School Me on Compression
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Launching!
Joined: May 2012
Posts: 232
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From: Mayfield, KY
School Me on Compression So within the next week we should finally be starting the process of getting my z28 running again. All the mods I'll be using are in my sig. It's just going to be a fun street/strip car for awhile with a very small possibility of running a small shot of nitrous on it so I was wondering, would there be any advantages of bumping up the compression with a smaller head gasket? Any disadvantages? I just assumed it would be healthy to replace the gaskets on the 70k mile LT1 I just bought since its still on the engine stand. Other than knowing a smaller gasket will bump compression, I don't know much about compression but would like to learn more. I don't care about gas mileage or anything like that but I don't want the engine to be more prone of blowing a head gasket either lol Thanks for any suggestions
At 70K, your gaskets could still be OK, but, If you do change them, go ahead and choose the thinner gasket, it probably won't make much of a difference though. The nitrous will like the higher compression too.
I am running a couple cars with the Impala head gasket and ARP head bolts torqued per the factory sequence, then a 4th round to 90 FT LBS. We are running 175 of nitrous on the stock shortblock and compression is right at 11.5:1 with the shaved heads and the thinner gaskets.
youd be completely insane not to pull the heads at this point and regasket them, get a set of arp bolts too while your at it, you can cut the gasket down it wont hurt anything, use one of the online calculators for CR, dont be afraid of 11:1
Thread Starter
Launching!
Joined: May 2012
Posts: 232
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From: Mayfield, KY
Well I have googled it and everyone talks about it being a good thing for N/A and nitrous set ups on our LT1s but they don't really say why it's good to bump it up a little. Its not a huge increase in power or so thats what ive read and like the first guy replied, it wouldn't make a big difference. So that's why I was just curious if higher compression has other advantages.
But my friend that I'm doing all the work with in his shop is an ASE Master Technician so he will be there for the whole process and will check out the heads. But for the past month or so he's been pretty busy with another LT1 swap so I dont really want to bug him about mine. I just thought it would be good to get as much information as I can from you guys before me and him start on my engine.
But my friend that I'm doing all the work with in his shop is an ASE Master Technician so he will be there for the whole process and will check out the heads. But for the past month or so he's been pretty busy with another LT1 swap so I dont really want to bug him about mine. I just thought it would be good to get as much information as I can from you guys before me and him start on my engine.
I am running a couple cars with the Impala head gasket and ARP head bolts torqued per the factory sequence, then a 4th round to 90 FT LBS. We are running 175 of nitrous on the stock shortblock and compression is right at 11.5:1 with the shaved heads and the thinner gaskets.
No way in hell would I torque to 90lbs.
Might think it makes for a tighter seal but the other thing that is likely to do is pull the bores out of round.
Plenty of us have run that much and more compression without ignoring proper torque specs the way you are suggesting.
Believe the proper spec per ARP is 70ft.lbs. in three steps. Stock is 65ft.lbs.
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No way in hell would I torque to 90lbs.
Might think it makes for a tighter seal but the other thing that is likely to do is pull the bores out of round.
Plenty of us have run that much and more compression without ignoring proper torque specs the way you are suggesting.
Believe the proper spec per ARP is 70ft.lbs. in three steps. Stock is 65ft.lbs.
Might think it makes for a tighter seal but the other thing that is likely to do is pull the bores out of round.
Plenty of us have run that much and more compression without ignoring proper torque specs the way you are suggesting.
Believe the proper spec per ARP is 70ft.lbs. in three steps. Stock is 65ft.lbs.
In fact, I called ARP about this 3 years ago when I built my first LT1 because the local machine shop told me to go higher than the spec sheet when using the ARP teflon sealer. Their tech said that with their teflon thread sealer instead of their supplied assembly lube that I would be fine at 90 FT LBS for some extra clamping force on a thinner head gasket. 20,000+ street miles, 50+ nitrous passes, and lots of street play with 25+ bottles later through the same motor and we are still running... In fact, I have about a dozen LT1/SBC motors running like this without any issues. I've even swapped heads on 2 of the motors for bigger ones and the bores look perfectly fine with several thousand miles on them.
