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?

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

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.

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.

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.

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.

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

story of my car :)

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.

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

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

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.

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

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

Volume doesn't matter, Mass does.

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

I am running 195/50/15's but they seem to be a bit "short" compared to their theoretical 22.7" diameter. Either that or my tachometer is off :)

Interesting side note. With MS3 is the tachometer driven by the MS3? I ask because Data logs show tachometer to be accurate at idle, and my rev limiter is currently set at 7200 and that is where it kicks in on my tachometer... but data logs showed only 7000 when limiter kicked in.

If the car wasn't torn apart for my BEGi S6 installation I would go out and data log speed vs RPM (steady state runs vs quick run through gears like most of my logs) to see what I could dig up.

Later,

Keith

I really don't use all the revs to do fast laps on the track. Although judging by the fact that the video I took when I screwed up this motor at Pacific I was heading for running out of 6th gear with the 3.636 rear end. Rapidly rising speedometer was just reaching the 140mph mark I was already in 6th gear and hadn't reached the kink yet still had half the front straight left. It dropped power and my instinct was to upshift which turn turns out doesn’t work from 6th and I went to 5th. New repave of turn 8 just puts you on the front straight stupid fast would have liked to have gotten a full lap I think I would have crushed it.. I discovered my timing I think jumped advanced about 6 degrees somehow and knock sensor flaked out.

What the 8600 rpm rev limit is for is autocross. Its way past the power band but it allows me to reach high enough top speed without shifting and yet I have a gear that I have instant throttle and boost response coming off any slow mid or high speed autocross corner in second gear. The initial acceleration is way more important for autocross than running it out past the bulk of the powerband. It’s been working real well for me this year I should have planned to go to Lincoln my Pax performance against national level drivers this year says I should be in the mix at the top. I'm contemplating focusing on autocross next year seeing how far I can go.

I’ve changed valve seals in the car without removing the head before. Rope down the spark plug hole used the piston to hold the valves up and I made a tool that I could lean against with my chest to compress the valve springs while I dealt with the callets retainers. Worked quite well actually seemed easier than having the head off and using a valve spring compressor.

Unfortunately this time the head needs to come off. Pretty sure combustion gasses are making it from the combustion chamber to the water jacket under load I don’t think it’s going through the head gasket. Combustion chamber had seen enough force to knock a hole in a piston. Rods and rod bearings looked fine however.