Magnaflow Exhaust & 67 Perfomance

[Kirk M.]

Two questions here:

1. I have a 1967 327/300hp automatic vert. Will I get any significant performance boost by installing magnaflow mufflers versus standard reproduction aluminized mufflers made by Corvette Central?

2. What kind of point deductions will I get with magnaflow muffler versus installing the reproduction aluminized mufflers manufactured by Corvette Central (322364)?

Thanks.

[John H.]

Re: Magnaflow Exhaust & 67 Perfomance

Kirk -

1. No performance increase - just louder.

2. Probably a couple of points for configuration - the whole system (pipes and mufflers) is only ten points.

[Joe R.]

Re: Magnaflow Exhaust & 67 Perfomance

Hi Kirk:

I don't know about the Corvette Central products and Magnaflow, but there was an "off road" muffler offered by GM that I think was a factory option in 1967. I have read that this muffler has three internal chambers instead of the standard five. It's a little bit louder than the standard muffler and presumably, lower restriction. I believe it is available in reproduction.

One possible glitch is that your Powerglide car has a 2 inch exhaust system instead of the 2.5 inch used on manual transmission cars. So, if you want to get the "off road" muffler you need to confirm that it is available in the 2 inch configuration.

I have been told that the standard 2.5 inch exhaust pipes will not fit past the Powerglide transmission, so you can't just swap them in. I think some custom pipes could be made to fit, though.

Most people will tell you that the performance gain you might get from these changes is too small to bother with, but you might still enjoy having a slightly louder exhaust.

[Duke W.]

Re: Magnaflow Exhaust & 67 Perfomance

A production 327/300 makes an honest 225 net HP in the 4000-4500 range and is wheezing at 5000. Especially if it has the 2.5" manifolds and pipes, a lower restriction muffler is not going to improve power by any significant amount. Power is limited primarily by head flow.

As a rule a straight through muffler offers less restriction than a reverse flow, but it can come down to design and construction details. A well designed and constructed reverse flow may beat a poorly designed and constructed straight through.

A 327/300 can be easily massaged to close to 300 net HP without affecting the idle characteristic and around 325 net HP with an LT-1 cam.

In this power range a less restrictive muffler can be meaningful.

Duke

[Kirk M.]

Re: Magnaflow Exhaust & 67 Perfomance

Thanks all. That is about what I thought, but I just wanted to check. For me, more sound is worse. My car is driver and a vert and between the engine noise, air and all, I have a hard enough time hearing my tunes. So, I think I'll stick with the standard aluminized mufflers from Corvette Central that are designed to fit the 67. Great info as usual and thanks for responding.

Kirk

[Keith B.]

Re: Magnaflow Exhaust & 67 Perfomance

Kirk: I purchased the Corvette Central Magnaflow 2.5" to 2.0" complete alum set-up last summer when they were offering free shipping. Absolutely love this exhaust system on my 66 427. My car was originally a N11 "0ff road" RPO and it was difficult to find an org N11, and when I did find the GM mufflers they were $2,000-$5K on ebay. Allens exhaust also offers their own version of off road exhaust and they are great people to deal with. There was a very noticeable improvement in power gain and overall performance with my Magnaflows, with just the right deep low growl to them. They make a very nice flow thru design so my BB breaths much better. I received a few points deduction in Sept/07 but my car Top Flighted and received favourable comments from the judges as to their set-up, and sound........ My .02 cents.......

[Duke W.]

Re: Magnaflow Exhaust & 67 Perfomance

The OE exhaust system offers rather low backpressure to small blocks, even if they have been massaged for more power.

Big blocks are a different story because they pump up to 50+ percent more exhaust gas volume through the system. Backpressure increases with the SQUARE of exhaust flow, so a SHP BB is going to generate more than four times that backpressure of an unmassaged 327/300.

This is why the current Z06/LS7 has 3" pipes and dual path mufflers. Otherwise, 500 net HP would just be a pipe dream.

As most have heard, sidepipes are more restrictive than the under-the-car system, so the worst combination in terms of excessive exhaust backpressure is a SHP BB with sidepipes.

Duke