FAQ: Down Pipe Questions (Series I SC)

Has anyone successfully installed a 3" downpipe on a '95 yet? I read this post from start to finish and found no evidence that anyone has. Dave Jr and I made one yesterday and will be attempting to install it today. Wish us luck. I will post later on our result.

Dave, I have searched all over this site and the bonneville sight, and have found no instance of anyone using a 3 in downpipe with a series 1. I have been curious for a long time how it would affect the performance. I'm very curious to see your results and would love to hear what it sounds like and see some pictures!

bigdave wrote:

Has anyone successfully installed a 3" downpipe on a '95 yet? I read this post from start to finish and found no evidence that anyone has. Dave Jr and I made one yesterday and will be attempting to install it today. Wish us luck. I will post later on our result.

..far as i know no one has.youll be numero uno! hook a brother up yo! sell me one. are you making it yourself?

3" downpipe build is complete. Sorry we didn't take any pics. Next time its on the lift we will take some. A few changes had to be made to mount it at the manifold, but nothing torches, welders and grinders couldn't fix. Also gutted the cat while it was out. Overall, a very noticeable difference in power. Dave Jr and I are very happy with the result.

robotennis61 wrote:

bigdave wrote:

Has anyone successfully installed a 3" downpipe on a '95 yet? I read this post from start to finish and found no evidence that anyone has. Dave Jr and I made one yesterday and will be attempting to install it today. Wish us luck. I will post later on our result.

..far as i know no one has.youll be numero uno! hook a brother up yo! sell me one. are you making it yourself?

Robo, I am astonished you haven't already opened your exhaust up. Why haven't you?

im sporting a 3" exhaust from the downpipe to the back.got a cherry bomb in the middle with a thrush turbo out back.single exhaust system.gives me a headach. but nice and burbly

Wow very noticeable! I need to do this somehow!

While I forgot to take pictures of the DP on the car, I did manage to get a few before we put it in.






It was definitely a project but well worth it. The combination of the downpipe and gutted cat have added quite a bit of power. It does have a nice little extra in the exhaust note that is undetectable with the windows closed for the most part. Even with the cat completely cleaned out, the exhaust doesnt have much of a scent to it. The car just feels so much healthier with this. If you have the means to fab one or have someone fab one, it is a great mod for a Series I.

I guess Dave Jr did take a few pics.

It looks awesome! Great work guys! Is there any loss of low end torque?

Thanks man!
I feel like most of the gains came in low end torque. Its very easy to break the tires loose. Just out of curiosity, I turned my traction control off and went WOT from 20 mph and it broke the tires freee like nothing. It was very cold out but the roads were dry and the tires had a good chance to warm up. The tires only have about 1000 miles on them also. It does feel stronger through most of the power band but I would say its mostly low-end toque!

Wow that must mean that the stock downpipe is quite a restriction then! That totally argues with what the guys on the bonneville forum said. They claimed that the series 1 exhaust already flows well enough, and that there wouldn't be a point to do work on the exhaust. This could open up a lot of potential for us series 1 guys, because not only does it make power, but how it makes power seems to be the important thing. It is allowing the engine to breath more, so I wonder if this means you could also run a smaller supercharger pulley than a stock car.

I had always wondered what kind of effect it would have too. I do feel that the stock downpipe is definitely a restriction. I know alot of the members here have said about the Series II that the downpipe is probably the single biggest restriction and I think that is the case on the SI as well! I dont have any way to know of the exact gains for sure but I am confident that it is a worthwhile mod for future modding as well!

I have a friend who went to school for welding, so I think this summer I may have the means to do this. Did you buy two 45 degree bent aluminum pipes to weld together, and how exactly did you fab up that flange?

Yep, two 45 degree bends. We cut the OEM pipe in front of the cat so it was easier to match the shape while cutting to size. For the flange, we measured the original distance between them and cut the OEM ends off each side. Then just shaved them down until they were able to line up for the studs. We bought new studs since the original ones had little thread left and needed new springs to clear the downpipe. It would be definitely be worthwhile to cut a downpipe from one at a pick and pull yard so you can use it to match up the shape and use that flange if you're not planning on making one yourself.

As Dave Jr said, we used two 45 degree bends, but steel from Napa. I went in the warehouse and matched up with original downpipe. Cut at angles that would give us a shape as close to the original as possible then welded them together. I will dig up the invoice from Napa and post part #'s as well as the part# of the new donut gasket from Autozone that we used. One bit of advice, the new downpipe does need to be a bit longer at the front to clear the stabilizer bar do to the extra girth.I almost cut it to the length of the original dp and would have had to add a couple inches after the fact. We also had to remove some pipe between the cat and resinator to compensate for the new downpipe. All in all not a very difficult mod but you will need some equipment that the average DIY does not have.