12.5 : 1 compression

[Blake24]

when i get my motor built by TC racing i wanted a high comp piston around 12.5 : 1 ..........what are the reliability issues with this compression........i know i will have to run race gas which doesn't bother me because it doesn't seem like i go through that much fuel......thx GUYS!!

[VegasEx'r]

Ask Tom when you talk to him. As far as reliability, you'd run a risk of damaging a stock bottom end with a high CR, but I don't know how high you can safely go without doing some work on the bottom end.

[Dave400ex]

I would ask Tom. I`m not sure what he runs. If you want that high of Compression for the extra Bottom End you may have to get a New Rod and some other Bottom End Parts. Which TC would be more then Happy to Sell you.

[ChadEXer]

Tom runs a 12.5:1 piston in almost all his big bore motors. he assures me i wont have any problems out of mine! I think he is strengthening the bottom end but not sure!

[yellowrider]

hey chad i feel sorry for you man that must suck that you don't have your machine back already.. well when yuo do get it back you know you are going to be a winner in the open 400 class lol




i would get the 12 5 1 if i were you that would be sweet i even heard of a 13 3 1 i think i am not sure but i know that you can get the compression way up there

[ChadEXer]

Yeah it really sucks waiting this long! Warriorman warned me so i guess I kind of expected it! He told me 6 weeks and its already been 12. Somebody else called him to buy a pipe and he said he is getting ready to go to the nationals again. Dont look like it will be anytime soon:( He said he is a one man operation and doesnt trust anybody else to do the work! i guess maybe thats a good thing! Prime riding season will be over when i get it back!!

[yellowrider]

call him he should know that you are on exriders and if he wants a better name he better be able to get your motor back in time or at least not 6 weeks late i can understand 6 days but weeks that is a long time keep calling him


cause everyone is gong to ask you how the motor is and if it was built good and if it junk no one will buy it so it will keep him out of business but if its really good .... he will have lots of money coming in

[Tommy 17]

hey chad he only lives about 1 hour north of me... me and a couple friends will go up and steal ur motor back haha;) :D j.k...

it will def be worth the wait when u get it back... that things goin to fly!!!!!

[ChadEXer]

Im pretty sure it will be worth the wait!,,, it better be anyway!!!
hey 400EX21,,,dont you want to go up there and spy on him for me:D

[Dave400ex]

Yellowrider, Tom won`t get a Bad Name just by being so far behind. He already has a GREAT Name. Trust me, we have waited for a Motor from TC, and my Brother said he was happy he waited. Chad you will be happy.

[JustRace]

I was either told or a read somewhere that if you go above 11:1 comp you obviously have to run racing fuel and above that ratio you run the risk of taking out the stock rod.

[ChadEXer]

Tom replaces the stock rod in his big bores, he makes his own rods which he says are better than the Corrilo rods because you have to grind the Corrilo rods(not sure why but has something to do with clearing the crank when stroking it or something like that) Plus if you dont want to go with that high of compression then he wont, but i want to run race gas in mine!! i got some $1000 drag races to win:D

I wouldn't run a 12.5:1 with a stock rod,,,yeah it might hold up but if she breaks,,,,:eek: get out the fat wallet..

Not sure if this matters, but there has been a few articles, both on the net and in trade mags, about claimed compression ratios of pistons only being CLOSE to the claim with NO gaskets (upper or lower). The tested 11:1's were all running 10.0 to 10.3 with stock gaskets. Some articles said to use Sili-Seal on the bottom and .020" head gasket to get them within 10:7 or so. Most of the tests were done by liquid CC'ing the assembled motors, as apposed to cold cylinder pressure. Most info came from site searches ("compression"), but the original article that got me looking was in a trade mag (can't find which one right now but it was this month in one of the "big four"). It started with someone asking about changing gaskets on a new 400 to raise compression (and it worked well, for cheap, I guess)...T

[Scott]

You're right on it ynot. There was a long thread on here going through the same thing. Gabe and several others went on for several pages explaining things and talking about how to get the actual CR you want. With stock gaskets on the base, stock rod, and either the stock piston or the wB pistons (either one) the piston is still .042" down in the cylinder when it comes up to TDC. By thinning the base gasket (the bottom end is vented to atmosphere, so there's no pressure) you effectively move the piston TDC closer to the top of the cylinder, which increases your CR.

The other options would be legthening the rod, lower wrist pin location in the piston, or decking the jug. The gasket is the cheapest, easiest, and is reversible if you're not happy with the change for some reason.

All the pistons seem to be advertised based on what the CR would be if the piston was pretty close to zero at TDC.