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Old 02-14-2014, 02:15 PM   #1
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Default My turn!! A "budget" engine build discussion

Back story- About 3 years ago, I had an engine failure that, to this day, is still a mystery. I replaced the engine with a new long-block...OK, it had 900 miles on it. Well, it lasted 70k miles. About 3 weeks ago, I was out playing on the highway and rolled into WOT. The car bucked/misfired ~5k rpms in 4th gear and again in 5th. I backed off and noticed a ticking sound when I pulled off the highway. Rod-knock. Yay. I pulled the plugs and nothing looks crazy- no damaged plugs and what I could see of the tops of the pistons, no shiny spots.....really no sign of anything coming loose and bouncing around in the combustion chamber.

So here I am with an unplanned engine build that needs to be done fairly quickly. GOAL- I don't want to go crazy with a build and I would like to get a few more kittahpowerz out of the engine at the same time. Since I plan on sticking with the 2560RS turbo, I'd like to see how close to 300rwhp I can get OR bump from 14psi to ~17-18psi. So far, this is my to-do list:

Set in stone parts list-

Block--
Rods- Manley H-beam
Pistons- new OE BP-4W 9.5:1 units- oversized
Rings- OE Mazda
Bearings- OE Mazda
Gasket/seal set- OE Mazda
Gates "racing" t-belt
New OE t-belt tensioner/idler pulleys
949Racing waterpump
New Fidanza friction ring for flywheel
????? New Clutch

Head--
Valves- SuperTech SS (1mm oversize)
SuperTech valve seals
??????? other work/parts

The idea is a basic engine re-build using Manley rods and .5mm oversize pistons. The entire rotating assembly will be balanced as well. What I am on the fence about is should I spend the money on having the piston tops/skirts coated? I've looked into Calico's work and got a quote for the work and turn-around time. It adds about $250 to the build cost.

Next question/idea that I would like some insight on- head work.
Right now I'm planning on re-using the stock parts and just add the ST valves and have the head worked to accommodate them.
*Do I need to upgrade the valvetrain? (springs/retainers/shims/buckets)
*Will I be OK re-using what is in there now?
*Are there any parts that should absolutely be replaced with new at this point?
*Is there any other cost-effective and beneficial work I should have done to the head?
*Does going with oversize valves and the work needed pretty much cover the unshrouding process?
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Old 02-14-2014, 02:18 PM   #2
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Is the reasoning for oe pistons to keep tolerances tight and reduce slap during daily driven cold starts? Otherwise I'd go forged since you're going to run pump gas.

Also it sounds like your definition of "budget rebuild" is quite different from others.

Not in a bad way though, sounds like it will be great.

-I would not bother much with the head aside from cut the valves and surface head and replace stem seals.
-I would weigh the pros and cons of oem pistons vs forged on pump gas.

Everything else sounds great. Might want to look into oil pump.
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Old 02-14-2014, 02:20 PM   #3
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You are spot-on with the decision for stock pistons- car is daily driven and started in all temperature ranges that Oregon can throw at me. So the life of the cylinder walls is important.
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Old 02-14-2014, 02:21 PM   #4
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Coating OEM pistons seems like a waste of money to me.

It seems that money would be better spent towards getting a set of forged pistons...
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Old 02-14-2014, 02:27 PM   #5
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Why go oversized ? If you are boring and going with OS pistons, i honestly see no reason not to go forged. This is especially true if you are throwing $$ at the car with new OEM pistons and having them coated, i bet the cost of that will get you DAMN NEAR a forged setup.

Most of us stick with OEM pistons because we can keep the stock bores, throw a hone in there, and re-use the stock pistons without issue.

Going with forged pistons means buying pistons and machine work ($$)
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Old 02-14-2014, 02:33 PM   #6
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I'd find some lower comp oem pistons actually. like hte 9.1's from a 94-97 miata. Clean em up, coat em if you want, and enjoy perfect cold startups and oem wear with the comfort of being safe at 300whp on pump gas.

that's what I ran on my '00
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Old 02-14-2014, 02:36 PM   #7
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How much difference in tuning headroom is there between 9:5 and 9:1? I really liked the off-boost response/power of the 10:1 that I have/had...
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Old 02-14-2014, 02:41 PM   #8
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Quote:
Originally Posted by 18psi View Post
I'd find some lower comp oem pistons actually. like hte 9.1's from a 94-97 miata. Clean em up, coat em if you want, and enjoy perfect cold startups and oem wear with the comfort of being safe at 300whp on pump gas.

that's what I ran on my '00
agreed.

If you are doing the "budget" thing, i say go either full budget and re-use some OEM pistons with the stock bore size and skip the machine work and cost of new pistons, OR if you are going for machine work, buying "new" oem pistons, and coating them than you may as well just go forged.

Quote:
Originally Posted by Doppelgänger View Post
How much difference in tuning headroom is there between 9:5 and 9:1? I really liked the off-boost response/power of the 10:1 that I have/had...
Probably not a HUGE difference in det resistance, but same with the off boost response/power.. not a huge difference.

I say you need all the det resistance you can get with 300whp on pump gas using stock pistons.
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Old 02-14-2014, 02:45 PM   #9
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Well considering mazda allows 87oct on the 9.1's and only 91oct on 9.5's I'd say the difference is significant.

And you can just ramp up the timing more with the lower compression to make up for the response.

If you had e85 this would be an opposite conversation.
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Old 02-14-2014, 02:49 PM   #10
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Looks like about a $100 difference between OE pistons and the 83.5mm 9.5:1 SuperTechs.

