Hi Compression Question!

[FlyinRed]

I have an 11:1 425 now, Im forced to redo the bore and replace the piston (bad bore job) and want to go 13:1 at the same size (for cost reasons). The shop Im useing says he asked arround and says "I talked to a couple of people and they said that the 13:1 is too much, It blows head gaskets and pulls studs. " Have you guys heard of this and/or had this problem with running this kind of compression? Any other "side affects" come with running this setup, besides race/av gas? this is a hi hours 99 motor.

Thanks Guys

[YZROOSTINYA]

i would say that with 13 to one you would need larger studs to hold the head down better along with a very good gaske. plus a 13:1 piston is going to put alot of stress on the crank.

and you would need to run full race fuel

[VegasEx'r]

Sparks makes a stud kit that has 10mm studs instead f 8mm (or 12 in place of 10. I could be wrong on the sizes, but it is Sparks). I think that going to the larger stud size should protect the gasket, so you'd just need to buy another gasket.

[ChadEXer]

Yeah you can get larger head studs from Sparks or TC for about $80! Sparks runs a 15:1 in his 465 but he runs it on alcohol too which you can run a higher compression on alky safer than on gas! I have a 10.5:1 in my 505 stroker and i blew a head gasket!! Heck we think its possible that i even broke one of the larger TC head studs!!

[oregonrider89]

talk to an engine builder, sparks, powroll, duncan. they could tell you

oregonrider89

[CAIN730]

13:1 at 425 is really high for a high hours motor. There is no way you will pull that off on av gas. Your source sounds like he knows what he is talking about.

[methyman]

That 13.1 piston will also eat batteries and starters up and possibly break the stock connecting rod.

[Sick0]

I've also heard your connecting rod won't be able to handle all that compression. Plus I would think it would create alot more heat also. I think you would have a harder time cooling down the engine.

[Mity Mo]

I have this motor work in my engine. I have raced it for two years without a problem. I use the stock rod as well. The heat is a problem. I am trying to hook up a oil cooler now. It does affect batteries when its cooler. But as long as the weather is warm its no problem. And I have been running stock Honda gaskets and studs. Mo

[josh]

my friend at school that has a really modded 250r says he has heard of the 13's blowin stuff alot in the mostly stock 400 motors, and this dude in my weight training class says if you are goin to jump to a compression difference like that put a metal gasket on it coated with cylicone, other than that i haven't heard anything, good luck, i wouldn't go higher than a 12 to 1 cuz of reliability and stuff, good luck tho

[Sick0]

How much of a power increase is the 13to 1 piston over like a 11to1 piston.

[ChadEXer]

From a 13:1 to a 11:1 would probably lose about 3 hp roughly. Tom at TC says anything over 12.5:1 is asking for trouble, especially in a big bore motor!! Thats why we went to a 10.5:1 in mine.. We will be going up to a 12.5:1 now though becasue im converting to alcohol! You can run a higher compression safely on alcohol,,,alcohol is harder to get jetted correctly but in my opinion I dont see why everyone dont run alcohol! Sparks says it adds roughly 10 hp and cools the engine down tremendously compared to race gas!! Thats exaclty what I need, more hp and a cooler engine!!

[oynot400]

I am going to 13:1 on my stroker. I asked the same questions. Mike recommends a stainless steel head gasket, the stock one will not hold up on his motors. Heat is a problem that is why I am getting a larger oil tank, for now may be a cooler later. With a stroker anyway, it needs a stronger rod. I asked him about the head bolts, They are not a bad idea but the problems that he is seeing is people are over torqueing the studs and are pulling the treads out of the cylinder. If the installation is done right the stock head bolts will work just fine. ;)

[Mity Mo]

Everyoner doesnt run alcohol because of AMA rules. You cant use it in sactioned racing. Mo;)

[ChadEXer]

Originally posted by Mity Mo
Everyoner doesnt run alcohol because of AMA rules. You cant use it in sactioned racing. Mo;)
That explains it!!! The only rules in drag racing is to get to the finish line first!!

[Mity Mo]

That would definitely help out though. Of course I think I have smelled it a few times on the line at the NAtionals. Mo

[ChadEXer]

Originally posted by Mity Mo
That would definitely help out though. Of course I think I have smelled it a few times on the line at the NAtionals. Mo
I wouldnt doubt it!! With the power and cooling of alcohol i just have to do it, especailly with a motor the size of mine> I thought Tom at TC put a 10.5:1 compression piston in my bike but I just found out on the phone with him that he went ahead and put a 12.5:1 in it,,,so now all I have to do is come up with the money for a 41mm FCR setup for alky!!!

[oynot400]

What do they do different to the carb to run alcohol? :confused:

[ChadEXer]

An alky carb has much larger jets in it! A motor drinks alky twice as fast as it does gas!! So it has to flow alky much faster!! Alky is around $2.00 a gallon and the race gas I have to run is almost $7 a gallon, so even drinking alky twice as fast will still cost less on fuel!! Cant wait to see the difference a 41mm FCR on alky will make to the 505!! Wy wife says I cant get it until Christmas,,,its going to be my Christmas present,,one of them anyway:D