What Size Impco Carb?
What Size Impco Carb?
I'm getting all the parts and pieces together to build me a new work rig for the ranch. I'm using a Ford 300 six for the engine and plan on running propane only. It's also going to be turbocharged at not more than 8 lbs. I've got the propane system off an old 300 we used as an irrigation engine. It's an Impco Model 125 carb and a Model E regulator. After talking with my local propane guy, I think the regulator will work for me, but I'm thinking the carb may be too small. What do you guys suggest I put on this engine? I seriously doubt it will ever see anything above around 3000 rpm, but with the boost it's going to be putting a lot more volume through the engine than a stock 300.
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Re: What Size Impco Carb?
I would bet on a 200-series mixer.
The 125 is more suited for 4-cilinder engines in the 1.5-2.5 litre range.
The 125 is more suited for 4-cilinder engines in the 1.5-2.5 litre range.
Re: What Size Impco Carb?
200 or 225 , pending the required dimensions of the package fit up
200 being right angle entry and 225 being centre hat
both essentially using same internal parts
a 225 suits an EFI duct location easier and flows slightly more NA and is used commonly for engines 3.3 to 5 L
whilst the 200 is maybe a little physically stronger in hat design
and is designed more for dual on manifold installations, being avail left and right versions
or used as a low profile total replacement of a petrol carb,, when the vacant carb location is fitted with an impco throttle body
im using a 225 in blow through up to 15 psi , though envy the inherent strength in the casting design of the 200 , it will not suit the location of my install
200 being right angle entry and 225 being centre hat
both essentially using same internal parts
a 225 suits an EFI duct location easier and flows slightly more NA and is used commonly for engines 3.3 to 5 L
whilst the 200 is maybe a little physically stronger in hat design
and is designed more for dual on manifold installations, being avail left and right versions
or used as a low profile total replacement of a petrol carb,, when the vacant carb location is fitted with an impco throttle body
im using a 225 in blow through up to 15 psi , though envy the inherent strength in the casting design of the 200 , it will not suit the location of my install
when the going is hard, don't retard, remember your lubrication
Re: What Size Impco Carb?
Bumpstart, what engine are you running that on? Since I posted, I've run across this: http://www.scribd.com/doc/17379058/IMPC ... ing-Manual. Starting on page 91 they talk about matching the mixer to the engine. According to the manual, I would need a 425. If you are running a 225 mixer on a 300 CID engine at 15 lbs boost, then that would work for me as well, since I'm only planning on 8 lb. I'm just worried about running lean under load. I'm not planning on revving high, but if I'm pulling a trailer and need to downshift, I don't want to go lean enough to hurt my engine.
Also, since you seem to have experience with this, how do you boost reference your mixer? On a normally aspirated engine the mixer adjusts itself with engine vacuum; it won't be able to do this under boost. I've read several places it easy to do, but none of them explain how. LOL I've been researching this for over a year, but the propane/turbo combination isn't easy to find info on, and a lot of what I find is contradictory. Somebody with real 'hands-on' experience would be a BIG help.
Also, since you seem to have experience with this, how do you boost reference your mixer? On a normally aspirated engine the mixer adjusts itself with engine vacuum; it won't be able to do this under boost. I've read several places it easy to do, but none of them explain how. LOL I've been researching this for over a year, but the propane/turbo combination isn't easy to find info on, and a lot of what I find is contradictory. Somebody with real 'hands-on' experience would be a BIG help.
Re: What Size Impco Carb?
Hi Turbo300
Propane acts differently to petrol in that leaning out is not an issue like leaning out on liquid fuel. With petrol leaning out causes a hotter burn wheras with propane...leaning out causes a cooler burn which will not harm your engine.(just a power loss)
Running too rich with propane causes burnt valves and a hotter exhaust....the opposite to petrol.
Hope this helps
Cheers
Propane acts differently to petrol in that leaning out is not an issue like leaning out on liquid fuel. With petrol leaning out causes a hotter burn wheras with propane...leaning out causes a cooler burn which will not harm your engine.(just a power loss)
Running too rich with propane causes burnt valves and a hotter exhaust....the opposite to petrol.
