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? |
You have valve springs, the head is off, the labor is minimal to swap. Why risk it?
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Originally Posted by Savington
(Post 1159348)
You have valve springs, the head is off, the labor is minimal to swap. Why risk it?
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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 |
Originally Posted by Twodoor
(Post 1159534)
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 old thread There was something more recent, but this, I think, answers your question. |
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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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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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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Originally Posted by guttedmiata
(Post 1159677)
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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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 |
Originally Posted by Leafy
(Post 1159678)
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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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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Originally Posted by bcrx7
(Post 1159713)
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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Originally Posted by Leafy
(Post 1159719)
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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Originally Posted by Leafy
(Post 1159719)
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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Originally Posted by Leafy
(Post 1159678)
With boost it doesnt matter, just run more of it. If 20psi isnt flowing enough air mass through the head, 25psi might.
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. |
Originally Posted by Twodoor
(Post 1159681)
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 |
Originally Posted by Savington
(Post 1159854)
How would a higher rev limit help you in normal driving? Do you rev it to 7k on every shift?
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 |
Originally Posted by guttedmiata
(Post 1159853)
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. |
Originally Posted by Twodoor
(Post 1159859)
Doesn't everyone? :D 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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