Needing ideas

[69hurstolds]

IMHO, I'd leave it alone until you start your conversion. You'll be throwing good money away you can use for the end goal. Unless you're light years away from the swap. Then I'd do turbos and 2.5". Headers on a 305 isn't worth it unless you just want to go through that hassle.

 

[spicercars]

IMHO, I'd leave it alone until you start your conversion. You'll be throwing good money away you can use for the end goal. Unless you're light years away from the swap. Then I'd do turbos and 2.5". Headers on a 305 isn't worth it unless you just want to go through that hassle.

I agree

 

[Zeus785]

It may be a year or 2 before i do the LS swap, i got to get kids into college first.

Thanks for the ideas

 

[CMCE]

It may be a year or 2 before i do the LS swap, i got to get kids into college first.

Thanks for the ideas

Zeus- Stick with a 2.5" exhaust system. You will need over 500HP to start realizing any benefits from a 3" system. You will be much happier , SB or LS, with 2.5". The only manufacturer making complete systems for your car is Pypes. This X-Pipe system https://classicmusclecarexhaust.com/p/pypes-78-88-g-body-2-5-x-pipe-side-exit-sgg10 can be ordered with any of their 3 mufflers, or bought without mufflers. Race Pros flow the best of the three, and are the quietest. Street Pros are louder, and Violators are self explanatory. Get the Dynomax Super Turbo's if you want a quiet idle/cruise with a nice sound when you get on it. Check out the 'Exhaust 101' section on https://classicmusclecarexhaust.com/ to help you make an informed decision. They also carry manifold Downtubes so you can enjoy your car with a nice exhaust system for the next couple of years with the stock 305, then swap in the LS and still retain the same system. BTW, shipping is free from Classic Muscle Car Exhaust and Pypes has a $50 sale until the end of this month.

 

[565bbchevy]

This is the stainless kit from Jegs that a bunch of us bought when they were on sale for dirt cheap a while back.

https://www.jegs.com/webapp/wcs/sto...&submodel=&engine=&Nrpp=&No=&persistYmm=false

 

[pagrunt]

If you go with Pypes in 2.5" go with the side exit kit not the rear exit. I have gone thru two new kits with bad passenger side tail pipes, sent them to Pypes to have them find every kit they checked with the same incorrect bends. They sent me back the "best" two they had in house & told me to have a local shop rebend them to fit. With the side exit kits I've only heard they are a good fit. I'm using the Jeg's stainless kit with the Pypes mufflers.

 

[xcookpac]

I think with the 305 engine (even with mild performance mods) I doubt that you will be making more than 300HP. The larger the exhaust pipe diameter - the more CFM the exhaust pipe can flow. See https://www.exhaustvideos.com/faq/how-to-calculate-muffler-size-pipe-diameter/

Based on the above link it appears that a 2" diameter DUAL exhaust would handle the 305 engine horsepower fully.
See attached excerpt on exhaust diameter versus horsepower from the above linked website. If you are going to install a whole new exhaust system for the LS motor (a waste in my opinion) then go with the 2" for the 305. And, then convert to 2 1/4" or 2 1/2" when you have the LS motor installed. According to calculated CFM/HP, the 2 1/4" should be good to about 370HP. While the 2 1/2" exhaust tubing should be good to about 460HP. These HP figures assume true duals for the calculation.

For the cruise around town 305 with 300HP or less, I would use 2" pipe with the Walker 21598 mufflers (originally found on late 70s/early 80s Z28s and Trans Ams. These mufflers are relatively cheap (about $34/each on Rock Auto). I have these on my 85EC with a 305 (nice sound and note but not too loud on the highway). If you go the 2" route than you should be able to use the Monte SS tailpipes (Walker 45910 and Walker 45909 for L and R tailpipes) about $28/each on RockAuto. You would then need to have custom bent pipes from manifolds/headers to mufflers.

If it were me, I would install 2 1/4" pipe and mufflers and then have the pipes all custom bent. Remember you can order the 2" tailpipes and have the exhaust bender copy them over in 2 1/4" pipe. This way you can likely use the 2 1/4" system when you convert to LS power.

Just my two cents.

PS Many moons ago I used to work in a couple different muffler shops bending custom exhaust all day.