whats the top speed of your n/a
12-26-07, 11:07 AM
#27
Almost all factory speedo's are not accurate. The only way to know for sure what speed you are going, is to log actual rpms from a laptop, measure actual tire circumference, and do the math with gear ratio. This is how I verified 178, I didnt have a speedo. Hit 7050 rpms in 5th gear.
But I'd agree that wind speed is a huge factor. Basically if the wind is blowing at 5mph, you'll go 4-5 mph faster. The ground doesn't matter nearly as much at top speed. Really you need an airplane speedometer to get a fair measurement. Or just switch directions and take the average.
Last edited by ericgrau; 12-26-07 at 11:15 AM.
12-26-07, 11:38 AM
#29
I think most of my error above came from my own error, i.e., where i assumed the end of the on-ramp to be. I'd bet I'd get the same error on a much larger stretch. I'm saying 1-2mph is an upper limit. Your 0.1% (0.12-0.17 mph) may be more accurate for other cars too.
Btw, I love how some people like to always assume one stock thing or another is bad, but then they happen to pick something where proof is available and it always turns out good.
Btw, I love how some people like to always assume one stock thing or another is bad, but then they happen to pick something where proof is available and it always turns out good.
12-26-07, 01:21 PM
#30
best part, I did that on one tank of gas. 
Though, I was sad that I didn't hit 400.......I've hit it before with a very strange tune.
I did some further thinking and reserching into this topic:
I have two speedos in my car, an aftermarket gauge cluster and an APEX'i RSM-GP that displays metric speed only.
I was cruising at 115 kph on my RSM-GP for 99% of the trip. That's 71.4576871 mph. According to the .1% error calculator above, my trip meter was off 71.4576871 - 71.3860144 ~ 0.07 mph too high. That's my tripmeter error from actual.
Here's the funny part. My speedo in the gauge cluster was pegged at 75-76 mph. I think the aftermarket gauges are off, since the tripmeter, odometer and speedometer work off the speed signal from the speedo cable. That means my speedo error is (75-71.4576871 / 71.4576871) ~ 4.7% high from the RSM-GP and 5.1% high from actual. Makes it easier to avoid cops I guess. Still, it's nice to see that the tripmeter is within 0.1% of actual.
Though, I was sad that I didn't hit 400.......I've hit it before with a very strange tune.
I did some further thinking and reserching into this topic:
I have two speedos in my car, an aftermarket gauge cluster and an APEX'i RSM-GP that displays metric speed only.
I was cruising at 115 kph on my RSM-GP for 99% of the trip. That's 71.4576871 mph. According to the .1% error calculator above, my trip meter was off 71.4576871 - 71.3860144 ~ 0.07 mph too high. That's my tripmeter error from actual.
Here's the funny part. My speedo in the gauge cluster was pegged at 75-76 mph. I think the aftermarket gauges are off, since the tripmeter, odometer and speedometer work off the speed signal from the speedo cable. That means my speedo error is (75-71.4576871 / 71.4576871) ~ 4.7% high from the RSM-GP and 5.1% high from actual. Makes it easier to avoid cops I guess. Still, it's nice to see that the tripmeter is within 0.1% of actual.
Last edited by Roen; 12-26-07 at 01:38 PM.
01-02-08, 10:20 PM
#33
Senior Member
163
In my 1974 RX3 I used to have. This was a ITA RX3, but it had a Half-bridgeported 12A in it.
Was not very much fun actually. It was across the Howard Franklin Bridge, and it has a rythmic spacing to the expansion cracks.. and the frontend started to bob.... Let off at that point.
The speed was via tire diameter with the 1983 gearbox and 3.90 rear and 206/60/13s on it.
Ran 4th out to around 9K Shifted to 5th and ran it to 7800 or so. Decided things were too sketchy with those "aerodynamics". 163 was enough.
A friend has a 73 RX3, and he was getting the "bob" at around 145-150, but he has a spoiler on the rear that was causing him high speed fits.
In my 1974 RX3 I used to have. This was a ITA RX3, but it had a Half-bridgeported 12A in it.
Was not very much fun actually. It was across the Howard Franklin Bridge, and it has a rythmic spacing to the expansion cracks.. and the frontend started to bob.... Let off at that point.
The speed was via tire diameter with the 1983 gearbox and 3.90 rear and 206/60/13s on it.
Ran 4th out to around 9K Shifted to 5th and ran it to 7800 or so. Decided things were too sketchy with those "aerodynamics". 163 was enough.
A friend has a 73 RX3, and he was getting the "bob" at around 145-150, but he has a spoiler on the rear that was causing him high speed fits.
02-08-08, 05:18 PM
#34
Took my 7 to bout 250kph. I was not lookin at the revs. I was lookin at the sky while i bounced down the road and decided to slow down. Prob cud of gone faster it wanted to but the conditions were dodgey
03-18-08, 06:29 PM
#37
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35,000mi on 13B engine (mazda reman), Apex'i S-AFC II fuel controller (dyno tuned), APEX`i Power Intake, Pineapple Racing 6 port sleeve inserts. RB downpipe, testpipe, Apexi N1 dual catback.
