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RotorNutFD3S 02-27-2008 08:39 PM

Build questions
 
I'm working on acquiring all the parts I'll need to get my forged build going in the right direction, but I need some help with suggestions as far as some parts go. Also, I'm not trying to build something insane here, just a strong bottom end for now.
Answers I have will be in red.

I have the ETD H-beam rods, what bearings should I get? Are OEM good enough? Forking out for OEM. Check.

I'm looking to get 9.0:1 forged pistons, what head gasket would be recommended? OEM again. Check.
Also, I'm keeping the stock bore, what kind of work should be done to prep the block since there will be no overbore?
And are there any pistons out there that reduce or have no piston slap?

Are there any other parts that should be upgraded as well (if the OEM parts are not good enough for a forged build), main caps, oil pump, etc.? Besides the main and head studs, already getting ARPs.

samnavy 02-27-2008 09:43 PM

A decent set of rings.
Stock oil pump should be good if you're sticking with stock rev limiter.
I don't see any mention of the valvetrain or head, but a rebuild, unshrouding, and 3-angle job, plus maybe ceramic coating on the valve heads.
What about coating the pistons?

Exactly what are you planning to do with this motor?
I assume boost, but what turbo, how much boost, and what's the car gonna do?

patsmx5 02-27-2008 09:57 PM

Ok I seriously doubt you can build a motor with forged pistons without boring it. The ONLY way your gonna get by with using the stock bore is if it's in perfect condition. That means no scratches, no out of roundness, no eggshaping, no ridge, etc. Still, you would have to lightly hone it out for the new rings to break in properly. Mind you the motor is still the stock bore.

Forged pistons have a higher rate of expansion than cast pistons. Putting forged pistons in a stock bore they will expand and bind, trashing your motor. You need to have a machinist who truly understands what he's doing bore the motor the correct bore to allow for the expansion of the forged pistons, based on what alloy they are. Different alloys have different rates of expansion. More silicon = less thermal expansion.

IMO you don't need any ceramic coating for a mild build. Save that money for head studs instead (ok, you said that already) or some porting. If your a DIY kind of guy, buy a book on modifying cylinder heads and read up. 100 bucks for a book and some bits could get you A LOT more HP. Run a Mazda head gasket, they are fine. Head studs will allow you to run more ft/lbs on the head safely and offer more resistance to a failing head gasket. Have the head decked if it's not flat of course.

RotorNutFD3S 02-27-2008 10:00 PM

^samnavy - I'm not concerned with the head, valvetrain, etc. at the moment. The focus is only on the block.
For your answer, most forged pistons I've looked at come with rings as well, unless I'm mistaken. And why coat them?
And yes, staying with the stock redline.

The plan is to have a strong bottom end so I can cross the lines with the 2560R I have on there for now, and if I decide to move on to a larger turbo, I can go for it and the bottom end is already beefed up and can handle it. Like I said, no insane goals, just strong.

^patsmx5 - Thanks for the insight. The block would be going to a machinist anyway, just want to know what is correct procedure for having stock bore sized forged pistons. And it sounds like if I get a piston that has a higher silicone content, it will expand less which means little to no slap when cold. Correct? And the machinist would basically have to do a bore that would allow for the expansion, but not so much that it's an overbore. Right?

neogenesis2004 02-27-2008 10:12 PM

Just put in the rods, some forgies, and bearings. You'll be good to go. I used ACL bearings because you can get them for cheap as fuck on ebay. BUT you may have to pay for more machine work to use them, which will greatly offset any savings.

I say fork out for oem bearings because you can likely just drop them in, you will or your machinist will measure first of course.

My wisecos have 0.004" of cold clearance with confirmed 0% slap at cold start. My mains have 0.002", rods 0.0015", wrist pins I believe are 0.0015". Those are the main clearances of concern for you. I went bigger on my mains to the wide end of recommended clearance because I will be spinning my motor far beyond the stock redline.

