Compression Ratio Question.
Thread Starter
Joined: Nov 2001
Posts: 572
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From: North Florida
Re: Compression Ratio Question. LOL, dude, you might as well ask which lid is the best. You'll get less different opinions <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />
I am of the "nitrous likes compression camp".
If this is a street car, I'd cap it at around 12:1 with the reverse cooled heads. If it's a race car, I'd look at 13.5-14:1. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
- Matt
I am of the "nitrous likes compression camp".
If this is a street car, I'd cap it at around 12:1 with the reverse cooled heads. If it's a race car, I'd look at 13.5-14:1. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
- Matt
On The Tree
Joined: Apr 2002
Posts: 111
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From: Owensboro,KY
Re: Compression Ratio Question. LOL, ya I know I am going to get alot of different answers. Thanks for the reply.
Keep them coming guys... I need suggestions please. Technical knowledge to support your answers would help too.
Keep them coming guys... I need suggestions please. Technical knowledge to support your answers would help too.
Teching In
Joined: May 2002
Posts: 6
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From: Plano, TX
Re: Compression Ratio Question. nitrous + high compression = NO GOOD, GO BOOM! N2O and blowers share a lot of the same performance qualities and restrictions, and compression is one of these. think about it this way: when nitrous enters the combustion chamber it is in a very condensed form. when the molecules split and the oxygen combusts, it expands exponentially, which gives you your extra power. the greater the ratio from BDC when the nitrous is filling the chamber to TDC where it is compressed the most and then forced to rapidly expand by combustion, the greater the total pressure on the heads, head bolts, head gaskets, pistons, rods, etc etc etc. this is the same reason you retard timing when using N2O and blowers, keep in mind that you are igniting the mixture before it is even fully compressed.
On The Tree
Joined: Apr 2002
Posts: 111
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From: Owensboro,KY
Compression Ratio Question. I am currently having built a 383 LT4 (not a LS1 I know-please no negative comments <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" /> ) with Lunati 4340 Forged Crank, Rods and Pistons; 2 to 4 bolt splayn cap conversation. AFR 195 cc LT4 Heads, and the rest of the whole nine yards.
The actually question is: What compression ratio do you guys recommend for a 200 Wet Shot of Nitrous? I always hear conflicting stories on If Nitrous likes Compression or Not. I do not want to sacrifice too much CR, I will loose N/A power!
However I do not want to go too high either (more probable detonation,etc)
Also I have not picked out the Cam specs as of yet. It must be Lunati... any suggestions?
Thanks in Advance. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />
<small>[ June 11, 2002, 12:21 PM: Message edited by: Andy West ]</small>
The actually question is: What compression ratio do you guys recommend for a 200 Wet Shot of Nitrous? I always hear conflicting stories on If Nitrous likes Compression or Not. I do not want to sacrifice too much CR, I will loose N/A power!
However I do not want to go too high either (more probable detonation,etc)
Also I have not picked out the Cam specs as of yet. It must be Lunati... any suggestions?
Thanks in Advance. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />
<small>[ June 11, 2002, 12:21 PM: Message edited by: Andy West ]</small>
Re: Compression Ratio Question. One thing that you shouldnt over look is your ignition. Check out MSD they have an ignition retard that will only retard the ignition when you push the button and put it back where is was when you let go.
Re: Compression Ratio Question. I have 11.5 to 1 compression and can easily run a 150 shot with no retard or race gas. For a 200 shot I run a light mix of race gas...probably 97-98 octane and have no problems. Anymore than that and I need to retard timing a bit (which has been difficult since we have no real timing retard equipment for LS1s).
I dont know what the LT1 can get away with for a streetable compression ratio...but I would build it for best power on motor and then add the shot ontop. you have alot of options for your car for timing controls to retard if necessary...and then can still add race gas if needed. Sounds like running nitrous is a secondary concern to you over running well on motor. I would use a reasonable CR for an LT1 and go from there. I have some good LT1 freinds running 383s and 396 LT1s with decent compression 10:1+ and 200 shots with no problems.
The incredibly low temps of the nitrous intake charge really helps with detonation and allows for aggressive CR.
I dont know what the LT1 can get away with for a streetable compression ratio...but I would build it for best power on motor and then add the shot ontop. you have alot of options for your car for timing controls to retard if necessary...and then can still add race gas if needed. Sounds like running nitrous is a secondary concern to you over running well on motor. I would use a reasonable CR for an LT1 and go from there. I have some good LT1 freinds running 383s and 396 LT1s with decent compression 10:1+ and 200 shots with no problems.
