proper exhaust dimeter 1

[heavyd85]

i am pieacing together a performance esxhaust system for my 1995 4cyl 2.2l toyota camry. im looking at about 125hp befor modifications,the car has a cold air intake and nology spark wires.maybe 10hp more. my question,would 2.5" dimater pipping for my exhaust system be to much for my cars engine . should i down size to 2.25" or am i ok. *the exhaust header i bought has a diameter of 2.5" so i used that as my guide

 

[Viper488]

I'd suggest measuring your exhaust backpressure. David Vizard suggests about .2psi for a no hp loss exhaust system.

Pay as much attention to the muffler you stick on the end of it. You don't want a muffler with perforated core that's restricting exhaust flow.

See if you can find info on the net from others with a car like yours. There's a forum for every make isn't there?

Part of what's right for your car depends in the end on your ability to adjust fuel air mixture as what it should be set at may vary a bit with which exhaust plumbing you use.


The nology plug wires may hurt more than they help..

 

[jbthiel]

First, you didn't state cam specs or rpm range of interest.

Second, the size of the exhaust pipe isn't nearly as critical as the header diameter and length.

Third, you probably wouldn't notice the difference if you still have a near stock catalytic converter.

 

[Rob45]

I'm not familiar with that Toyota engine, but if it's a 4-valve design, exhaust backpressure will have very little effect on performance, David Vizard's ancient wisdom notwithstanding.
The reason is that the exhaust overlap factor on is vastly lower on a 4-valve engine as compared to a 2-valve of the same specific output.

 

[evelrod]

There is a lot of engineering that goes into all this, but sad to say, in every race car I have built over the years, it comes down to "cut and try" on the dyno.
If someone has a "magic" bullet, I'm ready for it!

My current 1380cc Austin engine @ 130+hp uses a full length two inch pipe for best performance with and without the Flowmaster Hushpower II muffler.
The 1594cc DOHC Lotus Cortina (185hp) also uses two inch for best torque full length with muffler and a two and a quarter pipe at 54" side exhaust (open) for best power (and noise).
The 2TC Toyota 1600 (160hp) uses the same 2 1/4" at near 60" side exit, also. All these were set up and "cut to size, trim to fit" on the dyno.

Rod

 

[Knap]

Rod

You may be inyerested or wish to comment on the following written by a fellow MG owner

Exhaust tuning theory is actually fairly simple, it’s all about getting the negative (and, hence, scavenging) pressure pulse to arrive at the exhaust valve as it is opening. To do this we have to set the pipe lengths and diameters correctly.

The formula for Primary pipe length is:

P = [(850 x ED) / RPM] - 3

Where:
RPM is the engine speed to which the exhaust is being tuned.
ED = 180° plus the number of degrees the exhaust valve opens before BDC.
P = Primary pipe length (on a 4-1 manifold), or Primary pipe length plus Secondary pipe length (on a 4-2-1 manifold), in inches.

Generally road engines will require the manifold to be tuned to the max torque rpm whereas race engines will be tuned to work either at max bhp rpm or a speed midway between the max bhp rpm and max torque rpm.

4 -1 manifolds restrict the the power band whereas 4-2-1 manifolds give better mid-range power but reduce top end power by as much as 5-7%.

Generally speaking with a 4-2-1 manifold the starting point for Primary pipe length is 15 inches, thus Secondary pipe length is P - 15 inches. Changing the length of the Primary pipe tends to rock the power curve around the point of max torque. Shorter Primaries gives more top end power but less mid-range, and vice-versa. There is, however, little change in the peak torque or the rpm where this occurs.

Ideally the Primaries should come off the cylinder head in a straight line for around 4 inches before any turns occur.

Inside diameter of the pipe can be gained from:

ID = ? [cc / {25 x (P + 3)}] x 2.1

Where:
cc = cylinder volume in cc.
P = Primary length in inches.

In some engines it can be useful to have a 'step' between the exhaust port and the Primary (ie the Primary bore is greater than that of the exhaust port). This tends to be the case in engines with rectilinear exhaust ports.

