posted on March 16, 2011 10:45
It's no secret that we take our sweet ass time developing our products so I've had some OE and aftermarket Nissan VR38DETT engine parts on my desk and in my shop bay for the past couple years. What stood out at first was the stock piston because it doesn't actually stand out at all. It doesn't look like anything that belongs in a high output twin turbo V6. It looks like a scaled up, ultra heavy version of a Nissan xxyyDE (xx=econobox Nissan engine designation, yy=displacement in liters) cast aluminum piston. The only unique features would be the oil cooling chamber underneath the dish of the piston and the hard anodized top ring groove. I'm guessing that Nissan made the VR38DETT piston "strong" by adding plenty of material wherever it was questionable. Adding weight is an effective way to make a piston strong in the case of OEM style fixed operating parameters (480bhp & 7000rpm) and a limited budget ($90k+ for 911 turbo performance). The flip side of course is that when you run the engine outside of those fixed parameters, whatever headroom that Nissan designed into the engine goes away real quick.
I always pay extra attention to pistons because I believe the piston is the most important part of the engine. Sure the sum of the parts is what makes a good engine, but far too many people shrug off how important a piston really is. The piston is usually the most fragile internal component of the bottom end and yet it takes the bulk of the forces created by combustion events. It is has to deal with thermal shock by being constantly massively heated and instantly cooled, accelerated and forced up and down by massive forces, has to transfer these forces to the wristpin and connecting rod all 720° of crank rotation, and all the while it has to be able to live in harmony with smaller components that are inserted into it that are made of unlike steel alloy materials such as wristpins, piston rings, and clips. Keep in mind that the piston also has to slide up and down at a gazillion meters per second against a cylinder bore also made of unlike material. You get the picture: a piston has a lot of things going on compared to the other internal components of an engine. Yet despite all of the critical roles a piston plays within an engine, people continue to take forged pistons for granted.
Way too many people think that just because they have forged pistons, their engine is king fucking kong. In fact, that couldn't be further from the truth. Forged pistons come in a variety of qualities just like exhausts, valves, or any other vehicle components do. A generic shelf piston made to fit your engine might be fine in some cases (e.g. dyno queen, occasional drag racing, to lengthen your forum signature, etc.), but if you plan on really using your engine in real life, you'll need a piston that is specifically designed for your engine that utilizes special materials, special coatings, special machine operations, optimized ring packs, optimized ring heights, optimized compression height and ratio, ultra strong lightweight wristpins, and most importantly a bespoke skirt profile that is designed specifically for your engine (i.e. a NASCAR cup car iron cylinder block skirt profile isn't going to benfit your aluminum, solid deck, sprayed liner VR38). This is where a Cosworth piston comes into the picture. Our shelf pistons come with all of these trick features and are specifically designed for your engine. How and why are we able to perfect pistons for your engine? Because we've been building engines for over 50 years, have some of the world's best engineers at our disposal, and because we actually build and test the engines that we design and manufacture pistons for. We do not have 3000 piston applications in our catalog shared by 10 generic forgings and 12 generic skirt profiles. All Cosworth pistons are machined from bespoke forgings (or in some cases billets). On top of all that, our experience with Nissan's V engines goes far beyond our Performance Parts business.
It really does.
Also extremely important is the quality of the machine work, assembly, and ancilliaries (ECU, injectors, pumps, etc.), and engine tuning. The more attention to detail, the better an engine will perform and the longer it will last. I used to see a lot of engines built with off the shelf generic forged pistons that suffered from "black death" even when owners claimed "I had less than 2000 miles and only had 20 dyno pulls". At the other extreme, I see Cosworth engines disassembled after 5000 race miles with virtually ZERO scuffing. Premature scuffing can be the fault of ignorant piston manufacturers, lazy machinists, inexperienced engine builders, inexperienced tuners or any combination of.
