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Diesel bashing thread! (Only kidding - pros and cons discussion)

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Goodluckmonkey

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A place to let it all out....

This debate regularly crops up, and having been both side of the fence I can appreciate the pros and cons with both vehicles.

In our little fleet we currently have

2005 FRV 2.0 V-tec (150hp)
2004 Accord 2.2 I-CDTI (190ish hp)

For me, the pros and cons aren't what internet folklore would have me expect, and they're both great engines, just that they excel in very different situations.

Both cars are from the same era and manufacturer, have manual gearboxes and are of similar weight.
Of course, the diesel started off with almost the same hp output too, with both engines being made with economy and refinement as priorities, so if I initially compare to the accords pre-mapped state we've a reasonably level footing to pass judgement upon.


I'll explain all shortly....
 

Goodluckmonkey

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The petrol:

Town and the A road. This is where this motor shines, flexibility that the does just doesn't have (myth 1) as its never caught off boost and will pull from nowhere. Roundabout at 1200rpm in 4th? No problem, Incline at 1500rpm in 6th? Ahh, go on then.
Situations where the diesel is below it's boost threshold, the petrol just pulls, the motor's smoother, more refined and a joy if you're happy pottering around doing something like the speed limit.
Oh, and throttle response the diesel in standard form just doesn't have. Ticks the throttle and it goes, touch the gas in a stock CDTI, and you have a half a second of turbo lag to overcome.

A 60 mile round trip yesterday primarily on a-roads with 5 of us in the car netted a 39mpg average, so there's that economy myth busted too. (In the right environment of course)

The motorway however, still smooth and refined, but an indicated 70mph returns approx 35/36mpg, with an indicated 80 slightly better at 39/40mpg. This is where the petrol loses out.
 

Goodluckmonkey

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The diesel:

Even in stock form, the diesel is the motorway king. Sitting in top in the fast lane it's smooth and silent, and the turbo's spun up ready for effortless overtaking. My CDTI usually returns 50-odd mpg on motorway runs, and has seen mid 60's on occasion when having a go at hypermiling the old girl. This is where a petrol car just cannot compete in terms of the performance you get for the amount of fuel it uses (Or doesn't use)

The downside is the short local journeys, always laggy as a standard car, often below the boost threshold, and once it makes boost, it's quick to fall flat on it's face. Everyone that spouts that diesels are more flexible are both right and wrong. Yes on the motorway you stay in top, huge available torque at 2500rpm means huge joy and a gearstick left alone.
Round town and out on the smaller roads however, you're constantly stirring the 'box in comparison (and mine's the 5 speed!) and the diesel can't compete for ease of use.
 

Goodluckmonkey

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Fuel economy will always be cited as the biggest reason for diesel ownership.
Around a year ago my work.situation changed, and my diesel was no longer required to be a motorway muncher doing 2.5k miles a month.

Here's how the two currently stack-up in my experience based on a mix of local roads, a little 50/60mph stuff, and about 100 motorway miles per tank.

K20 petrol - avg. 32mpg
N22 diesel - avg. 38mpg

Having owned petrol hondas in the past, and a diesel for 25k now, I can guarantee that as a long term prospect, given the diesel mptpr's appetite for wearing components out with it huge torque, that a petrol Honda is cheaper to own in my situation.

Where's your diesel God now????
 

Goodluckmonkey

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In the interest of fairness, the diesel god drives a stage 2 mapped CDTI with EGR off, is smashing out miles in the fast lane and laughing at petrol drivers while he passes filling stations again and again, because he does enough motorway miles for it to make economic sense. :D
 

F6HAD

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We have the same frv and Tourer ICTDI in our household and I would agree with everything you've said.

Had the FRV mot'd yesterday, worked out my Mrs is doing less than 7k miles a year.. just isn't worth getting her a diesel.
 

Goodluckmonkey

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That's the conclusion I came to too once we'd discussed it.
Kate does 7-8k a year, and it made no sense to run a diesel.
 

