SuzukiSavage.com - Print Page

SuzukiSavage.com
/cgi-bin/YaBB.pl
General Category >> Rubber Side Down! >> What is a safe redline?
/cgi-bin/YaBB.pl?num=1647440327

Message started by stinkywheels on 03/16/22 at 07:18:47

Title: What is a safe redline?
Post by stinkywheels on 03/16/22 at 07:18:47

I've got a Savage with (supposedly) with big bore higher compression piston, ported head, hotter cam, roundslide carb. I say supposedly as I haven't torn into it but it runs considerably better than the wifes stocker. I'm putting this engine from this modded Savage into a butchered Cafe bike I'm building. What is a safe redline for these bikes? I've not taken it over 6K as I really don't know what the bottom end will take. I don't really know what you can rev these to safely.

Title: Re: What is a safe redline?
Post by TheSneeze on 03/16/22 at 07:39:26

I am not sure what the redline is for the Savage, but the valve train is usually the limiting factor when it comes to RPM.

Title: Re: What is a safe redline?
Post by verslagen1 on 03/16/22 at 08:53:19

6500 rpm is mfg spec, and it will do more w/out blowing up.
According to the gearing commander, 97 mph is max speed in stock form.
SO, unless you are winding it out in 1st gear... [smiley=evil.gif]

Title: Re: What is a safe redline?
Post by LANCER on 03/16/22 at 10:46:38

Some engines have hit 8000 rpm momentarily without ill effect.
That is not recommended however.

Title: Re: What is a safe redline?
Post by stinkywheels on 03/16/22 at 10:51:26

Thank you that is helpful. I'm not new to bikes, just Savages. I need to jet it and would like to know what it'll do, or not do. It's a chain drive and can mess with sprockets again if need be. I've got quite a few.
33203736292422202B74450 wrote:

6500 rpm is mfg spec, and it will do more w/out blowing up.
According to the gearing commander, 97 mph is max speed in stock form.
SO, unless you are winding it out in 1st gear... [smiley=evil.gif]

Title: Re: What is a safe redline?
Post by Gary_in_NJ on 03/16/22 at 10:52:53

With all of the mods on your engine, the redline is all but meaningless. I would suggest that you put the bike on a dyno and do a few pulls, noting what rpm the power peaks, and then drops by 5-7%. Assuming that the valve springs can handle your lift and duration, that's your redline.

Title: Re: What is a safe redline?
Post by stinkywheels on 03/16/22 at 10:54:20

I doubt it'll see that on purpose, buuut things do happen. Thanks. If I ever get in the engine I'll see if it's got some of your parts in it.
5B56595452450500370 wrote:

Some engines have hit 8000 rpm momentarily without ill effect.
That is not recommended however.

Title: Re: What is a safe redline?
Post by stinkywheels on 03/16/22 at 11:02:51

It's probably only ever gonna see a butt dyno. I've already thrown more money in the toilet on this bike than I should. I'm just going to have more fun on it, be kinda nice to it. I might put a Keihin flatslide on it and see if it likes an accelerator pump of not. I've got lots of faster bikes, I just wanna play with something simple without taking all the fun out of it.
757F7B717A73777E202622120 wrote:

Title: Re: What is a safe redline?
Post by stinkywheels on 03/16/22 at 11:04:05

With a 94mm stroke I thought piston speed might come into play.
0F10353238313D2E375C0 wrote:

I am not sure what the redline is for the Savage, but the valve train is usually the limiting factor when it comes to RPM.

Title: Re: What is a safe redline?
Post by Dave on 03/16/22 at 11:04:54

Even in a modified engine - there is not a lot of reason to spend too much time up around 6,000 rpm. The strong point of the big single is the torque and the ability to pull strongly in the mid range rpm. On my engine I hold the throttle open and when I feel the pull from the engine starting to weaken - I shift to the next gear. I believe that is up around the 6,000 - 6,500 rpm area......but I seldom look at the tach while I ride that way.

