MPG

[Toms306]

Can I just point out, to settle the 15th HDI vs PD argument between CAR and Toms306, the common rail, electronic pumped PD is overcomplicated and problematic compared to a HDI, but the common rail, electronic pumped HDI is overcomplicated and problematic compared to the rotary injection pump, ECU-less, indirect injection XUD, which gets nearly as much to a gallon (and practically the same with a HDI box) as the HDI but it far cheaper to tune, run (veg oil) and maintain than either!

Basically, your both wrong.

There's no common rail in a pd though. It's also no more complicated than a HDi, literally the only difference with fuelling is the HDi uses a mechanical pump to pressurise the fuel and the pd uses what's effectively a mechanical pump for each injector. Both solenoids operate in exactly the same way at the nozzle end. Which Chris seems to have failed to understand, yes its a different delivery system, but it does exactly the sane thing, even using the same sensors and actuators! It even uses an edc15 ECU the same as the HDi iirc....

And hdis aren't more complicated than xuds either.....give some computer geek a mechanical pump he'll have no idea what to do....give him an ECU he can write a map. Just because new tech is different doesn't make it MUCH more complicated, its how you personally percieve it, different people find different things easier.

What's interesting though, is I'm looking at a car atm with with a 6 speed box and gt1749 vnt turbo (same as the golf)....BUT with common rail instead of pd.....if I go for it, will be interesting to see what the mpg difference is... Obviously there's a few more variables, but still...

Im always right...

regards to other question, most likely completely different engine design using unit injectors, HDI on 306s is the first version of commonrail, since then theres been different revisions and improvements, higher rail pressures, piezo-electric injectors and vnt turbos, all attribute to better atomisation of fuel in cylinder leading to better mpg

Im always right...

regards to other question, most likely completely different engine design using unit injectors, HDI on 306s is the first version of commonrail, since then theres been different revisions and improvements, higher rail pressures, piezo-electric injectors and vnt turbos, all attribute to better atomisation of fuel in cylinder leading to better mpg

Well, I wouldn't say always right.

The block/bottom ends are almost identical weirdly, the piston 'hole' is even the same shape and everything, so it can only be the top end that makes the difference, and even then the older PD is still only 8 valve, so that just leaves the injectors. But I can't really see how the unit injectors are much better for mpg, the only real difference is the top mechanical 'pump' type part, the nozzle end and solenoid opening operation is near enough the same isn't it?

Granted the VNT turbo will help mpg, as it's nearly always slightly on blow. And the 6 speed 'box helps on a run, but when you're averaging like 30mph (just going off the trip computer, I can't work out avg speed in my head lol) then even the 'box can't make much difference either.

I was really surprised when I stripped the Golf how there wasn't loads of extra sensors and clever things, infact, it only has the same sensors as a HDi (one extra but thats MAP for the VNT), I was expecting loads of amazing new tech, that just wasn't there lol. I'm just struggling to get my head around how you can have two engines that seem extremely similar, but one has twice the power, tonnes more torque and still gets over 60mpg with ease while the other left the factory with 90bhp and will struggle to even hit 50mpg unless you drive it carefully.


As for apples and oranges Chris, I'd say more like Granny Smiths and Pink ladys...they're not totally different. And PDs mainly cost more because they're in VAGs....1.4 petrol Golfs cost over twice as much as 306 1.4s, but they're no better.

I'll stop talking about VAGs now though.........but it's ridiculous I can have a better VAG discuassion and learn more about them over here than I can on the Dub forum.

Did you not read that line?
better atomisation of fuel in cylinder means using less fuel for same energy and less emissions which means more mpg.
and as dave said, the gearing is a considerable help too, the ratios on 306s is terrible in general and not as well calculated or engineered, hate to admit it but its true

Yes I read it, but its gotta be well atomised to run well with a DI engine in the first place, I just can't see how slightly better atomisation would make such a major difference, I'll take your word for it though. I agree the higher ratios are better (sit in 6th at ~40 just above idle and watch the mpgs mount up), but the low ones (1,2,3) are still awful as with any diesel....there's really no point in 1st as it doesn't get you anywhere, I know its meant for tugging a caravan or whatever though lol.

Anyway....I'll stop now.