EDIT: Also, the wiseco spec sheet states their pistons can be installed with as low as 0.0025" of p-w clearance for an NA installation. If you look at the shop manual this falls well below the max spec. They recommend 0.0035" for a general boosted app. I went with 0.004" because I plan on running high boost, and the coatings my pistons have will keep them cool under extreme loads as well. SOOOOOO, don't beleive all the forged piston crap you hear on the intarweb, either here or anywhere else. The amount of expansion between the 2 main Al alloys used in forged pistons accounts for about 0.0005" of difference in diameter. So its nearly insignificant..... You can always get a great price on wisecos at raceeng.com and they usually stock them.

patsmx5 02-27-2008 10:19 PM

Sort of, it's hard to punch a block out .0018 to get the piston clearances to your spec. Much easier is to buy .010 over pistons and punch the block .014 per Neo's suggestion. (Neo that sure sounds loose to me, why .004? Planning on running 20PSI?) I'd bore it .010 myself. As for pistons with more silicone content, cast ones are good. Forged are stronger but don't have the silicone. It's a trade off. The clearances have to be just right for a forged motor. Too loose you get piston slap, which will score the walls and eventually lead to failure, too tight and thermal expansion causes them to bind, causing more friction and heat, and they seize up.

neogenesis2004 02-27-2008 10:27 PM

You post speaks with inexperience.... Its just as easy to bore/hone out 0.0018" as it is 0.014. The silicon content in cast pistons obviosly makes them expand near 0, but what I was personally refering to was the difference in expansions btw the 2 main types of forged pistons.

Also, piston slap will have little effect on a cast iron block like we have. Aluminum is far softer. Worst case senario is that you have to buy new pistons in like 4 yrs and get your bores honed out 0.001". Then you'll be good for another 4 yrs. The simple matter is that piston slap usually only occurs for the first 30 seconds the car is turned on until they warm up and you drive off. There is no load during this period and I would hardly say it hurts them. You will only run into major longevity issues when you run like 0.006" of clearance or more on a drag motor.

I do plan on running over 20+psi on my motor. I have built it with 7.5-8:1 cr specifically to run as much boost as possible on pump gas. I can guarantee you that it is also making a good amount more power NA right now than a stock motor. Albiet, my cylinder head has a whole lot to do with that.

Ask splitime how his honda motor with vitara pistons is doing. I believe his slap all the time, even while driving and its been going strong for years now.

patsmx5 02-27-2008 10:42 PM


Originally Posted by neogenesis2004 (Post 220545)
You post speaks with inexperience.... Its just as easy to bore/hone out 0.0018" as it is 0.014. The silicon content in cast pistons obviosly makes them expand near 0, but what I was personally refering to was the difference in expansions btw the 2 main types of forged pistons.

Also, piston slap will have little effect on a cast iron block like we have. Aluminum is far softer. Worst case senario is that you have to buy new pistons in like 4 yrs and get your bores honed out 0.001". Then you'll be good for another 4 yrs. The simple matter is that piston slap usually only occurs for the first 30 seconds the car is turned on until they warm up and you drive off. There is no load during this period and I would hardly say it hurts them. You will only run into major longevity issues when you run like 0.006" of clearance or more on a drag motor.

I do plan on running over 20+psi on my motor. I have built it with 7.5-8:1 cr specifically to run as much boost as possible on pump gas. I can guarantee you that it is also making a good amount more power NA right now than a stock motor. Albiet, my cylinder head has a whole lot to do with that.

Ask splitime how his honda motor with vitara pistons is doing. I believe his slap all the time, even while driving and its been going strong for years now.

FWIW I have bored a block for forged pistons before, so not speaking out of my ass here. I bored it for .003 thousandths clearance, but this was a dodge 360 that was gonna be a nitrous motor, not a boosted motor. If there is any out of roundness, a ridge, etc, then trying to get it out with a single .0018 is tough. Wish such a light pass, it's possible for the cutter to skip, not cutting a perfect bore as there is more tension to making a light cut. It's much easier to do it .010 over.

IIRC, forged pistons are not as hard as cast pistons or Hypernumatic pistons. Agreed the bore is much harder obviously. Worst case scenario is he installs his pistons with insufficient clearances and they seize up under high load. If he ever overheated the motor or had a little detonation, the higher temps and tight clearances could cause a seize as well. I've seen this happen before. My advice is to have a reputable machinist build the motor with a knowledge of what you plan to do with it.

So you ever decide If my HG was sticking out into the cylinders the way I unshrouded my valves? ;) I've seen motors with piston slap last a while too, but it's compeletly avoidable with a competent machinist.

neogenesis2004 02-27-2008 10:46 PM

No, but I decided that you totally killed you quench.

patsmx5 02-27-2008 10:50 PM


Originally Posted by neogenesis2004 (Post 220553)
No, but I decided that you totally killed you quench.

