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Low Compression


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#1 phoenix1

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Posted 19 September 2018 - 10:17 AM

Hi guys .I have a 1380 engine with about 120 psi compression .It was built by one of the best but it is getting on a bit . I was thinking it should be in the 160 to 180 psi range .Because it is 1380 I realise there is no simple rebore and I was wondering if just changing the rings might help. I have checked by putting oil in the cylinder and it raised it to about 160 psi. Am I looking at an expensive sleeving or a block change. It pulls very well as it is, it has 1.25 rockers and a scatter cam etc . What do you guys think. Do I leave it or improve.its only a toy but I don't like anything not performing correctly . Thanks in advance  Bryan



#2 nicklouse

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Posted 19 September 2018 - 10:39 AM

are all the cylinders about the same?

 

if yes I would not be too concerned as the pressure reached when cranking has many variables. speed of rotation, cam design etc



#3 phoenix1

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Posted 19 September 2018 - 10:45 AM

Yep all about the same. I was just wondering what people roughly thought it should be. I don't realy want to go and go the expensive route and pull the engine  , but ?



#4 Spider

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Posted 19 September 2018 - 10:51 AM

If the bore is worn, and it was sleeved to go again, you'll find you'll get 3+ times the life from it. The CI of the Block isn't brilliant.



#5 Cooperman

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Posted 19 September 2018 - 01:57 PM

You have just realised the reason for not going to 1380 cc. You will need special sleeves and because the block has been offset bored there is a risk with boring for the sleeves.

Best advice would be to source a 1275 block which has been bored no more than once (i.e.to 1293 cc), then going to the next size up and fitting 21253 pistons.

Of course, the existing 1380 block may take sleeves to take it back to 1275, but I don't think standard sleeves are available for a 1380 bore size back to 1275. Special (=expensive) sleeves may well be needed.

With a 1275 a-Series, the best thing to do is to always go to the next size up until you get to +0.060" then beyond that fit standard sleeves to get it back to 1275. That way you will have literally hundreds-of-thousands of miles from the same block.

There is really almost nothing to be gained from going to 1380 on a road going car. it might be different for a pure competition car, but race/rally people don't mind the expense of squeezing the last bit of power from an engine. The only thing a 1380 gives over a 1275 is bar-room bragging rights  ;D .






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