Is 56 mph too slow for motorways?

UK PROFESSIONAL DRIVERS FORUMS THE UK PROFESSIONAL DRIVERS FORUM (INTERACTIVE)
41

Manwell:
In that case, if an engine burns an increased amount of fuel as it draws more air in, why does’nt it go into self destruct mode, as happens when the bearing seals go on a turbo and the engine starts to burn engine oil and over revs itself to into oblivion :smiling_imp:
No mate, its your right foot that controls the amount of fuel burnt, and the more fuel that gets burnt increases the compression produced, and that in turn spins the turbo faster forcing more air into the engine to burn the extra fuel more efficiently :sunglasses: Hence the small amount of smoke produced by turbo engines under hard acceleration until the turbo catches up.

Any engine with a turbo uses turbo boost at all times, just different levels of boost depending on the amount of fuel being used, governed by the pump governer/electronic engine managemnt system

A turbo is designed to operate through nearly all the rev range. The vanes inside are spesiffically designed to be at maximum efficiency at around 1500 engine rpm (around max Torque & max economy) above this the vanes become innefficient. This stops the turbo spinning about 100,000 rpm causing it to rip itself apart, but it also enables it to supply air at pressure over more of the rev range. the turbo provides no more boost above what it supplies above where its max efficiency, the engine preovides more power above this range by increasing the fuel mix. Todays engines also have a POWER BOOST type system. This is where the engine has a maximum power at 2100 (mainly for arable & marine) where the engine runs at 2100 but if there is an extra high load exerted the engine revs will fall and the engine produces extra power band at around 1900 rpm that will try to hold it from falling further

No engine will over rev in any circumstances other than when the governor is tampered with ( ive dont it myself to get more speed out of a tractor but the enging doesnt like it)

finally you should let the engine idle to stop heat build up in the turbo & so the turbo isnt spinning too fast when you switch of & cut the oil.

42

HI all

Speed limiters seem to have been a top topic of conversation ever since the inception of the 56mph ruling.

Me personally drive a truck that is set to around 62mph, but this is purely cause it is an Irish truck. Really makes no odds to me as when in UK I can not make any head way as (please this is not a slagging) quite a few of our day cab friends see the Republic registered truck and do all they can to hold me up, give nasty stares and even result to hand signals as I go by! Why is this, are they jealous because they are being paid large sums of money for being home every night!!!

One of my esteemed Irish colleagues was pulled over in Chester by the ministry there is a surprise Irish truck being ulled (LOL), anyhow…his limiter was set to 60. He claimed and stated the highway code states trucks max speed limit is 60 and he was quoted chapter and verse about construction and use regulations of vehicles of a certain age have to be set to 54 mph with a percentage for error meaning the max is 56.

I actually had this confirmed to me by a fitter at our local Volvo dealer…the construction and use regs actually state the speed limiter should be set to 54 mph with a 5% margain giving you a max of 56.

43

The new Daf engine, the G Spot or something is fitted with two turbos, a low pressure and a high pressure unit to overcome the turbo lag at differing speeds.

A turbo is a compromise that runs for nothing, it doesnt cost anything to run if you are not sat pumping fuel into the engine when it doesent need it. Most trucks will pull and work better below the limiter, I am happy sat at 50 52 on the cruise letting the engine management do the work. When I come to a hill I catch trucks doing 56 because the turbo can start to work earlier