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Old 07-11-2017, 12:47 PM   #1
surferjohnhawaii
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Default Full frame build for sti go kart

I have built the Honey Badger Subaru ( http://imgur.com/a/au2BV ). It's all custom and really awesome (minus the understeer in issue). Feel free to ask any questions or send advice!

The motor is the 2004 forester XT turbo (300hp, 300ftlbs) mated to a 2008 WRX transmission (yes it's AWD!) using the forester xt cv joints and hubs/brakes. the car weighs about 1500lbs and I want to have more oversteer when on the power. Currently it has power understeer, which is neither fast or cool.

Overall it's super fun on the track and street, super light and the power to weight makes the acceleration insane. I highly recommend it to anyone who has time to do it.

Thanks for any suggestions or links to parts!

John
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Old 07-11-2017, 04:24 PM   #2
rtv900
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pretty awesome

I guess it's completely limited to asphalt though as it looks like it has virtually no ground clearance and that front end overhang would make for a nasty day if you tried to approach a steep hill on dirt going fast

You don't want to lift that a bit and take it off road?
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Old 07-11-2017, 04:31 PM   #3
JonnyWachter
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interesting, you put the intake over the hottest part of the engine, yet had no restriction on where you could have actually routed it.
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Old 07-11-2017, 04:46 PM   #4
isotopesope
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Quote:
Originally Posted by surferjohnhawaii View Post
I want to have more oversteer when on the power. Currently it has power understeer, which is neither fast or cool.
what are your current alignment specs? front and rear spring rates? front and rear tire pressures? does this thing have swaybars? if so, what sizes?
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Old 07-12-2017, 12:05 PM   #5
surferjohnhawaii
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Quote:
Originally Posted by rtv900 View Post
pretty awesome

I guess it's completely limited to asphalt though as it looks like it has virtually no ground clearance and that front end overhang would make for a nasty day if you tried to approach a steep hill on dirt going fast

You don't want to lift that a bit and take it off road?
Typically yes it will be for on road track use and spirited drives once it's street legal. But, I have a set of mud tires in mind and the suspension is fully adjustable and I can get at least 6inchs of ground clearance for flatish forest roads. It's mostly for street and track fun, I wanted an awd go kart...
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Old 07-12-2017, 12:07 PM   #6
surferjohnhawaii
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Quote:
Originally Posted by JonnyWachter View Post
interesting, you put the intake over the hottest part of the engine, yet had no restriction on where you could have actually routed it.
I wanted to keep the stock routing, I likes the top mount look. In addition the engine is wrapped in thermal blankets and vents the engine heat away from the intake and intercooler.
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Old 07-12-2017, 12:20 PM   #7
surferjohnhawaii
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Quote:
Originally Posted by isotopesope View Post
what are your current alignment specs? front and rear spring rates? front and rear tire pressures? does this thing have swaybars? if so, what sizes?
Currently it has -2.5 degree camber front, -1.5 degree in the rear. No Tow in front and 1/16inch toe out in the rear. Spring rate is 56lb/inch with adjustable preload, rebound and compression. No sway bars as it doesn't really roll due to the high spring rate and low weight. Tires were at 29psi hot.
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Old 07-12-2017, 12:50 PM   #8
isotopesope
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a higher rear spring rate and higher front tire pressure can help decrease understeer. have you tried preloading the rear further? i'd also try bumping up the front tire pressure 2lb at a time to see if it helps.

does raising the suspension make any difference?

have you considered a LSD?

I am by no means a suspension expert, but i know these little changes can make a difference. your build is impressive though; looks like a lot of fun!

also, again, not an expert, but wouldn't rear toe-IN be better to decrease understeer?
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Old 07-12-2017, 11:09 PM   #9
surferjohnhawaii
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Quote:
Originally Posted by isotopesope View Post
a higher rear spring rate and higher front tire pressure can help decrease understeer. have you tried preloading the rear further? i'd also try bumping up the front tire pressure 2lb at a time to see if it helps.

does raising the suspension make any difference?

have you considered a LSD?

