Andrew Morris

Hi Guys

can anyone help me?

what do i need to know about converting my 1965 dynamic 88 425 rocket from single to dual exhuast system. i have found threads about thorntons manifolds and the left hand exhaust manifold needs to be replaced with the reproduction one, but does the right need to be changed or modified and will the guys doing the pipe and muffler work need to change anything else?

thanks for the help much appreciated

Andrew from Aus

Allan R

Andrew.
You can change to a Thorntons if you want to - it's going to cost a lot of money to buy and ship them down under though.

The easiest thing to do (and effective too) is put a block off plate on the crossover manifold and run your pipes straight back on both sides. Just make sure you have a crossmember that has 2 exhaust bumps to accomodate the the pipes.

You should expect that this will also make your car noisier. If you want to keep the noise down, do what the factory did. Install a resonator on each side on the pipe just after the rear axle hump. I did this with my 72 Cutlass S and I'd do it again.

One last thing. Are you considering putting in a crossover pipe? Here's a neat little article I found on the Mustang forums that explains it really well - and it applies to Olds too. http://mustangforums.com/forum/2005-...explained.html

Andrew Morris

thank you very much thats great

joe_padavano

You MUST use the Thornton repro on the driver's side to run dual exhaust on a 65-70 full size car. You have no choice on the passenger side, you must use the existing RH manifold and cap the port for the crossover. That's how the factory did it. The only option is to cut and weld your own manifolds. Others have done this, but it's difficult to properly weld cast iron.

Oldsmaniac

Agreed unless you want to create an unsightly abomination of pipe routing resembling something out of a Three Stooges episode.

Oldsmaniac

On the passenger side an early Toro exhaust manifold can be used if you want to nix the crossover port and plug. The bend though is slightly different than the stock manifold and a pipe will need to be made to compensate. The toro manifold on the drivers side WILL NOT WORK.

Andrew Morris

thanks guys

ok so i need the thorton drivers side reproduction exhaust manifold and then track down a toro right hand side manifold? this will make the pipe work easier?
i am having trouble getting an exhaust specialist to assist!! the economy is so good down here they dont need anywork???????? P.A

cheers
Andrew

Oldsmaniac

The Toro manifold was only a suggestion and not needed. A simple plug can be made for your existing rt side manifold and stock exhaust pipes used. You can order the complete factory dual exhaust on line from places like Classic Exhaust and do it yourself providing you have the correct left side manifold. Resonators are recommended if you like a quieter sound.

Andrew Morris

thank you

Allan R

J, Sorry if I started out giving wrong info. Just a question though. Why MUST you use the Thornton repro? I'm not that familiar with the 425 but USA Parts Supply shows a stock of new and used exhaust manifolds for the 425 that look very suitable for conversion to a dual system. Pls have a look at http://www.usapartssupply.com/upload...75_catalog.pdf Page 56/57. Now if their pic is for a Thorntons then I withdraw my question.

I get the impression that 425 manifolds have some kind of wierd design that isn't even close to my 350.

MDchanic

Allan, I believe that the problem is not with the 425, but with the '65 to '70 B-bodies.
Those years were "rear-steer" cars, with the centerlink located behind the steering box, so (if I'm not mistaken) there isn't room to take an engine pipe down and back from the center-positioned crossover outlet, and it has to be taken from the rear of the manifold.

- Eric

rocketraider

You don't HAVE to use the Thornton reproduction S casting manifold. You can use an original factory S manifold. You WILL have to use one or the other due to interference the steering box presents.

The RH is a simple matter of blocking off the crossover port.

Once the manifolds are in place, it should be relatively simple to either custom bend pipe or install a reproduction exhaust system.

Oldsmaniac

The USA parts manifold is the same as the Thorntons. It is the steering box and linkage that causes the problem. 1971 up do not have this problem only 65 to 70 BB B bodies.

Rocket Richard

I tried looking for that original S manifold but it seemed impossible to find. I got the Thornton manifold for my 66 Dynamic with the 425 and had a recommended exhaust shop install it, put the cap on the passenger side manifold, and bend and install new exhaust pipes & mufflers. The guy at the shop new all about my car and was excited to work on it.... if you can find a guy like that to work on your car it's a big bonus.

Thanks again to Joe for his advice back then. I am happy with the results.

Allan R

thx for the clarification Eric. I thought, 'what the heck' and wanted to see what that looked like. There are some very good pics posted on WAC that show the PS pump and the lines back to the steering box and linkages. Kind of different from what I'm used to, but 'ok'. So the DS exhaust manifold is the problem, not the PS. That one gets 'plugged'. The 65 Assembly Manual shows a great picture of how the crossover goes under to the PS. Was there anything like a heat shield to protect the oil pan? Just curious.

MDchanic

Not sure about te '65, but I don't remember seeing one on either if my '68s.

- Eric

Oldsmaniac

That crossover pipe had no heat shield and almost touches the oil pan. 99% of the 65 to 70 B bodies used the single exhaust setup without detriment.

rocketraider

The factory crossover pipe is double walled which gives some insulation. There's enough airflow underneath the car that heat is drawn away from the oil pan.

I'm pretty sure all factory installed exhaust pipes from manifold to muffler were also double-walled, though that part was more for noise reduction. Some years the shop book specifies checking for collapsed inner pipe for complaint of poor high speed performance.

bigoldscruiser

Be aware of one other problem. The trans shifter rod is in the way of the pipe on the driver's side. The factory used an arched rod for clearance. If you can't find one, you can modify the original straight rod for clearance. I cut mine, welded in an offset piece and bent the original straight rod to do the job.

sachseDD

Hi Rocket Richard! Do you have a chanse to post some pictures about the done job? I'm running a 66 Dynamic88 Conv. 425 with single exhaust... ending in a double exhaust with 4 exits... weldet together by someone. Now I would like to make an "official" dual system.