hi guys, i'm new to hotrodding 6.5's and some of my calculations & specs may be off.. (hopefully not!) but i am not new to blown gas engines or large diesels so using my experiance from both,

here is my theory... the 6.5 has some inherent weakness' with head bolt spacing being one... knowing this, and all other things being equal; deck surface ect... If i use the .010 thcker fel-pro's on my undecked block it should lower my compression about 3/4's of a point, and cylinder pressure will be lower also... Is it worth it??? I dont know... But here goes, ok the .010 thicker fel-pro's are "not intended for racing applications" and ARE intended for decked blocks... They are the same compressed thickness on either block decked or not... With 12 psi boost on a stock compression 6.5 (21.6:1) gives you approx final compression of, 39.2:1. With the lower compression on the .010 head gasket engine of approx. 20.9:1 with the same 12 psi should give you a final compression of approx 37.9:1 Which is almost equal to running 11 psi with the stock compression 21.6:1 so in conclusion is anyone running 12+ psi on a decked block with the .010 fel-pro's??? if so this should be a budget friendly way to lower compression/cylinder pressure on these motors providing correct intake alignment ect.. It should give a little more reliability on a mild build... once again this is from my experience with blown gas engines so dont bite my head off please... i'm currently running a street/strip 8-71 blown big block combo in a 57 chevy doorslammer with 910hp/727tq @13psi and grew up around a nastalgia blown gas 55 chevy so i'm somewhat familiar with boost fed engines but by no means an expert... Thanks for reading and for any thoughts on the subject... Jimmy

Interesting post, have you considered the "net-lash" non-adjustable valvetrain and the extra .010? I know longer pushrods would take care of that, the rocker end must be hardned for those to last more than a few weeks. If your using more boost with less compression, wouldn't your cylinder pressure be the same at boost? Just a couple of thoughts.
Don

I dont think you'll have a valve train problem, that .010 would be roughly 1/4 turn on your old chevy gasser's rocker arm.

I have the .010 thicker gaskets with studs on my 93 and the valve train seams ok(no noise), just wish I had the rest of the truck put back together so I can drive it.

The hot ticket with these 6.5's is a 18:1 engine. With that kind of ratio, there are some here running holset turbos pushing over 20 psi with no reported problems. From my limited knowledge and experience, I would think that any attempt to reduce the factory CR would be a good thing. If you really want to go nuts do a search under 'intercoolers'. You can peice one for under $500 and pick up some reliability and performance. Actually you don't 'pick up', its more like releasing or reclaiming. Do a search under 'feeding the beast'. That should help some too. Welcome to the place.

daustin,
didnt think about it... may actually mess up valvetrain geometry more than preload, there should be more than enough lifter preload built in to make up the .010 with the hydrualic lifters and non-adjustable valvetrain...
i think i already stated in the last post. yes the final compression will be the same if you add the correct amount of boost... since your forcing more air/fuel into the cylinder to make up the lost compression. power potential is greater, thats why they make 18:1 conversions, to keep cylinder pressure manageable and raise power potential no??? what is there to think about???

sshewins,
that makes sense with 18:1 and 20psi boost your final compression would be around 42.5 final comp... question is anyone doing it with a decked block and fat head gaskets??? as that would be the equavalent to 15 psi on the stock deck hight/pistons and with the fat gaskets 42.2 final comp... but i'm not at the point to do a total rebuild and convert to 18:1 and am happy with the stock performance in the future deff getting an air-charge-cooler though... big difference on egt's

I don't know the formula "for every * you drop you get this amount of HP" stuff, but a cooler definately drops IAT's, which in turn drops EGT's which makes parts last longer. Most that I've read from also report an increase in MPG, which is always a good thing. I've also read that when you reduce the flame temp your gaskets live longer.

