stprasinz Posted August 6, 2008 Share Posted August 6, 2008 ok lets see here stock r200 from a 1983 turbo 280zx (I belive to be 3.54.. right..) stock rims with 205 65 15's... 5th gear 62-6500 rpms.... pulled all the way.. I thought I was in 4th.. grabbed the shifter to grab 5th..... whoaw.... (24 lbs boost stage 2 race only cams, stainless undercut valves, 40 over bore, 60 mm tb, 3" manderal, 440cc injectors,(modifed stock afm on stocxk ecu) alluminum fly, act 4 puck, turbonetics 60-1, huge front mount..... 96 in the 1/8th coughing out of the hole ( no boost in 1st gear) .....................now I have 125 wet shot of nitrous and was running under 15 lbs of boost.. but I toasted my build motors pistons skirts...... was searching for info on a big block swap and came across this... any info on a 427 bbc swap?????? 390hp with 460 ft lbs stock below 5000 rpms......... intake, header, and 125 shot of nitrous..... Quote Link to comment Share on other sites More sharing options...
91_4x4runner Posted August 7, 2008 Share Posted August 7, 2008 That's 180mph according to the sources I checked....... How many miles did it take you to reach that speed? Calculated here: http://www.f-body.org/gears/ Ratio's here: http://www.zhome.com/ZCMnL/tech/GearRatios.html ok lets see here stock r200 from a 1983 turbo 280zx (I belive to be 3.54.. right..) stock rims with 205 65 15's... 5th gear 62-6500 rpms.... pulled all the way.. I thought I was in 4th.. grabbed the shifter to grab 5th..... whoaw.... (24 lbs boost stage 2 race only cams, stainless undercut valves, 40 over bore, 60 mm tb, 3" manderal, 440cc injectors,(modifed stock afm on stocxk ecu) alluminum fly, act 4 puck, turbonetics 60-1, huge front mount..... 96 in the 1/8th coughing out of the hole ( no boost in 1st gear) .....................now I have 125 wet shot of nitrous and was running under 15 lbs of boost.. but I toasted my build motors pistons skirts...... was searching for info on a big block swap and came across this... any info on a 427 bbc swap?????? 390hp with 460 ft lbs stock below 5000 rpms......... intake, header, and 125 shot of nitrous..... Quote Link to comment Share on other sites More sharing options...
Mikelly Posted August 7, 2008 Share Posted August 7, 2008 Interesting incident happened to me the time before last at VIR... We were in my porsche, which is extremely aerodynamic. I snicked it into 6th gear and pulled a 180MPH "displayed" digital read out on the 4000+ft. back straight. Just as we hit that speed the car was buffeted by a gust of wind and forced into the next lane... easily 6ft... Almost ruined a good nomex suit and oakley fireproof underwear... I later found that the digital display in these cars is known not to be accurate. I was probably only doing in the 170s...But still... Things get hairy at those speeds... Mike Quote Link to comment Share on other sites More sharing options...
jtl260z Posted August 8, 2008 Share Posted August 8, 2008 Interesting incident happened to me the time before last at VIR... We were in my porsche, which is extremely aerodynamic. I snicked it into 6th gear and pulled a 180MPH "displayed" digital read out on the 4000+ft. back straight. Just as we hit that speed the car was buffeted by a gust of wind and forced into the next lane... easily 6ft... Almost ruined a good nomex suit and oakley fireproof underwear... I later found that the digital display in these cars is known not to be accurate. I was probably only doing in the 170s...But still... Things get hairy at those speeds... Mike I work for a Porsche dealer and you are correct, the gauges are off by a little at higher speeds. I don't remember the exact amount but the percentage of inaccuracy increases the faster you go. Quote Link to comment Share on other sites More sharing options...
ShaggyZ Posted August 8, 2008 Share Posted August 8, 2008 I work for a Porsche dealer and you are correct, the gauges are off by a little at higher speeds. I don't remember the exact amount but the percentage of inaccuracy increases the faster you go. The percentage increases? Or is it just the number that increases? The number would increase regardless of a percentage increase as the speed increases. Speedometers are almost never perfectly accurate from the factory and any changes to tires, for example, will skew the percentage further - even tire wear and tire stretch at high revolutions. But you all know that, so I digress. Quote Link to comment Share on other sites More sharing options...
jtl260z Posted August 11, 2008 Share Posted August 11, 2008 Both. The percentage starts off low and increases as you go faster. I am aware that changes can cause accuracy to be off. I Quote Link to comment Share on other sites More sharing options...
jtl260z Posted August 11, 2008 Share Posted August 11, 2008 The percentage increases? Or is it just the number that increases? The number would increase regardless of a percentage increase as the speed increases. Speedometers are almost never perfectly accurate from the factory and any changes to tires, for example, will skew the percentage further - even tire wear and tire stretch at high revolutions. But you all know that, so I digress. The percentage increases. For example, you might be off .5% at 100 MPH and 1.0% at 120 and increase from there. Factory speedometers were only designed to be accurate up to a certain MPH (usually around 80). BTW, I am well aware of the things that will cause further speedometer inaccuracy. Quote Link to comment Share on other sites More sharing options...
