k24madness

iTrader: (6)

After running my new motor about 10hrs I checked leakdown, compression and valve lash. I lost all of my valve clearances on 3 or 4 intake valves. Several others were also very tight. The number 4 cylinder was the worst causing 20% leakdown. After removing the shims it came back to 98%.

I pulled the head and had a local machine shop check the valves. He said several were not "square" and recut them. He also had to "reface" the #4 valves. After further though I opted to replace all 8 intakes. I did not feel I could trust them after that.

So the million dollar question is why did this happen? None of the exhausts were affected. I am running the same cams/springs (supertech heavy doubles) on both exhaust and intake.

I called supertech and they suggested it was from valve float. If that were true why just the intakes? Would the 11-12 PSI of boost cause the intakes to float sooner than the exhaust? Is the valve more susceptible to distortion due to it's size and back cut stem?

Redline was set at 8k. It did see 9,200 a few times due to driver error.
The other possible clue is very very very slight traces of detonation on the plugs. The strongest one being #4. Would a detonation hit cause the valve face to distort?

My plan is to add a 030 shim to intake springs and increase valve spring pressure slightly, replace all valves. Address fueling problems to eliminate any detonation possibilities.

For those curious about the detonation the car runs E85, 1000cc ID's with low rail pressure. Because of the low rail pressure the injectors are maxed out now. The car also runs lean when fuel gets low. Both of those issues will be solved before running again.

Why say you arm chair engine builders? I could have sworn TNT had issues with his supertech valves too. The guys at supertech said they see this sometimes but only on intake valves. I would expect the exhaust to be the weaker one due to heat.

Savington

iTrader: (31)

AFAIK exhaust seats are cut wider so I would expect the intakes to show weakness first. You also have the mass/velocity of the air as well as boost to contend with on the intake side. IIRC you have cams so you'll know whether your intake ramps are different than your exhaust ramps. Are you using heavy doubles or something else?

18psi

iTrader: (76)

you overspun it and ran it way too lean
the symptoms make sense

k24madness

iTrader: (6)

Intake and exhaust cams are the same. Shorter duration with high lift = pretty aggressive ramps. I am running the supertec heavy doubles.

Do you feel it's all related to valve float?

k24madness

iTrader: (6)

I would not go so far as to say "way to lean" It was consider safe by the tuner but less than ideal. I trust his opinion! I think the starvation in the corners is what prompted the detonation. Surge tank will solve that.

Savington

iTrader: (31)

It's basically the only way to mess up the intake valve in that way. Even if you are pushing as hard as you can (via det) on the face of the valve, the valve will still ride on the backside of the camshaft and close at the same velocity it normally does. The cam is what closes the valve, the spring's job is purely to hold the valve and bucket against the cam lobe. Damage happens when the valve isn't contacting the cam when it closes, and the only way to do that is to float it.

It sounds like your cam ramps could be too aggressive for the springs.

k24madness

iTrader: (6)

Ok so then that means some more spring pressure. The shims supertech is sending will bump seat pressure by 7psi.

ctdrftna

iTrader: (1)

What are your cam specs? I took the inner springs out of my supertechs to get the spring pressure to integrals specs for my big cams. I can't see you running out of spring pressure on such low boost unless your running in the .490 lift with very low duration.

I think its a little more to do with the over rev than anything else.

TNTUBA

iTrader: (1)

I had this exact issue. When we NDIed everything it was apparent that it was valve bounce in the seat....not float over the nose. We determined that the seat pressure was too weak to hold the valve on the seat against the boost pressure we were seeing. (Pretty simple math, area of the valve in square inches x PSI subtract that number for your seat pressure and you have your "real" seat pressure) As the valves were bouncing on the seat they were literally lapping themselves and eroding the seat. I found it by keeping an eye on valve clearance between races.

