Safe rev limit?
06-10-2002, 09:08 PM
#1
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Safe rev limit?
I am going to have a set of chips burned for my motor, and wish to have a rev limiter put on it. (Since redline comes quick with 400hp at the crank and the tires on fire) What is a safe redline you have all run?
Info:
Fully Rebuilt '87 block
'86 Rods
K27/8 @ 18psi
MAF/ARC-2
Exhaust
Fuel
ETC
I am thinking 7100 would be about right.
TIA!
Info:
Fully Rebuilt '87 block
'86 Rods
K27/8 @ 18psi
MAF/ARC-2
Exhaust
Fuel
ETC
I am thinking 7100 would be about right.
TIA!
06-10-2002, 09:12 PM
#2
Three Wheelin'
Join Date: Sep 2001
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I've put 20,000 miles on my current motor with a 7000rpm limit without any problems, both at 12psi and 20psi. I hit the limiter at every stop light in 1st and 2nd.
And yes, redline does come awful quick in a done up motor =).
And yes, redline does come awful quick in a done up motor =).
06-10-2002, 09:18 PM
#4
Nordschleife Master
The rods from '86 turbo's are forged while the rods from all other year turbo's are cast.
Forged = better
back to the redline...
Doesn't the engine have rod-bearing oiling issues at such high rpm levels? Maybe if you cross-drilled the crank that redline would be more reasonable. Just saying what I've read...I dont have any first hand experience in this area.
Forged = better
back to the redline...
Doesn't the engine have rod-bearing oiling issues at such high rpm levels? Maybe if you cross-drilled the crank that redline would be more reasonable. Just saying what I've read...I dont have any first hand experience in this area.
06-10-2002, 09:26 PM
#5
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[quote]Originally posted by adrial:
<strong>Doesn't the engine have rod-bearing oiling issues at such high rpm levels? Maybe if you cross-drilled the crank that redline would be more reasonable. Just saying what I've read...I dont have any first hand experience in this area.</strong><hr></blockquote>
I thought the rod-bearing oiling/failure issue was due to high cornering loads, not high rpm operations?
<strong>Doesn't the engine have rod-bearing oiling issues at such high rpm levels? Maybe if you cross-drilled the crank that redline would be more reasonable. Just saying what I've read...I dont have any first hand experience in this area.</strong><hr></blockquote>
I thought the rod-bearing oiling/failure issue was due to high cornering loads, not high rpm operations?
06-10-2002, 09:41 PM
#7
Nordschleife Master
[quote]Originally posted by rage2:
<strong>
I thought the rod-bearing oiling/failure issue was due to high cornering loads, not high rpm operations?</strong><hr></blockquote>
I think its due to both. In one case (high cornering loads) the oil sloshes away from the oil pickup...and the entire engine is starved for oil...no oil pressure.
In the other case (high RPM's), the circular motion forces (centripetal) actually prevent the oil from flowing through the crank to the bearings...specifically this is a problem with the #2 I believe. This is where cross-drilling the crank helps to cure the problem.
Again, this is only what I've been told not what I've seen personally.
Perry, with a cross drilled crank thats a more reasonable redline...I remember Deman motorsport mentioning that ~7200rpm or more was the theoretical redline for our engines if it wouldn't be for the oiling issues.
<strong>
I thought the rod-bearing oiling/failure issue was due to high cornering loads, not high rpm operations?</strong><hr></blockquote>
I think its due to both. In one case (high cornering loads) the oil sloshes away from the oil pickup...and the entire engine is starved for oil...no oil pressure.
In the other case (high RPM's), the circular motion forces (centripetal) actually prevent the oil from flowing through the crank to the bearings...specifically this is a problem with the #2 I believe. This is where cross-drilling the crank helps to cure the problem.
Again, this is only what I've been told not what I've seen personally.
Perry, with a cross drilled crank thats a more reasonable redline...I remember Deman motorsport mentioning that ~7200rpm or more was the theoretical redline for our engines if it wouldn't be for the oiling issues.
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06-10-2002, 11:30 PM
#8
Race Car
Adrial
In saying centripedal, are you suggesting that the force (towards center axis) on the oil between the rod (large end) and the cranshaft center line, causes the oil to backflow even with the existence of 5 bar oil pressure and extreme centrifugal force at that RPM level...?
That's not possible....
IMO, of course........
