caterham crossflow engine spec

[suffolk009]

HI everyone,

I used to own a lovely '96 ex academy car. It had a lovely crossflow engine, perfect for everyday use, could perhaps have done with a bit more on track (but then we all think that).

I'm now at the start of an engine build - another crossflow but for a different car - and was wondering what the likely spec of that engine would have been. I figured this would be a good starting point for working out the spec. I can't seem to find any detailed spec sheets. Cam types, pistons, what was uprated, what was replaced with Caterhams own special bits and pieces, that sort of thing.

I'll be using twin 40s again, beyond that everything is up for change.

Hope someone can help.

Regards, Tim

[Golf Juliet Tang]

I have a '96 era Scholarship car. I still have the original AX block Crossflow in it which has recently been refreshed. 93,000 miles on the clock.
I'll post some more details later.

[Richardsix]

I am a bit like you, I have a crossflow in my six at the moment, dont know what spec it is but boy does it pull, I know it has dished pistons but that is all i know, but alas, it is coming out to be replaced with a zetec!

[bdx]

Twin 40's limit the hp to about 150 bhp iirc

[suffolk009]

For Richardsix, if you're anywhere near Suffolk, I might be interested in your x-flow?

Tim

[EFA]

BDX - Roger King used to get 180 on twin 40's.

The chap who designed the 135bhp 1700 SuperSprint crossflow for Caterham in the mid 80's when Lotus T/C's became unavailable, Peter Cooper was a friend of mine. Peter passed away a coupole of years ago.

Caterham's spec was pretty basic.

711M block bored +90 for 1698cc
Twin 40's on Holbay designed manifold
Kent 234 cam
Std cam chain and drive.
1300 van pistons modded to give 10.5:1 compression
Big valve gas flowed head, matched to manifolds.
4 branch long primary exhaust

This spec delivered a healthy 135bhp - enough to give the Caterham a 5.6sec 0-60 time.

[suffolk009]

That Supersprint spec was pretty much what I was aiming for. Can't afford to go with all steel internals. Was thinking about the 244 cam though. I read in the authoratitive book that you should then change cam chains, and pistons will need pocketing but otherwise very similar.

Does anyone have any first hand experience of a good head man in Suffolk/Essex/Cambs borders?

[Golf Juliet Tang]

Suffolk
How about taking it to Ratrace in Potters Bar? Not far from you. Rob Morley was the man who built Vegantune VTAs so knows his way around a Kent Crossflow block.
I'll post more once mine has been on a rolling road (4 October)

[Golf Juliet Tang]

Suffolk
How about taking it to Ratrace in Potters Bar? Not far from you. Rob Morley was the man who built Vegantune VTAs so knows his way around a Kent Crossflow block.
I'll post more once mine has been on a rolling road (4 October)

[Richardsix]

Suffolk, I am in Essex, would be keeping the twin 40's at the mo as I may need them.
Richard

[Sam_68]

EFA said:

Caterham's spec was pretty basic.

711M block bored +90 for 1698cc
Twin 40's on Holbay designed manifold
Kent 234 cam
Std cam chain and drive.
1300 van pistons modded to give 10.5:1 compression
Big valve gas flowed head, matched to manifolds.
4 branch long primary exhaust

This spec delivered a healthy 135bhp - enough to give the Caterham a 5.6sec 0-60 time.

The Crossflow in my Sylva (built by East Lincs Motorsport) produces circa 155bhp on twin 40's and is very tractable; it's nominally 1600cc (ie. + allowable overbore for racing, giving an actual 1634cc, IIRC), so there would be more to come if you went to 1700 or more on a thick wall block.

Basic Spec. so far as I can remember it is as follows:
Kent 244 camshaft
Powermax pistons
Duplex timing chain with vernier sprocket
Steel rocker posts, shafts and spacers
Heavily ported head ('fraid I don't have details of valve sizes or compression ratio to hand)
Polished conrods & everything lightened and balanced (but standard crank).

The standard crank is supposed to have a safe limit of 8,000rpm. My engine has a rev limiter set to 7,800rpm, and has proved reliable at that (though it breaths a bit heavily and blows a bit of oil when you use lots of revs).

In terms of cam selection, the main thing limitation is powerband: the 234 cam used by Caterham has a quoted powerband of 2,000-7,200rpm and starts to run out of breath at the upper end. The 244 cam in my engine runs from 3,000 - 8,000 (fortunately, with light cars it still gives plenty of torque for pootling around at low revs, and of course you'll always be well into the powerband if you're trying to drive quickly), hence I'd suggest that the Kent 244 cam (or equivalent) is the optimum for a road car on a standard crank. The 254 cam, which is the next step up, takes the powerband to 4,000-8,500rpm which means you reach the limit of the crank before you fully exploit the camshaft and this, coupled with teh redcution in low-end torque, means that it's not worth it unless you go to an all-steel engine (and even then, the reduced tractability at low revs might outweigh the benefits).

