Cost vs. performance on pistons - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


Engine Performance This section is for discussion on all engine building related questions.
Sponsored by:
Sponsored by:

Reply
 
 
 
LinkBack Thread Tools Search this Thread
Old 04-14-2009, 04:24 PM   #1
Supporting Vendor
Thread Starter
iTrader: (3)
 
Join Date: Jul 2006
Location: San Diego
Posts: 2,865
Total Cats: 493
Default Cost vs. performance on pistons

I'm tentatively gathering data for a tear down and rebuild of my motor which will be inevitable and so I want to have all the info researched and know the plan before that day comes.
This car is the uber-budget build, fast and reliable, things done "right" but nothing but the necessities - if the coolant isn't getting too hot at races, then I don't need a reroute sort of thing. So, consider that context in your responses, if it were absolutely necessary to have everything on the bottom end forged, I'd do it but it's not..
Anyways, I know I will be doing forged H-beam rods. Now to the pistons.. First off, I've heard mention of using automatic pistons and I can't find in any searches the actual compression ratio specs of one - can anyone help me out there?
I want to drop the compression some. Builds like Hustler's have convinced me that a marginal compression drop allows much more power from boost than is lost from lower compression. So, if auto pistons are a lower compression, sweet deal.
Now, on to the cost issue - assuming auto pistons are a lower compression and would work well (and yes I would get nice rings for them), I would have the engine guy do a slightly loose bore and go with those pistons and new rings with the H-beam rods, but are would the cost of the pistons + new rings + tri-coating (is this necessary?) add up to almost the cost of forged pistons which come with rings? Because if so, no sense in not getting the forged ones, but if it is a more affordable option, why not go with the coated auto pistons?

Anyways, discuss...
Thanks
-Ryan
ThePass is offline   Reply With Quote
Old 04-14-2009, 04:34 PM   #2
Elite Member
iTrader: (46)
 
Stein's Avatar
 
Join Date: Dec 2007
Location: Nebraska
Posts: 4,812
Total Cats: 138
Default

Interested in the responses as I have a 96 automatic motor at home. IIRC, compression is 9:1 instead of 9.5:1 for similar 5 speed motors.
Stein is offline   Reply With Quote
Old 04-14-2009, 04:35 PM   #3
Boost Czar
iTrader: (61)
 
Braineack's Avatar
 
Join Date: May 2005
Location: Chantilly, VA
Posts: 72,900
Total Cats: 1,792
Default

I don't believe there was a difference in compression in auto vs 5-sp in a 1.8L.

94-95 have been rated at 8.8:1
96-97 9.0:1


Quote:
Starting with the 3/95 start of the ODB-II implementation (VIN 14193) the pistons were changed with a slight dome to increase the compression ratio to an actual 9.0:1. The '94-3/95 pistons were factory rated at 9.0:1 but actually was around 8.8
Braineack is offline   Reply With Quote
Old 04-14-2009, 04:37 PM   #4
Elite Member
iTrader: (9)
 
Saml01's Avatar
 
Join Date: Jul 2007
Location: NYC
Posts: 5,730
Total Cats: 2
Default

I would get the higher 10:1 pistons. Better mid range. If you know how to tune you can be perfectly safe with a slightly higher compression.

I wouldnt bother with all that voodoo with coating pistons and stuff.
Saml01 is offline   Reply With Quote
Old 04-14-2009, 04:50 PM   #5
Tour de Franzia
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

I considered tri-coating 9.0:1 pistons and I was basically $100 shy of forged slugs. Think about the headroom and pizza mind.

I firmly believe that even on budget builds, "do it once and do it right" with the fundamentals or engine internals. Audi, mitsu, subaru, and toyota go with forged guts for a reason on their sportscars.

