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Piston damage analysis

Lol pull timing, I run microsquirt sans knock sensors. It's been a joy since I've lowered the compression back to 8.5-1. I tried tight squish, I got tired of changing head gaskets, the head got so thin the timing belt was getting loose. It'll turn over the 275/40/17' hankook rt615's no problem 3.35 1st gear T5/3.91 rear modded G80. B21F+t, B21 intake manifold.

Just getting theoretical on your ass. :-P
 
No spacers on the small end, if they rods are crank steered.

if the rods are crank steered, you don't need them (but they wouldn't hurt either).

Thanks guys, learning so much new stuff.

Emailed maxspeedingrods, and they are indeed to correct ones with a 23mm little end. They promptly gave me a little discount and free shipping, awesome. Put in the order and they should be here within about a week.

So excited, this engine is gonna be close to bulletproof :). Well apart from the discussion that is the compression ratio of course :), but hey, if need be, that can easily be fixed. At least the bottom end is solid.
 
Don't need a machine shop to tell you if it needs bored, just buy a set of telescoping guages and measure the bore in the thrust direction and perpendicular. Check against specs and make the call.

Sure, but I could't easily get my hands on a decent bore gauge and he offered to measure it, so win win. Oh and also I wanted a pro to judge the ring ridge.
 
Lol pull timing, I run microsquirt sans knock sensors. It's been a joy since I've lowered the compression back to 8.5-1. I tried tight squish, I got tired of changing head gaskets, the head got so thin the timing belt was getting loose. It'll turn over the 275/40/17' hankook rt615's no problem 3.35 1st gear T5/3.91 rear modded G80. B21F+t, B21 intake manifold.

Nice, good to hear, that's some serious rubber. That reminds me, need to check if my car is fitted with a G80, getting tired of those one wheel peels:).
 
Higher compression ratio does result in more thermodynamic efficiency, meaning more power out of boost. Doesn't mean your car wont run with lower compression. Higher compression will be more prone to knocking meaning without a proper ignition map for the compression your ECU may pull timing and negate the gains from higher compression.

Actually one of TB smart-er-er guys Janne aka Wagner posted some years ago some data that showed un-optimal ignition timing/curve costs more than lowering comp to some reasonable level...
the thing that hasn't seemed to penetrate here very widely is what the Honda and VW/Audi boys can get away with with their little 81-82mm bores and so many really nice motors like 3GSE, SR20DE and SR20DET, GMs XE 16v, E36 M3, and the latest Evo 10 and FJ Subie and a pile of French hot 2,0s with their "ideal" 86mm bore, 86mm stroke and pent-roof heads with that spark plug right in the middle,, is not saying that "we" with the relatively huge 92 and 96mm bores and a spark plug way over on one side, can do the same in terms of compression and boost...

I know a whole lot of experts sneer and say "I ran 9.8 and XX boost for years and I drove 110% every day and every shift..and never had any problems, so neener neener.."
Fine..
Everybody is always right..
Everybody's opinions are all exactly equal.

me though I'd prefer 8:1 and some fun boost and good ignition curve than be worrying about blowing rign lands out with no warning..
 
This is true, everyone's opinions are equal. Which means yours is equally as worthless as mine :-P
All the high compression stock engine GM guys would beg to differ on the CR discussion, as do many tuners.


So, if you're like John, and you don't know how to tune (or how/where to ask for help) by all means go low and slow. As they say, ignorance is bliss. If you don't know what you're missing, you'll never miss it. :roll: I don't see any honda comments. Your straw-man is weak and so are you old man!

Me personally, I tow the fast car with the 10:1 turbo car (that's a 96mm bore size x 8 for the kids at home, with 2v heads sitting on top. They're aluminum too). It's a new swap, I've only put 3 years on it and only had a few runaway boost situations. Hasn't been out yet (but soon. stupid lifters, stupid transmission. Stupid car that blows the tires off from an 80mph roll) :godlike:


Anyway, Some of us actually do these things much to the chagrin of others, and a lot of us that do, have great success with it-again, much to the chagrin of others. Personally, I feel that low compression is a band-aid for ****ty engine management and ****ty tuning, and it comes at a cost. Perhaps just a transient cost, but a cost none the less. If you're running a system that isn't always repeatable in what it does (looking at you, LH), or one that's almost as old as John (looking at you, K-jet), then sure. You have little to no control except gross adjustments and prayer. Run low compression and be satisfied with mediocre results if that's the case.


