What's the story behind "girdled" heads?

[Wiseguy92]

I am curious where the girdled heads came from? Were there a lot of failures with striped head bolts in cyls from extra compression and this is how they saw best to fix that?
I have a lot of experience with high compression ratio two stroke snomobile engines and there are no girdled heads at all in that form of racing.
I have seen pics of DASA engines and Thrust engines and they don't girdle their stuff. Is it because they are all billet construction and not cast cyls?
Any input would be great, tks


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[shaunsteezy]

the stock cylinders have weak spots where the water jacket is too thin it will crack under high compression. i think i saw some one on here post pics of their cylinder cracked because they thought it was "too cold" or some bs but w/o a girdled head your risking cracking it. if i had a pic i could circle the area

 

[paczowski123]

Insurance mainly from the problems he spoke of above. Especially when running an AM pipe like a B-pipe in which the weight of the mani/headpipe all sit on the cylinder casting..the increased vibration and loss of rigidity from removing the stock pipe/bracket can cause the cylinder casting to crack..I have seen many nasty pictures from water pissing out from around the cylinder, to heads blown clean off the top of the casting taking the top part of the casting with it...especially with higher compression on non girdled heads or milled stockers..many get away with it, to me it wasn't worth my money..plus the girdled heads look so much better

 

[JetManiac]

Above 2 posts cover it well. A/m billet cylinders are thicker and stronger so girdle kit is unnecessary. A/m cast cylinders like TPE are beefier so they don't need it either.

 

[IWannaYama]

Interesting.. I was always told with a 701 you don't need a girdle head unless your ported

 

[paczowski123]

Interesting.. I was always told with a 701 you don't need a girdle head unless your ported

I've read the same, many have different opinions. Some say it just a pipe, some say it's pipe and porting, and some will say pipe/bumped comp. yada yada..to me, it was worth the piece of mind of protecting my investment..I ran my stock 701 w/ a B-pipe 3/4 of last summer with no problem..but the winter when I went with a bored/ported/higher comp. setup I went girdled..wasn't gonna risk it..

 

[CARBONX2]

It is hp that breaks the cylinders, I have broken a ported cylinder with the ski out the water on the trailer. I was running 180psi on 97oct and a Riva Waveblaster stage 2 pipe

 

[crazy4sand]

Also, someone told me it helps distributes the weight on the exhaust side the pipes are so heavy it likes to crack at the manifold...

 

[paczowski123]

It is hp that breaks the cylinders, I have broken a ported cylinder with the ski out the water on the trailer. I was running 180psi on 97oct and a Riva Waveblaster stage 2 pipe

I would relate that to the vibration/stress..idk about horsepower, unless you were joking?

 

[crazy4sand]

Oh and I personally don't run them cause I don't want to deal with the battle or consistently replacing orings and from experience you need to re tourq them every so often, I stick with stock heads cause their more reliable in my opinion, I just mill them and add a second cooling fitting...

 

[Roseand]

Words from zack @ php. When the engine is running, the cylinder is actually pretty much trying to pull itself off of the cases. There is a ton of pressure on the cylinder from the get go, and the weak casting is at risk, especially when you add more horsepower. He basically told me that you can't just say that high compression increases the risk of cracking, rather any increase in power whether it be from a pipe, porting, etc. will put more stress on the casting. The girdled head sandwiches the cylinder so the pressure is taken off of that area..If that makes sense. I can't explain it as good as zack, but he summed it up like that to me. And yes, heavy pipes don't help either.

 

[ProSouth]

Oh and I personally don't run them cause I don't want to deal with the battle or consistently replacing orings and from experience you need to re tourq them every so often, I stick with stock heads cause their more reliable in my opinion, I just mill them and add a second cooling fitting...

i've run ada heads for the last couple years and i've re used o rings after pulling the heads. regreased and reinstalled. and i always torqued mine in a sequence like oem and havent ever had to retorque them, my engine now is at 220psi. not to say that it wont happen, but i've been issue free with ada heads

 

[JetManiac]

Oh and I personally don't run them cause I don't want to deal with the battle or consistently replacing orings and from experience you need to re tourq them every so often, I stick with stock heads cause their more reliable in my opinion, I just mill them and add a second cooling fitting...

If you are replacing orings, then there is a problem. I never replace orings unless head is off for some other reason. I can't ever remember blowing an oring, that happens when a sleeve has dropped or cylinder out of true, etc.

Stock heads are fine, but even milled you still dont make as much power. Stock head gasket is super thick so your squish is still way to big for optimal performance. Also dome/squish angles are different with a/m domes.

 

[paczowski123]

Words from zack @ php. When the engine is running, the cylinder is actually pretty much trying to pull itself off of the cases. There is a ton of pressure on the cylinder from the get go, and the weak casting is at risk, especially when you add more horsepower. He basically told me that you can't just say that high compression increases the risk of cracking, rather any increase in power whether it be from a pipe, porting, etc. will put more stress on the casting. The girdled head sandwiches the cylinder so the pressure is taken off of that area..If that makes sense. I can't explain it as good as zack, but he summed it up like that to me. And yes, heavy pipes don't help either.

Yeah that makes sense..the girdled head also helps protect the weak link of the head to cylinder mating. The threaded castings are very thin and being that bumping compression puts more stress on the threads and head, it can blow them off..the higher horsepower and vibes I could see being the culprit of the mid casting cracks..

 

[paczowski123]

If you are replacing orings, then there is a problem. I never replace orings unless head is off for some other reason. I can't ever remember blowing an oring, that happens when a sleeve has dropped or cylinder out of true, etc.

Stock heads are fine, but even milled you still dont make as much power. Stock head gasket is super thick so your squish is still way to big for optimal performance. Also dome/squish angles are different with a/m domes.

Plus like I said you get that billet bling with this mans sweet logo on it ordering from him

 

[CARBONX2]

I would relate that to the vibration/stress..idk about horsepower, unless you were joking?

No jokes, broke it on the trailer. I had built each part of the engine to match the next for power and flow. I had run it before with a leaking o-ring and it was a handful, once I fixed the o-ring and revved it on the trailer, it went BANGGGG

 

[JT_Freeride]

No jokes, broke it on the trailer. I had built each part of the engine to match the next for power and flow. I had run it before with a leaking o-ring and it was a handful, once I fixed the o-ring and revved it on the trailer, it went BANGGGG

Possible water or built up fuel in the engine.

 

[CARBONX2]

No, the leak was minor, just a slight roughness on the engine and plug foulling. With the leaking o-ring on circuit racing, I had to barely touch the throttle on corners otherwise it would spin out(This was in a WB1). 701's can be vicious if built correctly

 

[Wiseguy92]

Thank you all for the input. I get the theory's behind all the points made and I'm sure the extra billet and outboard mounting hardware improve the strength a bunch and take the stress away from the castings. Sled stuff has light weight tuned pipes that weigh very little so the weight isn't a consideration. Being a racer I know the value of every ounce of weight you can remove from your toy to get all the power to the ground/water. I was considering eliminating the 8 bolts and trimming the billet dome covers back on my 927 WDK. I weighed all the hardware tonight and with the billet included it would only save just over 2lbs so it's not worth it to me. Tks again for the opinions guys....


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