: 70' Deville Str8 Pipe Conversion + FlowMaster



SilkyBrown
09-03-08, 03:47 PM
I recently bought a 1970 Deville Convertible. I have been told by a number of people that i should consider doing a Str8 Pipe conversion, essentially ripping the Catalyctic converter off and attaching a str8 pipe to a resonating muffler (FlowMaster, MagnaFlow). This precedure is said to slightly increase the HP as well as help the car run and sound better.

What exactly would change from doing this conversion?
Is this a worthwhile project to do?
How would i benefit?

If i do go ahead with this project, which brand of Muffler performs better as well as has a better, Quieter sound? Flowmaster vs. Maganaflow.

Any suggestions would be greatly appreciated.

Thanks in advance.

jayoldschool
09-03-08, 11:48 PM
First of all, your car doesn't have a catalytic converter.

Now, on to the muffler. The factory Cadillac muffler is very well designed. It accomplishes high flow while being very quiet. If you don't believe me, look up "Smokey Yunick" and see that he used to suggest the Cadillac muffler on street applications. I personally think that Cadillacs should be quiet. I do like cars with a growl (like my 71 Pontiac and my 95 Impala SS), but I think that Caddies that are loud are "redneck". GM spent lots of money getting the most HP possible out of that factory muffler (1970 was the king of HP).

If you really want to try a different muffler, go with the biggest (case size, not pipe) Magnaflow you can find, or look for some type of "Turbo" muffler. A high performance muffler really only benefits at full throttle. Do you hammer on your car on a regular basis?

So, what will you accomplish? Not much. A noisier car, and a little bit more HP at full throttle.

SilkyBrown
09-04-08, 08:14 AM
No i dont hammer at all.. And i was under the impression that i did have a catalyctic but imma go do my research to make sure. The reason i want to change the muffler is because i have a few small leaks coming from the pipe running accross the bottom of the car. I figured if i was going to change the pipe i might as well swap a Flowmaster muffler while i'm down there. I heard they are quiet, but louder at higher rpm. Which is what i want, since i dont drive fast anyways.

jayoldschool
09-04-08, 11:06 AM
It will definitely be louder at idle and part throttle. It will be very loud (compared to stock) at full throttle. I can shoot a little video of my 95 SS for you and post it if you like. It has stock pipes, still has cats, has small case turbo mufflers, and resonators deleted. Sounds very mean with a nice growl. Not trashy like flowmasters. Quite appropriate for the car. However, if my Cadillac sounded like that, I would be embarrased.

For you, go with stock replacement pipes and muffler.:thumbsup:

SilkyBrown
09-04-08, 12:04 PM
makes alot of sence. The sound coming from my stock muffler already sounds a bit mean. I figured with the Flowmaster or a MaganFlow it would just make it sound a little bit meaner.. Didnt think it would have a huge drastic effect. I dont want it sounding like a Muscle car. I want it to idle quiet. And when i slowly accellorate i want to hear a quiet guzzle. But if the Flowmaster is gonna make it too loud forget that. I did some research and you where right, cadillac only started making catalytic converters in 75' so im good. I have an leak in my exaust manifold, so i hear a slight clicking sound when i press on the gas. The mechanic told me that its a very mild leak which i wouldnt neccessarily have to replace. He said its kind of a big job to do just for a slight clicking sound. I figured ripping my catalytic converter and replacing the muffler with a Flowmaster might help bleed the sound out. But if its gonna make my Caddy sound cheezy forget that! Thanks for the advice jay

jayoldschool
09-04-08, 05:25 PM
Glad to help:thumbsup:

Your leaking "exhaust manifold" may be missing/loose/broken manifold bolts. When the car is cold, go feel/look for them all and see if there are any missing/loose/broken. If they are loose, snug them down. If they are missing, replace. If they are broken... come back for more advice.

Aron9000
09-06-08, 09:58 PM
Magnaflow makes a really nice exhaust. I had a magnaflow catback on my 1999 Camaro Z28, but thought it was too quiet. Can't hear it at idle, very mellow at low revs, sounded nice at full throttle. I wanted something louder for that car though.

Fleet
09-11-08, 03:25 AM
No i dont hammer at all.. And i was under the impression that i did have a catalyctic but imma go do my research to make sure. The reason i want to change the muffler is because i have a few small leaks coming from the pipe running accross the bottom of the car. I figured if i was going to change the pipe i might as well swap a Flowmaster muffler while i'm down there. I heard they are quiet, but louder at higher rpm. Which is what i want, since i dont drive fast anyways.
Catalytic conveters first appeared on Cadillacs for the 1975 model year. Fortunately, the 1970 model year didn't have one.

SilkyBrown
09-11-08, 08:45 AM
Catalytic conveters first appeared on Cadillacs for the 1975 model year. Fortunately, the 1970 model year didn't have one.

I know i figured that one out but the only concern i have with that is that i'm from Canada, and we have very strict Emissions laws way more harsh than the U.S. I'm thinking maybe a previous owner was forced to install one in order to pass the emissions test.

Is there a way of locating the catalytic on the underbody or is it hidden? I think the best way to do it is to check it out for myself rather than relying on Year specifications.

jayoldschool
09-11-08, 09:36 AM
Silky, I'm in Canada too (Ottawa). Our emission laws aren't as strict as many US states. Back in the 70s and 80s, we had no emission testing, so there is no way anyone would have added a cat to that car. By the time the test DID arrive in the 90s, your car would have been emission test exempt.

Trust me, it doesn't have a cat.

SilkyBrown
09-11-08, 03:38 PM
Silky, I'm in Canada too (Ottawa). Our emission laws aren't as strict as many US states. Back in the 70s and 80s, we had no emission testing, so there is no way anyone would have added a cat to that car. By the time the test DID arrive in the 90s, your car would have been emission test exempt.

Trust me, it doesn't have a cat.

I'm in Ottawa too!! U just put my mind to rest. That was my only concern. Now i can concentrate on my other upgrades. Thanks again