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I've had all these images for about a year now, thought I'd put them in this thread (click each to enlarge)

K20A6 and K24A3 petrol curves


N22A1 diesel curves




K24A3 and N22A1 side-by-side




but they don't have the same axis, so I put them into a spreadsheet and normalised them




Having got them into a spreadsheet, I could add the gearbox ratios for each


K24A3 with GZT5 ratios (standard CM2 gearbox, 1st/2nd/3rd/4th/5th = 32/62/85/112/140 mph)



N22A1 with AWD6 ratios (standard CN2 gearbox, 1st/2nd/3rd/4th/5th = 24/48/77/109/140 mph)



and finally, N22A1 with GZT5 ratios but modified diff to give same road-speed at 4k5 rpm as K24A3 at 7k rpm (1st/2nd/3rd/4th/5th = 32/62/85/112/140 mph)









It begs the question ...."why give engine A, that has higher torque on the crankshaft than engine B, even more torque at the wheels at the expense of flexibility" ?
 

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That is interesting data Brian, and nicely presented.

We also have a petrol car at home, which I drive sometimes. But I actually prefer the relaxed power delivery of the diesel, whether simply tootling around the countryside or cruising along motorways (where my Accord is truly outstanding in many ways, not just because of being diesel). The Toyota needs to have its neck wrung to make power, which admittedly it then does in a far more exciting manner than my diesel, but I rarely want to drive like I'm on a track day...

I think I agree with your point about gearing... I find first gear too low, so it runs out of steam far too quickly then the change to second is too big a jump. Maybe I should move off in second, but I'm mindful that I'm still on the original clutch and DMF...
 

freddofrog

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Jon_G said:
That is interesting data Brian, and nicely presented.

We also have a petrol car at home, which I drive sometimes. But I actually prefer the relaxed power delivery of the diesel, whether simply tootling around the countryside or cruising along motorways (where my Accord is truly outstanding in many ways, not just because of being diesel). The Toyota needs to have its neck wrung to make power, which it then does in a far more exciting manner than my diesel, but I rarely want to drive like I'm on a track day...
If we look at the curves side-by-side (with standard gearboxes), although I don't give the full curves in each gear (because I was showing at WOT so those are the torques one would experience at change-up to the next gear) , we can see that once we reach 3rd gear in each car, there isn't much difference.

Furthermore, both 2nd and 3rd in the CM2/CL9 are more flexible than on the CN2/CN1, because those gears are relatively flat and have plenty of torque at the wheels. They are flexible, one doesn't need to reach high rpm, although even if one does, on the stock set-up it is not loud.


I am truly puzzled why the lower gears on the CN1/CN2 are not flexible whereas they have to be flexible (in higher gears) on the motorway.




ahh you've answered the question while I was typing LOL

Jon_G said:
.
I think I agree with your point about gearing... I find first gear too low, so it runs out of steam far too quickly then the change to second is too big a jump. Maybe I should move off in second, but I'm mindful that I'm still on the original clutch and DMF...
 

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Really interesting data.. but for gods sake lads, get a life
 

Goodluckmonkey

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It does confirm what the butt dyno feels if you thrash a diesel, power always falling off.

When you ride the torque curve on it though, it's totally different however.
2000 through 3000/3500rpm is where i tend to drive it. Its good for relaxed progress if you're constantly accelerating.

The real issue is if you compared them on partial openings below 2000rpm, the diesel's just useless at pottering round town.
 

Richard B

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Goodluckmonkey said:
The real issue is if you compared them on partial openings below 2000rpm, the diesel's just useless at pottering round town.
Depends on your objective. City traffic generally is pottering speed only, and I tend to do OK letting the car potter. Get it over 1600 revs and the car moves away smoothly in the first 3 gears. I'm generally surrounded by automatics that have the annoying habit of stop/starting in single car lengths. Letting the car move at idle in 1st allows me to average out that movement so I generally keep moving as long as I judge the gap length correctly. I try focus on keeping moving and minimising braking. That results in about 38MPG in the worst kind of traffic.

