probably goin to have a new exhaust system made and my existing shorty headers wont allow me to run the down tubes down the tranny tunnel so i guess the way to fix that is to install long tube headers. my question is will my 305 benefit from this or will it be detrimental for it?? id like to get 1 5/8s if possible but i guess the engine will be at the point soon where 1 3/4 will be needed any how.

 

I doubt you will see any gain going to 1-3/4" with TPI 305. 1-5/8" would be a better choice. Lontubes in general perform better than shorties, if you can put up with the extra hassles, i.e. ground clearance, fabbing custom exhaust, expense, etc.

 

There have been multiple articles in Chevy High performance on a 406 where they have 1 5/8" headers that will make 450 HP/ 500 lb/ft of torque...granted these are long tube headers, but the intermediate length ones will only be a bit behind the long tubes...

So, for your combo, I agree with Ricktpi...get a set of 1 5/8" shorty style headers and a single 3" pipe all the way back...that will be more than enough to allow high 12's out of your combo...

Good luck,

 

Thats not necessarily true. Long tubes make more torque at lower RPMs and make for a lower power peak, shorties will allow for a higher power peak and more upper RPM power. Your choice between the two should be based on how much and where you want to power to be.

 

Some good points made...

But in the real world, the power difference between 1 5/8"
or 1 3/4" primarys , and for that matter shorty headers and long tubes, are usually in the SINGLE DIGITS.

I had the opportunity a few years ago to watch somewhere in the neighborhood of 200 dyno runs on different combo's from mild to WILD...this was a flywheel dyno, but we'd rigged up a "rack" that allowed us to use full exhaust, different mufflers etc, mainly for our own enjoyment and out of boredom...and because having access to a dyno is just too cool

The BIGGEST difference is ridding your engine of the stock exhaust manifolds and getting headers....the other differences are minor at best.

I've used long tubes on other platform cars as daily drivers, and if I had ground clearance problems on those cars that weren't lowered, I can imaging the scraping with my IROC since it rides low from the factory.

Now there are exceptions to this....

IF the headers being replaced are restrictive in nature, or maybe like 1.5" primary tubes, you will see some bigger gains on the healthier engines.....

We did see almost 20HP going from 1.5" tube headers to 1.75" headers on a pretty stout 383.....

that being said "most" header designs for our cars are pretty similar...except for the older "stepped" Edelbrocks....and even the newer ones...the welding on those things looks like I did it with some coat hanger and a propane torch...


But that's just my opinion...


HTH