383 pistion help with N2O
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From: Enid, OK
383 pistion help with N2O Im the middle of specing out a build for a friend that recently let a rod fly. Iv got most parts in mind but am having a little trouble finding a off the shelf pistin that will yield me my compression that I want and hold some N2O. Seems most ring lands arnt quite up to the task or they are for 6.0 rods. If we must go custom that is an option as well.
Specs:
-4 bolt block
-Compstar 3.75 crank 4340 alloy
-5.7 inch Compstar rods with 2000 ARP bolts
-12-1 SCR (or just under depending on the quench distiance I end up with)
-0 decked block (to further enhance quench but depending on pistion compression height)
-200 shot off a fogger system
-AI 215cc Trickflow 23 deg heads (58-63cc chamber, still playing with the numbers but need a pistion first)
-Custom grind cam as Im not happy with what is off the shelf to get DCR where I want and the amount of overlap I want, looking 236/244 range on a 114LSA, lift isnt much of a concern as its a N2O build and the exhaust side is where power is primarily found but will be somewhat healthy
Goals for build
Car Isnt a DD but does get driven to the track and on nice days that we cruise with our car club so it sees alot of low RPM driving and then high RPM use on the gas at the track. Thats my primary reason for going with the 5.7 rod over the 6in rod because of oil ring intrusion and oil consumption being a concern(even thou a forged pistion motor will use more oil, I know). I understand the geometry diff between the 2 and all the other factors that have been beaten to death like side loading, friction, dwell time, RS ratio, Lighter rotator ect.
I cant seem to find a Mahle pistion list? Im considering most makers Diamond, Weisco, Mahle, but will look at anything if it suites my needs. Thanks in advance
Specs:
-4 bolt block
-Compstar 3.75 crank 4340 alloy
-5.7 inch Compstar rods with 2000 ARP bolts
-12-1 SCR (or just under depending on the quench distiance I end up with)
-0 decked block (to further enhance quench but depending on pistion compression height)
-200 shot off a fogger system
-AI 215cc Trickflow 23 deg heads (58-63cc chamber, still playing with the numbers but need a pistion first)
-Custom grind cam as Im not happy with what is off the shelf to get DCR where I want and the amount of overlap I want, looking 236/244 range on a 114LSA, lift isnt much of a concern as its a N2O build and the exhaust side is where power is primarily found but will be somewhat healthy
Goals for build
Car Isnt a DD but does get driven to the track and on nice days that we cruise with our car club so it sees alot of low RPM driving and then high RPM use on the gas at the track. Thats my primary reason for going with the 5.7 rod over the 6in rod because of oil ring intrusion and oil consumption being a concern(even thou a forged pistion motor will use more oil, I know). I understand the geometry diff between the 2 and all the other factors that have been beaten to death like side loading, friction, dwell time, RS ratio, Lighter rotator ect.
I cant seem to find a Mahle pistion list? Im considering most makers Diamond, Weisco, Mahle, but will look at anything if it suites my needs. Thanks in advance
Another happy medium is the 5.85" rod. A bit more on the custom side, but it's a happy compromise between the 5.7" and the 6.0" rod. They seem to be getting more popular these days.
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From: Enid, OK
Iv also considered a 5.85 rod but compstar at the moment doesnt make that length in a H beam. plus pistion selection becomes almost nill as they are just becoming popular
On The Tree
Joined: Oct 2011
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From: Eastern Kentucky
Mahle is pretty easy to figure out the part number. You'll want a 1.425 compression height so the first numbers will be SBC425. That's a small Chevy with 1.425 height. The next three numbers are the bore over standard. In the case of 30 over that would be 030 so now we have SBC425030 and the last three numbers are the piston style (F) flat top (D) dome (I) inverted dome, and the cc's. A flat top with 5cc reliefs would be F05.
So your part number would be SBC425030F05. If you wanted an inverted dome with -16cc volume just change the F05 to I16. The Mahle for a 6" rod does not have the oil ring protruding into the pin boss.
