3.5 with 3.0 heads compression ratio?
08-03-2009, 03:12 PM
#1
3.5 with 3.0 heads compression ratio?
does anyone know what the exact compression ratio would be if you put 3.0 heads on a 3.5 block? i did some searching and i saw different answers and i want to know what would be the exact specs.
08-03-2009, 05:55 PM
#2
Its simple math, Ill see if I can find the CCs on the heads and the exact CC of the 3.5 engine.
vq35de=3498cc
3498cc/6 cyl=583 cyl volume
Combustion Chamber cc =46cc
583+46=629
629/46=13.673913043478260869565217391304:1
Now that's just static, I don't know what it'll be running. you need to consider volumetric efficiency +valve overlap and all that jazz.
the 46 CC is compliments of Google search and may be incorrect, If you find a more accurate CC plug it in and do the math.
See post #4
vq35de=3498cc
3498cc/6 cyl=583 cyl volume
Combustion Chamber cc =46cc
583+46=629
629/46=13.673913043478260869565217391304:1
Now that's just static, I don't know what it'll be running. you need to consider volumetric efficiency +valve overlap and all that jazz.
the 46 CC is compliments of Google search and may be incorrect, If you find a more accurate CC plug it in and do the math.
See post #4
Last edited by asand1; 08-03-2009 at 06:38 PM.
08-03-2009, 06:21 PM
#3
08-03-2009, 06:36 PM
#5
MOHFpro90, you may be dyslexic,
He wants to put 3.0 heads on a 3.5.
Why don't you use the 3.5 heads and manifold? I know that 3.0 heads will give you 11.5:1 of compression instead of 10.3:1 ...
...3.5 heads on a 3.0 block would give you 8.9:1 of compression instead of the stock 10.0:1.
He wants to put 3.0 heads on a 3.5.
Why don't you use the 3.5 heads and manifold? I know that 3.0 heads will give you 11.5:1 of compression instead of 10.3:1 ...
...3.5 heads on a 3.0 block would give you 8.9:1 of compression instead of the stock 10.0:1.
08-03-2009, 07:05 PM
#7
MOHFpro90, you may be dyslexic,
He wants to put 3.0 heads on a 3.5.
Why don't you use the 3.5 heads and manifold? I know that 3.0 heads will give you 11.5:1 of compression instead of 10.3:1 ...
...3.5 heads on a 3.0 block would give you 8.9:1 of compression instead of the stock 10.0:1.
He wants to put 3.0 heads on a 3.5.
Why don't you use the 3.5 heads and manifold? I know that 3.0 heads will give you 11.5:1 of compression instead of 10.3:1 ...
...3.5 heads on a 3.0 block would give you 8.9:1 of compression instead of the stock 10.0:1.
Im sorry, you are correct. I just realized that.That link does however give you the 3.5 block/3.0 heads Compression Ratio. You are correct on that 11.5:1 CR.
Yes.
08-04-2009, 01:27 PM
#9
here is one thread that said 12:1
http://forums.nicoclub.com/zerothread?id=284103
http://forums.nicoclub.com/zerothread?id=284103
08-04-2009, 03:07 PM
#10
Btw, that second link inlucded a 12:1 with different valves and ports.
08-05-2009, 09:02 AM
#13
08-05-2009, 10:59 AM
#14
08-05-2009, 11:09 AM
#15
As that thread talked about, there are the heads that are essentially the 3.5 heads with the 3.0 CR which would be perfect for n/a, great flow with high CR.
But the 3.5 heads themselves would be better for boost over the 3.0 heads on a 3.0 or 3.5 block.
08-05-2009, 02:11 PM
#16
Already doneExept I believe it has stock 3.5 cams.
There are no dynos that I know of, but the top end is significantly stronger than another 3.5 swaped 4th gen with a modded 350z intake manifold which dynoed a little over 250whp tunning with a vafc2.
08-05-2009, 03:11 PM
#18
edit: btw, you comin to the meet later this month?
Thats my answer.
