[Wilka_SS]

Hi guys, I have a tsp custom cam which is a 227/239 635/635 on a 115 with tsp cnc heads which they standard mill 10 thou. I am currently running oem lt1 head gaskets and after looking at the flycutting required cams im afraid going to the 0.028 headgaskets would be too thin and id run into piston to valve issues, but was curious about the 0.040 ones (0.055 stock) is there a thread someone can post for me as to the headgasket to compression ratio relationship on the lt1?

[17camaroSS]

Originally Posted by Wilka_SS

Hi guys, I have a tsp custom cam which is a 227/239 635/635 on a 115 with tsp cnc heads which they standard mill 10 thou. I am currently running oem lt1 head gaskets and after looking at the flycutting required cams im afraid going to the 0.028 headgaskets would be too thin and id run into piston to valve issues, but was curious about the 0.040 ones (0.055 stock) is there a thread someone can post for me as to the headgasket to compression ratio relationship on the lt1?

I just got done with my shortblock, I flycut for my cam and will be running a .028 gasket with plenty of clearance. The compression will depend a lot on how much you’re flycutting also.

[Wilka_SS]

That's why I'm trying to understand the relationship, I'm not trying to make the motor a 13:1 motor where its unhappy on pump gas

[cmitchell17]

Originally Posted by Wilka_SS

That's why I'm trying to understand the relationship, I'm not trying to make the motor a 13:1 motor where its unhappy on pump gas

I am curious as well, I told TSP I wanted as much taken off as they could give me considering PTV, I have a similar size TSP cam 228/236-.635/.635-114. They told me they took off .030 but I didn't see it marked or engraved on the heads anywhere so just took their word for it (which honestly doesn't seem that good of a word with TSP)

I calculate now I have 12.25:1 compression, I want as much as I can get because I run 100% E85, if I had my choice I would be at 14:1, but I don't see anyway to get to that much compression even with an aftermarket rotating parts. I also don't like the idea of messing up the factory piston shape given that supposedly 5 million hours or something like that of CFD time was spent by GM on getting the piston top shape for correct mixture motion, although I suspect a lot of it was optimizing for emissions considerations so there is probably some room to reoptimize it for airflow capacity and detonation resistance maybe.

So by my calculations the .028 with .010 milling would be 12.65
with the .040 ones it would be 12.21
and with a stock .052 it would be 11.80

I am using the SBC spec that is about 1cc per .0055 inches milled. I have no idea how much the piston and valve relief volumes are but I back calculated and iterated until I got to the stock compression ratio of 11.5, which for some weird reason ends up being 0 cc for piston dome volume and 1.17 cc for valve relief volume so I'm not sure what's going on there. I am also assuming the pistons are .008 below deck.

[Wilka_SS]

Originally Posted by cmitchell17

I am curious as well, I told TSP I wanted as much taken off as they could give me considering PTV, I have a similar size TSP cam 228/236-.635/.635-114. They told me they took off .030 but I didn't see it marked or engraved on the heads anywhere so just took their word for it (which honestly doesn't seem that good of a word with TSP)

I calculate now I have 12.25:1 compression, I want as much as I can get because I run 100% E85, if I had my choice I would be at 14:1, but I don't see anyway to get to that much compression even with an aftermarket rotating parts. I also don't like the idea of messing up the factory piston shape given that supposedly 5 million hours or something like that of CFD time was spent by GM on getting the piston top shape for correct mixture motion, although I suspect a lot of it was optimizing for emissions considerations so there is probably some room to reoptimize it for airflow capacity and detonation resistance maybe.

So by my calculations the .028 with .010 milling would be 12.65
with the .040 ones it would be 12.21
and with a stock .052 it would be 11.80

I am using the SBC spec that is about 1cc per .0055 inches milled. I have no idea how much the piston and valve relief volumes are but I back calculated and iterated until I got to the stock compression ratio of 11.5, which for some weird reason ends up being 0 cc for piston dome volume and 1.17 cc for valve relief volume so I'm not sure what's going on there. I am also assuming the pistons are .008 below deck.

I'm glad I'm not the only one looking into this, with all these big na cars chasing records and shops putting out cars idk why more information on this isnt published. My next question is will I have adequate piston to valve or will I have to flycut? I prefer to not go down that road also as this is a procharger oriented cam I'm just having fun in the meantime to see what I can get out the car for now. I've raced a couple hefty na set ups and my car does very well considering cam and converter size.

