3" too big???

[fast.asleep]

When a mechanic friend puts on my headers he wants to install dual 3" oval pipes and 50 series Flowmasters. (on my mostly stock '87) I wouldn't mind the 3's but not if it will hurt performance. Would 2.5's be better or should I go with the three's?

please help

Will

 

[LD85]

I would say dual 3" is too big for amostly stock car, unless you have a SC etc.


On my 406 I have 1-3/4 headers into 3" collectors into a 3" Y-pipe into dual 2.5" mandrel bent exhaust pipe into Magnaflow dual 3" tips,, just my .02

 

[drags1998]

You dont need 3" But it will add a different(cool) tone to the exh. And it looks cool too!!!! Some people think 3" will hurt bottom end power, I have NEVER found this to be true!! Good Luck!!!

 

[mr.corvette]

You dont need 3" But it will add a different(cool) tone to the exh. And it looks cool too!!!! Some people think 3" will hurt bottom end power, I have NEVER found this to be true!! Good Luck!!!

My friend,,
I have just the same thinking, I have been driving around with dual 3", no cats, and a small damper at the end, for quite a while now, and everybody said that I will loose all my power. Bs, it had never been running better, and what a sound, Mmmm. Nice.
just my2c.
take care friends.

 

[Mad-Mic]

You dont need 3" But it will add a different(cool) tone to the exh. And it looks cool too!!!! Some people think 3" will hurt bottom end power, I have NEVER found this to be true!! Good Luck!!!

why do you think in drag racing they run open headers?

 

[fast.asleep]

thanks for the reply's guys.

I'm convinced, 3" it is. I can't wait to hear them

Will [wringing his hands]

 

[norvalwilhelm]

I feel 3 inches is too big for your combination. A 3 inch exhaust besides killing torque is also much louder then 2 1/2 inch. Also the through holes in the crossmember will not take that large a pipe.
A 2 1/2 inch exhaust will take you to about 500 horse.
That said I run a full 3 inch exhaust with a modified crossmember and super turbo mufflers. I am also running a much large combination with alot more horse then 500

 

[bossvette]

why don't you bring that beast to Cruise-Fest 2004 and put it on the Dyno we need 5 more signed up to get the dyno shop for the day, May 21

 

[c4cruiser]

I have a 3" B&B Triflo system on my 92 and it was worth about 10HP and 15-20 ft-lbs of torque. The Triflo's are fairly loud but also have a fair amount of resonance inside. At first, I did notice a slight loss of low-end power, but it quickly came back, due to the ECM relearning.

You may notice the same differences when you have your 3" system installed. If you don't have to worry about emissions testing, you might want to consider long tube headers (Hooker 2149's) or at least dumping the pre-cats.

50-Series Flowmaster will be much quieter than a 40 Series or the American Thunder ones. A friend had a set of 40's on his 76 along with headers and no cat and I could hear him on the freeway when he was a half-mile ahead of me!!

BTW, norvalwilhelm, C4's don't run the exhaust thru the frame or holes in teh crossmembers, they sit entirely below the body with the exception of the X-frame under convertible C4's. I can drop my entire exhaust in one piece in less than 10 minutes. That is one sweet motor!!

 

[Bob Chadwick]

I feel 3 inches is too big for your combination. A 3 inch exhaust besides killing torque is also much louder then 2 1/2 inch. Also the through holes in the crossmember will not take that large a pipe.
A 2 1/2 inch exhaust will take you to about 500 horse.
That said I run a full 3 inch exhaust with a modified crossmember and super turbo mufflers. I am also running a much large combination with alot more horse then 500

Talk to the muffler manufacturers, they will tell you the same thing about the low end torque.

 

[CKA_Racing]

The following info was taken from an article in Corvette Fever June 1998 issue.
Exhaust shoot out! By Jim Van Dorn
Dyno results on stock Grand Sport LT4.
HP/TORQ
Stock:
299/307

BB Triflow catback 3-inch:
310/310

Dynomax mufflers only:
304/310

Borla Corvette Challenge cat back 2 3/4 inch:
304/309

Flowmaster cat back 2 1/2 inch:
306/309

Power Effects cat back 2 3/4 inch:
299/308 - flaps in closed position
311/313 - flaps in open position

As you can see the is very little difference between them all especially when you consider cost.

Some interesting comments they had were, "Borla teamed with Doug Rippie Motosports in developing their Corvette Challenge cat-back 2 3/4 inch system. Rippie's original request for the larger-diameter pipe was made when he fitted his mega-horsepower former Lemans engine (600+hp) to a production ZR-1. Rippie later related, "We found the 3-inch system was great for horsepower, but (it) lost torque. The 2 3/4 inch system was the best of both worlds."

I have an issue with the above. If that's true why is it the Triflow 3-inch tested pushed 310 torq and the Borla pushed 309torq. Could it be that they are really referring to how the max torq moves to a lower rpm with the 2 3/4 and moves up higher in the rpm's for the 3-inch? Is this possible?
I can feel a difference in low-end torq if I closed the flaps on my PE system. Feels like it has more but maybe it's just available sooner.


They also tested sound levels at 70mph cruise, at idle, interior sound. What's interesting is that they don't mention resonance at all. I'm thinking the Cruise @70mph sound level test would be as good indication of how loud the resonance is.
Stock 94
Triflow 107
Dynomax 96
Borla 100
Flowmaster 97
Power Effects 100(Closed) 103(Open)<this turns it into a straight pipe, you can see inside the exhaust.

107 DB is loud for most folks.

Amazing how people think bigger is always better no matter what. It's the American way I guess. For a street car, go 3" if you plan to really highly modify the engine, 2/34 should do fine up to around 450HP.
Draw your own conclusion but you can easily see the the answer.
If you do install the 3" going into flows and more than likely Hi-flow cats, I won't be surprised at all if we see you posting in the near future about how bad the resonance is. If you are half deaf, then the resonance should have little effect on you. Good luck on what ever you decide.

 

[Bob Chadwick]

Could it be that they are really referring to how the max torq moves to a lower rpm with the 2 3/4 and moves up higher in the rpm's for the 3-inch?

That's how it's been explained to me. You get more power its just where in the power band you get it.

 

[fast.asleep]

Thanks for that article summery CKA,

Now I'm having serious second thoughts about the 3". (there is no way I'm going to put up with 107 db)

Considering the cost of 3" oval tubes and the resonance factor, it looks like I'll go with 2.5" pipe.

thanks everyone,

Will

 

[l98vette1986]

3" will NOT HURT TORQUE.
Backpressure does not help make more torque.
as long as you have a good full length set of headers, you will not have any trouble. you could run 4" pipes, and it still would not matter. The key to makeing torque w/ an exhaust system is no back pressure, and tuning length of pipe. This being said, you will be OK w/ a 2-1/2" exhaust system. Run a dual setup w/ either an H or X pipe. If you plan on making high HP, go w/ the 3".

 

[WhalePirot]

The most critical sizing is at the headers, where proper velocity is what makes headers properly scavenge (tuned) at a certain RPM. Too large header pipes kill that velocity.

Way downstream is the 3", or whatever, past the CAT, which might be the bottleneck in all these tubes, anyway.

Also, the 3" pipes don't tuck under the car as well as smaller pipes.

You're not going to hear 107db with any size pipes on ANY muffler.