An example of "black death"
Here's the skirt wear of a Cosworth XFE ChampCar piston after 1500 race miles. The XFE generates 750bhp @ 11,750rpm. The picture doesn't show very clearly where the wear is, but you can see that there's very little skirt wear in total due to correct skirt and ring land profiles.
Here is a piston from a production based, long stroke (94mm) Cosworth YDX Formula Atlantic engine after 2000 race miles. The YDX is based on a Mazda MZR 2.3L and generates 300bhp at 8,500 rpm. No matter what type of engine, Cosworth gets it right.
Wednesday, March 16, 2011 3:17 PM
Very trick stuff, I like when companies sit back and perfect things instead of rushing to market to get the easy sales.
but don't give SAE credit for 4340 :-)
Wednesday, March 16, 2011 3:38 PM
Eric, excellent, detailed article! I think you convinced me with your arguement for the piston being the most important part of the engine. I had to digest it because I kept thinking about most true catastrophic, block is truely toast failures i've seen, involved connecting rods. However, the amount of force exacted on a piston every combustion cycle over the life of the piston is truely amazing as you pointed out.
I'd love to hear a little bit more about how Cosworth does its parts reliabilty testing before bringing products to market. I've always loved the glimpses of information that OEs and High End companies like Cosworth give on how they R&D products. Truely Fascinating!
I'm still debating the GTR best bank for your buck statement. I keep thinking an Evo could be purchased and built to reliably beat out the GTR, Porsche 911 turbo, etc. For less than the cost of a GTR
Wednesday, March 16, 2011 3:41 PM
"Bang for your buck", stupid qwerty keypads!
Wednesday, March 16, 2011 3:56 PM
Eric, thanks a lot for sharing. Really great stuff. Love the details !!!
However, all the reciprocal mass reduction is worth it only when a good dyno tune is done :)
Take your VQ38 with Cosworth bottom end to Mr. Joe Smooch (a SPE online) and let him tune it on the dyno, and I guarantee you that eventually the engine will blow eventually. It might take a little longer than stock, but it will nontheless.
Wednesday, March 16, 2011 4:05 PM
Great article Eric. It's amazing how generic the OEM GT-R components look.
What kind of bearing clearances did the OEM spec call for? And how much were you guys able to tighten that up using your pistons/rods (assuming you are using non-OEM bearings)?
Wednesday, March 16, 2011 4:07 PM
Awesome Read Eric! It makes me wish I had a GT-R to tear down and rebuild with Cosworth components.
Wednesday, March 16, 2011 4:59 PM
very interesting article and thanks to cosworth for their engineering skills to produce these components.
Wednesday, March 16, 2011 7:21 PM
I'm curious, how does Cobb's GTR make 800 hp and not blow the motor? Does it boil down to using E85 instead of regular gas or what? In MotoIQ's article about a year ago on the Cobb Time Attack GTR, they mentioned the engine made almost 800 hp and was internally stock.
Neat look at pistons, I never knew there were so many differences between forged pistons. I just thought forged was forged and that was it. You learn something every minute, especially here.
Wednesday, March 16, 2011 9:25 PM
As far as I know the COBB GT-R blew three engine last season.
Wednesday, March 16, 2011 9:51 PM
@8695Beaters, there's a fatigue life curve. The less you stres something, the longer it'll last. The more you stress it, the shorter the life. Same difference as how long you'll last bench pressing 95lbs vs. 185lbs. Maybe you can get 185lbs five reps before failure, but you can get 95lbs fifty reps. Well, the stock bottom end are like being able to get five reps at 185lbs, and the Cosworth bottom end can get fifty reps of 185lbs.
Wednesday, March 16, 2011 10:27 PM
Skull: SAE uses the "4340" designation to define a grade of chrome moly. JIS would be SNCM 8 and DIN would be 1.6565 for the same alloy. I wasn't giving SAE any credit.
