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Compression Issues - Rebuild Time; Any contacts out there?
Topic Started: Sat May 19, 2012 6:17 pm (693 Views)
Woodcutter
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Ok so I finally got round to finding out why my car gets beaten by little old ladies in Micras. I have been feeling for some time that the power is not what it should be and low end power is lacking to the point of stalling on pull away unless i rev the nuts out of it.

When you lose power over time you dont really notice it going, a few HP here and there so each time you drive it it doesnt actually feel much different. Its not like losing it all in one go when you would notice it. A little like getting fat or old i guess.

Anyway so I did a compression test this afternoon and below are the results, a little shocking but not unexpected given what i already knew...

1) 130 PSI
2) 150
3) 138
4) 120

From what I have researched I should be looking to get around 170-180 PSI out of each cylinder so overall I am down about 25% so in power ratio where i should be expecting around the 200bhp mark i am probably getting 150. Now that tallys nicely with the rolling road tune I had done a while back where it only pulled 130bhp on the first run (i wasnt there and lucky i was sat down when they called me with the result). So after a bit of tweeking with the timing they got it to 160bhp which is still way short :(

So a rebuild is required and I guess at 150k it is to be expected and would be a nice refresh. Now I have a couple of dilemas, do I rebuild with new internals and have a fresh engine to complement the EFI which is on it already or do I rebuild it with low compression pistons and get a M62 supercharger bolted on. The latter is now quite doable as the efi is fitted and has 8 injectors so I have enough scope with fuel it would just be all the fitting plumbing and wideband sensor required. This would get me the power gains I want as I didnt want to go the massive power turbo route.

I cannot do the work myself and really dont have the time. Also I dont want the car to be off the road for many months so I am looking around for a firm that could do the engine rebuild to a high standard or even if feasible do the charger install. I have looked around and cant really find anyone and if previous experience is anything to go by I have found alot of people say they can do work on these cars but then turns out they dont have the knowledge or experience and end up hashing it up. I really cant afford that to happen. Does anyone on here have suggestions or recommendations? :help:

Lastly a technical question, if compression is so low and the engine is worn would this be causing the engine to run very hot through poor detonation? I have noticed that my engine generates a huge amount of heat in the engine bay now. The water temp is fine but the under bonnet temps are so high it has now melted my dip stick! :no: feckknows

Thanks in advance for any thoughts or guidance.


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Lewis 190E 2.5 16
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Shame about the results but rightly said to be expected, you'd need to carry out a cylinder leak test to determine the cause of the poor compression but IMO I'd go for new piston rings and top end work, 3 angle cut valve seats, new stem seals. But whilst it's apart and if budget will allow a set of Je pistons are going to set you back around £250 each with rods approx. Things will get costly but you only live once. Get the internals right now and think about adding a supercharger next year. There are companies that will produce custom v belts to run chargers and of course you already have the efi standalone set up so your pretty much set just need to run some boost piping and coolers and mod the inlet manifold and create a plenuim chamber. Should be sweet for 260-280hp :)
Edited by Lewis 190E 2.5 16, Sat May 19, 2012 7:12 pm.
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Woodcutter
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Lewis - thanks for the reply. I have looked at getting the forged rods and pistons but my question is this... If I am going down the charger route would I not need to get low compression pistons? If I paid to rebuild the engine standard now with the view to supercharging it later would i then not need to rebuild it again to lower the compression to allow forced induction? this is where I am stuck at the moment, either i do or i dont else its double the work later. Finding someone to do it is also a challenge :-/

280BHP sounds good tho B)
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Lewis 190E 2.5 16
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Low comp pistons, thicker head gasket and a head skim will lower the compression. It's trial an error and going into the unknown...
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alogaparaloga
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I would say that it is better to have a detailed check of the bottom end as you will have to rebuild the top end anyways. What is the original compression ratio you have?
Dropping the compression ratio can be done with a custom metal gasket and stock internals.
All you need is to measure combustion chamber cc and do some calcs.
If you want to invest your money right, get the block, crank and rods crack inspected.
Then think how far you want to go as by then you will know if it's worth spending the extra money for pistons and other upgrades.
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Woodcutter
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alogaparaloga
Sun May 20, 2012 12:32 am
I would say that it is better to have a detailed check of the bottom end as you will have to rebuild the top end anyways. What is the original compression ratio you have?
Dropping the compression ratio can be done with a custom metal gasket and stock internals.
All you need is to measure combustion chamber cc and do some calcs.
If you want to invest your money right, get the block, crank and rods crack inspected.
Then think how far you want to go as by then you will know if it's worth spending the extra money for pistons and other upgrades.
I am unsure exacly what the stock compression should be as there are a few different sources and I think NAM spec is different. I suspect somehere around 9.7:1. I guess the other option is to stick with NA and up the compression and add cams but like Lewis says you only live once.

The whole engine bottom and top will be rebuilt with the various tests carried out to ensure it is crack free etc. I have a couple of firms local to me that specialise in rebuilds but mainly for standard cars so no real ability to help me with any upgrade modification ideas. Thats where I am struggling to find anyone who can take on the work.

If I had a ford or a nissan i could just open the yellow pages. But thats why i like this car because you cant.
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