Compression Ratio question
Compression Ratio question I'm building a stock cube (347) forged engine with an APS turbo kit. I have a set of -13CC dish pistons on the way, I as previously planning a set of 6.0 L heads. Where would that put my compression ratio? or would i be better off going with LS6 heads? Using 6.125 connecting rods if that helps. I found a calculator but too stupid to use it i guess.
If anyone has any cam reccomendations also i"d greatly appreciate it.
Thanks
If anyone has any cam reccomendations also i"d greatly appreciate it.
Thanks
The static compression level be 8.4:1 with 317 and 9.0:1 with LS6 heads. I would go with the LS6 heads. 8.4:1 compression level will be a complete dawg when not in boost.
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well to start off with... the stock combustion chamber on 6.0 l heads (both lq4 and lq9) is 71.06 cc's. with a 12.2 cc dish piston and a 68cc comb chamber your comp ratio is gonna be 8:14 with a 76 cc combustion chamber your comp ration is gonna be 7:82 so with a 71.06 combustion chamber and 13 cc pistons your lookin at right about 8:0. however your head choice is gonna depend on a couple things. if your tranny is automatic and you have a stall say 3000 stall and your turbos start to spool around 3000 you should have almost no lag, if you have a manual then you will have a small amount of lag. however the higher the compression the lower the amount of boost you will be able to run... but the better throtte response. there are so many factors that apply here. do your research and decide for yourself. there is so much knowledge on here its ridiculous but some more often than not is curbed by opinion.
Thank you, that helps a lot.
I have an M6 car, I was planning for 9.0-9.5 compression ratio. Looking for about 650 or so HP and probabally never over 12 pounds of boost out of a forged 346.
I have been reading and researching day and night. Maybe i haven't been using the right search terms, I've read the turbo FAQ a half dozen times or so already.
so then would 5.3 liter heads with the 59CC combustion chamber then put me about 9.5? so much knowledge so little time and memory
thanks again
I have an M6 car, I was planning for 9.0-9.5 compression ratio. Looking for about 650 or so HP and probabally never over 12 pounds of boost out of a forged 346.
I have been reading and researching day and night. Maybe i haven't been using the right search terms, I've read the turbo FAQ a half dozen times or so already.
so then would 5.3 liter heads with the 59CC combustion chamber then put me about 9.5? so much knowledge so little time and memory
thanks again
Personally, I come from the lower static compression is better camp (8.0 myself) and usually advise people go with a lower compression.
Especially on turbo cars because they never stay at the boost they first intended and the lower compression gives you to run higher boost on race gas.
My personal opinion is something in the high-8's, low-9's would be optimal.
Especially on turbo cars because they never stay at the boost they first intended and the lower compression gives you to run higher boost on race gas.
My personal opinion is something in the high-8's, low-9's would be optimal.
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MY builder recommened 9.5 if I run alc injection and 9.0 if just wanted to run pump 91 to 94.
I went with 9.5. Car is great off boost and with big power you spend a lot of time off boost in the city. If you spend a lot of time in boost then likely you will be spending a lot of time in jail! LOL
I didn't want a doggy car. I think 9.0 is a nice overall ration and 8.5 maybe for a track car that wants to run higher boost on pump with no alc. But alc systems are not that expensive or you can of course run race gas or equivalent at the track. Heck I think would have run 10 to 1 or 10.5 to 1 if could get e85 where I live.
I went with 9.5. Car is great off boost and with big power you spend a lot of time off boost in the city. If you spend a lot of time in boost then likely you will be spending a lot of time in jail! LOL
I didn't want a doggy car. I think 9.0 is a nice overall ration and 8.5 maybe for a track car that wants to run higher boost on pump with no alc. But alc systems are not that expensive or you can of course run race gas or equivalent at the track. Heck I think would have run 10 to 1 or 10.5 to 1 if could get e85 where I live.
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This discussion is making me second guess my build now, lol. I'm using Probe -16cc dished 4.030 pistons in an iron block..Right now with the 64cc heads I have now I will be at 9.3:1. If I get 72cc heads I will be at 8.5:1. It's a 3400 stalled TH400 drag car. Hmmmm. What to do....
Edit: I will be using Shawn at Va Speed for my cam. I recommend emailing him a complete breakdown of your build and having him do a cam for you.
Edit: I will be using Shawn at Va Speed for my cam. I recommend emailing him a complete breakdown of your build and having him do a cam for you.
If you want to run huge boost on pump gas then you might want 8.5 or lower. If you want to run the aps standard turbos then likely you should be running them mabye 15psi tops. So if you want to do that you can do that fine on 9 to 1 on pump 92 or whatever and 9.5 to one if you run alc injection or keep timing a bit down.Boost makes more power than timing.
