to be low on power, so I put it on a mobile dyno at the track last summer. Below is a graph showing 4 pulls. Note, it was a hot day and I didn't hear any bad upper or lower engine noise. After the dyno I found compression to be 119-121 across all cylinders. Adding a tablespoon of oil got me +5psi on all cylinders. Blow-by through the oil-fill hole (valve cover) feels like a hair-dryer on Hi-setting, and the vc gasket I replaced about 10 hrs ago (track time) was leaking in several locations. After pulling the vc I check the chain/sprockets and they were on-mark, and the cam lobes were all smooth and looked great. I'm also getting a little unburnt oil appearing on the lip of the exhaust, and the spark plugs were dark/carbon. I have not checked fuel pressure nor the ignition system, but the engine does run smooth albeit low on power.

I will soon begin the project of an engine R&R, but hope to find a consensus that the current engine has wasted piston rings. Also, why does the dyno show irregular power from above 4k rpm? Is it the S4 cams exaggerating the compression loss?

Specs: OEM-JDM SR20DE high-port w/ JWT's S4 cams, flywheel, and ECU, timing at 15*, HS header (gen 5-6?), 2.5" -> 3" side-exit exhaust w/ an 8" cherrybomb, and HS cold-air K&N intake, UR crank pulley, and a gutted PS pump. Similar set-ups have dyno numbers around 150hp?

Seems about right I think, remember the ~140hp the sr20de is rated at is off the crank, so to be getting nearly 120hp/120tq at the wheels isn't bad Imo.. I bet if it wasn't 100+ degrees it would have made a little more.

Do you have to follow certain rules regarding what engine u can use? If not just get a ve off eBay an slap it in, instantly gain 40hp if not more

NASA's PT race group is ultimately regulated by a power:weight ratio, thus most B13/B14 can't exceed 150-160hp. We use an OE SR20DE w/ bolt-ons. One racer in the mid-atlantic underwent a dyno-reclass (usually reserved for engine-swap cars) using a SR20VE, but he had to keep everything in OE form - stock air box, exhaust manifold, ECU, etc to keep the power down.

With the mods I have, I expect my engine should make around 150 at the wheels. I didn't mention before that I also have a UR crank pulley and a gutted PS pump (since I have a Sentra E steering rack,) and no AC.

You wouldn't be the first guy disappointed by a dyno

Sorry I only just saw this now but something is off on your engine for sure....

Our G20 with 100% stock engine (stock ecu, stock cams, stock pulleys) with ONLY SSAC exhaust manifold yet stock airtake (stock airbox) and fidenza flywheel showed us 134whp on the dyno last time we ran it.

Meanwhile, our previously owned 200sx SE-R PTE car with JWT ECU and JWT C4 cams showed us a measly 124whp and a messy dyno like you show here.... we changed the engine, went back to stock ecu and cams and suddenly we had 132whp again... In our case the headgasket was a mess, oil pressure was low and the leakdown was bad before the change.

Your compression pressure is too low. As per the Service manual, 149 psi is minimum. Standard is shown as 178psi.

You should perform a leakdown test with the valve cover off to better find where the loss of compression is. Use your ears to guide you. From the timing chain area, probably the piston rings. From up top, valve seals probably. Exhaust side gets hammered and those seals wear faster. Assuming nothing horrible happened.

i didnt see the compression numbers not sure if those were edited in later maybe, but yeah thats pretty low..

I'm borrowing a leak-down tester for the weekend. The engine is coming out none the less, but it's a wise suggestion that should lead to a better understanding of the low compression.
Thanks!

Photo showing dyno of 134whp (a healthy sr20 100% stock engine with only the fidenza flywheel and SSAC exhaust header yet stock airbox like I said)