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Old 08-20-2014, 02:40 PM   #1
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Default RPM limit of a stock 99 head?

So it looks like I toasted my head maybe a crack in the combustion chamber as well as blowing a hole in a piston during my on track catastrophe a few weeks ago. As rebuilt bottom end I believe started pressurizing the coolant system with combustion gas. Don't think its going through the head gasket.

Going to put basically a stock head on for a while on my built 2.0L and wondering how much I need to lower the rev limit if at all. I was running up to 8600 rpm I might move the stiff valve springs over and not worry about it. I also have a set of OEM sodium filled GTR exhaust valves I'm considering using but Id have to re-shim it.

Anybody have any hard evidence where the stock springs start to not work?
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Old 08-20-2014, 04:01 PM   #2
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You have valve springs, the head is off, the labor is minimal to swap. Why risk it?
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Old 08-20-2014, 06:20 PM   #3
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You have valve springs, the head is off, the labor is minimal to swap. Why risk it?
Yea that donned on me. Ill just move the valve springs over.
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Old 08-20-2014, 11:31 PM   #4
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Now for those of us with no handy dandy springs to move over, what is the answer? So far I have maintained the stock redline in my MS3, but I know that after I get the forced induction installed over the next couple days the temptation to go to higher revs will be singing it's siren song in the back of my head... so how far is too far on stock head and block?

Keith
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Old 08-21-2014, 08:25 AM   #5
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Now for those of us with no handy dandy springs to move over, what is the answer? So far I have maintained the stock redline in my MS3, but I know that after I get the forced induction installed over the next couple days the temptation to go to higher revs will be singing it's siren song in the back of my head... so how far is too far on stock head and block?

Keith
Along with oil pump issues:

old thread

There was something more recent, but this, I think, answers your question.
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Old 08-21-2014, 09:56 AM   #6
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In less you're going for insane lap times like Bob, there's no point. BPs are crying for mercy at 7,000 rpms, I can't imagine what they feel like at 8,600. Very m.net post, yuck.
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Old 08-21-2014, 11:48 AM   #7
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The stock 99 head valve floats somewhere around 8300-8400 rpms, thats about all I can say. And even running with an 8k rev limit the car I dealt with dropped a valve due to a failed valve spring retainer clip after a couple years of auto-x.
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Old 08-21-2014, 12:36 PM   #8
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If it's a stock head it isn't going to breath decent above 7k anyway. Especially if it's got a bunch of extra air being crammed into it.
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Old 08-21-2014, 12:38 PM   #9
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If it's a stock head it isn't going to breath decent above 7k anyway. Especially if it's got a bunch of extra air being crammed into it.
With boost it doesnt matter, just run more of it. If 20psi isnt flowing enough air mass through the head, 25psi might.
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Old 08-21-2014, 12:42 PM   #10
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The rev limit question from me has more to do with a 6 speed in a car with the stock 4.3 ring and pinion... I currently drive it as a 3 speed using 2, 4, and 6 for normal daily driving. A bit more RPM would make it more livable until I can source a 3.636.

Keith
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Old 08-21-2014, 01:27 PM   #11
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Quote:
Originally Posted by Leafy View Post
With boost it doesnt matter, just run more of it. If 20psi isnt flowing enough air mass through the head, 25psi might.
story of my car
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Old 08-21-2014, 02:12 PM   #12
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You can technically change the valve springs with the head on by pressurizing the cylinder with air at TDC and removing the springs and swapping them over!
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Old 08-21-2014, 02:20 PM   #13
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You can technically change the valve springs with the head on by pressurizing the cylinder with air at TDC and removing the springs and swapping them over!
You can also use the rope trick. where you fill the cylinder with rope (or string) to hold the valves up.
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Old 08-21-2014, 02:49 PM   #14
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You can also use the rope trick. where you fill the cylinder with rope (or string) to hold the valves up.
Yes! Specially if your cylinder has leaks as it would suck to find out the valves have fallen in after 15minutes
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Old 08-21-2014, 03:05 PM   #15
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You can also use the rope trick. where you fill the cylinder with rope (or string) to hold the valves up.
Interesting. Anyone ever try this with a balloon or similar?
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Old 08-21-2014, 09:15 PM   #16
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Quote:
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With boost it doesnt matter, just run more of it. If 20psi isnt flowing enough air mass through the head, 25psi might.
I would love to see dyno results with a stock head that continues to climb past 7k. Everything I've seen starts to drop around 6800.

I'm also pretty sure that if it's capable of 25 psi it's already there. Your logic says the head doesn't matter, I'll just run 100 psi. You can't cram more air into chambers and runners that won't take more air. It isn't psi, it's volume.
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Old 08-21-2014, 09:27 PM   #17
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Quote:
Originally Posted by Twodoor View Post
The rev limit question from me has more to do with a 6 speed in a car with the stock 4.3 ring and pinion... I currently drive it as a 3 speed using 2, 4, and 6 for normal daily driving. A bit more RPM would make it more livable until I can source a 3.636.

Keith
How would a higher rev limit help you in normal driving? Do you rev it to 7k on every shift?
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Old 08-21-2014, 09:49 PM   #18
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How would a higher rev limit help you in normal driving? Do you rev it to 7k on every shift?
Doesn't everyone? Just kidding.

OK, so it might not help in the daily driving, but at the drag strip toping out 5th gear will get me to 105 mph, revving it out to 7500 would get me to 113 mph. At my race weight 250 whp should have me trapping around 108...

Later,

Keith
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Old 08-21-2014, 10:09 PM   #19
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Quote:
Originally Posted by guttedmiata View Post
I would love to see dyno results with a stock head that continues to climb past 7k. Everything I've seen starts to drop around 6800.

I'm also pretty sure that if it's capable of 25 psi it's already there. Your logic says the head doesn't matter, I'll just run 100 psi. You can't cram more air into chambers and runners that won't take more air. It isn't psi, it's volume.
Volume doesn't matter, Mass does.
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Old 08-21-2014, 10:35 PM   #20
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Quote:
Originally Posted by Twodoor View Post
Doesn't everyone? Just kidding.

OK, so it might not help in the daily driving, but at the drag strip toping out 5th gear will get me to 105 mph, revving it out to 7500 would get me to 113 mph. At my race weight 250 whp should have me trapping around 108...

Later,

Keith


What tire size are you running? I am having trouble making sense of these numbers given the ratios and using FM's calculator page.
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