Post by enigmas on Apr 19, 2021 7:43:39 GMT
Having several different manifold and fueling options available I thought it about time to update the way fuel is delivered to my P76 V8 powered MK3 P5 coupe.
Currently the engine as setup looks like this.
For the last 38 years it has used the original P76 twin throat down draft carburettor (WW Stromberg) as seen below.
A perfectly reliable carburettor but really quite an antiquated design.
There's also an LPG gas mixer/ring fitted between the carburettor and the air filter. The primary fuel is LPG with petrol as a backup fuel, although in reality I removed the petrol tank decades ago.
This is the actual carburettor with the gas mixer fitted.
The LPG tank resides where the petrol tank was once located. I'm going to fabricate a smaller capacity tank (approx 20-30 litres) and this will reside behind the current LPG tank. There'll be 2 separate fillers either side much like some Jaguars have.
The primary upgrade though is to a P76 manifold I've modified to take 2 CD Zenith Stromberg carburettors (actually from a couple of Volvos.) One of the main differences with these Stromberg CD carbs is the bodies are not drilled for the Rover V8 style PCV system. Instead I'll be utilizing the existing inlet manifold PCV valve of the P76 V8. Apart from that the carburettors have all the good qualities of tight mixture control with the added benefit of an air bleed screw behind the temperature sensitive mixture compensator (fitted to the side of each carb if you're not aware.)
If interested, look closely at the last picture, the yellow cover of the temperature compensator can be see on the left hand side carburettor. Just to the right of the compensator is the brass head of the mixture air bleed screw. This allows further minute air bleed adjustment to the mixtures of each carburettor during idle conditions
The initial modification to the manifold was done ages ago and then put aside. The most recent changes since then have been the fabrication of suitable linkages both for the throttle and in this case the manual choke for petrol operation. The linkages took me about 3 days (5 -6 hrs each day) as I didn't want any unnecessary free-play in the system.
Here's the manifold minus the linkages.
Here's some of the linkages in place.
Here's a view of the first stages in fabricating/sorting the choke linkages.
Here's a view of the open throat and radiused air filter mount on one of the carbs.As well the LPG gas feed to the carburettor can be seen at the base of the filter mount.
Here's a view of the manifold with the LPG feed hoses and stepper motor in place.
* The stepper motor will maintain the correct A/F ratio via a small module and an oxygen sensor fitted to the exhaust system. The module also incorporates a screen showing current time A/F ratios whilst driving.
* In the last image the choke balance bar has been changed (bent into a slight U shape for improved geometry.) There is still another bell-crank yet to be fabricated to change the pull-angle of the choke through 90° so that the original choke T handle cable will fit straight on.
Once that's all done I'll spend some time detailing and painting various bits and pieces. 😎
Currently the engine as setup looks like this.
For the last 38 years it has used the original P76 twin throat down draft carburettor (WW Stromberg) as seen below.
A perfectly reliable carburettor but really quite an antiquated design.
There's also an LPG gas mixer/ring fitted between the carburettor and the air filter. The primary fuel is LPG with petrol as a backup fuel, although in reality I removed the petrol tank decades ago.
This is the actual carburettor with the gas mixer fitted.
The LPG tank resides where the petrol tank was once located. I'm going to fabricate a smaller capacity tank (approx 20-30 litres) and this will reside behind the current LPG tank. There'll be 2 separate fillers either side much like some Jaguars have.
The primary upgrade though is to a P76 manifold I've modified to take 2 CD Zenith Stromberg carburettors (actually from a couple of Volvos.) One of the main differences with these Stromberg CD carbs is the bodies are not drilled for the Rover V8 style PCV system. Instead I'll be utilizing the existing inlet manifold PCV valve of the P76 V8. Apart from that the carburettors have all the good qualities of tight mixture control with the added benefit of an air bleed screw behind the temperature sensitive mixture compensator (fitted to the side of each carb if you're not aware.)
If interested, look closely at the last picture, the yellow cover of the temperature compensator can be see on the left hand side carburettor. Just to the right of the compensator is the brass head of the mixture air bleed screw. This allows further minute air bleed adjustment to the mixtures of each carburettor during idle conditions
The initial modification to the manifold was done ages ago and then put aside. The most recent changes since then have been the fabrication of suitable linkages both for the throttle and in this case the manual choke for petrol operation. The linkages took me about 3 days (5 -6 hrs each day) as I didn't want any unnecessary free-play in the system.
Here's the manifold minus the linkages.
Here's some of the linkages in place.
Here's a view of the first stages in fabricating/sorting the choke linkages.
Here's a view of the open throat and radiused air filter mount on one of the carbs.As well the LPG gas feed to the carburettor can be seen at the base of the filter mount.
Here's a view of the manifold with the LPG feed hoses and stepper motor in place.
* The stepper motor will maintain the correct A/F ratio via a small module and an oxygen sensor fitted to the exhaust system. The module also incorporates a screen showing current time A/F ratios whilst driving.
* In the last image the choke balance bar has been changed (bent into a slight U shape for improved geometry.) There is still another bell-crank yet to be fabricated to change the pull-angle of the choke through 90° so that the original choke T handle cable will fit straight on.
Once that's all done I'll spend some time detailing and painting various bits and pieces. 😎
