Ariel.Club Forum

Okay, a full car sim for identical atoms (K24 may be heavier mind), puts the difference between the two engines in 310 and 300bhp trim within the hundreths of a second mark - I.E, way within the margin of error on it.
That holds for brutal 0-60 attempts in 3rd gear, roll-ons from 30-60mph, 60-120mph which would be the bulk of your track work, 1/4 mile, etc, etc.

The only place I can see an advantage for the K20 that's glaring is if you're actually hitting the limiter in top, because it can manage a couple of mph more on the other ratios, assuming the k24 redline is the same as the Nomad (yeah, those longer ratios work out pretty similar road-speed wise in the end, the change points are all within 5mph of each other on either combo).
Of course, if you're on the road doing 30 in 4th or 40 in 6th and then roll on, the K24 has a noticable advantage.

edit: To be honest the main performance difference will probably be down to how much heavier the K24 install is.

power figures is half the picture.
you really need a power graph to see the power band and where the gear ratios leave you in that powerband after each shift.

another thing to note is the k20a and k20z differences vs k24z.
the k20 a&z both have true vtec  (3 lobes) on the intake and exhaust cams, both have 50deg vtc and and rev to 8600.

but this new k24z isn't designed for performance.
it only has vtec on the intake cam, the vtc is 25 degrees and the integrated exhaust ports do nothing for performance. great for simple downpipes though.

[img width=768 height=768]http://66.media.tumblr.com/7fad65f7d94a8c39c80ea6ebc0f3ab9a/tumblr_o2e0ihMqaO1ur31qyo1_1280.jpg[/img]

the older k24a3 is the ideal 2.4.
k20 style head with a 2.4 bottom end.

on a side note,

the ep3 civic uses a 4.7fd
the cl9 accord type s uses a 4.3fd
the fn2 and fd2 civics use a 5.1fd
and some lotus k20 guys had a 3.9fd made which can be found for sale online.

shame the shorter fd makes 1st gear even more useless than it already is.

i think the atom needs a much longer 1st gear with progressively shorter ratios and with a max speed of 140mph in 5th, leaving 6th as a cruising gear. 

The shorter final drive is interesting, but as discussed whilst torque is the physical phenomenon, power is most important measure as it takes rpm into account. This allows for the effect of gearing. That is specifically why it is used.

What you want is to hit the rev limit in your top gear at the end of the longest straight on track. The pay off is reduced economy, noise etc. if you run lower gearing. Could I live with gearing shorter than a 2ltr Atom? Maybe a little, but not much. A shorter 6th would be good though.

Peter255
i' don't want any polemic with you but sorry to say that imù' really suprised when i read this from you :
[color=blue]"Nomad map has peak torque @ 4300rpm [u](zero use on track)[/u], and peak power (only 235BHP) down @ 7,200rpm!"[/color]
and this :
[color=blue]"When the 2.4 has to change gear the 2ltr still has nearly 1,000 rpm to go. AND the longer gearing on the 2.4 which reduces torque to the wheels by a significant factor (in second gear 13% as earlier shown)."
[/color]

In particular in your last words, because the torque disponible to accelerate at each [u]speed[/u] (on the better gear of course) on a track after a corner is the more important.
a 2.4 SC (300 Nm for the 2.4 NA and so a conservative 350 Nm is minimum for a 2.4 SC) on its best gear will have more torque to give on the wheels at 90Km/h or at 150 Km/h than the 2 L SC on its best gear (max torque of a 310 is near 270 Nm and a 350 hp is, in the very best case, 320 Nm) !
And just for your information, with the 2.4 L there is a shorter final drive option who exists for the Nomad so i imagine for the Atom to, if you feel that your gearing is to long (and it'll be for the 6 gear for sure but you'll never use it on track, or in Nardo perhaps  ;D).

But of course you can have a different opinion ... till you'll test one. ;)

Yeah, but it has more torque to start with, and with the lower rev limit they're effectively shorter gears, hence lengthening them.

I get your point on the power and gearing. I am just worried about the upshift to 6th on track!  :(

But I still want some data here rather than opinion. I want to see some measured stats / data.

Do we even have factory stats on the 2.4 s/c Atom engine? All I have heard is they make just under 300BHP. I have also heard the 310 figure for a 2ltr is conservative by comparison. But this is all just talk... ???

