How is redline calculated?

[80GS1000]

Did a search and didn't see an answer to this question:

How is redline calculated for a given engine? A stock GS1000 redlines at 8500 RPM, but the very heavily modified Yoshimura racebike version of the GS1000 had a redline at 10500 RPM.

How can you tell how high you can safely rev an engine after modifications?

 

[tkent02]

Run it up until something bad happens.....

Run it up until something bad happens.....

Then make the red line a little less than that.
At the factory they probably blow up a whole bunch of them, and then reduce the max RPM number a certain percentage. I've gotten away with going past redline on a lot of bikes and cars over the years, nothing has blown. So I know they redline them at a lower number than the highest possible. The probably have to be conservative because of the sheer number of engines they build, and the number of idiots who will abuse things and push their luck.
As far as an increase, you need to know what the weak link is, perhaps valve springs or whatever it is that might fail first on your particular engine, and fix that.
Then go out and take a chance.
If it blows up you went too far.

 

[Tarbash 27]

tkent's answer seems exactly how they would do it. Dont forget, engines also start loosing power after there max hp, so extra rpms wouldnt really do anything on a stock engine. Since the yoshimura was heavily modified with lighter, stronger and more balanced parts, it probably made more power at those extra rpms. Also its a race engine, not a daily driver, they were most likely torn down and rebuilt every few races.

 

[RacingJake]

On a Dyno, no need to spin the motor any faster when the the torque is droping faster than the horsepower is raising. Cams and valve springs are the limiting factor to RPM's.

 

[drhach]

Redline

Redline

It can be detrermined in a few ways. Probably at the factory they spec'd it for what they wanted and then built to that tolerance. In other words, you know the stresses at 10,500. You add what is called a factor of safety and you design to that. Obvioously that would give you two things, an over built engine and something that isn't fully understood until it gets to the test phase. If Suzuki built engines and then ran them up until they failed they woyuld have gone out of business a long time ago. That is terrible engineering. These days, if you have the computer power (money) you can run simulations before you ever build the parts. Whole engines are designed and run before they are ever physically built. That at least gets you close. It is one of the reasons that todays bikes are hogiher performing than their predecessors.

I guess another way might be to use a dyno. It wouldn't tell anything about when the engine would fail but it would tell you when the power band drops. You don't need to go past that point anyway so if your engine can tolerate that given RPM, that is where you want the redline.

 

[pano]

From "Superbike Preparation by Jewel Hendrix...

a 1/4 ounce of unbalance 4 inches from the center of a rotating element is equal to 7 lbs at 2000 rpm, 28 lbs at 4000 rpm, 63 lbs at 6000 rpm and 112 lbs at 8000 rpms. It doesn't go on to say what it would be at 10,500 but implies it would put a hell of a strain on the crank and race bikes should have the pistons and connecting rods balanced to reduce the strain. The Yosh bike is most certainly balanced.

Also from "Guide to Motorcycle Dragracing by Mike Nelson

He says no need to balance for street or bracket bike and adds; a rule of thumb when building a engine with stock connecting rods, aftermarket pistons and wrist pins is 4500 feet per minute piston speed. He includes and example calculation for a Gs 1100 at 10,500 rpm.

1. convert stroke to inches (66mm x 0.0393 = 2.59 inches)
2. Multiply inches by rpm (10,500 x 2.59 = 27,195)
3. Divide by 6 to yield the piston speed (27,195/6 = 4,532)

I did not check the math and don't intuitively get why you divide by 6 in step 3.

I am sure the Suzuki engineers consider the stock mfg tolerances among other things when they set the rpm redlines.

 

[Guest]

there was something in CW about the current design method being centered around G forces. something insane like 7500 G's as the piston changes direction.


At those conditions, not only would you black out, your head would F****g explode!

 

[Dave8338]

Also from "Guide to Motorcycle Dragracing by Mike Nelson

He says no need to balance for street or bracket bike and adds; a rule of thumb when building a engine with stock connecting rods, aftermarket pistons and wrist pins is 4500 feet per minute piston speed. He includes and example calculation for a Gs 1100 at 10,500 rpm.

1. convert stroke to inches (66mm x 0.0393 = 2.59 inches)
2. Multiply inches by rpm (10,500 x 2.59 = 27,195)
3. Divide by 6 to yield the piston speed (27,195/6 = 4,532)

I did not check the math and don't intuitively get why you divide by 6 in step 3.
.

