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Old 03-26-2013, 11:15 PM   #1
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Default why 8500 redline?

i was curious to see what the highest revving production car was and lookign through the list it seems like the magic number for alot of production cars is between 8000 to 8500 rpm.

is that just because everyone is doing it or is there a design limitations or cost cutting behind it?

if lexus can get their LFA V10 to 9000k why most manufacturers stop at 8500 for production car?
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Old 03-27-2013, 02:25 AM   #2
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Default Re: why 8500 redline?

Inertia is the killer - valve train, piston speed, rods and rod bolts, crank harmonics.

Most of our energy and money, when enhancing our engines to go faster, gets focused on stronger/faster/lighter. It translates into $$ that goes into expensive production cars but quickly is compromised for less expensive cars as design is balanced with cost to hit a sweet spot in the market.

Look at the parts list commonly seen with our cars: forged pistons, eagle rods, stiffer valve springs - sometimes exotic (e.g. beehive), lighter / enhanced valves, lightened rockers, ARP studs and bolts, block stiffeners (e.g. GSR/Type R), sleeves.

Once the engine is modified to avoid flying apart, we turn to improving airflow, and then modifying the supporting systems to keep up: TB, intake, exhaust, P&P, fuel delivery (e.g. injectors, pumps), gear ratios, LSD, better compounds for the tires, etc.

Along with or after that, more subtle work to reduce friction and alter the combustion chamber (quench, volume).

Every one of those items has significant costs, even in production volumes.

Mark
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Old 03-27-2013, 05:22 AM   #3
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Default Re: why 8500 redline?

In terms of longetivity, production line cars limit rpms because they think it will save the end results..
Our R8 V10 does around 8500rpms or so. Our Lambos vary, and same with alot of our motors.. Most companies now and days are about torque, you dont need alot of rpm to produce alot of raw power.
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Old 03-27-2013, 05:54 AM   #4
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Default Re: why 8500 redline?

Quote:
Originally Posted by mark@silbernage View Post
Inertia is the killer - valve train, piston speed, rods and rod bolts, crank harmonics.

Most of our energy and money, when enhancing our engines to go faster, gets focused on stronger/faster/lighter. It translates into $$ that goes into expensive production cars but quickly is compromised for less expensive cars as design is balanced with cost to hit a sweet spot in the market.

Look at the parts list commonly seen with our cars: forged pistons, eagle rods, stiffer valve springs - sometimes exotic (e.g. beehive), lighter / enhanced valves, lightened rockers, ARP studs and bolts, block stiffeners (e.g. GSR/Type R), sleeves.

Once the engine is modified to avoid flying apart, we turn to improving airflow, and then modifying the supporting systems to keep up: TB, intake, exhaust, P&P, fuel delivery (e.g. injectors, pumps), gear ratios, LSD, better compounds for the tires, etc.

Along with or after that, more subtle work to reduce friction and alter the combustion chamber (quench, volume).

Every one of those items has significant costs, even in production volumes.

Mark
Very well put. Thanks for posting
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Old 03-27-2013, 08:58 PM   #5
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Default Re: why 8500 redline?

Also think about other items spinning at the same speed of the motor like alternator, P/s, water and oil pumps.
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Old 03-28-2013, 01:57 AM   #6
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Default Re: why 8500 redline?

Piston speed is the limiter, almost everything else can be made to turn faster, but you can't make the pistons change direction any faster before stuff starts breaking.

You'll not see many cars where longevity is at least a minor concern breaching 25m/s, even at NASCAR or F1 levels. That's just what current material technology is capable of handling at the moment, reliably at least. It is all a function of stroke.

The formula for your safe RPM limit is:

Rmax = (25/(2S))*60 where S is stroke in meters.

Let's check those numbers against some knowns.

B16 - 74mm stroke - 10135rpm
B18 - 87.2mm stroke - 8601rpm
F20C - 84mm stroke - 8929rpm
H22 - 90.7mm stroke - 8269rpm
Current F1 2.4 V8 - 40mm stroke - 18,750rpm
Lexus LFA - 79mm stroke - 9494rpm

All those adhering to the same 25m/s limit, but very different RPM limits.

It's all in the stroke.
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Old 03-29-2013, 01:21 PM   #7
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Icon4 Re: why 8500 redline?

Quote:
Originally Posted by mark@silbernage View Post
Inertia is the killer - valve train, piston speed, rods and rod bolts, crank harmonics.

Most of our energy and money, when enhancing our engines to go faster, gets focused on stronger/faster/lighter. It translates into $$ that goes into expensive production cars but quickly is compromised for less expensive cars as design is balanced with cost to hit a sweet spot in the market.

Look at the parts list commonly seen with our cars: forged pistons, eagle rods, stiffer valve springs - sometimes exotic (e.g. beehive), lighter / enhanced valves, lightened rockers, ARP studs and bolts, block stiffeners (e.g. GSR/Type R), sleeves.

Once the engine is modified to avoid flying apart, we turn to improving airflow, and then modifying the supporting systems to keep up: TB, intake, exhaust, P&P, fuel delivery (e.g. injectors, pumps), gear ratios, LSD, better compounds for the tires, etc.

Along with or after that, more subtle work to reduce friction and alter the combustion chamber (quench, volume).

Every one of those items has significant costs, even in production volumes.

Mark
once again couldnt say it better myself
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Old 03-29-2013, 02:28 PM   #8
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Default Re: why 8500 redline?

There are two types of motors, under-square and over square. Like Kozy explained it has to do with your stroke. The longer your stroke the longer it take to do one revolution. The shorter the stroke the shorter amount of time it takes for one revolution. A "stroked" engine means it has longer rods,crank throw, or combination of the two. A stroked motor produces more torque in the lower Rpm's.

Balancing is just as important as stroke. a ITR crank is balanced up to 10,000 rpms, a H series block is not. You will get crank-walk "wobble" if you rev that high. Installing lighter parts helps wind up faster, but the entire assembly has to be balanced perfectly otherwise it will blow up in your face. Most noobs slap a high rev limiter chip in there ECU and rev the **** out of it. Then wonder why there motor exploded on them in less then a month.

You also need a proper amount of oil to keep everything lubed and cool. High Rpm's cause ALOT of friction, so proper oil pressure is needed and a thin viscosity oil for high rev applications. Super thin oil isnt good for everyday driving.

Manufacturers had to find the middle ground between how much engine work to do and price of overall car. Nobody is going to pay $35K for a civic even if it can rev to 11K stock. You would buy a better platform to start with for that kind of money. Your average Honda is a family car, commuter car, only a percentage of the market will be interested in the performance aspect. So they build there motors just a good as they need to be for the masses.
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