Quote:
Originally Posted by Saml01 View Post
I would get the higher 10:1 pistons. Better mid range. If you know how to tune you can be perfectly safe with a slightly higher compression.
he probably wants to make some torque. Do you consider 4000rpm mid range? I'm making 252wtq there, that's roughly 275wtq on a dynojet. I consider that midrange. I've auto-x'd my car a few times too, and the powerband is fine. I wouldn't want boost to come on any higher, but never had a complaint yet.
hustler is offline   Reply With Quote
Old 04-14-2009, 04:51 PM   #6
y8s
2 Props,3 Dildos,& 1 Cat
iTrader: (8)
 
y8s's Avatar
 
Join Date: Jun 2005
Location: Fake Virginia
Posts: 19,038
Total Cats: 407
Default

while sam doesn't subscribe to voodoo, I doo.

see a piston will die from detonation whether it's forged or cast. the coating provides a little thermal protection and reduces (some of the swain coatings) liklihood of detonation. here's your voodoo:

Quote:
Originally Posted by swain has a jesus fish in their ad in GRM?
TBC™ Ceramic Thermal Barrier:
For most naturally aspirated and mild boost motors TBC™ is our tried and true ceramic thermal barrier coating. Swain’s TBC™ has come a long way since it started the internal engine coating revolution back in the 1970’s. Now in its 5th generation of development, Swain’s TBC™ uses Swain’s exclusive “Smart Coat” technology which allows the ceramic to expand at the same rate as the piston. TBC™ coated pistons run cooler and retain much more of their tensile strength. TBC™ protects against high temperature oxidation, eliminates hot spots, and encourages proper flame travel. The ceramic also spreads the heat evenly over the entire coated surface reducing detonation, pre-ignition and allowing the use of lower octane fuel. Less heat is conducted through the wrist pins and rods keeping the crank, bearings, oil and entire bottom end cooler.

GoldCoat™ Ceramic Armor™ Ceramic Thermal Barrier:
As the use of Nitrous, Turbo Chargers and Super Chargers have become common place; Swain Tech developed GoldCoat™ Ceramic Armor™ to protect piston tops in these demanding motors. GoldCoat™ offers the same benefits of TBC™, but adds an extra layer of extra high temperature ceramic to provide even more protection at higher temperatures. GoldCoat™ deals with the heat spikes and thermal shock of boosted motors better than any other piston coating.
but swain is MOTHER EFFING PRICEY last time I looked.

still, it is good insurance.

but if you're going to be under 250 rwhp, you might not need forged or coated. what power level are you looking at?
y8s is offline   Reply With Quote
Old 04-14-2009, 04:55 PM   #7
Elite Member
iTrader: (46)
 
Stein's Avatar
 
Join Date: Dec 2007
Location: Nebraska
Posts: 4,812
Total Cats: 138
Default

Brain, to counter your quote, here is a quote from the solomiata page so I don't know which one is correct:

"In 1996 the peak HP rating of the Miata 1.8 motor was raised to 133 hp from 128. This comes soley from the new for 1996 ODBII software having the ability to lean out the above 6000 rpm fuel curve. There have been rumors that there was a running change to the pistons to up the compression ratio to 9.5:1 during the 3/95 cutover, but I have not seen any documentation to prove it. "

My reference to the auto being lower compression may be rumor as well.
Stein is offline   Reply With Quote
Old 04-14-2009, 05:11 PM   #8
Elite Member
iTrader: (33)
 
RotorNutFD3S's Avatar
 
Join Date: Jan 2007
Location: Newnan, GA
Posts: 2,539
Total Cats: 29
Default

If my research on pistons was correct, 1.6L Miatas were the only ones to have a different piston for automatic or manual configurations. I could find no evidence of this happening on the 1.8L.
I will also say that the SoloMiata quote, for once, is actually wrong about the compression ratio. My '95 R had the same pistons as the ones I pulled from a '96 (they have a slightly raised dome), however the '94s I pulled were completely flat topped and would be the ones rated by Mazda at 8.8:1. Also had a set of MSM pistons (same as '99-'00 - 9.5:1) and they had an even higher dome than the '95/'96 pistons (9.0:1).
RotorNutFD3S is offline   Reply With Quote
Old 04-14-2009, 05:20 PM   #9
Elite Member
iTrader: (9)
 
Saml01's Avatar
 
Join Date: Jul 2007
Location: NYC
Posts: 5,730
Total Cats: 2
Default

Quote:
Originally Posted by y8s View Post
while sam doesn't subscribe to voodoo, I doo.

see a piston will die from detonation whether it's forged or cast. the coating provides a little thermal protection and reduces (some of the swain coatings) liklihood of detonation. here's your voodoo:



but swain is MOTHER EFFING PRICEY last time I looked.

still, it is good insurance.

but if you're going to be under 250 rwhp, you might not need forged or coated. what power level are you looking at?
Cmon man, seriously. Coating pistons on a street driven gas engine? Come on.