Bruce: I'll cover more of the development process in the future. I wish I was in the marketing department so I could write this crap at work, but being the dedicated employee I am, I write this crap at home. As for the EVO beating a GT-R or Porsche turbo, I believe the EVO definitely has a chance in raw performance, but I tell you what: you're not going to be able to pick up a hot chick after the track in an EVO that goes faster than a seriously built GT-R or Porsche. The EVO is missing the baller appeal, comfort, two cylinders, and a wide power band. I guess it just depends on what you want in a car.
M-P: I believe the larger side of the VR38 rod bearing oil clearance spec is .0028" which huge relative to modern Japanese production engines. Our clearance spec is .0022-26" I believe, but I need to verify that.
Beaters: All pistons are not created equal. I think that will be a title of a future write up.
Glad you guys like the write up on the components. I'll try to write more in the future.
Wednesday, March 16, 2011 10:35 PM
A little deonation damage on the VDX piston?
Wednesday, March 16, 2011 10:45 PM
Na, that's poor focus from the Motorola Droid camera at the perimeter of the focal area plus some carbon build up.
Thursday, March 17, 2011 6:05 AM
Yes I understand about stress life and so on (2nd year Mech-E), but I point you here: http://www.motoiq.com/magazine_articles/articletype/articleview/articleid/1523/locked-and-loaded-cobb-tunings-time-attack-nissan-r35-gtr.aspx Is there a mistake in the article or what?
Thursday, March 17, 2011 7:06 AM
Beaters: What Eric, spdracerut, and JDMized are pointing out is that yes, the Cobb GT-R is making 800hp on stock internals, but that it will not (and apparently has not if JDMized is correct) last very long when compared to a well engineered aftermarket forged set of internals. So, I don't think there is a mistake in the article...it's just pointing out what was known so far about the car (which was that the engine apparently had lasted 10 races at that point and seemed reliable).
Also, E85 shouldn't make much of a difference in how much power the motor can handle. Forces on a piston/rod are forces on a piston/rod. E85 just has the added benefit of being less prone to detonation. Less chance of detonation means less chance of huge spikes in cylinder pressures and forces on the piston/rod that will lead to catastrophic failure. This then leads to more boost and power because you aren't detonating.
Thursday, March 17, 2011 7:21 AM
Beaters, that was a LONG time ago. Race cars, unless a spec series, are always in a continous state of development. At that point in time, the COBB GTR had been doing okay. As they were some of the first to mod the hell out of a GTR and race it, and with it being a relatively new car, they were probably taking it relatively easy on the powertrain at the begining as there wasn't much data out there on how strong things were (engine, tranny, diffs, etc). At the point the article was written, maybe they had just turned up the power. At the end of last year, they had pretty much destroyed part of the drivetrain; can't remember if it was one of the diffs or transfer case. Looking at F1 and MotoGP, they are always trying new aero and go-fast parts pretty much every race; the cars and bikes at the end of the season are significantly different than at the start.
Thursday, March 17, 2011 9:12 AM
I have a confession...
The picture of the underside of the piston and tooling marks get's me aroused.
I have a serious problem.
I'm so ashamed.
Thursday, March 17, 2011 10:47 AM
Dude, I totally understand what you mean....haha
I definitely looks like a bio-mechanical vagina from Predator or some shit like that...lol
On a more serious note:
Eric (or Mike) do you guys think you could cover the pros and cons of different alloys usage for piston's application?
I found this article online:
I don't know how accurate it is. With more and more SPE browsing the net these days, I take everything with a grain of salt.
Thursday, March 17, 2011 10:50 AM
@Aaron LeBeau: I have a GT-R putting about 540 awhp (Mustang) to the ground on the stock internals. I would dread the cost of dropping the engine to have it upgraded with these babies!
Thursday, March 17, 2011 11:01 AM
This is what Steve @ COBB So-cal said:
"We lost 1 engine due to con rod failure with stock parts.
