Hi guys, my current setup is a Impco 300 snorkel setup sitting on top of a 600 Holley squarebore...problem is, when I last had to take the carby off I noticed that its actually sitting on a standard Ford 4 bbl manifold with the spreadbore pattern and in between theres a pretty restrictive looking adapter plate. I mean, its REALLY restrictive by the looks... anyway, I was thinking that as the carby's really acting as a throttle (I've not run this car on petrol) would I be better off getting hold of a thermoquad to replace the holley? What would this do (if anything) for response low down compared to the holley? I'm actually thinking more about higher rpm too - the secondaries is where things look pretty horrible with the adapter plate...

(oh, btw this is on a 351 Cleveland in an XB..)

Any thoughts would be appreciated !!

The Impco 300 is what will be holding you back.
If you don't use petrol get a 425 mixer and mount it to your 600 base.
That will make it go heaps better.
If you can find a square bore manifold put that on too but it wont be that big of an issue.
Its pointless being concerned about a airflow restriction on a standardly used adaptor plate when you feeding a 351 with a 300A.

Thanks for the reply! yes, I've heard about these 425 mixers - would that work with the same converter I have or would that need replacing too?

If it is a model L or B2 convertor it should be fine.

Ah cheers, I'll have to check out which one it is...any ideas how hard to get hold of these 425's are? Any ideas on price and would you reckon new or second hand?

yep, L model...cool! So, $64 question...if I do put a 425 on it, should I stick with the holley on the adapter, or go quadrajet?

Either base depending on your manifold to match it with! If you have a squarebore holley manifold then use a holley, If you have a spreadbore than use the thermoquad base. I have a new thermo quad base sitting in the shed.

There is also a OHG 450X that flow more than the 425, which is what I have on my 351!

Hey mate,

Did you end up changing to a bigger LPG mixer or switching back to petrol? I'm surprised nobody mentioned going straight LPG & fitting up a gas research TB & modifying the converter with a spring to properly work with the GRA?

Cheers

ToranaGuy

to be honest I haven't done anything, still have my impco 300 on there..couldn't find a 425 and don't really want to throw too much cash at it....but yeh I'd love to go with a GRA setup!

Well mate, keep an eye on Ebay, every now & then reasonable priced 425's come up for sale. Going GRA would require a bit of cash thrown at it, because the converter needs a spring kit, then you need the GRA TB & to get it tuned, which involves stepped metering rods and fiddling around to get it right.

This one Ebay - Impco 425 decent priced

That is unless you can find a bargain at a you pull it / pick a part style wreckers. I picked up a GRA for peanuts because the guy wouldn't listen to me, I said it was a gas mixer, and he booked it out as a EFI TB, which was half the price of the gas mixer lol! A whole of $35! Yep, that's correct, a gas TB that is around $450ish new last time I checked.... I don't need it right now, but it was too cheap to pass up, it will end up on one of my projects.

Hell, it might make it's way onto my red EB Xr8 if I go forced induction, because they are much easier to setup for boost than the impco gear........or even onto my Hz pano if i crack the s**t with the quadrajet & new gen mixer and decide to go straight gas......options...... lol.

Cheers

ToranaGuy