Thinking about using the Thornton short headers on my 69 442 convertible project. I have the original 400 engine. Does anyone have any thoughts/experience with these re quality etc.. or should I be looking at a different option. Thanks

 

I have them on my 350 ragtop - they're a nice upgrade from the stock manifolds both visually and in the more agressive engine note they create, but not seemingly adding any overall power. A worthwhile addition in my opinion if your expectations aren't set on on achieving a measurable performance improvement from them.

 

... and that's what I've seen here in several threads on the topic. If you want a different sound or look, knock yourself out. However, if you're looking for a palpable performance improvement, either go for long tube or leave the manifolds and spend your money elsewhere.

 

The only sound that headers will change is the tick-tick-tick at idle that headers cause due to the thinner pipes as compared to iron manifolds. The muffler and exhaust configuration has a much greater impact on sound. As for looks, that's your call. As I've posted many times, shortie headers get you all the cost and leaking gasket headaches of real headers without the pesky extra horsepower. Your money, your car.

 

Joe is correct (as if there was ever a time he wasn't )

I do recall noting they did change the exhaust note a bit aggressively on my ride but not huge - I installed them at the time I still had dual Flowmaster 50's and the tone did change slightly but not appreciable like a muffler change would provide - I've since gone with dual Borlas and that produced the most obvious audible changes.

I got my Thorntons during a holiday sale a few years back when they were notably cheaper than current pricing. They've held up well but that's also in context to seeing only about 3k miles a year drive time on my ride.

 

I have Thornton SS shortie headers on my 350 In my ‘80 Cutlass. They fit in place of an exhaust manifold and use OEM dual exhaust downpipes. They go in from up top, no need to lift the engine like you would have to with long tube headers. Starter clearance issues aren’t a big problem either. As for performance, I think they are choking my engine down a bit but with the 1/2” thick flanges and eom connections at the down pipes at least I won’t be forever changing collector and header gaskets. Not at all useful for all out performance cars but they look good and cut the maintenance down on my spare time cruiser.

 

Maybe I'm just the exception, but I have not had issues with flange or collector gaskets on my 350 with Heddman full length headers. Is it because they are from the 1990s and were made better than the current offerings? I do not know. But I have not had issues with gaskets in the 30+ years they have been on the engine.

 

Thanks for the input, guys. I've upgraded my engine a bit so I'd like to get some bang for my buck with the headers. Thinking it's going to be long pipes.

 

I strongly suggest Remflex gaskets with any headers.

 

You will appreciate it and overall be happy you did it.

Forget about dyno this and dyno that, nothing is better at gauging power gains than actual track time. Even if you never go to the track or fully test your car. Track results are best to formulate an opinion on a mod. Otherwise it's just unsubstantiated bench racing.

Hot Rod Magazine June 1968 tested a stock stick Olds 350 F85, 3330 lbs curb. 1/4 mile mph went from 93.07 mph to 96.15 mph after long tube headers, a performance tune, and slicks. That's a 22 hp gain, then take into account that big blocks generate a more substantial gain than small blocks with full length headers.

Shorties will be a waste of time money and effort judging from your mindset.... Although the added complications from long tubes may make you think twice after the fact. But the gain is real, you can stand on it.

 

thanks. any suggestion on brand of long tubes

 

You have the more desirable exhaust manifolds on that G400 now. The center ports are divided, whereas the 68s had one open center hole.
A stock engine won't see much gain with headers. Certainly not worth all the associated hassle for minimal gain IMO. The opposite is true for a mid to heavily modified engine.

Look into extrude honing.

Put your money and time into fine-tuning what you have now. You may not be using all the engine has to offer. Super-tune the carb and timing curves. A free-flowing mandral bent exhaust system with free-flowing mufflers are nice. A free-flowing air filter element is good. (pic attached note high quality filter and gap on the lid)

A vacuum gauge and a wideband open-loop oxygen sensor are your best friends.