Engine rebuild input

[socal pat]

Well I am joining Bogie. I just bought a shop hoist and will be pulling my motor soon. Here is your chance to talk me into or out of forged pistons. For sure I'm doing 9:1's with beefier rods. If I can save $500 on OEM pistons it would be nice, but only if I'm not sacrificing too much in strength. I've heard about the cold piston slap, but is there more to be concerned with?

While we're at it do you have any recomendations as to bearings and other hardware? Thanks all, I'll keep you posted on the progress. I miss my SC'd Miata already.....sniff

[Tom @ Fast Forward]

If you are building a race engine, go for it, If you are building a street engine, no way. Although they could go for ages on a track, they drink too much oil on the street. As much as 1 quart per tank of fuel.

[Banshee]

what happened to your engine?

[socal pat]

Don't know yet. The autopsy will be in the next week or two. Things were running smooth and strong until......rat a tat tat.

[Tom @ Fast Forward]

I wonder if it fell into the #4 crank bearing issue? That did have an effect on the 99/00. It was really a thrust bearing issue but people mistakenly called it a bearing issue. You can tell rather easily by measuring the end play of the crank. It sometimes showed up as transmission noise as well.

[socal pat]

Not only are you right about that possibility, but even '99-'00's that were in spec for thrust were (are) known to cause the problem with heavier clutches, which is why Flyin' Miata includes the clutch switch bypass kit with every Happy Meal they sell. I kept meaning to do the clutch-switch bypass and just never got around to it.

[BlownMX5]

When I rebuilt we used JE forged pistons. So far, I haven't experienced the oil consumption Tom mentions. In fact, I've seen no oil use at all between the first few oil changes. The noise is another thing. For the first 20 seconds after startup when it's cold, it sounds like a dang diesel. One thing I think is kind of interesting is that we went with Carrillo stroker rods which are 8mm longer and then had pistons made which are 8mm shorter from wrist pin to piston top. This maintains the 9:1 CR but improves the rod-to-stroke ratio. The cost of custom-made pistons from JE was the same as off-the-shelf ones. The pistons were $575 and the rods were $790. Can I tell the difference? No, but it makes sense to do based on the stock Miata ratio and is backed up by other sources (http://www.e30m3performance.com/tech_articles/engine-tech/rod-ratio/index.htm). Now, mine's a '94 and I don't know if yours is different or not.

Other than that, we used Clevite 77 rod and crank bearings and ARP studs throughout. Also, stainless steel chrome-hardened valves with bronze guides.

[Tom @ Fast Forward]

Maybe JE uses 4032 for the material?

[99mx5]

Sorry to hear that Pat. My original engine was replaced by Mazda under warranty for the thrust bearing issue at 15K miles and two weeks before my warranty expired. I got a brand new long block. My car just hit 40K miles and the engine has 25K miles on it with approximately 6K boosted miles. Keep us posted.

As for pistons, Id just get lower compression factory pistons from a '97.

[socal pat]

Thank you sir. The shortblock I found is simply listed as 94-97 with 9:1 CR. Is there something about that 1 year (97) that sets them apart?

[SOL General]

I was thinking about doing a rebuild on my engine which a '91 before I get the FFS supercharger. Does mazda offer lower compression pistons that what I currently have? My motor is stock now, but I wanted to upgrade some things like maybe the rods? What would be the best way of going along with this? Do rods make a difference? Should I Lighten, knife-edge and balance the crank? Or is that bad news for a stock engine. I want to use it as a street car but I would like the performance and reliability if I were to track use it.

[99mx5]

Thank you sir. The shortblock I found is simply listed as 94-97 with 9:1 CR. Is there something about that 1 year (97) that sets them apart?

My only guess is that its the latest year for the low compression 1.8 engines. I dont know exactly what the differences are in the 94-97 1.8 pistons, maybe a good topic to search about.

[Tom @ Fast Forward]

I think the engines are basically identical. The main difference between the 94-95 and 96-97 is the ECU. I believe 96 is when OBD-II kicked in. IOW, the differences were basically external to the block/head.

[socal pat]

Good, I didn't make a mistake. The shortblock will be here by the end of the week. Now, to decide whether to put these pistons in my block or just re-work the new one. Maybe I'll let my machine shop decide.

