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Old 09-06-2005, 03:42 PM
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What part dictates your Redline?

I have a 355 with a cam that goes to 5800RPM and an Edelbrock Performer that goes to 5500RPM. Will that be the redline? 5500RPM because of the intake restriction?

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Old 09-06-2005, 04:41 PM
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Well, for one, it doesn't make much sense to spin much past where your powerband ends. I look at a redline as an RPM which it is unsafe to spin past for structural integrity reasons. The weight, and balance of the internals (combined with lenght of stroke, etc.) help determine the safe RPM limit of an engine. A lightweight, fully balanced engine is going to spin higher than a heavier unbalanced. Likewise, an engine with a shorter stroke is going to be able to spin higher than one of similar size and weight, but a longer stroke. This is do to the rotational forces that put stress on the crank and rods (causing them to stretch with up and down movement).
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Old 09-06-2005, 04:52 PM
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Red Line is when it flies apart. You only get to hit it once!

Manufacturers give you max rpm for intakes and cams. There is also valve float, head runner size, valve size, and carb cfm rating. An edebrock perf will max at 5500 rpm. An xe268h cam will max out at 5800 rpm and the valves will float at 6300 rpm.

What you should concern yourself with is shift point. Watch your tach under WOT. The car will climb very quickly in rpm then the climb will slow right down. You want to shift just before it starts to slow down the climb. This will keep you accelerating at the quickest rate.

If you have a rev limiter. Set it about 500 rpm above the shift point. If your late on your shift you will keep accelerating but not as quickly. If you hit your rev limiter you will slow down considerably.
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Last edited by bracketeer; 09-06-2005 at 05:01 PM.
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Old 09-06-2005, 04:54 PM
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RPM is dictated by the valvetrain with a iron fist, but there are some other factors.
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Old 09-06-2005, 04:55 PM
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What part dictates your red line?.......the weakest one!
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Old 09-06-2005, 07:53 PM
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piston velocity is a key factor I think. spacially depending on the alloy/weight.

If you can get everything else to keep up(ignition/valvetrain/breath/comp limits) I think piston velocity is the one that shouldn't be exceeded.
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Old 09-07-2005, 08:41 AM
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Old 09-07-2005, 02:03 PM
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i thought the redline was determined on how well the rotating assembly is balanced.
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Old 09-07-2005, 04:27 PM
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piston speed does it in. it will find the weakest link.
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Old 09-07-2005, 05:59 PM
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Like everyone said........it's the part that breaks first.

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Old 09-07-2005, 08:26 PM
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Malibu73... Dont think your question has been answered just yet...?

Bracketeer has good input to this...
The cam may pull good to 5800 rpm but the intake is limited to be effective to 5500 rpm... The engine will or should pull good up to the 5800 rpm of the cam if the other componets can handle it...? It might tend to flatten out past the rpm rating of the intake due to runner volume and or port size of the heads... A stock built or mild build SBC should have no problem going to 5500 rpm but much above that is where good parts come into play (forged pistons, ARP bolts in the bottom end and so on) balancing will make it live longer for sure at higher rpm`s...

A red line so to speak is determined by the quality of the parts and the assembly of such... BUT...!!! this is not to for tell the future... Even in good high performace parts there can be flaws... Many a good build has new windows in it for what ever reason and some times can be hard to find...


Build it with a target rpm in mind then build it for 1K rpm more and it will survive most likely for a long time...


BTW just saw a cool article on TV about Formula 1 engines... Damn things turn 19K rpm...!!!! No wonder they sound like a pissed off Hornet hive...
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Old 09-07-2005, 09:53 PM
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If manufacturers always list RPM ranges for intakes and cams then why doesnt that always apply in a real world application? Example: My friends (very ugly) 1977 camaro with a very mild 350 ran its fastest time shifting at 6000 rpm but the cam and intake are both rated at a max rpm of 5500. The engine isnt anything too special. Comp 268, 8.5:1 compression, performer intake, 600 carb and SR Torquer heads best time was 14.70. So if the cam and intake were rated to 5500 rpm then why was it fastest at 6000 rpm?

Also, my cam is rated at 2000-6000 rpm but my transmission routinely upshifts at 6400-6500 and it pulls hard all the way to the shift. But it doesnt even start to pull at all until almost 3000 rpm. I think this is largely because the rpm rating on the intake is 3500-8000 rpm. But...

It would seem to me that the cam would be more of a factor in setting the rpm band of an engine more than anything (provided that the springs and rod bolts and other like parts can handle the rpm) because it is what actually lets air into and out of the cylinders.

Furthermore, when you compare similar grinds from different manufacturers the powerbands on the cams can vary greatly. For example...A Comp 280H has a powerband of 2000-6000 and a Crane 286 hydraulic has a powerband of 3200-6200. Both have a 230 duration @.050, the Comp has a more lift but the Crane has a little more advertised duration. The biggest difference is that the Comp has a 110 lobe separation and the Crane has 106 lobe separation. What is the biggest factor in determining cam operating ranges?
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Old 09-08-2005, 05:58 AM
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Blazin72...

Bracketeer has answered your first couple of questions, also you answered your own question with your intake and the aftermarket heads will allow an engine to work better at a higher rpm as well... (read above post first)


As for what determins a cams useful rpm range is figured between the duration and lobe sep. with a simple thought that the lower the lobe sep. then more duration is needed to keep the rpm range... Of course this is combined with the proper lift... Lobe profiles are really wild and different between types of cams as well... Roller cams are just crazy but really get the job done...
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Old 09-08-2005, 06:12 AM
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I think Blazin72 almost answered his own question. You have to consider trans and rearend gearing and the torque curve. Shifting at an rpm above the advertised range may drop the rpm into a better spot on the torque curve, creating better acceleration in the newly selected gear. If you have the actual torque curve of your engine (from a dyno session), your gear ratios, and a pretty good idea of the converter slippage at certain rpm's, you could map out a starting point of where to shift the car. But nothing will replace test and tunes where you record the weather conditions and vary the shift points up and down.
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Old 09-08-2005, 07:29 AM
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Quote:
Red Line is when it flies apart. You only get to hit it once!


That is the best answer I have ever heard.Great.
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