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Verdad Gallardo No way in hell would I torque to 90lbs.
Might think it makes for a tighter seal but the other thing that is likely to do is pull the bores out of round.
Plenty of us have run that much and more compression without ignoring proper torque specs the way you are suggesting.
Believe the proper spec per ARP is 70ft.lbs. in three steps. Stock is 65ft.lbs.
Might think it makes for a tighter seal but the other thing that is likely to do is pull the bores out of round.
Plenty of us have run that much and more compression without ignoring proper torque specs the way you are suggesting.
Believe the proper spec per ARP is 70ft.lbs. in three steps. Stock is 65ft.lbs.
as said above though there is a torque diference in the sealant/lube used on the bolts so there is some merit to it
same here thats very high.........id immagine not only would you risk breaking a bolt or pulling threads but it'd pull bores and the deck out of round/flat.......just another "well it worked for me" thing .........im running over 14:1 with arp studs torqueed to 70ft/lbs with 0 issues
as said above though there is a torque diference in the sealant/lube used on the bolts so there is some merit to it
as said above though there is a torque diference in the sealant/lube used on the bolts so there is some merit to it
Now I did have a friend pull threads on his motor with studs and he tried going to 100 FT LBS, I really don't know why he did that. lol
Cap beat me to it.
I love it when folks dismiss the expensive, lengthy and dependable engineering that GM conducted and blindly substitute their "more must be better" modifications on something as simple as torqueing a damn head bolt. Im sure ARP will gladly replace the block should thread damage occur.
I love it when folks dismiss the expensive, lengthy and dependable engineering that GM conducted and blindly substitute their "more must be better" modifications on something as simple as torqueing a damn head bolt. Im sure ARP will gladly replace the block should thread damage occur.
I can tell you that the threads of a single 7/16" bolt will be subject to a clamping force of just around 600# at 60# torque. Increasing that torque to 90# subjects the fastener to a clamping force of over 1000#. That's one thousand pounds pulling on the block in a single threaded hole.
65-70# is more than enough.
65-70# is more than enough.
So arp, the ones who designed the bolt, said to go to a higher torque spec with the teflon sealer yet they are wrong? And gm spec is 65 and you guys use arp's to 70? Which is more than the engineers at gm speced for? Are my notes correct here?
Negative. I rely on GM torque specs across the board regardless of aftermarket fastener with the only exception being the opti rotor which gets thread locked and is torqued to "goodentite".
you are missing a sentence i wrote a few posts back..........torque is partly a measurement of the friction on the bolt due to thread contact, oil vs silicone vs a proprietary material from arp will all require different torque specs, read arp literature it will also say this.....usually they all vary within 10-15ftlbs of each other which is why when we saw 90 over the reccomended 65-70 it was questioned......you can see this for yourself, torque a set of rod bolts with oil to lets say .005 bolt stretch then torque them to .005 bolt stretch with moly lube.......you'll be shocked the difference
The rest of us use ARP bolts at 8% over factory spec which is to account for the FASTENER difference. The fastener needs to stretch just a little .
You are going almost 40% over OEM spec. The bolt may tolerate this but you are very likely pulling the tops of the bores out of round. You are really want to pretend 8% over OEM and 40% over are similar?
I would also ask the question again about how many times did you do this with proper torque spec and have it fail?
http://arpinstructions.com/instructions/134-3601.pdf Here are the written ARP instructions. It even mentions using thread sealer without mention if jacking the torque spec up 21% over spec as you say the 800 line jockey told you to. I would trust that over the person answering the 800 line has to say.
You are going almost 40% over OEM spec. The bolt may tolerate this but you are very likely pulling the tops of the bores out of round. You are really want to pretend 8% over OEM and 40% over are similar?
I would also ask the question again about how many times did you do this with proper torque spec and have it fail?
http://arpinstructions.com/instructions/134-3601.pdf Here are the written ARP instructions. It even mentions using thread sealer without mention if jacking the torque spec up 21% over spec as you say the 800 line jockey told you to. I would trust that over the person answering the 800 line has to say.
