1.6 versus 1.8 - Relative merits

[Julian Thompson]

John Barker from EVO reckons the 1600Superlite is the best Caterham and even Caterham admit that the 1.8 doesnt rev as hard or as freely as the little 1.6.

 

Bearing in mind that anyone serious about power would have to swap pistons and crank anyway to get more than about 185bhp safely, do we think the 1.6 is a better starting point?

 

Is there a discernable difference in the "lazyness" of the 1.8, since it is considerably longer stroke (88 ish mm versus 79)?

 

8JU

[Mike C.]

On a circuit, my previous 1.8 S/S was definitely a touch quicker than Gusto's near identical 1.6 S/S. It was only marginal but, on the straights (particularly from Camp to Avon Rise at Castle Combe), the 1.8 would pull away from the 1.6 quite noticeably.

 

Mad Manx

[Andy. N]

I'm at the point where I need to decide whether to fit the 1.6 ss, or the standard 1.8 with the possibility of later upgrades. The car will be used mainly on the road, with the odd track day and maybe club sprints.

 

I would be very interested in anyones's views of the relative merits of the 1.6 and 1.8 units.

 

Andy N.

[Mike C.]

I ordered my previous Caterham as a standard 1.8.

 

I did the first 50O miles the road, running it in, and it was fine.

 

But when I did my first track day, it clearly lacked the upper end urge you need on a circuit. It went straight back to the factory for the Supersport upgrade, change up light, 13" wheels and properly set up suspension. The improvements were sensational.

 

Although my current Superlight has the 6 speed box, I never felt at a disadvantage in the 1.8 S/S with a 5 speed.

 

Mad Manx

[PACR]

When you say 'rev freely' does this mean that the cluth is down or you are in neutral? Because by my reckoning the engine turns which turns the wheels. The engine speed is directly related to the road speed in a given gear, assuming no wheel spin. The engines rev-a-bility is therefore controlled by the power output being able to accerate the car. So the 1.6 accerates more quickly than the 1.8?

 

It's late and I'm off to bed now so I'll settle for 'go for a 1.8 if you are going to upgrade later as the SS kit needs chucking out for high specific outputs. If you later decide not to go the whole hog, for £999 Caterham will retro-fit the SS conversion which gives a nice character and more poke'. I decided to start with a 1.8 but then Railtrack shares went up so I got the 1.8 SS, and I'm very happy with it.

 

Piers

[New Barbie]

My understanding, which I'd stress is from research rather than raw experience, is that it depends how far you want to go.

 

If you want to upgrade to 200bhp+ levels in a K, then you're going to have to rev high and you'll need to strengthen the bottom end to cope. In this case I'd start with the 1.6 and you can up the capacity to 1.8 when you change the internal components, crank, pistons etc.

 

If you are looking to achieve less and probably have a reliability concern then the 1.8 is probably better as the stock bottom end 1.8 is good for 7600rpm I think so you can just change the top end and still achieve a high spec engine but at less cost and less angst about costs to keep such a highly tuned engine running.

 

Better yet is look at Dave Andrews site or look at what can be done with a K and decide (Peter Carmichael probably has one of the best K series I know of outside an R500)

 

I have done a lot of research into the various options open to me and I've got lots of facts and prices from the various engine specialists. My personal choice would be go 1.6 to start as you can still get a lot out of it and you haven't in effect made too many upgrade decisions at that stage other than increasing the bore which you've no choice on anyway.

 

 

 

 

 

 

[Peter Carmichael]

Rev freely means runs under power in gear up to its power peak and a bit beyond without sounding like a tank.

 

The 1.8 has a longer stroke which means shorter rods and more extreme rod angles. This makes it harsher with more out of balance forces. The engine is still sweet to rev otherwise people wouldn't build versions that rev to the stratosphere (that'll be me then)

 

The 1.6 has a longer rod and a shorter stroke which makes it smoother. For any given revs, it will be pumping less air through the engine and will be making less torque. However when you scale the action up the rev range, it does pretty much as well.

 

Essentially the 1.8 is like having a shorter diff compared to the 1.6 which probably makes the 1.6 matched to the 3.62 diff and the six speed box the best option.

[PACR]

Ah, thanks Peter. I thought it would be a bit odd to judge an engine when it wasn't doing anything useful!

 

Is it that the inherent out of balance forces are magnified with the longer stroke? Are these forces significantly larger? Is it a largely subjective matter that can be detected from one to the other but in isolation it would be difficult to detect?

 

Piers

[Peter Carmichael]

The out of balance forces in a straight four purely come from the rods. The general up and down motion of the pistons and rods is balanced - when the #2 and #3 are descenting #1 and #4 are ascending. The rods however shorten vertically as they move out to an angle to the side and this happens to all the cylinders in synch giving an out of balance force. This force counter-rotates in the main bearings at double crankshaft speed.

 

Just to give you an idea, the difference between 1.6 and 1.8 @7600rpm is ~8kN vs. ~11kN. Alfa Romeo Twin Spark fours (and some others - Porsche 944 etc.) have counter rotating balancer shafts to smooth this out.

[DanB]

>Just to give you an idea, the difference between 1.6 and 1.8 @7600rpm is ~8kN vs. ~11kN. Alfa Romeo Twin Spark fours (and some others - Porsche 944 etc.) have counter rotating balancer shafts to smooth this out.

 

As do Honda Blackbird bike engines. Useless piece of information No. 168 ;-)

 

Dan

Furrybird Q660KKL

[WILL FLY]

One spanner in the works, if you buy a bog standard 1.8 and put a 500 quid Emerald ECU on it, it will develop roughly the same power /torque as a 1.8SS 140/124, mine develops 138/140 and is otherwise standard. See the graphs on www.willfly.net and follow the modifications and engine mods links. When you want to go beyond SS levels you won't have wasted a grand on cams and an ECU that noone wants.

[Julian Thompson]

This is v interesting ! The tuners all swear by the 1.8, but the obviously very technially adept people here are indicating to me that in actual fact, my thoughts on the 1.6 seem founded.

 

Can we have a couple more posts regarding a direct comparison between a tuned 1.6 and a tuned 1.8 ?

 

Perhaps check out my latest post "Who's got the fastest 1600?"

 

Cheers

 

8JU

[Peter Carmichael]

I should have said...

 

... at equivalent revs, the 1.6 is going to be flowing less air than the 1.8. Typically this means that the 1.8 switches off earlier in the rev range. The 1.8 and 1.6 produce similar power levels because their bore (and valve area) are the same. They just do it a different points in the rev range.

 

It all comes down to gearing in the end. The 1.6SS with a 3.62 diff and 6in ACB10s on 13 inch wheels gets the gearing absolutely spot on for its output. Roy, I think, could tell you how inappropriate it can be to match a standard 1.8 with a 3.92 diff.