08-05-2009, 06:03 PM
#19
08-05-2009, 06:16 PM
#20
08-05-2009, 09:05 PM
#21
I found out between 11.5.1 and 11.8.1 will be the compression ratio,going to start this project soon as an na setup of course although 3.5 heads flow well the high compression with stock 3.5 cams in 3.0 heads with 2000 vi some tuning is an excellent set up 3.5 flows around 301 cfm 3.0 280 cfm i have a blown de and a dek laying around heads should be pretty good.
08-05-2009, 09:41 PM
#22
I found out between 11.5.1 and 11.8.1 will be the compression ratio,going to start this project soon as an na setup of course although 3.5 heads flow well the high compression with stock 3.5 cams in 3.0 heads with 2000 vi some tuning is an excellent set up 3.5 flows around 301 cfm 3.0 280 cfm i have a blown de and a dek laying around heads should be pretty good.
Im interested in your setup though, I really would like to see what numbers you hit! Could compare to mine even though I am staying 3.0
08-07-2009, 01:43 AM
#23
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Join Date: Nov 2007
Location: North Coast NSW, Australia
Posts: 217
VQ30 combustion chamber volume + VQ35 bottom end = 12:1 compression.
http://www.nismo.co.jp/en/products/c...ne/vq35de.html
Has a nice picture of the combustion chamber differences too
12.7:1CR requires custom pistons and deeper valve notches if you want to run any decent lift or duration cam.
http://www.nismo.co.jp/en/products/c...ne/vq35de.html
Has a nice picture of the combustion chamber differences too
12.7:1CR requires custom pistons and deeper valve notches if you want to run any decent lift or duration cam.
08-07-2009, 07:52 AM
#24
VQ30 combustion chamber volume + VQ35 bottom end = 12:1 compression.
http://www.nismo.co.jp/en/products/c...ne/vq35de.html
Has a nice picture of the combustion chamber differences too
12.7:1CR requires custom pistons and deeper valve notches if you want to run any decent lift or duration cam.
http://www.nismo.co.jp/en/products/c...ne/vq35de.html
Has a nice picture of the combustion chamber differences too
12.7:1CR requires custom pistons and deeper valve notches if you want to run any decent lift or duration cam.
But thank you for proving me wrong.
08-07-2009, 09:21 AM
#26
Originally Posted by Nathan over @ my350z
Jeff will soon be able to confirm or refute what I have been saying about these heads.
But hears a little Math
Swept area + unswept area divided by unswept area = CR
Swept area: 3498cc devided 6 (cyls) = 583cc
Head CC 46cc + Head gasket area, aprox 5cc : total unswept area 51cc
583 + 51 = 634cc devided by 51 = 12.43 CR
But hears a little Math
Swept area + unswept area divided by unswept area = CR
Swept area: 3498cc devided 6 (cyls) = 583cc
Head CC 46cc + Head gasket area, aprox 5cc : total unswept area 51cc
583 + 51 = 634cc devided by 51 = 12.43 CR
Thread link for reference: http://my350z.com/forum/engine-and-d...d-m-_-m-2.html
08-07-2009, 12:21 PM
#27
Its simple math, Ill see if I can find the CCs on the heads and the exact CC of the 3.5 engine.
vq35de=3498cc
3498cc/6 cyl=583 cyl volume
Combustion Chamber cc =46cc
583+46=629
629/46=13.673913043478260869565217391304:1
Now that's just static, I don't know what it'll be running. you need to consider volumetric efficiency +valve overlap and all that jazz.
the 46 CC is compliments of Google search and may be incorrect, If you find a more accurate CC plug it in and do the math.
See post #4
vq35de=3498cc
3498cc/6 cyl=583 cyl volume
Combustion Chamber cc =46cc
583+46=629
629/46=13.673913043478260869565217391304:1
Now that's just static, I don't know what it'll be running. you need to consider volumetric efficiency +valve overlap and all that jazz.
the 46 CC is compliments of Google search and may be incorrect, If you find a more accurate CC plug it in and do the math.
