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Guest Anonymous

How much material to take of a 121 head for 9.2:1 compressio

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Guest Anonymous

Hey guys, I just got a 2002 with a blown headgasket off a friend for $1400. I love this car! I just got the cylinder head off and need to get it checked and machined, it's a 121 head, how much do I need to deck it to bump the compression up to 9.1-9.5:1 or so??

Also the M20 head has larger intake valves right? What does it take to fit the larger valves to the smaller 121 head? thanks!!

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Guest Anonymous

I just did that a week ago. I found a good e12 head and swapped the 121. It has bigger combustion area than the 121.

good luck..

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Guest Anonymous

is intending to do from his message.

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Guest Anonymous

decrease the compression ratio?

For about every .5 mm you take off the cylinder head you increase the compression ratio by about .5. This is according to the Restoration Guide by McCartney. He suggests that you don't want to take off more than 1.5mm.

-Jaycen

72 tundra tii

72 agave 2002

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Guest Anonymous

If they're bathtub- topped, you're there already.

If not, then check the bores- if they're not perfect, it might be time to think about new (custom) pistons. A set of stock slugs is over $400, adn Ireland and others will sell you customs for $600 or less.

Cutting that 121 head is not such a good idea- there are just too few of 'em left, and then your cam timing is off, your water jackets are getting thin, and your car karma just goes to hell in a handbasket.

As to the valves, measure 'em first, as the 121 came with both the small and large valves. The large valves can be fitted- the land is just bored out to match, as the seat has enough meat to take it.

But then, you're going to DCOE's, right? Or maybe a 40/40? And a 292 cam (or better?) 'Cause otherwise, you really won't get all the benefits that this work is capable of giving... and you're into the car another 3k for starters.

IMHO, of course...

t

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Guest Anonymous

...and don't forget other things that make a nice M10, like balancing.

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Guest Anonymous

I'm not sure what you mean by bathtub topped pistons, but the pistons I have in there are have a raised portion in the middle. So did someone put some high compression pistons in here already for me?

The pistons and bores look good to me, there is stil crosshatching on the walls and no play with the pistons to wall.

If I was to swap a better head in it, what is better than a 121 with large valves? I haven't seen ANY 2002's in the junkyards around here so I really don't know where I'd get a different cylinder head.

Besides I already to the head to the machine shoop for cleaning and pressure testing so if it checks out I'm going to use it.

So which pistons do I have and what compression ratio? :) thanks guys

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Guest Anonymous

Flat top pistons got you 8.3:1 c/r

Low Bathtub/popup was USA Tii=9.0:1 c/r

Medium popup was Euro Ti=9.3:1 c/r

High popup was Early Euro Tii=10:1 c/r.

.

.

Mac.

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Guest Anonymous

Wow thanks a lot :)

I'm not sure if I have low, medium or high popup pistons, I will measure the height of the popup, what are the height values for the 3 types of pistons?

I assume the Euro pistons are pretty rare here in the US, can I safely assume I have 9.0:1 tii pistons? I will measure them tonight when I get home though :)

Does anyone know the combustion chamber volume of the 121 head so I can calculate it myself?

Also I'd like to see if my head has been decked before, do you know the deck height of a stock 121 head?

Thanks for all the help guys

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