I can think of much better things to spend 200 bucks on.
Saml01 is offline   Reply With Quote
Old 04-14-2009, 05:23 PM   #10
Elite Member
iTrader: (46)
 
Stein's Avatar
 
Join Date: Dec 2007
Location: Nebraska
Posts: 4,812
Total Cats: 138
Default

Quote:
Originally Posted by RotorNutFD3S View Post
If my research on pistons was correct, 1.6L Miatas were the only ones to have a different piston for automatic or manual configurations. I could find no evidence of this happening on the 1.8L.
I will also say that the SoloMiata quote, for once, is actually wrong about the compression ratio. My '95 R had the same pistons as the ones I pulled from a '96 (they have a slightly raised dome), however the '94s I pulled were completely flat topped and would be the ones rated by Mazda at 8.8:1. Also had a set of MSM pistons (same as '99-'00 - 9.5:1) and they had an even higher dome than the '95/'96 pistons (9.0:1).
Interesting. Thanks for that. I need to check, as I would have sworn today that my 96 auto pistons are actually dished. I'll check tonight. The head is off of it.
Stein is offline   Reply With Quote
Old 04-14-2009, 05:40 PM   #11
Elite Member
iTrader: (33)
 
RotorNutFD3S's Avatar
 
Join Date: Jan 2007
Location: Newnan, GA
Posts: 2,539
Total Cats: 29
Default

Quote:
Originally Posted by Stein View Post
Interesting. Thanks for that. I need to check, as I would have sworn today that my 96 auto pistons are actually dished. I'll check tonight. The head is off of it.
If that's the case, something interesting there for sure. Please post back with what you find.

Quote:
Originally Posted by Saml01 View Post
Cmon man, seriously. Coating pistons on a street driven gas engine? Come on.

I can think of much better things to spend 200 bucks on.
You're just focusing on the top coat, most people go with a tri-coat option. If you're using OEM pistons, it can't be a bad idea to help them out in any way that you can. The top coat helps as y8s described, but the side skirts are coated in a dry-film lubricant, so less friction = less heat, and the undersides are coated to help shed the oil off faster, which helps keep as much oil in circulation as possible. I paid $140 ($35/piston) for the tri-coating with Swain, a justifiable cost in my book.

If you figure $440 for a set of Supertech forged pistons w/ rings from Belfab and then the machine shop charges you more to overbore the cylinders than just to hone them (3 of the ones I got prices from quoted $75-$150 more for an overbore). So say $515 at the least, possibly more depending on piston and labor.

So even if you're buying a new set of OEM pistons (about $120 for all 4), having the cylinders honed ($50-$75 depending on shop), you still come out at least $180 under the cost of going with oversized forged pistons, which is great for a budget like what the OP is aiming for.

I personally went with the tri-coated option as I didn't have to buy the pistons and I'm not searching for insane power numbers, just something to support a nice bump in power. Oh, and not to mention I was tired of hearing piston slap during warmup on the cars around here running forged pistons, even though everything is properly clearanced inside the engine. That wear and tear has to add up sooner or later.
RotorNutFD3S is offline   Reply With Quote
Old 04-14-2009, 06:33 PM   #12
y8s
2 Props,3 Dildos,& 1 Cat
iTrader: (8)
 
y8s's Avatar
 
Join Date: Jun 2005
Location: Fake Virginia
Posts: 19,038
Total Cats: 407
Default

I would think a street driven motor with all those miles would be a BETTER reason to put the coatings in your motor.
y8s is offline   Reply With Quote
Old 04-14-2009, 08:12 PM   #13
Junior Member
 
Join Date: Nov 2008
Location: San Diego
Posts: 65
Total Cats: 0
Default

If this is a cost vs. preformance issue i dont see much preformance for the dollar. So i would spend the money somewhere else. Where? that depends on what u have and what else you need. The tuning of the ECU may net more power and torque. Is the injector duty cycle over 80%? then maybe bigger injectors. Boost toping out at 18psi @ 6400RPM and not making any more power past 6500RPM? Then maybe a bigger turbo. These are all if's and but's to where your cars at and where you expect it to be (HP level's).
LowBoostn is offline   Reply With Quote
Old 04-14-2009, 09:37 PM   #14
Elite Member
iTrader: (46)
 