Cheers Adrial
In saying centripedal, are you suggesting that the force (towards center axis) on the oil between the rod (large end) and the cranshaft center line, causes the oil to backflow even with the existence of 5 bar oil pressure and extreme centrifugal force at that RPM level...?
That's not possible....
IMO, of course........
Cheers Adrial
06-10-2002, 11:51 PM
#9
Nordschleife Master
[quote]Originally posted by 951and944S:
<strong>Adrial
In saying centripedal, are you suggesting that the force (towards center axis) on the oil between the rod (large end) and the cranshaft center line, causes the oil to backflow even with the existence of 5 bar oil pressure and extreme centrifugal force at that RPM level...?
That's not possible....
IMO, of course........
Cheers Adrial</strong><hr></blockquote>
Like I said...I'm just quoting what I've been told by reputable sources. It doesn't cause the oil to backflow I don't think...rather not be able to flow through...I think what I'm missing is a good enough mental picture of what it all looks like when its all assembled and spinning.
I'll try to explain though.
EDIT: Yea, that whole explaining thing didn't work out...
Someone help me?
I know this was an issue for 928 engines too...because they are double a 944 engine...This was talked about at the tech-session @ deman motorsport...
Thanks for putting it mildly 951and944S <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" /> <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
<strong>Adrial
In saying centripedal, are you suggesting that the force (towards center axis) on the oil between the rod (large end) and the cranshaft center line, causes the oil to backflow even with the existence of 5 bar oil pressure and extreme centrifugal force at that RPM level...?
That's not possible....
IMO, of course........
Cheers Adrial</strong><hr></blockquote>
Like I said...I'm just quoting what I've been told by reputable sources.
It doesn't cause the oil to backflow I don't think...rather not be able to flow through...I think what I'm missing is a good enough mental picture of what it all looks like when its all assembled and spinning. I'll try to explain though.
EDIT: Yea, that whole explaining thing didn't work out...
Someone help me?
I know this was an issue for 928 engines too...because they are double a 944 engine...This was talked about at the tech-session @ deman motorsport...
Thanks for putting it mildly 951and944S <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" /> <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
06-11-2002, 01:03 AM
#10
Race Car
Adrial
[quote] Thanks for putting it mildly 951and944S <hr></blockquote>
Errr sorry for that, or were you being serious, hard to tell, but really I've read the articles Adrial, and I'm not buying...
Centripetal force can be artificially produced by using a hinge and weight on a rotating object, as far as I know, it cannot have an effect on oil at the long end of a crankshaft throw.
Centripetal=moving or acting towards the center of an axis, thus
Centrifugal=away from an axis
Yeah, it's hard to explain, but, take a lenght of hose, with a constant supply of water, with an opening at each end, one supply and one exit.
Spin the hose in a circular motion, your hand being the axis, the constant supply of liquid is forced out to the end of the hose and will exit if you increase the speed at which you are spinning the hose, increasing centrifugal force.
Add pressure to the supply and you see my point.
They explain the necessity of crossdrilling, suggesting that the "weight" of the oil, not yet making it out of the orfice (rod journal hole) will force it to become static, non moving, or have reverse effect through centripetal force, but they fail to explain "the pressure"...
Adding another hole of equal dimension is what worries me, (crossdrilling) without making two holes, equaling the dimension of the one hole, you effectively "open the end of the hose" moreso, thus affecting the design.
However, the minute clearance between the rod bearing and the crankshaft rod journal probably compensates for this causing no ill effect, and the only possitive effect being that now the rod bearings are simultaneously lubricated, benifitting if nothing else, the temperature of the bearings and the oil.
For most, even race engines, a simple chamfered exit hole at the rod journal will suffice.
The area of the pan where the #2 rod bearing resides is shallow and gets little slingging lubrication as the crankshaft passes through oil in the sump.
Oh but what about the #1 bearing, it's in the shallow part of the pan also.....?
It's proximity in relation to the oil pump makes it safe, but marginal, because it lacks sump depth for scavenging but excells in being first in line to recieve pump pressure, the #2 gets the shaft (pun intended) in both respects and is unable to live when it's deficient sump supply is affected by cornering...
That's why overfilling has been a slight remedy.
It has been successful to some extent right..?
So how can centripedal force explain this then..?
Just trying to explain this Adrial, not meant to demean your post or anything, that would be below the belt IMO.....
