The 400 Chrysler engine in our AMC Javelin is a really tight fit...the stock log style exhaust manifolds are only an inch or so from the shock towers and steering shaft. Which mopar BB exhaust manifolds work the best on the 383/400 engine? Or do you have any ideas about headers with the center port pipes routed up and back to clear the shock towers?
I am currently installing a Summit 6401 camshaft and a Holley street dominator intake. We have a 4160 Holley 600cfm vac secondary carb, but my gut tells me it will be too small for our engine. What carb size do you recommend? In case it makes a difference for carb size and type, our transmission is a 727 with a RMVB, 3000rpm torque converter and we have an 8.75" rear end with a spool and 4:56 gears.
The car weighs just under 3000lbs.
Thanks!

You need at least a 750 double pumper. I would buy some cheap headers and cut and make them to fit.

Thanks for the input.

I'll hunt down a 750 dbl pumper and sell the 600 Holley I have. I'll find a cheap set of headers either new or used and do some fab work to make them fit. Lots of the cheaper ones have small diameter primary tubes...what diameter should I look for, or is this a case of 'anything is better than using iron manifolds'?

Is there a secret to putting smooth bends in the header tubes when we modify them? I'm afraid to chop up the shock towers too much because they appear to be very structural in the AMC chassis. I don't want to squash and mangle the header tubes too much either. I've seen butchered headers in some engine swap cars before that have hammered in or squashed tubes that look like they are just as restrictive as manifolds would be, at least on some of the cylinders. We want to keep the tube lengths the same too...we want to do our exhaust headers properly!

We are modifying the engine mounts from the mock-ups we have been driving the car with. As a race-only car, would solid engine mounts be acceptable or should we stick with a 'revised version' of the stock rubber engine mounts and steel adaptor plates we have now? One of our goals is to make the engine quick to r & r compared to the cobby way it was mounted before.

We have been using the stock AMC transmission mount, which fits perfectly. Should we retain that rubber mount or can it be solid as well?

Thanks, I know these might be dopey questions but this is our first build and we want it to be done nicely!

how about block hugger headers from a street rod
they are center dump style

Block huggers will not gain much in performance, although they are probably better than manifolds. Consider it a middle ground option between manifolds and full length headers. But it might be easier to find and possibly even cheaper to modify an in-expensive set full lenght tubes.

What have you done to raise compression ? I think you are going to be a little disappointed in that combo if the 400 is stock.

Sounds like you need a custom header , buy a pair of flanges , some mandrel bends and make a set that fits.

On the motor mounts you might want to consider an engine plate ?

For now we are planning on leaving the stock heads and pistons alone, at least until our budget allows us to upgrade, since the engine does run well now. I've read in another thread on moparts that using a 6401 cam in a low-comp 400 engine doesn't make great torque but will have pretty good top end. We don't want to spend money on anything now that will hurt us later on as we can afford more upgrades, so we were hoping the 3000rpm torque converter and 456 gearset would at least get us up into the rpm range where our engine will make some power, especially since our car is so light.

Do you think a smaller carb, like 650cfm , would be better for our low-compression combo? My guts tell me the biggest restriction is going to be the exhaust manifolds, but is the street dominator intake also inappropriate for our engine? You guys have been a great help in giving us some ideas on building headers so far!

Thanks!