Improved throttle mechanism

[Les Pettitt]

I am sure that a lot of you CR sixers will have already upgraded your throttle mechanism but which supplier did you choose? Does it just bolt on? Do you use the original throttle and choke cables? Is it a worthwhile upgrade? I am particularly hoping to cure poor/lumpy idling. I am happy to wait and look at the alternatives on offer at the International butI would be grateful to hear about your experiences. Many thanks.

[JohnC]

I'm curious what these improved mechanisms are - I've not seen one here in Sydney yet. Do they include the throttle bodies, or just the mechanism?

 

Even the earlier cars can suffer a lumpy idle if the throttle bodies become worn - wear in the spindles/plain bearings and slight warping of the spindles both conspire to allow air leakage around the butterflies when 'closed', and that results in a lumpy idle. The linkage isn't even in play (ouch!) at that point.

 

Have you tried getting anyone to recondition what you already have? I'm going down that route (on my CP car), so I'll report back once it's done. Throttle bodies drilled & bushed, spindles turned & sleeved, and mechanism bronze bushed throughout (main shaft and vertical links).

 

John

[Richard Crawley]

I'm curious what these improved mechanisms are - I've not seen one here in Sydney yet. Do they include the throttle bodies, or just the mechanism?

I believe both the throttle bodies & linkage are different on the CR to CP series engines but it’s the CP linkage (or at least it’s principles) that make the difference to smooth idling & good pick up. I believe the CP linkage can be fitted to the later CR series bodies with all their benefits but you need to ensure that the bodies, spindles & the rest of the system etc. is not knackered! All you require is readily available (at least in the UK) from most of the major tuning suppliers.

[Roger H]

John (et al) - If you have not had the throttle bodies bushed yet - be careful!!

 

When the bushes are installed, they are fitted protruding into the inlet duct, then reamed back to be flush with the aluminium body. This must be done this way to get the curvature of the ends of the bushes to match the sides of the inlet. The clearance at the sides of the butterflies is critical at this point, and if the manifold bearing surface (when the butterflies are closed) is affected at all, you will get air leakage around the butterfly. This will prevent a complete seal which will result in the inability to achieve a smooth idle.

 

I say all this from experience and even though my machinist is superb, it was not something that was obvious untill well after the fact. It took me weeks to finally realise what was causing the inability to achieve exactly equal inlet airflows when tuning.

 

Les - IMHO, there is no question that a good overhead linkage is better and easier to adjust than either of the OE setups. The principle is the same as the CP series, but is mounted above the manifolds.

 

I bought one from Revington's but unfortunately I cannot recommend it. The rubber bushings are inadequate (I replaced them initially with eurethane), and the whole mounting assembly is too lightweight and flexes when throttle is applied, causing a lack of synchronisation in the opening of the butterflies, particularly at low revs.

 

I modified the mounting brackets and replaced the bushings with rose joints and it is now quite acceptable. The modifications were not difficult but for the (high?) initial cost of the unit, I expected better. I only use the single choke cable controlling the metering unit mixture - not the increased idle cable which, for me, is an un-necessary complication. The unit uses the original throttle cable.

 

It is not difficult to build a simple system of levers to do the job and I'm surprised at the apparent lack of availability of a decent setup for a reasonable price - maybe someone can recommend a better one.

 

Hope this helps

 

Regards

Roger

[Les Pettitt]

Roger

Many, many thanks for your reply. It is exactly the kind of feedback I wanted. I have seen the Prestige overhead linkage and thought it looked very heavy and over engineered but in the light of your comments perhaps it is the way to go. As you say, these things aren't cheap and I don't want to spend £150 to £200 and be disappointed.

Regards

Les

[Richard Crawley]

I don't want to spend £150 to £200 and be disappointed.

Blimey, that sounds rather expensive; I would have thought you could improve matters for a lot less! I spent only a fraction of that & mine runs faultlessly; but I did start with an original CP linkage system!

[jonlar]

Here's the link to Prestige

 

http://www.prestigeinjection.fsnet.co.uk/throtlink.htm

[Richard Crawley]

All my stuff came from Pumfords & at quite reasonable cost; don't know if they are still going!