Hey Folks,
I'm always thankful when I find help on forums. Just want to return the favour when ever I can. During install, they were touching the frame. My installer called them about the tight fit, and they suggested motor mounts may help. My installer agreed, we replaced the decades old motor mounts and that did it. I had no real issues. They are designed to fit factory exhaust. The one bolt under the dipstick is a tough one. I am happy with the fit. They have a nice thick flange, and the welds and finish seem decent. Here are some pics of the install.

 

What down pipes were used? Custom? My Sanderson shorties are also very close, new motor mounts may be needed on my car as well.

 

Very nice!
They look great!
I have a set for my 455,not installed yet.
Polishing the flanges must be to time consuming,I see yours are polished,mine arrived polished except for the flanges.I'll have to correct that,I like the look of yours.

 

These headers were designed to bolt up to factory downpipes. They pretty much bolted right in. The new motor mounts made a big difference in getting the needed space away from the frame. Motor mounts were only $25, so it was no big deal. These came with the flanges polished as you can tell by the photos. Haven't really driven too far with them, as it is almost time to put it away for the season. So far, no leaks. Will continue to monitor and tighten bolts if neccesary. Very happy so far. I would give these Thornton headers a thumbs up for fit and finish. Time will tell how they stand up long term.

 

They look great,I think they will hold up well over time.
Does the car sound any different with these installed?
Did you use the special bolt tightening sequence? I noticed they mention this in the ebay ad but don't include any instructions about this when the package arrives.

 

I did inform the installer about bolt up sequence. They did not come with any instructions. I didn't really notice any difference as far as sound. I am still dealing with my drone issue, so I may not be able to hear it. Being that these are shorties, I don't think they will really add any performance or sound above the stock manifolds. I just like the look.

 

Same here,I didn't get them for performance.A product like this can not compete with long tube headers.
I have a street engine with plenty of power so loosing out on 20 or so HP by not using long tube is no big deal to me.
I bought them so I don't have the issues that come with long tube headers and they give the non stock look that goes with my bling.

 

Great pics and info. I have just installed Thornton headers to my Cutlass, but I’m having trouble with the dipstick. There is a lip on the dipstick tube that stops it fitting through the headers. I ground off the lip but it turns out it was a crimp, joining the dipstick tube together. So now my dipstick tube is in 2 pieces. Did you encounter any problem like this? Thanks

 

You may not get an answer to your question since this thread is over five years old. Somebody may speak up and help you.

 

I hit the same issue with my 350. The way I worked around it was that I installed the dipstick first and then slid the Thorton headers over the dipstick into position.
This was all done on the engine stand so not sure if you will be able to do the same way if the engine is installed in the car. You may be able to push the dipstick up from the bottom - through the headers and then slide it back into the hole in the block.