Perhaps. I was detonation free with a 100 shot before the headwork, and had detonation afterward above a 75 shot. I assumed it was for lack of squish and leaner AFR's though, and sure enough with MS II I'm now running the 100 shot on the stock timing curve detonation free. Just as a test, I ran it with 87 octane and a bottle later still no detonation. Couldn't have hurt squish too bad, though it surely didn't help any. I'd rather have all the extra flow though.

RotorNutFD3S 02-28-2008 11:54 AM

I've been doing more searching, and the 01+ block has the main bearing support plate which is a desireable feature it seems for heavy duty builds, but does it really make a huge difference, or would I be just as good off with a '94-'00 block?

Zabac 02-28-2008 12:12 PM

you'll be fine with the 94+ block
if you do not plan to over-bore, you should be fine with just honing, but again, a machinist will know best...
you seem set on the rest and i wouldnt change anything myself
i plan to build a block sometime soon so im trying to learn as much as i can from others posts
thanks to all contributing valuable info
Dan

Splitime 02-28-2008 12:37 PM


Originally Posted by neogenesis2004 (Post 220545)

Ask splitime how his honda motor with vitara pistons is doing. I believe his slap all the time, even while driving and its been going strong for years now.

Heh, it's true. It sounds like my 1.6l is a diesel motor. 30k+ on it and no issues. Hell... i spiked to 27psi one night and all is good.

:)

patsmx5 02-28-2008 12:37 PM

Yea you'll be fine without the girdle support. Your already planing on using main bearing studs so the main bearings will be fine. The best way to reduce loads on the crank would be to buy lightweight pistons/rods and have them balanced. If you keep your RPMs below say 7-7.5K you'll be fine don't worry about it.

m2cupcar 02-28-2008 12:38 PM


Originally Posted by patsmx5 (Post 220532)
...Putting forged pistons in a stock bore they will expand and bind, trashing your motor....

Nonsense - no different than sticking any size forged piston in the corresponding bore size. Think about it. If you have a XXmm bore then you spec an XXmm forged piston, it's all the same. Machinist should check the bores and if they're perfect you don't need an overbore.

patsmx5 02-28-2008 12:47 PM


Originally Posted by m2cupcar (Post 220838)
Nonsense - no different than sticking any size forged piston in the corresponding bore size. Think about it. If you have a XXmm bore then you spec an XXmm forged piston, it's all the same. Machinist should check the bores and if they're perfect you don't need an overbore.

Nonsense? I don't know what factory clearances are on the stock 1.8, but generally speaking forged pistons require more clearance because of higher thrermal expansion. If his stock clearance is .002 and it's perfect, and he drops in some forged pistons, they will seize. It's NOT all the same. If the bores were perfect he could have it honed and them put in pistons, not just drop them in. You guys go ahead and do whatever you want, I know how to bore a block.

EDIT: For example when I did the 360 block, the pistons were .040, so the block was bored 4.042 I think, then we honed it to get the last .001. Left a good crosshatching for the rings to break into and the motor has no piston slap and is still running.

m2cupcar 02-28-2008 01:28 PM

In researching forged pistons for my F stroker, both Wiseco and Venolia stated that I just need to spec a stock sized "non overbore" piston for my "mint" block. Nothing else is needed. I can only assume that the piston is designed to fit the stock bore. :dunno:

I doubt his block is perfect, but if it is, I don't see the point in an overbore. I'd at least ask the manufacturer of the piston.

patsmx5 02-28-2008 02:24 PM

Don't assume anything, find out what your clearances are and what they should be.
My Haynes Manual shows factory piston-to-bore clearance for 1.8L of:
standard: .0016 to .0020
service limit: .006
I would not trust these numbers 100 % since it's a Haynes manual. I'd make sure it's what the Mazda FSM shows.

Neo suggested using .0040 as that's what he is using for is forged pistons. That's fine. If I ever build a forged motor, I'll probably do the same.

RotorNutFD3S 02-28-2008 03:02 PM

So it sounds that if the engine is in good shape, I can use a non-overbore piston. If there are some issues, overbore will be the next step.

