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VR41DETT build

General Engine Building Discussion

Talk about engine building here. New products, tricky questions or showcase your work - If it's engine building related it's welcome here.


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Hi guys!

I'm new here at the forum and also a novice to engine building, so before starting my build I decided to learn everything I can form the HP Academy engine building course. I'm living in Shanghai, China, where I'm working, but my car (and engine) is in Helsinki in my native country of Finland where I visit every now and then. I've been building my R35 bit by bit since I got it in 2010, but haven't touched the engine myself so far. I had a built engine already, but unfortunately melt a piston and decided to DIY next iteration of the engine. The car was dynoed 985hp on E85 the summer before and I did some more upgrades this summer to get rid of some remaining possible bottlenecks. I was at the limit of my ASNU 1650 injectors and forgot to turn the boost down before my first pull at an airfield event. Apparently I also had some lambda related problem as ECU never saw the damage coming and Ecutek safety trips didn't kick in. My theory is that things got too hot because of lean mixture (which ECU didn't see because lambda was faulty), which caused spark plug to glow, which caused knock, so excess heat and knocking destroyed the piston: hole in the middle. I was also was stupid enough to forget to start logging before so no data to investigate. Live and learn...

So, with this bad luck I had (actually my stupidity to not take it easy and check logs first) I got the chance to finally learn to build a VR38. I'm a mechanical engineer by my background, so I'm familiar with all the principles but haven't built an engine myself so far. Of course, when you break something it's chance for some upgrades as well, so I decided to make it a 4.1L stroker this time. With EFR6758 turbos this should be a super quick spooling set-up that will make over 1000hp. I want to build the engine with the high quality parts and take great care in build process so that I can have a solid and reliable powerplant that can take all the beating I will give it.

Spec for the new engine is:

-Brand new VR38 block

-Sonny Bryant 4.1L billet stroker crank

-Mahle pistons, 9:1 compression ratio

-Carrillo H-beam rods with CARR bolts

-ARP main and head studs

-King main and thrust bearings

-Cosworth 0.8mm head gasket

My stroker kit came from ETS as a fully balanced set.

New set-up will also have 12 x 1050cc injectors to make sure I have adequate fueling and won't have a risk of going lean again. 12 injectors will also make drivability better compared to using big injectors, I want to have stock drivability but 1000hp on tap when I feel like pushing it.

I'm looking for recommendations, tips, tricks etc. from you more experienced guys, I want to do the build once and do it right the first time. The thing I've been wondering is when building from all new parts, should I measure all bearing clearances or would plastigauge be good enough to check that tolerances are what they should be? Wouldn't do harm to do both, but I don't have a micrometer and bore gauge myself, so I'd have to find someone I could borrow them from as I don't really want to spend money on tolls that I won't be using that often.

Sorry to hear about your engine failure. When you see a hole in the middle of a piston like that it is almost always the result of pre ignition just FYI.

It looks like you have a pretty complete set of high end parts for the rebuild that shouldn't be a problem given your power aims. As a rule I always measure everything as assumption seldom works in our favour. Some of these clearances will be checked and adjusted by the machine shop - Particularly for aspects such as the piston to bore clearance. My preference is to use a micrometer and bore gauge to check oil clearances however if you use it properly, plastigauge can also offer good results.

I decided to get myself a set of measuring tools as they are pretty inexpensive in China. Quality is not at Mitutoyo level, but should be good enough as we are measuring differences anyway. Better to measure everything as Andre said.

Litchfield had an interesting article about their VR38 engine building process: http://www.litchfieldmotors.com/blog/a-detailed-look-at-a-gt-r-engine-build

I had torque plates made by my friend who does cnc machining, will get the bores honed by a machine shop with ARP studs torqued down. My block is 222222 Nissan spec which translates to 95.51mm bore size, so honing to this factory size with torque plates would make bore to piston clearance just on spec (0.08-0.10mm) with my Mahle pistons that measure 95.43mm. Will of course take pistons to the shop as well so they can measure everything with their tools and better skills.

I've been wondering about ring gaps, there's a different spec for blown gas and blown alcohol engines. Mine will be flex fuel and also driven and tracked in areas where I can't access E85, so I suppose I should set the gaps according to regular gas as rings will expand more than when using E85.

Main and big end bearing clearances should be 0.05-0.06mm, does that seem ok? I will be using Millers Nanodrive CFS 10W60, which worked well with my previous set up.

Also thinking about going a degree (or two?) colder in plugs. OEMs are 8's (NGK DILKAR8A8) and I've been hearing good things about NGK Racing plugs, considering getting 9's (NGK R2558E-9) for my new engine.

Soon I can start assembling my short block!

If you're developing a flex fuel system then you are best to base aspects such as your ring gaps around pump gas, however there are a few caveats to consider. For example if you're expecting to primarily be running on E85 when the power is high and really only relying on the pump gas tune to get around when you can't fill with E85 then you could focus your spec more towards E85 and gap your rings a little tighter. In reality it's probably a coin toss though and not something that I'd worry about over thinking. A little additional ring gap is always a safer option than going too tight.

Your clearances are about where I'd be aiming for that particular engine.

A question regarding ARP head studs... a friend says that someone told him you shouldn't tighten ARP studs to recommended torque because it's too tight and will cause the block to deform. I otherwise think that ARP engineers know better that some 'backyard engineer', and in high power applications you should have all the clamping force you can get. So my approach would be to tighten to ARP specifications (156Nm) with stress plates, get block honed and torque heads to ARP specs. I wouldn't use ARP studs without honing though.

What's your experience on this, what would you recommend?

I'd 100% recommend the ARP specifications for torque. Your friend is right however that these can distort the block - Particularly with an alloy block, but that is why we use a torque plate during the boring and honing process.