Our Bonneville Report
09-07-2010, 02:26 PM
#46
Rennlist Member
usually valve float only has the effect of losing power. the boost pressure pushing on the back of the valve is so slight, all it could do is keep the valve open a tad longer, and that would be a power loser too. the valve spring broke due to it being sized wrong, or defective. we are only talking 6000rpm here anyway. this isnt rocket science. stock springs might work fine, but if not, only because of the extra lift of the custom cam. even then, a stock spring would probably work.
now the question that i had before, is that peak HP is at 6000rpm , so why do you care to go over that?? Dont say gearing, because you can easily use a 26 to 26.5" diameter tire to get to 235mph at 6600rpm. BUT, if you want more than 570hp to get there, you better be able to do something with the gearing, like go to a 2:1 rear end if that can be modifed to do that somehow. (or get a 28" diameter tire to do it.
Otherwise, what is the sense of running 700hp if you cant use it when you need it? Im just a little confused about this part.
now the question that i had before, is that peak HP is at 6000rpm , so why do you care to go over that?? Dont say gearing, because you can easily use a 26 to 26.5" diameter tire to get to 235mph at 6600rpm. BUT, if you want more than 570hp to get there, you better be able to do something with the gearing, like go to a 2:1 rear end if that can be modifed to do that somehow. (or get a 28" diameter tire to do it.
Otherwise, what is the sense of running 700hp if you cant use it when you need it? Im just a little confused about this part. Isn't the pressure inside the cylinder also almost 15 psi higher at points when the valve float is likely? The only time when the intake valves are going to float is right after the max intake lobe lift (and possibly bouncing off the seat but that's another story.) The static pressure differential between the cylinder and the port near the intake lobe max lift is small and not influenced much by boost. Right?
So where is this boost-induced valve float coming from?
Maybe there's some additional kinetic pressure from the denser charge hitting the back of the valve, but so far nobody here has made that argument.
So where is this boost-induced valve float coming from?
Maybe there's some additional kinetic pressure from the denser charge hitting the back of the valve, but so far nobody here has made that argument.
09-07-2010, 02:33 PM
#47
Nordschleife Master
Guessing here, but maybe under high boost and rpm the flow through the intake valve is starting to choke, and that results in significant pressure differential across the intake valve as it closes, where normally aspirated the differential would be close to zero or even negative?
OTOH a 2" intake valve is only about 3 sq inches, so the force would be triple the differential, but even if it was 15 psi that would only be 45 lbs of force, doesn't seem that much.
OTOH a 2" intake valve is only about 3 sq inches, so the force would be triple the differential, but even if it was 15 psi that would only be 45 lbs of force, doesn't seem that much.
09-07-2010, 03:04 PM
#48
Rennlist Member
and the valves are only 1.5" anyway. anyone ever push down a valve spring? 50lbs leaning on it, doesnt do anything. anyway, on a 38mm valve, the area is near 1.75sq", so the pressure on the valve surface when closed would only be 25lbs. nothing.
anyway that flow starts to slow and stop at BDC, even any kinetic energy of the air flow wouldnt do much. anyway, is this really the issue of the spring braking. valve float doesnt effect the springs. those spirngs wobble and wiggle around and if here is coil bind due to the lift, that could have caused it. but its not from boost. if it is, I would sure like to hear a intellegent reason why.
anyway that flow starts to slow and stop at BDC, even any kinetic energy of the air flow wouldnt do much. anyway, is this really the issue of the spring braking. valve float doesnt effect the springs. those spirngs wobble and wiggle around and if here is coil bind due to the lift, that could have caused it. but its not from boost. if it is, I would sure like to hear a intellegent reason why.
Guessing here, but maybe under high boost and rpm the flow through the intake valve is starting to choke, and that results in significant pressure differential across the intake valve as it closes, where normally aspirated the differential would be close to zero or even negative?
OTOH a 2" intake valve is only about 3 sq inches, so the force would be triple the differential, but even if it was 15 psi that would only be 45 lbs of force, doesn't seem that much.
OTOH a 2" intake valve is only about 3 sq inches, so the force would be triple the differential, but even if it was 15 psi that would only be 45 lbs of force, doesn't seem that much.
