What head gasket to use?
05-06-2010, 01:01 AM
#23
your running a dome so you got to put a -6.0 in the cc section..
i also just got 13-1 using .039 gasket with a zero deck and no cc's a true flat top with a 57 head,4.030 bore an 3.75 stroke
i dont trust online calculators..i can pull up 20 of them and get 15 diff answers using the same data.
05-06-2010, 01:10 AM
#24
Nope the part number is sbc125030d05 and its +6
When doing the math I had just checked a website calculator and found out that with a 4.030 bore 3.75 stroke and this piston and 57cc head and using a .040" head gasket I would have 11.9 compression ratio. Where did you get your info. I know your better than me with this stuff but im really confused now.
When doing the math I had just checked a website calculator and found out that with a 4.030 bore 3.75 stroke and this piston and 57cc head and using a .040" head gasket I would have 11.9 compression ratio. Where did you get your info. I know your better than me with this stuff but im really confused now.
You sure your deck height on your block is 9.00??? or did they take it from 9.025 to something else..because 6.00(rod)+1.125(piston)+1.875(crank) = 9.00 so if your block is 9.00 your at zero deck plus then 6cc worth of dome sticking up.
Also sorry to tell you this but that is not a good n2o piston at all for a big shot..i wouldnt go over 200 on it with that comp height..all of the heavy n2o 23 degree motors i know of run a 1.18 or more for a ring stack..most are in a 1.24 range and this is for 250-600 shot size small blocks..ls1 engines like a 1.12 ring stack aka comp height
Last edited by suicidal racing; 05-06-2010 at 01:19 AM.
05-06-2010, 01:26 AM
#25
with that calculator i got 12.58 comp using a .080 gasket..
your running a dome so you got to put a -6.0 in the cc section..
i also just got 13-1 using .039 gasket with a zero deck and no cc's a true flat top with a 57 head,4.030 bore an 3.75 stroke
i dont trust online calculators..i can pull up 20 of them and get 15 diff answers using the same data.
your running a dome so you got to put a -6.0 in the cc section..
i also just got 13-1 using .039 gasket with a zero deck and no cc's a true flat top with a 57 head,4.030 bore an 3.75 stroke
i dont trust online calculators..i can pull up 20 of them and get 15 diff answers using the same data.
Why would you put neg 6 in the cc section?
the site does say its a positive 6 not a neg. go to the site the guy posted above and look at it. SO if I put all the info in I get 11.98:1 compression. thats with a .041" gasket too.
05-06-2010, 03:17 AM
#27
what your doing is saying the piston has a -6cc for valve reliefs..trust me its -6.0 cc you have to put in not 6.0 cc which would mean his pistons have a 6cc in them for valve relief..
if he looked at mahles site an order them he must of been thinking that the comp on there page to the right would be where he would be around but what he didnt take into account is them compression guesses are for a 64cc head most the time an a .039 gasket with a standerd deck height of 9.025 which would get him right around 12-1 like they list on the site
Last edited by suicidal racing; 05-06-2010 at 03:25 AM.
05-06-2010, 04:29 AM
#29
.030 is pretty tight, I was running .033 and a few pistons kissed the heads, not really a big deal though especially if you're pushing the limit on pump gas (i was and it bit me). I don't really think there's much difference in quench once you're at .040 and below as far as knock suppression, you're just raising compression that much higher at that point. I would start asking around how much you can take out of that chamber to offset that dome, or shop around for a different piston. A smaller chamber with a flat top is ALWAYS more efficient than a big chamber with a dome, especially when you're on limit as far as compression goes. Either that, or get a hefty solid roller and aftermarket PCM.
05-06-2010, 10:29 AM
#30
.030 is pretty tight, I was running .033 and a few pistons kissed the heads, not really a big deal though especially if you're pushing the limit on pump gas (i was and it bit me). I don't really think there's much difference in quench once you're at .040 and below as far as knock suppression, you're just raising compression that much higher at that point. I would start asking around how much you can take out of that chamber to offset that dome, or shop around for a different piston. A smaller chamber with a flat top is ALWAYS more efficient than a big chamber with a dome, especially when you're on limit as far as compression goes. Either that, or get a hefty solid roller and aftermarket PCM.
The poor piston choice is limiting your build right now.
