The Technical Questions Thread

[cmcpokey]

What exactly happens when you grenade a transmission?

thats a bit of a generic term, but it pretty much means that while driving, a gear will break, thus sending bits of metal through the rest of the gears. these gears now break, and the process continues, and you are left with a container of metal fragments. or sometimes it is so violent it busts through the bottom of the casing, and you are left with the empty shell of what used to be a transmission.

[Commodore GS/E]

Sorry for the late answer...but i ment the older four-cylinder engine.

[group c n b man]

Do you get down often ?

Not very. I normally go there about twice a year for the big days like the GT and Touring Cars. How often I go there used to depend on whether my dad was working or not since he is the only other car fan in the family. But now that I can drive I can go as often as I like since I live only about 45 mins away roughly. Assuming I can remember the correct junction to leave the M90 at .

I might get a season pass one of these years. However, you know as well as anyone what the weekend weather can be like at Knockhill sometimes. Sun burn and hypothermia at the same time .

[Kitdy]

What specific design elements must BMW use to keep using I6s compared to other manufacturers who use V6s? Packaging - yes - but specifically what needs to be different in the engine bay and elsewhere?

[pimento]

The dimensions? I'm pretty sure there's nothing really that different technically.. obviously there's differences with manifolds and whatnot, but different engines have different requirements.. plz2be explaining the question moar kthxlol.

[Kitdy]

The dimensions? I'm pretty sure there's nothing really that different technically.. obviously there's differences with manifolds and whatnot, but different engines have different requirements.. plz2be explaining the question moar kthxlol.

Well a V6 fits in the engine bay in a very different way than an I6 - the I6 is very long and narrow, whereas the V6 is short and wide. So how does this affect where shit is in the bay? What other things need to be different in a car with an I6 as opposed to a V6?

As an aside, is it possible that BMW isn't playing a part in the 6 cylinder displacement dick wagging contest like other manufacturers because there is a disadvantage either packaging wise or enginewise to a large, say 3.5L+ I6? Or is it just them pursuing a more efficient way of generating power a la forced induction and smallish - for these days, what with all the 3.5L+ blocks in North America 6 cylinder?

[Ferrer]

BMW's not enlarging their engines is probably to do with not being possible to enlarge them. In any case the turbocharged sixes do pretty well and pretty much make up completely for the lack of displacement.

As for packaging issues, this the case in a front wheel drive car, see Volvo and Daewoo with their tranversal mounted straight sixes. Especially Volvo, desgined the engine especially to fit in the engine bay of their cars. V6s have no such problems in those cars.

However a BMW is rear wheel drive and has a relatively large engine bay, so no packaging issues when fitting their straight sixes. They even fit in the 1 Series, no problem at all.

[pimento]

I believe the current crop of I6s tops out at 3.0 litres, going larger would require a clean sheet design. I guess they decided that turbos would bridge the gap to the V8s. As far as affecting where shit is in the bay, it's not too different really.. belt driven stuff still hangs off the front of the engine, reserviors still go on the bulkhead..

[Commodore GS/E]

I think the problem is that they would have to design a whole new engine if they wanted to build in a bigger one (maybe because they have already reached the maximum bore or because they don't want to weaken the engine block), but which sense would that make? I think BMW sees simply no need in a huge I6 (>3,5l) because they already have a V8 that covers the perfomance numbers of those engines. I wouldn't mind a new 3.5, though . Maybe we can hope for the future because I6's have normally better fuel economy than V8's...
But really, i never knew that Chevrolet (everywhere else Daewoo) built straight sixes into their Epicas . I mean Daewoo!?

[Ferrer]

But really, i never knew that Chevrolet (everywhere else Daewoo) built straight sixes into their Epicas . I mean Daewoo!?

Yep, 2 and 2.5 litres.

Always has seemed like an interesting car to me.

[Kitdy]

How do (relatively) high revving OHV engines (say the LS7.R, or the new 5.5L in the GT2 'Vette) deal with valve float and manage to rev so (relatively - for OHV that is) high?

[Matra et Alpine]

Money and better materials
Better materials and shaping on cam shafts.
Lighter cam followers.
Roller lifters.
Lighter stronger valves. Titanium, Icconel etc
Stronger dual springs and stronger retainers.

Like piston speed, valve speed can be viewed and evaluated seperately.
The valve acceleration and distance to move determine valve bounce, not the engine it's running in.
The drawback in the LS7 is being one inlet, one exhaust you are stuck having to move a larger mass and with a larger opening needing a stronger valve head. So all the techiniques form faster revving engines can be applied but won't meet their levels of valve control ( assuming equal spend/tech )

So, no real answer, but hopefully basic info assists.

[CapnBoost]

I realized I don't know much about automatic transmissions.

Other than heat, what actually causes damage to them and how do you build them to take more abuse?

[henk4]

How do (relatively) high revving OHV engines (say the LS7.R, or the new 5.5L in the GT2 'Vette) deal with valve float and manage to rev so (relatively - for OHV that is) high?

other than that, the Formula 3 1-liter screamers from the second half of the sixties did 10,000 revs with OHV engines.

[csl177]

How do (relatively) high revving OHV engines (say the LS7.R, or the new 5.5L in the GT2 'Vette) deal with valve float and manage to rev so (relatively - for OHV that is) high?

Valve spring design and lighter materials, higher spring rates and secondary springs. Anything to eliminate float at high RPM.

I realized I don't know much about automatic transmissions. Other than heat, what actually causes damage to them and how do you build them to take more abuse?

Modified torque converters and fluid valve bodies, gear cutting, bearings and fluids specific for application.