How to get Cubic Inch Displacement (CID)
CID = .7854 x Bore squared x stroke x number of cylinders
ex: .7854 x 3.346" x 3.346" x 2.756" x 1 = 24.23 cid ( 400ex)
How to convert to Cubic Centimeters (CC's)
CC = .7854 x 85mm x 85mm x 70mm x 1 = 397216.05
397216.05 divided by 1,000 = 397cc
(mm ----> inches mult by .03937) or (inches ----> mm div. by .03937)
How to convert to Liters
Liters = .7854 x 85mm x 85mm x 70mm x 1 = 397216.05
397216.05 divided by 1,000,000 = .398 Liters
How to get Compression Ratios
C.R. = cylinder volume + Deck height vol. + Head gasket vol. + combustion chamber vol. DIVIDED by Deck height vol. + Head gasket vol. + Combustion chamber vol. = Compression ratio
Compression Reading
To find the lowest reading you have to get the highest reading and multiply by 0.75.
ex: 195 psi x 0.75 = 146 psi being the lowest amount you can have throughout all the cylinders.
How to get Horse Power
HP = RPM x Torque div. by 5252
ex: 6200 x 275 div by = 324.6382331 or about 325 HP
Common 400ex Bore Sizes
Standard bore- 397cc or 85mm
402cc- .040 over or 86mm
406cc- .060 ever or 86.5mm
416cc- .080 over or 87mm
426cc- .120 over or 88mm
440cc- .160 over or 89mm
also...
440cc with an extra 4mm stroke = 460cc
416cc with an extra 4mm stroke = 440cc
FREQUENtLY ASKED QUesTIONS
Will running an engine without a muffler blow my rings/ burn my valves?
No. On a 4 stroke you do not need back pressure for it to run right. What you will need to do is check your jetting though. Opening up the exhaust is creating a lot more air flow thus leaning out your fuel mixture. Not doing so could make it overheat enough and ruin engine parts though. A two stroke engine is a different story though, in most cases it needs quite a bit of backpressure. It will rely on the positive back pressure to push the fuel air mixture back into the cylinder that the ports are letting out.
Will a higher octane gas make my engine put out more power?
Higher octane gas DOES NOT make more power. Higher octane gas allows you to run a higher compression ratio without the chance of spark knock/pre-ignition or detonation which is when the heat and compression of the engine will actually ignite your fuel/air mixture before the spark plug(s) fires. In most cases you will actually make more power off of a lower octane fuel because it ignites easier and faster, that is if the engine can handle it. Running a really high octane fuel ( like 110 ) on a stock engine will not give you any power, there is actually a good chance that you will loose power. Example: an air cooled engine can run on 93 octane from stock compression up to an 11:1 compression ratio. A liquid cooled engine on the other hand can run 93 octane till about 12.5 - 13:1 ratio because it is running at way lower temperatures than an air cooled engine. After that you will have to start running a higher octane fuel to compensate for the heat and compression the engine will be putting out.
My engine is smoking, whats it mean?
Blue Smoke- Means that you are burning oil. If its when you first start it up and it smokes for a few seconds then its your valve seals. If it smokes when your running thru the RPM's then your rings are shot.
White Smoke- If you have white smoke then it can be two things. If it has some white smoke when you first start the engine if its been sitting for a few days, then its more than likely condensation thats built up in the exhaust. Dont worry about it. But if you have white smoke coming out even when its been running for a while then you more than likely have a bad head gasket and your getting anti freeze in your engine.
Black Smoke- Black smoke will usually mean that it is running to rich.
How to read a spark plug to see if the engines jetted correctly:
Lean- White in color or burnt up looking
Fouled- Black or wet appearance.
Perfect- Dark Grey - Light Brown in color.
What is the best way to polish something?
After experimenting with different ways to polish something and actually have it come out the way i had hoped, ive found out that the best way to go is Mother's Mag and Aluminum Polish.
- To polish aluminum, i just simply smoothed it out with a low grit sand paper and worked my way up higher until i got the fine scratches and imperfections out of it. Then just wipe on the polish with a clean rag and keep buffing it on until it leaves a really dark haze, then take another clean rag and wipe it off. You'll now have a Chrome looking finish!
- Stainless steel doesnt really require any polish (IMO). just start out with like 180 grit and slowly work up to 2000 grit paper and it will shine really good.
The difference between the XR400 and the 400ex engine:
400ex: 85mm piston and 70mm of stroke. Comes stock with 9.1:1 compression ratio. Electric start only. The camshaft is a big difference. Lift and Duration .316 .302 .234 .238
XR400: 85mm piston and 70mm stroke. Comes stock with 9.3:1 compression ratio due to a thinner headgasket. The camshaft is also different. Lift and Duration- .326 .321 .240 .244
Just a fact about buying a piston for your 400ex from Wiseco. Whenever wiseco offers a piston for the 400ex engine they base their compression ratios off the XR engine. Example- If they say its an 11:1 piston its really going to be a 10.8:1 compression. To fix that problem you can put on a XR headgasket and that will bring it back up to the true compression ratio due to the 400ex having a thicker headgasket.
More to come
