Paul (Notts)
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| posted on 29/5/08 at 04:35 PM |
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What’s causing this
Having just changed my diff so that I can do 0 – 60mph in 2nd gear I have been out playing
Best 0 – 60 time was 4.9 sec on a slight uphill straight.
Very pleased with this as one of my original build aims was to go under 5 sec 0-60.
However when I look at the data from my vepor2 I always get a strange section in the HP curve and it also shows up on the acceleration graph.
( ignore the actual hp figures as they will increase when I put in the true weight and drag coefficient – both underestimated.)
Any ideas what causes it ?
As the slope decreases after it am I underfueling there?
It’s a 3.5 rv8 on a webber 500
Paul
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Paul (Notts)
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| posted on 29/5/08 at 04:37 PM |
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pic
 
Rescued attachment hp1.jpg
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Benzine
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| posted on 29/5/08 at 04:42 PM |
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changing from first to second?  idk
[Edited on 29/5/08 by Benzine]
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Paul (Notts)
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| posted on 29/5/08 at 04:47 PM |
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no gear change just pulled away in 2nd
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charlierevell
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| posted on 29/5/08 at 04:57 PM |
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Mine did that when the last chap had it RR'd
I think its a lean patch on the fueling from what i recall...
Edit: It must be that as thats what it says on the graph below!!!! Duuuuh
[Edited on 29/5/08 by charlierevell]
EDIT2: Reading thru some replies to when Liam had this done it looks like its down to the cylinders not filling properly due to pulsing in the inlets
not being spot on at those revs.
So if your Carb based I think it could be you ram tube length could be the problem.
[Edited on 29/5/08 by charlierevell]
Tango orange is an 'IN' colour!!
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nib1980
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| posted on 29/5/08 at 05:06 PM |
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cam change over point
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smart51
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| posted on 29/5/08 at 05:33 PM |
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Most bike engines have a dip at about 1/3 max revs. Its probably a resonant frequency of the cylinder volume and inlet lengths. Airboxes are often
tuned to resonate at that frequency to fill in the trough a bit. Take the air box off and lose the resonance, but maybe gain a bit of top end
breathing.
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ReMan
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| posted on 29/5/08 at 05:36 PM |
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So max HP is 120ish?
From a RV8?
Rhetorical question, as mine shows about 70hp from the which i though was a bit low too 
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Paul (Notts)
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| posted on 29/5/08 at 05:45 PM |
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As far as I understand the veypor 2 it needs you to do a couple of tests to find the friction caused by road resistance and air resistance before it
will give you a true hp figure.
someting along the lines of driving at 70 and putting the clutch in then free wheeling down to 30 or something like that.
this coeficcient is then used in the hp calculation. Along with the weight of the car.
Paul
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snapper
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| posted on 29/5/08 at 05:46 PM |
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Don't have my Weber book here at the moment but looks like under fueling from the the point where the carb transitions from idle jets to
progression drillings then on to the main jets.
Could be that your accellerator pump gives a big shot of fuel and when that is used you go lean for the rest of the curve.
If you are getting under 5 with 120bhp then imagine what you will get with the carb sorted
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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NeilP
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| posted on 29/5/08 at 06:05 PM |
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Hey Paul - Doesn't being able to spin both rears in a straight line for ages b
put a HUWAGE grin on your chops...
If you pay peanuts...
Mentale, yar? Yar, mentale!
Drive it like you stole it!
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mr henderson
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| posted on 29/5/08 at 07:05 PM |
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Be good to have an AFR meter, find out if it's rich or weak at that point. Could just be a weird harmonic happening ih the inlet tract though,
slowing the airflow. Which manifold are you running? The edelbrock works well with the Weber (which of course is a re-badged Edelbrock)
John
John
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