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~6700 RPM 8-valve motor resonance?

740Weapon

740Weapon

Traitor
Joined
Aug 2, 2004
Location
Salem MA
Hello everyone.

I am now running thelostartof 6800 RPM chips (which BTW kick ass) in my B230FT. But at around 6700 RPM i hear this incredibly loud buzzing and my knocksense light goes on and stays on. The wideband AFR is fine. I haven't tried these RPM at light throttle yet to see what happens. will try after work.

The buzzing sound almost exactly like if you were WOT with a bad catalytic converter heat shield.

the motor has never been opened up except for an IPD cam. so stock valves, springs, etc.

So the qestions become:

for those of you that have ventured to these RPMs, what am I hearing? Is it valve float? some piece of sheetmetal vibrating like crazy? resonance of crank? Other?

I would hate to get under the hood with a mechanics stethescope while the motor spins at these RPM in neutral.
 
something's rattling. neither mine nor sam's cars ever made any funny resonating noises at really high rpm (well, maybe when the valves floated, that always sounded kinda wierd, but that was usually into the 7's at that point). I would bet something is loose and hitting a certain harmonic right around then. good luck figuring out what.
 
What kinda shape are your driveline mounts in? Are any of the rubber hangers broken? My car is actually pretty smooth at 7k with a stock block.. but I've got double valve springs..
 
TerribleOne said:
What kinda shape are your driveline mounts in? Are any of the rubber hangers broken? My car is actually pretty smooth at 7k with a stock block.. but I've got double valve springs..
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every piece of rubber in the car has been replaced in the last 3 years except for the rear subframe mounts which were in good condition when checked last.
 
it's a known fact that stock redblock valvesprings are good to about 7000-7250rpm.
when they age you might get valvefloat earlier, like around 6800rpm, so yes, you are pushing the envelop here.
The camlobes will be hammering on the shims&buckets that are not completly closed = valvefloat. This hammering might trip the knocklink and make strange sounds.
you should try to avoid valvefloat because if you have bad luck the shims might pop out of the buckets and then get broken by the hammering camlobes. The camlobes and buckets can be damaged in the proces.

other possible source of sound: a loose downpipe can hit the body when the engine moves from side to side on its supports. (torsion)
 
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Yeah.. If you're a severe duty driver you may need to replace your mounts more often. Stock valve springs could be good to 7000 but like the above stated.. if theyre worn, and you haven't checked them, you dont know.. so to me that's a recipe for disaster. Plus I rarely see these cars make power up that high.. unless you're trying to run the motor out to get a better bite on the next gear and keep you in your RPM range.. and even then you're probably way off the fatness of your torque curve..
 
Is something loose? my down pipe came unbolted from the frame once and that made a loud sound and i though it was something in the cat to.
 
With all the miles on these engines. The rpm that valve float is happening gets lower than when the springs were new. On my 82 B21FT I revved it upto somewhere around 6800 and at valve float it popped out the valve keepers which let the retainer loose. This dropped the valve into the cylinder which then got pounded by the piston which bent the head of the valve. This will more than likely be what happens to you if you continue to goto valve float. I got away with it a bunch of times but then if finally bit me. The newer valve springs are also not quite a stiff as the older larger ones in my B21FT. So, I'd probably stick around 6500-6600 and avoid the valve float. Don't forget that putting a cam with more lift in the engine with old valve springs means they are being stressed more than the stock cam. So, this would also affect when valve float happens.

Now that I have a refurbished head with new stock valve springs, etc on the same engine. It revs to 7k without any float and it sounds awesome doing it. I am also using the equivalent cam to yours which is the enem V15 turbo cam. So, if you do want to explore those higher rpms it'd be best to plan on some refurbishing using at least new stock springs
 
I'd get something a bit stiffer if you're going in there. the rope trick works really well to r&r springs with the head on the car.
 
linuxman51 said:
I'd get something a bit stiffer if you're going in there. the rope trick works really well to r&r springs with the head on the car.
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I agree. That's why when I had the 531 done by D&F I had them use dual Isky springs. I plan on 7500 to 8k with the engine that gets that head. The 405 was the first head I had done which turned out so well that I went for more upgraded parts with the 531.:oogle:
 
Hmmm this thread has convinced me to think twice of going over 6k rpm on my stock 190k mile b230ft.
I'm not putting the RSI stg 1 cam in until I have upgraded the valve springs.
 
MrSteve said:
Hmmm this thread has convinced me to think twice of going over 6k rpm on my stock 190k mile b230ft.
I'm not putting the RSI stg 1 cam in until I have upgraded the valve springs.
Click to expand...
Me too, but then I realized I'm running a 530 head on a junkyard squirter +T, so it doesn't really matter if it blows up.
 
Mine's smooth as glass and quiet til I hit the 6800 limiter. I'd guess something's loose. Voice of experience here...check your trans mount. When they go, they create a nice vibration when the center starts resting on the x-member.
 
MrSteve said:
Hmmm this thread has convinced me to think twice of going over 6k rpm on my stock 190k mile b230ft.
I'm not putting the RSI stg 1 cam in until I have upgraded the valve springs.
Click to expand...

I put an enem V15 n/a cam in my 270k mile 1993. The flywheel is so heavy and with the cam advanced 4 degrees. It doesn't even want to rev over 5k. That's in first and second. Third will rev to 4k when getting on the highway but that's about it. I think if the flywheel was lighter it would be much better. I like the tall rear ratio and would keep that. My Simons sport exhaust probably isn't the best flowing muffler I could put on their either so I'm sure that's not helping. So, I guess you could say it's rev limited. :lol:I wouldn't let the miles stop you from putting in a cam to make the power better. It still drives better than stock. You can always swap the cam into a new head when you install it.
 
dl242gt said:
I agree. That's why when I had the 531 done by D&F I had them use dual Isky springs. I plan on 7500 to 8k with the engine that gets that head. The 405 was the first head I had done which turned out so well that I went for more upgraded parts with the 531.:oogle:
Click to expand...


I think I'm running the same Isky springs in my 944 and my 244.. they came as a set of 16, can't remember where I put the box so I can get the part number.. I'll try to find it..
 
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