Milled Heads - 951

[SabrToothSqrl]

I'm told SBT mills out the combustion chamber, to lower compression and or performance, or is it to clean up damaged heads?

I have a photo of the difference. I'm seeing a lot of these heads, but I prefer the unmolested parts...



I'm told it lowers compression and peak HP. which at 130 down to say 120 most people may not notice....

I just wanted some feedback from others on this.

 

[Krispy]

Have you measured the combustion chamber volume? Obviously the SBT will have larger volume and therefore lower compression, but by how much would be interesting to know.

I suppose SBT re-cuts the area primarily for clean-up to salvage heads that have been damaged when pistons were melted, also I am sure that a lower compression engine has a better chance making it through the warranty period.

http://www.seadooforum.com/showthread.php?67928-combustion-chamber-measurement

Check the above link for combustion chamber measurement and specs.

It would be cool to see how SBT changes them.

[video=youtube;8QJKkCFFTEI]https://www.youtube.com/watch?v=8QJKkCFFTEI[/video]

 

[SabrToothSqrl]

I guess I could put both on an engine and test. I'm told lowering the compression does make them last longer... still such a shame to reduce the HP of an engine. Does SBT do this to all their engines?

 

[mikidymac]

As stated above the only way to make sure would be to measure the volume. A smaller volume would increase the compression because you are compressing the same cylinder volume into a smaller space. You can't tell just by looking at it because they could be milling the head to reduce the volume then cutting the outer area to get the squish clearance back into spec. The only way to tell is to check the volume. I am not sure if the entire thing with SBT reducing compression is fact or fiction but if you have compared their parts to others like OEM, WSM, or Hot Products their quality is not at the same level so it would not surprise me.

 

[Strizzo]

Nvm looks like you edited

 

[racerxxx]

If you look at a 97 WHITE 951 head it is cut just like your pic, stepped not flush to the squish band--a notable difference being the squish band is double cut right where it meets the dome(there is one on Ebay now-see below). It also was said that the 97 951 was squeezing more out of it than the 130 hp IIRC. A 787 head is cut the same way, stepped roughly 0.020". You could possibly bring some of it back in by running a thinner base gasket maybe, or cutting the deck of the cylinder. I'm sure SBT runs a thick base gasket too. The way they are cutting the head is actually making the combustion dome "deeper" from the deck of the cylinder thus slightly lowering the compression, not raising it. Like others have posted CC'ing the dome will tell you, also check the squish. If you can get the correct squish it's really a moot point if SBT cuts their heads or not. I'd bet that they cut them to save the detonated heads not necessarily to get them through warranty periods. There are plenty uncut OEM heads on Ebay.


Hard to make it out but you can see a little step in there but the double angle cut on the squish band is visible.
http://www.ebay.com/itm/Sea-Doo-951...pe-No-Dents-RX-GTX-GSX-947-carb-/140892049312

 

[SabrToothSqrl]

Interesting... I'm sure it's lower cost to mill a head than to replace it. I saw a new in box on eBay for $375!

So maybe it's not as big of a deal as I'm thinking? I just want to make sure my favorite ski (02XP) has all the HP it should... all OEM everything but the prop.

Damn my OCD...

So if SBT does this, I'm thinking they'd do it to all their engines, since you don't usually get your engine back...