What determines an engine's redline?
Thread Starter
Race Director
Joined: Mar 2008
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From: coffee
What determines an engine's redline?
Just a question for the experts.
I've got a 290HP GMPP 350 crate engine that will serve as a mule motor during my restoration that has a recommended redline of ~5200 IIRC .
I intend to upgrade the heads and cam eventually, and it got me thinking of how high do I want I want to spin the thing?
As I understand it, redline is limited mostly by the valvetrain, but I did not know what most after market heads (I'm thinking AFR's) and hydraulic roller lifter cams were good for.
I'm not going to spend much time north of 5500 in any case, but was curious.
I've got a 290HP GMPP 350 crate engine that will serve as a mule motor during my restoration that has a recommended redline of ~5200 IIRC .
I intend to upgrade the heads and cam eventually, and it got me thinking of how high do I want I want to spin the thing?
As I understand it, redline is limited mostly by the valvetrain, but I did not know what most after market heads (I'm thinking AFR's) and hydraulic roller lifter cams were good for.
I'm not going to spend much time north of 5500 in any case, but was curious.
Race Director
Joined: Sep 2002
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From: San Diego - Deep Within The State of CONFUSION!
The redline may be limited by valve train characteristics for sure. But definitely it's related in Hot Rodder's terms anyway, by the RPM at which the whole system stops increasing HP.
If your max torque is for instance, at 5250RPM and max HP is at 5500, it's just a waste of gas and time to rev any higher than either of those numbers.
If your max torque is for instance, at 5250RPM and max HP is at 5500, it's just a waste of gas and time to rev any higher than either of those numbers.
Thread Starter
Race Director
Joined: Mar 2008
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From: coffee
Hoping to avoid that level of definitive confirmation.
FWIW, the engine has four bolt mains, nodular crank, powdered rods and cast aluminum pistons. I'm eventually wanting healthy low end, so I'm not looking to rev the thing to the moon in any case, but just wondered where you start getting in to trouble with stock-ish quality bottom end hardwear.
Thanks.
Burning Brakes
Joined: Jun 2009
Posts: 840
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From: Syracuse IN
In the marine industry, the pre Vortec motors had a consistant WOT of 4,500 rpm. The WOT rpm was increased to 5,000 rpm on 1st generation Vortec which was around 98 and then again another increase in WOT rpm to 5,500 rpm in 2004. These are for Small block engines. The standard 496 has a WOT rpm of 4,600 and the 496 HO has a WOT rpm of 5,400 rpm. We routinly run these motors for hrs at a time in the 4,000 to 5,000 rpm range. The valve train is all roller lifters but still stamped steel rockers. Al
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Brett Foote
Le Mans Master
Joined: Apr 2007
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From: Graceland in a Not Correctly Restored Stingray
The suggested safe max rev limit for a given reciprocating assembly is commonly calculated from how high an average piston speed the parts are considered capable of sustaining. For a 350, 5200 RPM only produces a average piston speed of 3016 fpm with a max of 4953 fpm. Mild by true high-perf engine standards IMCO, but you'll need to account for the quality of bits and assembly of your engine in deciding how far to push it.
As for how high it will actually wind, that's a far different matter determined by many variables.
As for how high it will actually wind, that's a far different matter determined by many variables.
Melting Slicks
Joined: Mar 2002
Posts: 2,164
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From: Beringen
Usually the valve train is the first thing to go when being overreved.
What destroys the engine next is vibration.
Last is the G-forces on the rods and crank.
With your engine i'm pretty sure, the valve train is the limiting factor to go higher.Next is intake tract, cam, then crank and rods.
What destroys the engine next is vibration.
Last is the G-forces on the rods and crank.
With your engine i'm pretty sure, the valve train is the limiting factor to go higher.Next is intake tract, cam, then crank and rods.
Melting Slicks
Joined: Apr 2006
Posts: 2,084
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From: Airdrie Alberta
One thing is for sure...you don't want to rev it this high!
http://www.youtube.com/watch?v=26X_s28ilYs
http://www.youtube.com/watch?v=26X_s28ilYs
Safety Car
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From: Indy Indiana
Thread Starter
Race Director
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From: coffee
Le Mans Master
Joined: Sep 2001
Posts: 7,739
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From: Unreconstructed, South Carolina
FYI ... GM powder metal rods are good but they have a limit too.
Anecdotal limit:
Lotsa regional CT racers run GMPP crates x602 & x603 (zz4) ... all have the very
same GM x688 PM connecting rod as that GMPP 350/290 crate should have.
