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425 Impco on a crossflow

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Depends on what throttle you're using, what adaptor you have going from mixer to throttle, and what adaptors you need from throttle to whatever manifold you have.

I think the default throttle used on 425s is 4 barrel Holley pattern, for which the adaptor from mixer to throttle is pretty tall. The air filter that goes with it is quite tall too, so even without any adaptors I think you'll have issues in an XF.

I had a 300 on a Redline 2 barrel I my Cortina, and that was pretty tight to the bonnet using the standard Chrysler air filter.

Maybe you could look into an EFI throttle instead, so everything could be a lower profile?

Sent from my CPH1607 using Tapatalk

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Yes, I have all my 425's on 4 barrel Holley throttles.

It currently has a 300 adapted to the Weber throttle (dedicated LPG), but want to go to a 4 barrel for more performance potential.

 

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"should" fit under the bonnet if you cut out a bit of bonnet brace or skinny 6" filter, (but will choke it)

my XF has aussie speed, east west plate (12mm), QFT 600 & 9x2" plus filter top filter (is about 3" in total height), & proflow nut did rub bonnet (can see in pic), now just a 5/16"nut.

I hammered the bonnet brace to start with but rubbed when changed to filter top so I cut out a section, will copy & weld in some plate when I get a good bonnet for it

v8rPacO.jpg

P9CUiLH.jpg

the main problem is the top section of the impco 425 mixer, & needs close to 3" filter to clear it

9"x3"filter with base upside down & dome top has 8.65mm clearance above impco top

9x3" filter, base normal & flat top 8.17mm,

6x2 filter with base, from top if filter to impco was 5.5mm (see pic), I couldn't find my 6" lid or 6x3" filter.

2aj2oq8.jpg

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At least you can run a drop base on the 425, the Holley looks like it would foul with the bowls with a small diameter base like that. But good info on the 3" hat on the 425. That's something you really need to work around with bases and adaptors to get the height right.

One other out-of-the-box idea, if height is still an issue, might be to tilt the engine slightly using spacers under the mounts and/or elongating the through-bolt holes to tip the engine down on that side.

Sent from my CPH1607 using Tapatalk

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I did that trick on a Valiant slant 6 a while ago. Shortened the L/H mount bracket 3/4" to stand the engine up a bit, and get some clearance for a long runner 4 barrel.

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Without a east west plate would help a lot (12mm) & new aussiespeed manifold is setup for east west or north south no adaptor needed. Yeah didn't think of a drop base, But you do have the Gas vapor hose. Just measured from bottom to top of Holley base plate & impco is 158mm, so if 9x3 with flipped base & dome top overall 167mm (plus filter stud & nut, or bolt), & as per pic of my XF from rear of manifold flange to top of air cleaner is 174mm

 

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I just measured the overall height difference between a 600 vac Holley and a 425 on a 650 Holley throttle plate, the Impco is 30mm higher.

Not having the plate saves 12mm, but that leaves it 20mm higher.

I measure the 425 on the Holley throttle plate as 162 mm high, so close enough to your measurement of 158 mm.

If yours is 174 mm and clears (just), I should be able to get it to work.

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