I was on a forum with a lot of younger folks....and it had some older experienced guys as well. One of the Noobs was saying how he always takes the engine to the redline before shifting to the next gear. One of the older guys told him that the redline on the tachometer is like the local bar - you can go there occasionally and likely be alright.....but if you hang out there all the time you will likely get into trouble!

Title: Re: What is a safe redline?
Post by LANCER on 03/16/22 at 12:33:26

In the upper rpm’s he engine uses some oil.

Title: Re: What is a safe redline?
Post by Ruttly on 03/16/22 at 13:24:18

When my butt gets numb from high rpm buzz , time to back off a bit
Don’t even think about farting !

I don’t look at the speedo why would I have a tach.

Title: Re: What is a safe redline?
Post by ohiomoto on 03/16/22 at 19:59:24

Jesus, just crappity smacking shift when it feels right.

Title: Re: What is a safe redline?
Post by Ruttly on 03/16/22 at 20:34:34

Ride it like you stole it , not like you own it , it’s more fun !

Title: Re: What is a safe redline?
Post by TheSneeze on 03/16/22 at 21:36:11

5C5B5A5C5E5C475C330 wrote:

Jesus, just crappity smacking shift when it feels right.

I'll cosign this one...

Title: Re: What is a safe redline?
Post by buster6315 on 03/19/22 at 21:07:30

When the engine power 'noses over', time to shift. KISS principle :)

Title: Re: What is a safe redline?
Post by Gary_in_NJ on 03/20/22 at 05:38:40

The OP explained that his engine is far from stock. Unlike the stock OEM engine where power drops well before redline, the OP’s engine may pull hard right into valve float. His concern about setting a safe RPM, while extracting the investment into his built engine - is real.

The LS650 engine doesn’t have a tach because it isn’t really necessary (and Suzuki was pinching pennies). That’s not true for a built engine. Giving advice like “shift when power falls off” is useless. Redline is set to protect the valve train, it’s not just a line on the tach.

Drag Bike is the one who should comment on this.

Title: Re: What is a safe redline?
Post by Fast 650 on 03/20/22 at 07:58:15

Sounds like his engine is essentially the same as DBM's big bore hotrod engine. Wind drag in 5th gear becomes a natural rev limiter that will keep it from exceeding 6500 rpm. It will rev higher than that in the lower gears but HP begins to drop at about 5500 rpm and torque falls off above 4000 rpm, so revving it past that yields diminishing returns anyway. Shifting when you feel power start to drop is valid advice in that light.

Title: Re: What is a safe redline?
Post by TheSneeze on 03/20/22 at 11:47:12

Even though I agree with the "shift when it feels right", I will be installing a tach on my bike. At times it's not comfortable sitting on both sides of the fence! :o ;D ;D ;D

Title: Re: What is a safe redline?
Post by ohiomoto on 03/20/22 at 17:40:59

You need a tach because of "performance" mods???

Bunk! Motocross bikes have way more power than any LS650 and no one is looking at tachometers to decide when to shift. ::) ::)

Pretty sure moto GP riders aren't looking at their tach between shifts either.

I'll keep my eyes on the road thanks.

Title: Re: What is a safe redline?
Post by Gary_in_NJ on 03/20/22 at 19:28:36

A modern dirt bike can safely rev to 15,000 rpm, but most sign-off around 13,500. Valve float isn’t an issue…the power will fall on its face as you exceed 13.5k.

Yes, you can modify an engine to the point that the engine makes power well into the point where there is valve float, at which point power will fall off permanently. I don’t understand why this is an issue. The OP is making a wise equipment choice for his bike.

Oh, modern MotoGP bikes have EFI. The redline is set by the computer and the rider shifts at the shift light.

Title: Re: What is a safe redline?
Post by verslagen1 on 03/20/22 at 20:56:16

686F6E686A687368070 wrote:

I'll keep my eyes on the road thanks.

Once your ear is tuned to the tach, you won't be looking at it either.

Title: Re: What is a safe redline?
Post by DragBikeMike on 03/21/22 at 12:41:36

IMO, the tachometer is a useful tool, and necessary to protect the engine. Stinkywheels asked “what is a safe redline?” I suspect he wants to make sure he doesn’t destroy his engine.