So what is the stock diameter- 83 or 83.5?
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Old 02-14-2014, 02:51 PM   #11
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*edit: nvm

83
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Old 02-14-2014, 02:54 PM   #12
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You've got a GT2560RS, why worry about off-boost response? What's your boost threshold, 1500rpm?

How much extra are the OS valves and the machine work to fit them vs refreshing the ones you already have? If saving money and moderate power are your goals, why not keep the stock valves and spend that money on dual valve springs for more revs/lower chance of a money shift? That's assuming you already have the 99 head with solid lifters. With 16 valves vs 4 cylinders, headwork gets a lot more expensive than bottom end work. And since we know the stock head can handle >400whp, why spend the extra moolah?
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Old 02-14-2014, 02:54 PM   #13
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Quote:
Originally Posted by 18psi View Post
*edit: nvm

83
???

NLM lists- No Limit Motorsport: Supertech P4-MA8350-P2 Racing Pistons (Set of 4)
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Old 02-14-2014, 02:56 PM   #14
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yeah stock is 83 and .5 over is 83.5

and yeah I wouldn't do headwork aside from a refresh on a 2560 car running a basic fm setup

....unless you're really not going for a budget build haha
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Old 02-14-2014, 03:05 PM   #15
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So you hammered the OE bearings out after 70k miles and you're not going to upgrade them?

+1 ST valves are a waste of money for you. I would do forged pistons, but if you insist on spending the money on new OE, at least drop the compression and use the '94 pistons.
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Old 02-14-2014, 03:09 PM   #16
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Quote:
Originally Posted by thenuge26 View Post
You've got a GT2560RS, why worry about off-boost response? What's your boost threshold, 1500rpm?

How much extra are the OS valves and the machine work to fit them vs refreshing the ones you already have? If saving money and moderate power are your goals, why not keep the stock valves and spend that money on dual valve springs for more revs/lower chance of a money shift? That's assuming you already have the 99 head with solid lifters. With 16 valves vs 4 cylinders, headwork gets a lot more expensive than bottom end work. And since we know the stock head can handle >400whp, why spend the extra moolah?
I'm basing, so far, what I would like to have/do based on what I know and my experience. But I am always open to learning...or to correct errors in what I know...or to hear "you're doing it wrong" lol

To the best of my knowledge, having a higher comp. ratio makes off-boost driving a little nicer...and helps a little with MPGs. Not that MPGs are a #1 concern, but getting 30-32mpg when driving with a light foot is nice.
I also know MT has a lovely pool of knowledgeable people, so insight like yours is what I am after

I figure the gain in flow with the OS valves would be a good trade-off for the cost vs. simply turning up the boost (to my understanding of higher boost/increased IATs vs better flow with lower boost).
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Old 02-14-2014, 03:19 PM   #17
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Quote:
Originally Posted by Savington View Post
So you hammered the OE bearings out after 70k miles and you're not going to upgrade them?

+1 ST valves are a waste of money for you. I would do forged pistons, but if you insist on spending the money on new OE, at least drop the compression and use the '94 pistons.
I was told, that the ACL race bearings wouldn't be too happy on the street/daily driven and "normal" 3k oil change intervals. While I have no reason to not trust who told me this, I have no experience with said topic...and am impressionable with information.

I suspect the detonation that killed the bearing is because of the gas here and a tune with too much timing. Never had issues with detonation...ever...on east coast 93. I feel tuning on the gas out here would be a solution to the detonation I ran in to..and not a problem with the bearings. But I could be wrong.

Also, what kinda of wear am I looking at with forged pistons? I'm under the impression the wear is "significant", as in, I'm not going to get 100k out of the engine. Though I am ALWAYS adamant about letting the engine get plenty warm before any kind of high revvs or any boost at all.
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Old 02-14-2014, 04:05 PM   #18
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You didn't get 100k out of you last OEM block, so why do you care if you get it out of forged pistons? I am in the camp of if you are going to overbore any then you might as well go with forged pistons. I picked up my set from NLM back in 2010 when they did their last group buy here and was happy with the transaction.

In my built motor I am running the 8.6:1 84mm supertechs and off power response was fine fine. I also could manage to get 30-31mpg if I was light footed and was mostly doing interstate driving.

If you want a set of 94 oem pistons I have a used set out of my old motor. I think they have about 115k on them. I can get pictures this weekend for you if you want. Just shoot me a pm.
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Old 02-14-2014, 04:40 PM   #19
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So, how bad is the wear on the walls when using forged pistons on a daily driver? I personally don't know people who drive a car 25k+/yr and are running a forged setup.

Difference in cost aside, and comparing benefits- Would the increased flow w/lower boost* be better/safer for tuning over just cranking up the boost to make up for what the OS would flow compared to stock?

*Anyone have any ideas on how much difference in boost vs power between the two? I.e. 290rwhp w/OS valves would be done at XXpsi vs. stock valves running XX psi: would this be a 1-2psi difference or a 4-5psi difference....or is the difference just splitting hairs?

Also, why would coating stock pistons be a waste compared to coating forged pistons being "good" if trying to achieve the same 300rwhp goal?
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Old 02-14-2014, 04:53 PM   #20
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Don't get me wrong, I'm the furthest thing from the experts here. All I do is read about what the real experts say and have done.

But I don't see how >$250 for valves plus machine work could be more cost effective than turning up the boost, which is free. If you want to comfortably hit 300whp, I would think replacing your 2560 with a 2860 would still be cheaper than headwork. And still give you more headroom than the OS valves would.
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