[BlownMX5]

Maybe JE uses 4032 for the material?

Dunno. But, when I mentioned that the popular forged piston for a Miata was Wiseco, my engine guy said he called them "Seizeco" :rolleyes:. No offense to anyone running Wisecos.

[Kyp J]

Dunno. But, when I mentioned that the popular forged piston for a Miata was Wiseco, my engine guy said he called them "Seizeco" :rolleyes:. No offense to anyone running Wisecos.

I used Wiseco 9:1 and haven't had any problems or oil consumption but I haven't gotten it extremely hot since then. Hopefully I won't with all the cooling upgrades. I didn't know of any alternative forged pistons and I think my builder looked for some. Maybe it was the rods he looked for as an alternate to whatever FM sells but I didn't go with fancy rods.

[SOL General]

Would the HKS Steel HeadGasket (http://www.2kracing.com/product_info.php/products_id/4315) be able to lower the compression ratio a little bit to squeeze a litte bit more power in there or would it be useless to do that?

[FormerDatsun510Man]

I am also getting my engine rebuilt on my '00. I ended up keeping it real simple. I think the main culprit for my problems was that the CR is too high. So I am bringing it down with 9:1 factory pistons. Other than that it is getting rebuilt stock as I think that is going to end up being the most reliable setup for a street car that is the only transportation for me. I think now that I am running a more efficient setup with good fuel management (PC Pro) the next engine won't experience problems. Especially if I can keep myself from throwing on a 150mm pulley.

I look into forged rods while retaining stock pistons, however when I saw the cost soar with going that route I decided to stay with the KISS technique. Thus my setup is going to end up not going for 300rwhp afterall. Well, at least for this engine. Maybe when I finally get a place and can own two Miatas I can have the luxury to do that. Once I get this engine in I am really curious what even the little 120mm pulley will do. I hope somewhere north of 220rwhp. Then I think the final pulley size I will do is the 130mm. Or is that pulleyboy talking again? :)

Sorry for the thread drift...

Bill

[SOL General]

What advatage would forged rods with stock pistons have over stock/stock? Would it really make that much of a difference?

Would lighten, knife-edge and balance the crank have many advatages for a reliability and longevity or just for power?

Sorry im asking stupid questions, this is just something im not that smart in.

[Tom @ Fast Forward]

SOL,

I think the advantage is that the stock pistons are actually very good for that level of power. However, if something does go wrong (big knock at high RPMs) the forged rods might not bend or break so easily. Bill is doing exactly what I would do, if I built another engine. If I was going for 300WHP (like the delusions of grandeur that I had when I built the last one) I would do the rods and pistons and dedicate it to the track.

[socal pat]

Well guys, just got back from the machine shop and it looks like the following is in my future.

OEM 9:1 pistons (junkyard)
H-beam rods which my builder will supply (~$500)
1mm oversized valves for more flow, less boost ;)
Tom's fuel rail with 280-330 injectors
coolant re-route
I think this should support ~220whp

[Tom @ Fast Forward]

Pat,

Don't go too far over 300cc on the injectors.

[socal pat]

10-4 where did you end up getting your 280's?

[Tom @ Fast Forward]

I got them from my local injector supplier. Neat thing was that they came with the new seals. All three. Saved me some bucks from Mazda.

[Kyp J]

For what it is worth, with stock 2001 injectors, the bigger (whatever brand some people were pushing a year or so ago) fuel pump and a 115mm pulley, I am always a bit rich in some areas of the PC pro.

However, when I had my engine rebuilt, the head guy said he could do some porting for $xxx which seemed like a good idea at the time. I am wondering if somehow it caused reduced flow since I am getting a bit more boost pressure than expected and would explain my richness since the fueling expects more air at that boost than I may be getting. The opposite of Tom's discovery of low boost numbers on certain throttle body adapters. I should have gone with bigger valves instead.

Anyway, what I meant to say is, I would imagine whatever size 2001 stock is (270?) should be plenty. (in my possibly incorrect opinion)

[Tom @ Fast Forward]

Almost sounds like the 'ported' inlet on the MP62. Those worked so well people lost over 10WHP. ;) Boost and flow both went down.