I was using weak springs and stock valves at the time. I went up to a much heavier spring and stainless valves on the intake side and have had no issues since...even with increased boost pressure and increased RPM.

k24madness

iTrader: (6)

Thanks for all the feedback guys. All indications point to valve float/bounce. I'll double check seat pressures and make sure they are within spec. I will also install the 030 shims as per supertechs recommendation. I kinda remember there being a copper shim with the valve supertech heavy double spring kit. It would not surprise me if the first shop left them out. At 74lbs seat pressure (specs) I would not expect to be having a problem.

k24madness

iTrader: (6)

Update: I just spoke to an engine builder who said that "Web Cam" cams have very aggressive ramps and need a LOT of spring pressure, He said they make great power but are hard on the valves when getting up there in RPM's. On the otherhand the intergal cams require much less spring pressure. He runs supertech singles and runs miata motors up to 9k with them.

Even with all the above in mind he thinks the problem is detonation. It does not take much to distort (tulip) the valves.

With all the above in mind I will solve the problems and keep a close eye on the plugs for detonation signs and watch valve clearances closely. If the problems continue after fixing the detonation I will choose a milder cam design.

Twibs415

iTrader: (8)

Just ran into the same thing sorta. intake valve number 2 over sized supertech got mushed. The head does have narrow seats so maybe this one was a bit to narrow plus i zinged the motor pretty good a few times. was running a msm cam, supertech singles and SUBs.

Ill widen the seat a hair and drop in a new valve. im putting in custom ground cams and supertech doubles. car is N/a. we will see in a year when it comes apart again.

k24madness

iTrader: (6)

Ok the problem became a bit clearer this week. The original head builder left out the stock lower spring seats. This reduced the supertech heavy doubles to 62lbs instead of the 74lbs desired. Now subtract from that the 16.6lbs of force (boost *valve area) from the supercharger against the valve and you can easily see why the intake valves floated.

We are going to shim the intakes for about 85lbs and the exhaust for 74lbs. I am also going to install a wastegate after the rotrex to purge all boost after redline. That way if I money shift to 9k at least the valves won't have to contend with boost. I planned on the wastegate anyway to bleed off boost after 7k to flatten HP to fit in ST2 class.

TNTUBA

iTrader: (1)

Just following up in this thread. I've lost another intake valve. Valve lash has gone to zero on first intake valve on #2 cyl. Don't have the head apart yet but I would assume it's another seat issue.

tpwalsh

What cams and seat pressure are you using? Assuming that you want to make that information public.

k24madness

iTrader: (6)

Sorry to hear TNT.

FWIW I am now running 85lbs of seat pressure on the intake valves and bleed boost at redline to help with money shifts. This with custom cams and 11psi of boost. I'll report back after more run time.

emilio700

iTrader: (3)

I'm guessing not enough valve spring initially, not det. We use the ST light doubles on everything now. Heavy doubles (74lbs) if it will have it's limiter set above 8000. 8500 twists/distorts the OEM crank a bunch. 9200 seriously bends ****.

TNTUBA

iTrader: (1)

This season I was on stock cams with 67lbs of seat pressure. Running C-16 fuel and professionaly tuned buy DIY Autotune in Atlanta.

Im running close to 24 PSI boost and a 7,800 RPM redline. So Its not over revs. and there are no signs of valve float.

Talking to the machine shop that works on my heads (Nationally recognized shop that only does head work) we are thinking the margins on the seats are more the culprit. When we rebuild everything this winter we are going to wider margins and a better valve spring than the STs. The cam grinder who ended up building my new cams made a very strong suggestion on a set of springs and a spring pressures which I am going to try.

If not. I guess Ill just add intake valves to my list of wear items.

emilio700

iTrader: (3)

FWIW, we always run generous seat width in both our race motors and CNC heads. Only for nationals level grenade motors should smaller seats be run. We usually see exhaust valve seats wearing as first cause of bad leakdown but over aggressive intake cut can sag a motor even sooner. The way I look at it, the heads flow poorly no matter what so why make them unreliable too.

TNTUBA

iTrader: (1)

Thanks for that feedbak Emilio. This is a Nationals Level grenade motor. But I'm starting to realize that to "finish first you first must finish." O had previously thought that these heads flowed so pourly that any help they could get would be worth it.. .but I agree with you after looking at data. They are gonna flow like crap no matter what.