Those dirt bikes and moto GP bikes mentioned earlier have rev limiters. Google “Honda CRF 450”, “Suzuki DRZ400”, or “Husqvarna 701” and you can find where those factory limiters are set. Best as I can tell, the Savage does not have a rev limiter. I’ve had mine to 8K several times and it didn’t hit a limiter. If it has one, the factory set it at well over 8K.

The two most critical concerns are valve float and average piston speed.

You never want to lose control of the valves. Valve float risks a collision between an open valve and the piston. It also wrecks the valves & seats when the valves crash into the seats because the follower has separated from the deceleration ramp on the cam lobe. You don’t have to run the valve into the piston to wreck things up. Smashing valves into the seats does a right fine job of trashing the sealing surfaces and spring retainers. It also can lead to a snapped off valve (something we see on this forum all too often).

If you want to get reasonable service life, the average piston speed on a street engine should remain below 4500 fpm. That shouldn’t be a problem on the Savage. The stroke is 3,701”. Average piston speed at 7500 rpm is 4626 fpm. I don’t think anyone is gonna spend much time at 7500 rpm, but it gives you a good reference. If you want to get good service life from the engine, 7300 rpm will keep your average piston speed below 4500 fpm.

Stinkywheels said he had a “big bore high compression piston”. If it’s a Wiseco pop-top, there should be a ton of room between the valves and the piston when the piston is at TDC. If he has a Wiseco flat-top, things are real close. That “redline” thing starts getting to be a serious concern, especially on an engine without a rev limiter.

The higher gears aren’t nearly as concerning as the lower gears. In first & second gear, you can bury the tach in an instant. Folks are also more inclined to practice the proverbial “power-shift” in the lower gears. Nothing like winding that sucker up to 7500 in first and then missing the shift to second. Of course, a tach won’t help much in that situation, but at least you will have a better idea of why your motor quit runnin.

The few dyno runs I have done show that the stock engine quits makin power about 5500 rpm. The available high performance cams start signing off about 6500 rpm, but still make good power all the way to 7K. There really isn’t any good reason to run it past 7K. I can’t explain why I constantly do it. I just can’t help myself. A quick glance at the tach brings me back to reality. Whoa!

I also use my tach for speed indication. I hate taking my eyes off the road to look at the stupid tank mounted speedo. The tach is a sweet addition. In fifth gear, 3K = 45mph, 3.5K = 55 mph, and 4K = 65mph. Helps me stay out of trouble with the local constable.

You don’t need a tach, but it’s mighty nice to have one.

Title: Re: What is a safe redline?
Post by TheSneeze on 03/21/22 at 15:19:09

All good points, Mike.

Title: Re: What is a safe redline?
Post by zipidachimp on 03/23/22 at 21:20:46

If you have ever watched a Nascar or Indycar race with a camera inside the car, I'm totally amazed that valve springs, bearings etc. can run at max rpm for upwards of 2 hours without exploding. Truly awesome !
Cheers! 8-)
ps: and 12 hr and 24hr races?

Title: Re: What is a safe redline?
Post by TheSneeze on 03/23/22 at 22:47:24

Don't make me digress... I am a huge F1 and Indycar fan!