Cheers mate.... <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
[quote] Thanks for putting it mildly 951and944S <hr></blockquote>
Errr sorry for that, or were you being serious, hard to tell, but really I've read the articles Adrial, and I'm not buying...
Centripetal force can be artificially produced by using a hinge and weight on a rotating object, as far as I know, it cannot have an effect on oil at the long end of a crankshaft throw.
Centripetal=moving or acting towards the center of an axis, thus
Centrifugal=away from an axis
Yeah, it's hard to explain, but, take a lenght of hose, with a constant supply of water, with an opening at each end, one supply and one exit.
Spin the hose in a circular motion, your hand being the axis, the constant supply of liquid is forced out to the end of the hose and will exit if you increase the speed at which you are spinning the hose, increasing centrifugal force.
Add pressure to the supply and you see my point.
They explain the necessity of crossdrilling, suggesting that the "weight" of the oil, not yet making it out of the orfice (rod journal hole) will force it to become static, non moving, or have reverse effect through centripetal force, but they fail to explain "the pressure"...
Adding another hole of equal dimension is what worries me, (crossdrilling) without making two holes, equaling the dimension of the one hole, you effectively "open the end of the hose" moreso, thus affecting the design.
However, the minute clearance between the rod bearing and the crankshaft rod journal probably compensates for this causing no ill effect, and the only possitive effect being that now the rod bearings are simultaneously lubricated, benifitting if nothing else, the temperature of the bearings and the oil.
For most, even race engines, a simple chamfered exit hole at the rod journal will suffice.
The area of the pan where the #2 rod bearing resides is shallow and gets little slingging lubrication as the crankshaft passes through oil in the sump.
Oh but what about the #1 bearing, it's in the shallow part of the pan also.....?
It's proximity in relation to the oil pump makes it safe, but marginal, because it lacks sump depth for scavenging but excells in being first in line to recieve pump pressure, the #2 gets the shaft (pun intended) in both respects and is unable to live when it's deficient sump supply is affected by cornering...
That's why overfilling has been a slight remedy.
It has been successful to some extent right..?
So how can centripedal force explain this then..?
Just trying to explain this Adrial, not meant to demean your post or anything, that would be below the belt IMO.....
Cheers mate.... <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
06-11-2002, 05:10 AM
#11
Race Director
"In saying centripedal, are you suggesting that the force (towards center axis) on the oil between the rod (large end) and the cranshaft center line, causes the oil to backflow even with the existence of 5 bar oil pressure and extreme centrifugal force at that RPM level...?"
Actually it's the other way around. The oil wants to be flung outwards. But because the hole in the rod-journal is on the side, oil at the outermost reaches of the journal has to flow back towards the crank to make it out the hole. Check out the diagrams I drew here: <a href="http://forums.rennlist.com/cgi-bin/rennforums/ultimatebb.cgi?ubb=get_topic&f=18&t=000669&p=" target="_blank">Topic: 951 rebuild </a>
On all high-rpm engines I've ever seen (15,000rpm motorycles, 9000rpm Hondas, etc.) the oil-hole on the journal has ALWAYS been at the outermost surface of the journal. This allows centrifugal/centripedal force to actually enhance oil-pressure feeding out of the journal; the faster you rev, the more force pushing the oil out. As it is drilled on our cranks, oil-pressure must be used to push oil back towards the crank centerline in order to get out the journal hole. It appears the perp-drilling at 90-degrees to the existing hole mentioned by Huntley (not crossdrilling) is the correct solution.
"The area of the pan where the #2 rod bearing resides is shallow and gets little slingging lubrication as the crankshaft passes through oil in the sump.
Oh but what about the #1 bearing, it's in the shallow part of the pan also.....?"
I think the #2 rod-bearing issue is something internal to the crank. Some connection between the main and rod-journals where the oil-supply isn't as good to the #2 rod. That's the only way the #2 rod-bearing can be isolated from the rest. If it was an oil-pickup issue, all the journals would be affected evenly.
Actually it's the other way around. The oil wants to be flung outwards. But because the hole in the rod-journal is on the side, oil at the outermost reaches of the journal has to flow back towards the crank to make it out the hole. Check out the diagrams I drew here: <a href="http://forums.rennlist.com/cgi-bin/rennforums/ultimatebb.cgi?ubb=get_topic&f=18&t=000669&p=" target="_blank">Topic: 951 rebuild </a>
On all high-rpm engines I've ever seen (15,000rpm motorycles, 9000rpm Hondas, etc.) the oil-hole on the journal has ALWAYS been at the outermost surface of the journal. This allows centrifugal/centripedal force to actually enhance oil-pressure feeding out of the journal; the faster you rev, the more force pushing the oil out. As it is drilled on our cranks, oil-pressure must be used to push oil back towards the crank centerline in order to get out the journal hole. It appears the perp-drilling at 90-degrees to the existing hole mentioned by Huntley (not crossdrilling) is the correct solution.
