The Impco's are only usefull to a point. Mine has reached the end of its usablilty so I'm having to go for the dual research setup too.
The 425 with mods is still an excellent choice for just about any 302 or mild 351, but now i'm starting to look for power 5500+ rpm the impco just can't flow enough to keep the A/F ratio happy.
I agree the GRA setups are ugly.... but hard to tune? Everyone i've ever spoken to reckons their easier to tune than the impcos and don't have the typical 'rich as a pig' at idle and leaning out at redline problems... like the 425's tend to do.
The 425 with mods is still an excellent choice for just about any 302 or mild 351, but now i'm starting to look for power 5500+ rpm the impco just can't flow enough to keep the A/F ratio happy.
for a fairly stock 302C then you would recoment impco converters over a gra system then?
i was just planning to do some mild head work, an exhaust, and maybe bore it out a little?
1. The impco's, despite being rated at 425cfm, flow the fuel equivelent of a 600-650cfm petrol carby. I know this because a previous engine that I converted from petrol to LPG ran a 600 holley and was pretty much spot on for the engine. Same engine with only a dizzy regraph (not even a cam change) was spot on with dead stock 425 impco. I know a lot of people here with impco's would agree a 465 holley could not supply enough fuel, but their 425's handle it fine.
So me running 2 unmodified impco's would not only require a tunnel ram, but an engine that would require a 1050 holley if it ran petrol... my engine is not that wild.
2. Unlike the impco's the GRA carbs can be tuned individually and only one of them works at part throttle, so its a lot easier to get the A/F ratio consistant at both light throttle and WOT. At low RPM dual impcos would be putting so much unburned LPG out the exhaust that it'd make your eyes water.
for a fairly stock 302C then you would recoment impco converters over a gra system then?
i was just planning to do some mild head work, an exhaust, and maybe bore it out a little?
Yep a 425 Impco for sure.... and it'll save you $1000 or so on the install too. For a mild 302 i'd suggest a 600 holley baseplate.
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