[bdx]

[quote=EFA]BDX - Roger King used to get 180 on twin 40's.

Achievable with the chokes bored out, nice power though

[EFA]

I think the point here is also budget. The xflow I had in my first Caterham was built by Vulcan, had a 244 cam and gave about 145bhp. The 135bhp engine relies on less "race" components so is cheaper.

A stock GT spec crossflow on Webers gives 100bhp. Stick an A2 cam in with no other mods and you get 110bhp.

I would look personally at a 1.8 Zetec - available from a scrpayard, standard engine on carbs with 3d ignition gives 165bhp. Bombproof compared to a crossflow, and overall your costs will be much lower.

Plently of ign and inlet maifold bits come up on ebay.

[suffolk009]

I'm familiar with the Zetec route, but in this instance it has to be crossflow.

The argument appears to be narrowing - I've been reading, talking to tuners, and with everyones help here - I think it's now between the 234 and the 244 cam. 135bhp or 150bhp. Obviously I want the extra (who wouldn't!) but can it be justified moneywise and will it still be lovely to drive. Everyone seems to agree that 160+ in a crossflow is race-engine teritory and horrible to pop to the shops in. Will the 244 cam still have good traffic manners?

Thanks again to everyone for their help.

Tim

[kenny.R400]

Hiya, I've built 2 x/flows in the past for 7's I've had, both times using the same,identical spec which were not a million miles from Arnies description.

711M Block with a +.090"

1300 GT pistons gashed to take the extra valve lift of the 244, simple job, first set I did with a hacksaw and file before I had a milling machine.

244 Kent cam kit

Duplex timing gear

Took flash of rods and made sure each weighed the same.

Big valve head with largest valves poss., ported by Bannister racing engines (non unleaded heads BTW)

H/P H/C Oil pump

Facet pump and regulator, blanked off Mech pump offofice.

Roger King style breather system, using Burton Block breather back to cover and on to catch tank.

Lightened but safely lightened flywheel.......that made a huge difference to speed of rev climb

Bothe engines ran on 45 webber and Dellortos respectively and were both set up at WGT rolling road.

First engine ran on modified Sunbeam ignition system, second ran with Aldon bits.

Both gave just about 120 @ wheels when done but certainly felt quicker.

The 244 engines were a doddle for ordinary driving as well as on track with no trauma at low speeds. You could tell the cars with a 244 cam as the noise of the valve overlap as it climbed up to the rev band was so mechanical and knocky, very worrying the first time I heard it.

Great spec for a x/flow IMO and no real worries about drivability or longevity following the well trodden route of the 140bhp spec.

Good luck with it

Edited by kenny.R400 on Monday 27th September 07:46

[elan_fan]

Burton alloy head with largest valves (Ivey valves wasted stem?)
244 cam
vernier sprocket duplex chain
Aldon dist to suit cam 103FXYS?
Lotus twincam pistons 83.5 mm with the crown machined down (far far lighter than xflow pistons)12:1 cr
roller rockers
QED light flywheel for twincam allows 8 1/2 inch clutch
GT rods tuftrided
GT crank tuftrided
cosworth rod bolts
assuming you are starting with AX block
custom exhaust manifold

[Sam_68]

suffolk009 said:

Will the 244 cam still have good traffic manners?

Yep, it's absolutely fine in a light car like a Seven, provided the carbs are jetted right and the ignition timing correctly set.

Mine was originally built with a single carb., mind you (to comply with the class rules in place at the time in the 750 Kit Car championship) and with a single carb, jetted for maximum power, it was a serious PITA on the road... anything less than 3,500 rpm and it just spat and coughed when you gave it any throttle.

One thing worth mentioning, though, is that if you go for a fairly high compression ratio and fixed ignition advance, geared starter motors are worth their weight in gold: the standard inertia starter can really struggle to turn the engine over.

[Iamscotticus]

Guys, Blokes,
18 years later, I have a Caterham "Super 7 Sprint" of mid eighties vintage with the Escort 4 speed. I am trying to get the build sheet for it.
I am pretty sure 1ts a 1600 on twin 40s and 4-2-1 exhaust. Ital axle of course.
Im pretty sure its not a 244 as it doesn't sound lopey enough. I suspect an A2 cam only because I read Caterham used them.
Please advise.
Thanks

Edited by Iamscotticus on Friday 19th October 20:08

[BertBert]

Perhaps tell us the question?

[Trackdayguy]

Sounds a blast, gotta love those old non complicated crossflow engines