Hope this helps
Cheers
Re: What Size Impco Carb?
hello.. using impco 225 and model E ( and supplementary model L ) on a 13B turbo rotary.. not on a 6.. hybrid t04 turbo.. wheel HP is up there around 300 at 15 psi
the airflow demands between a 4-5l engine and a ( 86-91 ) 13bt are not all that different
even the stock ( suck through ) 13bt airflow meter is rated for 720 cubic metres per hr ,,
( nearly bang on 425 cfm airflow into the engine at WOT at the stock 8 psi boost )
in oz,, the 225 is used as the common fitup for NA 3.8L holden/chev v6
3.3L, 4L and 4.1 L ford 6's ( 200- 250 ci )
and ford and holden /chev ..4.9-5l v8 ( 300 ci )
.. all ex NA EFI ..
whilst the 425 is more intended to replace a carb .. using a 4 barrel baseplate on 5L v8
( and commonly the 300A is fitted on the carbed 6 )
yes,,on paper.. or in NA mode 225 is a little on the small side on 4L + engines
.. but under boost in blow through,, it is a completely different story
.. and as such the efi duct fit up and simple layout of the 200/225 is much desired over the 300 and 425
.. it ( 200/225 ) is much more commonly ( and successfully ) turned to blow through duties than the other two less simple mixers . a case of simple is best
. the tiny losses from being apparently undersized when in NA mode have lesser impacts under boost
and in fact the total pressure drop in the mixer is not significant in the context of airflow pressure drop pumping losses through some types of intercoolers
keeping it small ,, keeps it responsive to tip in throttle movements , especially in the context where there is no true throttle pump enrichment circuit
as for boost reference,, you hook the convertor up to the reference port nipple that is from the mixer hat
( on 225 it comes from the rear of the backplate but is sourced before the restriction of the air gas valve assembly )
you will usually need to encorp a throttle closed blow off valve that returns boost to aircleaner on shut throttle to prevent a surge or stall on gear changes
( you can also fix this a little with tricky tee and pill bleed on the convertor reference line ,, more on that later if you need the tweak )
you will find that it may trend a little rich further and further into boost
( as in the post above mine .,,, mixtures dont need to be excessively rich like petrol ,, and can be detrimental )
and as such the pill and bleed method on the ref line can be also used to adjust things when you start to tune it under load
if your motor has the option of EFI manifolds and throttle body ,, fit it up.. and put the 225 in front of it .. ali fab an adapter if you have to...
hook the mixer reference line to the convertor.. fit a blow off valve.. close the plug gaps a little ( hopefully you already have a decent HEI ignition and not points ) // and that is about it
the airflow demands between a 4-5l engine and a ( 86-91 ) 13bt are not all that different
even the stock ( suck through ) 13bt airflow meter is rated for 720 cubic metres per hr ,,
( nearly bang on 425 cfm airflow into the engine at WOT at the stock 8 psi boost )
in oz,, the 225 is used as the common fitup for NA 3.8L holden/chev v6
3.3L, 4L and 4.1 L ford 6's ( 200- 250 ci )
and ford and holden /chev ..4.9-5l v8 ( 300 ci )
.. all ex NA EFI ..
whilst the 425 is more intended to replace a carb .. using a 4 barrel baseplate on 5L v8
( and commonly the 300A is fitted on the carbed 6 )
yes,,on paper.. or in NA mode 225 is a little on the small side on 4L + engines
.. but under boost in blow through,, it is a completely different story
.. and as such the efi duct fit up and simple layout of the 200/225 is much desired over the 300 and 425
.. it ( 200/225 ) is much more commonly ( and successfully ) turned to blow through duties than the other two less simple mixers . a case of simple is best
. the tiny losses from being apparently undersized when in NA mode have lesser impacts under boost
and in fact the total pressure drop in the mixer is not significant in the context of airflow pressure drop pumping losses through some types of intercoolers
keeping it small ,, keeps it responsive to tip in throttle movements , especially in the context where there is no true throttle pump enrichment circuit
as for boost reference,, you hook the convertor up to the reference port nipple that is from the mixer hat
( on 225 it comes from the rear of the backplate but is sourced before the restriction of the air gas valve assembly )
you will usually need to encorp a throttle closed blow off valve that returns boost to aircleaner on shut throttle to prevent a surge or stall on gear changes
( you can also fix this a little with tricky tee and pill bleed on the convertor reference line ,, more on that later if you need the tweak )
you will find that it may trend a little rich further and further into boost
( as in the post above mine .,,, mixtures dont need to be excessively rich like petrol ,, and can be detrimental )
and as such the pill and bleed method on the ref line can be also used to adjust things when you start to tune it under load
if your motor has the option of EFI manifolds and throttle body ,, fit it up.. and put the 225 in front of it .. ali fab an adapter if you have to...
hook the mixer reference line to the convertor.. fit a blow off valve.. close the plug gaps a little ( hopefully you already have a decent HEI ignition and not points ) // and that is about it
when the going is hard, don't retard, remember your lubrication
Re: What Size Impco Carb?