[17camaroSS]

Originally Posted by cmitchell17

I am curious as well, I told TSP I wanted as much taken off as they could give me considering PTV, I have a similar size TSP cam 228/236-.635/.635-114. They told me they took off .030 but I didn't see it marked or engraved on the heads anywhere so just took their word for it (which honestly doesn't seem that good of a word with TSP)

I calculate now I have 12.25:1 compression, I want as much as I can get because I run 100% E85, if I had my choice I would be at 14:1, but I don't see anyway to get to that much compression even with an aftermarket rotating parts. I also don't like the idea of messing up the factory piston shape given that supposedly 5 million hours or something like that of CFD time was spent by GM on getting the piston top shape for correct mixture motion, although I suspect a lot of it was optimizing for emissions considerations so there is probably some room to reoptimize it for airflow capacity and detonation resistance maybe.

So by my calculations the .028 with .010 milling would be 12.65
with the .040 ones it would be 12.21
and with a stock .052 it would be 11.80

I am using the SBC spec that is about 1cc per .0055 inches milled. I have no idea how much the piston and valve relief volumes are but I back calculated and iterated until I got to the stock compression ratio of 11.5, which for some weird reason ends up being 0 cc for piston dome volume and 1.17 cc for valve relief volume so I'm not sure what's going on there. I am also assuming the pistons are .008 below deck.

You can most definitely see just under 14:1 with a factory bottom end, even with the factory heads. You just need to be willing to flycut the pistons enough to allow it.

[17camaroSS]

Originally Posted by Wilka_SS

That's why I'm trying to understand the relationship, I'm not trying to make the motor a 13:1 motor where its unhappy on pump gas

If I was in your situation, I personally would go with the .040 gasket. Gives the little bump in compression and allows for a better quench. You’ll be in the “safe zone” with that for the 93 octane you’re wanting to run.

[cmitchell17]

Originally Posted by 17camaroSS

You can most definitely see just under 14:1 with a factory bottom end, even with the factory heads. You just need to be willing to flycut the pistons enough to allow it.

Do you know how much the pistons are above the deck? So 14:1 is possible with all stock parts just milling the heads and cutting the pistons for bigger valve relief?

Do you think you could do it on untouched pistons if you went with a smaller lift and duration cam?

[17camaroSS]

Originally Posted by cmitchell17

Do you know how much the pistons are above the deck? So 14:1 is possible with all stock parts just milling the heads and cutting the pistons for bigger valve relief?

Do you think you could do it on untouched pistons if you went with a smaller lift and duration cam?

.006 above deck. With milling, flycutting, and a thinner headgasket it is definitely doable. Doing it without any flycuts would either run you into the valve tagging the piston or having very little PTV clearance.

[KingLT1]

Originally Posted by cmitchell17

Do you know how much the pistons are above the deck? So 14:1 is possible with all stock parts just milling the heads and cutting the pistons for bigger valve relief?

Do you think you could do it on untouched pistons if you went with a smaller lift and duration cam?

14.1 with a small cam would likely have really high dynamic compression and require full E85 or maybe even higher(e98) to keep detonation at bay.

[cmitchell17]

Originally Posted by KingLT1

14.1 with a small cam would likely have really high dynamic compression and require full E85 or maybe even higher(e98) to keep detonation at bay.

My goal is to build a 100% E85 only motor, I know a lot of people don't like that idea and either say well what if its not available? or why don't you just put a turbo on it?

I just want to see if I can optimize it just for running on E85 and maybe try to gain back a little efficiency lost. I tried to do this on a LQ9 as well and I got some 706 4.8/5.3 heads to mill and put on it but then I calculated I would only be at around 11 something. So even for LS stuff it seems there is no budget way to accomplish this either. I can't find anyone else around who has done something like this and if there is there is not any documentation on it or it usually turns into a turbo build.

[Wilka_SS]

Originally Posted by 17camaroSS

If I was in your situation, I personally would go with the .040 gasket. Gives the little bump in compression and allows for a better quench. You’ll be in the “safe zone” with that for the 93 octane you’re wanting to run.

If I were to do that would I have to flycut my piston or would just have to clay it and see. I think minimum tolerance is .080

[cmitchell17]

Originally Posted by Wilka_SS

If I were to do that would I have to flycut my piston or would just have to clay it and see. I think minimum tolerance is .080

If I could redo my build I would have bought a fly cutting tool and tried to get TSP to mill more (I am assuming they milled to what they thought was a safe limit) and get a .028 head gasket like above. I am assuming the .028 head gasket will still work with our stock rods and piston assembly and not be to close.

What did you ever end up doing?