Its just super healthy, my last dyno was back in the summer of 2005 my max whp was a 151.13 whp at 7600rpm on a Dynojet. My running conditions were 102.20 *F, 29.70 in-Hg, Humidity: 21%. I was hoping for more but they only got a 5 or 6 rwhp gain out of the S-AFC II. This is on stock ports. I was not very happy with the shop I went to at that time. I am going to get re-dyno tuned on 4/3/08 at Tuxedo Park Racing, I am sure they can pull a few more hp out of her with a good tune and it won't be near so hot outside. I will post what my new numbers are after I get re-tuned. You can see everything else thats I have done to the car on my car domain page, link is in my singature.
Its just super healthy, my last dyno was back in the summer of 2005 my max whp was a 151.13 whp at 7600rpm on a Dynojet. My running conditions were 102.20 *F, 29.70 in-Hg, Humidity: 21%. I was hoping for more but they only got a 5 or 6 rwhp gain out of the S-AFC II. This is on stock ports. I was not very happy with the shop I went to at that time. I am going to get re-dyno tuned on 4/3/08 at Tuxedo Park Racing, I am sure they can pull a few more hp out of her with a good tune and it won't be near so hot outside. I will post what my new numbers are after I get re-tuned. You can see everything else thats I have done to the car on my car domain page, link is in my singature.
Last edited by George84; 03-18-08 at 06:42 PM.
03-18-08, 07:30 PM
#39
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That top speed is on a level road. I have been wanting to make a top speed video lately, I will be sure to post it when I get it made. The only thing I can think of is that your GTUs 4.30 rear is limiting your top speed in 4th gear. And thats how I can get to the higher top speed in 4th due to my 4.10 rear. Congrats on making it to 170whp though, what kind of dyno was that on and what gear was that pull in?
03-18-08, 08:02 PM
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Thats why. I am staying in 4th to get to that speed, but I am past redline, when I put it into 5th I can barely hold that speed. It must all be due to the 4.10 to 4.30 rear end difference.
Last edited by George84; 03-18-08 at 08:29 PM.
03-19-08, 08:41 AM
#42
the thing is, i don't know if I'm making more power in 5th gear @ 6000 rpm than you are in 4th gear @ 8300 rpm, we'd probably have to compare dynos. I'd probably have to make more than 26% more power than you, which would be quite hard to do. I suppose, if I bounce off the rev limiter in 4th gear, I'd hit 151 mph.
Would you happen to have a dyno sheet? I'd need to find mine too.
Would you happen to have a dyno sheet? I'd need to find mine too.
03-19-08, 12:56 PM
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That was a few years ago, but I will look for it. Otherwise I am getting re-dyno tuned on April 3rd and I will post that if I cant find my old one. My next dyno will not be on a dynojet like the last time, it will be on a Dynapack 3000 instead.
03-19-08, 02:18 PM
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I can't find it, I looked all over. I will keep my eye out for it though.
BTW, that pull on the last dyno I did I was in 3rd gear, and the longer the pull the higher your your hp will show. So a 4th gear pull will show higher hp numbers than a 3rd gear pull with the same car. At least that is according to this "Dynamometer Rant" http://www.tuxedoparkracing.com/tech...selection.html
BTW, that pull on the last dyno I did I was in 3rd gear, and the longer the pull the higher your your hp will show. So a 4th gear pull will show higher hp numbers than a 3rd gear pull with the same car. At least that is according to this "Dynamometer Rant" http://www.tuxedoparkracing.com/tech...selection.html
Last edited by George84; 03-19-08 at 02:24 PM.
03-19-08, 03:54 PM
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No, the dyno does not need to know your gear ratio for that to have this effect. This is from that site I posted "Regardless of the length of the pull, the dyno is still measuring accurately - the car is truly producing more horsepower at the wheels during the longer pull because it is expending less effort at any given moment accelerating the drivetrain! Again, the longer the pull the higher the recorded power at the wheels. The heavier the drivetrain components, the greater this effect. In real world testing, we typically see a 10-15 horsepower gain on very long pulls over moderate length pulls."
03-19-08, 04:39 PM
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It looks like crap because I had to take a pic of it while on my monitor to figure out how to change the file type so I could post it. I can email whoever the good copy of the Adobe file if you need to see it better. 
don't mind the blue lines and numbers, long story, and this was the only copy of the dyno I could find.
don't mind the blue lines and numbers, long story, and this was the only copy of the dyno I could find.
03-19-08, 04:54 PM
#50
No, the dyno does not need to know your gear ratio for that to have this effect. This is from that site I posted "Regardless of the length of the pull, the dyno is still measuring accurately - the car is truly producing more horsepower at the wheels during the longer pull because it is expending less effort at any given moment accelerating the drivetrain! Again, the longer the pull the higher the recorded power at the wheels. The heavier the drivetrain components, the greater this effect. In real world testing, we typically see a 10-15 horsepower gain on very long pulls over moderate length pulls."
Personally, I think it has to do with the gears: the greater force applied to the drum is cancelled out by the shorter run in a lower gear, and conversely for a higher gear. But higher gear ratios sap more power in the driveline. I think this is where the power differences come from.
Hell, no one seems to know for sure.