Purple People Eater Sh*t itself today

Let me clarify the numbers a touch:

Option 1: Deck the block .010" and do nothing to the stock pistons compression will go from 17.5:1 up to 18.1:1 but you will also lose .010" of piston to head clearance which is fine, but will make most aftermarket cams no longer drop-in.

Option 2: Deck the block .020" and deck the stock pistons .010" and compression will go from 17.5:1 up to 18.3:1 but you will still lose .010" of piston to head clearance which means few if any aftermarket drop-in cams will fit if you ever decide to upgrade and there's a slight chance of pistons hitting the head if you ever turn up the wick and run super high EGT/high RPM on a race setup.

Option 3: Deck the block .040", deck the pistons .040", maintain factory piston to head clearance so future drop-in cams will still fit, and compression will increase from 17.5:1 up to 18.3:1. The downside is the fire deck is now a little thinner and weaker than stock so this might not be a good option for a big 1000+HP build.

I would choose option 1 since it's the best bang for the buck and if you ever want to run a bigger cam, install a thicker headgasket.


***Displacement of the motor is the swept volume, piston decking, block decking, etc. have no impact on displacment. Crank throw and bore size changes are the only ways to increase displacement***
 
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What is stock protrusion supposed to be. I said take .010 before because I figured stock protrusion was already near max/hitting the head/valves. But if I can run a little more protrusion on untouched pistons, I would love too.
 
Big Blue24 said:
Let me clarify the numbers a touch:

Option 1: Deck the block .010" and do nothing to the stock pistons compression will go from 17.5:1 up to 18.1:1 but you will also lose .010" of piston to head clearance which is fine, but will make most aftermarket cams no longer drop-in.

***Displacement of the motor is the swept volume, piston decking, block decking, etc. have no impact on displacment. Crank throw and bore size changes are the only ways to increase displacement***
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I'm no expert, but I like this idea. The last part is true too.
 
Big Blue24 said:
Let me clarify the numbers a touch:

Option 1: Deck the block .010" and do nothing to the stock pistons compression will go from 17.5:1 up to 18.1:1.

Option 2: Deck the block .020" and deck the stock pistons .010" and compression will go from 17.5:1 up to 18.3:1 but you will also lose .010" of piston to head clearance which means few if any aftermarket drop-in cams will fit if you ever decide to upgrade and there's a slight chance of pistons hitting the head if you even turn up the wick and run super high EGT/high RPM on a race setup.

Option 3: Deck the block .040", deck the pistons .040", maintain factory piston to head clearance so future drop-in cams will still fit, and compression will increase from 17.5:1 up to 18.3:1.

I would choose option 1 since it's the best bang for the buck and if you ever want to run a bigger cam, install a thicker headgasket.
Click to expand...

Option 1: Sounds the best to me. That jump from 18:1 to 18:3 probably wouldn't be enough to worry about the extra cost. So long as stock non-ic pistons are the same as stock ppump and vp pistons. Not sure exactly what this block was, but it is a storm block so that narrows it down a bit.

Option 2: This truck will stay stock cam for the rest of its life, no chance in turning it up. If this engine ever does come out and go in something else, then I will throw in a thicker gasket, and shave the pistons that little extra.

Option 3: Clearly the best, but that extra .2:1 doesn't sound worth the cost of machining the pistons.

Thanks Will.
 
Thanks again to everyone. I'm not so good with this math stuff. I know more compression makes better boom boom, but thats my limit.
 
madmikeismad said:
Option 1: Sounds the best to me. That jump from 18:1 to 18:3 probably wouldn't be enough to worry about the extra cost. So long as stock non-ic pistons are the same as stock ppump and vp pistons. Not sure exactly what this block was, but it is a storm block so that narrows it down a bit.

Option 2: This truck will stay stock cam for the rest of its life, no chance in turning it up. If this engine ever does come out and go in something else, then I will throw in a thicker gasket, and shave the pistons that little extra.

Option 3: Clearly the best, but that extra .2:1 doesn't sound worth the cost of machining the pistons.

