Crossflow won't go over 6000rpm

[bstark]

No jokes please

 

This may be a case of TADTS, but I want to check if this is normal and if there's an easy tweak.

 

Engine is a Steve Parker Racing 1700cc unit with double valve springs and a 234 cam, running on twin 40's, 4-2-1 manifold and new Powerspeed side exit (was std Caterham rear exit previously).

 

It's a really torquey, sweet spinning engine which is great on the road and pretty effective on the track but there are times when sprinting (like yesterday at Brands) when an extra, say, 500rpm would be really handy as it's just the wrong time to change gear.

 

When you get to 6,000rpm currently it sort of hits a brick wall and just pops and bangs until you change up.

 

Now the part of me thinks this sounds suspiciously like a rev limiter has been fitted (ancillary bits such as carbs, manifold, ignition etc. were originally off the 1600 Sprint engine installed before I bought it) - is there an easy way to check? Or could it be something else?

 

Bob Stark

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[Graham Perry]

Or you may have a broken valve spring ☹️

[I.Mupferit]

Or just plain weak valve springs. Se7en-Up had this same thing on his X/Flow when he first got the car. A new set of springs soon sorted it out.

 

Brent

 

2.3 DURATEC SV Reassuringly Expensive

R 417.39 😬

[DaveMorris]

Rev limiter would be fitted across the positive and negative poles on the coil. Check to see if more than one wire going to each terminal. There should be a positive and negative going to the distributor. If there is another then follow this through to wherever it goes.

 

234 cam should rev to more than 6000/ Mine did (though I have had several rebuilds in the past few years 😳).

 

Agree on posts above re valve springs if no rev limiter fitted.

 

X-flow(er) power now resting. Trying Vx for a change.

[Pezky]

Sounds like a rev-limiter, my xflow does the same when it hits the limiter. I would have thought it would go past 6k even if weak springs etc.

What sort of ignition system is fitted?

[bstark]

Hmmm....

 

Rev limiter sounds more pleasant than broken / weak valve springs... Are they easy to check with the rocker cover off (ie. will it be obvious to an engine numpty?). Steve told me he fitted double springs to his engines FWIW.

 

Dave - thanks for that - I'll check.

 

Q102 - it's the Lucas ignitor setup that I presume came from Caterham. so still has a dizzy but no points.

 

 

Bob Stark

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[Big Brother]

My problem was the engine had been fitted with single valve springs.

5700 was the maximum revs I could get ☹️

 

Swapped to double springs and managed to get 7200 a couple of times 😬

 

As your engine has been built by a well known and respected builder, I'd start with the limiter first.

 

Steve

 

 

SE7EN-UP!

---

_{Friends help you move. Real friends help you move bodies}

---

 

[Crudders]

Bob - I had something similar on my first engine and that was definitely weak valve springs, cured by a head overhaul which included new double springs (everything else was put back to the same spec.).

 

I may be talking out of my bottom but ISTR that some Lucas ignition systems had a rev limiting rotor arm - may be worth checking. As to how you go about identifying one, I'm sorry I haven't a clue.

 

Crudders

[I.Mupferit]

The rev limiting rotor arm is quite easy to identify, I had one on my Lotus Cortina. It has a counterweight on it which moves out against a spring with centrifugal force and will eventually short out at the extremity of its travel to cut the sparks to the engine.

 

I found you can alter the rev limit by filing bits off to lighten the counterweight and thus raise the limit or alternatively put a blob of solder on it to increase the weight and therefore lower the limit.

 

Brent

 

2.3 DURATEC SV Reassuringly Expensive

R 417.39 😬

[Dee Pee]

My crossflow is on an Ignitor distributor with Emerald ECU etc and has been for 8 yrs. Soft cuts at 6500 and hardcuts at 7100. If I knew how to adjust/map the Emerald system I'd lower both figures to prolong the engine life. Been reliable though

 

 

[bstark]

Thanks Guys - I'll check it out tonight when I get home

 

Bob Stark

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[bstark]

OK - just checked the coil (dizzy is a right pain to get to by the looks of it - under the front carbs), and there are 6 leads going to it... 3 on the negative and three on the positive. (each terminal has two connectors - one wire to one, and two wires to the other).

 

They disappear immediately into a covered bundle and aren't traceable by eye. If I had to guess I would assume 2 to the dizzy, 2 to the rev counter, leaving 2 - would a rev limiter be a likely choice? If so, where's it likely to live.

 

May be more sensible for me to get 7-Indulgence to look at it 😬

 

Bob Stark

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[Pezky]

Depends who fitted it, have a feret about under the dash, little blighter will be there somewhere 😬

[Manxseven]

what colour are the wires?

 

Caterham Fireblade here

 

 

Edited by - Manxseven on 10 Sep 2007 20:50:53

[DaveMorris]

With that number of wires on the coil then rev limiter is possible.

 

Agree with Q102 - under dash is likely - unless you have a little box (about 2 matchbox size) on bulkhead on engine side (people often fit them near to where the steering column comes thru).

 

HOWEVER - if you can see definite pairs heading off in different directions in the loom (or look at teh colour of the wires at the dizzy and same for the rev counter) then by process of elimination you could remove the wires to the rev limiter - effectively taking it out of the loop.

 

Worth putting it back in the loop though, even if you change the limit. Many rev counter types (recent ones anyway) have their instructions on the net - so you could download them and be able to change the limit.

 

X-flow(er) power now resting. Trying Vx for a change.

[cskip]

Tracing the coil wires shouldn't be that hard. Another option is to look at the colours of the wires at the coil, presuming that the normal coding rules have been applied you should be able to work it out. Four wires to the coil for tacho and iginition power should be white. This leaves two wires to trace.

 

A vehicle wiring colour coding guide can be found:

 

http://www.team.net/sol/tech/LucasColours.html

 

Skip.

 

West Hants Luddite

See CSKIP here

[bstark]

Handily, all six are white 🙆🏻 (or white with a black stripe for the -ve).

 

There is a finned silver Lucas 'amplifier' box fitted to the bulkhead next to where the column goes through, if that's related...

 

Bob Stark

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[Pezky]

That will be for the ignition system, should be another box somewhere.

[bstark]

Thanks again for the replies on this - turns out there is a home made (think bits from maplin) limiter up under the dash - disconnected the engine now apparently pulls strongly to 7,000rpm 😬 (and felt good for more) and feels stronger than before from about 4,500.

 

7-Indulgence are going to fit a new limiter to 6,500rpm so I don't blow it up through exuberance. Can't wait to try it

 

Bob Stark

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[eric]

my limiter WAS 6800

 

It is no more in the car (old electronic item ...)

 

 

happy engine, happy driver

[bstark]

OK - I have the car back now and WOW! What a difference that's made 😬 😬 🥰

 

Just in case anyone else has a similar experience and isn't sure if its worth investigating, it's now obvious that the homemade limiter was thieving power from about 4,800rpm. My car is so much quicker above that now - really noticeable. Dead chuffed with the result . (7-Indulgence again).

 

 

Bob Stark

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