New here, and as I mentioned in my intro post in the New Members forum, I've got a '67 Imperial.

I'm interested in swapping out the stock intake for an Edelbrock Performer. I thought it would be a straight-forward swap, but I read about a rebuild of a later Imperial that had hood clearance issues.

Edelbrock says the carb pad height of the Performer manifold is 4". Anyone know off hand the pad height of the stock cast-iron manifold? The stock engine is a 440 rated at 350 hp, if that helps.

I figure it's the original engine, and although it runs pretty nice, it probably has a rebuild in its future. The plan is to run a Performer intake now, and when it needs to be rebuilt, put in a stock bottom end, Performer cam and 440 Source Stealth Heads painted Imperial Blue so that it's, well, stealth. Probably 440 Magnum manifolds to keep things quiet. Hope is for about 450 hp with lots of torque.

 

Personally I would keep it stock. Stock manifold is not that bad other than being heavy

 

I have a 68 Imperial, with the later 906 heads (larger exhaust valves). I had installed a CH4B intake manifold. Made little difference. A dual exhaust that I installed later made better difference at higher rpm. The car remained a good highway performer, until the valve springs started losing their "grip"!

I am now doing a head job in this car, with larger valves and a carefully selected cam (0.477" intake) from Mopar performance. Also, slightly increased compression ratio. I have had huge delays from a transmission leak that the shop is a bit over-charging for. I am hoping for about 400 hp (net, note the original gross hp is really meaningless).

You have to be careful when you select a cam with these big and heavy cars. The 2.94 rear is great or high speed driving, but it may not be forgiving with an excessive cam.

 

I totally agree. My understanding is that Edelbrock has the "Performer" series parts (cam, intake) designed for more power right off idle, so it's pretty mild.

You increased your compression ratio? It was already 10:1. Are you still able to run 91 octane? One of the reasons I was thinking about running aluminum heads was that the 440 Source heads don't cost a whole lot more than rebuilding iron heads, and the aluminum might let me run lower octane with the same compression.

 

I have not driven this modified 440 Imperial yet. FRUSTRATED! But given the fact that the cam has larger duration than stock, it should be more forgiving in terms of spark knock. My other Imperial (that may also have a slight cam upgrade) runs happy with mixture 89/93 in the summer with timing right at or a bit over specs. And she runs good.

One thing to remember. Chrysler was a bit conservative on the compression ratio because engines built up a lot of deposits back then. With modern gasolines, this is no longer an issue, so you can raise the compression ratio some. Plus, the 906 heads were excellent compromise between restriction and in-cylinder motion.

What I do not like with aluminum heads is they do not tolerate overheating well. A set of 906 heads (or even later heads from the 70's) are fairly inexpensive, and probably better than your 918 (?) heads.

 

According to Mopar Muscle magazine, in 1967 all Chrysler products, including Imperial, got the 915 head, from New Yorker to Magnum. So that and $2.50 will get me a cup of coffee.

 

....915, thanks for reminding me. The 915's still had the 1.60 exhaust valves, and the intake ports were a bit more restrictive than the 906. The 906 heads had the 1.74" exhaust, and they were a bit better developed. But given how crappy the average engine from the 60's was, even a stock 67 440 will do better than most luxo-boats of the era.