The incredibly low temps of the nitrous intake charge really helps with detonation and allows for aggressive CR.
On The Tree
Joined: Apr 2002
Posts: 111
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From: Owensboro,KY
Re: Compression Ratio Question. Thanks guys,
I am well aware of how nitrous works and how bad too much timing and compression is.
What I am not sure of is.. What is a good compromise on the CR? I do not want it too high. It seems to me 13.5-14:1 might be pushing it.
On the other hand I do not want to loose N/A performance by lowering the CR too low.
Right now I am thinking around 11.5 or 12.1
Does this sound like a good idea?
PS.. I also need help on the cam. I want a nice and hot cam, yet that is still descent for a half way daily driver. So I feel mid-high range torque is of the most importance to me. I also need the cam to work well with Nitrous.....
Any Suggestions on the Cam specs?
*Im not sure if the LT1-LS1 difference will change the cam much or not*
I am well aware of how nitrous works and how bad too much timing and compression is.
What I am not sure of is.. What is a good compromise on the CR? I do not want it too high. It seems to me 13.5-14:1 might be pushing it.
On the other hand I do not want to loose N/A performance by lowering the CR too low.
Right now I am thinking around 11.5 or 12.1
Does this sound like a good idea?
PS.. I also need help on the cam. I want a nice and hot cam, yet that is still descent for a half way daily driver. So I feel mid-high range torque is of the most importance to me. I also need the cam to work well with Nitrous.....
Any Suggestions on the Cam specs?
*Im not sure if the LT1-LS1 difference will change the cam much or not*
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Launching!
Joined: Apr 2002
Posts: 231
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From: Australia
Re: Compression Ratio Question. [QUOTE]Originally posted by Andy West:
What is a good compromise on the CR? I do not want it too high. It seems to me 13.5-14:1 might be pushing it.
On the other hand I do not want to loose N/A performance by lowering the CR too low.
Right now I am thinking around 11.5 or 12.1
Does this sound like a good idea?
That compression, with our limited number of head bolts/studs, and a decent nitrous set-up = blown head gaskets. OK, use Copper head gaskets, O-ring the heads or block, use head studs, torqued then retorqed after usage, and about 11:1 comp, with a bigger nitrous kit. That will not give you the best HP on nitrous though, as low comp with more N20 is the best. Think of it as a supercharged engine...
Cheers. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
What is a good compromise on the CR? I do not want it too high. It seems to me 13.5-14:1 might be pushing it.
On the other hand I do not want to loose N/A performance by lowering the CR too low.
Right now I am thinking around 11.5 or 12.1
Does this sound like a good idea?
That compression, with our limited number of head bolts/studs, and a decent nitrous set-up = blown head gaskets. OK, use Copper head gaskets, O-ring the heads or block, use head studs, torqued then retorqed after usage, and about 11:1 comp, with a bigger nitrous kit. That will not give you the best HP on nitrous though, as low comp with more N20 is the best. Think of it as a supercharged engine...
Cheers. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
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Verdad Gallardo On The Tree
Joined: Apr 2002
Posts: 111
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From: Owensboro,KY
Re: Compression Ratio Question. Ok, to compromise 11.5:1 it is.
Any cam suggestions? The only suggestion I have gotten so far (from a friend) is "around 560-580 lift and around 230-245 duration @ .050" <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" />
How does this sound? <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
Any cam suggestions? The only suggestion I have gotten so far (from a friend) is "around 560-580 lift and around 230-245 duration @ .050" <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" />
How does this sound? <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
Re: Compression Ratio Question. On my new motor, I'm planning 11.7:1 and running a direct port 200 HP injection of N2O. With the SII LS6 heads and 373 CI I'm not too worried about n/a vs n2o trade offs. The cam I'm having ground is a 230/235 .595/.601 112. A 114 LSA would be a little better for the N2O but I need to keep the power band as low as possible.
Richard
Richard
On The Tree
Joined: Apr 2002
Posts: 111
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From: Owensboro,KY
Re: Compression Ratio Question. If I do 230/235 .595/.601 112 I would have to upgrade the springs on the AFR Heads, which is not a problem. That is some serious lift! <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />
Thanks for the suggestion. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
<small>[ June 17, 2002, 12:31 AM: Message edited by: Andy West ]</small>
Thanks for the suggestion. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
<small>[ June 17, 2002, 12:31 AM: Message edited by: Andy West ]</small>