05-06-2010, 06:30 PM
#32
yes you could but thats not a gasket i would use for alot of juice..how much juice are you looking to spray anyways?
your top ring on your pistons is to far up for a huge shot even with hell fires you would lift a ring more then likely.
if you building this motor as a n2o motor your doing it all wrong..the ring lands are an issue and then sticking in a gasket that thick is another
your top ring on your pistons is to far up for a huge shot even with hell fires you would lift a ring more then likely.
if you building this motor as a n2o motor your doing it all wrong..the ring lands are an issue and then sticking in a gasket that thick is another
05-06-2010, 07:35 PM
#34
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OK so would these be a better decision then????
SBC125030F05 4.03" 3.750 6.000 0.927 1.125 -5cc 406 11.1
I calculated these in the c.r calc and I got a total of 12.11 inputing a + number for valve reliefs?
lmk guys I really need to order some pistons and need to know will these handle a big shot?
SBC125030F05 4.03" 3.750 6.000 0.927 1.125 -5cc 406 11.1
I calculated these in the c.r calc and I got a total of 12.11 inputing a + number for valve reliefs?
lmk guys I really need to order some pistons and need to know will these handle a big shot?
05-06-2010, 07:48 PM
#36
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Well I have to use the forged crank and rods that I have 
I dont have all the money in the world to change setups. I got a steal on this bottom end and all I want to do is change the pistons to a nitrous piston and have at most 12.5:1 c.r. So I really need to use the bottom end But ONLY change the piston.
So will that piston work for my setup and be good on spray?
I dont have all the money in the world to change setups. I got a steal on this bottom end and all I want to do is change the pistons to a nitrous piston and have at most 12.5:1 c.r. So I really need to use the bottom end But ONLY change the piston.So will that piston work for my setup and be good on spray?
05-06-2010, 07:57 PM
#37
Well I have to use the forged crank and rods that I have I dont have all the money in the world to change setups. I got a steal on this bottom end and all I want to do is change the pistons to a nitrous piston and have at most 12.5:1 c.r. So I really need to use the bottom end But ONLY change the piston.
So will that piston work for my setup and be good on spray?
I dont have all the money in the world to change setups. I got a steal on this bottom end and all I want to do is change the pistons to a nitrous piston and have at most 12.5:1 c.r. So I really need to use the bottom end But ONLY change the piston.So will that piston work for my setup and be good on spray?
You are at an advantageous part of your build where you haven't acquired all of the parts and are still in a phase where you can change any part of your build without consequence. Instead of rushing through things, I highly suggest you do more research on what it takes to build a proper nitrous-ready rotating assembly. At this point you have two options:
1- Use the 6" rod and a flat-top piston. There are a few risks involved with using a 6" rod. A quick search and you'll find them. Go too big on your shot and it's curtains. If you toned down the shot (200 or less) you'd probably be okay though.
2- Sell the rods and get a 5.7" or 5.85" rod and the right piston. Spray away.
The choice is obvious, IMO. Pick your poison.
05-06-2010, 08:03 PM
#38
you want a 1.18-1.24 comp height for a n2o piston on these motors..but seeing you have 6" rods you are stuck to a 1.12 comp hieght with that deck height..
So for you to run a decent n2o pistons which would be a 1.27 for the best piston to put on it you would then need to run a 5.85 rod and that would put you piston below deck by .005
(dh)-(half stroke)-(ch) = max rod lenght that can be used
9.00 - 1.875 - 1.27 = 5.855
or
(rod) + (half stroke) + (ch) = how high the piston will be below or above your known deck height.
5.85 + 1.875 + 1.27 = 8.995
Last edited by suicidal racing; 05-06-2010 at 08:20 PM.
05-06-2010, 08:14 PM
#40
i was just correcting it..ive had 6.125 rods in n2o motors
an i agree he needs a diff rod..he would of been good if they only took .10 off the deck height of his block instead of going right down to 9.00..then he would have no problem finding a piston for that and would of been able to run a 6" rod with a 1.27 ch piston to put him at .005 below deck
an i agree he needs a diff rod..he would of been good if they only took .10 off the deck height of his block instead of going right down to 9.00..then he would have no problem finding a piston for that and would of been able to run a 6" rod with a 1.27 ch piston to put him at .005 below deck