Brad850 Posted November 26, 2012 Report Share Posted November 26, 2012 About to do a compression test. Have a dumb question that I can't find an answer to anywhere.. Suppose you have a 2.3 turbo with 180 all cylinders vs the same car with lets say 150. Assuming both cars are mechanically in perfect condition (other than compression).. is there any way to estimate how much power loss the 2nd car will have? Link to comment Share on other sites More sharing options...
boxpin Posted November 26, 2012 Report Share Posted November 26, 2012 Bottom line, lower compression will result in less power. Link to comment Share on other sites More sharing options...
Brad850 Posted November 26, 2012 Author Report Share Posted November 26, 2012 Well I know what the acceptable ranges are. My question is how much power loss can you expect being on the very bottom end of that range (156) compared to being at 185. If thats even measurable. Link to comment Share on other sites More sharing options...
volvoguy23 Posted November 26, 2012 Report Share Posted November 26, 2012 well the t5 motor puts out (stock) 222hp at 180 psi in all 5 techinically speaking so i figured 1.235hp for each psi for all the cylinders combined times that by 156 (minimum comp.) and i got 192hp i have no clue if this even accurate but it seems about right lol i couldnt find anything on what power loss is expected on lower compression...oops i used 180psi instead of 185 should still be pretty close though Link to comment Share on other sites More sharing options...
Brad850 Posted November 26, 2012 Author Report Share Posted November 26, 2012 Going by your calculation that means if you upgraded the ecu (275 hp), you'll have an even bigger loss due to low compression, which wouldn't make sense I don't think. Stock loses 30 (222-192) and tuned loses 37(275-238). So I don't think you can estimate it like that. Not a bad idea though. Wouldn't be surprised if no one knows lol. There's probably too many factors for anyone to accurately test it. Link to comment Share on other sites More sharing options...
volvoguy23 Posted November 26, 2012 Report Share Posted November 26, 2012 Yea lol I didn't think you could use hp and compression in the same equation but it sounded good... Link to comment Share on other sites More sharing options...
Fudge_Brownie Posted November 26, 2012 Report Share Posted November 26, 2012 While I do not have a direct answer for you, I think I can tell you why it doesn't matter If you're going to get a compression test off your car and then try and calculate horsepower loss, you're making the assumption that the gauge is accurate. Many people seem to believe the gauges aren't highly accurate when it comes to the number, and that you are primarily looking for strong variance between the cylinders. I don't have evidence to support this, nor have I seen any, but if we believe the number is not very accurate, trying to calculate horsepower loss is a waste of time. You can 'baseline' using the same gauge to see if condition changes over time. But much like a dyno, it can be different to directly compare two vehicles' numbers from different dynos. Link to comment Share on other sites More sharing options...
Rsterns Posted November 27, 2012 Report Share Posted November 27, 2012 Lower compression also allows for higher boost given that everything else in the system is OK. Link to comment Share on other sites More sharing options...
Brad850 Posted November 27, 2012 Author Report Share Posted November 27, 2012 Got ya. Guess I'm just scared of the numbers I'm going to find but the car flys so I guess I'm not too worried. Thanks guys :tup: Link to comment Share on other sites More sharing options...
sacrifice Posted November 27, 2012 Report Share Posted November 27, 2012 Lower compression also allows for higher boost given that everything else in the system is OK. This is only partly true. Engines being built for high boost applications are built with components to keep the compression ratio low while providing a structurally sound build. It is not safe to say that because the ratio has been lowered due to wear that increasing boost will enhance performance. Temporarily, yes. In the long run, no. Link to comment Share on other sites More sharing options...
mdlimy Posted November 27, 2012 Report Share Posted November 27, 2012 This is only partly true. Engines being built for high boost applications are built with components to keep the compression ratio low while providing a structurally sound build. It is not safe to say that because the ratio has been lowered due to wear that increasing boost will enhance performance. Temporarily, yes. In the long run, no. but hey, if he has a good crankcase ventilation system then sure, bring on the boost! :lol: Link to comment Share on other sites More sharing options...
EricF Posted November 27, 2012 Report Share Posted November 27, 2012 The numbers in compression tests can be misleading, as gauges can be pretty inconsistent from one to the next. Another factor to consider is that cam timing plays a role in cranking compression as well. Being that our cars all have adjustable gears from the factory (and I have seen them set at various levels before tinkering by dummies like myself), I bet that accounts for some of the variations in cranking compression between a lot of these cars that we see. Most of these engines have almost identical cylinder wear upon teardown (in terms of cylinder ridges), so I think the sometimes very significant differences in readings we see here are probably more attributed to different gauges and cam timing. Just a hunch ;) Link to comment Share on other sites More sharing options...
Gideon35T Posted November 27, 2012 Report Share Posted November 27, 2012 With 100k-300k miles on our motors there's simply too many variables to accurately determine such a thing. Also, Fudge's point is huge. The gauge wont be accurate but it is consistant which allows you to check for gross inconsistancy only. Besides, does the specific number (hp) that you're making actually matter? Does it do the job ... Yes, then good ... No, then more powa! Link to comment Share on other sites More sharing options...
Brad850 Posted November 27, 2012 Author Report Share Posted November 27, 2012 Yup there is probably no point in even doing the test right now then. I'm really not even trying to determine the exact amount lost, I kinda just wanted to know if it would be considerable/very noticeable. Link to comment Share on other sites More sharing options...
Fudge_Brownie Posted November 27, 2012 Report Share Posted November 27, 2012 It still makes sense to baseline the engine. And see if you see oddly low numbers (like 100-range) or high variance, compare with another gauge to see if there is some consistency. Link to comment Share on other sites More sharing options...
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