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Thread: Built Head + Metric Mechanic Rally Cams + M52?

  1. #1
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    Built Head + Metric Mechanic Rally Cams + M52?

    Hey all-

    Bit of an odd thread here. So, I have been working on a 24v E30 swap that has, naturally, spiraled out of control. I am looking to finish things up without continuing to go overboard financially, which brings me to this thread.

    I have an iron M52b28 for the swap. Originally, I was going to drop in a 3L M54 rotating assembly, but talked with a few folks who said it wasn't worth it, so I sold it off. Then I was going to open the bore and drop in an S52 rotating assembly, but it was a lot of work and didn't end up going that route.

    So now I just have this M52b28 bottom end, but I have an awesome top end, and want to know if anyone has experience with running a great flowing top end on an M52.

    I have:

    -a ported/polished S52 head with 1mm oversized intake and exhaust valves + dual springs
    -Metric Mechanic Rally Cams
    -OBD1 Intake Manifold
    -Long Tubes
    -Underdrive pulleys
    -24# injectors

    The top end made 276whp (dynojet, uncorrected) on a 3L S50 build from the previous owner (with different headers and 3.5" MAF).

    So my question then is, should I run this combo? I imagine I'm going to lose a ton of low end, but since the head flows really well it "may" still work out okay. I have experience in mismatched combos in the past and am trying to get a gauge from someone who has done something similar before I assemble it all.

    Mainly just looking for thoughts on this from those who have ran bigger cams on an M52, what kind of power they made, etc.

    The simple answer is: "Just get an S52 bottom end man". My response to that is: I've been looking for ages and can't find any shortblocks for sale, and don't want buy a longblock and strip it all down + be left with even more parts to worry about selling.

    Thanks gents.

  2. #2
    Join Date
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    Built Head + Metric Mechanic Rally Cams + M52?

    The E30 is a lighter car than an E36.
    I think you will be fine, but the power as you have indicated will all be in the upper RPM range, even with a 3.2L bottom end. I would keep the revs limited to 6800 unless you do some additional freshening of the bottom end.
    Mated with a 6-speed gearbox, this car will be a hoot to drive.
    Call Metric Mechanic and get their take on your setup if you are really concerned.


    Sent from my iPhone using Tapatalk

  3. #3
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    I would run the head on an M52 if I could not spend the money on an S52 bottom end. But I hate leaving power on the table, so I would try to find an S52. People buy the cams for $300 all day and a good head is worth a couple of hundred so you may be able to recover some of the longblock money if you cannot find a shortblock. If this is too much trouble for you, then you know what your option is. I also like the added torque of the greater displacement and think it would help offset the tradeoff from the wilder cams and headwork.

  4. #4
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    shortblock? longblock? can somebody please explain this to me?

  5. #5
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    Quote Originally Posted by samy01 View Post
    shortblock? longblock? can somebody please explain this to me?
    A short block is just the block, crankshaft, pistons, rods and bearings (may or may not inclue oil pump and pan), a long block is the short block and the head(s) but not the accessories (alternator, ac compressor, manifolds, etc).
    A better description may be a story block and a tall block, but the convention is short vs long.

  6. #6
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    Quote Originally Posted by AWDBOB View Post
    Hey all-

    Bit of an odd thread here. So, I have been working on a 24v E30 swap that has, naturally, spiraled out of control. I am looking to finish things up without continuing to go overboard financially, which brings me to this thread.

    I have an iron M52b28 for the swap. Originally, I was going to drop in a 3L M54 rotating assembly, but talked with a few folks who said it wasn't worth it, so I sold it off. Then I was going to open the bore and drop in an S52 rotating assembly, but it was a lot of work and didn't end up going that route.

    So now I just have this M52b28 bottom end, but I have an awesome top end, and want to know if anyone has experience with running a great flowing top end on an M52.

    I have:

    -a ported/polished S52 head with 1mm oversized intake and exhaust valves + dual springs
    -Metric Mechanic Rally Cams
    -OBD1 Intake Manifold
    -Long Tubes
    -Underdrive pulleys
    -24# injectors

    The top end made 276whp (dynojet, uncorrected) on a 3L S50 build from the previous owner (with different headers and 3.5" MAF).

    So my question then is, should I run this combo? I imagine I'm going to lose a ton of low end, but since the head flows really well it "may" still work out okay. I have experience in mismatched combos in the past and am trying to get a gauge from someone who has done something similar before I assemble it all.

    Mainly just looking for thoughts on this from those who have ran bigger cams on an M52, what kind of power they made, etc.

    The simple answer is: "Just get an S52 bottom end man". My response to that is: I've been looking for ages and can't find any shortblocks for sale, and don't want buy a longblock and strip it all down + be left with even more parts to worry about selling.

    Thanks gents.
    I don't have any useful info for you but I would love to see a pic or two of your ported head. I've heard there isn't a whole lot of room for improvement but can understand the value if the valves have been oversized. Thanks.

  7. #7
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    You can actually do a lot to these heads but it’s not cheap. I have a CNC ported head with +1mm valves. There are various levels of porting, from just smoothing and cutting down guide tube extensions to significant reshaping. To do bigger valves right you have to unshroud them or you won’t get much benefit. For flow numbers look at Post #17 in the link below — unfortunately pictures are gone.

    https://www.bimmerforums.com/forum/s...5#post27846415

    This is a CES head, but VAC, Metric Mechanic and others do similar work. To get the most out of the head, you need bigger and better valves, better valve springs, more aggressive cams, etc. You might end up spending $5k total. I have the CES head with mild Schrick cams on a turbocharged built S52 block.

