Exciting day - rebuild of 78 coupe

Mad4slalom

Mad4slalom

Well-known user
johng said:
It's been a while, but thought I'd give an update on the Air Fuel Ratio situation. My lovely wife bought me a wideband sensor kit for my birthday and I've had a bung welded into the exhaust.
View attachment 28157
The surprising result was that I found the car was running a bit rich at idle, which gradually leaned out as you increase revs up to 2000rpm and then shot up to 17.5:1
The value that was measured at the MOT station was actually in terms of lambda (it was a value of 1.22), I'd multiplied this by 14.7 to get an AFR of 18:1. I realize now that was wrong, because the value of 14.7 is for pure petrol. For the E5 that I'm using it should be 14.4 and that makes the MOT measurement an AFR of 17.6:1. Basically, the MOT station measurement was correct all along!
Taking the car for a drive it was running at 17.5:1 whilst cruising anywhere from 45 to 60mph, hopefully I haven't done the exhaust valves any damage.
It was simple to fix the idle mixture, just needed to go from 4.5 turns out to 3.5 turns out and also it was easy to fix the cruise mixture as well. On my carb you can adjust the Adjustable Part Throttle from outside of the carb and winding this up brought the cruise AFR down to 14.3.
Here are the results I ended up with.
View attachment 28158

One other little job that seems to work well was for my Air Con. The air box that houses the evaporator is very close to my headers and gets too hot to touch, which can't do much good for the cold air inside it. I've now covered the box with some self adhesive aluminised fiberglass sheet. Now the box doesn't get hot at all and the air con seems to work much better (although maybe that just because it's not very hot out now).
View attachment 28159
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That is interesting johng, did you have any symptoms or just the mot readings? My 72 has a bung to access the exhaust flow, but was set up in buffalo NY and altitude my be different to cornwall.
Mine has always smelt a bit rich so maybe i should find a holley carb guy and have a tune 🤔👍
 
johng

johng

CCCUK Member
When I fitted the headers and sidepipes I was a bit concerned that being more free flowing this might make the car run a bit lean. Also, I'd stripped down the carb previously to clean it out and found that a previous owner had made some dubious alterations (the jets were smaller than standard, the rods were from an earlier carb and were the wrong length and the rod hangers had been bent presumably to account for the wrong length). I decided to put it all back to standard and then get the AFR measured to see where I was.
Strangely enough the carb is now set up pretty much exactly as it would have come from the factory and isn't running lean at all (except for a strange blip at 1000rpm which I don't understand).
 
Roscobbc

Roscobbc

Moderator
Carbs really are such old tech. If that was a Holley I'd put the 'blip' down to the carb 'transitioning' from idle jetting and on to main jet.
Not 100% sure how the Rochester operates off idle jetting and on to main jets but it could simply be a characteristic of the carb?
 
johng

johng

CCCUK Member
So it's been a bit of a disappointing day. I gave my car a good clean and polish this afternoon and discovered that the lovely shiny "chrome" finish on my sidepipe covers has not been as durable as I had hoped:( It has lasted all of 1 year.
It's lost it's shine along the bottom edge. I'm guessing that water has got under the clear coat where it will be thinnest along the edge. Also I should have had paint protection film put on the end section of the covers in front of the rear wheels. It looks like I've knocked the clear coat and the silver off whilst reversing down my gravel drive. At the moment it doesn't look too bad if you only look from above, but I'm going to have to think of a plan B.

IMG_20250204_202207_819.jpg
IMG_20250204_202234_940.jpg
 
Nassau65

Nassau65

CCCUK Member
In all fairness to you, the chrome on the covers as supplied from the vendor was probably not of the best quality. Yes, looks lovely when new, but in most cases will not be great in a few years time.
A friend bought a set of repro knock off’s for his mid year. The chrome on the cones and spinners only lasted a year before showing signs of rust, and the car was hardly ever out of the garage.
If it was me, I would use as is for as long as they look reasonable and then get them re chromed to a better standard.
 
Nassau65

Nassau65

CCCUK Member
I love side pipes, always have done. The look is great. What I never liked is the rusty appearance of the Hooker type in chrome once a few years old.
The factory 1969 covers in aluminium to me looked great, and if wanted could be highly polished for that bling look. Even in their dull appearance I think they still look good.
 
johng

johng

CCCUK Member
Nassau65 said:
If someone chromed them from new, someone must be able to do them again surely.
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Nobody chromed them, I had them coated in silver (actual pure silver) and then clear coated. It's explained in pages 29 /30 of this thread and was in the club magazine last year
 
teamzr1

teamzr1

Supporting vendor
Heat is high temp to 250F degrees
Also, that vendor has a clear coat high temp


This one says to 90 C

 
Nassau65

Nassau65

CCCUK Member
johng said:
Nobody chromed them, I had them coated in silver (actual pure silver) and then clear coated. It's explained in pages 29 /30 of this thread and was in the club magazine last year
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Right, sorry my mistake. Thought you bought them from the supplier already “chromed”.
 
johng

johng

CCCUK Member
teamzr1 said:
Heat is high temp to 250F degrees
Also, that vendor has a clear coat high temp



This one says to 90 C
Click to expand...
Paint might well be where I end up, but if you read the reviews you'll see they look more like silver paint than chrome. It is possible to get a paint finish that looks like chrome, but it's probably not going to be durable enough. To achieve the chrome effect you have to paint over a high gloss basecoat and this means it's not resistant to shock or abrasion.
 
Nassau65

Nassau65

CCCUK Member
I’ve had a look, can’t see chrome heat resistant paint, I seen aluminium which would be the same look as the factory covers.
 
Chuffer

Chuffer

CCCUK Member
johng said:
Paint might well be where I end up, but if you read the reviews you'll see they look more like silver paint than chrome. It is possible to get a paint finish that looks like chrome, but it's probably not going to be durable enough. To achieve the chrome effect you have to paint over a high gloss basecoat and this means it's not resistant to shock or abrasion.
Click to expand...
Where are you located ? It might be worth contacting Sandwell UK Ltd to see what they can suggest . They are a specialist coatings company based in Towcester and do lots of work on components for the race car fraternity and classic cars . They shot peened my Valve ( rocker covers ) and coated them in Silver Xylan 1270 which chemically bonded to the steel and withstands very high temperatures and doesn`t discolour . It cost me ÂŁ100 for the pair six yeas ago .
Sandwell UK Ltd.
2, Foundry Place
Towcester
Northamptonshire NN12 6FP
Tel : 01327 350205
 
johng

johng

CCCUK Member
Chuffer have you got any photos of your rocker covers? Looking at the specs for Xylan 1270 it says it is low/medium gloss. Does it look like unpolished metal or is it more like silver paint?
 
Chuffer

Chuffer

CCCUK Member
johng said:
Chuffer have you got any photos of your rocker covers? Looking at the specs for Xylan 1270 it says it is low/medium gloss. Does it look like unpolished metal or is it more like silver paint?
Click to expand...
It is a medium gloss ( satin ) paint finish . It has good abrasion resistance and it has not discoloured or faded . These are the best photos I have at present but can take more close ups next time I am down at the workshop where it lives . Pity we didn`t have this conversation earlier as I was over there this morning . It`s 9 miles away !!Vette in Workshop.JPGDSC_4842.JPGEngine bay.JPG
 
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