Title: Re: What is a safe redline?
Post by Armen on 03/28/22 at 07:54:16

So, a million years ago I had a ‘79 XL250 Honda. Great bike, but not much power. At the time, Honda offered a line of parts called ‘HPO’, for ‘High Performance Options’. On the list was a ported head with oversized intake valves, a high compression oversized piston, and a few other goodies.
When the valve cover leak got so bad that I had to address it, I took the opportunity to lose my mind.
I got a round slide Mikuni carb (larger than stock) and pod filter, to replace the Keihin which had corroded it’s mixture screw in place. Then I got a 4” Supertrapp exhaust. Along the the HPO head, I got a Megacycle cam, and sexier valve springs. And the HPO high compression piston brought the displacement to 275 ccs. I was ready to rock!
It took a while to get some bugs out, but when it was sorted out it was awesome.
The bike didn’t have a tach, just paint marks on the speedo for where to shift. With the new goodies, the Motor could go WAY past those shift points. I geared it taller to take advantage of the power increase. With the stock motor, top speed was about 75 MPH. With the breathed on motor, over 85.
One day when I was heading down the highway revving the nuts off the bike (as usual), and there was a loud bang/clunk sound from the bottom end.
I got a truck and got the bike home.
Minor disassembly revealed that the crank main bearings had blown their lunch. I guess the combination of more power and more revs was deadly.
Years later I was reading a bearing book put out by one of the bearing manufacturers, and it stated that if you can reduce a bearing’s RPM by 10%, you can double it’s life. Working the formula backwards, I guess spinning those crank bearings at a few thousand RPMs more than stock greatly shortened their lives.
I was so disgusted by the magnitude of time and money lost, that I put the bike in the local paper for a few hundred dollars, and sold it to the first person who called.
So, the moral of the story is to make the bike work better at lower RPMs, not to raise the redline to the sky.

Title: Re: What is a safe redline?
Post by Gary_in_NJ on 03/28/22 at 09:01:02

Hp = Tq x rpm/5252

It's easier to increase rpm than torque. But it's more satisfying to ride a big fat torque curve.

Title: Re: What is a safe redline?
Post by buster6315 on 03/29/22 at 06:47:01

Then the quoted figures of 31hp and 37 torque are incorrect?

Title: Re: What is a safe redline?
Post by Gary_in_NJ on 03/29/22 at 09:55:58

77606661706723262420150 wrote:
Then the quoted figures of 31hp and 37 torque are incorrect?

You need to know the rpm where these peeks occur. It usually doesn't happen at redline, certainly torque doesn't. Typically peek HP & peek torque happen at different rpms.

Title: Re: What is a safe redline?
Post by buster6315 on 03/29/22 at 20:15:16

Try 30 hp @5400 & 34 torque @3400rpm

Title: Re: What is a safe redline?
Post by DragBikeMike on 03/29/22 at 22:34:23

Armen: "So, the moral of the story is to make the bike work better at lower RPMs, not to raise the redline to the sky."

Yep, that's where the new Wiseco flat-top shines. That sucker really sweetens up the middle of the range. Part throttle performance is off the hook. Problem is, the engine just keeps makin power well past 6K. You need some good self discipline to resist the urge to keep stretchin it out. I suspect it will pull like He11 all the way to destruction.

Don't overlook load. That balancer assembly has to be beating its ball bearings to death, even at cruising speed. Just imagine what it's doin when you amp up the speed 1500 rpm beyond what the designers intended. And BMEP, it's gotta be 150% or more above what the the stocker develops.

But I'm a sick dude. Can't help myself. You wanna play you gotta pay. ;)

Title: Re: What is a safe redline?
Post by LANCER on 03/30/22 at 02:53:55

Sick dude indeed...I understand the concept perfectly...you know how tendency’s are. [ch128526]

Title: Re: What is a safe redline?
Post by Armen on 03/30/22 at 06:34:55

The local Duc shop has a Dyno. Like most dyno folks, they fell in love with peak HP. Built some hot bikes. I have a 98 900SS, last year with carbs. They told me that I should use the FI 99 or later cams, more peak HP. Told them the last thing I cared about on the street was peak HP, that I’m all about mid-range.
Fast forward a few years and they build one of their guys a 900SS racer. After a while, they realize that mid range wins races, not peak HP.
I remember an interview with Don Tilley, who build the winningest 883 Sportsters in the class. He said the same thing-most folks worship at the altar of peak HP. Races are won by mid range acceleration.
Basically, you use the peak HP at the last part of the fastest part of the track. The rest of the time, its low and mid range.
While it’s nice to open up the powerband (one of my bikes only makes power between 2500 and 5500), I just don’t like revving the nuts of the motor. Not fun going down the road with the motor vibrating so much.
That, and having fragged my XL makes me a bit cautious about buzzing the bike to 8K.

Title: Re: What is a safe redline?
Post by Dave on 03/30/22 at 17:44:22

There is an old saying from the days they would publish HP numbers in the sales brochure.

