After Saturdays dyno run, I began to suspect the compression test I had done a couple of weeks ago may have been wrong... an essentially stock NA zed with low compression does NOT make 126rwkW!!! I can see how a false low reading can occur if the guage is not seated properly in the sparkplug hole, but can the reverse happen, ie. a high reading? Went back to MI Automotive today and their test shows 175psi across the board, except for #6 which gave 180. Hopefully these figures are right and the engine is NOT sick. Fingers crossed,
I remember your last post showed VERY low figures I do believe they were wrong. If your engine was making such low compression as you said, you woudln't have to dyno it to be able to tell. There are a lot of things which can alter the readings i think, especially if the test is done when the engine is cold/hot. There is a lot of people who don't believe in comp tests as the results can vary so much that the readings are usually pointless. You shouldn't re-build your engine from just going by results of a comp test.
sounds pretty healthy to me doug..... I think 180psi is what the stock NA engine is anyway. May explain your excellent dyno results. You have exhaust and pod filter yeah??? It makes sense. Robs and grants dyno figures would also be higher if they had filter and exhaust mods, allowing the car to breath easier. Cheers
In my experience, some gauges can be a bit optimistic and read high. Whether this is unintentional and due to poor construction on the gauge, or wear and tear, or whether it's intentional, to compensate for lower 'real' readings due to slow cranking, closed throttle bodies etc, I dunno. When checking compressions, I always make sure I do them when the engine is hot (apart from doing a cold test if I want to check for a specific problem), always chock the throttles wide open, always ensure that the battery is well charged, and if not, I leave a charger connnected during the tests, always crank over exactly the same number of turns (usually 5), and lastly I always do a reverse check (eg 1 to 6, then 6 back to 1), to detect and compensate if necessary for a discharging battery cranking at lower speeds on the final cylinders. It also helps if you can see the gauge during the cranking, as sometimes you can pick differences between cylinders this way. It's pretty unusual for even a worn engine to show consistently low compressions - usually they will vary, and one or two will be lower than the rest. If they're all even, then I'd be suspecting the gauge accuracy before I'd suspect a worn engine. False high tests should be impossible if the gauge is accurate and the same method is used for all cylinders. Carbon buildup will increase compression slightly, but then it's a real compression increase, not a false one.
Thanks, Everyone! (Heaves HUGE sigh of relief) Dave, thanks for the details. This guy did the job with the engine just cool enough to get the plugs out without burning his fingers, 1 to 6 then 6 to 1, but only 3 turns. I didn't notice if he chocked the TBs. Next step is to get a carbon clean of the fuel system and injectors. My PREVIOUS mechanic was going to remove the plenum to do the injectors, not even telling me it was possible to do with them still in the engine. Huuuuge price difference!!! Now, the BIG problem! What am I going to do with the money I was going to put aside for a rebuild? (Dreams: 1. Chip and tune 2. Headers 3. U/D pulley...
200hp nos! It took my mate a fair while to blow his N/A engine with a 250shot nos used almost weekly. He never had a pressure gauge though so that was the most likely cause.
Its time for mods doug!!! Mod the bitch!! But I swear, if you beat me to a set of mag wheels, there's gonna be trouble.. Cheers
Before my NA engine died... the car would take up to 30 seconds to start in the morning... Compression test while the engine was hot showed it was still ok (120 approx using Conzult), but it wasn't until the compression test was done until the next morning (without starting the car), that the true figures of 80 and lower showed up - due to the worn out values not seating. I hope that's not the case, but a second opinion is laways good.
Previous figures ranged from 125 (1,2,4) to 150 (6) I hope it's not a case of hearing what I want to, but the higher figures (175) seem to make more sense.
Grant had his tested today... at nissport. Testd at 175 ish all round. So there is no reason to believe yours is not the same.