What is "a fun amount of boost" anyway? That's a non-sequitur. Either the setup makes power or it doesn't, boost is just a number. Is 10psi boring boost and 20psi fun boost? On what turbo? What about 30psi? Is 15psi then just garden variety boost? Inquiring minds need to know :omg:


This is all meant somewhat tongue-in-cheek, like I said several posts up, your car, do whatever you want with it. If you really want to set john off on a tangent, start telling him that longer rods suck :lol:
 
It might be easier and cheaper for the average turbobricker to get god results with compression ratios in the lower spectrum. A stock ancient 7.5:1 b21 longblock can easily give you 350whp with enough boost, timing and a few bolt-ons (90+ mani and na k-jet intakte) . Not the best powerband, but it works and is cheap ����
 
I got plenty of experience in breaking piston ring lands over more than one setup, large turbo and NA :D

I would definitely agree that the tuning / timing mapping is the most important ingredient. What is optimal completely depends on the specific combination of hardware you have - turbo sizing, optimal boost range for that turbo, head flow, etc., etc. Much better to start with a more conservative timing map in your engine's peak torque range & then add carefully using logging or det can. I would have saved myself much headache & head gasket failures (in addtion to the broken pistons) if I had heeded that advice much earlier :D

Dropping compression makes off boost driving miserable.
 
I got plenty of experience in breaking piston ring lands over more than one setup, large turbo and NA :D

I would definitely agree that the tuning / timing mapping is the most important ingredient. What is optimal completely depends on the specific combination of hardware you have - turbo sizing, optimal boost range for that turbo, head flow, etc., etc. Much better to start with a more conservative timing map in your engine's peak torque range & then add carefully using logging or det can. I would have saved myself much headache & head gasket failures (in addtion to the broken pistons) if I had heeded that advice much earlier :D

Dropping compression makes off boost driving miserable.

I thought reliability and longevity were maybe the most important..:oops:

And the last line "dropping compression"...Truthiness award contender ya got there>

8.0:1 on a B21 is raising compression.
And the all the yakitty yack about compression is more truthiness..
Compression ratio depends on when intake valve closes...everybody ought to know that, so talk of compression ratio without reference to intake valve closing is just flapdoodle..
And in the context of a turbo motor compression ratio must be looked at as a variable thing: it all depends on the volume of additional air that gets crammed into the engine.

So driveability on or off boost depends on cam timing and when the turbo begins cramming more volume of air in...

I've driven Redblocks with 8.0 and T cam and off boost they are fine..and when the turbo begins to spool at 2200 they drive more fine.

All this fapp-talk and nobody even mentioned what I consider the Number1 variable and that is hanging over everything: which fuel?

Whatever, carry on fapping..
 
Mine is 8.5-1 I don't suffer any of those characteristics. Have you driven an 8.5-1 car to know what your talking about or just repeating what you've read on the all knowing internets?
I've heard more from an engine builder who has done race engines a couple of decades than read from the internet:-P

I've had a reasonably powerful whiteblock with T6 pistons meaning 8.5 compression, and the same engine with Wiseco and 9.5 compression. There is a noticeable difference and 9.5 gave a sligthly better fuel economy too. Though it had only 700hp with T6 pistons and 800hp with Wiseco, both on E85.
 
I thought reliability and longevity were maybe the most important..:oops:

And the last line "dropping compression"...Truthiness award contender ya got there>

Desire for reliability & longevity are a given, no? Otherwise the criteria under discussion really wouldn't matter.

I'm referring to personal experience. Raising static compression (using established measurement criteria) improved power/response in off-boost performance. Also improved dramatically the performance of my NA Fiat :) Cam timing & lift are other variables, obviously.
 
Desire for reliability & longevity are a given, no? Otherwise the criteria under discussion really wouldn't matter.

I'm referring to personal experience. Raising static compression (using established measurement criteria) improved power/response in off-boost performance. Also improved dramatically the performance of my NA Fiat :) Cam timing & lift are other variables, obviously.

Static compression limits your dynamic compression under boost. There's a limit to how much you can raise the pressure in the combustion chamber before detonation happens regardless of timing. See diesel engine for more information. I love my n/a Toyota with 11.5-1 from the factory but it won't take more than about 7psi (anecdotally, mine is not boosted) before bad juju happens. People who boost the 2zz-ge, monkey wrench racing specifically, lower compression to 8.5-1 and use Carrillo rods to replace the factory H beams. They have a 400hp 1.8l Celica that does 202mph but it's doesn't have 11.5-1 compression ratio I guarantee it.

