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 Post subject: Flat spot and gearbox help
PostPosted: Fri Jan 20, 2017 8:35 pm 
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Joined: Sat Feb 15, 2014 6:11 pm
Posts: 7
Location: Maitland
Hi, we built this g13b for the brothers ip car, can anyone help out on how to get rid of the flat spot??. Oh, and a 4th gear for a mk1 would be great too!


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 Post subject: Re: Flat spot and gearbox help
PostPosted: Sat Jan 21, 2017 9:12 am 
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Joined: Fri Sep 03, 2010 10:41 am
Posts: 1242
Location: Bunya QLD 4055
What cams and throttle body/bodies do you have?

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If "X" is an Unknown quantity, and a Spurt is a drip under pressure, then an "EXPERT" is an "Unknown Drip Under Pressure".
Why dont they just call it "Womenapause" instead.


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 Post subject: Re: Flat spot and gearbox help
PostPosted: Sat Jan 21, 2017 12:39 pm 
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Joined: Sat Feb 15, 2014 6:11 pm
Posts: 7
Location: Maitland
224@.050 and 354"lift,stock mk1 dizzy. Cultus intake
With 50mm tb.


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 Post subject: Re: Flat spot and gearbox help
PostPosted: Sat Jan 21, 2017 5:31 pm 
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Joined: Fri Sep 03, 2010 10:41 am
Posts: 1242
Location: Bunya QLD 4055
Factory Rally 952 cams. Which flat spot are you referring to? At 4.5k or the 6.5k? Are you using a std ECU or chipped? If an AM ECU perhaps it is the tune. That's not bad figures for that setup. To let us help it would be better if we new the whole setup. ECU, Compression, Porting, Exhaust, etc. From memory Mk 1 has vacuum advance and it may not be compatible with the cam timing unless modified. Need others to comment, NEO, Techie?

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If "X" is an Unknown quantity, and a Spurt is a drip under pressure, then an "EXPERT" is an "Unknown Drip Under Pressure".
Why dont they just call it "Womenapause" instead.


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 Post subject: Re: Flat spot and gearbox help
PostPosted: Sat Jan 21, 2017 5:45 pm 
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Joined: Sat Feb 15, 2014 6:11 pm
Posts: 7
Location: Maitland
The one at 6.5k, its running a microtech ecu on e85 at around 12-1 comp.when it was on the dyno the tuner tryed some timing and fueling changes trying to solve it. The exhaust isnt great atm, an old set of 4-2-1 with 2' pipe. Just keen on some fresh ideas


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 Post subject: Re: Flat spot and gearbox help
PostPosted: Sat Jan 21, 2017 5:54 pm 
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Joined: Sat Feb 15, 2014 6:11 pm
Posts: 7
Location: Maitland
Just to add, vac advance removed, as for the head, reshaped chamber ,shaping around valve stem boss's and valve throats.no major port enlarging and no os valves.


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 Post subject: Re: Flat spot and gearbox help
PostPosted: Sat Jan 21, 2017 6:01 pm 
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Joined: Sat Feb 05, 2005 6:51 pm
Posts: 1763
Location: Chch - Quake Capital
Do you have a resonator or expansion chamber at around 4ft from the exhaust valves? scavenging effect may help.


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 Post subject: Re: Flat spot and gearbox help
PostPosted: Sat Jan 21, 2017 6:30 pm 
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Joined: Sat Feb 15, 2014 6:11 pm
Posts: 7
Location: Maitland
Good idea, might be choked a bit. Currently just 2" pipe with 2x12" hotdogs to stay under noise restrictions


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 Post subject: Re: Flat spot and gearbox help
PostPosted: Sat Jan 21, 2017 6:43 pm 
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Joined: Sat Feb 05, 2005 6:51 pm
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Location: Chch - Quake Capital
Billzilla has a graph on this page with distances from the valves to the resonator or muffler
http://www.billzilla.org/engexhaust.htm

If it was my car I'd look at a perforated resonator at 4ft something (like this http://www.adrenalinr.com/productdetail ... ductID=608) and then one hotdog and then see what happens on the dyno.

Keen to hear other peoples thoughts.


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 Post subject: Re: Flat spot and gearbox help
PostPosted: Mon Jan 23, 2017 3:24 pm 
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Joined: Mon Aug 25, 2003 12:00 am
Posts: 1664
Location: Adelaide
could also be the frequency of the intake (Helmholtz effect).

Check out the graphs here http://redlinegti.com/dyno/
you will find most NA cars have a dip along the curve somewhere.

There is a good article on it that I have scanned
http://users.on.net/~moylee/Intake/

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 Post subject: Re: Flat spot and gearbox help
PostPosted: Tue Jan 24, 2017 4:41 pm 
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Joined: Sat Feb 15, 2014 6:11 pm
Posts: 7
Location: Maitland
Thanks for the info and the links, makes for intresting reading. Happy were the engine is sitting on that dyno ranking as i think we can get a few more hp with some slight changes to come.


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