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i havn't look at the stock compression specs but if the 04-05 made more compression it wouldnt be because of the crank or rod, the only thing i could see it being would be a different head design.

if someone knows the answer please chime in, and the next question i have is if u put an 04-05 head on an 06+ would the compression go way up?
 

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It's exactly because of the crank and rod. I know there are some differences in the heads but I don't believe it's enough to make a real noticeable difference. Like i said 05 had higher compression by half a point so if you put that same piston in an 06 you will loose half a point. I've gone through this with all the top guys on here. One of the biggest reasons guys like to run the wr cranks is because you gain the extra 10cc of stroke and a lot more compression. I know because I've done all this already.
 
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i havn't look at the stock compression specs but if the 04-05 made more compression it wouldnt be because of the crank or rod, the only thing i could see it being would be a different head design.
i heard that if you change the cases the compression goes up. i plan on going to a 04 head and cases. 1 point for the case change and .5 points for the head change. 14.1 here i come.
 

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Dylan don't forget to Use the pink power band when you do the case swap or you will have a bad bog lmao
 

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One of the biggest reasons guys like to run the wr cranks is because you gain the extra 10cc of stroke and a lot more compression. I know because I've done all this already.
the wr crank is the same stroke as the 06+ so if you put the 06+ crank in an 04-05 bike you will gain an extra 10cc and alot more compression, so since the 06 bikes already have the longer stroke it should have more compression if everything else on the motor was identacle.
 

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I'm pretty sure the 06 has a shorter rod than the wr crank. I know the wr is 12.5:1 compression Stock. More stroke doesn't always mean more compression. I know for fact that 04 05 have more compression than 06 and up. Do your research on here and you will find what I'm telling you is true. Terse explained a lot of this in previous threads. Maybe he can chime in and clarify a few things.
 

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Discussion Starter · #28 ·
Now I know why I had so many pm's on this subject :icon_biggrin:

CAPis the only piston maker saying it will INCREASE compression when installing a '04/'05 spec piston into a '06 motor.

Stock comps:

'04-'05 = 11.9

'06-'07 = 11.4 with 1.4mm "total" increase in stroke. .7mm TDC and .7mm BDC. '06 uses a short rod with long throw crank. Also has a undesirable rod angle because of the short rod.

How can a motor with .5 less comp WITH a total 1.4mm stroke GAIN compression over a 11.9 comp 1.4mm LESS stroked motor with a UNMODIFIED piston... no relocated wrist pins. They use the exact same pistons through the years on the yfz, only wrist pin c-clips changed.

CP has not explained this to ANYONE.

Break out the calculators and do the math.

Installing a CP '04 spec piston designed to increase compression from 11.9 to 13.5 is a gain of 1.6 points.

If that piston gains 1.6 points then installing the same piston into a '06 motor that has 11.4 stock compression will be... follow the math 11.4 + 1.6 = 13.0

'04 spec'd 13.5 piston will net 13.0 in a '06 motor WITH the same 1.4mm longer stroke.


IF CP ever explains their math to "anyone" please tell me, cuz my math does not equal their highly tuned Alien inspired mathmatics. This I think is why we still to this day do not have flying cars. We are to stupid to understand physics and mathmatics on such a highly advanced plain of thinking we might as well all still be peeling bannanas in trees picking bugs out of each others hairs.
maybe this will help
 

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That's the exact post I was trying to find. Good job on the search.
 

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OK, I'll try this again.

IF you set the engine up correctly, then the +1.4mm increased stroke will gain compression....

If you are going to the trouble of rebuilding a motor, and installing a new high compression piston, why would you not set it up correctly?

Using the following specs for comparison purposes, we can then see what happens to compression....

Compression Ratio = (displacement+trapped volume)/(trapped volume)

Bore = 95mm
Stroke = 62mm
Displacement = 439.46956cc
Combustion chamber volume = 21.5cc
Deck height = zero
Head gasket = 1mm (or ~ 0.040" - 0.3937" to be exact...)
Total trapped volume = 38.23822cc's which includes the dished area of the piston
Compression Ratio = 12.5:1

Now using the same specs as above but with the added stroke of the newer +06 crank...,

Bore = 95mm
Stroke = 63.4mm
Displacement = 449.393cc
Combustion chamber volume = 21.5cc
Deck height = zero
Head gasket = 1mm (or ~ 0.040" - 0.3937" to be exact...)
Total trapped volume = 38.23822cc's which includes the dished area of the piston
Compression Ratio = 12.75:1

Now, the above is ONLY true IF you set the TRAPPED volume the same on both setups. To do this, you either have to vary the base gasket thickness, head gasket thickness, or even perhaps deck the cylinder. Otherwise, you will not get the increase in compression.

Since the rod is shorter on the newer 06+ motors, this drops the compression IF you don't take the time to setup the motor correctly. The drop in compression comes from the fact that you now have a larger trapped volume (the area above the piston at TDC) since the rod now places the piston at a point slightly lower in the cylinder at TDC...

I chose to deck the cylinder on my setup. I'm running a CP 13.75:1 shelf piston that I setup with a decked cylinder (decked by -0.028"). With the cylinder decking and with the current squish setting which I have, I am right at 14.25:1 compression using a CP shelf 13.75:1 piston.

It's all in how you setup the piston to cylinder deck relationship combined with the squish setting that makes the difference.

Basically, if you setup the 04/05 and 06+ motors with the same trapped volume, you will get an increase in compresssion, which is exactly what CP is telling you.

I've talked to them via phone, plus emails to see what they had to say regarding the subject.

These are things we should be taking into account anytime we are "building" a motor for increased performance. This also helps us take into account variations within the manufacturing processes of all the parts in question, such as the cylinder, crank/rod, piston, etc., and thus take these tolerances into account when we setup a motor to perform to it's best potential.