I'm not ignoring the lower rev limit, it doesn't matter, 300bhp is 300bhp. It does for talking about torque alone, but since power takes torque and rpm into account (and by that factor, gearing) it doesn't matter.

I can even do a full vehicle simulation if you like with the corrected gear ratios.

[quote="PhillipM"]
Why do you need torque data?

You know it has more displacement, you know it makes more peak torque, you know it's a similar engine configuration, and you know it makes similar peak power at lower rpms. So you know it's holding more torque to it's redline. The thing holding the power back is piston speeds and head flow. Same as it is for the F20c vs the F24C.

The old engine is making (roughly) 310bhp@~8.4krpm, roughly, and about 225-230lbft of torque.
The new engine, given it's likely to be similar to the Nomad, should be making that 300 or so horsepower around 7000rpm. That means it's making 220lbft at peak power, or more, if that estimated 300 is conservative.
So if you plug that backwards then what you get is that from approximately 6800 to 7000rpm the new engine will be making a knats less power than the old one at peak power rpms. So for 200rpms you're loosing out on an extra 5bhp average (give or take, rule of thumb figures).
And everywhere else the new engine is making more power.
[/quote]

I don't really [b][i]know[/i][/b] any figures. Do you? If so please share the data. Do you have figures for a 2.4 with the Atom map? [u]CAN ANYONE HELP?[/u] There is nothing on the Ariel website.  :( The n/a Nomad map has peak torque @ 4300rpm (zero use on track), and peak power (only 235BHP) down @ 7,200rpm! I hope the 2.4 Atom map is better at the top end. But how much? Is this all estimation and assumption from what you have been told..... by people wanting to sell 2.4ltr cars.... Because they have no choice... Because they can't get new 2ltrs from Honda but have signed an exclusive engine deal? ;) Exaggeration to maintain sales, or at least cherry picking of stats would not surprise me. Far better to do back to back independent tests and we can directly compare the graphs.

Also you are ignoring the lower rev limit. When the 2.4 has to change gear the 2ltr still has nearly 1,000 rpm to go. AND the longer gearing on the 2.4 which reduces torque to the wheels by a significant factor (in second gear 13% as earlier shown).

It is clear you have you own view and that's fine.  :tu: I simply want to test the two preferably back to back so I can be sure of the differences. We are doing this next month so then I can inform my potential purchase. :)

i'm sometimes suprised of what i'm reading here  ;D
First , after having owned and driven (on roads and tracks) all the Atom production of engine since 2005 : 220,245, 275 Mugen, 300, 310, 350 and V8, i have a Nomad 2.4 L N/A in the garage for a friend and i drive it. Even with a minimum of 100 Kg more than the Atom, and despite the longer gear and an aero of a shoe box, the torque is really surprising :tu: (when i saw the Nomad numbers i have doubt considering the torque number in the documentation for the 2.4 NA, but they are really here !). For information the accelration with 2 heavy guies on board is still a little bit better than a 991 (997) Porsche till 140 Km/h. I can easily imagine the torque of the 2.4 L with SC because i tested, as passenger only , the Factory Nomad : that's really great on all the rpm range. So in the light Atom, a 2.4L SC will better for road driving than the past 2L SC, no discussion.

Second , on track : i have some experience on track and car races  ;) and i can garanty you that the high end difference of about 10 hp will have no consequence because the 2.4L SC has much more torque (on a wide range and even on max torque) than the 2 L SC. And on track, the capacity of the car/Atom to accelerate after a corner is not given by the max power but only by the torque. I can add that the 2.4 L SC will be easier to drive fast on track than the 2 L SC, again because of the torque.
So, to my opinion, both the 2.4 L NA or SC are in every case better than the 2 L despite the only problem/down : the fact to cut the pleasure to rev the engine to 8400 rpm  ;D.

[quote="Peter255"]
It does look better too! I love the red crackle finish, and that tubular manifold. Proper!
[/quote]

Can't help with the manifold (and 1-4-1 doesn't make sense), but for the cover: [url=http://www.frost.co.uk/vht-red-wrinkle-finish-310ml.html]http://www.frost.co.uk/vht-red-wrinkle-finish-310ml.html[/url]

Why do you need torque data?