Thanks, bumpstart. I'm putting all this on a Ford 300 (4.9l). It's a pull-out from a wrecked F-150. It is set up for EFI, but I had planned to remove the throttle body and mount the mixer in it's place. You suggest leaving the throttle body in place and mounting the mixer in front of it, correct?
The purpose of all this is to have a 'new' work truck. I've got a 1974 F-250 chassis-cab with a four-speed I'm going to put it in. The turbo is a Holset HE 341, the best I can tell (it has no ID tag on it). It will be what you refer to as a tray truck. I'll use it on my ranch as my rolling workshop, hauling all my tools, welder, etc. No heavy towing is planned, I've got a '76 Crew Cab 460 for that, but if it has the power that figures show on paper, if I can get a good tune and not worry about melting something, that could change. I'm planning on running a Duraspark II ignition system. I'm trying to build something that will save me money over the current '79 351m gas-burner I'm running right now. Gasoline prices are killing me. Even if I only get mid- to high teens mpg, the cost savings on fuel will pay for the rig in around two years (by my calculations).
I've got both a Model E and a Model L vaporizer. Would I need to run them in tandem, or would the Model E work for my lower boost pressure?
I had forgotten about the fact that running lean with propane wasn't the same as with gas. I'm trying to research turbos, propane systems, and drivetrain design all at the same time, and my head is spinning a bit. LOL
The purpose of all this is to have a 'new' work truck. I've got a 1974 F-250 chassis-cab with a four-speed I'm going to put it in. The turbo is a Holset HE 341, the best I can tell (it has no ID tag on it). It will be what you refer to as a tray truck. I'll use it on my ranch as my rolling workshop, hauling all my tools, welder, etc. No heavy towing is planned, I've got a '76 Crew Cab 460 for that, but if it has the power that figures show on paper, if I can get a good tune and not worry about melting something, that could change. I'm planning on running a Duraspark II ignition system. I'm trying to build something that will save me money over the current '79 351m gas-burner I'm running right now. Gasoline prices are killing me. Even if I only get mid- to high teens mpg, the cost savings on fuel will pay for the rig in around two years (by my calculations).
I've got both a Model E and a Model L vaporizer. Would I need to run them in tandem, or would the Model E work for my lower boost pressure?
I had forgotten about the fact that running lean with propane wasn't the same as with gas. I'm trying to research turbos, propane systems, and drivetrain design all at the same time, and my head is spinning a bit. LOL
Re: What Size Impco Carb?
Just to correct a couple of mistakes
The Ford 6 cylinder 3.3L, 4L, and 4.1L are not all ex NA EFI. 3.3 Litres (pushrod) were never EFI and 4.1 Litres (pushrod) had EFI as an option in some models except Luxury models (Fairlane and LTD) where it was standard. The 4 Litre (OHC), starting with the EB Falcon if I remember correctly, were all EFI but not all were multipoint. The 3.9 Litre (OHC) and 3.1 Litre (OHC) starting in the EA Falcon were mostly centrepoint with some 3.9 Litres being multipoint (mostly the Fairlaine and LTD with some Fairmont and Falcon owners selecting the multipoint 3.9). Most taxis went with the Impco 225. I have seen a few Ford 5 Litre V8 engines (they are the old Windsor 4.9 with EFI but Ford insisted on calling them 5 Litres) in E series Fords fitted with Impco 200.
What Holden/chev NA 3.8 would that be? the VN-VR Holden 3.8 is a Buick/Pontiac engine, the VR-VT 3.8 is the Buick/Pontiac Ecotec. The 3.0-3.6 AlloyTec is a derivative of the Cadilac Northstar V8. Holden has never released a Chev V6, nor has it released an EFI petrol Chev V8 prior to the Gen 3, apart from the Suburban V8 which was a 5.7 litre Vortec (the other option was the 6.5 Turbo Diesel). Holden V8 has had 4 sizes, 253 (4.2 litre) 304 (4.9 litre) 308 (5 litre) and 350 (5.7 litre). The 253 and 308 (carby engines) are usually fitted with Impco 300A (both engines) or 425 (308 only, they are way to big for a street 253). 304 and 350 (EFI engines) are usually fitted with single GRA S480 or S510 throttle bodies, or Impco 225. Some people convert them to "carby style" manifolds and use twin GRA throttle bodies or Impco 425.bumpstart wrote:in oz,, the 225 is used as the common fitup for NA 3.8L holden/chev v6
3.3L, 4L and 4.1 L ford 6's ( 200- 250 ci )
and ford and holden /chev ..4.9-5l v8 ( 300 ci )
.. all ex NA EFI ..