Here's my 8.5-1 B21F, doesn't seem too laggy to me but maybe you can point out where it's suffering
<iframe width="560" height="315" src="https://www.youtube.com/embed/TGXmH6EnPZQ" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>
 
Desire for reliability & longevity are a given, no? Otherwise the criteria under discussion really wouldn't matter.

I'm referring to personal experience. Raising static compression (using established measurement criteria) improved power/response in off-boost performance. Also improved dramatically the performance of my NA Fiat :) Cam timing & lift are other variables, obviously.

Fiat head like this one?
31732245.jpeg.jpg


That combustion chamber? Yes i see now..It's exactly the same shape and configuration as a B230 8v head..same plug location, same 96mm bore...or real close..72mm..
But I see how the direct, personal experience is transferable to this discussion..
I can see how burning all the way across 36mm from plug to cylinder would take the exact same time as burning across 96mm with the plug over on one side.
Diameter and plug being completely irrelevant to the time for flame front to propogate over a distance.

You win.:nod:
 
Static compression limits your dynamic compression under boost. There's a limit to how much you can raise the pressure in the combustion chamber before detonation happens regardless of timing. See diesel engine for more information. I love my n/a Toyota with 11.5-1 from the factory but it won't take more than about 7psi (anecdotally, mine is not boosted) before bad juju happens. People who boost the 2zz-ge, monkey wrench racing specifically, lower compression to 8.5-1 and use Carrillo rods to replace the factory H beams. They have a 400hp 1.8l Celica that does 202mph but it's doesn't have 11.5-1 compression ratio I guarantee it.

Here's my 8.5-1 B21F, doesn't seem too laggy to me but maybe you can point out where it's suffering
<iframe width="560" height="315" src="https://www.youtube.com/embed/TGXmH6EnPZQ" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>

Terrible..Barely drivable off boost, it almost looks like the car is going backwards.

Poor thing!

As for above the question of what that limit is is really hard..Well it seems to be hard for OEMs...But then again they may computer model swirl and tumble and and every varible possible that because they aren't on enthusiast forums because they're stuck in some old era, not like the kids here! Oh if only they'd listen...

By the way have you done any calcs for dynamic compression with 1 or even better 2 bar boost? That black thing sitting over <-------- there has 8:1 static, is mapped for 2 bar boost and peak torque is somewhere around 3200.....and whn that thing with those cams (very mild cams, like 199 dur @ 050) the dynamic compression is like 21.65:1...really..
That's where the yank comes from. Its geared stock more or less like any other road car..I never noticed any difficulty or unpleasantness driving it around off boost --then again it seem to want to make boost even from very low rpm....
 
Are we conflating the effect of intake pressure with dynamic compression ratio? No one was talking about cams.

Not aimed at you John, just the discussion in the last two pages.
 
That combustion chamber? Yes i see now..It's exactly the same shape and configuration as a B230 8v head..same plug location, same 96mm bore...or real close..72mm..
But I see how the direct, personal experience is transferable to this discussion..
I can see how burning all the way across 36mm from plug to cylinder would take the exact same time as burning across 96mm with the plug over on one side.
Diameter and plug being completely irrelevant to the time for flame front to propogate over a distance.

You win.:nod:

No, I'm talking about 70's OHC 8v technology - my X1/9 is cast block/OHC 8V aluminum head just like the redblock. I didn't think you jumped to conclusions so readily.

X19_0073d.jpg
 
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Chaps, question about the ring gaps.

Looking at the little sheet that came with the piston kit: here.

I think I fall under the "Street moderate Turbo/Nitrous" category.
That would mean:
1th ring - - - - 0.0050 per inch - - - - - would mean about 19 thou
2nd ring - - - 0.0055 per inch - - - - - would mean about 21 thou

Does that sound about correct? I'm seeing numbers much higher scattered around the forum.
 
Chaps, question about the ring gaps.

Looking at the little sheet that came with the piston kit: here.

I think I fall under the "Street moderate Turbo/Nitrous" category.
That would mean:
1th ring - - - - 0.0050 per inch - - - - - would mean about 19 thou
2nd ring - - - 0.0055 per inch - - - - - would mean about 21 thou

Does that sound about correct? I'm seeing numbers much higher scattered around the forum.

Don't set it up with too little gap! I've seen what that does! "It lacks power when under load; stalls and won't turn until it has cooled off."
That one earned the name "Miracle rebuild." It got sleeved after the new rings oversized the cylinders. Doh!

Follow instructions to the letter + .001" cuz yer a savage.
 
I'd set it up a little on the loose side myself as well. if you hit it with enough smack, the gap will tighten up a bit ;)
 
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