You know it has more displacement, you know it makes more peak torque, you know it's a similar engine configuration, and you know it makes similar peak power at lower rpms. So you know it's holding more torque to it's redline. The thing holding the power back is piston speeds and head flow. Same as it is for the F20c vs the F24C.

The old engine is making (roughly) 310bhp@~8.4krpm, roughly, and about 225-230lbft of torque.
The new engine, given it's likely to be similar to the Nomad, should be making that 300 or so horsepower around 7000rpm. That means it's making 220lbft at peak power, or more, if that estimated 300 is conservative.
So if you plug that backwards then what you get is that from approximately 6800 to 7000rpm the new engine will be making a knats less power than the old one at peak power rpms. So for 200rpms you're loosing out on an extra 5bhp average (give or take, rule of thumb figures).
And everywhere else the new engine is making more power.

[quote="kelvin12382003"]
I just prefer k20Z engine. :vroom: :vroom:
[/quote]

It does look better too! I love the red crackle finish, and that tubular manifold. Proper!

I just prefer k20Z engine. :vroom: :vroom:

Firstly the 2.4 does not (from what I have been told) make the same max power as the 2ltr. The 2.4 makes ~300, and the 2 makes ~310. Which is interesting as the long stroke engine even with 20% more displacement DOES NOT make 20% more power. If it was a true red top 2.4 (and not just a longer crank 2ltr) it should make circa 310*1.2=372BHP! So for its displacement advantage it is significantly down on max power output. If the engine got anywhere near 370BHP I wouldn't even question it!

Does anyone have any comparable independent DATA (not opinion) over the comparison between the torque from the 2lts and 2.4 from say ~6000 rpm upwards? On track that is where we need and use the full power. This is almost exclusively where a 2ltr is driven on track. On the high lift cams via VTEC. I suspect the 2.4 is comparable around 6000 rpm (at best), before dropping off to its lower limit. The 2ltr then screams on to its higher limit. This is exactly where the 2ltr car comes alive and really delivers. Hence the 2.4 is probably worse for track (6000-8250rpm). That's the point. Not once have I said the 2.4 is worse on the road. Indeed I completely agree for the Nomad off road, and on road in an Atom the 2.4 should be faster 99% of the time. That is not in question.

I am concerned if I buy a 2.4 next year (as I am considering) on track it will be slower. For me that's un-acceptable. To spend a LOT of extra cash and time selling my car to get a slower but newer model. And I get the new car might be faster until 6,000 rpm, or on road. But that's not the point! And the higher gearing is also a bad thing for me. I don't care about economy or relaxed cruising. I want speed and acceleration.

Plus if your running a s/c 2ltr Atom on the road do you really need more torque low down? Having driven mine for thousands of road miles both all across Europe and on occasional weekend drives IMO no. The thought never crossed my mind (unlike more top end power on track!!!!). I think the 2.4 makes sense for N/A cars, and for the Nomad. When s/c in an Atom I suspect its a backwards step... for me at least.

Anyways I want to get DATA to understand this not opinion. Hence a dyno day already arrange for a back to back comparison of 2ltr and 2.4s (in no way connected to Ariel).

[quote="phil4"]

Quite.  And is why in the previous decade Honda and others with similar to VTEC (eg. VVTi/VVTLi) and similar had high revving engines, but pathetic torque... think previous generations of Civic Type R and the S2000.  Often said they'd struggle to pull the skin of a rice pudding.

As you say, on a track if you're doing it right, you'll be at the top of the rev range most of the time, and indeed is why the VTEC kick in points are where they are, so if you change up at redline, you're still in the VTEC zone for the next onslaught.

Very different thinking to a nice surge of midrange torque for a smooth overtake on the road.
[/quote]

That's disingenious too, the ENTIRE point of the VTEC system is that it allows you to have both - the decent torque low down as well as the better breathing to hold the torque to high rpms.
Don't confuse what people claim with their arse dynos when they try something with a flat torque curve as being truth.

An F20C cracks out 153lbft of torque from 2 litres. That's up with the best torque outputs in it's class. Better than most.
It's the same argument people use when they claim rotaries are torqueless - a Renesis has 80% of it's peak torque from about 2k to 8krpm - but because there's no 'kick' people relate it in their heads to 'no torque'.
It's also why they rave about turbo diesels that go nothing-everything-nothing. Even when they're driving a 110bhp Passat.