SPF owners...anyone change sidepipe mufflers?

[camcojb]

I recently had my SPF on a chassis dyno while tuning in an aftermarket EFI with a small block Chevy. It made 415 h.p. and 438 ft. lbs. to the tires but fell off after 5000 rpm. This car should make 50+ more h.p. than it is. After initially thinking we were running out of air, I started looking at the sidepipes. To support 550+ h.p. you need 2 1/2" i.d. minimum on the mufflers. It's hard to tell for sure but these mufflers are 1 7/8"-2" MAXIMUM i.d. I had a super-charged motor in the car before this one and it laid down after 5500 rpm. I didn't put two-and-two together until now.

Anyone else come across this? We have a custom fab shop here in Sacramento that will have a muffler for these pipes. When I figure out which one to use I'll re-post if there's any interest. The problem is unless you dyno the car you may not be able to tell you're losing the power; these things are fast even with mild engines. I will put the car back on the dyno after the muffler swap and post the "after" numbers for comparison. By the way, the tuner who is helping me found 100 h.p. to the wheels on a big-block Cobra after swapping the mufflers. He is very well-known in the Cobra field.

Jody

[Tim Votaw]

Jody, by all means share what you come up with. As you may be able to tell from some of my past posts, higher performance exhaust systems are not in plentiful supply, at least for the SPF cars. It's still a one-size-fits -all approach.

My experience with a hear-say shop was less than satisfactory, so if you have a source that can/will produce some options and back them up with performance data, bring it on!

I'd daresay there are more like us out there waiting for some improvements to become available without having to run a gauntlet in our search for them.

Tim

[jgrice]

Keep us posted.

This is a similiar finding to what DoubleVenow identified in a recent post.

He is in Ohio and does a very good job at rebuilding the pipes with large dia mufflers.

Jeff
SPF #186

[a427sc]

Lobac makes a 24" and 28", 4" dia muffler with a 3 1/2 inlet, no stub. Just cut your pipe, weld on the muffler and measure off the turn-out to fit. They will make custom internals for you with either a 1" or 7/8" inner tube, and will add extra baffles (swirl plates) if you want. Be sure to look inside the collector at the way the 4 pipes converge. Often there will be some shrouding from the way the tubes are joined.
To be really trick, use the Burns stainless clamps so you can change over to straight pipes for some extra commotion in the neighborhood.

[Randall Thomas]

I looked at my SPF (#729) and the I.D. of the muffler inside is considerably larger than the number you mentioned... around 2.400".

Maybe it's an earlier design (?)

I turn my big block easily in the 8,000 range with no apparent restriction.

THEORY: "bigger cubes- squashes more air thru smaller pipes". Yep, works for me ;-)

/Randall

[CobraEd]

You all need to read the thread "sidepipe rattle" under the Classic Roadsters section and also the "Classic Roadster Exhast" thread under shop talk.

We have all just gone thru this whole experience. You can read about the technology, the solution, where to buy the best custom stainless (or aluminized) sidepipe mufflers cheap and what the performance results are. I can tell you this; those of us who swapped out our mufflers have a performance difference that would make you think that the whole motor was swapped out.

You are correct in your finding. Youre pipe ID as AT MOST 2"

All of the info is in those two threads.

Ed

[coyled]

I am in the process of trying to solve this problem on my cobra. When I got my cobra from hi-tech a year and a half ago, they had a guy in Prescott Arizona, McCabe performance build some 1 7/8 to 2 inch step headers. The mufflers used were the standard glass pack on most cobra's. After speaking with many people, including the engine builder, I have been told how restrictive these things are. Also, I read double venom's posts. I also spoke with McCabe and he told me that he could not figure out why hi-tech had him put these junk mufflers behind my motor(660hp on the engine dyno).After speaking with McCabe some more,I found out he's been doing race car custom exhaust for 25 years, with lots of muffler experience the last 10 years. He said the best way to go is with a 3 1/2 inch i.d. 4 inch o.d. perforated tube. He is in the process of finding or making these mufflers. He said it might make less noise than the original mufflers, but will definately flow way better. Also, he is making a set of open pipes. I will let you guys know how it goes. He claims on a high horsepower application the mufflers will make a big difference. scott

[CobraEd]

All the CR guys who made the change went to 3" ID 4" case open chamber straight thru glasspack. Huge diff in power. In stainless steel inside and out $80 ea. So shiny they look like chrome. In aluminized steel $23 ea. Get them from Arizona Exhast in Pheonix. Ask for Lucien 602-415-9737.

I had mine made to spec for the above price. Mine are 36" long, 30" x 4" case, 3" ID nipples, 3" ID.

If you prefer 3.5" ID, I'm sure Lucien can make that too.

[This message has been edited by CobraEd (edited 09-21-2000).]

[camcojb]

Thanks for all the replies. My car number is 362 so maybe the new one have a larger bore. I contacted Arizona Muffler Fabrication and he can build what I want in a couple of days. We have a very good exhaust fab company here in Sacramento that I'm going to check with first.

Thanks again for the info. I will re-post the difference in the chassis dyno numbers when I'm done.

Jody

[JM427]

Coyled;

You're surprised that Hi-Tech used junk parts. I'm surprised you're surprised. I can show you shelves (literally) of junk Hi-Tech supplied with with my car, all of which I had to replace before I could finish the car. Be glad it's only the mufflers.

Jon

[coyled]

The list of hi-tech problems are too long too list.McCabe spoke with arizona exhaust. They do not have the perforated tube he is looking for. scott

[Mike Braddock]

Scott,

Can you elaborator a little more on the peforated tube you are speaking of? Do you simply mean a tube that has a bunch of holes drilled radially, or punched, flared holes, or ?? Thanks Scott.

Mike

[Mr.Fixit]

First, all sidepipe brands are different. CR are the worst in my opinion, SPF are not too damn bad. Second, the muffler is only a small part of the exhaust problem. Most cobra headers have sharp bends in the primary pipes, primary tube length is not optimized for the engine as it should, but for the length and bends being determined by where the motor sits and so the sidepipes look "right" Also, one size fits all pipe diameters on the headers. There's more to it than just the baffled section of the sidepipe. Unless you are only interested in how the motor "sounds"