I went to start the '69 after about 2 months today and it runs like crap. I cut the exhaust pipes off about 3 feet past the manifolds when I redid the rear suspension ( I was planning on replacing the exhaust anyway). It runs like it has a huge vaccum leak. Is this due to there being no backpressure now? I checked all the vac hoses and everything looks fine. I ordered out my new exhaust today at VetteFest from Mid America, 2 1/2 SS with DynoMax mufflers.

Thanks,

Matt

Did it run OK before you cut the exhaust off? A car does need a certain amount of backpressure to run properly. Depending on how a car is to be driven and how much power it's capable of putting out helps determine what size pipes are needed so there is an optimum amount of scavenging within the combustion chambers.

Drag cars that put out gobs of horsepower and torque at high rpm's don't have that problem and get away with open headers. Street cars run at varying rpm's so every part of their engine and exhaust system is a compromise.

After you install your new exhaust system the problem will likely go away.

Check the cap and rotor to see if they picked up moisture from sitting that long. I had the same problem with my Suburban after it sat for most of the summer and the cap was full of rust.

I drove mine up to get my exhaust welded up to my collectors and the trip was about 20 miles. My car ran great with just shorty headers. Lots of noise but it still ran great the whole trip. As you can imagine the ride home was much quieter. So, having no exhaust on my car made no difference that I could tell in the way mine ran. I have always heard that a certain amount of backpressure was a good thing.