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Low compression 253
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Bruvpig Offline
#1 Posted : Saturday, 9 April 2011 9:07:43 PM(UTC)
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Hi all, What is the difference between the high and low compression 253?
(besides compression....I know someone was itching to say that...)
What components are the same, and what changes?
How are they identified?
Were they made to use the "standard" petrol that was available at the time?
Brian
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jim Offline
#2 Posted : Saturday, 9 April 2011 10:09:06 PM(UTC)
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low was 8.0:1 high was 9.0:1 approx 11 hp difference,don't know why as the fuel back then could run comp ratings of 11.0:1 ....I had 10.5:1 then ,no problems.Maybe it depended on models?,as in Monaro = HC....passenger = LC?

Edited by user Saturday, 9 April 2011 10:11:54 PM(UTC)  | Reason: Not specified

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HK1837 Offline
#3 Posted : Sunday, 10 April 2011 1:36:43 AM(UTC)
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Pistons.
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jim Offline
#4 Posted : Sunday, 10 April 2011 1:42:53 AM(UTC)
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Pretty much.
Jim in Adelaide..
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cloudy Offline
#5 Posted : Sunday, 10 April 2011 3:11:45 AM(UTC)
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low comp old motors run better with unleaded fuel
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HK1837 Offline
#6 Posted : Sunday, 10 April 2011 3:42:45 AM(UTC)
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Low comp 186, 202, 253 and 308 used dished pistons to achieve low compression. Most smaller engines like 149, 161 and 173 used the open chamber heads. 179 was probably the same as 186. 138 may be the odd one out from memory.
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peter_flane Offline
#7 Posted : Sunday, 10 April 2011 3:44:31 AM(UTC)
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The cheapest fuel was 'Standard' and it was 87 RON, so it needed low compression. Our 1970 VW Beetle is 7.5:1 compression ratio, and it has 87 RON fuel listed in the owners manual.
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Dr Terry Offline
#8 Posted : Sunday, 10 April 2011 5:05:32 AM(UTC)
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quote:
Originally posted by HK1837
Low comp 186, 202, 253 and 308 used dished pistons to achieve low compression. Most smaller engines like 149, 161 and 173 used the open chamber heads. 179 was probably the same as 186. 138 may be the odd one out from memory.
'
There were no optional low compression versions of the 138, 179 or 308.

Dr Terry
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HK1837 Offline
#9 Posted : Sunday, 10 April 2011 6:06:10 AM(UTC)
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Low comp 138 prefix 2250L and later CC was available in LC and LJ. Also HC prefix in LH.

Low compression 308 prefix BV available in Bedford trucks and busses.

I wasn't sure about 179, but you are right, no such beastie.
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Bruvpig Offline
#10 Posted : Sunday, 10 April 2011 9:06:21 AM(UTC)
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So there was only the piston changes?
Was the compression height the same for the dished pistons and how would I know if I had one of these beasties?
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Dr Terry Offline
#11 Posted : Sunday, 10 April 2011 4:55:08 PM(UTC)
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quote:
Originally posted by Bruvpig
So there was only the piston changes?
Was the compression height the same for the dished pistons and how would I know if I had one of these beasties?

Yes, it was really just the change in pistons, they were dished (or further dished) but the compression height (at the edge of the piston) remained the same. The 138 was unique, it used the 149/161/173 head with a lumpy-top piston & the lo-comp just had a smaller lump.

The original method of ID was the engine number prefix, each lo-comp version had its own unique prefix. Of course these days many have been rebuilt, so they may now be just hi-comp. BTW these are (& were) very rare items, I've never personally sighted some lo-comp engines.

BTW, HK1837 is correct, I forgot about the lo-comp 138 & the Bedford 308. Should slow down on the red wine, no matter how good it is.

Dr Terry.

Edited by user Monday, 11 April 2011 7:04:18 AM(UTC)  | Reason: Not specified

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HK1837 Offline
#12 Posted : Sunday, 10 April 2011 6:31:29 PM(UTC)
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I'm the same, never seen some of them. I found a HQ Belmot sedan the other day with an L23 engine, and it was a 1974 build, 5 seater with seat separator and armrests. Pretty rare car. I think i've only ecer seen one or maybe two QS prefixed (HQ-HZ 253 low comp) engines. I think Dr Terry told me once he'd seen an 11QS.
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Bruvpig Offline
#13 Posted : Sunday, 10 April 2011 7:59:46 PM(UTC)
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Thanks gents, fountain of knowlege yet again...(even if grape flavoured!!)
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jim Offline
#14 Posted : Sunday, 10 April 2011 9:36:04 PM(UTC)
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Cloudy,They do run better on unleaded now,but I didn't think it would be an issue back then.
Jim in Adelaide..
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davequey74 Offline
#15 Posted : Monday, 11 April 2011 4:38:48 AM(UTC)
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silly question but...

which engine was more common? low or high compression?

my ute has 186 low compression engine, which suits me fine cause soon it'll have a turbo :-)
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HK1837 Offline
#16 Posted : Monday, 11 April 2011 4:54:09 AM(UTC)
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High comp by far by HK. Not sure about prior to that, but I don't recall seeing that many Y, 149E or 161W engines. HK onwards I reckon I could count the amount of 186L, QM, QE, QS etc engines i've ever looked at and taken note of prefixes on my fingers. To be honest the most low comp engines i've ever seen have been in CF Bedfords with FE prefixes.
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davequey74 Offline
#17 Posted : Monday, 11 April 2011 5:10:05 AM(UTC)
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i just had a look, my engine number starts with 186P, the head has a "L" stamp on it

so the head is off a different engine then?

and the engine is a high compression cause the heads were the same right?
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Dr Terry Offline
#18 Posted : Monday, 11 April 2011 7:03:12 AM(UTC)
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The optional lo-comp engines were ultra rare in any model series, hi-comp was the norm. A 186P is a hi-comp.

The L casting means large combustion chamber for my money & can only mean lo-comp if fitted to the smaller engine. All 179, 186 & 202 normal (hi-comp) engines will have an L cast head.

Dr Terry

Edited by user Monday, 11 April 2011 7:05:20 AM(UTC)  | Reason: Not specified

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HK1837 Offline
#19 Posted : Monday, 11 April 2011 3:47:13 PM(UTC)
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I agree. L and H on heads are only applicable when used on the engines that use large and small combustion chambers to achieve different compression ratios. I does become confusing sometimes.
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davequey74 Offline
#20 Posted : Tuesday, 12 April 2011 4:29:07 AM(UTC)
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confusing, hell yeah

so there's no difference in a L and H head when fitted to a high compression engine, the head is the same?
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