lpg carby

[aghatas]

gday, i want to go straight lpg on my 253, i have a four barrell manifold that can take either a holley or quaddy throttle body. does anyone know which throttle body works best with the impco 425? and is the 425 too much CFM for a 253? or should i be looking at a 225 instead? i have a mild lpg cam and performance manifold but the rest is stock.

[scribble]

I had a 425 on a 351 in a Fairlane some while back and used a 600 vac-sec Holley with the secondaries linkage modified to manual actuation and it worked very well.
cheers
Steve

[aghatas]

thanks for the reply, the quaddy base has mech secondaries already, what sort of a difference would the size of the openings make when choosing a throttle body for the lpg mixer? as per the impco 425 vs 225 i found somewhere that the CFM for the 425 is 460 and for the 225 it's 329. also am i right that the required CFM=CID x RPM / 1728 / 2 so for a 253 it would be
253 x 3500 / 1728 / 2 = 257 CFM. should i go the 425 or is it too much?

[Cane_It]

go the 425, i reckon those calculations are ok in theory, but i had a 450 holley on a 202 and found an extra 10 rwkw just from getting the secondaries set up right. so i'd say go the 425. I'll have one on my 308 week after next, so i'll let you know how it goes,

try these guys if you havent bought one yet...
http://cgi.ebay.com.au/NEW-IMPCO-425...QQcmdZViewItem

cheaper than anywhere ive been quoted in australia.... I bought mine from them

[craigvk]

[aghatas]

yeah i had seen that on ebay before, a mate of mine told me that when you buy a mixer brand new it has a restrictor in the intake and to leave it in for the 253. he also said that an Adapter plate locally is around $80 if your not going to use the holley throttle body.
cheers

[Cane_It]

yeah i had seen that on ebay before, a mate of mine told me that when you buy a mixer brand new it has a restrictor in the intake and to leave it in for the 253. he also said that an Adapter plate locally is around $80 if your not going to use the holley throttle body.
cheers

they charged me about $40 australian for the adaptor plate to run the quaddy throttle plate. I dont know about the restrictors, I'll ask about em when i get mine tuned.