Stein's Avatar
 
Join Date: Dec 2007
Location: Nebraska
Posts: 4,812
Total Cats: 138
Default

Well, I checked and I was all wet. My 96 auto pistons have a slight (maybe .020-.030") high dome in the center with about a 1/2" band of lower material around the periphery, so likely the same as stock.
Stein is offline   Reply With Quote
Old 04-15-2009, 03:22 PM   #15
Supporting Vendor
Thread Starter
iTrader: (3)
 
Join Date: Jul 2006
Location: San Diego
Posts: 2,865
Total Cats: 493
Default

As to my goals, right now I'm probably in the 200 whp/11 psi area which is right on the edge of what is generally accepted as the limit for preserving engine longevity.. I will probably not go above 250 whp but in the spirit of doing things properly the first time (with budget in mind), I am aiming to make everything good for 300 whp - the intercooler, the injectors/ecu, etc. all could do 300 if I chose to swap to a 19T down the road so when I crack open the motor I would like to close it back up with the ability to do 300, even if I may not actually push it that high.

The recommendation to go with higher compression pistons is one I will have to decline, I just don't feel comfortable with that - yes, I know y8s has pulled it off beautifully, but I want to create a car that is my daily and race rat e.g. something that has the highest probability of lasting for as long as possible and imo running high comp pistons on a moderately boosted motor, while possible with a good tune, leaves very little wiggle room for a slightly imperfect tune.

So.. you guys were saying the 1.8 pistons did not differ from manual to auto but that the 1.6 did... I have a 1.6 which is exactly why I am researching this - can anyone actually confirm or bring forward info about the 1.6 pistons from the auto? I'd love to find out that they are 8.8 or so...

Rotornut - thanks for that break down on what you found you could save by going with coated stockers instead of forged. If I can save close to $200 by doing a factory piston and the tri-coat over a forged, perhaps that w/ H-beam rods would be perfect for a budget 300 whp ceiling motor..

-Ryan
ThePass is offline   Reply With Quote
Old 04-15-2009, 03:38 PM   #16
Supporting Vendor
Thread Starter
iTrader: (3)
 
Join Date: Jul 2006
Location: San Diego
Posts: 2,865
Total Cats: 493
Default

edited
ThePass is offline   Reply With Quote
Old 04-15-2009, 03:45 PM   #17
Elite Member
iTrader: (9)
 
Saml01's Avatar
 
Join Date: Jul 2007
Location: NYC
Posts: 5,730
Total Cats: 2
Default

Quote:
Originally Posted by ThePass View Post

The recommendation to go with higher compression pistons is one I will have to decline, I just don't feel comfortable with that - yes, I know y8s has pulled it off beautifully, but I want to create a car that is my daily and race rat e.g. something that has the highest probability of lasting for as long as possible and imo running high comp pistons on a moderately boosted motor, while possible with a good tune, leaves very little wiggle room for a slightly imperfect tune.
You know why Chuck Norris named his cat after you? Because its a *****.


j/k
Saml01 is offline   Reply With Quote
Old 04-15-2009, 05:28 PM   #18
Tour de Franzia
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

I'm excited to see 1.6 guys going with the low comp / high-torque option. It works for subaru and mitsu pretty well, lol.
hustler is offline   Reply With Quote
Old 04-15-2009, 09:25 PM   #19
Junior Member
iTrader: (5)
 
Join Date: Mar 2008
Location: Dallas
Posts: 131
Total Cats: 1
Default

Quote:
Originally Posted by hustler View Post
I'm excited to see 1.6 guys going with the low comp / high-torque option.
juxt3r is offline   Reply With Quote
Old 04-15-2009, 10:56 PM   #20
Tour de Franzia
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

Quote:
Originally Posted by juxt3r View Post
you live in Dallas...where is your discussion on high compression, superchargers, and avoiding stand alone?
hustler is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Project Gemini - Turbo Civic on the Cheap Full_Tilt_Boogie Build Threads 59 12-15-2017 09:00 PM
OTS Bilstein to motorsports ASN conversion stoves Suspension, Brakes, Drivetrain 5 04-21-2016 04:00 PM
(Noob). Does MS3 use CEL? TheNomad MEGAsquirt 6 10-01-2015 11:47 AM
WTB Stock NB Pistons pdexta WTB 0 09-28-2015 12:18 PM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 11:29 PM.