When your piston travel is calculated, (in your example=2.59) you are only taking into consideration a single direction of travel. Since the travel exists on a rotational axis, up and down, you end up with a multiplier of 2. Therfore, you could mulitply your 27,195 x 2 and divide by 12 if you wanted and the answer would be the same. In the example that you've given, that step of the math was skipped and was just divided by 6 (") or 1/2 of a foot. You have to love math!! 8-[

Also, as was mentioned, there are several factors that determine the redline point. For the most part, balance is the largest key factor that determines where to set the redline. Vibration kills...and manufactures are limited to tolerance specs within the process of building these engines.
If the wieght of any two given components were exactly equal, there is a good chance that their mass would not be equal and therefor create a weak link in the part of lessor mass. (This is most noted in cast parts and less of a factor in billet machined parts)

All of these factors, combined with volumetric flow rates of the carbs, heads, and exhaust system (even more math), give you an equilibrium point that simply stated, "more RPM's will not equal more power" and increase the rate of failure. Hope I didn't bore anyone with blip. :-D

 

[80GS1000]

When your piston travel is calculated, (in your example=2.59) you are only taking into consideration a single direction of travel. Since the travel exists on a rotational axis, up and down, you end up with a multiplier of 2. Therfore, you could mulitply your 27,195 x 2 and divide by 12 if you wanted and the answer would be the same. In the example that you've given, that step of the math was skipped and was just divided by 6 (") or 1/2 of a foot. You have to love math!!

Also, as was mentioned, there are several factors that determine the redline point. For the most part, balance is the largest key factor that determines where to set the redline. Vibration kills...and manufactures are limited to tolerance specs within the process of building these engines.
If the wieght of any two given components were exactly equal, there is a good chance that their mass would not be equal and therefor create a weak link in the part of lessor mass. (This is most noted in cast parts and less of a factor in billet machined parts)

All of these factors, combined with volumetric flow rates of the carbs, heads, and exhaust system (even more math), give you an equilibrium point that simply stated, "more RPM's will not equal more power" and increase the rate of failure. Hope I didn't bore anyone with blip.

Boring, no. Fascinating from an engine theory perspective, yes!

What parts do you think the Yoshi GS1000 had balanced - the crank, connecting rods, pistons? How do you think Pops Yoshimura decided that 10,500 RPM was the magic number not to be exceeded by Cooley and the rest of the Suzuki team? From a practical shadetree mechanic perspective, how would you decide how high you can rev an engine that you've upgraded? On a dyno as suggested?

 

[Dave8338]

Most likely, any and all of the rotating mass was balanced independently and then again once assembled with a harmonic balancer (similar to those used when spin balancing tire and wheel combos on your car). My guess is that the rods were shot peened and forged. This helps greatly to improve the mass consistency and strength, and makes balancing much more accurate up to and over the force curve (the point where any given material fails as a result of it natural limits (M x V= F)). Also guessing that forged pistons were used along with lighter valves and stronger springs.
Almost a given that stronger rod bolts were used and that a lower end girdle brace (ties the main caps together with the block) might have been used.
Open up the top end with a port and pollish, larger carbs, bigger cams with higher lift and longer duration and match the exhaust, then check the final package with a frequency readout at higher RPMs to see that it is less than it would have come from the factory with and hit the track.
WOW...where did you say the track was, I'll bring the car!!! \\/

Dave

 

[koolaid_kid]

Dave, I concur. Certain parts add strength (shot-peened rods, forged pistons). Certain parts lessen moving mass (lighter valves). Certain parts are required for higher rpms (stronger springs). Balancing everything reduces vibration. Normally, this is the crank, rods and pistons.
Changing the cams and carbs allows the engine to achieve usable power in the higher rpm ranges.
All in all, it is a totally engineered package, not just bolt-ons like we tend to run on the street. And they know long before it hits the road what its limits should be.

 

[pano]

When your piston travel is calculated, (in your example=2.59) you are only taking into consideration a single direction of travel. Since the travel exists on a rotational axis, up and down, you end up with a multiplier of 2. Therfore, you could mulitply your 27,195 x 2 and divide by 12 if you wanted and the answer would be the same. In the example that you've given, that step of the math was skipped and was just divided by 6 (") or 1/2 of a foot. You have to love math!! 8-[ :-D

I see it now...thanks

 

[RacingJake]

Thats why my Sporty is like a sewing machine, two pistons on the same crank pin turning 7500 rpms results in both pistons reaching 4,700 feet per second. To bad 4,000 feet per second is consider the max for reliability.

 

[Dave8338]

Thats why my Sporty is like a sewing machine, two pistons on the same crank pin turning 7500 rpms results in both pistons reaching 4,700 feet per second. To bad 4,000 feet per second is consider the max for reliability.

The hogs are the only engines that are designed to run "rough" by nature. Someone should tell the engineers over there that is is possible to get the miss out and in the process, make a SMOOOOOOTH engine that will still power their bikes.... :-D Not to mention, 4,000 feet per second is ALOT of travel, I think that my 270 Browning runs about 3700 feet per second with a 150 grain bullet?