13:1 or 12:1 Compression for 440?

[NacsMXer]

I can't decide which compression I should go with on my GT Thunder 440 motor. I AM running a Carrilo Heavy duty rod so I wont have to worry about compression problems with that. Would 13:1 be too high maintenance in any way? Would it cause the bike to stall out easier than a 12:1 motor? I am going to be running 110 leaded purple race fuel so I would basically like to know if there are any disadvantages of going to 13:1 as opposed to 12:1. Thanks so much.

[sickmojave]

this may be a dumbass question BUT. will the starter crank over that much compression?

[K_Fulk]

Since you dont have a problem running race fuel and have a heavy duty rod. Why wuss out on the compression?

I'm going to run a 13:1 piston in my stroker.And I am getting my pison ceramic coated on top with a dry film lubricant on the skirts, A fst style oil cooler, and may even get my cylinder nickasiled to help get rid of the heat even more.

And if it lacks the cranking power pappy can hook you up with a battery with a lot more cranking power.

Maybe chef will see this and add some insight I think he is running a 14:1 piston.

[MIKE400EX]

K-Fulk,
A TBC coating on the piston top and a nikasil coated bore will keep more heat in the combustion chamber and may necessitate a higher octane fuel. Also the higher the combustion temp., the higher the head temperature. You may want to look into getting the exhaust ports TBC'd also. <<< That will help you as much or more than the additional oil cooling up top. You can also TBC the cylinder head, but it tends to chip off of the valves (too much pounding). Sounds like a good methanol setup!

[K_Fulk]

That was my deciding factor on the nickasil I was wondering if the two would work together. Is the nickasil worth the money?

I was thinking about tbc in the compression chamber but figured the carbon would end up ruining it anyway. Do you think it would make that much of a diffrence doing the exhaust ports? Would it get the exhaust out faster or keep the heat contained in the exhaust ports?

I was planning on running strait cam2 figured that would be plenty for 13:1. If not I have acces to vp race fuels too.

[MIKE400EX]

The nikasil coating will reduce ring friction a little. Employing it as a TBC on a steel or iron cylinders will help but certainly the effect would be hard to measure. Guessing that it would probably be at least $100 to nikasil coat & then finish the cylinder, unless you're running on the ragged edge, it wouldn't seem worth it. Note to self: you've wasted much more on much less.
The carbon problem is real. Ceramic TBC's that have any effect are usually porous (and about .005-.015" thick). Carbon loves to impregnate and bulidup on the ceramic which as you know will lead to hot spots, again here alky would be a better fuel because it burns cleaner. The thin TBC's do very little, especially on engines that are run for more than a few seconds at a time.
TBC'ing the exhaust ports will effectively insulate them, keeping a lot of the spent gas heat from soaking into the head and heating it up. As an added benefit it will help keep the exh. velocity up so you could also gain some more scavenging effect. Might help the lifespan of that front head stud too. OK... you're bored now and know some of what I do for a living..:tired:

[NacsMXer]

Thanks but I still need to know if the 13:1 compression would make the quad stall out easier. I have heard this and I dont know if this is true.

[xc400ex]

I have an 11:1 comp 426 and I ride with a guy that has a 13:1 comp 426 and neither one stalls out hardly. His is not any worse than mine I dont think it should matter.

[NacsMXer]

Cool thanks for confirming my thoughts. I heard this from somebody on a thread a little while ago and it got me thinkin about stalling. Im definitely going with the 13:1 then. Probably will need the HD stud kit too.

[jb500ex]

i had the 13:1 it does not stall out easy and the battery does start it no problem. i also did not havea problem with the stock studs, the key is too put assembly lube on them. i would highly recommend you get the haed gasket that mickey dunlap uses it's three piece steel and holds well, the cometics will rip apart

[Dave400ex]

I would get HD Studs just to be safe!

Good coating info on this site: http://www.hpcoatings.com/engine_coatings.htm

[cals400ex]

Originally posted by jb500ex
i had the 13:1 it does not stall out easy and the battery does start it no problem. i also did not havea problem with the stock studs, the key is too put assembly lube on them. i would highly recommend you get the haed gasket that mickey dunlap uses it's three piece steel and holds well, the cometics will rip apart


mickey does recommend the cosmetic head gasket. he said the best out there is the cosmetic flexsteel. and yes, it is 3 layers just like the honda one but it is a little thinner. i have that in my bike right now, but i am not running the compression of 13:1.

[NacsMXer]

Well this time around Lazarus at GT Thunder will be assembling and doing the work on my motor. He should know what is best as far as the HD studs go. I have a brand new OEM cylinder waiting to be resleeved and bored so I think the stock studs will hold up ok.

[BIGRED400]

I put this on my 11:1 416 http://swaintech.com/4whl.html and I am really happy with it, I have the PC9 on the piston skirts and on the top TBC.all for $40...............Does it hold up ??? We'll see in the long run ....check this out too http://swaintech.com/fastbike.html I'm happy with mine.:D

[jb500ex]

i didn't realize cometic makes that one. it's not their normal head gasket. sorry

[cals400ex]

no problem. yes, cosmetic does make a few. if you stay with the metal flexsteel ones you should be just fine.