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Old 12-05-2015, 06:41 PM   #1
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Default Head gasket layers question

I picked up a Felpro 9717 PT MLS head gasket for 94-00 Miatas to use on my VVT engine with coolant reroute at rockauto for $22. The box says Made in Japan and "replaces BP05-10-271, what is this? It seems thick, my caliper broke so I cant measure it. Do the stock oem gaskets have 3 layers or 4?
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Old 12-05-2015, 07:02 PM   #2
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I think that VVT engine do not need coolant reroute.
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Old 12-06-2015, 01:03 AM   #3
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The last two Mazda gaskets I bought were 3 layers.
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Old 12-06-2015, 04:54 PM   #4
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Originally Posted by elektron View Post
I think that VVT engine do not need coolant reroute.
You're wrong.
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Old 12-06-2015, 05:26 PM   #5
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A few basic truths:

The head gasket in the '90-'00 engines was of a very ordinary design.

The cooling system design in those engines, however, was pretty awful. The thermostat being located at the front of the head meant that the back of the engine didn't get much cooling when it was open.

In '01, coincident with the switch to VVT, Mazda changed the design of the head gasket. The blocked off most of the cooling ports around the #1 cylinder, and around the forward half of #2.



This improved the coolant flow through the engine somewhat, but it still wasn't as good as the original (FWD) design, which is what a rear-thermostat reroute restores. Worse, doing a reroute on an engine with the '01-'05 style head gasket will cause more harm than good, by completely stagnating the coolant around #1.


That said, btabor is on target wanting to install a '94-'00 gasket on his VVT engine and do a reroute. This is the best solution.



To directly answer the original question, I have no idea WTF BP05-10-271 is. Rosenthal doesn't recognize it, and I can't find it in any of the catalogs. The p/n for the '94-'00 HG is BP26-10-271, and the stock '01+ gasket is BP6D-10-217. It's possible that BP05-10-271 might have been used in the MSM engine, but that's only a wild guess.

Visually compare your gasket to the picture I posted above.
Attached Thumbnails
Head gasket layers question-80-undefined_c1e1809feaba60b2f2f71b65340bcb86b467f8f1.png  

Last edited by Joe Perez; 12-06-2015 at 07:15 PM.
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Old 12-06-2015, 05:37 PM   #6
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Originally Posted by Joe Perez View Post
A few basic truths:

The head gasket in the '90-'00 engines was of a very ordinary design.

The cooling system design in those engines, however, was pretty awful. The thermostat being located at the front of the head meant that the back of the engine didn't get much cooling when it was open.

In '01, coincident with the switch to VVT, Mazda changed the design of the head gasket. The blocked off most of the cooling ports around the #1 cylinder, and around the forward half of #2.



This improved the coolant flow through the engine somewhat, but it still wasn't as good as the original (FWD) design, which is what a rear-thermostat reroute restores. Worse, doing a reroute on an engine with the '01-'05 style head gasket will cause more harm than good, by completely stagnating the coolant around #1.


That said, btabor is on target wanting to install a '94-'00 gasket on his VVT engine and do a reroute. This is the best solution.



To directly answer the original question, I have no idea WTF BP05-10-271 is. Rosenthal doesn't recognize it, and I can't find it in any of the catalogs. The p/n for the '94-'00 HG is BP26-10-271, and the stock '01+ gasket is BP6D-10-217. It's possible that BP05-10-271 might have been used in the MSM engine, but that's only a wild guess.

Visually compare your gasket to the picture I posted above.
Fixed.

That's what I meant in my other post
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Old 12-06-2015, 06:35 PM   #7
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Thanks for all the info. I plugged that part number on the mazda competititon website and it came up with a gasket that is $48. The 99 head gasket is $49 or so. The felpro one looks exactly like the 99 oem gasket. I measured the felpro and even though it has 4 layers instead of the oem 3 layers it measures 0.032". I belive the oem is 0.040". I also shaved my head 0.030" so I think I will achieve a cr of around 10.8:1 which is exactly what I wanted since I will run 93 octane and tune with my MS3.
I'm hoping I'll make around 150whp with that compression, flat top and racing beat header.
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Old 12-06-2015, 07:15 PM   #8
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Fixed.
Yes, typoe. Thanks.
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Old 12-06-2015, 08:53 PM   #9
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Joe Perez. I have been researching how many degrees of timing a 0.030" head shave will cause. I have read anything from 0.5 to 2 degrees. I'm thinking on getting an adjustable cam gear and set it at 1.5 degrees advances on the exhaust side and start dyno tuning from there. Does that sound like a decent plan?
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Old 12-07-2015, 12:59 PM   #10
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Quote:
Originally Posted by btabor View Post
Joe Perez. I have been researching how many degrees of timing a 0.030" head shave will cause. I have read anything from 0.5 to 2 degrees. I'm thinking on getting an adjustable cam gear and set it at 1.5 degrees advances on the exhaust side and start dyno tuning from there. Does that sound like a decent plan?
Had to think about this one for a bit....