My car has great throttle off boost in fact it scares people with no boost even into the engine yet. But it is a built 408 so that helps too. Still unless you are running 20psi plus on maybe 91 octane dont' see where this low compression is necessary stuff comes in. Alc/meth injection kits are cheap these days . And you can always run some race gas at the track if you really want to have high octane .or you can make some up easily with xylene or toluene.
I would go 9 to 9.5. Under 9 makes zero sense to me.
My car has great throttle off boost in fact it scares people with no boost even into the engine yet. But it is a built 408 so that helps too. Still unless you are running 20psi plus on maybe 91 octane dont' see where this low compression is necessary stuff comes in. Alc/meth injection kits are cheap these days . And you can always run some race gas at the track if you really want to have high octane .or you can make some up easily with xylene or toluene.
I would go 9 to 9.5. Under 9 makes zero sense to me.
please keep in mind that it is better to have a larger combustion chamber. the smaller the combustion chamber the more the fuel is prone to preignite. that is why diesels don't really have a combustion chamber.
i have a forged 347 with 8.6:1 cr and 72cc heads.
my goal is a pump fuel friendly 700whp.
i have a forged 347 with 8.6:1 cr and 72cc heads.
my goal is a pump fuel friendly 700whp.
9.5 to 1 here! For my APS build i used a 6.0 LQ9 block with LS6 heads on my 02 35th LE auto and had mine built to a 9.5 to 1. I just had it tunned this weekend and made 633Hp on only 9 PSI! My original plans were to run about 15 PSI and had built everything built(forged) down to the rear end for it , but after taking a road test after the tune LOL i was happy as **** with it and left it at 9 PSI 
and the tires were breaking loose on the dyno too at that HP level LOL Mine is strictly a weekend/cruise ride by the way and money is really tight for me now since the economy **** itself LOL so i figuired 9 PS1 and having the AFR at a nice fat 10;1 under boost conditions should keep her nice and safe for a long time to come .It feels like a ******* rocket on the street too with no lag with the 9.5 to 1 CR. I'de say go with the 9.5 to 1 myserlf .I use to own a 87 GN with a stage 2 and made the mistake of building a low 8 to 1 CR. Its was killer mid to top ,but out of the hole (for street driving) it was a dog LOL If your doing any street driving at all ??? i wouldnt go below 9 to 1 myself (JMO) Good luck my man
and the tires were breaking loose on the dyno too at that HP level LOL Mine is strictly a weekend/cruise ride by the way and money is really tight for me now since the economy **** itself LOL so i figuired 9 PS1 and having the AFR at a nice fat 10;1 under boost conditions should keep her nice and safe for a long time to come .It feels like a ******* rocket on the street too with no lag with the 9.5 to 1 CR. I'de say go with the 9.5 to 1 myserlf .I use to own a 87 GN with a stage 2 and made the mistake of building a low 8 to 1 CR. Its was killer mid to top ,but out of the hole (for street driving) it was a dog LOL If your doing any street driving at all ??? i wouldnt go below 9 to 1 myself (JMO) Good luck my man For my APS build i used a 6.0 LQ9 block with LS6 heads on my 02 35th LE auto and had mine built to a 9.5 to 1. I just had it tunned this weekend and made 633Hp on only 9 PSI! My original plans were to run about 15 PSI and had built everything built(forged) down to the rear end for it , but after taking a road test after the tune LOL i was happy as **** with it and left it at 9 PSI and the tires were breaking loose on the dyno too at that HP level LOL Mine is strictly a weekend/cruise ride by the way and money is really tight for me now since the economy **** itself LOL so i figuired 9 PS1 and having the AFR at a nice fat 10;1 under boost conditions should keep her nice and safe for a long time to come .It feels like a ******* rocket on the street too with no lag with the 9.5 to 1 CR. I'de say go with the 9.5 to 1 myserlf .I use to own a 87 GN with a stage 2 and made the mistake of building a low 8 to 1 CR. Its was killer mid to top ,but out of the hole (for street driving) it was a dog LOL If your doing any street driving at all ??? i wouldnt go below 9 to 1 myself (JMO) Good luck my man
and the tires were breaking loose on the dyno too at that HP level LOL Mine is strictly a weekend/cruise ride by the way and money is really tight for me now since the economy **** itself LOL so i figuired 9 PS1 and having the AFR at a nice fat 10;1 under boost conditions should keep her nice and safe for a long time to come .It feels like a ******* rocket on the street too with no lag with the 9.5 to 1 CR. I'de say go with the 9.5 to 1 myserlf .I use to own a 87 GN with a stage 2 and made the mistake of building a low 8 to 1 CR. Its was killer mid to top ,but out of the hole (for street driving) it was a dog LOL If your doing any street driving at all ??? i wouldnt go below 9 to 1 myself (JMO) Good luck my man