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Mar 09, 2019, 12:23 PM
Did I make the A Main?
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Mini-Review

REVIEW: PR Racing SB401-LW


This will be an evolving thread as I build and review a PR Racing SB401-LW. Look for regular updates to this post as I plan to race this buggy in the 13.5T Latemodel Oval class at Thornhill Racing Circuit. Full disclosure, I recently picked up a sponsorship through PR Racing so be prepared to expect some bias, but I will do my best to identify potential areas to consider making upgrades to improve the quality of this kit where applicable.



A quick background on me: I started club racing around 2010 and have slowly improved my skills to where I'm one of the slowest of the fast guys at the club in my area, ha! I typically average between 96% -98% consistency and will occasionally pick up a win for club racing and often make the A Main for regional events in 13.5 stock. My first wheeler was an InTech ER-14 (clay), then I switched to a Schumacher CAT-K2 (clay+turf) and spent the last 16+ months running a TEKNO EB410 mostly on turf. Expect to see me try different things, I'm sure some ideas will fail, but that's where I always try to learn from my mistakes and I welcome you to share these experiences with me here on this thread.




Hits:
  • Loaded with upgrades in the kit for exceptional value!
  • Global Team Driver Support with setups posted on Facebook and PetitRC
  • One of the lowest LCG designs I've seen on the market!
  • Aluminum: hangers, motor mount, hexes
  • Carbon: towers, battery strap, ackermann, steering support
  • Easy access front/rear diffs for super quick tuning changes between rounds
  • Slide lock aluminum motor mount with Center slipper which is perfect for stock racing on medium to high traction surfaces
  • Aluminum shafts and shock standoffs are available as upgrade options for stock racing
  • Wire management braces for super clean wiring jobs
  • Aftermarket support from RideLow Racing (center gear cover) and Ardntcraft fan shroud

Misses:
  • Currently only 2 distributors in the US, but there is promise of a large distributor picking up PR soon!
  • Superseded by the 401R, very few Type-R parts are compatible
  • Probably more cost effective to sell the 401LW and buy a 401R than to upgrade with Type-R parts
  • Only 5 labeled bags A - E, will need to spend some extra time organizing parts during build
  • E clips used in gear diffs, probably worth it because they don't leak
  • No pill inserts in hangers limiting tuning changes to upgraded hangers
  • Center slipper maintenance requires complete removal of motor mounts

Summary:
For the price this car is hard to beat, it's very competitive right out of the box and reasonably durable too! I would highly recommend this kit for someone looking to get a 4WD Buggy on a budget... if performance is more important then consider getting the 401R instead which is more expensive but includes more upgrades than what you get with the 401LW... note that the LW arms use a softer plastic which will tend to be a little more durable than the graphite arms that come with the Type-R, however the 401R arms will be more responsive giving the consumer the option to consider both options.

Tips:
Check out more stuff on My Bookmarks page!
Last edited by bill_delong; Apr 08, 2019 at 09:29 AM.
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Mar 09, 2019, 02:04 PM
Did I make the A Main?
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Box measures 5"x9"x18":


Yellow wheels are included along with a clear lexan body, wing and wing reinforcement:


There are 4 large sealed bags with bag steps B+C combined into 1 bag:


One of the decal sheets had a portion of the stickers removed:
Mar 09, 2019, 02:37 PM
Did I make the A Main?
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A Bag

Parts are separated by dozens of other small bags without any additional labels, you will need to carefully organize your parts if you accidentally open a bag that is intended for a sub-step listed on a different page. Instructions for Bag A span out from pages 4-10 and sub-steps are labeled A1-A5 in the manual. Note that black grease is included in the kit.



Step A1: Note extra hardware that needs to be saved for later steps, this is fairly common throughout the build process, plan to spend extra time keeping hardware organized and double checking measurements, I highly recommend investing in a caliper similar to this 6 in. Digital Caliper:



Step A2: No diff fluid is included in the kit, manual recommends 5K for both front/rear diffs, but team drivers are recommending to start with 10K for a more stable setup, since I plan to run this car on Oval I will give 5K a try first just to see how it feels. Be sure to fill the diff completely to the top with all planetary gears installed, use your finger to wipe any excess off the top and this will ensure that you have a consistent feel after a rebuild every time. Also use a small amount of grease on the back of the gasket help hold it in place, also being careful to align the square slot on the gear with the square shaft of the out drive (TEKNO Diff Build Demo):



Use a toothpick or small pin to help align holes when fastening the main diff gear to the diff case:




I like to use the out drives as a skewer and reverse the order of the seals to be placed inside the
diff case and will apply grease first then slide the seals into place without any mess:



I like to use a silver sharpie to label the diff cases with the fluid that I have installed, simply use an alcohol swap to remove the ink if you wish to change fluids/markings later:



Step A3: Center Slipper assembly has no mention of thread lock, but I chose to place thread lock on both the M3x8mm screws used to secure the spring collet and the out drive. Be very careful that the slipper pads are properly seated in the spur gear!



