317 vs stock LS1 heads cylinder pressure
12-01-2011, 04:29 PM
#1
317 vs stock LS1 heads cylinder pressure I have a S475 turbo setup on a stock LS1. I have a set of stock LS1 heads that just had the valves done and were trued. I also have a set of 317's but they would need a valve job and to be trued. Should I just run the stock heads I have or is it worth getting the 317's done? I'm running E85 and this is for a 100% track car, zero street driven. What would be easier on the motor, lower compression and more boost (317's) making 700hp or higher compression and less boost (stock heads) making 700hp? If both make 700hp would they both have the same cylinder pressure?
Last edited by minytrker; 12-04-2011 at 02:20 AM.
12-04-2011, 01:23 PM
#6
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Pressure pushing down on top of the piston translates into output torque of the crank shaft. Doesn't matter if it is a fuel/air explosion, straight air pressure, or your hand pushing down on the piston (if that were possible). Therefore, looking at that aspect of it, it will not make a difference which heads you run.
However, As I'm sure you are aware, higher compression ratio is more likely to pre ignite and cause detonation. That is where the stress factor would come in. Since you are running E85 and only looking to make 700whp though... I wouldn't even consider detonation to be a problem, unless your tune is bad.
So... Higher compression, less boost, slightly increased chance of detonation or...
Lower compression, potentially same boost due to better flow, and a larger safety zone for detonation.
Personally, I would try the heads you already have worked over. For only 700whp, they will most likely be fine since you are running E85. Now if this were regular 93 pump gas, I would be going with the 317's for sure...
However, As I'm sure you are aware, higher compression ratio is more likely to pre ignite and cause detonation. That is where the stress factor would come in. Since you are running E85 and only looking to make 700whp though... I wouldn't even consider detonation to be a problem, unless your tune is bad.
So... Higher compression, less boost, slightly increased chance of detonation or...
Lower compression, potentially same boost due to better flow, and a larger safety zone for detonation.
Personally, I would try the heads you already have worked over. For only 700whp, they will most likely be fine since you are running E85. Now if this were regular 93 pump gas, I would be going with the 317's for sure...
12-05-2011, 07:31 AM
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That S475 is a pretty efficient turbo, and at 700HP should barely be breaking a sweat to keep the motor fed. I don't really see the need to mess with compression on E85, as the octane rating is right around 105. In fact you actually run a lot richer, further quenching the mixture (ie. cooler EGTs).
Detonation is not much of problem on E85, so much as you follow proper tuning protocol. However it does light off pretty easily, so pre-ignition may be a concern if you think you have other potential sources of ignition, other than your plugs, somewhere in the combustion chamber.
Detonation is not much of problem on E85, so much as you follow proper tuning protocol. However it does light off pretty easily, so pre-ignition may be a concern if you think you have other potential sources of ignition, other than your plugs, somewhere in the combustion chamber.
