What RPM is the fuel cutoff at anyway?
10-16-2004, 08:28 AM
#1
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What RPM is the fuel cutoff at anyway?
Hi,
At the track day I recently attended I was surprised to look down and find that I was at 10.1-10.2k rpms at one point. Down a certain stretch (in between T2 and T3 at NHIS) my usualy technique is to wind out second to what usually works out to be at or near redline at which point I let off and start braking before entering T3. Usually the point I let off at corresponds with my being right around 9k rpm. Apparently I'm getting better at T2 because I noticed that now I can get it up over 10k rpms before T3 (now I put it into third gear before entering T3).
My questions are:
1) where exactly is the fuel cutoff? 600-700 rpm overrev seems a bit much, and;
2) what kind of engine longevity (with proper maintenance) am I looking at doing 500-600 track miles a year?
Thanks.
At the track day I recently attended I was surprised to look down and find that I was at 10.1-10.2k rpms at one point. Down a certain stretch (in between T2 and T3 at NHIS) my usualy technique is to wind out second to what usually works out to be at or near redline at which point I let off and start braking before entering T3. Usually the point I let off at corresponds with my being right around 9k rpm. Apparently I'm getting better at T2 because I noticed that now I can get it up over 10k rpms before T3 (now I put it into third gear before entering T3).
My questions are:
1) where exactly is the fuel cutoff? 600-700 rpm overrev seems a bit much, and;
2) what kind of engine longevity (with proper maintenance) am I looking at doing 500-600 track miles a year?
Thanks.
03-22-2005, 01:12 PM
#2
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Re: What RPM is the fuel cutoff at anyway?
I once hit the rev-limiter by trying to make an aggressive pass through a mountain curve and mistakenly thinking the VTR was in second gear rather than first. And, the rev-limiter kicked-in--dead-nuts--at the bottom of the red line, scaring the be-Jesus out of me.) 
Thus, if you are hitting the red line and then still increasing engine speed 500 or 600 rpm's before the rev-limiter engages, I would suspect that the rev-limiter needs either adjusting or replacing--unless you get a kick out of pushing the envelope and have a budget that can easily accomodate an engine rebuild.
cheers,
--HotStreetVTR
Thus, if you are hitting the red line and then still increasing engine speed 500 or 600 rpm's before the rev-limiter engages, I would suspect that the rev-limiter needs either adjusting or replacing--unless you get a kick out of pushing the envelope and have a budget that can easily accomodate an engine rebuild.
cheers,
--HotStreetVTR
03-22-2005, 01:32 PM
#3
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Re: What RPM is the fuel cutoff at anyway?
Concerning VTR longevity, track days notwithstanding, there are several members of the Forum who have VTRs with over 100K miles and who have experienced no major problems. And, I would not be surprised at all if we have a few 200K-milers before too terribly long, especially since a good portion of us use nothing but high-quality fullly synthetic oil (cooler engine temperatures and more effective lubrication yield longer engine-life).
Even so, one thing that I would do right away to ensure longer engine-life would be to replace the OEM cam-chain tensioners with properly-installed APE manual cam-chain tensioners--all the better to avoid the risk of crying along the roadside when an engine breaks in a most radical fashion.
cheers,
--HotStreetVTR
Even so, one thing that I would do right away to ensure longer engine-life would be to replace the OEM cam-chain tensioners with properly-installed APE manual cam-chain tensioners--all the better to avoid the risk of crying along the roadside when an engine breaks in a most radical fashion.
cheers,
--HotStreetVTR
03-23-2005, 08:45 AM
#5
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The rev limiter cuts ignition on one cylinder. It is there to keep the engine from revving higher than it can run safely. I take mine to well over 10,000 RPM on a regular basis. It is a conservative number. Rev away!! (or buy a Harley).
I put an HRC ignition in for this year, which doesn't have a rev limiter, so I'll have to watch the tach carefully.
I put an HRC ignition in for this year, which doesn't have a rev limiter, so I'll have to watch the tach carefully.
04-03-2005, 06:53 AM
#7
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Just because it's still "pulling" doesn't mean you're not getting REAL close on clearance. I wouldn't chance running it over the redline much. Being a V twin and can't see the advantage anyway, your power doesn't drop off that much when you grab another gear.
In you are in top gear, and at a track day, then yeah keep the throttle pinned. But if you are in second or third, don't torture the bike for nothing...
I agree that it's the ignition that cuts off during an over-rev, and yeah I hope it's working right when you get into the 10's that seems a bit much. :0
I do more wheelies then track days, and very often I tend to not get everything on "lock" balanced out until I'm at 9k rpms, 2nd gear, and then I'm holding that for around a mile, so I'm sure my day is coming for my motor to one day quit on me due to the combination of being reved up too much, and also of course being starved for oil due to being upright instead of horizonal. I highly doubt I'll see the 100k mile mark.
In you are in top gear, and at a track day, then yeah keep the throttle pinned. But if you are in second or third, don't torture the bike for nothing...
I agree that it's the ignition that cuts off during an over-rev, and yeah I hope it's working right when you get into the 10's that seems a bit much. :0
I do more wheelies then track days, and very often I tend to not get everything on "lock" balanced out until I'm at 9k rpms, 2nd gear, and then I'm holding that for around a mile, so I'm sure my day is coming for my motor to one day quit on me due to the combination of being reved up too much, and also of course being starved for oil due to being upright instead of horizonal. I highly doubt I'll see the 100k mile mark.
04-04-2005, 06:03 AM
#9
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Just because it's still "pulling" doesn't mean you're not getting REAL close on clearance. I wouldn't chance running it over the redline much. Being a V twin and can't see the advantage anyway, your power doesn't drop off that much when you grab another gear.
I'm good for the go
sckomar ,
http://www.skracing.com/home.htm
can get you those tensioners . Tell them the guy from Oklahoma sent ya . I buy most of my aftermarket hard parts from them .
JE pistons are only $220.00 from SK Racing also ...hint hint - build that thing and put some anger in the motor
04-04-2005, 10:37 AM
#10
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Re: What RPM is the fuel cutoff at anyway?
My Dyno runs and several other SuperHawk Dyno runs i have seen show that the peak HP is around 9600 RPM and drops off from there. The torque peaks around 10000 rpm and sort of levels of with a slight drop till rev-limiter kicks in at 10500.
Thi sbeing said, why push it to rev limiter kick in as you are already past the peak performance. If you are bumpnig the rev limiter regularly on a track day then you need to change gearing or a different gear if not already in top gear.
Buy different sprockets / chain combo's
Thi sbeing said, why push it to rev limiter kick in as you are already past the peak performance. If you are bumpnig the rev limiter regularly on a track day then you need to change gearing or a different gear if not already in top gear.
Buy different sprockets / chain combo's
04-04-2005, 12:59 PM
#11
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I agree, there is no reason to hit the rev limiter. A "built" motor will pull to redline, even in top gear. I've only actually hit the rev limiter a couple of times, when I've chosen the wrong gear to pass a car on the highway. At the track I shift at about 9600-10k. the engine seems plenty happy. I did a teardown/inspection over the winter and everything was hunky dory after five 200 mile track days and a lot of street riding. valve seats are going to need attention after 15-20k miles, no matter how you ride. Expect your exhaust valve seats to be pitted. the longer you wait the deeper you'll have to sink the valves to get below the pitting.
04-04-2005, 01:13 PM
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I would be careful about disabling the rev limiter to spin it faster with the stock valve train. I don't know how much safety margin there is on valve spring stiffness. If a valve floats and hits a piston, the valve retainers fly out and the valve falls in to the cylinder....
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