I was going to just tag this to the thread that I've taken the quote below from but decided rather that threadjack I should start my own one. Here we go!
I've read the linked piece and can see the reasoning (but elsewhere while researching this stuff I read that the poppets actually deliver a more targeted spray than an injector can which is why GM chose the set-up but can also see that there is still an element of that in that conversion) but as I'm not going down that route my questions relate to air flow.
I'm going to number the questions and anyone with any thoughts on any of the questions, please chime in with your thoughts.
1) Am I correct in thinking that the delivery tubes are routed to be clear of the runner mouths so as not to impede air flow?
2) Does the spider block impede air flow to the rearward cylinders?
3) Has there ever been a manifold for a carb set up that had the the throttle body located non centrally (as opposed to forwards on the CSFI Vortecs?
4) Does the TBI (even though it isn't a Vortec) have its throttle body central or off-set?
5) Between Vortec CSFI, TBI, and carb manifolds are there differences that relate to where the fuel is introduced. Ie. does a TBI or carb manifold have features that are there solely to aid even mixture distribution to the cylinders - something that isn't a concern with the CSFI system?
6) What is there in the way of a gasket between the upper and lower manifold halves on a Vortec?
The reason I ask all of this is that my Vortec is running on LPG (propane) and the LPG is introduced via a mixer venturi upstream of the throttle body (at the engine end of the trunking that carries the MAF sensor). Thus, mixture distribution isn't necessarily catered for by a manifold that relies on injecting fuel into the individual runners. The LPG is already in gas form when introduced but is still heavier than air and therefor can potentially suffer the same inertial effects that gasoline from a carb can. I'm looking at that spider block and pipes and thinking that isn't helping the cause at all.
My intention is to replace the inlet manifold gasket in the next few months and I'm only retaining the gasoline system as a 'get me home' provision should I run out of LPG before I can get to an LPG filling station (they are few in number and often have restricted opening hours). I don't even need the gasoline for start up - it'll happily fire up from cold on LPG.
So what I'm thinking about is (A) a way of simplifying (primarily getting rid of that spider block and pipes) the gasoline system right down to emergency only use and/or (B) should I consider another manifold (carb) with possibly a central throttle body to aid fuel (LPG) distribution and if that is viable, am I looking at both halves or is there an upper half that would mate with the existing lower. (My understanding so far is that the only lower manifold suitable for the Vortec heads is the marine one (but that they are hard to locate) but what about an alternative upper one?
On top of all this, I want to retain (preferably/presumably) my existing throttle body (with its TPS), don't want to lose cruise control and have in mind also the aggro to benefit ratio in that I don't want to have to (overly) fabricate unique parts, relocate other components (clearance) or introduce unreliability.
So, if anyone can help with any of the above please throw your ideas in - I'm open to all ideas. At the very least I'm keen to achieve plan (A) ie be rid if all the gubbins inside the manifold but I understand that the injectors must be downstream from the throttle plate to run with the existing PCM which I really don't want to change or mess with as I have a separate ECU for the LPG system. I'm also thinking about ditching the EGR (which I wouldn't countenance with a diesel but for a lightly stressed gasoline engine is OK IMO). I know this can lead to detonation but bear in mind the octane rating of LPG is higher that that of gasoline.
Thoughts?
He has swapped the original poppet injectors to the MPFI. Here’s an article that goes a little into the difference:
https://www.fourwheeler.com/how-to/1012or-csfi-to-mpfi-vortec-engine-fueling-fix/
I've read the linked piece and can see the reasoning (but elsewhere while researching this stuff I read that the poppets actually deliver a more targeted spray than an injector can which is why GM chose the set-up but can also see that there is still an element of that in that conversion) but as I'm not going down that route my questions relate to air flow.
I'm going to number the questions and anyone with any thoughts on any of the questions, please chime in with your thoughts.
1) Am I correct in thinking that the delivery tubes are routed to be clear of the runner mouths so as not to impede air flow?
2) Does the spider block impede air flow to the rearward cylinders?
3) Has there ever been a manifold for a carb set up that had the the throttle body located non centrally (as opposed to forwards on the CSFI Vortecs?
4) Does the TBI (even though it isn't a Vortec) have its throttle body central or off-set?
5) Between Vortec CSFI, TBI, and carb manifolds are there differences that relate to where the fuel is introduced. Ie. does a TBI or carb manifold have features that are there solely to aid even mixture distribution to the cylinders - something that isn't a concern with the CSFI system?
6) What is there in the way of a gasket between the upper and lower manifold halves on a Vortec?
The reason I ask all of this is that my Vortec is running on LPG (propane) and the LPG is introduced via a mixer venturi upstream of the throttle body (at the engine end of the trunking that carries the MAF sensor). Thus, mixture distribution isn't necessarily catered for by a manifold that relies on injecting fuel into the individual runners. The LPG is already in gas form when introduced but is still heavier than air and therefor can potentially suffer the same inertial effects that gasoline from a carb can. I'm looking at that spider block and pipes and thinking that isn't helping the cause at all.
My intention is to replace the inlet manifold gasket in the next few months and I'm only retaining the gasoline system as a 'get me home' provision should I run out of LPG before I can get to an LPG filling station (they are few in number and often have restricted opening hours). I don't even need the gasoline for start up - it'll happily fire up from cold on LPG.
So what I'm thinking about is (A) a way of simplifying (primarily getting rid of that spider block and pipes) the gasoline system right down to emergency only use and/or (B) should I consider another manifold (carb) with possibly a central throttle body to aid fuel (LPG) distribution and if that is viable, am I looking at both halves or is there an upper half that would mate with the existing lower. (My understanding so far is that the only lower manifold suitable for the Vortec heads is the marine one (but that they are hard to locate) but what about an alternative upper one?
On top of all this, I want to retain (preferably/presumably) my existing throttle body (with its TPS), don't want to lose cruise control and have in mind also the aggro to benefit ratio in that I don't want to have to (overly) fabricate unique parts, relocate other components (clearance) or introduce unreliability.
So, if anyone can help with any of the above please throw your ideas in - I'm open to all ideas. At the very least I'm keen to achieve plan (A) ie be rid if all the gubbins inside the manifold but I understand that the injectors must be downstream from the throttle plate to run with the existing PCM which I really don't want to change or mess with as I have a separate ECU for the LPG system. I'm also thinking about ditching the EGR (which I wouldn't countenance with a diesel but for a lightly stressed gasoline engine is OK IMO). I know this can lead to detonation but bear in mind the octane rating of LPG is higher that that of gasoline.
Thoughts?