Anyway, in looking at pistons, some companies list the overbore by +.010, +.020, etc. Now with the stock bore being 83mm (which is what I've read, please correct it if I'm wrong), what is an 83.5mm piston? Is that +.010, +.020?


Originally Posted by patsmx5 (Post 220898)
Neo suggested using .0040 as that's what he is using for is forged pistons. That's fine. If I ever build a forged motor, I'll probably do the same.

Is that for a stock bore sized piston?
Don't the pistons come with a spec sheet telling you (or your machinist) how much they expand, and thus how much material to remove from the cyl. walls?

patsmx5 02-28-2008 03:24 PM


Originally Posted by RotorNutFD3S (Post 220911)
So it sounds that if the engine is in good shape, I can use a non-overbore piston. If there are some issues, overbore will be the next step.

Anyway, in looking at pistons, some companies list the overbore by +.010, +.020, etc. Now with the stock bore being 83mm (which is what I've read, please correct it if I'm wrong), what is an 83.5mm piston? Is that +.010, +.020?


Is that for a stock bore sized piston?
Don't the pistons come with a spec sheet telling you (or your machinist) how much they expand, and thus how much material to remove from the cyl. walls?

Ok, your not understanding everything. Buy some .010 or .020 over pistons and give it all to a good machinist and let him do his thing. Tell him you want .0035- .0040 piston-to-cylinder bore clearance. Why are you afraid to bore out the motor? It's extra displacement, which is HP. Not a lot, but hell if you can choose between 0,3, or 5 hp, which would you pick?

RotorNutFD3S 02-28-2008 04:34 PM

And this is exactly what I don't want. I'm trying to understand this whole thing, but I don't want people telling me "just go do this." That doesn't help me learn anything.

And I'm not afraid to bore it. After reading up on this on the various Miata boards, the consensus is that it is unnecessary to do so on a Miata when there is no extreme power goal. Also, no point in weakening the block if I don't have to. I don't think a bore up to .020 over would do any harm really, but I just don't want to do it.

m2cupcar 02-28-2008 04:45 PM

Yes, pistons come with a spec sheet. If the bores on your engine are "perfect" (I highly doubt that's the case), the machinist can hone your bore to meet the specs of stock sized forged piston. IMO the best thing to do for a "necessary" overbore with boosted engine is to go with the smallest overbore, focusing on cylinder wall thickness for boost strength.

patsmx5 02-28-2008 06:02 PM

Guys .020 or .060 from the cylinder walls is NOT Gonna hurt the cylinder walls. It's a thick ass cast iron clylinder, you will never hurt it. It's the strongest thing in your motor. It's more displacement, which our undersquare engines can use. By increasing the bore .060, you could unshroud the combustion chambers that .060 as well, which helps flow. More flow and more displacement is...... desirable. Do the math but that's surely a few % more displacement. Boring it the minimum is ok so it can be rebuilt again. They do this for commercial equipment, where they would like to get several rebuilds out of the engine for maximum service life.

Sorry Rotornut but reread my post. You were asking stuff I outright already answered.

patsmx5 02-29-2008 02:45 AM

Ok, using the factory specs of 3.2678" bore and 3.346" stroke, I get 112.25 cubic inches of displacement.

Let's punch this motor .020 over.
3.2878" bore and 3.346" stroke= 113.63 cubic inches (.000 to .020 displacement changed 1.378 inches)
1.23% more displacement then stock.
1.43 cubic inches larger than stock.


Now let's punch it .040 over
3.3078" bore and 3.346" stroke=115.01 cubic inches (.020 to .040 displacement changed 1.385 inches)
2.46% more displacement then stock.
2.76 cubic inches larger than stock


.060 over
3.3278" bore and 3.346" stroke= 116.35 cubic inches (.040 to .060 displacement changed 1.400)
3.65% more displacement then stock.
4.1 cubic inches larger than stock

Though insignificant, as bore size increases, area increases exponentially. This can be seen as the change in displacement is not the same for each .020 iteration. For example, look at the change in displacement for .020 and .040. The difference between them is 1.385-1.378=.007. However, this is not the case for .040 to .060. Here, the change is .015. Hence it's exponential by a factor of 2. This is because the formula for area is pie times radius squared times height.

