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Old 01-29-2008, 11:54 AM   #1
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Default boring out engine block

Anyone here ever bored out a 1600 (1598cc) block?
IF so how much did you go?
I have a rebuild ongoing and plan to bore out and FI (10-12psi) an engine i have in the garage.
I can source 1mm =(1640cc) ,1.5mm=(1660cc) and 2mm=(1680cc) oversize pistons in comp ratio,s from 8.5;1 to 9.4;1- but i wasnt sure if i really wanted to go out as far as 2mm oversize.

Any help/info greatly appreciated
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Old 01-29-2008, 12:00 PM   #2
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Most people go .5mm, some push it to 1mm without issue. I wouldn't go any further than that, thing was already bored out from a 1300cc
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Old 01-29-2008, 12:15 PM   #3
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Mine is .5... I was originally going to go 1mm, however, if something ever happens to the motor, you want to allow some space.
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Old 01-29-2008, 01:01 PM   #4
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If you don't need to do it, then why if you'll run boost? The power gain is insignificant IMO. I've done two 1.6s - one to .040"/1mm and the other to .020/.5mm - but neither were boosted.
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Old 01-29-2008, 01:52 PM   #5
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Quote:
Originally Posted by m2cupcar View Post
If you don't need to do it, then why if you'll run boost? The power gain is insignificant IMO. I've done two 1.6s - one to .040"/1mm and the other to .020/.5mm - but neither were boosted.
If the engine is being rebuilt, you might as well do it right the first time IMO. If your doing it just for the sake of it.... nah.
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Old 01-29-2008, 01:58 PM   #6
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Yea it's a hard call to make. Larger bore and pistons adds displacement, which is great. However, it's not much, but it's some. If you had to choose a header that gave you 3hp or 5, which would you choose? Still, larger pistons are heavier, so smaller is lighter and that's a plus. If you punch it out to the max, you won't be able to rebuild that block again without sleeving it.

FWIW, if you do bore it out to the max, you can also open up the combustion chambers on the head to reflect the new bore, and gain some power there as well, as you can unshroud the chambers. If it were me I'd punch it to the max.
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Old 01-29-2008, 02:44 PM   #7
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Quote:
Originally Posted by patsmx5 View Post
Yea it's a hard call to make. Larger bore and pistons adds displacement, which is great. However, it's not much, but it's some. If you had to choose a header that gave you 3hp or 5, which would you choose? Still, larger pistons are heavier, so smaller is lighter and that's a plus. If you punch it out to the max, you won't be able to rebuild that block again without sleeving it.

FWIW, if you do bore it out to the max, you can also open up the combustion chambers on the head to reflect the new bore, and gain some power there as well, as you can unshroud the chambers. If it were me I'd punch it to the max.
Its a "second/spare" engine and not a daily driver either - so i,m not overly concerned about having to ever re-work it ,if it ever died.
Think i,ll stick with 1.5mm oversize 9:1 wiseco,s.
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Old 01-29-2008, 02:55 PM   #8
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1.5 is a pretty thin wall...1 should be plenty and allow you the piece of mind.
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Old 01-29-2008, 04:01 PM   #9
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My point being for the cost of an overbore that cash could go elsewhere and sure reap more benefits (that and thinning the cylinder walls isn't so desirable for boost).

I've got a 40-50k mile block that I'm using for my next engine build. It's getting a different crank, pistons, rings and rods - so in effect a rebuild. and the cylinder walls look absolutely new, the bores perfectly round - I'm not gonna touch 'em. I'll put that money towards the forged pistons.
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Old 01-29-2008, 04:13 PM   #10
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Quote:
Originally Posted by m2cupcar View Post
My point being for the cost of an overbore that cash could go elsewhere and sure reap more benefits (that and thinning the cylinder walls isn't so desirable for boost).