    Definitely not the cheapest power you can buy. Maybe do an S54 swap instead and get a younger and better motor.

  8. #8
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    Quote Originally Posted by pbonsalb View Post
    I would run the head on an M52 if I could not spend the money on an S52 bottom end. But I hate leaving power on the table, so I would try to find an S52. People buy the cams for $300 all day and a good head is worth a couple of hundred so you may be able to recover some of the longblock money if you cannot find a shortblock. If this is too much trouble for you, then you know what your option is. I also like the added torque of the greater displacement and think it would help offset the tradeoff from the wilder cams and headwork.
    I am in the same line of thought. My budget doesn't currently allow for an S52, but I am going to try my hardest to make it happen. However, the consensus seem to be that it will be fine on the M52 if that's what it has to be. I've seen a few M52s w/S52 cams and bolt ons make 225whp. Makes me curious to see what this setup will make.

    Quote Originally Posted by gdavid View Post
    I don't have any useful info for you but I would love to see a pic or two of your ported head. I've heard there isn't a whole lot of room for improvement but can understand the value if the valves have been oversized. Thanks.
    Quote Originally Posted by pbonsalb View Post
    You can actually do a lot to these heads but it’s not cheap. I have a CNC ported head with +1mm valves. There are various levels of porting, from just smoothing and cutting down guide tube extensions to significant reshaping. To do bigger valves right you have to unshroud them or you won’t get much benefit. For flow numbers look at Post #17 in the link below — unfortunately pictures are gone.

    https://www.bimmerforums.com/forum/s...5#post27846415

    This is a CES head, but VAC, Metric Mechanic and others do similar work. To get the most out of the head, you need bigger and better valves, better valve springs, more aggressive cams, etc. You might end up spending $5k total. I have the CES head with mild Schrick cams on a turbocharged built S52 block.

    Definitely not the cheapest power you can buy. Maybe do an S54 swap instead and get a younger and better motor.
    It's normally big bucks to have it done right. I happened to fall into this cylinder head from a great forum member (paging Jacques). Hopefully it works well- I think it will because it made great power on his car.

    After the holidays I'll get some pictures up.
    Last edited by AWDBOB; 12-19-2017 at 10:56 PM.

  9. #9
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    If I had to guess, the M52 with the worked head and cams might end up 15% behind an S52 with it, which is about the same as the displacement difference and about the same as the difference between an M52 with S52 cams and an S52. For about $1000 and some work DIYing the install and selling off parts, you could get an S52 shortblock and capture the other 15% potential gain.

  10. #10
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    Bobbie,

    You should use a thin Cometic headgasket to bump the compression up, but beware the oversize valves and the OEM pistons. There might not be room for the reduced piston to valve clearance with the increased lift of the cams and reduced combustion chamber volume from thinner headgasket. In fact now that I think about it, you should put some time into checking clearance no matter what you do with the block/headgasket/head. Those cams and the bigger valves could cause issues.
    Last edited by jakermac; 12-22-2017 at 08:15 AM.

  11. #11
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    A vanos limiter might help. I probably would not run a thinner gasket for this reason. Do you know the cam specs so you can research what others have done? For the larger valves has anyone dremeled the stock reliefs as a cheap fix/insurance? I read of one person a while ago nicking valves with a fresh big valve head on a stock block but forget the details — think it was an S52. I have JE pistons that have bigger reliefs and have the mild Schrick cams do I do not even limit vanos.

  12. #12
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    Quote Originally Posted by jakermac View Post
    Bobbie,

    You should use a thin Cometic headgasket to bump the compression up, but beware the oversize valves and the OEM pistons. There might not be room for the reduced piston to valve clearance with the increased lift of the cams and reduced combustion chamber volume from thinner headgasket. In fact now that I think about it, you should put some time into checking clearance no matter what you do with the block/headgasket/head. Those cams and the bigger valves could cause issues.

    Quote Originally Posted by pbonsalb View Post
    A vanos limiter might help. I probably would not run a thinner gasket for this reason. Do you know the cam specs so you can research what others have done? For the larger valves has anyone dremeled the stock reliefs as a cheap fix/insurance? I read of one person a while ago nicking valves with a fresh big valve head on a stock block but forget the details — think it was an S52. I have JE pistons that have bigger reliefs and have the mild Schrick cams do I do not even limit vanos.
    I probably won't run a thinner HG, but I will certainly be claying this setup. There is [supposedly] plenty of meat up top on M/S52 pistons to take some room out as far as I have been told (no first hand experience). In the past I have just taken a spare valve, attach some sandpaper, and attach to a drill. Seems primitive, but it has always worked pretty well. Clay again afterwords and you're good to go!

    However, this is all my first go around with a 24v BMW motor, so I'm not sure what ideal distance would be between P/V (0.12"?), and I am also, not sure how vanos works as far as how much more space I need to account for. Assuming I'll have to activate it when I clay the motor via air+12v?

    If it all works out, I've scored a 70k S52 bottom end finally. Not sure if the reliefs are different on S52 vs M52 pistons. Perhaps I'll wait awhile to save up and just put some pistons in the S52 (if I get it).

    Thanks again gents. I just got a full running M20 to put in the car so I can take the slow road on the 24v stuff and do it right.

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