whilst the 425 is more intended to replace a carb .. using a 4 barrel baseplate on 5L v8
( and commonly the 300A is fitted on the carbed 6 )
The Ford 6 cylinder 3.3L, 4L, and 4.1L are not all ex NA EFI. 3.3 Litres (pushrod) were never EFI and 4.1 Litres (pushrod) had EFI as an option in some models except Luxury models (Fairlane and LTD) where it was standard. The 4 Litre (OHC), starting with the EB Falcon if I remember correctly, were all EFI but not all were multipoint. The 3.9 Litre (OHC) and 3.1 Litre (OHC) starting in the EA Falcon were mostly centrepoint with some 3.9 Litres being multipoint (mostly the Fairlaine and LTD with some Fairmont and Falcon owners selecting the multipoint 3.9). Most taxis went with the Impco 225. I have seen a few Ford 5 Litre V8 engines (they are the old Windsor 4.9 with EFI but Ford insisted on calling them 5 Litres) in E series Fords fitted with Impco 200.
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456
Re: What Size Impco Carb?
Maybe you could clarify the engine. from your original post I took it to mean you have a straight six out of a junked F150 pick up. The EFI version of this engine in Canada was a twin throttle body. Storm lists many engine designs where some exist here and others don't, specifically the Holden engines . Engines converted here used an adaptor that would allow mounting of a 300 mixer ahead of the throttle body with an aftermarket air cleaner or an additional adaptor returning to the factory plastic air cleaner. Another available adaptor allowed use of a 225 or 425 setup to the factory throttle body. I don't think anyone ever used a 425.
The straight six engine was designed for torque at fairly low RPM. This engine seldom exceeded 4000 RPM. This means the CFM requirements normally aspirated are around 300 at 4000 RPM. You want to add a turbo charger with 8 pounds of boost. Max CFM will increase to approximately 450 if I have calculated correctly.
The mixers are capable of the following CFM at -1.5" WC normally aspirated.
125 202 CFM. Not anywhere near enough.
200 276 CFM Still not enough
225 329 CFM Now were talking
300 348 CFM Some extra if you need it
300/50 series 432 CFM
425 460 CFM
I expect each of these will have an increased CFM according to boost. Your increasing boost 1/2 atmosphere so each of the numbers above would increase accordingly with a multiplication of 1.5 with the only issue being can the chosen mixer supply the appropriate amount of fuel at the boosted pressure. I can't answer that but most of the posts from those already boosting there mixers indicate they can. A 225 seems to be the ideal for your set up. This selection would of course change if you plan on running higher RPMs.
Most of my experience is on stationary engines when it comes to TCing so I would have to defer to those on this site that have direct experience on cars and trucks.
The straight six engine was designed for torque at fairly low RPM. This engine seldom exceeded 4000 RPM. This means the CFM requirements normally aspirated are around 300 at 4000 RPM. You want to add a turbo charger with 8 pounds of boost. Max CFM will increase to approximately 450 if I have calculated correctly.
The mixers are capable of the following CFM at -1.5" WC normally aspirated.
125 202 CFM. Not anywhere near enough.
200 276 CFM Still not enough
225 329 CFM Now were talking
300 348 CFM Some extra if you need it
300/50 series 432 CFM
425 460 CFM
I expect each of these will have an increased CFM according to boost. Your increasing boost 1/2 atmosphere so each of the numbers above would increase accordingly with a multiplication of 1.5 with the only issue being can the chosen mixer supply the appropriate amount of fuel at the boosted pressure. I can't answer that but most of the posts from those already boosting there mixers indicate they can. A 225 seems to be the ideal for your set up. This selection would of course change if you plan on running higher RPMs.
Most of my experience is on stationary engines when it comes to TCing so I would have to defer to those on this site that have direct experience on cars and trucks.
Re: What Size Impco Carb?
