HP loss through mufflers

ERA535 · #1 (**permalink**) 10-11-2001, 11:44 AM

Hi Bob,
I have read a few posts recently stating that the side pipes are very restrictive and result in some pretty incredible power losses.
What are your thoughts on this?
Thanks,
Pat

CobraEd · #2 (**permalink**) 10-11-2001, 11:54 AM

Not to jump in on Bob, but rumor has it that ERA uses mufflers with 2 1/4" straight thru pipes inside the sidepipe. If in-fact this is true, maximum HP potential may not be realized. (Bob, If I am wrong, sorry, let us know)

Ed

427Aggie · #3 (**permalink**) 10-11-2001, 01:58 PM

Bob can confirm this but I spoke with a gentleman and SAAC this year and was told that he had a set of stainless pipes made by HRE....Bob may be able to confirm what he told me. I was told that where the collector meets the muffler their is no tapper down to the 1" or so pipe that goes through the muffler. This results in a dramatic backpressure and I was told that he gained 50hp with the HRE pipes.

Matt

Bob Putnam · #4 (**permalink**) 10-12-2001, 06:09 AM

The standard steel sidepipes have a fiberglass-packed muffler inside with 2.25" entrance/exit - no tapered transition. I'm sure there's some power loss there but I'm afraid the pipes would get LOUD if it was more efficient.

The stainless pipes are internally baffled and I haven't seen the details of the baffles.

I don't know anything about the HRE pipes. I'll ask Peter whether he's seen them.

CobraEd · #5 (**permalink**) 10-12-2001, 06:37 AM

Pat,

As I suspected!! If you want, I have the number of the guy in Arizona who makes custom sidepipe mufflers to spec for the Cobra guys. Many of us have used him. We have gone to a 3" id straightthrough glasspack with a louvered core. BIG HP gains, and the sound although somewhat loud is terrific. Very deep and mellow. All of the people who have made this change absolutely love the sound, deep, thundering low rumble with all of the high frequency raspiness filtered out. Although loud, not at all offensive.

For a 36" bullit muffler that has a 4" OD and a 3" id, he charges $28 in aluminized steel (for painting or ceramicoat) and $80 for T-304 stainless steel inside and out.

You are loosing a lot of HP with only 2 1/4id pipes. Not even a generic muscle car would run that small, let alone a worked over Cobra engine. It is all a matter of what is important to you though.

Let me know if you are interested, I'll give you his number. I can also tell you what is entailed in installing them.

(Bob, you might want to give these a try. For a lousy $28ea. for a quick test what do you have to loose? Let me know if you want the number).

Ed

Dominik · #6 (**permalink**) 10-12-2001, 06:51 AM

Ed,
very interesting!
Are you telling me that this muffler will replace the sidepipe muffler section of the "original" sidepipe?

I just cut out the muffler between the collector and the bend?

Sorry, I don't have the dimensions here.

28$? That is nothing ...

Dominik

CobraEd · #7 (**permalink**) 10-12-2001, 06:58 AM

Dominic,

You got it. It is so simple, . . so cheap, sounds terrific, and adds tons of HP. It is a win win situation! One of the best kept secrets out there, . email me, or give me a call and I can give you all the details on how to size the muffler for ordering, and some options for installing it.

Ed
W-202-268-8264
H-703-803-6995

WestCoastBill · #8 (**permalink**) 10-12-2001, 08:36 AM

I've got to agree with Bob,"some horsepower loss" will result from the 2 1/4" baffle. Some torque may be gained on the other hand and thats what "feels" fast. I've heard the claims of massive gains made with bigger pipes, but does anyone have actual, firsthand knowledge, obtained on a dyno. Other factors would be, was it a stock/mildly modified/small cubic inch motor or a big block monster race motor that needed more breathing room. The bigger pipes would be louder, and therefore maybe "seem" faster. But does anyone have any actual proof. I talked myself out of going bigger after reading a magazine comparison of 2 1/2" versus 3". There was no difference. Bill

427Aggie · #9 (**permalink**) 10-12-2001, 09:00 AM

I will tell you that my early next year plan is to buy a set of the stainless pipes from HRE and see what I get from them. I will be doing a dyno in the next few weeks and then when I change pipes I will let you know what I get.

Unless Bob can make me a custom set that is less restrictive and really loud

Matt

CobraEd · #10 (**permalink**) 10-12-2001, 09:21 AM

In case anyone wants the number for the 3" id mufflers, the name of the company is Arizona Exhast in Phoenix. The owner is Lucien. In the old days he used to work for Shelby, he is a great guy and has made many of these custom mufflers for the Cobra community. His number is 602-415-9737.

Slide · #11 (**permalink**) 10-12-2001, 04:31 PM

This is a real interesting thread! Bob, are the pipe/muffler dimensions the same for the FIA cars? Matt, I'm looking forward to your dyno results-but do you really want it louder? my ears are still ringing!

Bob Putnam · #12 (**permalink**) 10-13-2001, 08:28 AM

The 427 uses a 4"OD pipe, I think the FIA is 3.75".

Victor Severino · #13 (**permalink**) 11-19-2001, 03:05 PM

Here's a question: I have decided to put in an undercar exhaust...the kind that exits in front of the rear tires. How much more HP loss am I likely to get from this arrangement? I will be using a 428 scj engine. thanks

Bob Putnam · #14 (**permalink**) 11-20-2001, 06:38 AM

Vic,

Probably 25-50 peak bhp loss. Just remember that there won't be as much loss at lower rpm. The car will still scare me anyway.

If you are willing to put up with more noise, there are mufflers that have no penalty at all. It's all what you are looking for.