lemmiwinkz

im curious about increasing the bore to about 98-100mm in a NA application. i noticed that the vq37vhr and the 380rs motor both have the same bore but larger stroke as the vq35de's. (vq37vhr = 95.5mm bore, 86mm stroke 380rs = 95.5mm stroke, 88.4mm stroke) why is this?? i would have thought they would have increased the bore and not the stroke. ive been looking around and cant find anyone that has done this in a NA application and was wondering why? with a 98mm bore piston and darton sleeves we could get to 3.68 Liters and with 100mm bore to 3.83 Liters. sorry if this has been asked before but i could not find any info.

lemmiwinkz

no one has any info? i just thought cars like our would be better suited for larger bores and less stroke but maybe im wrong. hope someone could chime in.

T_K

iTrader: (5)

I'd imagine it's virtually maxed out from an engineering standpoint.

The entire engine was probably engineered with specific clearances in mind. That includes shape and thickness of the coolant paths, along with the thickness of the metal in between. The amount of coolant flow, and the amount of heat it can effectively remove was more than likely designed around a specific cylinder wall geometry (thickness, height, etc) and material choice (x thickness aluminum + y thickness liner). Extending beyond the OEM bore, and replacing with a different material is a lot of changes(material differences: steel/iron vs aluminum, and process differences: forged vs cast). Different metals expand differently under heat, have different thermal capacities, and conduct/transfer heat at differing rates. Same metals processed differently, cast vs forged, experience similar differences.

Even if everything was a perfect fit, over time (repeated thermal expansion and contraction) theres just naturally a higher chance of problems, when compared to the OEM design, especially when you consider how much more time and resources the design engineers probably spent getting it "right." Even if the OEM design is prone to the same issues, for instance a cylinder lining of a different material, it might have been designed for a gradual failure, if not then definitely a failure after a known number of cycles.

Kwame

iTrader: (78)

Any car running a BC 4.15 Stroker Naturally Aspirated is running a 100mm Bore, so it has been done in a NA application. The issue with increasing the bore v.s. increasing the stroke is that increasing the bore decreases the thickness of material between the cylinders (a.k.a. the cylinder walls). The only way to reinforce the cylinder walls for strength is to run aftermarket sleeves. The problem with sleeves are that their aren't a whole lot of people who know how to properly install them.

lemmiwinkz

ya ive seen the stroker kits but was just wanting to increase bore and not stroke. i was kinda wondering if any one did this and had any significant gains. i know the guys at Momentum Performance have done this but both the cars ive seen this done to had their turbos in them. i was looking at the Darton sleeves but have not heard anything on the difficulty of installation, could you maybe expand on that more? however i have seen temperature increases with the darton sleeves, however the car i saw with them was a stroker and twin turbo so im not sure if it was just the strokers fault that was increasing temps. they also got it back down to regular temps iirc with a pathfinder mod, nismo thermostat, bigger radiator, and oil cooler.

thanks for any help
kyle

lemmiwinkz

does no one have any more thoughts on this? does anyone think that making the bore larger and leaveing the stroke alone is even a good idea or what this would do power wise?