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YFZ450R/Redline 421 serval hybrid


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Been talking about it for years. Been planning it out for months. Time to get started.

 

THIS BUILD WILL TAKE SOME TIME. I work on the road and will be doing all the fabrication in the spare time while I’m home. Sometimes for 2-3 days, sometimes for 2 months.

 

The goal: build the best chassis I know of and give it more power than it will ever need. It will be a high-abuse build. I will rape it in the woods, I will roll it in the dunes, I will case it on a track, and I will be letting others ride it. I refuse to build something where I feel like I need to bring a 48” game box full of tools everywhere I go.

 

The chassis:

 

YFZ450R

-Xcel lower subframe w/rail modified stem location

-Walsh long travel arms w/modified shock mount

-Walsh MX swingarm

-my pull rod design

-Evol RC2 w/Evol mod by BNR

-Podium RC2 by BNR

-extended and dropped stem flag

-LSR stainless axle

-Walsh subframe

-Rath bumpers and monster peg nerfs

-Walsh stem

-Walsh stem clamp

-Mika Metals CR-Hi bars

-Behringer master cylinder

-WC full clutch setup

-Imprint grips

-DWT MXR-V3 on DWT beadlocks

-Maddie Razr Cross fronts on DWT rims

-Galfer lines and rotors

-Precision Elite steering stabilizer

 

The engine:

-Redline ported race gas 4mil serval

-CPI SBIF

-VF4

-33PWK

-94whp @ 9400rpm

-51.2lb.ft @9100rpm

-Redline pro mod trans

-Chariot water pump and basket

-being rebuilt atm.

 

Immediate problems:

 

1. There is no rear engine mount in the frame. OEM runs the swingarm bolt through the rear of the 450 engine itself. Part of the frame is cast aluminum. Using 4943 filler makes welding cast a little better, but I still try to avoid it if at all possible.

 

Solution: 7/8” .120wall 4130 where the 450 bracket was. Weld a support to the rear mount for the banshee engine. Not optimal, but absolutely doable. Front engine mounts will have to be beefy as a result.

 

2. Pipes. I’m using CPI for this build since I already have them and they performed very well on this engine. However, I have wildly insufficient room to make them fit. Again, I’d have to hack part of the aluminum chassis off and make a new piece from scratch to weld back to the cast aluminum section and then bolt to the lower frame rail.

 

2b. Pipes will stick out way too far. It’s easy, but it’s poor craftsmanship. To tuck them in requires a different radiator location altogether.

 

2c. Arlan is a busy man. He will get my business one day, but this build at this time isn’t going to allow it. Plus, $1700 for a set of pipes (reasonable, honestly) when I already have a set, shipping both ways, and months of downtime aren’t in the cards atm.

 

Solution: remake the entire front aluminum section from 4130. I can save about 4-5lb this way, create a way to actually route the pipes, mount the radiator(s) wherever I want, and it will be stronger. I will have to cut the pipes in at least 5 places to make them fit.

 

3. Radiator. Won’t fit anywhere. Neither the 450 or banshee one.

 

Solution: I will have to order a core and make the tanks. I’ll also have to run a fan since it makes the power it does and since it will be an all-purpose build, so a DC conversion will have to happen. Will be thick as hell. I may have to run two.

 

4. Filters. Pods sit directly between the shock and frame rails.

 

Solution: stainless tube to move them back. There will be some necessary shaping to make them fit.

 

5. Tank is a fuel injected one

 

Solution: block off the pump hole. Fortunately, the lowest point in the tank sits PERFECTLY for the pingel to have a good location.

 

6. Kicker. Likely will interfere

 

Solution: cut and weld that hoe.

 

It will not be a quick build. I could do it in a week, but I wouldn’t trust it to stay together and I wouldn’t take pride in it.

 

Will post pics and updates as I remember to. I will try to be as thorough as possible and provide every detail I can remember.

 

 

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You can see just how close the flange is to the frame here. This is going to be a huge problem, but one that I have a solution for.


7a4da104f217206f9b5f471f54a81e2b.jpg

I will make the front section from 1” .083 and 1” .095 wall chromoly. There will be a ton of other little pieces involved.

For instance, making the a-arm brackets (0.125” 4130 plate), radiator mounts (0.83” 4130 plate), gussets (0.75” 0.83 wall 4130 tube), etc.

First things first, make a jig, order materials, and get to work.


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Just ordered 80’ of 4130 chromoly in varying sizes. I will only be doing the front chassis section and upper frame rails. I have plans for the rear later on, but that’s still a long way away.

I know some of you know these things but others don’t. In my opinion, the all time greatest build threat is “Rezlo’s fast street track S14 build.” Years ago, I learned a lot of fundamentals from that thread. I want this to get close to that.

So...

For race quad frames (and trophy trucks, roll cages in race cars, kit planes, etc.), 4130 chromoly tuning is used. The difference between tube and pipe is that tube measures outside diameter while pipe is measured inside diameter. A 1” tube will fit inside a 1” pipe. All chassis fabrication where round material is used is done using tube.

4130 is my choice. When choosing a material for a project, just do your research. 4130 and DOM are the major choices. 4130 is stronger so to get the same strength, it’s lighter than DOM. For the same strength, 4130 is about 30% stronger than regular steel.