For a 4-2-1 system then, Primary pipe diameter is calculated as above. Secondary pipe diameter is given by:

IDS = ?(ID x ID x 2) x 0.93

Where:
ID = calculated inside diameter of the primary pipes.

The pipe diameter can be used to change the peak torque rpm – a reduction in diameter of 0.125 inches will drop the peak torque rpm by 500-600 rpm in engines over 2 litres and by 650-800 rpm in smaller engives. Increasing the pipe diameter by 0.125 rpm has approximately the opposite effect.

The total length of the Collector and Tailpipe (to the front of the silencer) sould be equal to P + 3 inches (or any full multiple of P + 3 for a road car).

Tailpipe internal diameter is given by:
IDT = ?[(cc x 2) / (P + 3) x 25] x 2

Where P is calculated as above.

Collector length is given by:

CL = [(ID2 – ID3) / 2] x CotA

Where:
ID2 = diameter of Collector inlet
ID3 = diameter of Collector outlet.
CotA = Cotangent of angle of Collector taper (which ideally should be around 7-8° (certainly less than 10°).

The design of the collector should be such that the inlet pipes terminate abruptly otherwise the tuned exhaust pressure wave will carry on into the tailpipe and the calculations done to get the negative scavenging wave back to the exhaust valve on time will all be wrong.

 

[NormPeterson]

(1) Am I to read the meaning of "?" and "x" in formulas such as

"ID = ? [ cc / {25 x (P + 3)}] x 2.1"

to read as follows when written in Excel

"= 2.1 * SQRT[ cc / {25 * (P + 3)}]"


(2) Does the "25" in the formual for IDT belong in the numerator or the denominator?


Norm

 

[patprimmer]

Knap

All very interesting, but he is looking for tail pipe diameter.



Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[oab]

Knap says,,,

"Exhaust tuning theory is actually fairly simple, it’s all about getting the negative (and, hence, scavenging) pressure pulse to arrive at the exhaust valve as it is opening."

As there is about 60 to 70 psi still in the cylinder, when the exhaust valve opens, what difference is a negative pressure of a few psi in the pipe going to do?

The exhaust negative pressure pulse, should arrive at the same cylinder, in time for the inlet valve to open.

Harvey.

 

[evelrod]

Knap

Yes, all very interesting. They don't take into account 'reversion' or intake tuning...all relevant, IMO. I have (some where, I think) a book that lists all the various formula that I used when I did the setup for the Locor back in the early 80's. It's been a long time. Be that as it may, the headers for the Locor, a 2000lb. sedan were of the 4-2-1 variety. In actual dyno tests with 4-1 we only lost 9+ hp. top end---close to your projected loss...we also lost nearly 1000 rpm bottom end range and a bunch of mid range torque (I don't recall the exact numbers) and that was a killer for a boxy sedan.
The 1380 Mini uses a proprietary LCB header and 2" piping with a Flowmaster Hushpower II muffler when necessary. I did not put any effort into the header design, just the tailpipe. The hp difference was negligible but the torque curve varried by as little as 5% and as much as 12%. Now that is NOT negligible, IMO. My efforts were to close the gap without going broke in the process. So far, so good, but it took a lot more than just tail pipe sizing.
The OP asked about tail pipe size and I simply posted some options.

Harvey

It may seem like it would be insegnificant...it's not.

Rod

 

[evelrod]

Obviously from reading this thread and, my last post...as we have seen in the "Engineering Language/Grammer Skills" forum, engineers can't smell wortha crap.

Rod ;o)

 

[GregLocock]

"Exhaust tuning theory is actually fairly simple"

well it made me grin

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Knap]

Pat

I only recently spotted this post on another forum, and have not yet had chance to ask the author any questions, so did not wish to take any part out of context, however it did refer to tailpipe.

The total length of the Collector and Tailpipe (to the front of the silencer) sould be equal to P + 3 inches (or any full multiple of P + 3 for a road car).

Tailpipe internal diameter is given by:
IDT = ?[(cc x 2) / (P + 3) x 25] x 2

Rod

Maybe not a "magic bullet" but my next project is probably an A series and the Lotus Cortina brought back a few memories.

http://www.popularhotrodding.com/enginemasters/articles/hardcore/0505em_exh/index1.html

"Exhaust tuning theory is actually fairly simple" - Maybe to Vizard!

 

[Warpspeed]

This is fairly simple really, as we are only talking about the tailpipe AFTER any tuned tube header/collector system.

The stark reality is that you need to make a compromise between back pressure and noise. The first thing you probably need to do is measure the back pressure of the system that is on the car right now to see where you are.

A reasonable rule of thumb is that each psi of back pressure is costing very roughly about 1% power. From that you can decide for yourself if fitting a larger diameter pipe is going to be worthwhile.

But also realise that sufficient noise attenuation with a very large low back pressure system is going to be almost impossible to achieve.

So decide for yourself noise/versus back pressure.

I am told that a great many well designed factory cars aim for about 4 to 6 psi total back pressure these days.

That suggests a 4% to 6% design power loss. Anything with much less back pressure than that is probably going to be unavoidably noisy. Anything with substantially higher back pressure, could certainly do with some improvement. but that is the sort of practical range to work in for a road car.

 

[GregLocock]

Bear in mind that the cat is about half of the back pressure

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[evelrod]

Knap,
Best of luck on the A.
I build my own engines, do my own port work, etc., but I have read all of Vizard's stuff and all the folks that help out with my valve jobs, dyno work and parts are all personal friends with Vizard, he used to live nearby in Riverside. I think he may just be smarter than me.

Warpspeed,

Perhaps I'm just not as talanted as some, but no matter how much time I spent on the calculator (pre computer era) and reams of paper wasted...it always came down to "cut to size, trim to fit"!

Rod ;o)

 

[DelSol]

Hi guys, sorry to bring this thread back from the dead. Rod, interesting to see you are using the hushpower II muffler. What is your opinion on this particular unit?

I am considering it for use on my 1.6L DOHC Honda motor. This appears to be a similar application to your Lotus. The power output is currently around 180hp, at just under 8000rpm.

The existing exhaust is set up with high flow cat, and two small straight-through glasspack mufflers. Pipe size is 2.5". I need to reduce the low frequency noise from the exhaust, so my plan is to swap one of the straight through mufflers for the hushpower. Let me know what you think

My main concern is the flow restriction. How do you think the the hushpower would fare on a more powerful motor, say around 300hp?

 

[evelrod]

DelSol

I have the Hushpower II (2"in and 2" out) on the 1380cc Mini Cooper C/S vintage race car at this time and the power and tq percentages pertain to that application. I don't have noise ratings, but Laguna Seca mandates no more than 101db and I was well under that it would appear.

The 1594cc Twincam had a 6", 16 plate SuperTrapp for 105dba noise rating at SCCA races (Open 54" side exit pipe was in the high 120db range). With this configuration we picked up nearly 10hp and improved the rpm range but did not markedly affect the max tq. (this was late 1980's)
Currently, this car is undergoing restoration back to it's configuration of the late 1960's for vintage racing. I am planning to try the Hushpower as well as other Flowmaster mufflers for the "new" car.

We never checked the Toyota as it was only used at an SCCA drivers school...it was not nearly as loud as the Lotus. It's just been 'sitting' since rebuild in 1997...don't know for sure what I am going to do with it...maybe a "planter"?

Bottom line...I rather like the Flowmaster as I picked up 3hp over an open pipe and lost only 8% or so in mid range tq. (the main reason I use a muffler only when I am required to do so by the track or rules). The straight thru designs that I have tried cannot come close to those numbers in this application.

Rod

 

[DelSol]

Sounds good Rod. I might get one and see how it goes. I am in the process of connecting an exhaust pressure sensor to the ECU so I can log the backpressure differences.

John.