3.5 with 3.0 heads compression ratio?
Sounds good. 
I would humbly beg to differ in the case of the VQ35. It has 3 things working against it versus a VQ30 (in order of importance):
1. Lower tumble flow (the primary reason for the .3 compression increase)
2. More combustion chamber volume (more area for the flame front to cover...also more area for end gasses to hang out and light off)
3. Larger bore (ditto)
There have been countless cases over the past few years of VQ35 owners complaining of audible partial throttle knock from maximas to FX35's and everything in between. On the flipside, almost every instance of this in VQ30's has been attributable to an "out-of-spec" engine control issue. The issue seems to have been eliminated with the HR and VHR series. They've been confirmed to have smaller C/C volumes. Can't speak to other head design features though.
Guess who just signed up over at SAE.org
There are other factors but the VQ is not prone to them in 99% of N/A cases.
It has 3 things working against it versus a VQ30 (in order of importance):1. Lower tumble flow (the primary reason for the .3 compression increase)
2. More combustion chamber volume (more area for the flame front to cover...also more area for end gasses to hang out and light off)
3. Larger bore (ditto)
There have been countless cases over the past few years of VQ35 owners complaining of audible partial throttle knock from maximas to FX35's and everything in between. On the flipside, almost every instance of this in VQ30's has been attributable to an "out-of-spec" engine control issue. The issue seems to have been eliminated with the HR and VHR series. They've been confirmed to have smaller C/C volumes. Can't speak to other head design features though.
Guess who just signed up over at SAE.org
k im going to bring this thread back.
im working on a 3.5 swap in the next couple of weeks, and im debating if i should use 3.0 heads or the 3.5, no matter what i use its getting an SSIM because i have one here. what would be the power differences between them because it looks like there are some small modifications that have to be made to bolt the 3.0 heads on the 3.5 block.
im working on a 3.5 swap in the next couple of weeks, and im debating if i should use 3.0 heads or the 3.5, no matter what i use its getting an SSIM because i have one here. what would be the power differences between them because it looks like there are some small modifications that have to be made to bolt the 3.0 heads on the 3.5 block.
Power differences would be large if you did some port matching on the 3.0 heads. The problem with that is, the 3.5 LIM and heads would take some work to get them to flow decent, as the port shape/sizes are different.
If you use the 3.0 heads and want to do the SSIM, you'll have to stick with the 3.5 LIM and shape/port the head and LIM some. Worth it? IMO, yes, if you have the ability to.
If you use the 3.0 heads and want to do the SSIM, you'll have to stick with the 3.5 LIM and shape/port the head and LIM some. Worth it? IMO, yes, if you have the ability to.
You could have some sort of adapted made. Personally, I would use the 3.5 LIM and 3.0 heads and get everything to match up as best you can.
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