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Old 02-28-2005, 04:17 AM
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Crack the wip or give "er" a nudge ?

Well i have a rebuilt cleavland and was wondering, how hight can i rev the engin safley (like a general number not to breach). This moter is raced up a bit but its fairly stock, other then a 670 double pump. 4 barrel , stock intake, headers, large valves 10.1 comp, Any help would be awsome, even if i new what the stock 351 cleavlands could rev to in 1970.

thanks guys n gals
bill

ps. im still breakin in motor

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Old 02-28-2005, 08:55 AM
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Actually the valves should float out and not really do any damage. My neighbor was a hard headed old man that used to buy,fix up and sell cars. I saw him one day trying to sell a mid 80's chevy to a guy. He was only asking about $500 and this guy kept saying its got 150,000 mile on it the motor might be bad. Well the neighbor got mad and said there nothing wrong with the motor. To prove his point he gets in starts it up. Leaves it in park and holds it to the floor. Well im next door and this motor is screeming for 5 minutes. It just went to around 6000 rpm and stayed there floating out. Scares me and I would never do that but the guy bought the car. Unless your running a solid cam the valves will float and stop the rpm.
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Old 02-28-2005, 11:18 AM
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Well im im guessing your (floating out) means that the valves kinda stay more open? But how does that work cause the valves still have contact with the rockers/pushrods/lifters and the lobes on the cam, hmmm explain this to me a bit more (im still relitivly new to motor internals)

thanks for the help
bill
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Old 02-28-2005, 11:23 AM
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The valve springs can no longer control the motion of the valve. The lifter jump the ramps of the cam lobe. It's bad, Very bad, It's a great way to destroy an engine.

To answer 5000 is safe enough asuming a good state of tune.
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Old 02-28-2005, 11:37 AM
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:0 So i guess i wont be letting the valves "float out" any time soon!
And 5000rpm is good .... sounds good, but ya i still need to adjust the either timeing or the fuel mixture. After just cruizin down the road if i put my foot down (a little) it mabe gains a few hundred rpm then bang! backfires then sort of stuggels up ... I don't know , it just seems to me that if it where just tuned a little it would friggin growel.. It's just kinda struggeling. Ill take it into the shop this week its got a leak in the intake and needs tires and rims so if you could give me any ideas it would really help out


thanks
bill

Ps mabe.. its running too rich like sort of chokin on fuel?
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Old 02-28-2005, 12:43 PM
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Isn't a back fire indication of a too lean carb?
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Old 02-28-2005, 06:44 PM
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7000 rpm is a good number to stay under with a stock Cleveland, likely the stock springs will give out long before that though.
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Old 02-28-2005, 06:52 PM
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Ford springs go out around 7,200 RPMs. Go out meaning enough for the valves to hit the pistons. Go ahead ask me how I know this.
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Old 03-01-2005, 02:39 AM
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So you think that it may be too lean of fuel as aposed to too much... k well ill try fiddling with it.. and do you think its possible that the timing is too adv.. or to reta... ?

thanks
bill
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Old 03-01-2005, 12:36 PM
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hmmm... probably 5500-6000 rpm tops, if you have heavier valve springs the valvetrain won't last as long, but you'll be able to coax a few more revs out of it. I really don't think it'd be worth it though unless it was balanced, cammed, performance cylinder heads, etc.

get it running really well before you try to rev it alot.

when a valve hits a piston, it is bad, very bad.

good luck,
matt
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Old 03-01-2005, 12:59 PM
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Ok then Chevellss ill do that but to tell you it is camed, balenced and the heads are fully rebuilt with monster valves, hardend seats and its ported but alass i do think that its got stock springs .... so then yess i keeper under 5200 ... for a while at least... hehehe

thanks
bill
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Old 03-01-2005, 01:11 PM
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Under 5200 is probably a good idea anyhow, If I remember right there is an oiling issue with those motors, when you start reving them high. The fix has something to do with tapping into the main oil supply passage and re-routing oil to one of the mains.
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Old 03-01-2005, 04:12 PM
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Don't run it at all if you have a big cam in it with stock springs. The springs need to be matched up to the cam's lift, otherwise you'll run into all kinds of problems. What cam is in it? 4V heads need RPM to make power, so you'll REALLY be holding it back if you don't wanna go above 5K. I'm running 4V heads on my 393 and plan on shifting it around 6500 RPM, even with the CID increase. What cam is in it?

The oiling system is the same as alot of other motors and isn't an issue until you get into the 7-7.5k range. It became a common myth because C's were spun stupidly high, and people don't/didn't realize that alot of the big oiling mods were on 8000+ RPM motors.
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Old 03-01-2005, 04:37 PM
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Quote:
Originally Posted by "70" Cougar
Ok then Chevellss ill do that but to tell you it is camed, balenced and the heads are fully rebuilt with monster valves, hardend seats and its ported but alass i do think that its got stock springs .... so then yess i keeper under 5200 ... for a while at least... hehehe

thanks
bill
Just how big of a cam do you have in there? First and foremost there really isn't a reason to rev it much past the cams ending powerband. Just remember RPM's are what kills an engine. Thats like asking how hard you can press on an egg before it breaks. Im sure many people wanna know . . .but given the cost of your "egg" do you really want to find out firsthand?
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Old 03-02-2005, 03:29 AM
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Well the man that rebuilt my motor said he put a 250 mega isky grind in it.. ? if that sounds right. and i dont know.. i wont be reving the motor much past 3 untill i can get it running smoothly. But i do have lots of oil pressure (50-75) so i think the oiling system is fine for quit a bit.

bill
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