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Roar test #1: Cadillac dominates as Alonso’s car sets top six pace


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https://www.motorsport.com/imsa/news/roar-test-1-cadillac-dominates-as-alonsos-car-laps-in-top-six-993052/

 

 

Joao Barbosa set the pace driving the #5 Auto Express Cadillac DPi, posting a best time of 1m37.266s early in the session. That put him 0.262s faster than the Wayne Taylor Racing Cadillac of Renger van der Zande.

Bruce

2016 Cadillac ATS-V gray/black

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Apparently they are still running the 6.2 liter V8.  Any news on the 4.5 liter V8?

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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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I finally did find something on the 5.5 liter.  Yes, all the DPi Cadillacs are running the 5.5 liter engine now.  The principal difference between it and the 6.2 liter is the stroke, 52 mm, down 10 mm from the older engine.

The simplest way to do this is to use a new crankshaft, 5 mm longer rods, and the same deck height.  New cam, intake and exhaust tuning, and port shaping in the heads, with a higher red line, can keep the horsepower about the same and spread the torque curve over 13% wider RPM range, making the car easier to drive and even harder to beat.

Note that maximum theoretical breathing is proportional to RPM, but engine stresses and vibrations are proportional to the square of the RPM.  The pistons, rods, and crankshaft must be about 27% stronger to provide the same reliability margins with 13% higher operating RPM.

The amazing thing about this engine, like the previous versions, is how they get the horseower with an OHV engine and not a DOHC configuration.  With OHV, not only do you have vibration modes in spring-loaded roller tappets, pushrods, and dual valve springs, but there are mechanical restrictions on port angles and valve/port placement that are relieved with a DOHC arrangement.  Then, you have the interesting complexity of VVC with a single camshaft axis in the lifter valley as opposed to separate intake and exhaust camshafts.  But you are relived of the multiple issues of three cam chains and an idler sprocket.

By using longer rods and a shorter stroke, piston stresses and higher order engine vibration is less than it would be if you dropped the deck height and shortened the rods by scaling the whole engine down.  And, you get to keep the intake geometry; the old intakes will fit, and you can simply re-tune for higher RPM.  The penalty is, of course, weight.  This could be an exceptionally smooth engine for its output.

Whenever you re-cast the crank and cams, you have a clean sheet of paper on going to single plane crankshaft and the firing order.  Going to a single-plane crankshaft drastically reduces the rotating mass but there is a huge increase in second-order vibration, which is canceled in a dual-plane crankshaft V8; this is the reason that Cadillac went to a dual-plane crank V8 for 1924 and no one has produced a single-plane crank V8 for road and street use since then.  The huge crank support strength that is necessary to contain secondary vibrations in a dual plane crank V8 is not the same as that required to hold together a single-plane crank V8, but I suppose that a new design would not be necessary.  The motor and transmission supports would be quite different, though.  For racing only?  I would consider a single-plane crank.  Put rubber biscuits in the driver's seat and steering linkage.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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the funny thing about the 5.5L to me is we had heard it was coming for 3-4 years; so long that people began to think it was misdirection.  So it going into the race cars finally is interesting.  Now if corvette gets this as a base engine (with TT as optional) with more power than 460 hp LT1 6.2L that will be fun.

Bruce

2016 Cadillac ATS-V gray/black

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Any engine revision for the Corvette will likely include a horsepower increase.  To do that you will need a higher redline and improved breathing, which requires revamping the intake, ports and valves, and exhaust designs.  The ECM, cam, fuel injection intake rams, heads, valves, and the exhaust back to the mufflers will not be interchangeable with those of the 6.2 liter engines.

If they keep the deck height, the engine weight will be about the same or a little less due to weight savings in the crankshaft.  A vibration-free, free-breathing, high-revving engine with a level torque curve can be a real treat to drive with either manual or automatic transmission.

The all-aluminum new LT 6.2 liter is a very light engine, only a couple of pounds heavier than the Northstar 4.6 liter, so the weight of the 5.5 liter shouldn't be out of line for its size.  And, any difference in weight will not drive chassis tuning is needed for the new engines.  Changes in the engine characteristics, of course, will drive chassis tuning, gearing, and driving techniques, all of which seem to have survived the initial learning curve in great style.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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  • 2 weeks later...

The new 5.5-litre normally-aspirated engine in Cadillac's DPi contender has had its restrictors reduced in diameter by 0.6mm to 31.6mm after dominating the official pre-race test at Daytona earlier this month.

Read more: https://www.motorsport.com/imsa/news/cadillac-performance-pegged-for-daytona-24-hours-997297/

Bruce

2016 Cadillac ATS-V gray/black

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So, they will use performance measurements to determine restrictor and rev limiter specs so that nobody dominates.

Run the tests on bias-ply mud tires.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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