I believe what you are asking is whether shaving the head by 0.030" will cause the camshaft timing to become retarded, and thus, require compensation by the use of adjustable cam gears. Correct?

The answer is no.


Well, in theory, decreasing the distance between the camshafts and the crankshaft will alter the valve timing. But compare the change being made (three one-hundredths of an inch) to the nominal distance between the crankshaft and the camshafts (a foot and a half, maybe?) and then try to get a sense of proportion as to the magnitude of the change here. I'm going to do the math, but we're talking about a change on the order of maybe a few tenths of a degree, if not a few hundredths? Whatever it is, it's going to be so small that you'll never be able to measure it, as the slop inherent in the cam belt will outweigh it by several orders of magnitude.

Trying to correct for such a minute change is like trying to improve the fuel economy of the vehicle by removing that one dead mosquito that's stuck to the front bumper. Theoretically plausible, but utterly impractical in the real world.
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Old 12-07-2015, 01:45 PM   #11
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Quote:
Originally Posted by Joe Perez View Post
Well, in theory, decreasing the distance between the camshafts and the crankshaft will alter the valve timing. But compare the change being made (three one-hundredths of an inch) to the nominal distance between the crankshaft and the camshafts (a foot and a half, maybe?) and then try to get a sense of proportion as to the magnitude of the change here. I'm going to do the math, but we're talking about a change on the order of maybe a few tenths of a degree, if not a few hundredths?
It's quite a bit more than a few tenths of a degree, and it has nothing to do with the distance between the crank and the cams. It's a function of the angle of the timing belt as it runs between the idler pulley and the exhaust cam pulley, and the diameter of the exhaust cam pulley. I'll measure that angle next time I have an engine timed and on the stand.
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Old 12-07-2015, 01:57 PM   #12
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It's quite a bit more than a few tenths of a degree, and it has nothing to do with the distance between the crank and the cams.
(...)
I'll measure that angle next time I have an engine timed and on the stand.
In for the results- very curious.


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It's a function of the angle of the timing belt as it runs between the idler pulley and the exhaust cam pulley, and the diameter of the exhaust cam pulley.
Which, all else being equal, is dictated by the linear distance between the centerlines of the crankshaft and the camshafts. The only way you can change that angle is to remove or add material at the interface between the block and the head.

Unless you happen to have a variable-diameter exhaust cam pulley.
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Old 12-07-2015, 02:04 PM   #13
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I tried to calculate the logic, but my head started to hurt.

My 0.8mm deck+skim resulted in 13 degrees (almost one tooth) retard, but I have not been able to figure out the math (which bugs me).
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Old 12-07-2015, 02:15 PM   #14
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I honestly think 13 degrees is not true. I calculated it on my Honda Crx when I was in high school, back in the days and it came up to 3 degrees with a 0.040" shave.
It would be nice to get results from someone who actually measured with a timing wheel.
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Old 12-07-2015, 02:17 PM   #15
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Another thing, most people in this forum states the oem gasket is 0.040", I read from Quinn at clubroadster.net that it is 0.020" and then read from Emilio that it is 0.031" (which is the same as my felpro).
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Old 12-07-2015, 02:38 PM   #16
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I might try to measure the thickness of the VVT head gasket I just removed and compare it to the eBay MLS 94-00 head gaskets I have on hand.
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Old 12-07-2015, 02:39 PM   #17
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Quote:
Originally Posted by btabor View Post
I honestly think 13 degrees is not true. I calculated it on my Honda Crx when I was in high school, back in the days and it came up to 3 degrees with a 0.040" shave.
It would be nice to get results from someone who actually measured with a timing wheel.
My VVT is measuring the angle continuously.
And my builder set the exhaust cam one tooth -2.5 degrees advanced to get to zero.

But the blue gates belt can be skewed of course, with half a tooth extra
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Old 12-07-2015, 02:44 PM   #18
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My VVT is measuring the angle continuously.
And my builder set the exhaust cam one tooth -2.5 degrees advanced to get to zero.

But the blue gates belt can be skewed of course, with half a tooth extra
I'm pretty sure each tooth is 12 degrees not 2.5. So much misleading information, one person says one thing the next one says something completely different
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Old 12-07-2015, 02:48 PM   #19
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Each tooth is 7.826 degrees.

46 teeth.

360 degrees.

360/46=7.826086956521739
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Old 12-07-2015, 02:52 PM   #20
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Quote:
Originally Posted by btabor View Post
I'm pretty sure each tooth is 12 degrees not 2.5. So much misleading information, one person says one thing the next one says something completely different
Sigh,

one tooth is 15.65 degrees (720 degrees and 46 teeth)
15.65-2.5 = ?

or have you ordered the "JDM 60-teeth wheels"?

Counting to 46 is not that hard, is it?
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