Hope this helps,

i've been looking at piecing an air-charge-cooler since i got it the truck :) air-charge-cooler seems to = win-win :) besides a little more turbo lag, but for me its not a big issue because i'm mostly looking for towing performance/reliablility pulling grades loaded around here so its deffinatly on the list of upgrades down the road...

hi guys, i'm new to hotrodding 6.5's and some of my calculations & specs may be off.. (hopefully not!) but i am not new to blown gas engines or large diesels so using my experiance from both,

If i use the .010 thcker fel-pro's on my undecked block it should lower my compression about 3/4's of a point, and cylinder pressure will be lower also... Is it worth it??? I dont know... But here goes, ok the .010 thicker fel-pro's are "not intended for racing applications" and ARE intended for decked blocks... They are the same compressed thickness on either block decked or not...

so then all your calculations are moot??,. static and dynamic pressures are calculated differently,.i,m definitely not the physics genius around here,. but pressure and volume ..blah blah blah??,. two different sized spaces but with the same pressure in each, yada yada yada??,..
nick

so then all your calculations are moot??,. static and dynamic pressures are calculated differently,.i,m definitely not the physics genius around here,. but pressure and volume ..blah blah blah??,. two different sized spaces but with the same pressure in each, yada yada yada??,..
nick
phantom, first off i was not calculating dynamic compression... dynamic compression is a more involved calculation involving cam timing, injection timing ect... i was calculating static compression and final compression under boost... and im not saying cylinder pressures will be spot on match adding more boost to a lower compression engine but it will get you in the ball park of a safe cylinder pressure... because i've read several threads saying that the thicker head gasket is weaker... i was trying to point out it seems to be an effective way of lowering compression under modest boost... yadda...yadda... yadda... and if you cant follow along, its best to not join the conversation at all... unless you have some figures to back up your yadda..yadda...yadda???

seeing as you didn't get my point first time, i'll re-iterate it,. if the gaskets both compress to the same thickness,. then what are you trying to calculate that is different?? i,m sorry if you took yada yada yada to mean anything offensive, i didn't mean it be so,. it just struck me as a thread about nothing if the gaskets both compress to be the same thickness,.
hence the seifeld type reference,.
Good luck with your trailblazing efforts on lowering the compression and gaining lower egt's using only different gaskets,.,. if i were to be exploring this type of mod,. i,d definitely get cometic to make a set of gaskets to my specs, then use studs,.i,ve thought about turning .050 off the pistons,. and then have them ceramic coated,.what do you think ?
Nick
YRMV.

Phantom, I believe you missed or misunderstood Jimmy's point....The .010 gasket is the same compressed thickness on a DECKED block, as is a .010 gasket on a NON-decked block. It is not the same compressed thickness as a standard head gasket....Thus compression ratio will change, although ever so slightly.....which is the basis of his reason....

Phantom, I believe you missed or misunderstood Jimmy's point....The .010 gasket is the same compressed thickness on a DECKED block, as is a .010 gasket on a NON-decked block. It is not the same compressed thickness as a standard head gasket....Thus compression ratio will change, although ever so slightly.....which is the basis of his reason....
thank you 9c1cap, and sorry i took it the wrong way phantom... sometimes i have a hard time putting things in the simplest way possible on here, and still getting my point accross... :o:

Phantom, I believe you missed or misunderstood Jimmy's point....The .010 gasket is the same compressed thickness on a DECKED block, as is a .010 gasket on a NON-decked block. It is not the same compressed thickness as a standard head gasket....Thus compression ratio will change, although ever so slightly.....which is the basis of his reason....

Hmmm,. i read things too literally i suppose,. and compressed height of the GASKET is now not the same i understand here? so in essence then that means the compressed height of a +.010 gasket is indeed .010 taller?,. not the same 'compressed' height as a stock one,(as was stated)
maybe a better explanation might include the phrase "DECK height" and, and a proper explanation of the deck height lowered by .010, a thicker gasket added, will keep the cylinder head located the exact same distance from the crank centre line as before,.
I just comment on what i read,..i was under the impression (from the original post) that the .010 thicker gasket would compress to the same height as a stocker,. but would conform to irregularities between the deck and head, better than a stock gasket,.i.e a cylinder head or deck with a .0005-.0025 warp,.sorry my mistake ,. i guess?
Nuff said.
nick

no prob phantom... sorry i took it the wrong way, i've posted on other forums and i'm used to guys replying just to "stir the pot" so sorry i jumped the gun... sometimes its hard to get what's in my head into the post... sorry if i confused anyone but i was trying to be thorough in my explaination. i had read a few posts saying the thicker gasket was weaker without stating why??? and it probably is, in a high output application... but but for a mild application like mine i think its actually better... for the reasons i stated above... again sorry for any confusion / attitude... Jimmy