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Old 06-09-2018, 08:58 PM   #51
lookforjoe
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Originally Posted by John V, outside agitator View Post
I thought reliability and longevity were maybe the most important..

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.
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Old 06-09-2018, 09:24 PM   #52
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Originally Posted by lookforjoe View Post
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
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Old 06-10-2018, 01:16 AM   #53
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Quote:
Originally Posted by lookforjoe View Post
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?


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.
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Old 06-10-2018, 01:27 AM   #54
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Originally Posted by VB242 View Post
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
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....
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Old 06-10-2018, 01:43 AM   #55
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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.
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Old 06-14-2018, 10:21 AM   #56
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Originally Posted by John V, outside agitator View Post
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.
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.


Last edited by lookforjoe; 06-14-2018 at 10:31 AM..
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Old 06-15-2018, 07:29 AM   #57
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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.
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Old 06-15-2018, 03:34 PM   #58
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Originally Posted by OkeyDan View Post
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.
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Old 06-15-2018, 03:53 PM   #59
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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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Old 06-16-2018, 03:44 AM   #60
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Understood, thanks.

I will set it up 1 or 2 categories higher.
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