I've noticed that truck drivers generally do the same thing.
 

freddofrog

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Richard B said:
Depends on your objective. City traffic generally is pottering speed only, and I tend to do OK letting the car potter. Get it over 1600 revs and the car moves away smoothly in the first 3 gears. I'm generally surrounded by automatics that have the annoying habit of stop/starting in single car lengths. Letting the car move at idle in 1st allows me to average out that movement so I generally keep moving as long as I judge the gap length correctly. I try focus on keeping moving and minimising braking. That results in about 38MPG in the worst kind of traffic.

I've noticed that truck drivers generally do the same thing.
I do the same thing with the 2.4 petrol. It pulls easily from just under 1000 rpm in any gear, in city traffic, or queues on motorways.

I use 1st or 2nd gear, and with the flexibility of the K24 engine in the 1k rpm to 3k rpm range, the car will easily pull from 5mph to 15mph in 1st, or 8mph to 24mph in 2nd, without having to dip the clutch. And don't forget, it will stay in 1st up to 30mph.

Only down side of course is that it doesn't quite have the same mpg as the diesel, even if one keeps below 3000 rpm at all times (and not going over 3000 rpm is extremely difficult to resist LOL)
 

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mwahab said:
I'll Just leave this here...

BUT (says me, trying not to appear too desperate) surely that merely reflects the greater number of diesel Accords sold and the far greater miles they've generally covered due to having been originally sold as fleet and leasehire vehicles?
 

Goodluckmonkey

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Agree Freddofrog. Even our little 1600 petrol civic is more flexible below 1500rpm than the diesel.
I know what you're saying Richard, because I do the same. It's just not as nice as driving a petrol in the same situation.
 

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Goodluckmonkey
You should test drive a reflashed k24 and add a review to this page vs your remapped diesel

Since having my cl9 back i think lpg is the way to go.
Its been on my cl9 for about 7,8years.about 80k miles. Has been trouble free.only holds 35ltrs cost £20 to fill. Gets 260 miles.it sees 7000rpm every day.what more can you want
 

honda_saj

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I am looking at getting lpg soon as well

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Jon_G

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honda_saj said:
I am looking at getting lpg soon as well
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Best to get advice from SpeedyGee on the 'other forum'... he's got a few horror stories about conversions he's seen! I've been round his place and seen the standard he works to, so if I ever want an LPG conversion then he'll be doing mine! Long trek for you though...
 

honda_saj

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He will be doing mine lol

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edgeoftime

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My mate has a new 1.8 civic, the ride is "frenzied" and it appears to be going quicker than you are. My Mrs has a 1.4 Jazz, and the the ride is "twitchy" so absolute concentration is required. My mk7 i cdti tourer was a dream to drive but my latest IDTEC tourer automatic is the best drive I have ever had, so relaxed around town or on the M roads, reels off the miles without trying. Every one to his own but I Know where I stand.
 

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^ but with it being an automatic you won't experience the daft close ratios they put on the manual version of the diesel
 

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Jon_G

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freddofrog said:
Still poor compared to an electric motor though!

And that's the bottom line for these sort of 'diesel Vs petrol' debates (however whimsical)... both fuels have plus and minus attributes but, on the bigger scale, the differences are miniscule. The only significant downside of electric vehicles is their range...
 

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Jon_G said:
Still poor compared to an electric motor though!

And that's the bottom line for these sort of 'diesel Vs petrol' debates (however whimsical)... both fuels have plus and minus attributes but, on the bigger scale, the differences are miniscule. The only significant downside of electric vehicles is their range...
and the limited lifetime of the batteries, and the pollution caused by making the batteries, and the CO2 caused by continual use of fossil fuels at power stations

in comparison to diesel engines and electric motors, petrol engines win win win ;)
 
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