Crossflow engine with 244 cam

[Brian Robey]

can anyone advise.....1700 crossflow engine with Roger King 155bhp upgrade including a 244 kent cam , forged pistons, steel rocker, larger valves, improved porting and tuftrided crank. Runs well but at 3000rpm constant load backfires badly through carbs. New distibutor and electronic ignition fitted by Redline last year, but still runs badly at 3000 rpm. I know that the power curve for the cam shows the main output to be between 3000 and 8000 but when the engine was 1st built and put on the rolling road by Roger it did not do this. Output figures at the wheels were :

2000rpm 27bhp

2500 42

3000 56

3500 62

4000 78

4500 92

5000 106

5500 118

6000 125

6500 121

Can anyone suggest a sensible solution or throw any light on the problem..perhaps this is a common problem with such an upgrade?

[Casbar]

My engine was the same spec and it ran really well.

 

Eventually I fittey a weber 3D mapped ignition system.

 

But I would say, your issues are nothing to do with the cam or engine spec. A Roger King 155 upgrade is common among xflow owners and the engines are normally stonking

 

Perhaps a rolling road session might be the solution.

 

Edited by - Casbar on 23 Jan 2008 13:54:56

[alextangent]

Could be a number of things, but worth checking for an air leak in the inlet manifold side.

 

Alex McDonald

A loud 1700 SS in bits

[Srcarter]

Brian, Have you a rev limiter fitted, possible cause

valve clearences

carb set up (to weak)

ignition timing, a good start to find the problem.

[Casbar]

Good point about an air leak, spray some WD40 on and around the inlet manifold and carbs when the engine is idling and listen for a rise in revs, if there is an air leak, the revs will rise (don't want to teach you suck eggs or anything)

[Brian Cookson]

Had similar with my crossflow. Eventually found one of the carb chokes loose. Quick fix by tightening the grub screw after slackening the locknut. (Seem to recall it's about at the 45 degree position). Re-tightened all the others and all was well. Hope this is of some help.

 

bc

[Brian Robey]

Thanks to all of yuo who have responded so far on the crossflow problem, some useful hints...I will have a quick look at the air leak possibility and chokes this weekend weather permitting!!! I was thinking of putting it on the rolling road at Southern Carburetters...anyone tried them?

[Neil MH]

I have a vague recollection of problems in that sort of rev range caused by idle jets - I think that Caterham upgraded the standard 1700ss on 40s from 45f9 to 50f9 to get over a hesitation around 2,500 to 3,000.

 

However, whether that has any bearing on your problem I don't know.

 

I had heard that Southern Carbs were good - but have not used them myself.

 

 

Neil

[Graham Sewell]

The problem with a lot of rolling roads is that they tend to only use full throttle to get the power reading, rather than light throttle (constant speed) for diagnostics. therefore, they have very little to do with day-to-day drivability.

 

I once tried using a rolling road to diagnose engine noises that were perfectly audible on the road, but in the confines of a garage with the echos from the exhaust, etc.... you could not hear yourself think.

 

Cheers,

 

Graham

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Low tech luddite - xflow and proud!