85mm pistons too big for boost? - 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 10-30-2012, 03:52 AM   #1
Elite Member
Thread Starter
iTrader: (6)
 
Join Date: May 2011
Location: Lebanon, TN
Posts: 1,668
Total Cats: 63
Default 85mm pistons too big for boost?

The motor I was building had some scoring in the bore. 84mm Supertechs were the plan. Word came back that it needed a little bit more to clean it up totally. So I'm waiting on 84.5mm Supertechs. Apparently they are 3 months back ordered. I can get 85mm ones though. My understanding is 85mm is the MAX bore for these motors and heard 84mm was the top for boosted. Figured 84.5mm was a stretch, but doable. I'm not concerned with rebuilding this block later, I can get another 1.8 block for cheap. Just don't want to do it now since I already have everything done, but the final boring with this block to my knowledge. More concerned with longevity.

So my understanding is this:
-Wait for 84.5
-Order 85mm and get a bigger head gasket and will this mess with squish/detonation/?????
-Is 85mm too big for boosted and make the bores too thin? Punch it big or go home?

The jump from 84mm to 85mm seems to be the break over point for things going weird. Learn me please.

A word with Supertech gives me the idea that the're pistons and big valves work together. Can't find out if the VVT head will work, but they are claying the block to find out. Basically I'm stuck waiting for pistons. Suggestions? Not interested in super pricey pistons, unless they WILL fit the big valves and VVT. The longer this build takes the more random crap I do to this car while it's apart.

Specs:
'99 Block
'01-05 VVT head
FM big radiator with coolant reroute +oil cooler in case it matters for heat concerns with bigger bore
TorqueZombie is offline   Reply With Quote
Old 10-30-2012, 04:11 AM   #2
Supporting Vendor
iTrader: (3)
 
emilio700's Avatar
 
Join Date: May 2005
Posts: 5,326
Total Cats: 1,348
Default

Sonic test it. I like to stay above. 120 for boosted engines, .150 preferable.
emilio700 is offline   Reply With Quote
Old 10-30-2012, 07:00 AM   #3
Senior Member
iTrader: (1)
 
Join Date: Jun 2006
Location: Sweden
Posts: 1,392
Total Cats: 58
Default

Get a new block and use the 84mm in the plan?
NiklasFalk is offline   Reply With Quote
Old 10-30-2012, 09:31 AM   #4
Murderator
iTrader: (76)
 
18psi's Avatar
 
Join Date: Apr 2008
Posts: 36,206
Total Cats: 2,587
Default

What Emilio said. We actually had a thread a while back where Andrew said the same thing: that he sonic tests all his built blocks or something.

I too would be a bit uncomfortable punching it out that much then boosting it. You're walking on thin ice at that point (literally). Even if you can get another block later, you'll be stuck with pistons that most wouldn't want.
18psi is offline   Reply With Quote
Old 10-30-2012, 11:16 AM   #5
Moderator
iTrader: (11)
 
sixshooter's Avatar
 
Join Date: Nov 2008
Location: Tampa, Florida
Posts: 15,691
Total Cats: 1,562
Default

Supertech isn't the only piston company out there either. Better lead times may be available.
sixshooter is online now   Reply With Quote
Old 10-30-2012, 04:17 PM   #6
Elite Member
Thread Starter
iTrader: (6)
 
Join Date: May 2011
Location: Lebanon, TN
Posts: 1,668
Total Cats: 63
Default

I was going to swap to FM's pistons, but aren't big enough. Talking to Supertech they said they do make the valve reliefs for bigger valves. So figured that was my best chance at having them fit +1mm valves. JE is about 8 weeks out for 84.5mm. Might look into CP, but don't know if they would fit bigger valves. I'm not stuck on the big valve thing, just would be nice bonus. Was going with the thought of Supertech pistons and valves being engineered to work together. I admit I may be out of my depth. I haven't kept up with engine internals in years.
TorqueZombie is offline   Reply With Quote
Old 10-30-2012, 04:39 PM   #7
Elite Member
Thread Starter
iTrader: (6)
 
Join Date: May 2011
Location: Lebanon, TN
Posts: 1,668
Total Cats: 63
Default

CP-nope, just 84mm

Wiseco- yes 84.5mm in 8.5-8.8 compression ratios. Seems a bit low for a street car and off boost performance. Maybe a bigger det threshold?

FM- (Wiseco)nope. only 84mm

JE- yes 84.5 and 9-1, but 9-10 weeks out. Would rather wait for the supertechs at that rate unless someone can say they are amazingly better for some reason.

Other ideas? Go custom, wait, or source a new block. Would rather not source an new block. I would have to ship that out of state, and it's a pain around here to source just a block. All I can find around here is full motors.
TorqueZombie is offline   Reply With Quote
Old 10-30-2012, 04:44 PM   #8
mkturbo.com
iTrader: (24)
 
shuiend's Avatar
 
Join Date: May 2006
Location: Charleston SC
Posts: 13,780
Total Cats: 1,107
Default

Quote:
Originally Posted by TorqueZombie View Post
Would rather not source an new block. I would have to ship that out of state, and it's a pain around here to source just a block. All I can find around here is full motors.
What I am afraid of if you go with 85mm pistons is that you will overbore and hone to spec, then sonic test and find out that the walls are to thin to run the pistons. Then you are stuck sourcing a new block anyways and having to go through everything again.

I would source a new block now and just go with 84mm supertechs.
shuiend is offline   Reply With Quote
Old 10-30-2012, 09:28 PM   #9
Senior Member
iTrader: (1)
 
Join Date: Mar 2008
Location: Cromwell CT
Posts: 1,109
Total Cats: 48
Default

my weiscos are 84.5 9.0:1 and im running +1mm valves in and ex with integral r1/r3 cams (.490 lift) and dont have issues, i clayed the pistons when i assembled i dont remember what i got, but i didnt have to flycut the valve pockets
ctdrftna is online now   Reply With Quote
Old 11-01-2012, 03:43 PM   #10
Junior Member
iTrader: (2)
 
Join Date: Nov 2010
Location: NoVa
Posts: 163
Total Cats: 0
Default

Quote:
Originally Posted by TorqueZombie View Post
CP-nope, just 84mm

Other ideas? Go custom, wait, or source a new block. Would rather not source an new block. I would have to ship that out of state, and it's a pain around here to source just a block. All I can find around here is full motors.
CP doesn't have them in stock or won't make them? They made me a set of 85mm pistons in 4 weeks or so...
g_reichow is offline   Reply With Quote
Old 11-01-2012, 11:43 PM   #11
Elite Member
Thread Starter
iTrader: (6)
 
Join Date: May 2011
Location: Lebanon, TN
Posts: 1,668
Total Cats: 63
Default

Yes, I called CP and they will make them for me for surprisingly less than I thought. I'm just going to wait for the Supertechs. I still have some piecing together of parts for other stuff. Basically if I have a motor by X-mas I'll probably still need to finish other things. So either way I'll be waiting. Plus moving soon and not having the engine here is one less thing to move. It's the waiting that kills.
TorqueZombie 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
New M62 Miata owner Pist0n Meet and Greet 4 10-01-2015 09:18 PM
Going back to stock. Need some 1.6 parts. Trent WTB 2 10-01-2015 01:15 PM


Tags
85mm, big valve, pistons, supertech

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 07:15 AM.