Thanks Will.
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[ame="http://s358.photobucket.com/user/westonmerril/library/Piston%20Info?sort=6&page=1"]Piston Info Photos by westonmerril | Photobucket[/ame]
Book mark that album, it comes in handy. You'll see that there are 3 different P-pump pistons, and two different VP pistons. The wider the bowl, the more cutting X amount off of it will increase compression.
 
Hm, just need to reference these piston part numbers to the motors and setups they come from.. IC or non IC, and what power level of ppump.
curious about how the factory has these set up, since when I upgraded to a 215 I swear the trucks run worse off the low end.
 
3802132 is the part number on the invoice, but they're .020 so I don't know if you can still look them up the same?

I know they are non-ic for sure, but thats it. I know I'll probably have to swap injectors for 155*, but I don't care as I'm dropping timing back down to 18*. Anyone know at what timing you start to spray out of the bowl with those? I know I'll be a little safer because of the decked block. Which reminds me, will decking the block effect timing at all?

I'm really hoping with the bumped compression, lower timing, (hopefully) even faster spooling twins and stock cam that I can make a torque monster with this truck. I heard zach will be or already did release a new towing cam, so I may look into that in the future too. But I'm afraid if I do that, I'd have to run the thicker head gasket, lose the compression, and it would just all balance out.

Out of curiousity, how would one bump compression to something like 20:1? Just shave the pistons a lot more?

I've highlighted my questions this time because I scattered them around pretty good.
 
Use a 6.7 crank. That's what I'm doing. 6.7 crank, non-coated marines cut about .080, gonna run the piston to head clearance a bit tighter, my calculations look to be around 21:1 CR. But by the time I get it built, its gonna be at least summer now. Ryan at Hamilton recommended the 188/208 cam for my setup.
 
Tate said:
Use a 6.7 crank. That's what I'm doing. 6.7 crank, non-coated marines cut about .080, gonna run the piston to head clearance a bit tighter, my calculations look to be around 21:1 CR. But by the time I get it built, its gonna be at least summer now. Ryan at Hamilton recommended the 188/208 cam for my setup.
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Does the 6.7 crank increase stroke? At the prices I remember seeing them used, I can't afford one, but maybe in the race truck next winter. I know there's threads out there, but IIRC they all went nowhere. Is the 6.7 crank a straight swap? Same bearings and gear and everything?
 
Yes the 6.7 crank has a stroke of 4.88 vs 5.9 stroke of 4.72. That's why he is cutting his Pistons. Rods and bearings will swap fine but you will have to press your old gear on the 6.7 crank.
 
Ok so a total of extra .16, or .08 uptravel. I get it. Damn 21:1 would be awesome. so let's say you are already at 700 horsepower, how much power do you think would be picked up without changing any fuel or air?
 
madmikeismad said:
Ok so a total of extra .16, or .08 uptravel. I get it. Damn 21:1 would be awesome. so let's say you are already at 700 horsepower, how much power do you think would be picked up without changing any fuel or air?
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21:1 seems like a lot of compression? How do rod bearings and wrist pin bushings hold up with that much compression over long term?
 
madmikeismad said:
Does the 6.7 crank increase stroke? At the prices I remember seeing them used, I can't afford one, but maybe in the race truck next winter. I know there's threads out there, but IIRC they all went nowhere. Is the 6.7 crank a straight swap? Same bearings and gear and everything?
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The only interference I've had so far is that the big end on the #1 and #2 rod would touch the block, as there is an internal boss for where the oil cooler bolts. Die grinder fixed that. I still need to check cam clearance though. 12v rods cleared the block on #2 with less than .010" clearance, so it would turn fine, but should still be adjusted. I never checked the stock block with 12v rod in the #1 hole before I massaged it down.
 
Tate said:
The only interference I've had so far is that the big end on the #1 and #2 rod would touch the block, as there is an internal boss for where the oil cooler bolts. Die grinder fixed that. I still need to check cam clearance though. 12v rods cleared the block on #2 with less than .010" clearance, so it would turn fine, but should still be adjusted. I never checked the stock block with 12v rod in the #1 hole before I massaged it down.
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If I remember, I'll check this one when it comes out, if only for gee-whiz.
 
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