See post #4
08-07-2009, 05:17 PM
#28
Senior Member
Join Date: Nov 2007
Location: North Coast NSW, Australia
Posts: 217
http://virtualengine2000.com/ProgramDownload.htm
Download a computer program that does all the calculations for compression ratio Also has a bunch of other nifty calculators for V.E, head flow, etc. Compression is 12:1 as head gasket volume is consistent between piston at TDC and BDC, so a lot of the formula's I see floating around above are actually wrong No deck clearance volume, no piston dish/dome volume etc
Download a computer program that does all the calculations for compression ratio
Also has a bunch of other nifty calculators for V.E, head flow, etc. Compression is 12:1 as head gasket volume is consistent between piston at TDC and BDC, so a lot of the formula's I see floating around above are actually wrong No deck clearance volume, no piston dish/dome volume etc
08-07-2009, 05:29 PM
#29
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Join Date: Nov 2007
Location: North Coast NSW, Australia
Posts: 217
08-07-2009, 08:48 PM
#30
12.7:1 on a properly prepared engine is possible, even with pump fuel. Timing would need to be retarded a little to keep combustion surface area temps down to remove hot spots but some mild cams would remove the chance of low rpm, high load pre-ignition which often occurs in these setups. Mild cams have less dynamic compression at these rpm ranges(seen by less low rpm vacuum etc) so if anything, a cammed 12+:1 CR engine is about as likely to pre-detonate as a stock engine IF the timing and fuel maps are sorted. It will need to run a little richer than stock to keep things cool but the power and torque gains will be worth it
08-09-2009, 05:33 PM
#32
Have to take the 3.5 back when we drained the fluid water/ antifreeze came out first from the oil pan plus the oil is milky so we wont be using this motor 
Last edited by 96sleepergle; 08-10-2009 at 09:14 AM.
08-09-2009, 06:02 PM
#33
If you're rebuilding the motor why is a blown HG a big deal? 
Just replace the bearings and check the crank/cylinders for any wear/corrosion. Also check the block for warpage. Ya know, the usual stuff.
Unless you were gonna just drop it in..?
Just replace the bearings and check the crank/cylinders for any wear/corrosion. Also check the block for warpage. Ya know, the usual stuff. Unless you were gonna just drop it in..?
Last edited by nismology; 08-10-2009 at 12:54 AM.
08-10-2009, 09:21 AM
#35
Found a crack on the intake manifold rear from a 2003 maxima thats enough for me to leave this motor alone will look for another 3.5 after my brother returns this one ,seems like a lot of these 3.5 have same issues if its not the rods (rod fatigue) or its a blown head gasket i didnt want to build the 3.5 just wanted to do the heads as we are discussing now but im currently rebuilding a dek motor got most of it torn down will take some photos
09-05-2009, 10:13 PM
#36
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Join Date: Nov 2007
Location: North Coast NSW, Australia
Posts: 217
On this graph, the left hand scale is load(bottom is highest load) and the rpm is obviously across the top.
Normally, the 28 to 40 range from 800rpm to 4000rpm is normally coloured green(using this graph as an example as laptop with the software has problems with bluetooth at the moment), which is where the ECU listens to the knock sensor for low rpm, high load knock. This is because air is moving slowly but under a high amount of effort which creates more heat/energy and makes it prone to pre-ignition. More duration with more compression(more compression also means more vacuum on the intake stroke) means that it can draw the air in over a longer time period and equalise pressure in the cylinder before the intake valve closes and the compression stroke occurs.
Hence, light igntion advance would allow the engine to be more knock friendly. Also, most engines with performance cams are not driven with low rpm high loads placed on them as we all know, when going up hills or overtaking, drop it back a gear or two and enjoy the high rpm rush that cams provide! How many people do you know with performance cams that chug up a hill in top gear?
09-06-2009, 01:26 AM
#37
I would think lugging a cammed engine wouldn't be a good idea for the same reasons that they idle funny; exhaust being sucked back into the combustion chamber at low engine speeds and diluting the a/f charge (same reason vacuum goes down with overlap increases) which also reduces the velocity of said charge. The engine simply wouldn't be happiest there, not that it would necessarily be dangerous because of knock. I'd actually venture to guess it'd be safer from knock due to the EGR effect. It's higher dynamic compression that would make it more knock-prone at low rpm/high load no? That can be dialed out with the appropriate intake cam. 
Last edited by nismology; 09-06-2009 at 03:45 AM.
