bbundy

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?

Savington

iTrader: (31)

You have valve springs, the head is off, the labor is minimal to swap. Why risk it?

bbundy

Yea that donned on me. Ill just move the valve springs over.

Twodoor

iTrader: (2)

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

DNMakinson

iTrader: (3)

Along with oil pump issues:

old thread

There was something more recent, but this, I think, answers your question.

curly

iTrader: (25)

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.

Leafy

iTrader: (1)

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.

guttedmiata

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.

Leafy

iTrader: (1)

With boost it doesnt matter, just run more of it. If 20psi isnt flowing enough air mass through the head, 25psi might.

Twodoor

iTrader: (2)

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

soviet

iTrader: (10)

story of my car

bcrx7

iTrader: (5)

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!

Leafy

iTrader: (1)

You can also use the rope trick. where you fill the cylinder with rope (or string) to hold the valves up.

bcrx7

iTrader: (5)

Yes! Specially if your cylinder has leaks as it would suck to find out the valves have fallen in after 15minutes

Fireindc

iTrader: (13)

Interesting. Anyone ever try this with a balloon or similar?

guttedmiata

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.

Savington

iTrader: (31)

How would a higher rev limit help you in normal driving? Do you rev it to 7k on every shift?

Twodoor

iTrader: (2)

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

Leafy

iTrader: (1)

Volume doesn't matter, Mass does.

hankclaussen

iTrader: (5)

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