4 cylinder cars

[DarkSunrise]

Originally Posted by serialk11r

A really heavily tilted I4 would be pretty awesome.

The S2000 has a tilted I4, although not extremely so. It's CG height is around 18.7" I believe.

[malave7567]

Originally Posted by Calum

I thought that was due to strength issues and that they'd have to make braces that would basically circle the engine to prevent movement of the ends of the block.

I wouldn't be surprised if there was only a few pound difference between the pushrod v8 and the DOHC flat six. It would be interesting to find out for sure.

The C6 engine (LS3 at 415 lbs or so) is actually about 20-30 pounds lighter than the Carrera's non-turbo engine ("204 kg dry weight for Carrera and 230 kg for Turbo", http://www.rennteam.com/forum/page1.html?vs=3).

As for the 911 motor, I don't know. I don't know Porsches too well, but I used to own an LS3.

[AsianStyle]

Originally Posted by DarkSunrise

Keeping all else equal (suspension travel, roll center/suspension geometry, etc.), a straight 1-2" drop in COG will instantly make a better handling car. There's no question about that.

Yes, I fully agree with your statement. I don't think I wrote anything that goes against what you said.

I stated a straight drop (not accounting for geometry or other factors *hence black magic), does not equate to better handling. You can't just cut your springs and say instant better handling is what I meant.

The person I was responding to was talking about straight 1" - 2" drops that majority of people do mainly for looks, somehow equates to better handling.

Obviously lower COG car will be better, but I would sacrifice some of that for a better engine.

[DarkSunrise]

Originally Posted by AsianStyle

Yes, I fully agree with your statement. I don't think I wrote anything that goes against what you said.

I stated a straight drop (not accounting for geometry or other factors *hence black magic), does not equate to better handling. You can't just cut your springs and say instant better handling is what I meant.

The person I was responding to was talking about straight 1" - 2" drops that majority of people do mainly for looks, somehow equates to better handling.

Obviously lower COG car will be better, but I would sacrifice some of that for a better engine.

OK got it, that I agree with.

[strat61caster]

Originally Posted by ZDan

Some F1 designers dallied with flat engines a LONG time ago before deciding that V-engines were a better solution to get c.g. as low as possible.

My understanding was that the boxers were ditched due to packaging and aerodynamics. They can get a smaller narrower stiffer chassis with a V configuration than they can with a boxer. If aerodynamics are more regulated lets say endurance and GT racing and there's no benefit to a more compact engine the lower C.G. will win out.

See all of Porsche's racing success (continued to this day).

Compare the ridiculously successful 917 (with a flat engine) in 1970:


To the ridiculously successful Lotus 72 introduced the same year:



The packaging is entirely different and is the inherent drawback to boxer engines. F1 designers didn't ditch boxers because they could get similar c.g. out of a V, there were a multitude of factors which were more easily solved on the V's.

Edit: To be clear this is only a couple years after Ferrari tried a flat 12 in F1 (1965 Ferrari 1512), note the widest point of the car besides the tires:


And I guarantee you can feel half an inch of c.g. movement, I know when I was racing I was adjusting suspension in increments of 1/8th of an inch per corner and I knew exactly what I was doing and why I was doing it. Agreed that the flat engine isn't the magic bullet for lower c.g. better handling, I'm just being a pedantic asshole on the internet.


And I'll concede defeat on the emissions requirements, I don't care enough to work it out.

[Ganthrithor]

Originally Posted by strat61caster

My understanding was that the boxers were ditched due to packaging and aerodynamics. They can get a smaller narrower stiffer chassis with a V configuration than they can with a boxer.

Yeah, IIRC first they tried canting the flat engine at an angle to allow for bigger venturi tunnels, then they switched to a V engine to make more room because it was easier.

[ZDan]

Originally Posted by DarkSunrise

Yeah I dont think the boxer config will drop more than an inch, was just responding to his statement about 1-2" not being significant. that said, the 17.5" cg height for the c7 is a somewhat apples to oranges since it's got a dry sump.

C4 Corvette's c.g. height was reportedly 15". C6 Z06 was at 17.5". That also had a (semi) dry sump, but consider that the crank height was still the same as non-Z06s, so no benefit of lowering the engine for a dedicated dry-sump platform. In fact, with the oil tank situated pretty high up, probably no c.g. benefit whatsoever from its being dry-sump.

Originally Posted by DarkSunrise

The S2000 has a tilted I4, although not extremely so. It's CG height is around 18.7" I believe.

Maybe 12 degrees leaned over. Not a lot... Also, a lot of the S2000's frame structure is pretty high up.

Considering how low the car sits, 18.7" isn't terribly impressive! But the car's handling is pretty much sublime (aside from AP1 rear toe shenanigans!).

Originally Posted by strat61caster

My understanding was that the boxers were ditched due to packaging and aerodynamics.
Compare the ridiculously successful 917 (with a flat engine) in 1970:
To the ridiculously successful Lotus 72 introduced the same year:

The Lotus' V8 is mounted pretty damn low, I would bet its crankshaft is lower than the Porsche's.

Agree that aero and packaging were major considerations as well.

And I guarantee you can feel half an inch of c.g. movement, I know when I was racing I was adjusting suspension in increments of 1/8th of an inch per corner and I knew exactly what I was doing and why I was doing it.