I took the OP to mean a straight carby six, I am unaware of any other 300 ci six cylinder Ford engines. Any pics of the EFI variety?C3H8 wrote:Maybe you could clarify the engine. from your original post I took it to mean you have a straight six out of a junked F150 pick up. The EFI version of this engine in Canada was a twin throttle body.
I listed them to clear up mistakes in a previous post.C3H8 wrote: Storm lists many engine designs where some exist here and others don't, specifically the Holden engines
If the OP was able to get a GRA throttle body setup that would be what I would go for for a dedicated LPG system, thats just my preference.
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456
Re: What Size Impco Carb?
Yes, the engine came out of a 1992 F-150. It was an EFI engine. This is going to be a propane only engine. The chassis won't even have a gasoline tank. I had planned on removing the EFI throttle body, but I think I understand that you guys think I should leave it in place and use it's throttle plates. Correct?
I don't plan on the engine ever hitting 4000 rpm. As a matter of fact, 3k would most likely be as high as it will normally get revved. My 351m daily driver/rolling toolbox (which this build is to replace) never sees over 2500, even on the highway. My 460 rarely hits 3500 rpm. The 300/4.9 will be backed by a NP435 4-speed manual and if I can locate one in time, a three speed Brown-Lipe auxiliary to give me an under-drive and over-drive. If I've calculated correctly, my cruise RPM should be about 1850@65 mph.
From the information you guys have given me, it looks like I'll be fine with a 225.
I don't plan on the engine ever hitting 4000 rpm. As a matter of fact, 3k would most likely be as high as it will normally get revved. My 351m daily driver/rolling toolbox (which this build is to replace) never sees over 2500, even on the highway. My 460 rarely hits 3500 rpm. The 300/4.9 will be backed by a NP435 4-speed manual and if I can locate one in time, a three speed Brown-Lipe auxiliary to give me an under-drive and over-drive. If I've calculated correctly, my cruise RPM should be about 1850@65 mph.
From the information you guys have given me, it looks like I'll be fine with a 225.
Re: What Size Impco Carb?
yes keep your TB if it simplifies the install... the 200 and 225 do not come with throttle assembly
you add them to stock TB or use the impco throttle body,, also 200 and 225 can be supplied as "FB" designation .. to be used with the CDP-02 controller
( which uses a deliberately over rich gas/air valve assembly.. the controller tenuates the reference signal to the convertor .. .. as method to control vapour pressure to return mixtures to lambda )
this is to get around 'smog' laws as required on some year of build EFI cars .. im not so sure a 425 or 300 can accommodate this if regulations demand..
the 200 may be just undersized. but keep it in mind in situations where a 225 will not allow you to close the bonnet (hood)
it uses the same internal parts as the 225 .. and is inherently stronger in its casting
if you have two throttle bodies and thus need to fit two mixers then the 200 comes in left and right hand versions ..
however.. if your EFI ducting can be replaced with alum pipe and an adapter and a 225,, and the bonnet shuts.. this is most easy path .. then go there
.. the 200 option is there for those with difficulties in space , or two throttle bodies ,, or fitting an impco TB to replace a downdraft carb on carby manifolds
the 225 has a bulky centre duct inlet .. needs more space around it
..but fits easily in most efi duct locations in front of TB with simple mods or adapter
it will be AOK at 8 psi ( no mods ) .. provided you close the spark gaps to avoid backfire at all costs ..
( flange and a burst disk on side of the pipework between TB and mixer would also fix the issue if your engine design and ignition was prone to the occasional backfire .. as its cheaper than air/gas valve lids )
.. for mine at 15 psi i simply fitted a stud to replace the single bolt that holds the hat on,, fitted a rubber seal around the hat lip ,,and built decent ignition
.. to go further i will need to fab a girdle to support the flange pattern around the air gas valve cover
.. the 200 will not require any of these mods ... and under boost i would think the losses to the 225 would be negligible
////
a single model E is sufficient up to 300-330 bhp , i have an added L to take things further when required
.. it is teed into the low pressure gas feed line into the mixer ( from the E ).. the reference signal also tees onto the top of the L
PS
RE the GRA stuff
.. the GRA is to the weber carb ( fixed venturi ).. the same as the ( constant depression.. variable venturi ) CD stromberg is to the impco diaphragm mixers
.. each to their own .. i have seen examples of both , good and bad
the tiny trade off in pumping losses between the equiv systems at 8 psi will simply not be worthy of the trouble
especially in view of how easy off the shelf and available the impco stuff is in the north american markets
ie..
