I am about to install the 400 engine back into the car and we were wondering if it is better to install it with the dougs headers on the engine or if it is better to wait and install the dougs headers after installation. thanks

I don't have doug's headers but there was no way My engine was going to fit in with the headers on the engine.

years ago i had dougs headers they are a tight fit , install the engine first and headers after the engine is in.

My car has AC and Dougs headers.
They fit with just having to raise the passenger side a little.
Driver side was easy.
Tuck up to floor pan well.

Definitely after the initial engine install and yes, install the passenger side first despite what the instructions say.

You need to get the motor up and over to the drivers side to get the passenger side header flange to clear the oil dipstick tube.

could you tell a difference after installing the dougs headers in sound/performance? being a close fit to the floor boards do you get a lot of heat coming up in the cabin?

Sorry, I only drove my car once 12 years ago with the orignal engine/exhaust. I have not gotten my new exhaust on yet, so I have not driven it much since I got it running again. So I can't help you there.

I put a brush/spray on sound coating on my floor boards and then will install insulation from Quiet Ride. I am anticipating some heat issues so I am going overboard. However, ceramic coated headers are supposed to be cooler than those that aren't

yeah, I used herculiner, I striped off all the old undercoating and was very happy to see there was absolutely NO rust. I brushed on the herculiner and it turned out very close to the original texture. It was a messy job and took about 2 days to do but in the end results, it was well worth the $60 dollars. hopefully the heat shouldn't be to much of an issue.

I put a double layer of rubber insulation under the carpet.
Haven't noticed any heat problems in 5,000 miles.
sound is another thing, I get a resonance at 1,000 rpm's but I think it comes from the x-pipe and having the heads filed with aluminum.

next question: Is it better to use the header gaskets that come with dougs headers or should I use another type?(I have been told to NOT use paper gaskets, and I have often heard the best out there are the copper gaskets) I know this is a touchy area when it comes to headers so I am looking for any advice? Has anyone had any problems with the bolts from dougs headers coming lose?

I first used the paper ones that came with the Dougs but they soon burnt through. Replaced again with good after market an again burnt out.
Got copper and no more problems.
Dougs have a nice thick flat flange that the copper seals to.Use copper spray seal.
Have to check bolts once in a while.

i had dougs headers years ago and yes to both the floor did get hot and the bolts would get loose i would have to retorq them quit often.

Why did you stop using dougs headers? I think I am gonna go with the copper gaskets. still researching the bolts.... any ideas?

why i stopped using dougs headers? because back in my early 20s i was more into custom touches to my firebirds. now i am at 50s door , i am more into stock ,closer the way they came from the factory . not kicking rodders i still like performance by all means,but i lean more to (the purist) these days. i would prefer factory manifolds or long branch factory manifolds myself. to me the headers was more of a head ache bolts loosening , tight fit, heat from them ect. as far as research the bolts i do have one idea. i was a crew chief in u.s.a.f. on f4 and f16 bolts on aircraft are safety wired together in tightening direction to keep them from backing out from vibration . could be done on bolts for headers!

Lay the hedders in 1st.
Use jungy cords to hold them close to where they will be with engine installed.
Then lower the engine in place being carefull not to damage them.
Use copper gastets and six point bolts(3/8's head).

BTY, i've had Dougs for 4 yrs, and havent retightened them in 2.
Guess i better check'm this spring...

I have Doug Thorley three pipe headers on my 68. I don't know if they are the same as the Doug's headers now sold by Pertronix I had to put them in first then lower the engine into position. copper gasket,re-torqued the bolts once a year ago.

Thats bungy cords, jungy...

Okay, So we put the headers up to see how they would fit once the engine was installed. Needless to say, I think i've become a good fabricator! Passenger side was a breeze, plenty of room with no modification. Drivers side on the other hand was a tight squeeze. We had to trim the motor mount do the header will not rub... Is this normal or has anyone else had anyother problems with this? According to Doug's it says you should not have to do any modifing....