I've got a 40-50k mile block that I'm using for my next engine build. It's getting a different crank, pistons, rings and rods - so in effect a rebuild. and the cylinder walls look absolutely new, the bores perfectly round - I'm not gonna touch 'em. I'll put that money towards the forged pistons.
Aye- fair comment
maybes best with the 1mm o/b then.
what crank you going for m2cupcar?
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Old 01-29-2008, 04:26 PM   #11
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I agree- IF it needs an overbore go minimal. Boost changes everything.

I'm going to run an F2T crank in an FE block = 2200cc with stock FEdohc rods and either venolia or wiseco forged pistons.
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Old 01-29-2008, 04:43 PM   #12
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if your just trying to acquire some displacement then bore a 1.8 since it will not be daily driven it is not needed immediately right?
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Old 01-29-2008, 04:44 PM   #13
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True on a boosted motor, there is more heat and thicker cylinders would be better suited to handle the additional heat and loads. If it was a NA motor, I'd bore it to the max, but since it's an FI motor, just whatever it takes to punch them square and slaper' back together. Does anyone know how thick the cylinders are or the centerline?
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Old 01-29-2008, 04:59 PM   #14
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http://forum.miata.net/vb/showthread.php?t=216610
Have you guys forgoten Motorworx and his 1.6?
1991 1.6

Familia B6T block with oil squirters
B6T oil pump
Stock crank and rods
Arias 81.5 mm pistons for Toyota 4AG
TODA 1mm X 81.5mm MLS head gasket
HKS 264 hydraulic cams
Sheetmetal intake manifold/60mm SR20 throttle
HKS cast T2 exhaust manifold
Innovative Turbo wastegate
Custom built T28 turbo (originally GTiR SR20)
Custom down pipe and full 75mm exhaust
Custom intercooler using two late-FC3S cores in vertical.
Aluminum piping 60mm on hot side and 70mm on cold side
OS Giken twin plate clutch with custom discs
FD3S RX7 transmission
BP differential with Kaaz LSD
SDS EFI management with Denso 700cc/min injectors
Walbro 255 liter fulel pump

336.6 RWPS (332 RWHP)
272 lb.
1.3 bar
Quote:
Originally Posted by Scott Hayden
I did not think you could bore a 1.6L that wide. Mine is bored 1.5mm over using 79.5mm wiseco's.
Quote:
Originally Posted by Motorworx
TODA Racing in Japan doesn't even sell a piston for the B6 under 81mm. I cut several blocks in half, many years ago, to check cylinder wall thickness, and there's a lot there. I go as large as 81.5 and have never has a cylinder wall problem, even through 9,000 rpm.
This setup gives him about 1744.5 cc
I seems to have worked fine for him Also i had no issues when i went .40 over.
Stock bore is 78 mm

Last edited by magnamx-5; 01-29-2008 at 05:17 PM.
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Old 01-29-2008, 06:16 PM   #15
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YAY THERE IS HOPE FOR MY BORKE *** YET!!!!11!1
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Old 01-29-2008, 06:17 PM   #16
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I think it's a little different when you're a mechanical/fabrication wizard. And when going that extreme in an overbore, you're supposed to sonic test every cylinder for wall thickness. That way you avoid falling victim to any casting defects. What he did is just plain nuts vs. swapping in a 1.8 IMO. All I'm saying is if it's NOT needed to straighten out the bore, it doesn't make sense to put the dough there on a boosted engine.
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Old 01-29-2008, 06:36 PM   #17
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Quote:
Originally Posted by magnamx-5 View Post
http://forum.miata.net/vb/showthread.php?t=216610
Have you guys forgoten Motorworx and his 1.6?
1991 1.
Arias 81.5 mm pistons for Toyota 4AG


336.6 RWPS (332 RWHP)
272 lb.
1.3 bar


This setup gives him about 1744.5 cc
I seems to have worked fine for him Also i had no issues when i went .40 over.
Stock bore is 78 mm
Yikes- 3.5mm oversize, i wouldnt have thought it possible after looking at the "meat" between the clinders on my block, But hey works for him.
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