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2000 head on 2500 engine


rogerreed

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hi all, i have built a 2500 engine up from various bits. the head that came on this engine was bad so i put a head on which had 218225 stamped on it, from research i have found this head is eithier for a mk2 2000 or a mk2 2500pi. it has never ran right and misses on top end. are these heads compatible with a 2500 carbed engine? thanks marty

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Sure it's fine for that engine, as long as you are quite, quite happy it's for a 2500.
If it is for a 2000 then be happy with a compression ratio of at least 12:1.

A 2500 displaces 416mls per cylinder, while a 2000 does 333mls.    Without modification to a 2000 head that I would consider impossible, the larger stroke of the 2500 will be compressed into the smaller combustion chamber of the 2000, raising the CR to a level that will cause pre-ignition and destroy plugs, so misfire - no surprise!   Unless DJB can swear on a stack of manuals that yours IS a 2500 head then I would take it off and measure the combustion chambers.  A 2000 head will have a combustion chamber volume of 35-40mls (it may have been modified).  A 2.5 head will be 45-50mls.

You might be able to tell by measuring the height of the cylinder head.  The 2.5 will be taller.  But this a a parameter I never use, so I can't tell you what to look for.

What was wrong with the original head?  It's almost impossible for wear to make one irretrievable by new valve guides, new valve seats or a light skim of the face, though they can be ruined by over skimming or other 'modification' work.

John

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Sure it's fine for that engine, as long as you are quite, quite happy it's for a 2500.
If it is for a 2000 then be happy with a compression ratio of at least 12:1.

A 2500 displaces 416mls per cylinder, while a 2000 does 333mls.    Without modification to a 2000 head that I would consider impossible, the larger stroke of the 2500 will be compressed into the smaller combustion chamber of the 2000, raising the CR to a level that will cause pre-ignition and destroy plugs, so misfire - no surprise!   Unless DJB can swear on a stack of manuals that yours IS a 2500 head then I would take it off and measure the combustion chambers.  A 2000 head will have a combustion chamber volume of 35-40mls (it may have been modified).  A 2.5 head will be 45-50mls.

You might be able to tell by measuring the height of the cylinder head.  The 2.5 will be taller.  But this a a parameter I never use, so I can't tell you what to look for.

What was wrong with the original head?  It's almost impossible for wear to make one irretrievable by new valve guides, new valve seats or a light skim of the face, though they can be ruined by over skimming or other 'modification' work.

John

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yes quite sure the block is a 2500s. it has mm stamped on it. the head that came off had a couple of burnt valves. i had this other head which has bigger valves and is in really good condition, it also had double springs on the valves so i decided to use that instead. thanks for your help really appreciate it.

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A 218225 head was used on 2000's with dome pistons and 2500 engines . The early 2000 head is 3.300" in height and IS definitely not suitable . All 2000 dome piston and 2.5 engines used a 3.400" head ... The only exception is the 219016 head which was used on late TC&S engines with HS6 carbs . This was 3.475" .
The early 2000 Mk2 head up to ME 50000 engine no was part no 517528 ( Don't quote me on that one !)

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218225 is a Mk2 PI head (3.4" thick) and should be fine on any 2.5.

517528 is originally Mk2 Vitesse/GT6 and early Mk2 2000 (3.3" thick) - so intended for 2L engines with flat-top pistons.  Running one on a 2L engine with domed pistons is going to give a very high CR with probable pinking at low/mid rpm and full-blown detonation at higher rpm/throttle.  I don't know what the CC of the dome is but as the flat-top 2L engines have 9.5;1 CR as standard you are going to be running a fair bit more than 10:1 I think.

Nick

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Nick_Jones wrote:
218225 is a Mk2 PI head (3.4" thick) and should be fine on any 2.5.

517528 is originally Mk2 Vitesse/GT6 and early Mk2 2000 (3.3" thick) - so intended for 2L engines with flat-top pistons.  Running one on a 2L engine with domed pistons is going to give a very high CR with probable pinking at low/mid rpm and full-blown detonation at higher rpm/throttle.  I don't know what the CC of the dome is but as the flat-top 2L engines have 9.5;1 CR as standard you are going to be running a fair bit more than 10:1 I think.

Nick


Probably why I have to run so much advance on the ignition to get it running anywhere near right at the top end and why I have had to disconnect the vacuum advance to lessen the pinking at the lower end of the rev range. My car was an ex race car so might point as to why it runs so much compression. I will have to pull the motor apart to check on any other mods that have been made to it i.e. cam
The sooner I get my microsquirt running the ignition side of things the better.

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