Local feller (usually runs a built motor) ... but took opportunity to run a special new years day crate motor race at Dillon motor speedway. His car runs rear gear that typically puts him about 6800-7K at end of straights just before he lifts.
He left that gear in when he showed up with x602 crate. He was warned repeatedly during practice to change gear ... crate revving too hi ... he didn't heel. Crates usually geared there to top out about 6200. Oh well ... his was 6800-7K when a rod came loose. Motor's disassembled & I looked it over last week. Total loss. A couple rods & pistons & one head maybe OK ... block & remainder could bring about $12/hundredweight. At 6200 they rarely have a problem, but not so good much beyond that. Now keep in mind this is a repeated, hard, on-off-on-off cycle within every 20 seconds ... not a street car. YMMV.
FWIW ... x688 rod broke just about mid-beam ... Not just above big end.
Anecdotal limit:
Lotsa regional CT racers run GMPP crates x602 & x603 (zz4) ... all have the very
same GM x688 PM connecting rod as that GMPP 350/290 crate should have.
Local feller (usually runs a built motor) ... but took opportunity to run a special new years day crate motor race at Dillon motor speedway. His car runs rear gear that typically puts him about 6800-7K at end of straights just before he lifts.
He left that gear in when he showed up with x602 crate. He was warned repeatedly during practice to change gear ... crate revving too hi ... he didn't heel. Crates usually geared there to top out about 6200. Oh well ... his was 6800-7K when a rod came loose. Motor's disassembled & I looked it over last week. Total loss. A couple rods & pistons & one head maybe OK ... block & remainder could bring about $12/hundredweight. At 6200 they rarely have a problem, but not so good much beyond that. Now keep in mind this is a repeated, hard, on-off-on-off cycle within every 20 seconds ... not a street car. YMMV.
FWIW ... x688 rod broke just about mid-beam ... Not just above big end.
Thread Starter
Race Director
Joined: Mar 2008
Posts: 15,161
Likes: 17
From: coffee
FYI ... GM powder metal rods are good but they have a limit too.
Anecdotal limit:
Lotsa regional CT racers run GMPP crates x602 & x603 (zz4) ... all have the very
same GM x688 PM connecting rod as that GMPP 350/290 crate should have.
Local feller (usually runs a built motor) ... but took opportunity to run a special new years day crate motor race at Dillon motor speedway. His car runs rear gear that typically puts him about 6800-7K at end of straights just before he lifts.
He left that gear in when he showed up with x602 crate. He was warned repeatedly during practice to change gear ... crate revving too hi ... he didn't heel. Crates usually geared there to top out about 6200. Oh well ... his was 6800-7K when a rod came loose. Motor's disassembled & I looked it over last week. Total loss. A couple rods & pistons & one head maybe OK ... block & remainder could bring about $12/hundredweight. At 6200 they rarely have a problem, but not so good much beyond that. Now keep in mind this is a repeated, hard, on-off-on-off cycle within every 20 seconds ... not a street car. YMMV.
FWIW ... x688 rod broke just about mid-beam ... Not just above big end.
Anecdotal limit:
Lotsa regional CT racers run GMPP crates x602 & x603 (zz4) ... all have the very
same GM x688 PM connecting rod as that GMPP 350/290 crate should have.
Local feller (usually runs a built motor) ... but took opportunity to run a special new years day crate motor race at Dillon motor speedway. His car runs rear gear that typically puts him about 6800-7K at end of straights just before he lifts.
He left that gear in when he showed up with x602 crate. He was warned repeatedly during practice to change gear ... crate revving too hi ... he didn't heel. Crates usually geared there to top out about 6200. Oh well ... his was 6800-7K when a rod came loose. Motor's disassembled & I looked it over last week. Total loss. A couple rods & pistons & one head maybe OK ... block & remainder could bring about $12/hundredweight. At 6200 they rarely have a problem, but not so good much beyond that. Now keep in mind this is a repeated, hard, on-off-on-off cycle within every 20 seconds ... not a street car. YMMV.
FWIW ... x688 rod broke just about mid-beam ... Not just above big end.
Racer
Joined: Nov 2004
Posts: 485
Likes: 1
From: Oakville ON
I'm no expert, but I would stick to 5200 rpm with cast pistons. An old Hot Rod article wanted to she what a SBC would do with a buildup and the rod pulled the wrist pin out of the cast piston at 6500. Hence, redline was 6000, but maybe not for long ......
