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121 head and dual carbs

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Hi there!

My 2002 has the 121 head and I would like to know if I can just get the intakes and Weber carbs and install them or if I should find another cylinder head. I mean, does it physically fit? Do I really need bigger valves and more compression, either with a smaller chamber or different pistons? Cam recommendation?


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Guest Anonymous

New to head tech, I have the 121 head on my 76, what is the difference between it and the 12 head? Size of valvles? Overlap, clearance problems with piano tops? Need to have my head reworked and wonder if starting with wrong head? Dave

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Valve sizing is the same on both.

Re: Valves - didn't E12 come with 1mm larger intake valve? 47 vs 46 mm? While both had same 38mm exhaust. (You can easily fit the larger valve into 121 heads...)

The valve sizes won't matter re: simply fitting DCOES.

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The 121, E12 and E21 heads are all the same intake and exhaust shape.

The early 121 heads MAY have smaller (2mm smaller) intakes, or they

may not.

At any rate, that doesn't matter for the intake and exhaust.

The difference is in the combustion chamber- you have to use 121

pistons with 121 heads, E12 pistons with E12 heads, and E21 pistons

with E21 heads.

Yes, you could grind clearance into the head or the piston,

but at that point you'd know enough about this whole thing to not be

asking us about it. Not being rude, just saying that it's not a good idea

to do it unless you know what you're doing, and how to cc a head and

a piston crown.

The exception, of course, are the flat- topped pistons. They're universal, but also give you a universally low compression ratio.

as to what cam to use, you'd need to tell us what you want the car to do.

Anything from stock to 316 will WORK, they'll just behave differently.



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Ok, my 02 has 121 head and flat pistons and what I`m looking for is a not-so-radical street fighter so I will find out the compression ratio achieved with e-12 or e-21 head/pistons (maybe some one can answer that here?) and then start thinking about cam. Is that better?

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Guest Anonymous

"The 2002 engine was offered with four different cylinder heads during its 8 year production life. When building a high performance 2002, there are certain heads that may lend themselves to higher horsepower applications. Choosing among the various available options is dictated primarily by the intended application. All 2002 cylinder heads are designated by a number (either 121, 121TI, E12, or E21 2.0) which is cast into the head. The location of this number is on the intake side of the cylinder head, above the number four intake port. It is easily visible upon opening the hood.

Beginning in 1968, 2002's came with either the 121 or 121TI head. There is no real difference between these two types. They were referred to by BMW as having a "double-hemispherical combustion chamber." The valve diameters are 44mm intake, and 38mm exhaust. These heads were the standard heads on all 2-liter cars until mid 1972. Most 1972 2002tii's also used the 121/121TI head, but with larger, 46mm diameter intake valves. All else stayed the same. In mid 1972, ALL 2002's (tii's included) received a new head designated the E12. This is the so-called "smog" head. It featured a combustion chamber design taken from the big-six motors introduced 3 years earlier. It has 46mm intake, and 38mm exhaust valves. The major difference is in the combustion chamber shape. It features a "Tri-hemispherical" design, which attempts to provide a more complete burn of the air/fuel mixture. 1976 49-state 2002's came with a further revised E21 2.0 head, which also carried over to the 2-liter 320i's. It is basically an open-chamber modification of the old 121/121TI head, but with 46mm intake valves.

Over the years, the 121/121TI (early 2002 heads) have been the most popular with the performance and racer crowd, because of its smaller combustion chamber volume. Consequently, higher compression ratios are possible with this head, because of the availability of pistons. The E12 head also seems to work very well with few modifications. Since it already has the 46mm valves, it seems to flow well, and the revised combustion chambers seem to reduce detonation. As of date, there is little hard data regarding this subject. If you have a 121 or 121TI non-tii head, you probably still have the smaller intake valves. Luckily, it is not too hard to install larger ones (The larger valves can use the existing seats as long as they are enlarged.) Any competent automotive machine shop can perform this service.

The following piston options are available for the various 2002 cylinder heads:

121 Cylinder head:

8.5:1 CR U.S. "Spec" piston on 1968-1972 2002's

42.3 mm pin-to-deck, flat top

9.0:1 CR U.S. "Spec" piston used on '72 US-model 2002tii's

9.3:1 CR European 2002TI (twin-carb model)

42.1 pin-to-deck, 5.2mm dome

10:1 CR Early euro-spec 2002tii

42.5 mm pin-to-deck, 4.4 mm dome

E12 Head:

6.9:1 CR Factory "Turbo" pistons (used on 1974 2002 Turbo)

42.0 mm pin-to-deck, 3.7mm dish

8.1:1 CR flat-topped piston (much like the 8.5:1 CR used on the

121 heads) used on '75 US-model 2002's, also on most

US-model 3-liter cars of the era. (keep in mind that

the 2-liter 4-cylinder with the E12 head and 3-liter

6-cylinder cars can interchange pistons)

8.3:1 CR U.S. "Spec" piston on mid 1972-1974 cars

9.0:1 CR U.S. tii pistons

9.5:1 CR European tii pistons

E21 2.0 Head:

8.3:1 CR flat-topped pistons (used on 49-state '76 2002's,

US 2-liter 320i's)

9.3:1 CR domed pistons (used on european 4-cylinder 320i's)

Note: compression ratios given are with a stock head, and zero deck height.

Please note that Mahle is not the only OE piston manufacturer, Kolbenschmidt and Nural also supplied BMW with pistons. However, the majority of U.S. parts distributors usually supply Mahle products.

The pistons here are all high-silicon cast units. Mahle (one of the OE piston manufacturers for BMW) also offers a forged round top aluminum racing piston that yields a 12.5:1 compression ratio. These pistons, however, require clearance machining off ALL combustion chamber configurations to work. It should also be mentioned that along with these pistons available from Mahle, many American piston manufactures will make custom forged aluminum racing pistons for the 2002 with any compression ratio. Vendors such as Venolia, Arias, Ross and Wieseco have all produced excellent quality units at surprisingly reasonable cost. In addition, Cosworth also makes some excellent (though expensive) pistons for four cylinder BMW's."

From Filippo Morelli at Bimmers.com

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