.. the impco system works well out of the box
and in FB form is smog certified .. or at least certifiable if required
in australia,, GRA native country,. the GRA stuff has good support and local industry acceptance and accreditation
.. in canada and the US,, probs not so
be also aware that to run the GRA stuff into boost it is well understood that some mods,, especially to the throttle shaft bushing are required to hold anything over very mild boost
. . in saying that.. i do see examples ( in my rotary engine circles ) that have had the few mods,, and have been made to work well but at more cost and effort
ps ..holden engines post
.. i was trying to relate the ( hardly ) ' local ' engine cubes to the impco mixers..
200-300 ci engines ( regardless which reject bin the dies and presses where salvaged from )
..that may require smog tests.... and thus a feedback controller... almost universally have a 200/225 here ..
also..
under boost a blow through mixers rating goes up and the mixer pressure losses are marginal compared to those in a intercooler
also ..
there is also a requirement to provide throttle body in some impco mixers
you add them to stock TB or use the impco throttle body,, also 200 and 225 can be supplied as "FB" designation .. to be used with the CDP-02 controller
( which uses a deliberately over rich gas/air valve assembly.. the controller tenuates the reference signal to the convertor .. .. as method to control vapour pressure to return mixtures to lambda )
this is to get around 'smog' laws as required on some year of build EFI cars .. im not so sure a 425 or 300 can accommodate this if regulations demand..
the 200 may be just undersized. but keep it in mind in situations where a 225 will not allow you to close the bonnet (hood)
it uses the same internal parts as the 225 .. and is inherently stronger in its casting
if you have two throttle bodies and thus need to fit two mixers then the 200 comes in left and right hand versions ..
however.. if your EFI ducting can be replaced with alum pipe and an adapter and a 225,, and the bonnet shuts.. this is most easy path .. then go there
.. the 200 option is there for those with difficulties in space , or two throttle bodies ,, or fitting an impco TB to replace a downdraft carb on carby manifolds
the 225 has a bulky centre duct inlet .. needs more space around it
..but fits easily in most efi duct locations in front of TB with simple mods or adapter
it will be AOK at 8 psi ( no mods ) .. provided you close the spark gaps to avoid backfire at all costs ..
( flange and a burst disk on side of the pipework between TB and mixer would also fix the issue if your engine design and ignition was prone to the occasional backfire .. as its cheaper than air/gas valve lids )
.. for mine at 15 psi i simply fitted a stud to replace the single bolt that holds the hat on,, fitted a rubber seal around the hat lip ,,and built decent ignition
.. to go further i will need to fab a girdle to support the flange pattern around the air gas valve cover
.. the 200 will not require any of these mods ... and under boost i would think the losses to the 225 would be negligible
////
a single model E is sufficient up to 300-330 bhp , i have an added L to take things further when required
.. it is teed into the low pressure gas feed line into the mixer ( from the E ).. the reference signal also tees onto the top of the L
PS
RE the GRA stuff
.. the GRA is to the weber carb ( fixed venturi ).. the same as the ( constant depression.. variable venturi ) CD stromberg is to the impco diaphragm mixers
.. each to their own .. i have seen examples of both , good and bad
the tiny trade off in pumping losses between the equiv systems at 8 psi will simply not be worthy of the trouble
especially in view of how easy off the shelf and available the impco stuff is in the north american markets
ie..
.. the impco system works well out of the box
and in FB form is smog certified .. or at least certifiable if required
in australia,, GRA native country,. the GRA stuff has good support and local industry acceptance and accreditation
.. in canada and the US,, probs not so
be also aware that to run the GRA stuff into boost it is well understood that some mods,, especially to the throttle shaft bushing are required to hold anything over very mild boost
. . in saying that.. i do see examples ( in my rotary engine circles ) that have had the few mods,, and have been made to work well but at more cost and effort
ps ..holden engines post
.. i was trying to relate the ( hardly ) ' local ' engine cubes to the impco mixers..
200-300 ci engines ( regardless which reject bin the dies and presses where salvaged from )
..that may require smog tests.... and thus a feedback controller... almost universally have a 200/225 here ..
also..
under boost a blow through mixers rating goes up and the mixer pressure losses are marginal compared to those in a intercooler
also ..
there is also a requirement to provide throttle body in some impco mixers
when the going is hard, don't retard, remember your lubrication