On a formula race car, sure. On a production car like the FT86, nah. Besides, making 1/8" adjustments is changing suspension geometry which could easily have a greater effect on feel, you're not JUST changing c.g. height. I would bet money that in blind/blind testing, you wouldn't be able to reliably detect a 1/2" change in c.g. height on a stockish FT86, with NO other changes (difficult test to do!).

Agreed that the flat engine isn't the magic bullet for lower c.g. better handling, I'm just being a pedantic asshole on the internet.
.

Likewise! Bottoms up...

c.g. height is important, but I think that the FT86's is down to a LOT of attention to the design of the entire car and not just the flat engine.
Judging from pics of how the engine is situated, it looks to me like the engine and trans had to be mounted quite high in order to have room for the exhaust for the flat engine. I would still bet that a 45-degree laid-over I4 or a 90degree V4 would be able to have the crank much lower, and could have a similar c.g. height.

Vs. an upright inline-4, I'm betting 1/2" reduction in overall vehicle c.g. height. Which is certainly nothing to sneeze at.

[DarkSunrise]

Originally Posted by ZDan

C4 Corvette's c.g. height was reportedly 15". C6 Z06 was at 17.5". That also had a (semi) dry sump, but consider that the crank height was still the same as non-Z06s, so no benefit of lowering the engine for a dedicated dry-sump platform. In fact, with the oil tank situated pretty high up, probably no c.g. benefit whatsoever from its being dry-sump.

Maybe 12 degrees leaned over. Not a lot... Also, a lot of the S2000's frame structure is pretty high up.

Considering how low the car sits, 18.7" isn't terribly impressive! But the car's handling is pretty much sublime (aside from AP1 rear toe shenanigans!).

Ah didn't realize that Chevy doesn't lower the engine to take advantage of the dry sump option on the C7. Perhaps too much retooling for that. That makes the CG height on the C7 all the more impressive.

Also that's an interesting diagram of the x-bone frame on the S2000. Never realized it sat that high!

[strat61caster]

Originally Posted by ZDan

The Lotus' V8 is mounted pretty damn low, I would bet its crankshaft is lower than the Porsche's.

...

I would bet money that in blind/blind testing, you wouldn't be able to reliably detect a 1/2" change in c.g. height on a stockish FT86, with NO other changes (difficult test to do!).

Why do you focus on crankshaft height when talking about the effects of overall c.g. of the car? Sure the Lotus may have a lower crankshaft but I'll bet the Porsche drivetrain has a lower c.g. overall (engine to wheels).

I would absolutely take that bet.

[ZDan]

Originally Posted by strat61caster

Why do you focus on crankshaft height when talking about the effects of overall c.g. of the car?

I'm talking about how a flat configuration engine isn't necessarily the lowest-c.g. configuration as mounted in a car. The crank itself is pretty heavy, and the bearing supporting structures centered around it also have to be quite stiff and heavy as well. A flat engine will typically have its heads mounted lower than those on a V but the V engine will typically have its crank and supporting structures mounted lower.

It's not valid to assume that a flat engine as mounted in a car is going to have a lower c.g. A widish-angle V has greater potential for having a lower c.g. height.

Sure the Lotus may have a lower crankshaft but I'll bet the Porsche drivetrain has a lower c.g. overall (engine to wheels).

Possibly. I wouldn't be surprised if "optimal" angle strictly for c.g. height is somewhere in the 120-degree V range. For sure there is significant negation of the supposed low-c.g. benefits of a flat engine due to its crank usually having to be mounted significantly higher for exhaust manifold clearance.

I would absolutely take that bet.

Would have to be blind, of course! Repeated tests of the same car with enough ballast mounted either high or low to create a 1/2" change in overall c.g. height, with the driver unable to tell which configuration he's testing. Multiple tests in each configuration throughout the test.
Possible to do, but not exactly practical (and it would take some doing to *ensure* that the driver can't tell which configuration from visual cues or from "tells" from the crew).

You might do better than 50/50, but I doubt better than 65/35. Again, this is for a stock car, not a race car.

[strat61caster]

Originally Posted by ZDan

I'm talking about how a flat configuration engine isn't necessarily the lowest-c.g. configuration as mounted in a car.

It's not valid to assume that a flat engine as mounted in a car is going to have a lower c.g. A widish-angle V has greater potential for having a lower c.g. height.

I understand completely. The world is shades of gray and no matter what point I make you'll have fifty scenarios that contradict it. Cheers fellow wet blanket.


FYI the Lotus 72 I posted utilized a 90 degree 2.5L V8.

[fatoni]

i believe the cog thing is going to be clouded for a while since its impossible to look at the difference exclusive considering different cars are different. i think the bigger issue is that a v motor is built in a way that there is significantly less material and more strength. it kind of makes the cog debate less valuable when you think about it. i mean yeah, you might potentially be able to get a lower cog but if youre throwing another 100lbs into the equation, im sure a ballast bolted to the floor pan will lower the cog as well.

its also probably worth noting that many times, its not a theoretical perfection cars are built upon but a host of real life constraints. does that lotus use mac strust? defitely not ideal but if it allows you to fit more motor in a smaller car, there can be a feature that benefits the car more than the struts inhibit.