Did Nissan Lie about VH45DE static compression?

[Ezekial]

I think they did

Some quick calcs

bore = 93 mm stroke = 82.7 mm Supposed static compression = 10.2:1

ThereforeIndividual Swept Cylinder Volume = 561.7735507 ccSwept clearance volume = 61.06234247 cc(Swept Volume / (10.2 - 1)

So roughly 61 cc is the combination of cylinder head volume + gasket volume + topland volume)

GASKET VOLUMEGasket diameter = 94 mm (Bore + 1 ... educated guess)gasket thickness = 1.5 mm

ThereforeGasket volume = 10.40966726 cc

TOPLAND VOLUME (of little importance in this calc)Topland width = 8 mm (educated guess) Piston diameter = 92.98 mm (Bore - 0.02 tolerated piston to bore clearance)Deck height = 0 mm

ThereforeTopland volume = 0.023370936 cc

SoCombustion chamber volume SHOULD = 50.62930428 cc(Swept volume - Gasket Volume - Topland Volume)

NOW FOR MY SPECSMy desired static compression = 9.0:1 (to run 20psi) My required clearance volume = 70.22169384 (Swept Volume / (9 - 1))

My Required New chamber volume 59.78865565(Provided i run standard head gaskets and pistons as above)

So existing should be near on 50 cc (10.2:1) and I need near on 60 cc to achieve 9.0:1 to run 20psi boost

I just measured the one of the combustion chambers in one of the heads on one of my engines (ex jap import engine from what appeared to be a dead stock Q45 half cut) ... and it took 60 cc of vinegar

So did i do a miss calculation? I dont think i did ...

By that, either nissan lied (perhaps so as not to give up the full extent of the gains the vvt was providing or some other unknown reason) ... OR ... my heads arent standard (highly unlikely that a japanese guy would lower the compression when it still had extractors on it and no hint of previous forced induction)

What do you's think??

[maxnix]

I just measured the one of the combustion chambers in one of the heads on one of my engines (ex jap import engine from what appeared to be a dead stock Q45 half cut) ... and it took 60 cc of vinegar

Acetic acid in Aluminum (Aluminium toyou guys)?

Not for long, I hope!

Might want to measure again with glycerine.

[Ezekial]

oh come on ... cooking vinegar

if it doesnt eat the carbon it sure as hell isnt going to eat the alloy head

[Q45tech]

I always assummed they were speaking of running compression: WOT at the torque peak rpm [adding in the tuning effect VE improvement].

Was the word "STATIC" ever used in print or just "compression ratio".

The warning for premium fuel requirement could mean acts like 10.2:1 in US?

What are the real running clearances at operating temperature and redline measured by bore [ring land wear/skuffing]?

[Ezekial]

you are right. it only says compression ratio. i thought it was common practise that this was reffering to static compression ratio?

[RobertsnewQ]

Yeah, industry standard is always static compression ratio. I've never heard of a manufacturer using anything but.

Also, rod stretch, etc., etc. should have NO effect, or at best minimal, and that effect would never be accounted for in mfg. data.

HOWEVER I have seen among American manufacturers a tendency to overestimate CR. This could be the same thing. It could also be a case of manufacturing tolerances, although that is a big range. Are the pistons flat-topped?

Also, did you measure a stock head gasket? Most OEM gaskets are quite thin, and that could be a factor.

And Brian - I HIGHLY doubt that 15% acetic acid will have an effect on the aluminum!

[Ezekial]

yes i measured it mate. 1.5 mm thick after being torqued down

yes pistons are flat tops

[RobertsnewQ]

Well then it seems like a case of optimistic reporting

It sure pings like an engine with high compression on California crap gas.

[Q45tech]

After all who cares about measured static compression since only under a very narrow set of conditions [plus very cold air temperature] does the intake charge every reach 100%.

To me manufacturers are saying at the worst case the CR ACTS like 10.2:1 so beware of the gasoline you use.Only at the torque peak rpm. At cruise < 20% of the volume is filled and at a lower than atmospheric pressure.

What is important is that all cylinders be equal to <1%.

Search and read about DCR:http://www.empirenet.com/pkelley2/DynamicCR.html

http://www.kb-silvolite.com/calc.php?action=comp

Back in the old days [before emissions and VVT and dual intake valves] US engines had higher real CR but the cams [overlap] were so radical that they blew out/back most of the charge.

Today a street engine cannot function with more than 8.2 DCR and real 93 octane fuel.

[Ezekial]

yes i know with the 10.2 static and the 68? ABDC closing inlets that dynamic is around 8 which you can say is 9 on a turbocharged vehicle ... 9.0:1 dynamic and 20psi = ALOT OF STRESS on components

Hence why i am chasing 9.0:1 static which drops dynamic to around 7 or 8.0 for turbocharged applications ... and drops boost from 20 to around 16.5psi dynamic = very safe