What can happen when you float your valves.

[coop]

This is the result of a missed shift and subsequently hitting 7500 RPM in an ITS engine. Doh...

[Oiluj]

Ouch! Actually not as bad as it "could" have been... Cylinder wall looks OK from the picture.

[ajmcforester]

How that didn't tear-up the walls is quite surprising. please take picture when you get the piston out

[coop]

Unfortunately, this engine was built to .040 over, the limit of the rules and it did indeed damage the upper 3/8" of travel on the cylinder wall. Since I can't bore any bigger, it requires a new sleeve. My engine builder, Dave Rebello has some spare blocks so we went with another block. The new engine is ready for pickup and it dynoed at 204 hp with 197 torque, both up from my very good old engine. Can't wait to get it to the track with a rev limiter this time of course.

[Oiluj]

Dave really is the best. What compression ratio are you running?

[Zed Head]

This is the result of a missed shift and subsequently hitting 7500 RPM in an ITS engine. Doh...

[ATTACH=CONFIG]47836[/ATTACH]

Just curious, but are you saying that the valves floated and hit the piston, causing the crack, or that the stress of over-revving over-loaded the wrist-pin area of the piston, causing the same? Are the valves damaged?

I've seen it suggested that the L series valve train will rev to 8,000 RPM without float, so valve float at 7,500 RPM might be unusual. Still learning the limits of the engine design.

[coop]

I am running 10:1 compression ratio per the rules of the class and am required to run OEM valve springs. My shift point from 3rd to 4th is 6,800 rpm and I will only run it up to 7,200 rpm at the race start when going from 2nd to 3rd. These values were determined by graphing the intersection of the power curves between the various gears. When I took the head off this engine, four of the pistons had little smiles in the top where valves had indented them. The cracked piston had the worst indentation so I just assumed that the stress of the impingement combined with the forces up through the pin caused the failure. I would never run an L Series engine up to 8,000 rpm without some serious strengthening of the valve train and using forged pistons etc. I did not notice any damage to the valves, however.

Edited August 29, 2011 by coop
incomplete

[Zed Head]

Thanks for the story. Seems amazing that the valves could tap the pistons at that RPM and piston speed and damage the pistons (although "smiles" might not count as damage), yet not get damaged themselves.

Good luck with the new engine.

[robert84]

please take picture when you get the piston out

[myzblubyu]

Just curious, but are you saying that the valves floated and hit the piston, causing the crack, or that the stress of over-revving over-loaded the wrist-pin area of the piston, causing the same? Are the valves damaged?

I've seen it suggested that the L series valve train will rev to 8,000 RPM without float, so valve float at 7,500 RPM might be unusual. Still learning the limits of the engine design.

A couple of years ago my throttle got stuck, at 7,000 rpms I floated a valve and bent 1 valve. All 6 pistons had the half moon inprinted on the top. I put a new head on it and it's still going strong, I never took the engine apart, I just sanded/polished the top of the pistons with emery cloth. The compression of my motor is 10.6 to 1, a l28 block with stock bore and stroke, a fully ported E88 head (stock cam) and a clifford intake with a Eldelbrock 4-barrel. So yes a L series valve train can float at or past 7,000 rpm...

Edited September 27, 2011 by myzblubyu