"The area of the pan where the #2 rod bearing resides is shallow and gets little slingging lubrication as the crankshaft passes through oil in the sump.
Oh but what about the #1 bearing, it's in the shallow part of the pan also.....?"
I think the #2 rod-bearing issue is something internal to the crank. Some connection between the main and rod-journals where the oil-supply isn't as good to the #2 rod. That's the only way the #2 rod-bearing can be isolated from the rest. If it was an oil-pickup issue, all the journals would be affected evenly.
06-11-2002, 08:06 AM
#12
Nordschleife Master
[quote]Originally posted by 951and944S:
<strong>Adrial
Errr sorry for that, or were you being serious, hard to tell, but really I've read the articles Adrial, and I'm not buying...
--snip--
Just trying to explain this Adrial, not meant to demean your post or anything, that would be below the belt IMO.....
Cheers mate.... <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" /> </strong><hr></blockquote>
I was being serious. I didn't think you bashed me or anything, just a friendly "I disagree" <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
I think Danno explained it quite well. <img src="graemlins/bigok.gif" border="0" alt="[thumbsup]" />
I have one question...Is the crank angled from the bottom of the crank up towards the top (where the oil passage holes are)?
Like lets say you're oil and you're being flung around...do you have to go up a cliff to get to the oil passage hole or do you have to walk up a hill?
<strong>Adrial
Errr sorry for that, or were you being serious, hard to tell, but really I've read the articles Adrial, and I'm not buying...
--snip--
Just trying to explain this Adrial, not meant to demean your post or anything, that would be below the belt IMO.....
Cheers mate.... <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" /> </strong><hr></blockquote>
I was being serious. I didn't think you bashed me or anything, just a friendly "I disagree" <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
I think Danno explained it quite well. <img src="graemlins/bigok.gif" border="0" alt="[thumbsup]" />
I have one question...Is the crank angled from the bottom of the crank up towards the top (where the oil passage holes are)?
Like lets say you're oil and you're being flung around...do you have to go up a cliff to get to the oil passage hole or do you have to walk up a hill?
06-11-2002, 08:26 AM
#13
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I remember the discussion that Danno talked about. One thing I do remember was that most concensus from that thread was not to run the motors over 6000 to 6200 rpm, because you were already out of the torque band; and the oiling issues. Granted, with a good exhaust and that high rpm, the motors sound great but are they really doing any perfomance gains at that rpm,,,or doing limited damage?
06-11-2002, 10:23 AM
#14
Three Wheelin'
Just to make one thing a bit clearer (because you guys are talking way over my head here), centripetal force is what you feel on a fast spinning merry-go-round. Centrifugal force does not exist. It's more of a not so accurate term...my physics prof would eat us alive for using it.
06-11-2002, 10:58 AM
#15
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[quote]...most concensus from that thread was not to run the motors over 6000 to 6200 rpm, because you were already out of the torque band<hr></blockquote>
Most of our motors are out of the torque band by 4500 anyway. My shift point will be at the RPM where HP falls. That was 5750rpm with my last turbo. For downshifting purposes, you want a higher rev limit so you do not need to short shift corners as much. Larger RPM band=less shifting=faster times.
And the 7100 rev limit is just that, a limit. Like I said above, with 400+hp off the crank and a lot of light parts, you can light off the tires and blow into the 8000rpm range quick. I have a fast foot, but would rather have a computer as a fail safe that is a lot faster than me.
Most of our motors are out of the torque band by 4500 anyway. My shift point will be at the RPM where HP falls. That was 5750rpm with my last turbo. For downshifting purposes, you want a higher rev limit so you do not need to short shift corners as much. Larger RPM band=less shifting=faster times.
And the 7100 rev limit is just that, a limit. Like I said above, with 400+hp off the crank and a lot of light parts, you can light off the tires and blow into the 8000rpm range quick. I have a fast foot, but would rather have a computer as a fail safe that is a lot faster than me.