I need a bit of clarification on a few things.

If you increase the bore of a motor, but not the stroke that obviously increases displacement. Does increasing bore and leaving the stroke alone help the engine have a higher redline?

I know high stroke motors have difficulty revving high. So am I right in assuming a motor with a very high bore, say 90mm and a stroke of 60mm will have a much higher redline than say an engine with 75mm and stroke of 60mm?

 

That's generally the case, but really it comes down how strong the internals are. A longer stroke means that the piston and con rods have to accelerate and decelerate at a faster rate for a given rpm, and therefore generally is designed for a lower rpm environment.

 

Just because you have a higher bore, doesn't mean you can have a higher redline. The RPM redline is more dependant on the engine internals. A good bore stroke ratio is also important. I think they are finding slightly oversquare to be the best. But a good example of a high revving undersquare engine is the E46 M3's engine, redlining at 8000rpm with a bore of 87.0mm and a stroke of 91.0mm. In the case of the G's redline, it is probably some engine internals and the designed powerband not being oriented towards high revving power. If you wanted to make power at higher rpms, you would have to change some of the internals and probably a custom camshaft designed to make power at higher rpms. Bore alone will do nothing for your redline, maybe even lowering it if the balance of the engine is upset enough.

 

so you are saying the vq (I mean the 287 non revup ...) can be made into a true high rev motor (like with a 8k rpm redline) by changing into better internals (that can restand the increased stress at higher rpm) and utilizing camshafts that make power at higher rpm?

coz I know there is one fellow on my350z.com that has made his 287hp VQ into a 8k rpm monster by doing all the internals + camshaft and valve springs... Yet, I dunno how efficient can that be tho

 

Generally speaking, the valvetrain is the limiting factor for RPM capability. The strength of the pistons, rods, and bottom end is not so much for RPM enhancement as for surviving high compression/combustion chamber pressures. The stock bottom end on a VQ is probably good to 7500-8000 as long as you dont increase the compression or go FI.

So yes, a replacement of the cams and all of the associated hardware will be required to get up there. But even that alone will not help too much if you dont have the heads and intake plenum tuned to work with them. Then you have to reflash the ECU or have some form of fuel/ignition, valve timing management because the stock maps have no idea what to do up there.

Anytime you start talking about cams on a VQ, it can get expensive fast. The parts/labor to do heads, valves, and cams will probably run $4000. You might as well pull the motor and just go the whole way and build it for FI.

 

To achieve high redline, there are other issues too such as bearings and balanced parts. The higher the design redline, the closer the tolerances have to be.

If you want a true high-reving motor, you will probably get the best results (reliability) with an engine designed from the ground up for the rpm you are looking for. Ultimately, this is a project for a shop that has a lot of experience with racing engines. Take a look at the engine packages offered by SGP Racing in Houston as only one possible example.

http://sgpracing-store.stores.yahoo.net/sgpravqmo.html

Discuss your overall goals with folk like this who build engines for a living. You may be able to find what you are looking for with alternate parameters for less money.

 

If money were no object, what kind of pistons / rods should one buy for the VQ? I'm looking at a turbocharged application here..

 

The sgp link above is all you need. 8.5:1 pistons with forged/balanced pauter rods is good up to 700+ HP. Any time you go over 300 RWHP, don't forget you will be needing a clutch or a high stall converter/valve body upgrade too.

 

the VQ bottom end is good up until about 8K for a red line...but you would need to build the heads up...i know cosworth has heads that are good up to about 10,500rpm...i know not many of us will be up that high cause we arent looking to rebuild heads every 10k miles....but if i were to have those heads i would bring it up to 9K which is Honda status as far as revs go....if your going up in high revs like 9K you def need to change rods and pistons....i know JUN makes a nice little stroker kit for our cars which bring it up to 3.8 if you want more displacement but you can rev high with it also...theres also a 4.1 stroker kits for our cars but i wouldnt use that for a high reving NA motor....also if your gonna change rods and pistons and still use a stock crank make sure you get it balanced and blueprinted and micro polished for those high RPM's and a good set of bearings...while you got the motor apart doesnt hurt to put in ARP head and main studs and a good headgasket...do it right the first time lol