Steps A4-A5: Front/Rear Gear Box Assemblies
Be sure to use shims where noted, lots of care has been placed over the years to fix noisy transmission complaints, revisit these steps and adjust shims if necessary to remediate a excessively loud diff.



Last edited by bill_delong; Mar 10, 2019 at 01:09 PM.
Mar 09, 2019, 02:51 PM
Did I make the A Main?
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B Bag

Step B1: Front Assembly

There is a typo in the manual which has the FR block reversed as RF, most other brands that I have assembled typically reference these blocks as A,B,C,D blocks progressively from the front to the rear for easier identification:

A = FF (68480166)
B = FR (68480176)
C = RF (68480206)
D = RR (68480216)



Since I will be racing this car on Oval with a Latemodel body, there will be no risk of the carbon fiber towers from absorbing any direct impact from a crash, but if were to race this in a traditional buggy class with exposed edges, then I would seal the edges with CA glue to prevent the carbon fiber from splintering.



Step B2: Front Spindles - not indicated in the manual, I chose to apply thread lock on the M2x5 screws for the 12mm hexes... it cautions not to over tighten these screws but I had to really crank down hard to prevent the hexes from easily sliding off the axles, shrug:



Step B3: Front Suspension

I use the TEKNO Multi-tool to make it very easy to snap ball ends into sway bar ball ends and shock balls, etc, this tool is invaluable!



When snapping in the sway bar links on the arms with plastic ball mounts, I placed a small drop of shock oil on each plastic ball head to make it easy to snap the link in place using a flat head screw driver being careful not to put any lateral stress on the ball head... I have accidentally snapped these plastic balls off the arms of other brands of cars in the past and have learned these little tricks to make the build go a little easier



I plan to keep an eye on the stock hinge pin pivot balls, past experience with other brands of cars using these tend to wear fairly quick and generate a lot of slop, I plan to upgrade to these teflon machined pivot balls later on:



I was really pleased that I did not need to ream any holes on the arms, every fit was butter smooth with no binding anywhere, very high quality fit and finish comparable to many luxury brands on the market!



Steps B4-B5: Front Suspension
I took a little more time by using Ryan Lutz's method to assemble camber links, this is VERY IMPORTANT to ensure you can adjust your links later without risk of popping off the ball ends

Last edited by bill_delong; Mar 12, 2019 at 10:27 PM.
Mar 09, 2019, 02:56 PM
Did I make the A Main?
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C Bag

Step C1: Rear Assembly - fairly straightforward



Step C2: Rear Suspension - pretty much same experience a the front



Steps C3-C4: Rear Suspension *** note there is a typo in the manual which says "Front Suspension" but we are clearly working on the rear

Last edited by bill_delong; Mar 09, 2019 at 03:58 PM.
Mar 09, 2019, 04:18 PM
Did I make the A Main?
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D Bag - It doesn't matter what kit I build, the D Bag is always my favorite step, ha!

Step D1: Steering - Just look at all that pretty carbon!



***Take special note that the 5x8x0.1mm spacers (bottom of pic below) were not included in the D Bag, they were carried forward from an earlier step, not sure which hardware bag they were originally included, but be prepared for this!



Step D2: Steering
Manual shows to use 5x8x0.1mm shims "as necessary", but I already used them in Step D1, no more shims to be found! I went through my pit box and found some 5x7x1mm spacers that will get the job done to free up the slop, it seems that only 0.5mm thick spacers are what is really needed but these will have to do for now. It is worth noting that Bump Steer is effected by these spacers, so take this into consideration! I had originally tried to place them on the bottom (as recommended by the linked post) but it was binding on the top plate because the spacers I am using are too thick, since I am going to run this car in oval, I am not very concerned with getting the right size shims as this point, but will keep this in mind if I experience any bump steer related issues with my tune later on.



Step D3: Steering Servo
The stock plastic servo horn measures 14mm on center, while I realize that the car does come with a servo saver I have grown accustomed to always using an aluminum servo horn without exception and have chosen to use the Caster JR-1669FU horn which offers 2 holes with the smallest at 16mm on center which is pretty much industry standard for most 1/10 wheelers on the market:



I have placed a 2mm spacer on the horn to get the servo link aligned perfectly with the steering link and have chosen to mount the servo on the left side to get as much weight on the left for Oval setup:



There is not a designated mounting position for a transponder, I am using an MRT PTX-20-NS which uses the same 3 hole position as AMB RC3 style and have decided to use an existing hole for mounting the side guard plate and grinding away just enough material for the tab of the transponder to slide underneath:



Perfect fit as forward on the chassis as I can get without any binding on the servo arm, again trying to get as many components on the left side that I can

Last edited by bill_delong; Mar 10, 2019 at 12:57 PM.
Mar 12, 2019, 10:52 PM
Did I make the A Main?
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E Bag

Steps E1-E5

The kit came with 2 sets of black + green springs for both the front and rear!