09-07-2010, 03:11 PM
#49
Rennlist Member
Wow Carl. Impressive indeed !!
Proper recognition to you and your willingness to always include the "general public" in your adventures, along with play-by-play details, highs and lows with results and openness with your tuning and parts strategies. Greatly appreciated.
Great thread and contributions.
Proper recognition to you and your willingness to always include the "general public" in your adventures, along with play-by-play details, highs and lows with results and openness with your tuning and parts strategies. Greatly appreciated.
Great thread and contributions.
09-07-2010, 03:11 PM
#50
Developer
Thread Starter
Kibort, the peak HP was 6100 rpm because thats where the valve float began. We lost boost when the valve float began - it went right out the exhaust pipe. We did still continue to accelerate to 7000 rpm, but as the rpm got higher the valve float got worse, and we lost HP to where we had only 500 HP at 7000.
So I do not believe the max HP will be at 6100 when this is corrected. That is what it was on these pulls, but it is not conclusive as the engine is still in development.
PS: it isnt coil bind. That was carefully checked during the install.
So I do not believe the max HP will be at 6100 when this is corrected. That is what it was on these pulls, but it is not conclusive as the engine is still in development.
PS: it isnt coil bind. That was carefully checked during the install.
09-07-2010, 03:15 PM
#51
Captain Obvious
Super User
Super User
usually valve float only has the effect of losing power. the boost pressure pushing on the back of the valve is so slight, all it could do is keep the valve open a tad longer, and that would be a power loser too. the valve spring broke due to it being sized wrong, or defective. we are only talking 6000rpm here anyway. this isnt rocket science. stock springs might work fine, but if not, only because of the extra lift of the custom cam. even then, a stock spring would probably work.
now the question that i had before, is that peak HP is at 6000rpm , so why do you care to go over that?? Dont say gearing, because you can easily use a 26 to 26.5" diameter tire to get to 235mph at 6600rpm. BUT, if you want more than 570hp to get there, you better be able to do something with the gearing, like go to a 2:1 rear end if that can be modifed to do that somehow. (or get a 28" diameter tire to do it. Otherwise, what is the sense of running 700hp if you cant use it when you need it? Im just a little confused about this part.
now the question that i had before, is that peak HP is at 6000rpm , so why do you care to go over that?? Dont say gearing, because you can easily use a 26 to 26.5" diameter tire to get to 235mph at 6600rpm. BUT, if you want more than 570hp to get there, you better be able to do something with the gearing, like go to a 2:1 rear end if that can be modifed to do that somehow. (or get a 28" diameter tire to do it.
Otherwise, what is the sense of running 700hp if you cant use it when you need it? Im just a little confused about this part. He can use it in all the gears except 5th. You can get a pretty good momentum if you shift into 5th when the engine is making 700hp. Or am I wrong?
09-07-2010, 03:15 PM
#52
Developer
Thread Starter
Proper recognition to you and your willingness to always include the "general public" in your adventures, along with play-by-play details, highs and lows with results and openness with your tuning and parts strategies. Greatly appreciated.
09-07-2010, 03:20 PM
#53
Developer
Thread Starter
The weather here today is crap. As soon as its sunny (hopefully tomorrow) I will roll the car out and take some pics for you guys with the Bonneville nose on and all.
09-07-2010, 03:26 PM
#54
Developer
Thread Starter
Mark - I just saw your FDR question.
We are using a 2.20 transaxle FDR, but the rear tires are 28.4" tall Land Speed Tires (Certified to 300 MPH)
Depending on the frontal area and the Cd (coefficient of drag) and available traction, we see ourselves topping out from 238 to 251 MPH.
We are using a 2.20 transaxle FDR, but the rear tires are 28.4" tall Land Speed Tires (Certified to 300 MPH)
Depending on the frontal area and the Cd (coefficient of drag) and available traction, we see ourselves topping out from 238 to 251 MPH.
09-07-2010, 04:28 PM
#55
Rennlist Member
...wouldn't the rear flares be a disadvantage at that speed, since they are width designed and not cd designed? It's not painted, so maybe you'd consider removing them prior to shooting it, so you don't have to deal with any weird turbulence.