The Diamonds are also a great choice. They will change anything on that piston for $6.00 per piston engineering change. If someone screwed up the bore, Diamond will make you a 4.028 piston or a 4.034 or anything you want to get your clearance correct. They will even change the compression height. Anything you need. Six bucks extra per change. You can get exactly what you want instead of having to accept a compromise. We've all done that.
So your part number would be SBC425030F05. If you wanted an inverted dome with -16cc volume just change the F05 to I16. The Mahle for a 6" rod does not have the oil ring protruding into the pin boss.
The Diamonds are also a great choice. They will change anything on that piston for $6.00 per piston engineering change. If someone screwed up the bore, Diamond will make you a 4.028 piston or a 4.034 or anything you want to get your clearance correct. They will even change the compression height. Anything you need. Six bucks extra per change. You can get exactly what you want instead of having to accept a compromise. We've all done that.
run a 6" rod, its easier on the cylinder walls and there are many more options avaliable for off the shelf pistons...... and go to either wiseco or srp, IIRC they have taller top ring to piston surface distances which will keep you safer on spray with the heat and also get yourself a ring package with a steel top ring........dont forget piston to wall and ring gap clearances also to handle the 200shot......good luck!!! 
Thread Starter
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From: Enid, OK
First off thanks for all the replies. It seems most people are really pushing the 6.0inch rods. My first concern was clearance but after visualizing the rotator rod length wont affect clearance its the stroke. Main concern is the oil ring, I have seen that Mahle has a 6.0inch rod piston that doesnt get into the oil ring but they also use thinner rings and a ring land that isnt sufficent for the heat of N2O. Im not a fan of support rails so Im using 5.7 inch rods, ill take the increased side loading and friction for a pistion that I feel will hold up better. Ill give a few companies a call on monday and see what they have available. thanks
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run a 6" rod with a JE nitrous piston and call it a day. save a couple hundred dollars over the customs, and they should hold up fine for what you are doing. a 200 shot will not need anything crazy.
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From: Enid, OK
Iv noticed that im getting answers from the people who are out actully racing and running these combos which is exactly who I want input from, but remember this engine will see mostly low RPM street driving.
What seems to be the lift people are getting away with without having to go to a reduced base circle cam (reduced over what the normal grind already has)?
Last edited by BigDB; Nov 25, 2011 at 11:24 PM.
Ill look into what pistons are availible for them, seems compstar just introduced an ULTRA XD I beam that offers addition cam clearance in 5.85 and 6 inch. Iv always used H beams but seems the concensious is the I beam is a bit stronger.
Iv noticed that im getting answers from the people who are out actully racing and running these combos which is exactly who I want input from, but remember this engine will see mostly low RPM street driving.
What seems to be the lift people are getting away with without having to go to a reduced base circle cam (reduced over what the normal grind already has)?
Iv noticed that im getting answers from the people who are out actully racing and running these combos which is exactly who I want input from, but remember this engine will see mostly low RPM street driving.
What seems to be the lift people are getting away with without having to go to a reduced base circle cam (reduced over what the normal grind already has)?
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From: Enid, OK
Hellfire top rings, Total Seal seconds and standard tension oil rings, also get a 2618 forged piston for a big shot of N20. I have Mahle Power Pac forged pistons and was told by them not to run more than a 150 shot on those pistons.
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From: Enid, OK
This is what I was told by Callies that they dont recommend them over a 150.Not saying they wont get the job done but there are better options. Just got off the phone with Callies as Im wanting to use their rods and crank. They have a new Ultra XD I beam that has .050 additional clearance compared to the standard I beam. I dont have a price as of yet, supposed to get back to me today. Ill post up the part number and price when they get back to me.
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different forging of aluminum. some have more silica affecting the resiliancy as well as expansion when heated... read up on it.
two major types though, one is great for daily driving with a little abuse, and the other is stronger but a little rougher for daily.
two major types though, one is great for daily driving with a little abuse, and the other is stronger but a little rougher for daily.
I was stating that its just funny that they say 150 or 200 maximum when we well know that they can handle well beyond that...