Power difference between 1.6 5sp and auto

I've heard there is a difference in power output in the NA 1.6 5speed motors and the motors that came with automatic transmissions.
That is, apart from a difference in transmission alone.

I found one webpage that indicated that the cam spec on the automatics had less duration and lift on one of the cams.

Anyone have power numbers from dynos of cars with similar build, between the manual and automatic transmission ?
Wonding how much horse power difference the I might expect if I swap the cam from a manual motor into the automatic motor.

Jay Johnson

You would not want to do that.

Yes, but I will be right at that point when I replace the timing belt. This automatic motor has unknown service history and the dash is clocking 201k miles, but I know that it runs and has decent compression at 190-180-180-190 .
So, shortly after swap I this motor into my daily driver, I'll take a free weekend and do a pre-emptive timing belt replacement.

A little more background info:
I've found a crack in my cylinder head onmy 1.6 5speed, and I have a spare motor from a 1.6 automatic that I can swap in.
I have the 5speed cams out from removing the cracked cylinder head.

So, if the cam swap from manual to auto was known to be worth 10rwhp, I'll definitely do it.

I suppose that I'm just spoiled from my days with LS1 V8 performance, where every configuration and every mod has dyno's and E.T.'s showing the performance. This kind of data/info might not exist for NA Miata's.

Jay Johnson

Jay,

I'm glad the compression came out good. The engine ran good for me but that transmission was pathetic.

I would swap the cams. Why? I would swap the valve stem seals, since its burning a bit of oil. The rings are probably not the suspect since the compression checks.

The power difference is like 116 to 105 hp from what I've read. The cams are different and the C.R. is lower. It's not a lot but in a light car, a little power makes a lot of difference.

The pointy Miata board usually has good info, but it's really pointy..... http://forum.miata.net/vb/showthread.php?t=55570

On a side note, I'm looking at a different Miata this weekend. If all goes well, I'm buying it and driving it home Saturday.

So far, I've determined that the engine is not consuming the majority of the oil. There's oil leaking from somewhere and dropping to the ground.

I'll get a better look when I pull the motor out of the chassis. Initial guess is rear main seal, and valve cover gasket.

I hope to make some progress this weekend with decent temps Saturday.

The new stem seals and 5speed cams will be going into the motor when I get timing belt replaced on a future weekend.

Jay Johnson

Oil control rings are not responsible for compression, so you can have good compression and still have lots of oil consumption if the oil rings are bad/stuck.

Quote:

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Originally Posted by JayJohnson600

I've found a crack in my cylinder head

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Oooh, that sucks. Is that the first you saw of it?

I've got a couple of threads going in Tech and chat, etc.

http://imageshack.com/a/img703/7365/hnez.jpg

Jay Johnsonm

Quote:

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Originally Posted by OZMDD

Oil control rings are not responsible for compression, so you can have good compression and still have lots of oil consumption if the oil rings are bad/stuck.

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I'm sure this could happen, but the odds on it are pretty low in my experience. In my experience cylinders and rings tend to fail as an entire unit. I've never seen a one ring failure, although I'm sure it can happen, it would be rare. I have seen entire connecting rods hanging out the side of a block engine still running, and I've seen valves stuck in pistons with engines still running, but I've never seen one ring go bad in a cylinder and the others be okay.

If this is something the Miata engine is known for (failed oil control rings) and good compression, I'd love to see some examples, and then I'd like to know the design flaw that causes it.

Well, I don't keep a supply of motors with unusual failure characteristics on hand, but its a pretty well documented miata issue to have STUCK oil control rings. Some speculate that the coolant routing leads to some cylinders getting more carbon buildup than others, but if you search "2twisty flush" on m.net, you'll find plenty about varnish buildup and oil rings.

Okay looked up the 2 twisty flush. It seems to be mostly related to HLA noise on startup, which shouldn't have much to do with the pistol oil control rings. The diagram here shows they are on different oil loops:

http://mymiata.paladinmicro.com/MiataOFilters.htm

Honestly this sounds more like a sludge / maintenance related issue and not a ring issue at all. I still say if compression is good, the oil rings should be good too. If the oil ring fails, the metal to metal of the compression rings will have them fail shortly thereafter, and you will lose the entire cylinder.

For desludging and decarbonizing an engine, I've used seafoam before even on my old '92 Miata. I may use it on my new to me '91 again soon. Sludge buildup is evil, there is no doubt about that.