An extra 4.1 cubic inches is 3.65% more displacement, or 3.65% more power. However, it will also allow you to unshroud the combustion chambers .060, which will increase flow. I would say the benefits of unshrouding will be greater than the benefit of the larger bore, but at the minimum, equal. If only equal, that's 7.3% increase in power.

That's my inexperience showing. Night night.

RotorNutFD3S 02-29-2008 12:30 PM

Alright, so since .020 over is not that much of a change, does it affect what head gasket I need to use? Or can I still use the OEM gasket?

And if the sizes of the pistons are listed as 83.5mm, 84mm, and 84.5mm, what overbore are those?

Rishi 02-29-2008 01:32 PM

You can fit up to an 84.5mm bore on the stock gasket. As far as the bore sizes, here's the list.

83.5 = .020 over
84 = .040 over
84.5 = .060 over

Anyone know a piston mfg that has an off the shelf 9.5:1 compression ration piston in the 84.5mm size?

neogenesis2004 02-29-2008 01:43 PM

none of them

RotorNutFD3S 02-29-2008 01:44 PM


Originally Posted by Rishi (Post 221407)
You can fit up to an 84.5mm bore on the stock gasket. As far as the bore sizes, here's the list.

83.5 = .020 over
84 = .040 over
84.5 = .060 over

Thank you for that info. I assumed that's what it was, but wasn't 100% sure.

Rishi 02-29-2008 01:58 PM


Originally Posted by neogenesis2004 (Post 221411)
none of them

I guess it was wishful thinking! I guess I will have to do some more homework then.

Zabac 02-29-2008 02:06 PM

have them custom made mr. high roller

out of curiosity, why do you want 9.5 CR?

Rishi 02-29-2008 02:16 PM

I actually am de msming an msm. The stock CR on the car is a 9.5:1, so if I am gonna touch the current pistons, I want an apples to apples switch, otherwise I will just pull the current ones and coat or cryo them. FYI, I have managed to locate a 9.5:1 in an 84mm bore that is a couple weeks out if anyone else is interested. At a non Mr. High Roller price nonetheless!

RotorNutFD3S 02-29-2008 06:03 PM

On Raceeng.com, they list a 83.5mm Wiseco piston and list that it's for turbo applications, however, they don't list the C/R. Anyone that has dealt with this company know what it is?

Belfab only lists either a 8.6:1 or 9.5:1 at 83.5mm for their forged pistons. Anyone know if they can get a 9.0:1 for the same price? ($439) I called, but I was told they are at the Winston Cup race and to call back Monday, which I'll do, but if anyone knows now...

Also, any other places that currently sell forged pistons for a reasonable price? (Or will be in the near future?)

pschmidt 02-29-2008 07:38 PM

Have you found a place that sells reasonable bearing/gasket sets?

FM has a kit, but it's over $500.

RotorNutFD3S 02-29-2008 08:30 PM

You can get a quote from MiataRoadster.com or Rosenthal (www.finishlineperformance.com) has some sets on their site. You can also call them directly and get set prices. They're pretty flexible.

hustler 07-18-2008 06:57 PM


Originally Posted by RotorNutFD3S (Post 221503)
On Raceeng.com, they list a 83.5mm Wiseco piston and list that it's for turbo applications, however, they don't list the C/R. Anyone that has dealt with this company know what it is?

Belfab only lists either a 8.6:1 or 9.5:1 at 83.5mm for their forged pistons. Anyone know if they can get a 9.0:1 for the same price? ($439) I called, but I was told they are at the Winston Cup race and to call back Monday, which I'll do, but if anyone knows now...

Also, any other places that currently sell forged pistons for a reasonable price? (Or will be in the near future?)

they can't get any other compression ratios. If you're worried about off-boost performance, then go with a 1mm overbore, and just roll the timing forward off boost more. I have the 8.6 pistons, and after you surface the head you'll gain 1-2 tenths in compression.

M-Tuned 07-18-2008 07:09 PM

Here is my version of a MILD build

ETD/M-Tuned Connecting Rods
Stock Pistons (94-97)
New set of OEM Rings
OEM Bearing
ARP Main Bolts
ARP Head Bolts

I've personally tuned this combo in the 330+hp range and it works great!


I'm going to build the same for myself, but I plan on using the 99+ Pistons for a little more compression :)


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