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Author Topic: GT380 ground up build  (Read 2691 times)

Online CrabsAndCylinders

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Re: GT380 ground up build
« Reply #60 on: Jul 25, 2018, 01:32:19 »
Spectacular!
Lighter, Quicker, Faster.
ZX-14, 900F x 2, 1100F, R100, CBR600, SR500, GT500, RZ350, KZ1000 x 2, Moto Guzzi Lemans lll, CBX550, RD 350, 750 SOHC police special, RG250, TL1000R, GT750, KTM Super Duke 1290 R, Harris/Z-1, Norton 750 Commando, Green 77 KZ650

Offline JadusMotorcycleParts

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Re: GT380 ground up build
« Reply #61 on: Jul 28, 2018, 08:04:20 »
This is bloody epic!  At first I thought, whoa, ambitious!  Then I took a look at your instagram account and hompage and realised it's like childs play for you.  Watching here and following on insta with enthusiasm!

Offline themotoworks

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Re: GT380 ground up build
« Reply #62 on: Aug 09, 2018, 19:36:47 »


fairing pattern is mostly done, now to do the seat and tank cover.  tank will just be an aluminum fuel box that goes under a fiberglass cover, much faster this way since I want to paint it anyway.  also started taking the dimensions from the 2 stroke program and designing the pipes, I used cad to build them on the bike based on the chamber dimensions, then flatten out the sections and pie cuts so they should all go together seamlessly, going to use stainless because its pretty easy to cut and weld, hope they will look rad

Offline Pete12

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Re: GT380 ground up build
« Reply #63 on: Aug 10, 2018, 19:02:16 »
Can't wait to see the pipes - if they are like the rest they will be awesome.

Offline teazer

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Re: GT380 ground up build
« Reply #64 on: Aug 10, 2018, 20:04:37 »
Which pipe software did you end up using to design the pipes?

Offline themotoworks

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Re: GT380 ground up build
« Reply #65 on: Aug 11, 2018, 12:12:02 »
I used mota and optimized the pipe for most power at 8000rpm, there was quite a big predicted bump, so with the pipes and 10mm off the intake side of the piston skirt it's predicted 20hp per cylinder.  whether it hits that or not is in the air, but seems like a nice target

Offline teazer

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Re: GT380 ground up build
« Reply #66 on: Aug 11, 2018, 12:23:31 »
10mm off the intake is huge in any language.  Longer inlet duration tips the power curve around an inflection point around 5,000 to 6000.  More duration gives more potential top en, but loses below that point of inflection. At a certain point, the gains stop and the losses increase.

All the GT range had really mild port timing and teh ports were quite narrow, so there's lots of scope fro improvement there.

Did you run all your data through a version of MOTA or did you just use their exhaust design tool?

I haven't worked on a 380, but just finished a 550 with a lot less change in inlet timing but way more exhaust time area and that took over a second off the quarter mile and added 10mph at the top end and it's fun on the street too. 

Offline themotoworks

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Re: GT380 ground up build
« Reply #67 on: Aug 11, 2018, 12:43:12 »
I took a long time to measure all the parameters mota required, ran the simulation and with an approximation of the stock muffler, came in at around what the manual claims for HP, so I figured I was in the ballpark for baseline calibration.  Then I started playing around, seemed like intake timing was what made the biggest predicted improvement, then when I optimized the pipe, I got another 3-4hp per cylinder

Offline teazer

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Re: GT380 ground up build
« Reply #68 on: Aug 11, 2018, 16:59:05 »
When I played with GT380 data in MOTA earlier this year, I had to interpolate a bunch of numbers to get some comparative data. Real data is a whole lot more useful especially in identifying restrictions.

IIRC a 380 is 54x54, so it should be good to 9500 or maybe 10,000 albeit the bottom end won't last too long.  You should be able to run it past 9 from time to time though.  I seem to recall that the data worked better with 28mm GT550 carbs compared to stock but they are not as much of a restriction as they might seem.