Regards,

Rog
 

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That is not what cp says on the box. They claim 12.5 for 04 05 and 12.75 for 06 and up which is not the case. They don't provide any info on setting squish or having to modify anything to get compression. If you go through the trouble of doing all the math to setup for compression then yes you can get 12.75. Simply putting a piston specd to an 05 crank on a 06 crank you will loose compression no and or Ifs about it. If cp is gonna claim something then they should be sending an explanation of it with their product so the consumer can properly set it up. I have never received any information with a piston From Cp about setting squish. I agree with you buttermilk for the most part. But you could make an 05 have 12.75 by altering squish as well. These products are suppose to be simple bolt on parts and as I know from experience things are never as they seem but for a bolt on part it should be as advertised and in this case it's not.
 

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You might smack the head with the piston if you tried to do that on an 04/05....

I'd have to disagree with you on the "simple bolt on parts..." since we are dealing with the internals of the engine....

I've seen YFZ's (mine) that were simply bolted together with shelf parts that had the piston down the hole as far as 0.037" which is, in my opinion, way to far. Top that with a head gasket at 0.032", then you got a lot of room for improvement for best performance.

By the time you factor in cylinder height variances, gasket thickness variations, piston tolerances, etc. etc., why would you want to simply bolt something together and not know where you are regarding clearances, is beyond me. Simply can't expect a motor to perform to it's potential unless you get lucky and get it right by chance.

Regards,

Rog
 

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thing is cp is suppose to figure the compression of their pistons when they manufacture them. they are meant to be bolt on parts with safe clearances and compression ratios. is there more power to be made using the same piston? well my answer is absolutley, in this business nothing is ever 100% and everything influences everything else. most people will buy a piston because its what they need for the fuel they run. a lot of do it yourself guys dont have the knowledge to squeeze every ounce of power out of the engine which is fine, thats why they rely on the manufactures specs. but putting on the box 12.5 for 04 05 and 12.75 for 06+ is claiming it to be something its not. cp needs to correct this and make it clear to the consumer what they are getting. ive seen a lot of heads in the car world that are advertised to have a certain combustion chamber volume and 9 times out of 10 they arnet as advertised. i agree that in the drag racing world which is mainly what i do but more serious with the car stuff, any amount of power you can squeeze out of an engine safely is benneficial without a doubt. but for your average trail rider they dont need to squeeze every little bit out, they rather keep there machine running strong and relaible.
 

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To the best of my knowledge the pistons are identical.
 

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YFZ stock engines are not zero deck.

A total deck height of .020" in the hole plus the thickness of your gasket for a total of .045" is recommended..... sure you can make more power by going tighter, but if the crank and rod stretch the piston can hit the head at the piston's (I'll call it) rock over point at TDC.

Yes adding 10cc will add compression....

There is a slight head combustion chamber difference but not .5 points.

The rod is shorter on the 06 compared to the 04/05 cranks..... and at that point the 06 is NOT at the same TDC as a 04/05. Which is where buttermilk is talking about setting up the motor... he is correct in that.

04/05 cranks have a 102.5mm rod....

06 cranks gain +10cc of stroke and use a 101.5mm rod.....

WR cranks have the same +10cc gain and uses a 103.5mm rod.... so a wr crank has a 2mm longer rod so how can any YFZ engine use a zero deck height? They can't. Not even a WR engine uses a zero deck height. So that is completely wrong.

04/05 yfz has 11.9 comp

06+ has 11.4

total loss of .5 compression. With the slight head combustion chamber design.... all they did was unshroud the valves some.... and the different TDC (lower in the bore) of a 06+ crank you get a -.5 loss of comp. Most of it is with the crank.

ALL YFZ pistons are the same 04-09.

Any piston spec'd for a 04/05 will be atleast .2-.3 points less in compression in a 06+ crank motor.

ALL WR crank pistons on WR cranks will have the exact compression as advertised (given correctly spec-d parts).

A HR stroker crank +3mm has a 100mm rod and a 66.4mm stroke to further jumble this mess.

On paper CP did the math and spec-d a 04/05 piston and with the paper math yeah a +10cc stroke gain would add .5 compression...... but not on a shorter rod with a lower TDC location compared to the same 04/05 set up.

All piston makers spec their pistons useing the OEM gaskets. Sure you can alter compression and deck heights with other gaskets.... thinner or thicker... this is just one easy way to gain some power out of a engine.
 

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The WR piston has the wrist pin location offset to account for the longer rod (that's the reason the WR piston has to be used....)

To tell me that is's "just wrong" to set up a motor with zero deck height is "wrong" on your part. It's completely safe and doable. Even factory's on some motors set them up with zero deck.

In fact, my 513 Falicon setup with the JSR Tall cylinder is setup with zero deck as the parts come with the kit, and that ain't my doings....

ANY motor can be setup with zero deck. Safely. To say otherwise is incorrect.
 

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The WR piston has the wrist pin location offset to account for the longer rod (that's the reason the WR piston has to be used....)

To tell me that is's "just wrong" to set up a motor with zero deck height is "wrong" on your part. It's completely safe and doable. Even factory's on some motors set them up with zero deck.

In fact, my 513 Falicon setup with the JSR Tall cylinder is setup with zero deck as the parts come with the kit, and that ain't my doings....

ANY motor can be setup with zero deck. Safely. To say otherwise is incorrect.
Well re read what I said...

I said it is wrong that the yfz uses a zero deck. It does not.

The WR does not use a off set pin. It does however use a 18mm pin and the yfz uses a 20mm pin.
 

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And... the WR motorcycle has 12.5 compression stock .......... not 11.9 so that is .6 point higher then a 04/05 yfz...... so more compression longer rod = higher in the bore at tdc.
 
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