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SlammedRanger

400ex stroker (440ex) build thread

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Well lady and gentleman its finally time. I put a wrench on the quad to start the motor removal process. Here are some pictures of the new parts so far. This is going to be a full top and bottom end rebuild with the following

 

-All new oem bearings(everyone in whole engine)

-New oem oil pump assembly

-Cometic gasket and seal kit

-Custom cp 12:1 stroker piston

-Crankworks balanced and trued hotrods stroker crank

-hinson bullet proof basket

-hinson clutch kit

 

And thats just the start. There will be more budget pending.

 

Stay tuned!

 

 

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This is gonna be a fun build! Your combo might be really good for making torque.

 

What will the bore & stroke and rod length be? Are you gonna run the same cam profiles? What is your dynamic compression ratio gonna be?

 

I'm curious because the additional displacement will tame the cam down a bit. But other factors... Increased stroke & shorter rod length may alter piston deceleration/acceleration (dwell time) near BDC. Gross piston speed is increased and those two factors will alter the intake and exhaust events' port flow characteristics considerably too. Are there any cam options in the budget? :-)

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Here is the spec sheet for the custom piston. I do know that they shorten the rod by 2mm and the stroke is done by moving the pin in the crank. As far as cam goes i cant go any bigger without shortened valve guides so the cam isnt out of the budget but the extra machine work is ontop of the cam. I cant seem to find the rod length anywhere. Not stock or aftermarket or anything. And the dynamic compression has me stumped lol. Piston is 12:1 but i know there are alot of other factors in dynamic.

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Heres the cam numbers. Mine is a magnum which appears to be the exact same as gt thunder. From all the research and a confirmation by my machine shop guy 350 is max lift before the shortened valve guides are needed. Which my cam is maxing out that on one lobe the other has a tiny bit more room for error lol.

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Interesting build, I look forward to seeing the end result for sure 🙂

 

From the above Im thinking you'll be gaining more power, torque especially at a much lower rev range. I could be wrong, I'm no race engine builder by any means lol!

 

What carb will you have to use for this build, will the stock carb with oversized jets be big enough?

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I run a built fcr39mx full race carb already. By built i mean it has an aftermarket bowl, accelerator pump, and quite a bit of custom add-ons i did myself. This carb is a flat slide and is what everyone runs on the full blown 460cc kits(440 stroker). She will have no lacking of air thats for sure! LoL. I hope with my +1mm valves, port and polish, and cam lift it will try to throw me off the back. I am already planning on gearing up. Where i have it geared now is way low. 13/38. Stock is 14/39. I will be going to a 14/38 right off the bat. With intentions of maybe going 15/38 if i need to.

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Sports ATV'S is not something I've ever been into, currently considering it though. 

The gearing means nothing to me if I'm honest however, I did have a ride on a Polaris 525cc several years back that was geared for a big guy (22 stone!), It accelerated that fast I couldn't focus, my eyes were like the ball in a pinball machine haha!!

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Gearing is pretty simple. Each tooth you go down in the front is like 3 in the rear. Its all about mechanical advantage. The lower in front more torque and less top speed. Bigger means less torque and more top speed. The rear sprocket is opposite. Bigger in rear more torque. Smaller less torque. Thats why i went one smaller in rear to counteract the one down in the front. I had to drop my gearing for the tight corners and short straights at our local fair race.

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shoot, just strap a rocket on the back of it, call it a day !..lol.

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7 minutes ago, SlammedRanger said:

Wait a second i just lit a rocket........ rockets explode! LoL. Couldnt resist

at this build rate, I have a feeling this is gonna explode too !..lol.

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6 minutes ago, shadetree said:

at this build rate, I have a feeling this is gonna explode too !..lol.

Nah she will be plenty reliable. Unless your talking about the speed im building it at. And in that case yeah im gunna spend the winter on it. Clean everything up so the motor looks new. Go over every single detail 100 times and make sure i dont have to do it again lol. No rush. And honestly i still dont have the crank back from crankworks yet anyway so im in a holding pattern anyway.

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Its the 440cc bore that has cooling issues. I am doing a 440cc in a different way. Its gunna be a 416 bore but with +4mil stroke. So its still a 440cc but without the thinning of the cylinder and cooling fins.

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Had a half an hour of spare time today to start the motor removal process. Should have it completely removed tonight. And crankworks is supposed to have my crank and piston sent back later this week.

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4 minutes ago, shadetree said:

wellllllllllll..its not all apart ??!!!..lol.

Why rush? Crank and piston are still in arizona lol. I got alot of plans in the works for this build. Thinking i will be sand blasting the cases. Im gunna cerakote the side covers. Among other things. I just want the whole motor top to bottom new. And flawless in every way lol.

