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Old 02-02-2006, 07:43 PM
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How high can I rev?

Hey all, I have a '73 SBC350 rebuilt .030 over with an edelbrock perf., edelbrock 675CFM Q-jet, Comp 270H Magnum, #993 heads, ported/polished 2.02/1.60 valves, 1.52:1 roller rockers. 700R4 tranny, 1500 stall/lockup torque conv. 2.73 granny rear end.

The rating for my cam is 1800-5800, for the intake it's to 5500RPM's. I was wondering how high I could rev my motor without damaging it.

I've heard one guy say in another thread "I just rev it 'till it stops pulling'. I wonder if that would apply to my setup.

It's got the stock crank that's been turned, ARP rod bolts, high oil pressure (60PSI when in a high state of rev), about 8:1 CR. My theory is, if I revved it past where I have before (5500RPM's) that it would just stop pulling and I could shift, the thing is, I'm not sure if this is okay for the motor to go past what the intake is rated at.

What do you think?

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Old 02-02-2006, 08:19 PM
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fat freddy

Well we all like to believe we can REV it till it breaks , but it usually breaks before we're done listeni' to that SAWEET WINE So a good rule is if you are listening you should hear the tapping of the rvalves floating around cause they can't move as fats and the rest of the parts. but you should notice that the motor is only making noiseand your not really getting any more power from it.
I would dsy 55 oo is about good for a 350 block. maybe 6800 max.
Ihave had a 283 , 30 over and i holeshotted it at 7800. and it went fine.
but the 350 is sloppier.. I got a 400 S.b.c. with a cam and new lifetrs and a touqer two and a 750 double pumper. and it goes like a bear , but flattens out at 5000. so look at your power curve.are ya making power or just sweet noise. keep it at a 5500 to 6800 and then see what happens,
AND DON"T REV IT when it ain't for a good reason. and in gear.
that will kill a motor real fast.
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Old 02-02-2006, 08:20 PM
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its not the intake you have to worry about when high revving. you need to worry about valve float. what kind of valve springs do you have? what are the seat pressures? pushrods? lifters? i wouldnt really worry about the rotating assembly too much, its the valve train you need to look at.

If you rev till it stops pulling your taking a big chance on breaking something. call comp cams and see what redline they recommend...
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Old 02-02-2006, 08:23 PM
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Revving to the limit

Theoretically, your valve train should be able to rev about 1000 RPM over your peak RPM.
You state that your cam has an operating range of 1800-5800, meaning that if your engine will effectively put out peak power at 5800, then approximately 500 RPM over your peak Power point should be your shift point, or 6300 RPM.
The biggest limitation to you pulling good RPM will be your compression ratio.

A 1500 stall converter is a bit on the short side for optimum launches with your camming, but its not going to be too bad for a street car, especially if you are running an open differential, as you will be slightly below any serious torque output with this.

I ran your engine combo through my pc dyno, and used the assumption that you have small tube headers (1 1/2-1 5/8ths primaries) with muffled full exhaust.
I came up with 359 HP@6000 RPM, and peak torque 365@4500 RPM.
This if figured with a cam timing of 109 Degree centerline on Intake and 110 degree lobe separation. (110 degrees is the lobe separation for most Comp Cams). I played with the advance and retard of the camshaft a bit and it seems that this is the best set up.
That being said, based on these figures, I would say that 6500 RPM should be your shift point, and RED LINE. You should be able to turn 7000 or more, but I wouldnt push it over 7000 RPM on the big end. This is not to be taken as an endorsement to turn the engine that tight. Your carburetion is about optimum for this kind of RPM, so a bigger carb definately isnt a necessity.
Your gearing, as far as getting out of the hole can be a hinderence. I would recommend going down to about a 3.60-3.75 gear ratio with your setup.
As a side thought here, I bumped up the compression to 9.5:1 and with no other changes, came up with 393 HP@ 6000 RPM and 390 TQ@4500 RPM.
As you can see, running what I would recommend as the highest compression ratio for pump gas, would net you a considerable power boost.
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Old 02-02-2006, 08:39 PM
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125 shot of nos;et streets;12.80's at 113mph and 19mpg
hehehe i love it!!!!!!!!!!!!!!!!!1
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Old 02-02-2006, 09:14 PM
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Like Joe Piscipo said in the only one good movie he did: you can rev it to 12,000 or so, but "once, only once"!!!!
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Old 02-02-2006, 11:37 PM
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Quote:
Originally Posted by Fat Freddy
AND DON"T REV IT when it ain't for a good reason. and in gear.that will kill a motor real fast.
I've always been mystified by this, why does it hurt a motor to rev it in Park or Neutral? I mean, if you didn't "redline" it, there's no load on the motor, so....

Why?


Also, see my idea was that my cam goes to 5800RPM, but my intake goes to 5500RPM. So if I did rev past 5500 to 6000 say, that's only 200RPM's off my cam's 'powerband' but it's 500 off the intakes...uh..'air flowingness'... So what would happen? I mean, if I went past 5500RPM's, that means the intake cannot supply the engine with any more air, so would the mixture suddenly go real rich?

Just thinkin'............

Last edited by Malibu73; 02-03-2006 at 12:30 AM.
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Old 02-03-2006, 05:59 AM
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I dont think reving it would hurt it but I dont really see any use in it either unless your clearing the carb or checking throttle response on an injected motor that is being staged.

When you get past 5500 you notice that the pull goes away and the rpms climb slower. Eventually you can run it up 7000 grand or more, its just that it wont be getting it. The mixture will be fine.
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Old 02-03-2006, 06:20 AM
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Revving with no load means it will rev up quicker and can cause damage before you can let off. With a load, especially if the load is a moving vehicle, you can tell when the engine is no logner producing power and let off, or shift gears. The load acts as a buffer and keeps the engine from revving to freely, and from suddeny slowing as well. Slowing a high revving engine to fast can cause damage as well. I mean like revving up to 8 grand and just suddenly cutting the throttle. Over revving causes valve float, and floating the valves can cause things like burned valves or broken keepers, and in extreme cases pistons hitting the valves. I've seen burned valves because of it, and I've seen one where the pistons tapped the valves in an engine with a high lift cam and just enough clearance.
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Old 02-03-2006, 07:45 AM
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I have to assume your using a cast crank & cast pistons. That being said,I personally would stay within 5500RPMs. It may go a little higher without problems, but its a gamble.
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