09-07-2010, 04:50 PM
#56
Developer
Thread Starter
The rules require no streamlining behind the cowl. Everything has to be box-stock behind the cowl.
In this case (rear fender flares) what you are seeing is that this car had wide fender flares on it, they have been removed, and a set of OEM rear wheel skirts have been put back on so I have the OEM rear 928 profile.
I wish they were flush-mounted and smooth, but then again, the aero in this particular area is not as important as the aero in fthe front - and thats where we have spent most of our time.
I looked at building a purpose-built land speed car, but cost prohibited it. The Pikes Peak event left me with a full cage and fire suppresion system in the car, and a bunch of other safety goodies already in place. It was faster and cheaper to remove the big wing and wide tires and fender flares and convert the aero on this car. Will it be as clean as a purpose-built land speed car? No. But it should get the job done.
Here's a picture of the same car in road racing/hill climb trim:
In this case (rear fender flares) what you are seeing is that this car had wide fender flares on it, they have been removed, and a set of OEM rear wheel skirts have been put back on so I have the OEM rear 928 profile.
I wish they were flush-mounted and smooth, but then again, the aero in this particular area is not as important as the aero in fthe front - and thats where we have spent most of our time.
I looked at building a purpose-built land speed car, but cost prohibited it. The Pikes Peak event left me with a full cage and fire suppresion system in the car, and a bunch of other safety goodies already in place. It was faster and cheaper to remove the big wing and wide tires and fender flares and convert the aero on this car. Will it be as clean as a purpose-built land speed car? No. But it should get the job done.
Here's a picture of the same car in road racing/hill climb trim:
09-07-2010, 05:29 PM
#57
Rennlist Member
so, your peak hp will still probably be at 6000rpm, or do you suspect the cure will give you even more than 700hp? if not, why worry about it. make the top speed at 6100rpm, or with 28.5" tires, it should be over 235mph, but with wheel spin , you might be higher.
you know what im getting at. you might be able to not have to run the engine that fast, if you can run peak HP equaling your top speed. but heck, if you are going for a record and you want all that you can, sure, why not fix the issue.
you know what im getting at. you might be able to not have to run the engine that fast, if you can run peak HP equaling your top speed. but heck, if you are going for a record and you want all that you can, sure, why not fix the issue.
Kibort, the peak HP was 6100 rpm because thats where the valve float began. We lost boost when the valve float began - it went right out the exhaust pipe. We did still continue to accelerate to 7000 rpm, but as the rpm got higher the valve float got worse, and we lost HP to where we had only 500 HP at 7000.
So I do not believe the max HP will be at 6100 when this is corrected. That is what it was on these pulls, but it is not conclusive as the engine is still in development.
PS: it isnt coil bind. That was carefully checked during the install.
So I do not believe the max HP will be at 6100 when this is corrected. That is what it was on these pulls, but it is not conclusive as the engine is still in development.
PS: it isnt coil bind. That was carefully checked during the install.
09-07-2010, 05:32 PM
#58
Rennlist Member
momentium has nothing to do with acceleration.
the ONLY thing that runnng this engine past redline will do, is allow him to get to the top speed quicker, but thats not really the issue, and it really wouldnt even do that, if the HP falls as fast as it was rising from 4500rpm. (post shift to 6600rpm). so, even using the rpm after 6600, wouldnt buy you anything.
the ONLY thing that runnng this engine past redline will do, is allow him to get to the top speed quicker, but thats not really the issue, and it really wouldnt even do that, if the HP falls as fast as it was rising from 4500rpm. (post shift to 6600rpm). so, even using the rpm after 6600, wouldnt buy you anything.
09-07-2010, 06:05 PM
#60
Developer
Thread Starter
Mark: This is the first application of our new composite intake runners and plenum. I cannot assume that the peak HP will be at 6100 like a stock manifold, in fact, we deliberately moved the power band to more of a racing application than the OEM design for street use.
So yes, I will fix the issue so I can power all the way to 7000 and find out definatively where the peak torque and HP is for this intake/plenum/camshaft package. Leaving it alone and just reving to 6200 is not an option.
So yes, I will fix the issue so I can power all the way to 7000 and find out definatively where the peak torque and HP is for this intake/plenum/camshaft package. Leaving it alone and just reving to 6200 is not an option.