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2 hours ago, SlammedRanger said:

Why rush? Crank and piston are still in arizona lol. I got alot of plans in the works for this build. Thinking i will be sand blasting the cases. Im gunna cerakote the side covers. Among other things. I just want the whole motor top to bottom new. And flawless in every way lol.

if you do sand blast the covers ?, be very careful !!!!, you do not want to get grit into places it should not be in !!.

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I run some numbers based on the available specs that we have so far, in order to characterize this 440 motor build in my head. I'll share what I've learned here, then hush up, sit back and enjoy SlammedRanger's build.

 

TL;DR:

This motor should produce a fairly broad and relatively flat torque curve. Throttle response will be excellent. It will be noticeably quicker to accelerate & build RPMs than it was with stock crank & rod. Drive-ability should be quite good with gobs of torquey acceleration available where its needed the most, particularly in the low-mid RPM ranges, such as when exiting corners. Gearing up with sprockets changes will be required. This is a moderately safe build as well. Piston speed is relatively high, but is below 4700 FPM, so is not high enough to be concerned about. Shift points (peak RPM) will be lower than the previous build anyway, so that piston speed figure will be nearer to stock in reality, unless the head and camshaft are altered. Dynamic and effective compression ratios are moderate, no exotic fuels are required. Its gonna be reliable and inexpensive to operate and maintain. Its not a time bomb. There are room for improvements in ports flow, gross valve lifts, rod length, compression and exhaust header though, if money and time were not limiting factors.

 

The long version:

Basic stock specs for comparison purposes:

Bore/Stroke/Displacement: 85mm x 70mm = 397.37884cc (3.346447" x 2.755897" = 24.240109 CID)

Rod length: 122.7mm (4.830694")

L/R ratio: 1.7528

Piston Speed: 4,363.50 feet per minute @9500 RPM

 

Build specs:

Bore/Stroke/Displacement: 87mm x 74mm = 440.0875422cc (3.425187" x 2.913377" = 26.85579 CID)

Rod Length: 120.7mm (4.751954")

Piston Compression height: Stock wrist pin location

L/R ratio: 1.6581

Mean Piston Speed: 4,612.85 feet per minute @9500 RPM -- Peak Piston Acceleration during combustion occurs at approximately 68-69 degrees ATDC

Static compression ratio: 12:1

Effective stroke: 2.44 inches

Effective Compression ratio: 10.31:1

Dynamic Compression ratio: 10.23:1

Boost Compression ratio: 10.04:1

Dynamic Cranking pressure: 218.84 PSI

Piston travel percent: 16.1% -- Piston Travel is 0.47 inches up from BDC  at Intake Closing (55 Degrees)

Valves: +1mm larger than stock

Carb: 39mm FCR

Port flow figures are unknown

Exhaust header dimensions are unknown

 

Camshaft specs:

Grind: Single Pattern

Lift (inches) Intake: 0.350  Exhaust: 0.345

Advertised duration: Intake: 280°  Exhaust: 280°

Duration @.050" lift: Intake: 256°  Exhaust: 256°

Lobe Centers: Intake: 107°  Exhaust: 107°

Intake opens: 21° BTDC  Intake closes: 55° ABDC

Exhaust opens: 55° BBDC  Exhaust closes: 21° ATDC

 

Comments/opinion: This is a relatively safe, moderate output, short rod motor as spec'd. It is not optimized for maximum torque output, but that sort of design costs a lot of money and requires custom parts fabbing. I doubt if this motor would fit in the 400EX frame if a cylinder spacer was fabbed, a long rod swapped onto the crank and a longer timing chain was made. Then there are unknown bottom end strength limitations that would need to be discovered before increasing the effective compression much higher than it is now. If I were looking to improve on this motor without sacrificing reliability I would port and flow the head and swap in short valve guides, so the valve lift could be increased. But it is sensible as is.... I doubt if the piston will even need to be flycut for valves clearance.

 

The present camshaft is tame for this 440cc motor. I expect peak power may be found around 9100-9200 RPMs max, with the relatively flat torque curve beginning to drop off sharply between 7800-7900 RPM. This should be a sensible and cost-effective build in my opinion. There are gains being left on the table, but beyond this point torque gains will be small compared to dollars investments required to get them. It'll run down and pass a 450r as is... so why bother spending any more. Have fun with it. 🙂


 

 

 

 

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13 hours ago, shadetree said:

if you do sand blast the covers ?, be very careful !!!!, you do not want to get grit into places it should not be in !!.

Is that really a concern? I plan to have them down to nothing. Like removing all bearings and seals and anything that can be removed. And i will run it through the parts washer after i sand blast it to be sure i get all the sand out of everything. Is there something obveous im missing? Oil passages i will blow out with compressed air to be sure they are clear.

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