Then we installed forged pistons and rods with the stock crank. We had a loss of oil pressure due to debris in an oil galley that forced us to rebuild the engine to prevent failure. The engine was running fine so we used all the same parts, but with new bearings.
All of the running in time attack was on 800 WHP."
The Cobb guys (Jon and Tim) know their tuning and the COBB hardware is obviously proven so I think it's safe to say the stock parts suck at 800whp.
Alex: sure, one of these days I'll get to that unless Mike gets to it first.
Brent: If you plan on stepping up the power, it would be a whole lot cheaper to build the engine first with the parts you see here rather than wait for a failure because they you would have to pay for a block, perhaps a cylinder head, and other parts due to the failure. 401k's are over rated anyway!
Thursday, March 17, 2011 12:00 PM
I love the radial truss design on the rod ends. That's a really great touch, and a good transfer of race engine design into performance aftermarket products.
Thursday, March 17, 2011 1:33 PM
Eric we need to get you a better camera.
The Cobb car ran ok stock for a long time, about half a season as I recall, but blew up shortly after the article was written.
Still a half season of racing is pretty good for a stock engine.
I can't wait till Cosworth comes out with 4 liter stuff, another reason for me to get a GTR.
Thursday, March 17, 2011 3:13 PM
Eric...i was elluding to the fact that SAE didn't develop 4340 just uses the common nomenclature most likely originally adopted by ASM, or ASTM or even the GM or old BMS specs...but that's neither here nor there...
Those are some hefty bearing clearances...but are a little out of perspective without knowing the bearings working diameter, could you tell us what that might be, I usually look at bearing clearances as (.000X/in diameter)
there are some truly healthy GTR's out there,
I'm interested to see what you guys shall do about the gear box...because those internals deserve a pair of gt3071r's and 1100hp, and im not sure how happy the transaxle and diffs are going to be about that big a herd of ponies
Thursday, March 17, 2011 4:01 PM
thanks for your time and efforts Eric.
Interesting to note Nissan's lack of "performance parts" in such an awesome car. Imagine if they would've done some trick shit with the engine like Porsche or Ferrari. This really shows the engineering prowess Nissan possess if anything.
Basically they told Porsche with their "911 performance" to eat shit because their car is way bigger and heavier and still whoops it's ass with mediocre engine parts.
Friday, March 18, 2011 5:26 AM
Yet another great article. Thanks again, Eric.
Monday, March 21, 2011 1:46 PM
How much of the piston/pin weight savings was due to the smaller pin?
Have you had issues with the shorter skirt's increased rocking couple loads?
The COBB GTR blew up in a blaze of glory (literaly) in it's very first race as a Modified class car during Redline's season opener last year. I know cuz I was right behind it in our S2000 when it happened.... I believe the fugitive rod made contact with the starter motor which caused the ensuing oil fire. ;-)
Monday, March 21, 2011 1:50 PM
I would also love to read a MotoIQ article someday outlining the pros and cons of proper "I" and "H" beam rods. So many good/bad opinions of each design, inquireing minds want to know..... :-)
Monday, March 21, 2011 9:57 PM
Thanks, nicely done.
Wednesday, March 23, 2011 9:16 AM
JC: The Cosworth pin is 11 grams lighter than factory pin, but it is made of a different alloy so its not really a direct comparison. But there is an overall weight savings with the Cosworth pin despite being made of a superior alloy.
This is not a full race slipper skirt design so we have not had skirt issues. A full race slipper skirt piston (like the XFE piston you see above or one of our MX pistons) would have accelerated wear on a street car engine that saw a lot of warm up/cool down cycles.
One of these days Mike or I will write an I vs H beam rod story. The problem is that I do not have any access to I beam FEA data because Cosworth doesn't really use I beams. In fact, I can't think of an I beam rod being used in a real deal race engine that I've ever seen. I've only really seen them in American street and drag engines.
MotoIQ Proudly Presents Our Partners: