Would I take a big hp loss by using a 3" single exhaust...I just installed headers and need a new exhaust and I'm not sure what to get...

 

i would go with 2.5 all the way back. any larger and you lose low end torque

 

i would go with 2.25 or 2.5 duals. Why choke it with 3 inch?

 

Cross-sectional area favors that dual 2.5" scenario, but not as much as one might exppect:

a single 3: pipe has a cross sectional area of 7.07 inches square
a pair od 2.5" pipes has a cross-sectional area of 9.82 inches square

I believe fluid/gas flow is directly proportional to the area, so the dual 2.5" pipes should flow about 39% better. This does not account for any bends etc.

it's also more likely that your local exhaust guy can work with 2.5" plumbing. Mine didn't have the bender to work 3". I didn't need it anyway per Stan at FPA's reccomendation, the dual 2.5" was enough for the FE446.

My vote: dual 2.5" plumbing.

 

2.5" duals. You won't be happy with one pipe and headers. The cost is not going to be that much different.

 

Well an easy way is to figure out How much CFM you motor will need to get rid of..

your Hp X 2.2 = Total CFM

So say your motor makes 380 hp at 5500rpm... 380 X 2.2 = 836 CFM

As greg said...your local Exhaust guy should know this..and if he doesnt go to someone who does....So for your Duals you'd want something that flowed 418cfm per side...

Russ

 

Russ, aren't there other factors to add on a 2 1/2" system like running a X crossover to help the cfm flow as well length, muffler and number of degrees total bends? 2 1/2" pipe has a inside diameter of 2.345" id or 4.319 sq in. A 3" pipe is 2.830" id or 6.290 sq in. Duel 2 1/2" area of 8.636 sq in. CFM flow numbers must vary as exhaust gases have a higher temperature and lower mass density. Greg, your pipe areas are for OD, you should be working with tubing ID.

.....=o&o>.....

 

Oh Yeah Carl..I was just stating what the minimum flow should be out the tail pipe...LOL.. Yes those all have to be factored in...

That the reson I Designed my own headers for the Cobra Motor..Having them made up might not be in my best interest with the wife? I'll have to play that one by ear?? If ya know what I meen.... But with my own Design I picked up over 20lbs of TQ and about the same in HP at the peaks....and averaged alot more too..

A common Misconception with Headers..alot of guys will put them on..thinking they have a free flowing exhaust....and then the plug them up with some Cheap Muffler that doesnt flow.... all tho they may pick up some low end TQ..they flat kill the big end..

Now like Scouder had the right Idea....he built his tuned headers and used some Hooker Max Flows behind them to muff the sound (get the drone out) But still flow close to max..So I would bet even with him running Mufflers on the street he has little to no loss in power..

And a Couple of Header Manufactures I have talked to...will tell you that 1 3/4" primaries is all thats needed for any motor!! Wrong...... There is a guy on the Net54 and another one in the 460dotcom forum that have built there own headers with different size primary's and went to the Dyno just to prove the Manufacture's wrong, and both came up with more peak tq..and more peak hp...and a better average...

The header makers say..you need a certain amount of back pressure to build Tq...Well if you stop and think about it..anything on the exhaust port is going to cause a certain amount of back pressure..and when you add header reducers and mufflers and bends..How much back pressure do you need?

The Manufactures just want you to buy what there tooled up for..and what they have on the shelf for most applications... another words...one size primary fits all!! I say Bull*****.... Let me get off my soap box now!! LOL..It just pisses me off..

Russ

 

whoever said that about headers is full of ****. hell on a 500hp engine i would want 2 inch primarys not some mild 1.75 inch.

 

LOL.. Matt call any of your Header Manufactures and they'll all try an d sell you something they have on the shelf....Because they dont want to make a bigger header..they claim there is not enough call for them in one sentence..and in the next they tell you 1 3/4" is all you need..and I say Bull ***** to that!!

Russ

 

I disagree. Stan at FPA is a very knowledeable and friendly sort. He had to build my headers after I ordered them and he had every opportunity to jack up the cost by going to larger primaries and collectors. he insisted that the 1.75" primaries and the 2.5" ball collectors were more than adequate for the FE446.

Sure, there is some benefit to 2.125" primaries etc etc, but at what cost. Spend the money somewhere else.

 

I say, headers with the biggest primary pipe diameter available, 3" collectors, and 3" dual exhaust. Use free-flowing mufflers. Accept no restriction!

 

Wow guys I hope I didn't start another friendship war. Russ your "nats a$$
on" about large free flowing exhaust systems (you saw a few of mine but gtex has more photos) should anyone state you "need back pressure" to make a cam work the cam is wrong for the system intended. As stated manufactures want you to just buy what's available, no questions. Russ, cut the primaries so the ends become a point or cone in the center. When muffler manufactures state cfm flow numbers is this at high temp exhaust flow numbers or low temp carb flow bench numbers? Exhaust temps increase the speed of sound to above 1,300 ft/sec, what about flow numbers?
Does this belong on the "exhaust forum"?

 

Greg, I gots to know, is there a flow difference with a "ball connection" vs straight thru with a 3 bolt flange connection? My way of thinking (wacked at times) a smooth bore 3 bolt will have less turblence than a ball joint connection, as the end edge of the ball acts like a reversion cone. JMO.
.....=o&o>.....

 

Beemer, who cares if the ball collector flows less or not. They are SOOOO sweet compared to that worthless flange style!! OMG YES, no leaks!, ever!!!!