HP sells cars.......torque wins races! ;)

I read that the goal is to get the most area under the torque curve on a dyno run.......and that is the engine that will perform the best in the real world.

Title: Re: What is a safe redline?
Post by buster6315 on 03/30/22 at 20:52:54

Torque is very satisfying indeed! However, HP wins races. (drag) Horse
power is calculated with the time element.

Title: Re: What is a safe redline?
Post by DragBikeMike on 03/31/22 at 00:39:49

Armen, interesting that you bring up that old 883 class. As I recall, that class instituted a rule on rev limiters. The sanctioning body had the crews draw ignition modules from a hat (so to speak) prior to each race. Seems that the rev limiters had a fairly large tolerance on the factory setting, so the crews started buying up a ton of modules and testing them until they found the one with the highest setting. To circumvent the cherry picking the AMA instituted the luck-of-the-draw rule. That extra 25 or 30 rpm before it bounced the limiter must have been a significant advantage.

In a class that tight, every teeny weeny bit helps. It's pretty tough to do a lot with the power characteristics of a box-stock 883. I think all they were allowed to change was exhaust, air filter, and jetting. I believe shocks and a fork kit were allowed too.

I don't disagree. An engine with a meaty mid-range is killer, and a lot easier to hustle around a road course. BIG torque numbers also get the job done on a drag strip. Anyone who has ever messed around with a power adder can attest to that. Slap some nitrous on an engine and hit the squeeze button and you get max torque just off idle. Makes your heart stop the first time you try it. After that first hit you're hooked. You're on the dark side and never goin back (until somethin in that motor gives up).

For street use, the focus should always be on healthy mid range. But just look at this power curve. It's one of my old dyno pulls with a DR cam. The only reason Teddy shut it down was because he didn't wanna make a mess on his dyno. It wasn't makin any more power past 6500 but it also wasn't droppin off much either. All's I'm sayin is when you have an engine that delivers like this, it's hard to exercise self discipline. You can hardly feel the thing nose over. It's pullin just about as hard at 7500 as it is at 6500. DANGER ZONE! That's why its so much fun.

Title: Re: What is a safe redline?
Post by Gary_in_NJ on 04/01/22 at 11:23:12

That's an amazing torque curve. 80% max torque between 2,900 and 6,900 rpm, and 90% torque between 4k & 6k. Basically, power everywhere.

Title: Re: What is a safe redline?
Post by justin_o_guy2 on 04/01/22 at 12:11:40

16101F63616662520 wrote:

A question that has eaten on me for a long time is

Is there anything that can be done with that swinging weight to smooth it out?

Title: Re: What is a safe redline?
Post by DragBikeMike on 04/02/22 at 11:20:28

"That's an amazing torque curve. 80% max torque between 2,900 and 6,900 rpm, and 90% torque between 4k & 6k. Basically, power everywhere."

Great observation Gary. It's sorta like an electric motor that vibrates a lot. So much fun to ride at part throttle. That was with the old S&S Super-E carb (Armen calls it "a trash can with a trap door"). For that pull, it was also struggling with a modified stock muffler. I wish I had a dyno pull with the 97mm flat-top and a good free-flowing exhaust system. I suspect the shape of the curve would be identical, just a lot further up the scale.

I'm workin on a post that summarizes the results of the latest teardown and inspection. I've found a lot of interesting stuff related to the bearings. It will tie in nicely with this discussion on the redline. Definitely supports the concept of confining your ops to a reasonable range of rpm.

Thanks for starting the discussion Stinkywheels.

Title: Re: What is a safe redline?
Post by ohiomoto on 04/02/22 at 19:15:36

This bike is a turd, BUT...

It is a lot of fun to short shift it and any RPM.

DBM's dyno shows what's neat about this bike. It has a lot of OXpower!

Title: Re: What is a safe redline?
Post by TheSneeze on 04/04/22 at 21:40:18

"a trash can with a trap door"

This had me chuckling!! Almost spit my bourbon out my nose! Good reading after a week away, and then another week away after Thursday. Love checking in on you guys after a trip. Hopefully back at my motor after this next one. Excited to see what this motor has in store.