91_4x4runner Posted August 12, 2008 Share Posted August 12, 2008 The percentage increases. For example, you might be off .5% at 100 MPH and 1.0% at 120 and increase from there. Factory speedometers were only designed to be accurate up to a certain MPH (usually around 80).BTW, I am well aware of the things that will cause further speedometer inaccuracy. I know I'm a bit fuzzy on this, but I don't really see how the inaccuracy grows *specifically on the speedometer drive unit*. As per my truck, it has small gears on the output at the transmission tail. The cable goes directly to the back of the gauge cluster where it turns the speedo.. Can I get an explanation of how this "direct drive" can change percentage? I can see that tires stretching might cause a slight percentage change (assuming we're using factory spec tires to begin with). What else is there to skew the percentage? [/threadjack] Quote Link to comment Share on other sites More sharing options...
stony Posted August 12, 2008 Share Posted August 12, 2008 Well i was intimidated about all the "zcars are unstable above XXX speed" comments. this weekend i went 140 MPH in the z and it was straight as an arrow with no feel of on the edge heres a video Quote Link to comment Share on other sites More sharing options...
ShaggyZ Posted August 13, 2008 Share Posted August 13, 2008 The percentage increases. For example, you might be off .5% at 100 MPH and 1.0% at 120 and increase from there. Factory speedometers were only designed to be accurate up to a certain MPH (usually around 80).BTW, I am well aware of the things that will cause further speedometer inaccuracy. You're referring to an almost exponential increase. I think you're wrong. The percentage can stay the same and the numerical error increase. For example, 10% of 100mph is 10mph and 10% of 120mph is 12mph. Why do you think the percentage is also increasing? I'm open to correction. Also, where did you hear speedo's are designed to be accurate to 80mph? Every car I've driven has been off by no less than 5%, even below 80mph. I think the best they can do is make the gears in the speedo and speedo drive and the tire size be as close as possible, which decreases the overall percentage error and, as a consequence, the numerical error, but that number will increase. You can say "designed to be accurate up to a certain MPH" and be kind of right because that percentage, if it's only 1%, will be only .1mph off at 10mph and 1mph off at 100mph, which is extremely accurate and not likely. I know I'm a bit fuzzy on this, but I don't really see how the inaccuracy grows *specifically on the speedometer drive unit*. As per my truck, it has small gears on the output at the transmission tail. The cable goes directly to the back of the gauge cluster where it turns the speedo.. Can I get an explanation of how this "direct drive" can change percentage? I can see that tires stretching might cause a slight percentage change (assuming we're using factory spec tires to begin with). What else is there to skew the percentage? [/threadjack] Two more skewing factors: tire wear, wind resistance which causes slippage. I'm too tired to explain the increasing error other than to say... "it's math!" --- calculus to be specific. Quote Link to comment Share on other sites More sharing options...
jtl260z Posted August 13, 2008 Share Posted August 13, 2008 I know I'm a bit fuzzy on this, but I don't really see how the inaccuracy grows *specifically on the speedometer drive unit*. As per my truck, it has small gears on the output at the transmission tail. The cable goes directly to the back of the gauge cluster where it turns the speedo.. Can I get an explanation of how this "direct drive" can change percentage? I can see that tires stretching might cause a slight percentage change (assuming we're using factory spec tires to begin with). What else is there to skew the percentage? [/threadjack] It's not the "direct drive" part that is the problem, it's the gauge. The gauge was not designed to be accurate at high speeds. If you have ever seen a speedometer needle bounce at high speeds you will know what I am talking about. Even my brand new Autometer speedometer bounces when I get above 130. Quote Link to comment Share on other sites More sharing options...
Gollum Posted August 13, 2008 Share Posted August 13, 2008 I'm not sure I want to buy an autometer guage now (not that I was planning to). I've had several OEM guages up to that speed and beyond and they didn't bounce.... Quote Link to comment Share on other sites More sharing options...
Mikelly Posted August 13, 2008 Share Posted August 13, 2008 ask Pete Paraska about his Autometer temp. gauge and how it was reading 30+ degrees hotter than the water actually was... Mike Quote Link to comment Share on other sites More sharing options...
