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Re: Myth: Modern engines have tighter clearances?
[Re: 360view]
#177486
12/30/08 12:30 PM
12/30/08 12:30 PM
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Anonymous
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Anonymous
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A few more numbers that I happen to have access to right here.
GM 6.0, 2007, used in 1 ton van. 300hp, 360 ft-lb
rods.0008-.0021
mains .0008-.0025
piston to bore .0009clearance to .0012 interference (coated skirts)
This is from the factory service manual
Look like pretty normal V8 specs to me, definitely not tighter.
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Re: Myth: Modern engines have tighter clearances?
[Re: ZIPPY]
#177487
12/30/08 01:21 PM
12/30/08 01:21 PM
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Joined: Mar 2006
Posts: 9,910
Eighty Four, PA
B G Racing
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master
Joined: Mar 2006
Posts: 9,910
Eighty Four, PA
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Quote:
I guess my point was, just because machining + or - tolerances are closer, and finishes are better and smoother, really does not mean the clearances are any tighter. They aren't, at least not in the case of
that 5.7.
Relative to another comment above...at one time in the '90s it was fine to run the 2.0 Neon engine on 10w30 oil. If you took your car to the dealer, odds are good that's what they would pour in. Come 2005, and you absolutely can not run anything but 5w20 per the pwner's manual. Look up the clearances for both engines, and guess what...they have not changed over time either. I'd think if there were going to be any big changes they would show up in little 4 cylinder engines first, but even that doesn't seem to be true.
It's just something to discuss and throw around, I'm not trying to prove anything but I think the myth is funny. Tolerances may be tighter, I don't doubt that, but the desired end result is pretty much the same as always.
At the OEM level, it's not uncommon to scrap a few hundred engine blocks because the bores are oversize by like two microns. MICRONS. Pieces that could have went 150,000 miles without an issue. Sounds a bit wasteful just for the sake of maintaining tight tolerances, doesn't it?
 I did some research on the big commercial and industrial engines,and did find the clearences to be tighter and the allowable runout of componants held to near perfect tolerances.Most tolarences were held to .0000 on runout and clearences usually held to
.000 were .0008 to .0005 on a Volvo engine. 
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Re: Myth: Modern engines have tighter clearances?
#177488
12/30/08 02:38 PM
12/30/08 02:38 PM
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Joined: Jan 2004
Posts: 27,347
Today? Who Knows?
1_WILD_RT
Management Trainee
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Management Trainee
Joined: Jan 2004
Posts: 27,347
Today? Who Knows?
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Quote:
A few more numbers that I happen to have access to right here.
GM 6.0, 2007, used in 1 ton van. 300hp, 360 ft-lb
rods.0008-.0021
mains .0008-.0025
piston to bore .0009clearance to .0012 interference ( coated skirts)
This is from the factory service manual
Look like pretty normal V8 specs to me, definitely not tighter.
Go back & re-read the high lighted spec...Pay particular attention to the word interference... I don't recall any muscle car vintage engines with an interferenca fit spec for thew pistons..But it's been the norm in modern enginges since the mid 90's... 
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Re: Myth: Modern engines have tighter clearances?
[Re: 1_WILD_RT]
#177489
12/30/08 05:05 PM
12/30/08 05:05 PM
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Anonymous
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Anonymous
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Note what is in parenthesis--coated skirts.
The coating is using up the clearance and into interference, and the extra wears of almost immediately. I think they even had a separate spec for clearance once pistons had been run.
You could never run an uncoated piston with interference, it would gall instantly.
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Re: Myth: Modern engines have tighter clearances?
[Re: 1_WILD_RT]
#177492
12/30/08 07:12 PM
12/30/08 07:12 PM
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Joined: Jan 2003
Posts: 9,872
Weddington, N.C.
Streetwize
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master
Joined: Jan 2003
Posts: 9,872
Weddington, N.C.
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I'm not sure blueprint clearances are tighter but generally operating (at temperature) clearences are. So in that respect I'd be a little surprised if build tolerences are that much tighter. If you notice a lot of newer motors are pretty noisy (the GM LS motors especially) when they're cold. Plus add the fact that most motors run 5W and some even 0W oils so somethings got to be up. Most motors these days run at 192 degrees and some over 200. The main benefit of modern motors is the fuel injection which minimizes fuel wash and greatly enhance bore and ring longevity. I suspect coatings are more for protecting internal parts under extreme (hot or cold) start conditions than any real MPG savings, the gains at cruising speeds would be relatively infintesimal(sp?) compared to the bang for the buck gains of optimizing fuel mapping at cruising speeds
Last edited by Streetwize; 12/30/08 07:32 PM.
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Also they were working toward having main bearing fasteners & head bolts all extended to the central mass area of the engine rather than just through the main caps/cylinder heads..Main Bearing Girdles are also common on newer engines...