I am by no means a suspension expert, but i know these little changes can make a difference. your build is impressive though; looks like a lot of fun!

also, again, not an expert, but wouldn't rear toe-IN be better to decrease understeer?
You may not be a suspension expert, but you got it dead right. We have a higher spring preload in the rear. We softened up the front and it made it better but not gone. We have rear toe out as well. When we bumped up the front tire pressure it had the opposite effect and made understeer pushing worse.

We shall see where the lsd gets me when I add it.
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Old 07-24-2017, 07:05 AM   #10
geef
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Do you have figure of chassis?
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Old 08-01-2017, 09:16 AM   #11
Charlie-III
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Toe out on the rear usually helps with rotation. As the chassis loads up in a turn and rolls, the outside/loaded rear tire pulls the rear around, helping to turn.
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Old 08-06-2017, 06:18 PM   #12
Tdsigmon96
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Just in case you have your toe terminology backwards (everyone's been there)
From a top down view
Toe in = /---\ (promotes understeer)
Toe out= \---/ (promotes oversteer)
Just throwing that out there to help future readers.
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Old 08-08-2017, 10:29 AM   #13
sackytar
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Post some more pics of the chassis. What did you use for the main parts?
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Old 08-09-2017, 03:20 AM   #14
NSFW
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That must be a ton of fun to drive!

Have you driven it enough to see how evenly the tires wear? I'm just wondering if more camber up front would help them stick. More caster, too.
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Old 08-09-2017, 03:55 PM   #15
the2017WRX
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Wow. If you had to guess, how many hours have you spent on the project so far?

Regarding the understeer problem, what is your front-to-rear weight balance?
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Old 08-10-2017, 02:38 AM   #16
NSFW
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Quote:
Originally Posted by surferjohnhawaii View Post
...2008 WRX transmission [....] and I want to have more oversteer when on the power.
What's the front/rear torque split on that transmission?

The 04-05 Impreza STI 6-speed has a 35 front / 65 rear split...
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Old 02-16-2018, 11:48 AM   #17
v2rocket_aka944
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more work and plumbing but can you put the battery and radiator behind the driver?
that'll be ~50 lbs off the very front.
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Old 02-20-2018, 09:48 AM   #18
surferjohnhawaii
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Default More info

Hi all, sorry about the delay, works been a killer. This below is the mark 2 honey badger, due to blowing up mark 1 I went with a new frame... hope you like it.

All major components such as the fuel cell, fuel pumps, fuel cooler, dry sump tank, radiator, battery etc, are located behind the driver in the "trunk". There are aluminum tubes inside the bottom from rails to move the radiator fluid front to rear.

The main frame is all 1.75 in 0.95wall dom steel. And I've got about 80 hours build time at the moment, even with the major issues.

I was getting lots of understeer on the original car due to lack of lsd in the front allowing the car to push and no rear led to help bring it around, and the wrx 50/50 torque split did not help. With the 2005 sti trans and diffs it should rotate much nicer.

Due to no one in any state near me (wa) having an awd dyno that can fit a 76 in wheelbase I have to move my rear diff/ tires back to 88in total wheelbase to fit on dynos. I think it looks better this way, but not as deadly or twitchy which made it fun. But I can fit bigger mud tires on now and get 10 inches of ground clearance, so that's a plus?

https://i.imgur.com/8YPS79T.jpg

I went with a top mount intercooler because the piping for a front would not work for numerous reasons on this tiny car, and with the in-work heat shield and open hood style, my intercooler temps don't heat soak. And now i have a much larger intercooler.

Anyone have a spare set of sti r180 rear diff to 24 spline wrx hubs? $1100 from drive shaft shop is going to kill my budget!

Cheers
John

Last edited by surferjohnhawaii; 02-20-2018 at 09:50 AM. Reason: Forgot to mention...
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Old 02-20-2018, 01:26 PM   #19
wrxhard
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This thing is spectacular!!!!
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Old 03-28-2018, 12:19 PM   #20
ski.wrx
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Quote:
Originally Posted by surferjohnhawaii View Post
Anyone have a spare set of sti r180 rear diff to 24 spline wrx hubs? $1100 from drive shaft shop is going to kill my budget!

Cheers
John
You could check this guy out. He still has them available and much more affordable than custom axles

http://wordpress.suberdave.com/?page_id=275
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Old Yesterday, 08:30 PM   #21
TannerVA
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This is amazing, do you have a build log anywhere?
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