Dragonfly Posted August 14, 2008 Share Posted August 14, 2008 I know I'm a bit fuzzy on this, but I don't really see how the inaccuracy grows *specifically on the speedometer drive unit*. As per my truck, it has small gears on the output at the transmission tail. The cable goes directly to the back of the gauge cluster where it turns the speedo.. Can I get an explanation of how this "direct drive" can change percentage? I can see that tires stretching might cause a slight percentage change (assuming we're using factory spec tires to begin with). What else is there to skew the percentage? [/threadjack] Let me see if I can explain this in relatively easy terms… There are several different types of “accuracy†with the most common being indicated value (IV), full scale (FS), floor value (FV) and multi value (MV). I will use an S30’s 160 mph speedometer as the example for each of these accuracy types. IV: Lets say for example that the speedometer has an accuracy of +/-10% IV, what that means is if the speedometer reads 10 mph it will be within 1 mph or no worse than 9 mph or 11 mph but if the speedometer reads 100 mph it will now be within 10 mph and at 160 mph it would be within 16 mph. Now we know that is not realistic for a speedometer so IV is not the correct accuracy type. FS: Again lets use +/-10%, now the way this works is you multiply 10% X 160 mph giving you 16 mph so if the speedometer is reading 10 mph it can be within 16 mph or 0 mph to 16 mph but if the speedometer reads 100 mph you still are within 16 mph and at 160 mph you are still within 16 mph. Again we know that this is not the case with a speedometer so FS is not the correct accuracy type. FV: This is added to either IV or FS, as an example we could say that the speedometer is accurate to 10% IV + 5 FV so now at 10 mph we will be within 6 mph (10% of 10 + 5 = 6) or 4 mph to 16 mph but if the speedometer reads 100 mph you will be within 15 mph (10% of 100 + 5 = 15) or 85 mph to 115 mph and at 160 mph you will be within 21 mph. Again this will not work for our speedometer (nor will it work with FS + FV) so FV is not the correct accuracy type. MV: Multi value means that you use more than one percentage value across the range of the gage as an example lets say that we have an MV of 10%, 5% and 20% IV with the gage being divided between 0 to 20% (0 to 32 mph), 21 to 70% (33.6 to 112 mph) and 71 to 100% (113.6 to 160 mph). Using this example with the speedometer reading 10 mph we are within 1 mph or 9 mph to 11 mph, with the speedometer at 80 mph (typical Z cruising speed) we will be within 4 mph or 76 mph to 84 mph but when we get over about 112 mph lets say 120 mph we are looking at being within 24 mph or 96 mph to 144 mph. Now this is much more realistic for a speedometer so MV is the correct accuracy type. Now I know some of you are about to point out the overlap between the 112 mph and the 120 mph, well the way that works is if your speedometer is reading a full 20% off when that close to the 5% portion of the gage then the 5% portion of the gage would be reading greater than 5% and therefore would be out of tolerance and the gage would be adjusted to read more accurately. Now as a side note a floor value can be added to a multi value and probably is with speedometers (at least the older ones like in S30’s) because of the tension spring and magnetic cup design of the speedometer which is going to forcibly decrease your accuracy at higher speeds by the fact that the spring is getting tighter and the magnetic cup has more spring tension to try to overcome. Also the manufacturers of speedometers build them to be the most accurate in the range in which they expect most of the driving to be done which in the USA is between 35 mph and 80 mph. Dragonfly Quote Link to comment Share on other sites More sharing options...
Mikelly Posted August 14, 2008 Share Posted August 14, 2008 Excellent explanation DF! I now have GPS based data aquisition, so I'll not be basing any further statements (*from a track perspective of course) off of "speedometer readings. Mike Quote Link to comment Share on other sites More sharing options...
jtl260z Posted August 14, 2008 Share Posted August 14, 2008 Thanks Dragonfly, for the extreme explaination and for setting some doubters straight. Quote Link to comment Share on other sites More sharing options...
ShaggyZ Posted August 14, 2008 Share Posted August 14, 2008 Thanks Dragonfly, for the extreme explaination and for setting some doubters straight. Uh right... that's hardly what you said. At best, it sounds like a combination of what you and I stated. Quote Link to comment Share on other sites More sharing options...
jtl260z Posted August 15, 2008 Share Posted August 15, 2008 I'm not sure I want to buy an autometer guage now (not that I was planning to). I've had several OEM guages up to that speed and beyond and they didn't bounce.... The stock gauge bounces more at 140+. Of course, it could have been the road. Quote Link to comment Share on other sites More sharing options...
Poindexter Posted August 15, 2008 Share Posted August 15, 2008 All my Z will go, it seems is 95-100, mainly due to gearing I believe, but I had a friend who was a BMW dealer and while he slept in the passenger seat one fine morning on a long drive, I did an indicated 171 on a deserted, straight and freshly-paved highway in his chipped and modified BMW 750il. It felt pretty good. I have gone faster on asphalt, but that was in a Lear 35 on takeoff! Quote Link to comment Share on other sites More sharing options...
blue72 Posted August 17, 2008 Share Posted August 17, 2008 Had it up to 116 on the GPS this weekend (I solved my previous fuel delivery problem). Upcoming curve forced me to slow. Didn't get to try it again because I broke the transmission later in the day. Seemed entirely stable at that speed, and I was only at around 5,500 RPM. Not bad for a car with completely stock, rotted 36 year old bushings all around. Quote Link to comment Share on other sites More sharing options...
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