[ChallengeThis340]

Well i was having some fun the other day doing some donuts for a bunch of my friends when I hit the sweet spot in the donut and my RPMs shot up like a rocket. Before I even realized it I was bouncing off the rev limiter (MSD pill in the 6al) so I let off. It was only for a half second or so.

That's when I realized that my pill in the MSD was at 7000rpm and not 6700 (I thought it was at 6700). I was pretty sure that if ever by accident the car hit 6700 it would still be fine, but im a little worried about 7.

The car ran fine on the way home, no problems that I noticed. It's a 340 with forged eagle rods/ speed pro pistons. My question is, should I lower the rev limiter? This is the only time I have ever hit it in the 2 years I have had this motor, I don't plan on hitting it ever again....but it just worries me that if I do, next time it could kill the motor.

Could there be any potential problems with my motor that I may not know about now because of the over rev (again, being very paranoid...I love this motor lol).

Thanks

[dave-r]

For burnouts where there is little load on the engine you should have a much lower rpm limit than the normal shift point. Say 5000rpm. So a two stage rev limit is best. But if you only have the one limit stick with 6700 if you shift at 6500. However an engine when racing etc is never normally at high rps for more than a few seconds.

If the engine seems OK it probably is and you got away with it. But any sustained rpms above 5000rpm will hurt the engine eventually.

[ChallengeThis340]

Thanks, ill be sure to keep an eye on the tach from now on when doing stuff like that.

I never go above around 4k for a sustained time when burning out, but sometimes while in a donut or when speeding away after a burnout with the tires still spinning the rpm's jump quick and get up there fast. Im not holding it at over 4 though. It jumped up in rpm's fast but i only hit the rev limiter for a split second durning the donut and I let right off.

Thanks again

kris

[dave-r]

One thing you could check before you drive it again.

If you have adjustable rockers re-set the lifter pre-load or lash and check that all the lock nuts on the adjusters are good and tight. Sometimes high revs shakes them loose.

How do I know?

That is what happened to me and on the very next run I dropped two pushrods.

[fbernard]

One thing you could check before you drive it again.

If you have adjustable rockers re-set the lifter pre-load or lash and check that all the lock nuts on the adjusters are good and tight. Sometimes high revs shakes them loose.

How do I know?

That is what happened to me and on the very next run I dropped two pushrods.

On the paranoid side, you should remove the rocker arms shaft and check the spring height on all valves.
They should be equal (or pretty close). There might be a very slight difference between intake and exhaust valves though (depending on the lock type).

If you have the tool required to remove the locks and springs with heads installed, you can remove them on one valve and check out the valve locks. If it's OK and the heights are all equal, you deserve a beer.
If not, you need a Summit Racing catalog!

You may also be able to check installed spring height from a shop manual

If one valve has started to go through the valve lock, you'll only find out too late, when it punches completely through, and meets the piston - that happened to me 3 weeks ago. I did a run with a 4 speed trans and Indy heads, missed the gear change to 3rd (and went to 1st). Two intake valves started to punch through the locks, and one went all the way through.


If all is well, it's a 2 hour job to check everything's alright. If all is not, better find out while the valves are all up there... I did not, and I need to replace one valve, one guide, and a complete set of valve locks (and of course, I had to remove the heads).

Of course, you should take the opportunity to check that no pushrod is bent, but that only takes another 20 seconds per pushrod and a flat surface to make them roll.

On my car, it should have been visible, the valve retainer had started to rub on the rocker arm from below and was quite bright (all others are phosphate-black). With 5 people looking at it by the side of the road, no one saw a damn thing.
Measuring spring height is the surest way to go. And the surest way to avoid that : http://fb440.free.fr/indy/demontage.htm

Dave is right, a two-stage rev limiter is really sweet if you do burnouts on a regular basis, and nothing is more expensive and time-consuming than unplanned engine work...

Besides, unplanned engine work can keep you away from the Mopar EuroNats, and that sucks .

[dave-r]

Besides, unplanned engine work can keep you away from the Mopar EuroNats, and that sucks .

You too??

[fbernard]

[You too??

Yeah. I took part in the organization of a RWYB event on July 14th & 15th, so I only had time to make 4 runs. Screwed up on a gear change on the 3rd run : 1st to 7kRPM, 2nd to 7kRPM, and that's when I mistook 1st for 3rd - only for a split second. I was drifting on every gear change (5-year-old, hard as wood BFG tires), and I guess that helped minimize the damage (the car started to skid and I rammed the clutch pedal immediately). I can only imagine what would have happened with real traction!
My opponent said he heard a loud noise right before he got ahead of me. He was not so pleased when I started growing bigger in his rearview mirror and nailed him on the finish line, though.

I never should have made the 4th run, but I had promised a ride to a friend who also has an engine with Indy heads (and a Challenger that's been sitting on jackstands for 4 years).
And I never should have driven to and from the track with a 4.10 rear end on a car I had bought 9 days before...

The valve locks on one valve gave up after 150 km on the way home.

Next year is vengeance year : good traction, plenty of runs, Santa Pod, and Columbus. Hey, maybe even Vegas would be a nice start to the season!