09-06-2009, 04:09 AM
#38
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Join Date: Nov 2007
Location: North Coast NSW, Australia
Posts: 217
I was simplifying things a little but yes, the slow intake of air also allows EGR to occur which also introduces charge swirl etc and is another reason why excess fuel is added as some of the fuel vapour ends up in the ehxaust unburnt during valve overlap but since volumetric effiency(% of cylinder filled) is poor at these low engine speeds with a decent cam, the dynamic compression is similiar to stock in most circumstances.
Say 93% VE at 10.3:1CR on stock cam at 2000rpm would be a dynamic compression of 9.56 but a 85% VE at 12:1CR on a modified engine is around 10.2 and thus the fuel and timing maps can account for this 7% increase in dynamic compression
Say 93% VE at 10.3:1CR on stock cam at 2000rpm would be a dynamic compression of 9.56 but a 85% VE at 12:1CR on a modified engine is around 10.2 and thus the fuel and timing maps can account for this 7% increase in dynamic compression
09-06-2009, 06:48 AM
#39
I was simplifying things a little but yes, the slow intake of air also allows EGR to occur which also introduces charge swirl etc and is another reason why excess fuel is added as some of the fuel vapour ends up in the ehxaust unburnt during valve overlap but since volumetric effiency(% of cylinder filled) is poor at these low engine speeds with a decent cam, the dynamic compression is similiar to stock in most circumstances.
Say 93% VE at 10.3:1CR on stock cam at 2000rpm would be a dynamic compression of 9.56 but a 85% VE at 12:1CR on a modified engine is around 10.2 and thus the fuel and timing maps can account for this 7% increase in dynamic compression
). Since VE is a function of RPM you'd want the target dynamic compression to occur right where you'd want the engine to be happiest (power-wise).I guess the bottom line is that all else being equal a high compression engine can be as knock-prone during a high load/low RPM condition as a stock engine if the VE is low enough. Is that fair to say?
Or would there be some other factor at play?Edit: You have a PM.
Last edited by nismology; 09-06-2009 at 06:57 AM.
09-07-2009, 07:57 AM
#40
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Join Date: Nov 2007
Location: North Coast NSW, Australia
Posts: 217
Truth! And (regarding the unburnt fuel) if the overlap is excessive enough a cylinder will only fire every other power stroke since cylinder filling is so poor. Called "8-stroking" I believe?
Correct. However, with a turbo they call it anti-lag lol
Would also depend on the cam choice in that modified engine (I know you know...just for others). Since VE is a function of RPM you'd want the target dynamic compression to occur right where you'd want the engine to be happiest (power-wise).
Depends on if you want the engine to be peaky or have a wider power band. It is possible to have custom tuned length headers, with velocity stacked ITB's etc for a narrow 1000rpm power band where VE is over 110% OR have a nice 96% or higher VE over say 4000rpm etc. Theoretically, both engines would have similiar area under the torque curve.
I guess the bottom line is that all else being equal a high compression engine can be as knock-prone during a high load/low RPM condition as a stock engine if the VE is low enough. Is that fair to say? Or would there be some other factor at play?
There are other factors but the VQ is not prone to them in 99% of N/A cases. S/C or turbo can alter things a little though.
Edit: You have a PM.
Correct. However, with a turbo they call it anti-lag lol
Would also depend on the cam choice in that modified engine (I know you know...just for others
). Since VE is a function of RPM you'd want the target dynamic compression to occur right where you'd want the engine to be happiest (power-wise).Depends on if you want the engine to be peaky or have a wider power band. It is possible to have custom tuned length headers, with velocity stacked ITB's etc for a narrow 1000rpm power band where VE is over 110% OR have a nice 96% or higher VE over say 4000rpm etc. Theoretically, both engines would have similiar area under the torque curve.
I guess the bottom line is that all else being equal a high compression engine can be as knock-prone during a high load/low RPM condition as a stock engine if the VE is low enough. Is that fair to say?
Or would there be some other factor at play?There are other factors but the VQ is not prone to them in 99% of N/A cases. S/C or turbo can alter things a little though.
Edit: You have a PM.