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Gday everyone, Im from Australia and own a 66 VC Valiant Regal with completly stock everything except electronic ignition. Im wanting to get a bit more out of the 225 without pulling the engine out and apart. I have just purchased a 25 spline lsd with 3.50 gearset which should give a bit more go off the mark, Im looking to add an Aussiespeed Longrunner 2 bbl manifold, and some Dutra Duals or atleast a decent set of extractors, the thing Im not sure about is, will this be overkill on a stock engine, and what Holley Carb would best suit these add ons?
 

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Welcome to the forum, for starters. As far as the 225 add-ons go, the, even stock (so it runs properly in the tuning category), and dual exhaust back (a header would be a good addition over stock manifold, and a split to dual exhaust right at the collector), about the only other thing you can really do is add a better air cleaner to improve the air flow going into the 2bbl carb. Your rear gear selection is a good improvement, too, and saving a little money here and there to make those big improvements internally can be discussed when you want.
 
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As long as the engine and drivetrain is mechanically healthy, it should take an increase in torque OK.
Offenhauser made a 4-bbl intake, which I would consider over-carburetion. It would be similar to a Hyper-pak, except for the camshaft.



There have been turbocharger installations that you can find on an internet search. There is NOx injection that could be added. I have seen split-tuned headers that may or may not be cost effective:
https://www.hemmings.com/blog/article/slant-six-turbocharger-setup/
 

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One of the best in-line six resources used to be Clifford performance. Their expertise goes clear back to the Hudson Hornet. https://cliffordperformance.net/ On carburetors, Holley used to make a 390 cfm 4 barrel just for the 4 & 6 cylinder applications.
 
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GM draw thorough Turbochargers are very easy to adapt to inline 6 cyl Engines.

They're totally self contained and easily adapt to single barrel intake manifolds.

Assorted Buicks used them in the late 1970's and Trans Am in 1980-81

Pictured is a 1981 system but 1980 and earlier are preferred as they aren't feed back barbs.

Thanks
Randy

 

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Not much point installing 4 Bbl setup when head and camshaft so mundane. You can still improve the breathing and overall performance without pulling engine (or oil pan). Run some tests to see what your warm idle vacuum is and then a compression test, or better yet, a cylinder leak-down test. The gears are fine but will reduce your top speed since the engine cannot breathe well above 4000 rpm's. Remember, the actual rear end ratio is determined by diameter of rear tires. Stock camshafts are only good for off-idle thru 2500 or 3000. A little more cam would allow better breathing and mid-range, without hurting bottom-end. If your current idle vacuum is in the 16 to 18 range, you can definitely go with more cam. Just try to keep the vacuum above 12 inches.
One more improvement is the cylinder head. Stock ports and valves very limiting for power but if a cam is changed, go with the 318 spec springs. Also, a surface cut of about .050" will bring the C.R. to above 9 to 1. These slant heads could be cut by as much as .090" as there was plenty of metal. And, no need to cut intake surface. Some type of simple electronic ignition a 'no-brainer'.
 

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You can try to find a marine 2 barrel intake and carb.
- but as is its the camshaft thats the main limiting factor and it can be changed without pulling the head with the engine in the car.
If you whant big improvements its turbo time and that will make it necessary to use aftermarket fuel injection if you whant it to be succsesful.
 
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