They include emulsion shocks with both 2x1.6 and 1x1.8 pistons, I chose to drill out the 2x1.6 pistons and go with 2x1.7mm pistons on the front with 450CST oil, kit comes with 300CST fluid which will be too thin for oval racing:


For the rear shocks I bored out the pistons to 2x2.0mm and used the same 450CST oil to make it easier for maintenance using the same weight oil on front and rear:


Steps E6-12

I could not install the motor without having to remove the side guard:


I have a CNC and have machined a custom front bumper made of Kydex and rear wing mount made of carbon fiber to use both parts for body mounts for a late model body:


I used 2mm longer screws to fasten the front kydex bumper:


I used the same wing mount screws and went with a swept back mount design so there would be no risk of the rear tires ballooning up and can't touch the wing mount:


Final layout with electronics and oval tires installed:
Mar 19, 2019, 03:27 PM
Did I make the A Main?
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First race day was a success, I really wish I could've had more practice time to tune this car but the club ran a very tight schedule allowing me only 5 minutes to set the preload to help balance the car on corner exit. The car started to feel a little sluggish toward the end of my run but temps were around 140. I didn't get a solid run because I made a bunch of stops to adjust preload until it felt right. They ran the track wet during practice and bunch of dirt had collected under the rear center CVD shaft, I was thinking it might have caused some binding to slow the car down. Normally they run the track dry, but I will make sure to install the buggy body to prevent dirt from building up in the future in case they run it wet again.

During the first round, my car thermal-led at about 3 minutes into the race, I was sitting on TQ position at that point of the race too! I immediately went into the hobby shop and picked up a 28T pinion to replace my 32T gear and also got a motor cooling fan as well as an Exotek fan mount that wraps around the motor.

No heat issues during the second qualifier and I would take Q4 spot on the grid for the main. Things got a little dicey with a bad start for me getting taken out early and so I had a lot of ground to make up... I would eventually work my way up to 3rd and traded positions several times during the race, but would eventually secure 3rd place finish with only a 0.5 sec lead on 4th, it was a fierce battle and lots of fun!



Going into next race day I plan to try the following tuning changes:

1) Reduce drag brake from 35% to 20%... I am not used to using drag brake but was told this might help... my lap times are fairly close to my EB410, but I think I have too much drag brake and hope to find the sweet spot soon!

2) Change diffs from 5-S-5 to 7-S-3, the car has tons of steering which is nice, but still feels a pinch snappy on corner exit, I'm hoping this change will settle it down so I can lay on the throttle a little quicker coming out of the corner.

3) Add anit-squat... for same reason to get a pinch more rear traction on corner exit

4) Install Type-R front shock tower which sits 5mm lower, I already have the body as low as it will go and is resting directly on the LW front shock tower, but it would be nice to get it to sit 5mm lower to help increase down force and possibly improve corner speed a pinch.

5) Replace Trinity 13.5T MonsterMax with 13.5T Punisher with speed tune kit. The club allows outlaw motors and this should help give my car a little more punch.... I ran the Punisher in my EB410 but dropped in my spare Monster Max this past race day just to get my 401LW on the track.

6) Probably not gonna happen in time for next race day, but I do plan to install some ceramic bearings which I have on my EB410, that also gives another speed advantage where I am using the stock bearings in the kit for now. Currently the fastest bearings on the market that I know are AVID ceramic Aura single shielded bearings. They require more maintenance, and tend to be the most expensive, but are really worth the investment.

Look for more updates soon, next race day is scheduled for 30-Mar-2019!
Apr 08, 2019, 09:28 AM
Did I make the A Main?
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Very happy with the recent changes, I would actually get my personal record fast lap time within 0.07 sec of my EB410. I still feel like 20% drag brake was a pinch too much and I plan to reduce it to 15%. I actually went with 2K front and 5K rear which felt a lot better, I was struggling for steering after going up to 7K in the front. The Punisher upgrade was really nice too, no issues with any temps either

I would take 2nd on this race day:



After having a couple race days with my 401R, I have decided to sell my 401LW and will be replacing it with another dedicated 401R for oval... I can tell that the 401R generates a lot faster corner speed, and there are too many refinements with the 401R that I just won't be able to replicate with the LW that I figured it would be a lot easier just to switch chassis's.

This will conclude my review of the 401LW and I have updated my thoughts on the OP.

Thanks for following this thread


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