Yes, there are better or harder materials out there like titanium, 4140, etc., but with those come special fabrication practices. Titanium LOVES oxygen, but oxidized titanium is structurally useless. If you want to weld it, you have to keep argon coverage much longer, as well as argon on the back side of the material. Someone opening a door too fast is enough to ruin a titanium weld. Welding 4140 (the times that I’ve done it) requires preheat to slow the rate of cooling in the weld affected zone, otherwise cracks develop. I despise welding on already hot metal.

4130 doesn’t require preheat until you get to the .120” wall thickness range. In the one piece where I am using .120” wall, it will be preheated to around 580F or more.

For filler metals, again... DO YOUR RESEARCH. ER80SD2 is my choice. The strength of a chromoly design is in the design, not in the weld. The weld just has to do its part. Using 4130 filler is chemically consistent but can be too rigid and form cracks. ER70 rod is fine when welding 4130 or when welding it to existing structures like mild steel (none will be left on this build), but ER80SD2 is the prime option.

Wall thickness on this build will range from .035” to .095 and .120 in one special case. Tube diameter will be 1” for the main structure, 7/8 for a few braces and the lower engine mount, and 3/4 for the rear engine mount. I will also be using some 1/2x0.058 for fender brackets. I could go thinner, but I don’t want anyone to be drunk at a party and plop down on it and break it.

Another principal that I’m taking into consideration is the most forgotten of all hobbyists in motorsports: centralized mass. You can have 50/50 weight distribution at each end or side and still have very decentralized mass. This affects rotational inertia, AKA how hard it is to get it to turn or stop turning. I will be using a banshee engine (obviously) which has to be positioned well forward of the normal positioning in this chassis. That amount can be significant. To combat it, I will keep everything as far back as possible. From the radiator, to the fuel tank, even the way I gusset and mount the a-arms, everything will be moved back as far as possible.


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  • 2 weeks later...

Just the research and ability to actually do this kind of hybrid puts you a lot further ahead than most of the hack and slash attempts I've seen. Doing it on the yfz450r is even cooler, maybe Hettrick will put a lap on it.

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Just the research and ability to actually do this kind of hybrid puts you a lot further ahead than most of the hack and slash attempts I've seen. Doing it on the yfz450r is even cooler, maybe Hettrick will put a lap on it.

I sure do appreciate that bud. It won’t be easy but it it’ll be worth it.

Maybe he will! I already have one pro rider that wants to help out and dial it in but it’ll probably be a little more aggressive on he shock tune than what I need lol.


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  • 3 weeks later...

WIll be great to see an R finished.  Couple things from your post: Arlan is $2,500 +/- with no real timeframe.  I like your CPI Idea, tried and true.  If you go IMS the tank is not weldable, took me a long time to accept this. I was able to torch and bend the carb yfz IMS tank to clear plugs.   Cam's dune ported 421 serval would drink a stock tank so quick!  I thought I blew it up my first ride but it just ran out of gas that quick.  Have since demoted to an as cast Assassin.  Pods were a pain.  Snorkles to pods in back would not let 421 sing.  I ordered $400 worth of K&N Pods from Oreilys knowing I could return them.  I settled on one 5" 10 degree and one 5" 20 degree.  Was very nervous it would not be enough air but it works with my 85hp setup w/ 33's. Look forward to your updates!

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WIll be great to see an R finished.  Couple things from your post: Arlan is $2,500 +/- with no real timeframe.  I like your CPI Idea, tried and true.  If you go IMS the tank is not weldable, took me a long time to accept this. I was able to torch and bend the carb yfz IMS tank to clear plugs.   Cam's dune ported 421 serval would drink a stock tank so quick!  I thought I blew it up my first ride but it just ran out of gas that quick.  Have since demoted to an as cast Assassin.  Pods were a pain.  Snorkles to pods in back would not let 421 sing.  I ordered $400 worth of K&N Pods from Oreilys knowing I could return them.  I settled on one 5" 10 degree and one 5" 20 degree.  Was very nervous it would not be enough air but it works with my 85hp setup w/ 33's. Look forward to your updates!

Arlan on the pipes will be an eventual thing. I can make these CPIs work for now.

Fortunately, the stock tank will work with modification so that saves 2 days of fabricating aluminum sheet.

It depends on the design of the snorkels. Starting at 2.25” and working up to 2.75” at the pods will let it breathe enough if the length is good.

Only problem is that my work is unpredictable and I still haven’t received my tube notcher. I may have to take a job on Monday, or I may be off until February. Who knows? Lol

I have determined that tube software is going to be borderline necessary unless I want to waste tube. $300 one time for the software vs. $150 in trial and error on every new chassis design.

No physical progress has been made other than the engine being rebuilt but design progress is coming along nicely. Time will tell.


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  • 2 weeks later...

Waiting on the tube notcher (shipped Wednesday) and I’ve been with my grandfather in the hospital until just a few days ago.

Spare frame is ready to jig on the bench now.

Engine is waiting on a crank and gaskets.

Radiator situation is gonna be a huge holdup. I’ve made enough calls already to know it.


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Ricky Torres on the FB YFZ-Banshee conversion site had a real nice radiator made to his specs.  Was generally a budget build so I don't think the price was astronomical.  If you have any troubles looking him up for more datails, let me know and I'll help get you guys connected.

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